ANNUAL REPORT 2001metrology.aalto.fi/annual_reports/mri-annual-2001.pdf · 2018. 5. 7. · Helsinki...

Helsinki University of Technology

Department of Electrical and Communications Engineering

Metrology Research Institute Report 20/2002

Espoo 2002

ANNUAL REPORT 2001


Metrology Research Institute Report 20/2002

Espoo 2002

ANNUAL REPORT 2001Editor Petri Kärhä

Helsinki University of TechnologyDepartment of Electrical and Communications EngineeringMetrology Research Institute

Teknillinen korkeakouluSähkö- ja tietoliikennetekniikan osastoMittaustekniikan laboratorio

Distribution:


Metrology Research Institute

P.O. Box 3000

FIN-02015 HUT

Finland

Tel. +358-9-451 1

Fax. +358-9-451 2222

E-mail: [email protected]

© Metrology Research Institute

ISSN 1237-3281

Picaset Oy

Helsinki 2002

1

CONTENTS

1 INTRODUCTION....................................................................................... 3

2 PERSONNEL............................................................................................... 4

3 TEACHING ................................................................................................. 83.1 COURSES ............................................................................................................ 83.2 DEGREES ............................................................................................................ 9

3.2.1 Doctor of Science (Technology), D.Sc. (Tech.) ....................................................... 93.2.2 Licentiate of Science (Technology), Lic.Sc. (Tech.)................................................. 93.2.3 Master of Science (Technology), M.Sc. (Tech.) ....................................................... 93.2.4 Awards ................................................................................................................... 10

4 NATIONAL STANDARDS LABORATORY........................................ 11

5 RESEARCH PROJECTS......................................................................... 135.1 OPTICAL RADIATION MEASUREMENTS............................................................ 13

5.1.1 Intercomparison of characterization techniques of filter radiometers in theultraviolet region ............................................................................................................ 135.1.2 A portable field calibrator for solar UV measurements........................................ 155.1.3 Characterization of filter radiometers with wavelength-tunable laser source...... 165.1.4 Radiometric determination of radiation temperatures.......................................... 175.1.5 Study of fiber optic power measurements using photodiodes with and withoutintegrating sphere ........................................................................................................... 195.1.6 Development of absolute scale of spectral diffuse reflectance.............................. 205.1.7 Optical characterization of thin films.................................................................... 21

5.2 LENGTH METROLOGY ...................................................................................... 235.2.1 Iodine-stabilized diode lasers................................................................................ 235.2.2 Iodine-stabilized Nd:YAG lasers ........................................................................... 24

5.3 MICROTECHNOLOGIES...................................................................................... 255.3.1 Micromechanical resonators for RF-applications ................................................ 255.3.2 Finite element modeling of microsystems.............................................................. 265.3.3 Optical interferometry on a mechanical silicon oscillator.................................... 275.3.4 High-Q micromechanical silicon oscillators......................................................... 28

5.4 APPLIED QUANTUM OPTICS ............................................................................. 305.4.1 Integrated atom optics ........................................................................................... 305.4.2 Digital laser frequency stabilization ..................................................................... 315.4.3 All-optical 3-GHz frequency standard based on dark states of 85Rb .................... 325.4.4 Quasi-phase-matching in nonlinear laser frequency conversion.......................... 34

5.5 CHARACTERIZATION OF FIBER-OPTIC COMPONENTS ....................................... 355.5.1 Group-delay ripple in chirped fiber Bragg gratings ............................................. 35

2

5.5.2 Photonic crystal fibers........................................................................................... 365.5.3 Intercomparison of measurement techniques to characterize fiber Bragggratings ........................................................................................................................... 37

5.6 NOVEL COMPONENTS FOR OPTICAL TELECOMMUNICATIONS .......................... 395.6.1 Supercontinuum generation in photonic crystal fibers.......................................... 395.6.2 Fiber laser for L-band ........................................................................................... 405.6.3 Wavelength reference ............................................................................................ 415.6.4 Measurements of thermally poled waveguides with Bragg gratings..................... 42

6 INTERNATIONAL CO-OPERATION.................................................. 446.1 INTERNATIONAL COMPARISON MEASUREMENTS ............................................ 446.2 THEMATIC NETWORKS..................................................................................... 45

6.2.1 Thematic network for ultraviolet measurements ................................................... 456.2.2 Fiber Optics Technology Network......................................................................... 45

6.3 CONFERENCES AND MEETINGS ........................................................................ 466.4 VISITS BY THE LABORATORY PERSONNEL....................................................... 486.5 RESEARCH WORK ABROAD ............................................................................. 486.6 GUEST RESEARCHERS ...................................................................................... 496.7 VISITS TO THE LABORATORY ........................................................................... 49

7 PUBLICATIONS ...................................................................................... 517.1 ARTICLES IN INTERNATIONAL JOURNALS ........................................................ 517.2 INTERNATIONAL CONFERENCE PRESENTATIONS............................................. 527.3 NATIONAL CONFERENCE PRESENTATIONS ...................................................... 537.4 PATENTS........................................................................................................... 557.5 OTHER PUBLICATIONS...................................................................................... 55

3

1 INTRODUCTION

Expansion of the research activities of the Metrology Research Institute contin-ued in 2001. In the University’s present financial situation, new activities canonly be based on acquired funding which covers already almost two thirds ofthe total budget of the Institute. It should be noted that the fastest growing sec-tion of the budget is the direct funding from companies.

The research fields of the Institute include optical radiation measurements, mi-crotechnologies, applied quantum optics, and fiber optics where several signifi-cant developments were carried out in 2001. New equipment was constructedfor characterization of filter radiometers with a wavelength tunable Ti:Sapphirelaser. Such characterizations can be made only in a couple of other NationalMetrology Institutes. An all-optical 3-GHz frequency standard was developedusing coherent population trapping in rubidium vapor. The measured linewidthof this system is one of the narrowest ever reported. Collaboration with CrystalFiber A/S in Denmark was initiated to study novel optical properties of pho-tonic crystal fibers and supercontinuum generation in these fibers.

The Metrology Research Institute offers several courses where the practicallaboratory exercises are emphasized. For example, Fundamentals of Measure-ments is offered to all second year students of the Department. A new labora-tory course on microsystems was implemented in 2001. The Institute is activealso in post-graduate education and is partner in several National GraduateSchools. Seven master’s degrees and two doctoral degrees were completed in2001.

The Metrology Research Institute is an active participant within internationalresearch programs. European Union funded projects Improving the Accuracy ofUltraviolet Radiation Measurements and Fiber Optic Thematic Network (FO-ToN) were successfully completed in 2001. A project on Optical Communica-tion Wavelength References was initiated with the support of Nordic IndustrialFund. We take part in international activities within the framework ofEUROMET, CCPR and COST. The personnel of the Institute are chairing sev-eral international committees including the CCPR Ultraviolet Working Group,the Scientific Committee for the 5th Workshop on Ultraviolet Radiation Meas-urements and COST Action 265 Working Group on Photonic Crystal Fibers.

Erkki Ikonen

4

2 PERSONNEL

Helsinki University of TechnologyDepartment of Electrical and Communications EngineeringMetrology Research Institute (Mittaustekniikan laboratorio)P.O.Box 3000, FIN-02015 HUT, Finland

Visiting address: Otakaari 5 A, Espoo (Otaniemi) Finland

Switchboard +358 9 451 1Telefax +358 9 451 2222http://www.hut.fi/HUT/Measurement/

In 2001, the total number of employees working at the Metrology Research In-stitute was 39.

Telephone E-mail

Wallin, PekkaProfessor, Head of Department,Laboratory Director

451 22800400-445 699

[email protected]

Ikonen, Erkki, Dr.Tech.Professor, Head of the NationalStandards Laboratory

451 2283050-550 2283

[email protected]

Tittonen, Ilkka, Dr.Tech.Professor

451 2287040-543 7564

[email protected]

Ludvigsen, Hanne, DocentAcademy Research fellow

451 2282 [email protected]

Hänninen, JaanaAdministrative secretary

451 2288050-308 8403

[email protected]

Metsälä, SeppoLaboratory technician

451 2220

Ahola, Tero, M.Sc.Research scientist(till May 31)


http://www.hut.fi/HUT/Measurement/

5

Envall, Jouni, studentResearch assistant


Genty, Goëry, M.Sc.Research scientist


Hahtela, Ossi, M.Sc.Research scientist


Heiliö, Miika, M.Sc.Research scientist


Hovila, Jari, M.Sc.Research scientist


Kimmelma, Ossi, studentResearch assistant


Koskenvuori, Mika, studentResearch assistant


Kärhä, Petri, Dr.Tech.Senior research scientist,Quality manager

451 2289050-511 0307

[email protected]

Lahti, Kristian, M.Sc.Project manager(till May 31)


Lamminmäki, Tuomas, M.Sc.Project manager


Laukkanen, Tommi, M.Sc.Research scientist(till October 31)


Lehtonen, Mikko, studentResearch assistant


Lindvall, Thomas, M.Sc.Research scientist


6

Liukko, Anna, studentResearch assistant


Manoocheri, Farshid, Dr.Tech.Research scientist,Head of calibration services


Merimaa, Mikko, Dr.Tech.Research scientist


Nera, Kaisa, M.Sc.Research scientist


Nevas, Saulius, M.Sc.Research scientist


Niemelä, Arto, studentResearch assistant

451 2281

Niemi, Tapio, M.Sc.Research scientist, Student ad-visor


Nieminen, Juha, studentResearch assistant

451 4870

Niinikoski, Laura, studentResearch assistant


Noorma, Mart, studentResearch assistant


Nyholm, Kaj, DocentSenior research scientistCenter for Metrology and Ac-creditation


Rantakari, Pekka, studentResearch assistant


Simonen, Tarmo, studentNetwork and PC Administrator


7

Taina, Pekka, studentResearch assistant(till May 31)

451 4870

Toivanen, Pasi, Dr.Tech.Research scientist(till May 31)


Tsekurov, Nikolai, studentResearch assistant

451 5047

Tuominen, Jesse, studentResearch assistant


Vahala, Eero, studentResearch assistant


Vainio, Markku, M.Sc.Research scientist


Docents and lecturers:

Jokela Kari STUK, Radiation and NuclearSafety Authority

+358 9 759 881

Kalliomäki Kalevi University of Oulu +358 8 553 1011

Kaivola Matti Helsinki University of Technology +358 9 451 3151

Kauppinen Jyrki University of Turku +358 2 333 5670

Ludvigsen Hanne Helsinki University of Technology +358 9 451 2282

Ståhlberg Birger University of Helsinki +358 9 191 1

Franssila Sami Helsinki University of Technology +358 9 451 2332

Häkkinen Esa Helsinki Institute of Technology +358 9 310 8311

8

3 TEACHING

3.1 Courses

The following courses were offered by the Metrology Research Institute (Mit-taustekniikan laboratorio) in 2001. Those marked by * are given biennially.

S-108.180 Electronic Measurements and Electromagnetic Compatibility2 credits (Petri Kärhä, Esa Häkkinen, Kristian Lahti)

S-108.181 Optics2 credits (Erkki Ikonen)

S-108.186 Microsystem technology4 credits (Ilkka Tittonen and Sami Franssila)

S-108.187 Laboratory course on microsystems3 credits (Ilkka Tittonen and Sami Franssila)

S-108.184 Computer-based Measurements2 credits (Kristian Lahti)

S-108.189 Project Work in Measurement Technology2-5 credits (Pekka Wallin)

S-108.191 Fundamentals of Measurements Y2 credits (Mikko Merimaa)

S-108.194 Electronic Instrumentation3 credits (Pekka Wallin)

S-108.195 Fundamentals of Measurements A2.5 credits (Mikko Merimaa)

S-108.198 Biological Effects and Measurements of Electromagnetic Fieldsand Optical Radiation2 credits (Kari Jokela)

S-108.199 Optical Communications and Optical Instruments5 credits (Erkki Ikonen)

S-108.901 Electrical Engineering Project1-5 credits (Pekka Wallin)

9

S-108.903 Fourier Transforms in Measurements*4 credits (Jyrki Kauppinen)

S-108.911 Postgraduate Course in Measurement Technology7.5 credits (Ilkka Tittonen and Matti Kaivola)

S-108.913 Postgraduate Course in Physics of Measurement*3 credits (Birger Ståhlberg)

S-108.914 Research Seminar on Measurement Science1 credit (Erkki Ikonen)

3.2 Degrees

3.2.1 Doctor of Science (Technology), D.Sc. (Tech.)

Mikko Merimaa: Frequency Standards based on Diode Lasers.

Opponent: Dr. Lennart Robertsson, BIPM, France.

Ville Voipio: Instrument for Measuring pH with Optical Indicator Thin Film.

Opponents: Professor Vahid Sandoghdar, ETH Zurich, Switzerland and Dr.Juha Rantala, Guideoptics, Finland.

3.2.2 Licentiate of Science (Technology), Lic.Sc. (Tech.)

The Licentiate degree is an intermediate research degree between M.Sc. andD.Sc.

Kristian Lahti: Phase-Matching in the Optical Nonlinear Process of SecondHarmonic Generation.

3.2.3 Master of Science (Technology), M.Sc. (Tech.)

Mari Ylönen: Glass as pressure sensor material.

Markku Vainio: Optical nonlinear frequency doubling with a transmissiongrating laser.

Tero Ahola: Frequency-stabilized Nd:YAG laser at 532 nm.

Miika Heiliö: Digital laser frequency stabilization using a high finesse interfer-

10

ometer as a reference.

Pekka Hilke: Transmission of digital television channels in wavelength divisionmultiplexed fiber optic networks.

Jari Hovila: Characterization of the national standard of the unit of luminousflux.

Ossi Hahtela: Optical Interferometry on a mechanical silicon oscillator.

3.2.4 Awards

Thomas Lindvall: Award for the Master’s Thesis in 2000, issued by HelsinkiUniversity of Technology.

11

4 NATIONAL STANDARDS LABORATORY

Metrology Research Institute is the Finnish national standards laboratory for themeasurements of optical quantities, appointed by the Center for Metrology andAccreditation (MIKES). The institute gives official calibration certificates onthe optical quantities listed in Table 4.1. Recent changes include calibrationservices on new quantities - luminous flux, diffuse reflectance factor, and fiberoptic power.

During 2001, 46 calibration certificates were issued. The calibration servicesare mainly used by the Finnish industry and various research organizations.There are three accredited calibration laboratories in the field of optical quanti-ties.

The institute offers also other measurement services and consultation in thefield of measurement technology. Various memberships in international organi-zations ensure that the laboratory can also influence e.g. international standardi-zation so that it takes into account the national needs.

The Metrology Research Institute performs its calibration measurements undera quality system approved by MIKES. The quality system is based on standardISO/IEC 17025.

Further information for the calibration services may obtained from Farshid Ma-noocheri (Head of the calibration services) or Petri Kärhä (Quality manager).

12

Table 4.1. Calibration services offered by the Metrology Research Institute ofHUT.

Quantity Range Wavelength range Uncertainty (k=2)Luminous intensity 10 – 10 000 cd – 0.3 %Illuminance 10 – 200 lx – 0.2 %

200 – 5 000 lx 0.3 % – 0.5 %Luminance 5 – 40 000 cd m-2 – 0.8 %Luminous flux 10 – 10 000 lm – 1.0 %Spectral irradiance 10 pW mm-2 nm-1 – 290 – 380 nm 1.1 % – 2.8 %

500 µW mm-2 nm-1 380 – 900 nm 0.6 % – 1.1 %Spectral radiance 5 µW m-2 sr-1 nm-1 –

6 W m-2 sr-1 nm-1290 – 900 nm 1.0 %

Color coordinates (x, y) 0 – 1 – 0.1 %Color temperature 1 000 – 3 500 K – 0.15 %Optical power 0.1 – 0.5 mW 458.1, 465.9, 472.8,

476.6, 488.1, 496.6,501.9, 514.7, 543.5,633.0 nm

0.05 %

10 nW – 1 mW 250 – 380 nm 0.3 % – 0.8 %10 nW – 1 mW 380 – 920 nm 0.1 % – 0.3 %10 µW – 10 W 250 nm – 16 µm 2 % – 10 %

Transmittance 0.0005 – 1 250 – 380 nm 0.1 % – 1 %0.0001 – 1 380 – 920 nm 0.05 % – 0.5 %0.0005 – 1 920 – 1700 nm 0.1 % – 1 %

Spectral responsivity 250 – 380 nm 1 %> 0.01 A/W 380 – 920 nm 0.5 %

920 – 1700 nm 4 %Reflectance (5°–85°) 0.05 – 1 250 – 380 nm 0.5 % – 5 %

0.01 – 1 380 – 1000 nm 0.3 % – 3 %Diffuse reflectance factor 0.05 – 1 360 – 830 nm 0.4 % – 1 %Optical wavelength 400 nm – 1.55 µm – 0.01 nmFiber optic power 1 nW – 7 mW

(-60 dBm – +8 dBm)1310 nm, 1550 nm 1.5 %

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5 RESEARCH PROJECTS

5.1 Optical Radiation Measurements

5.1.1 Intercomparison of characterization techniques of filter radiometersin the ultraviolet region

P. Kärhä, N. J. Harrison*, S. Nevas,W. S. Hartree*, and I. Abu-Kassem†

* National Physical Laboratory (NPL), UK† Bureau National de Métrologie (BNM), France

Narrow-band filter radiometers are inwide use in radiometry in such areasas the realization of spectral irradiancescales or the measurement of radiationtemperature. Very low calibration un-certainties are often reported but thecomparability of the characterizationtechniques used has rarely been veri-fied in intercomparisons.

We developed two types of filter radi-ometers to measure the radiationemitted from UV sources at thewavelengths of 248, 313, 330 and 368nm [1]. The first type was based onsingle, wide band-gap solar blindphotodiodes. The second type utilizedtrap detectors based on silicon photo-diodes. Interference filters with anominal 10-nm bandwidth were usedfor the spectral selection with bothtypes of radiometers.

HUT and BNM characterized the ra-diometers for spectral responsivityusing conventional monochromator-based spectrophotometers. NPL util-ized their laser radiometry facility for

similar characterization.

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

300 305 310 315 320 325Wavelength [nm]

Res

pons

ivity

[A/W

]

λeff

∆λ

S (λeff )

S

Figure 5.1.1-1. Analysis of filter ra-diometer data. λeff describes theagreement of the wavelength scales.Integrated response S can be used tocompare spectral responsivitymeasurements.

New methods suitable for narrow-band radiometers were developed foranalyzing the spectral responsivitymeasurements. The effects of wave-length shifts were separated from thedata. (Figure 5.1.1-1). Spectral irradi-ance values that institutes wouldmeasure on black body radiators werealso compared.

14

Comparison of integrated response

-5 %-4 %-3 %-2 %-1 %0 %1 %2 %3 %4 %

300 320 340 360 380Wavelength [nm]

Dev

iatio

n fr

om m

ean

NPLBNMHUT

Figure 5.1.1-2. Comparison ofspectral responsivity measurementson wide band-gap filter radiometers.

Most of the results were in agreementwithin their uncertainties. The agree-ment between the participating labo-ratories in the spectral irradiance andspectral responsivity measurementswas roughly on the level of 0.1 – 2 %(Figure 5.1.1-2).

The study identified various aspects ofthe measurement facilities that re-quired improvement. The wavelengthscales of the participating laboratoriesdiffer more than the stated uncertain-ties would imply (Figure 5.1.1-3). Thisappears to be a point that has not ear-lier been properly tested, as intercom-parisons are usually performed usingspectrally flat artifacts.

Comparison of effective wavelengths

-0.4-0.3-0.2-0.10.00.10.20.30.40.5

300 320 340 360 380Wavelength [nm]

Dev

iatio

n fr

om m

ean

[nm

] NPLBNMHUT

Figure 5.1.1-3. Comparison ofwavelength scales.

The study did not demonstrate thatone of the filter radiometer types wassuperior to the other. The angularproperties of trap detectors are com-plicated, but solar blind photodiodeshave higher nonuniformity. These twocharacteristics may explain some ofthe discrepancies that arose during theintercomparison, as the beam geome-tries used for the filter radiometercalibration were not common.

The work has been carried out within projectSMT4-CT98-2242 “Improving the Accuracyof Ultraviolet Radiation Measurement,”funded by the Standards, Measurements andTesting program of the European Union.

[1] P. Kärhä, N. J. Harrison, S. Nevas, W.S. Hartree, and I. Abu-Kassem, “Inter-comparison of characterization tech-niques of filter radiometers in the ultra-violet region,” (submitted).

15

5.1.2 A portable field calibrator for solar UV measurements

P. Kärhä, L. Ylianttila*, T. Koskela†,K. Jokela*, and E. Ikonen

* STUK, Radiation and Nuclear Safety Authority† Finnish Meteorological Institute (FMI)

Stationary roof-mounted spectroradi-ometers are used to monitor the solarUV radiation passing through the at-mosphere. Calibration of these spec-troradiometers is problematic, becausetransportation to calibration laborato-ries may affect their calibration, andcalibration outside in the measurementsite is influenced by environmentalconditions. Another problem faced byfield monitoring sites is the length ofthe traceability chain. Several stepsare required to transfer the calibrationfrom the primary standards laboratoryto the spectroradiometers, which re-sults in increased uncertainty.

We have developed a portable detec-tor-monitored calibration system forsolar UV spectroradiometers [1]. Thecalibrator utilizes a 1-kW DXW lampas the light source. The output of thelight source is continuously monitoredwith two temperature-controlled filterradiometers at 313 nm and 368 nmwavelengths. The lamp is operated incurrent-stabilized mode. When theaging characteristics of the lamp areknown, the signals of the monitoringfilter radiometers can be used to cal-culate corrections for the spectrum asthe lamp ages.

Figure 5.1.2-1. Construction of theimproved calibrator.

The spectral irradiance in the output ofthe calibrator is calibrated either witha spectroradiometer or absolutelycharacterized filter radiometers. Theuse of latter provides the shortest pos-sible traceability chain for the calibra-tions.

16

Figure 5.1.2-2. Calibrator assem-bled on top of a Brewer spectrora-diometer.

In 2001, a second improved prototypeof the calibrator was issued (Figure5.1.2-1). Modifications include e.g.handles that make alignment more re-liable and improved cabling inside thehousing.

The calibrator has been thoroughlytested in both laboratory and in field.The results of the field calibrations in-dicate that the device works satisfacto-rily under a wide variety of environ-mental conditions. The device can beused in summer, when temperaturecan be as high as 30 °C and directsunshine heats the housing of the cali-brator. Successful calibrations havealso been carried out in winter, withlight snowfall and ambient tempera-ture of –7 °C (Figure 5.1.2-2).

The work has been carried out within projectSMT4-CT98-2242 “Improving the Accuracyof Ultraviolet Radiation Measurement,”funded by the Standards, Measurements andTesting program of the European Union.

[1] P. Kärhä, L. Ylianttila, T. Koskela, K.Jokela, and E. Ikonen, “A portable fieldcalibrator for solar ultraviolet meas-urements,” Metrologia (accepted).

5.1.3 Characterization of filter radiometers with wavelength-tunable lasersource

M. Noorma, P. Toivanen, F. Manoocheri,and E. Ikonen

Monochromators are traditionally usedfor characterization of the spectral ir-radiance responsivity of filter radi-ometers. The problems arising fromthe wide bandwidth of the monochro-mator and also from the non-uniformities of the filter radiometercan be avoided by using a scanningmethod (Figure 5.1.3-1). The irradi-ance responsivity is obtained by

moving the filter radiometer in rela-tion to a power-stabilized beam of awavelength-tunable laser. The scan-ning is repeated at several wave-lengths to cover the whole pass-bandof the filter radiometer. In addition,online monitoring of the laser wave-length completely removes the prob-lem of wavelength shifts, often presentin monochromator measurements.

17

xy translationstage

Ti:Sapphire laser beam

Monitordetector

Stabiliser

Spatialfilter

Iris diaphragm

Beam splitter

Iris diaphragm

Referencedetector

Neutral density filter

Fiber collimator

Figure 5.1.3-1. Setup for the filterradiometer characterization.

With coherent laser light, interferencebetween the filter surfaces can causespurious effects in the measured re-sponsivity. Wedged filters andanti-reflection coatings of air-glass

surfaces were used to reduce the ef-fects of interference. Measuring theresponsivity as a function of wave-length over a very narrow band nor-mally reveals any remaining interfer-ence effects. Ti:Sapphire laser wasused in the wavelength band from800 to 900 nm for the measurements.The results were compared with moreconventional monochromator meas-urements. It appears that filter radi-ometers can be characterized with anuncertainty lower than 0.1 % using thescanning method.

The work has been financially supported bythe Center for Metrology and Accreditation.

5.1.4 Radiometric determination of radiation temperatures

P. Kärhä, M. Noorma, T. Jankowski,T. Weckström*, and E. Ikonen

* Center for Metrology and Accreditation (MIKES)

According to the international tem-perature scale of 1990 (ITS-90), tem-peratures above 961.78 °C are definedin terms of a defining fixed point andthe Planck radiation law [1]. The de-fining fixed points include freezingpoints of silver (961.78 °C), gold(1064.18 °C) and copper (1084.62°C). A black body radiator operatingat a fixed-point temperature is used tocalibrate an optical pyrometer thatmeasures radiance at a single wave-length, typically 650 nm. This py-rometer is then used to measure thetemperature of a variable temperatureblack body that operates between and

above the defining fixed points.

We have studied an alternative ap-proach to define radiation tempera-tures in the range from 968 °C to 1450°C. The spectral irradiance in front ofa variable temperature black body ismeasured by using a high accuracyfilter radiometer. The filter radiometerconsists of a trap detector, a precisionaperture, and a set of temperature sta-bilized narrow band-pass filters. Allcomponents are absolutely character-ized.

The geometry of the measurements is

18

determined by the area of the openingof the black body radiator, the area ofthe precision aperture of the filter ra-diometer, and the distance between theradiometer and the black body radia-tor. Known geometry allows calcula-tion of the spectral radiance, and thusdetermination of the radiation tem-perature of the black body radiator.

-6

-5

-4

-3

-2

-1

0

1

2

3

900 1000 1100 1200 1300 1400 1500Temperature [°C]

Dev

iatio

n fr

om IT

S-90

[°C

]

380 440 500 600 700 800 900

Measurement wavelength [nm]:

Figure 5.1.4-1. Preliminary results.The graph shows differences of themeasured temperatures from theITS-90. Different symbols indicatemeasurements at different wave-lengths.

Preliminary measurements carried outare presented in Figure 5.1.4-1. Avariable temperature black body ra-diator was measured with four tem-perature settings using 7 different fil-ters for wavelength selection. Thetemperatures were also measured us-ing a pyrometer calibrated with a sil-ver point cell of ITS-90. The resultsare in good agreement at 1090 °C and

1300 °C temperatures. At 900 nmwavelength the deviation is only of theorder of +0.2 °C. The deviation in-creases with decreasing wavelengthprobably because of weaker signallevels with the filter radiometer. Larg-est deviation was noted at the tem-perature of 1450 °C, where the devia-tion is of the order of -5 °C.

The future work in the project willconcentrate in improving the meas-urement accuracy. A new method willbe tested for determining the irradi-ance responsivities of the filter radi-ometer [see chapter 5.1.3]. Distancemeasurements will also be improved,and measurements will be carried outwith different black body radiators.The reason for the large discrepancy at1450 °C will be studied. Linearitymeasurements of the pyrometer indi-cate that it is unlikely that the discrep-ancy would be due to the extrapolationof the ITS-90 based values. Meas-urements give useful information onthe emissivity properties of the blackbody radiators and offer improvementsbetween and above the fixed-pointtemperatures.

[1] H. Preston-Thomas, “The InternationalTemperature Scale of 1990 (ITS-90),”Metrologia 27, 3-10 (1990).

19

5.1.5 Study of fiber optic power measurements using photodiodes with andwithout integrating sphere

J. Envall, P. Kärhä, and E. Ikonen

Fiber optic power measurement is oneof the fundamental measurements intelecommunications. These measure-ments are needed for example to de-termine losses in telecommunicationcables, in the maintenance of telecom-munication networks, and in the de-velopment of several fiber optic de-vices.

We have developed a setup for cali-bration of fiber optic power meters.The calibration equipment consists ofthree InGaAs photodiodes (Figure5.1.5-1). Two of the photodiodes aremounted directly to adapters withstandard FC connectors. The thirdphotodiode is fitted into a 5-cm inte-grating sphere. The sphere has two in-put ports, one equipped with a similaradapter as the two detectors mentionedearlier, and one with no extra mount-ings. The second input port can beused for calibrating the sphere detec-tor within a sequence of measurementswithout removing the adapter.

Detectors, with their FC connectorsremoved, are calibrated with colli-mated laser beams against a pyroelec-tric radiometer traceable to a cryo-genic absolute radiometer. In addition,spatial uniformities and angular re-sponsivities have been measured. Thisdata is used to calculate corrections

due to the geometry of the beam fromthe fiber end.

FC connectorRemovable adapter

PhotodiodeAluminium case

LEMO connector

Diffusing black paint

Photodiode

Spectralon structure FC connector

Port 1

Exit port

Port 2

LEMO connector

Baffle

Figure 5.1.5-1. Physical structure ofthe detectors studied.

Lasers are available for calibrations atthe wavelengths of 1310 nm and 1550nm wavelengths. In future, it isplanned to include 850 and 1620 nmlasers. Calibrations can be performedwith single-mode fibers.

20

Characterization measurements carriedout so far indicate good results evenwithout using the integrating sphere.The spatial nonuniformities of theplain photodiodes are of the order of0.3 % throughout the active area of 5mm in diameter. The angular responsevaries less than ±0.2 % within the exit

angle of ±8°, where the radiationemitted by the fiber end subsists.These extremely good values elimi-nate the need of integrating sphere inpractice. The uncertainty obtainable ispresently of the order of 1.5 % (k = 2).


5.1.6 Development of absolute scale of spectral diffuse reflectance

S. Nevas, F. Manoocheri, and E. Ikonen

Measurements of spectral diffuse re-flectance play an important role invarious fields of industrial and re-search applications. In most cases, themeasurements are made relative to thereference standards. By internationalagreement, the primary standard fordiffuse reflectance is the perfect re-flecting diffuser. Since there is nosuch material that would satisfy thedefinition of the perfect diffuser, ab-solute measurement methods are em-ployed that relate the reflectance val-ues of a standard to that of the perfectreflecting diffuser. At present inEurope, there are only a few traceablescales of absolute diffuse reflectance.

The present scale of spectral diffusereflectance at HUT is based on directcomparison with standards obtainedfrom the absolute scales of PTB(Physikalisch-Technische Bundes-anstalt, Germany) and NRC (NationalResearch Council, Canada). In orderto overcome the limitations of a rela-tive scale, a facility is under develop-

ment that will provide spectral diffusereflectance, transmittance, and bi-directional radiance and transmittancefactors of a range of standards in ab-solute units.

Detector pos. 1(incident beam)

Detector pos. 2(reflected radiance)

Sample

Incident beam

Rotary stages

L

θθθθview

θθθθillumination

Figure 5.1.6-1. Basic layout of thegonio-spectrometric detection sys-tem. The bi-directional radiancefactor for certain geometries is de-termined by comparing two fluxes:the incident and the reflected intothe solid angle.

The developed facility will enablemeasurements of spectral diffuse re-flectance and bi-directional radiancefactor of samples under the most ofthe CIE recommended geometries ofillumination and view in the wave-

21

length range of 360-830 nm. The in-strument will involve the use of gonio-spectrometric detection system. Toprovide the facility with a monochro-matic source of radiation a state-of-the-art optical source system will be

implemented. We aim to reach an un-certainty of less than 0.2 % (1 σ) inthe visible spectral range.


5.1.7 Optical characterization of thin films

S. Nevas, F. Manoocheri, and E. Ikonen

Thin films are one of the buildingblocks in optical / opto-electronictechnology. It is often necessary tomeasure optical parameters of the de-posited layer: the complex index of re-fraction and the thickness of the film.The most common measurement tech-niques are based either on ellipsome-try or on determining spectropho-tometric properties of the layer. Weuse the latter approach exploiting ourhigh-accuracy reference spectropho-tometer for reliable transmittancemeasurements.

Typically, the coherence length of thespectrophotometer output is consid-erably smaller than the substratethickness and much larger than thethickness of the film. As a result, themultiple interreflections in the filmlayer are coherent while in the sub-strate slab they are non-coherent. Thisfact allows describing the spectraltransmittance / reflectance of thin filmsamples by using analytical equations.

67

72

77

82

87

92

97

400 600 800 1000 1200 1400 1600W avelength / nm

Tran

smitt

ance

/ %

0.0E+00

5.0E-04

1.0E-03

1.5E-03

2.0E-03

2.5E-03

3.0E-03

3.5E-03

400 600 800 1000 1Wavelength / n

k2.06

2.08

2.10

2.12

2.14

n

Figure 5.1.7-1. Characa Ta2O5 thin film deposquartz substrate: a) thfitted and bare-substratances; b) the obtainedimaginary, k, parts of tindex. The determined fis 883 nm.

b)

a)

200 1400 1600m

1.98

2.00

2.02

2.04

terization ofited on fusede measured,te transmit-

real, n, andhe refractiveilm thickness

22

We determine the complex index ofrefraction and the thickness of thelayer deposited on a known substrateby means of nonlinear least-squaresregression. During the fitting proce-dure, parameters of the dispersionformulas and film thickness are ad-justed until the calculated spectrummatches the measured transmittance.

Several samples of dielectric thinfilms deposited on optical-quality sub-strates have been investigated. Thetransmittances were measured in theVIS-NIR region and optical parame-ters of the layers were extracted fromthe spectra. Fitted and measuredtransmittances are in good agreementwith each other.

The accuracy with which thin filmproperties can be determined is highlydependent on the quality of the trans-mittance measurements. Factors suchas the accuracy of the wavelengthscale, stability and linearity of the de-tection system have a profound effecton the reliability of the retrieved pa-rameters. Our reference spectropho-tometer has demonstrated excellentcontinuity of the measurement resultsover the spectral range of 400-1600 nm. This provided a good start-ing point for the application of themeasurement capability for reliablecharacterization of thin films.The work has been financially supported byPlanar Systems, Guideoptics, and TEKES.

23

5.2 Length Metrology

5.2.1 Iodine-stabilized diode lasers

M. Merimaa, M. Vainio, K. Nyholm*, and E. Ikonen


Frequency stabilized He-Ne gas lasersat 633 nm are generally used for therealization of the definition of themeter and form the current basis foraccurate length measurements. How-ever, there is definite interest in fre-quency stabilization of diode lasers at633 nm, as their output power is com-paratively high and diode lasers areinherently compact. The invention ofthe femtosecond frequency comb fordirect link between optical and mi-crowave frequencies has recently in-creased the interest in diode laser fre-quency stabilization, as diode laserscan easily achieve power levels whichare sufficient for beat frequencymeasurements with the comb.

In 2001 the emphasis of the develop-ment of iodine stabilized diode lasershas been on the construction of a morerobust and hermetically sealed trans-mission-grating laser to obtain betterpassive frequency stability of the lasersource. The aim is to develop a com-pact laser source that can, without ad-justments, reproduce desired wave-length at a few GHz accuracy despite

changes in ambient temperature orpressure. In addition, the modulationproperties of the laser have been im-proved to shift the measurement tohigher frequencies where 1/f-type in-tensity and frequency noise of diodelasers is lower.

Figure 5.2.1-1. Photograph of theprototype laser.

Figure 5.2.1-1 shows a photograph ofthe developed prototype laser, whichis manufactured from Invar and alu-minum. The design has been opti-mized for small and mode-hop freefrequency change, if the temperatureof the laser body changes. Preliminarytests of the laser source are being car-ried out and the laser will be used inthe stabilization set-up in 2002.

24

5.2.2 Iodine-stabilized Nd:YAG lasers

K. Nyholm*, T. E. Ahola, M. Merimaa, and E. Ikonen


Traditionally, practical length metrol-ogy is carried out using iodine-stabilized He-Ne lasers at 633 nm. In1997, when Nd:YAG lasers stabilizedto iodine at 532 nm had demonstratedstabilities comparable to He-Ne lasers,the wavelength 532 nm realized byNd:YAG laser was added to thewavelengths recommended for thepractical realization of the meter.

Diode-pumped Nd:YAG lasers havemany attractive features for lengthmetrology, e.g. low intrinsic frequencyand intensity noise, and high outputpower. Moreover, the iodine absorp-tion lines are strong and narrow near532 nm forming an almost ideal fre-quency reference. Excellent frequencystabilities and repeatabilities havebeen achieved by Nd:YAG lasers sta-bilized to iodine using FM-sidebandtechniques. However, similar per-formance can be reached using stan-dard third-harmonic technique widelyused in frequency stabilization, as itprovides means to construct compactand relatively inexpensive systems.

In collaboration with the Center forMetrology and Accreditation, a diode-pumped Nd:YAG laser was fre-quency-stabilized to the Doppler-freespectrum of iodine at 532 nm. Thehigh power of the Nd:YAG laser and

the use of a PPKTP-crystal enable fre-quency doubling without an externalcavity and hence the use of third-harmonic technique. In Figure 5.2.2-1is shown the Nd:YAG laser system.

Figure 5.2.2-1. Iodine-stabilizedNd:YAG laser system.

In order to use third-harmonic tech-nique two piezo-crystals were attachedon the laser crystal: one for frequencymodulation and the other for fre-quency fine-tuning. Coarse-tuning isrealized by temperature control of thelaser crystal.

The performance of the system wastested in an international comparisonheld at the BIPM. The results showthat good relative frequency stability(7×10–14, 1 s, 40-cm iodine cell) andexcellent repeatability are achievableeven by using third-harmonic locking.

25

5.3 Microtechnologies

5.3.1 Micromechanical resonators for RF-applications

T. Lamminmäki, P. Rantakari, M. Koskenvuori, and I. Tittonen

The general trend towards the use ofsmaller, better integrable MEMS (Mi-cro ElectroMechanical Systems) RF-components to replace discrete RF-filters, oscillators and switches isshown in Figure 5.3.1-1.

RF-AmplifiersQuartzCrystal

RF-Filters

Integrated Single-Chip RF-circuit

RF-Switches

MEMSResonatorsMEMS

FiltersMEMS

Switches

Figure 5.3.1-1. Integrating the dis-crete RF-components into a single-chip RF-circuit.

Microscale mechanical resonators(Figure 5.3.1-2) fabricated on SOI(Silicon On Insulator) wafers can beused as building blocks for the RF-components. The excellent mechanicalproperties of single crystal silicon en-able low losses even for microscaleresonators, but the lack of piezoelec-tricity in silicon leads to a need fordifferent drive and excitation methodsfrom those used in conventionalquartz resonators. Therefore capaci-tive coupling is used to excite andread the resonance. Capacitively actu-

ated mechanical systems can success-fully be analyzed using FEM (FiniteElement Method) simulation tech-niques by simultaneously taking intoaccount mechanical, thermal andelectromagnetic dynamic interactions.FEM can also be used to estimatethose parameters that are later fed intothe circuit-simulation program re-vealing how the mechanical design ineffect works as a part of an RF elec-tronics circuit.

Figure 5.3.1-2. Length extensionalmode microresonator for 13 MHz.

The capacitive coupling of microscalestructures to surrounding electronicsusually leads to non-optimal couplingdue to the high impedance levels ofthe microstructures. This non-optimal

26

coupling in turn causes an increase inshort-term noise. Again, FEM-simulations together with state-of-the-art fabrication techniques can be usedto decrease the impedance levels and

short-term noise.

This collaboration between HUT/MRI, VTTElectronics, and VTT Automation has beenfinancially supported by Nokia ResearchCenter, VTI Hamlin, and TEKES.

5.3.2 Finite element modeling of microsystems

P. Rantakari, N. Tsekurov, and I. Tittonen

The finite element method is verysuitable for modeling complex 3D-microsystems, which are usually ex-posed to many physical effects. InFEM, the complex differential equa-tions of a 3D physical model withmultiple variables are transformed intoa series of linear equations to besolved numerically. In general, themodeling flow is as follows: createthe model → select a suitable elementtype → define the material properties→ mesh the model → define constrainsto subscribe the physical environment→ solve problem → analyze the re-sults.

Figure 5.3.2-1. Micromechanicalmicrophone designed at VTT.

Often a micromechanical device needsto be coupled to electronics. The cou-

pling is usually implemented with acapacitive transducer. This kind ofcoupled-field problem is very suitableto the FEM analysis.

Figure 5.3.2-2. Eigenmodes of theprestressed membrane.

One typical example of a coupled-field microdevice is a micromechani-cal microphone (see Figure 5.3.2-1).The sensing element of the micro-phone is a thin prestressed siliconmembrane. The response of the mem-brane to sound waves is detected ca-pacitively via electrodes.

At first, the mechanical properties ofthe microphone are modeled. The firstresonant eigenfrequency should bewell above 20 kHz to achieve a maxi-mum flat response (Figure 5.3.2-2).

27

Voltage sweep of 2D structure

0

1

2

3

4

5

6

7

8

0 0.5 1 1.5 2 2.5 3

U(v)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Capacitance(pF)Displacement(um)

Figure 5.3.2-3. DC-voltage sweepfor finding out the pull-in voltage.

Since the capacitive detection needs aDC-voltage difference between the vi-brating membrane and the electrode,one needs to solve how the electricfield affects the mechanical propertiesof the microphone. Figure 5.3.2-3shows results from the pull-in voltageanalysis of the microphone.

Finally, the dynamical behavior of the

microphone is inspected (Figure5.3.2-4). The gas damping by the sur-rounding air is modeled by a spring-damper element to correspond to theanalytical result of the gas damping ofthe membrane.

-0.0004

-0.0002

0

0.0002

0.0004

0.0006

0.0008

0.001

0.0012

0.0014

0.0016

-3.00E-05 2.00E-05 7.00E-05 1.20E-04 1.70E-04 2.20E-04 2.70E-04 3.20E-04

Figure 5.3.2-4. Dynamical behaviorof the microphone was inspected bytransient analysis.

The work has been financially supported byVTI Hamlin, Vaisala, Aplac Solutions, NokiaResearch Center, and TEKES.

5.3.3 Optical interferometry on a mechanical silicon oscillator

O. Hahtela, K. Nera, K. Lahti, and I. Tittonen

A HR-coated high-Q mechanical sili-con oscillator was employed as a pla-nar rear mirror in a Fabry-Pérot inter-ferometer (Figure 5.3.3-1). Active sta-bilization of the interferometer im-proves the stability of the resonanceand makes it possible to perform sen-sitive interferometric measurements.

The frequency locking of a laser to anoptical cavity usually requires thegeneration of an error signal with atypical slope at the resonance. TheHänsch-Couillaud locking methodutilizes polarization spectroscopy by

monitoring changes in the polarizationof the reflected light. A polarizationanalyzer detects dispersion shapedresonances, which give the error sig-nal for the electronic servo loop. Theerror signal contains informationabout the changes in the cavity lengthof the optical resonator and thus themotion of the mechanical oscillatorcan be observed.

28

Figure 5.3.3-1. High-Q mechanicalsilicon oscillator with HR-coating(R=0.98) is employed as a planarrear mirror in a Fabry-Pérot inter-ferometer, which has a finesse of100, FSR of 6 GHz and an opticalpassband of 60 MHz.

The error signal was detected with theuse of a spectrum analyzer. The noisefloor of the interferometer responseindicates that the sensitivity of the in-terferometer, or the minimum dis-placement in the oscillator positionthat can be detected, is∆xmin=1.7 ×10-14 m. This gives theoptomechanical sensor a high enoughsensitivity to observe for example theBrownian motion (∆xthe=1.9 ×10-13 m)of the mechanical oscillator at roomtemperature.

5.3.4 High-Q micromechanical silicon oscillators

K. Nera, O. Hahtela, T. Lamminmäki, and I. Tittonen

Mechanical oscillators that have a sta-ble resonance with a high quality fac-tor have applications as reference os-cillators, sensors and even in very so-phisticated high-precision experimentsfor observing quantum effects.

The main idea in designing a high-Qoscillator is to construct structureswith low mechanical energy flow fromthe active resonating part of the sys-tem. Balanced torsionally vibratingstructures have proved to be verypromising in this respect. At atmos-pheric pressure the most significantloss mechanism is gas damping. Foran oscillator working in vacuum themajor part of the mechanical energy

losses is caused by the coupling to thesupport structure and by internal fric-tion which in turn is a result of a vari-ety of physical mechanisms like ther-moelastic effects and phonon scatter-ing.

The influence of a dielectric coatinglayer on the Q-factor and the reso-nance frequency has been studiedsince the oscillators need to be coatedwith high-reflectivity coating in someoptomechanical experiments. Sincethe mass of the oscillator increaseddue to the coating, the resonance fre-quency (~68 kHz) decreased by aboutone percent. The decreasing effect ofthe coating layer on the Q-factor is

29

shown in Figure 5.3.4-1.

10000

100000

1000000

0.0001 0.001 0.01 0.1 1 10 100 1000

Pressure [mbar]

Q-fa

ctor

uncoated HR-coated

Figure 5.3.4-1. Influence of thehigh-reflectivity coating layer on theQ-factor of a mechanical silicon os-cillator.

We also studied the behavior of themechanical motion of oscillators as afunction of the temperature since thephysical effects that restrict the qualityfactor at low temperatures are rathervaguely known. In Figure 5.3.4-2 theQ-factor and the resonance frequency

of an RF-oscillator are presented as afunction of temperature. As the tem-perature was lowered below 50 K, theQ-factor began to increase rapidly. At4.2 K the Q-factor was roughly threetimes that of the room temperaturevalue.

0

5000

10000

15000

20000

25000

30000

35000

0 50 100 150 200 250 300

Temperature [K]

Q-fa

ctor

14.67

14.68

14.69

14.70

14.71

14.72

14.73

14.74

14.75

Freq

uenc

y [M

Hz]

Q-factor Freq

Figure 5.3.4-2. Q-factor and reso-nance frequency of a mechanicalsilicon oscillator as a function oftemperature.

30

5.4 Applied Quantum Optics

5.4.1 Integrated atom optics

T. Lindvall, A. Liukko, L. Niinikoski, I. Tittonen, S. Franssila*,A. Huttunen†, M. Rodriguez†, P. Törmä†, A. Shevchenko‡, and M. Kaivola‡

* Microelectronics Center, HUT† Laboratory of Computational Engineering, HUT

‡ Optics and Molecular Materials, HUT

The progress in laser cooling andtrapping of neutral atoms during thepast decade has produced a variety oftechniques based on the use of lightforces and electromagnetic fields toreach extremely low temperatures inatomic vapors and to control thetranslational motion of atoms. Thishas led to a field called atom optics,where the goal is to manipulate atomicsamples and beams analogously tohow light is manipulated in traditionaloptics.

Using modern microfabrication tech-niques it is possible to construct mi-cron-sized magnetic microtraps on thesurface of a substrate. These traps canbe loaded with cold atoms from, forexample, magneto-optical traps(MOT). This could allow the integra-tion of several atom traps and otheratom-optical components onto a so-called atom chip. Recently also Bose-Einstein condensation has beenachieved on an atom chip [1, 2].

Figure 5.4.1-1. Calculated equipo-tential lines for a magnetic atomtrap created by current-conductingwires.

The goal of the project is to developnew chip fabrication techniques andapply these for different atom-opticalcomponents. New components mustbe modeled before fabrication, seeFigure 5.4.1-1. During 2001 the firsttest chips were designed and then fab-ricated at the HUT MicroelectronicsCenter, see Figure 5.4.1-2. Some pre-liminary tests of the current-carryingcapabilities of the wires have alsobeen made (Figure 5.4.1-3). The partsfor the ultra-high vacuum system,

31

where the chips will be more thor-oughly tested, were acquired.

Figure 5.4.1-2. Photograph of oneof the test wafers containing atom-chip prototypes.

A suggestion to use a gravito-opticaltrap for the loading of an atom chipwas also developed [3]. The othertheoretical studies include investiga-tion of the influence of heating andnoise on the trapped atoms.

Figure 5.4.1-3. Scanning electronmicroscope (SEM) picture of a 10-µm wire that has been burned in amaximum-current-density test.

The work has been financially supported bythe Academy of Finland.

[1] H. Ott, J. Fortagh, G. Schlotterbeck, A.Grossmann, and C. Zimmermann,Phys. Rev. Lett. 87, 230401 (2002).

[2] W. Hänsel, P. Hommelhoff, T.W.Hänsch, and J. Reichel, Nature 413,498 (2001).

[3] A. Shevchenko, M. Kaivola, T. Lind-vall, and I. Tittonen, (submitted).

5.4.2 Digital laser frequency stabilization

M. Heiliö, E. Vahala, O. Kimmelma, K. Lahti, and I. Tittonen

Frequency stable coherent lightsources have a great significance inareas of optical spectroscopy, me-trology and communications. Veryhigh stabilities have been achievedusing the Pound-Drever-Hallmethod [1], where the laser fre-quency is locked to a high-Q opticalresonator using a phase modulation

scheme. We use this technique to lock aNd:YAG laser to an optical resonatorwith finesse around 4 000 [2].

One of the crucial elements of the stabi-lization system is the laser servo control,which tunes the laser frequency elec-tromechanically and electrothermallybased on the frequency fluctuation in-

32

formation given by the resonator(Figure 5.4.2-1).

Nd:YAGFI

PBS

PM

λ / 2

λ / 2

λ / 4

Digitalcontrol

Thermally stabilized environment Electrical signal

Laser

ModematchingopticsFI = Faraday Isolator

PM = Phase modulatorPBS = Porarizing beam splitter

Slow

Fast

Figure 5.4.2-1. Nd:YAG laser islocked to a high-Q optical reso-nator using a phase modulationscheme.

The servo control operates at a fre-quency bandwidth totally coveringthe technical noise of the laser. Thefrequency noise of our laser be-comes shot noise-limited approxi-mately at frequencies higher than100 kHz. Servo controls operating atthis high frequencies have tradition-ally been constructed using analogelectronics. In our experiment wehave been using a high-speed digitalsignal processor together with high-resolution A/D & D/A convertersincorporating efficient digital filter-ing. The 150 MHz processor clock

frequency ensures operation beyond thetechnical noise bandwidth and enablesthe use of a rather complex algorithmcombining the advantages of a tradi-tional fringe side locking and a PDHmethod. Locking methods based ontransmission measurements suffer fromdelay induced by cavity response time.However, the transmission intensityprovides the locking algorithm with ex-plicit information concerning triggeringand achieving the lock in general.

Figure 5.4.2-2. The standing opticalmode inside the interferometer cap-tured on a CCD.

[1] R. W. P. Drever et al, Appl. Phys. B. 31,97-105 (1983).

[2] T. J. Kane et al, Appl. Opt. 10, 65-67(1985).

5.4.3 All-optical 3-GHz frequency standard based on dark states of 85Rb

M. Merimaa, T. Lindvall, I. Tittonen, and E. Ikonen

A compact atomic frequency referencehas potential applications in areaswhere an intermediate step betweenthe Cs-atomic clock and a crystal os-cillator is desired. A relatively simpleway to realize an all-optical atomicfrequency reference using coherent

population trapping (CPT) was pro-posed by Cyr et al in 1993. Advancesin diode lasers have made such de-vices feasible and if sufficient stabilityis achieved these devices could beused for example in telecommunica-tions applications.

33

In CPT two laser fields interactingwith an atomic three-level Λ-systemare coupled by the ground state coher-ence and interfere destructively attwo-photon resonance. Since this two-photon Raman resonance takes placebetween two ground states thelinewidth is very narrow and the reso-nance forms an almost ideal frequencyreference. In practice the linewidthand the absolute frequency of theresonance are determined by the ex-perimental parameters.

-75 -50 -25 0 25 50 75

-30

-20

-10

0FW HM

23± 0.5 Hz

Sig

nal [

a.u.

]

Frequency [Hz]

Figure 5.4.3-1. The measured ultra-narrow CPT line.

In this work we use a diode laserequipped with an integrated microlensas a laser source. Optical feedbackfrom the closely mounted microlenscan be used to improve the spectrumwithout hampering the modulationproperties of the laser and the secondlaser field can be generated directly bymodulating the laser frequency viainjection current. The Λ-system of

85Rb is used in this work because laserdiodes operating at the frequency ofthe Rb 52S1/2-52P3/2 transition(780.24 nm) are easily available andthe modulation bandwidth of an edge-emitting diode laser covers the3.0357 GHz ground state hyperfine-splitting.

1 10 100 1000 10000

10-13

10-12

10-11

10-10

10-9

Cs-atomic

clock

H igh-quality

crystal oscillator

CPT stabilized

crystal oscillator

6.4× 10-13 at 2000 sσ(2

,τ)

Integration time τ [s]

Figure 5.4.3-2. Frequency stabilityof an oscillator locked to the CPTresonance.

Our system allows detection of ultra-narrow CPT resonance below 25 Hz asshown in Figure 5.4.3-1. An RF-oscillator has been successfully lockedto the resonance between the mF=0magnetic sublevels. Figure 5.4.3-2shows the measured frequency stabil-ity of the system. The frequency sta-bility slope is 3.5×10-11 τ-1/2 and thebest stability of 6.4×10-13 is reached atan integration time of 2000 s [1].

[1] M. Merimaa, T. Lindvall, I. Tittonen,and E. Ikonen, J. Opt. Soc. Am. B (ac-cepted).

34

5.4.4 Quasi-phase-matching in nonlinear laser frequency conversion

O. Kimmelma, K. Lahti, and I. Tittonen

Nonlinear crystals are used to convertlaser light frequencies. A critical re-quired condition for the constructiveinterference in a crystal is phase-matching. A special method to per-form phase-matching is the use ofquasi-phase-matching where the crys-tal orientation, corresponding to themaximum nonlinearity, changes peri-odically in alternating layers of differ-ent orientation (Figure 5.4.4-1).

Figure 5.4.4-1. Effect of phasematching type to the second har-monic intensity.

A quasi-phase-matched potassium-titanyl-phosphate (KTP) crystal isused to convert the 1064nm laser tothe second harmonic at 532nm. Thesize of the used crystal is 5x2x1 mm3.The setup adjustments to maximizethe output are carried on. The setuphas been designed in collaborationwith Laboratoire de Photonique et deNanostructures, CNRS-LPN (Dr.Kamel Bencheikh).

35

5.5 Characterization of fiber-optic components

5.5.1 Group-delay ripple in chirped fiber Bragg gratings

T. Niemi, G. Genty, and H. Ludvigsen

Characterization of group delay andamplitude properties of various com-ponents is important in designing ad-vanced optical networks. The phase-shift method is an established tech-nique for performing high-accuracymeasurements of these parameters.The accuracy in resolving the finestructure of the group delay, however,depends critically on the modulationfrequency used in the measurement[1]. The choice of the modulation fre-quency is, in general, a trade off be-tween the desired accuracy of themethod and the resolution of the elec-trical phase measurement. We havedeveloped a new method to evaluatethe error of the measurement and toimprove the accuracy of the phase-shift technique when high modulationfrequency is applied to achieve a highresolution.

The new method is based on the in-strument function for a group-delaymeasurement with the phase-shifttechnique. The measured group delaycan be written as

∫∞

∞−

== )2/(*)(.)sin().(~mcomp

uj

m

mcompmeas rectdue

uuu ωωωτ

ωωττ ω ,

where τcomp is the actual group delayof the component and τmeas is themeasured group delay. rect and * de-

note the rectangular instrument func-tion and the convolution operation.This formula can conveniently be usedto investigate the effects of the modu-lation frequency on the measuredgroup delay ripple of FBGs and esti-mate the error induced by the tech-nique [2]. The method allows the ac-tual group delay of the component tobe accurately reconstructed and it isapplicable to any arbitrary group delayprofile.

0 1 2 3 4-100

-75

-50

-25

0

25

50

75

100

Actual group delay

1 GHz

reconstructed

Gro

up d

elay

[ps]

Optical frequency [GHz]

Figure 5.5.1-1. Reconstruction ofthe actual group delay of a fiberBragg grating using the data meas-ured at 1 GHz. The measured dataand the actual profile are also plot-ted.

We have applied the method to recon-struct the actual profile of the groupdelay of the FBG presented earlier.The measurement data obtained formodulation frequency of 1 GHz is pre-

36

sented in Figure 5.5.1-1. It can be ob-served that the amplitude of the groupdelay is decreased from the actualvalue measured with low modulationfrequency. However, after reconstruc-tion the actual group delay profile isalmost completely restored. This newmethod permits an improvement of theaccuracy of the conventional phase-shift technique without any modifica-tions to the measurement setup. The

reconstruction is done by post-processing of the measured group de-lay

The work has been financially supported bythe Academy of Finland and TEKES.

[1] T. Niemi, M. Uusimaa, and H. Ludvig-sen, Photon. Technol. Lett. 13, 1334-1336 (2001).

[2] G. Genty, T. Niemi, and H. Ludvigsen,Opt. Commun. 204, 119-126 (2002).

5.5.2 Photonic crystal fibers

T. Niemi, G. Genty, and H. Ludvigsen

Photonic crystal fibers (PCFs) exhibitnovel and interesting optical proper-ties. To explore existing measurementtechniques to acquire these propertiesan extensive characterization of PCFshas been conducted in co-operationbetween several European laborato-ries. The novel features of these fibersinclude anomalous dispersion in thevisible wavelengths, single-mode op-eration over all wavelengths and highoptical nonlinearity. Example of alarge-mode area PCF is displayed inFigure 5.6.2-1.

The parameters of main interest in-clude polarization-related propertiesand chromatic dispersion. Chromaticdispersion of a 19 m long highly non-linear PCF with a core diameter of 1.7µm is displayed in Figure 5.5.2-2. Thedispersion is anomalous at this wave-length range.

Figure 5.5.2-1. Cross section oflarge-mode area PCF (Crystal Fi-ber A/S).

Various techniques to characterizepolarization-mode dispersion (PMD),polarization dependent loss (PDL),polarization beatlength along the fiberand chromatic dispersion have beenstudied. Standard measurement meth-ods work reasonably well for the mostof the parameters [1]. However, someso far unexplained features related tomeasurement of PMD at differentwavelengths make it clear that more

37

investigations will be necessary. High-resolution (OFDR) measurementmethods proved to be invaluable forthe characterization of the beatlengthand loss profiles of the short fibersamples at hand. The measurementsperformed so far indicate that the ho-mogeneity of the fiber is a source forlarge polarization dependence and ex-cess loss.

1500 1520 1540 1560 1580 1600-200

-150

-100

-50

0

50

100

150

200

D=165 ps/nm/km

Group delay Linear fit

Gro

up D

elay

[ps]

Wavelength [nm]

Figure 5.5.2-2. Group delay of thehighly nonlinear PCF around 1550nm.

This work which was lead by H. Lud-vigsen has been conducted in collabo-ration with the Group of AppliedPhysics/ University of Geneva, Na-tional Physical Laboratory and Serviced'Electromagnétisme et de Télécom-munications/Faculté Polytechnique deMons within the COST Action 265.

Crystal Fiber A/S in Denmark kindly lent thefibers to the COST group.

[1] M. Wegmuller, F. Scholder, A.Fougères, N. Gisin, T. Niemi, G.Genty, H. Ludvigsen, O. Deparis, andM. Wicks, “Evaluation of measurementtechniques for characterization of pho-tonic crystal fibers,” CLEO/QELS´02,Long Beach, CA, 2002, paper JThA4.

5.5.3 Intercomparison of measurement techniques to characterize fiberBragg gratings

T. Niemi and H. Ludvigsen

Fiber Bragg gratings (FBGs) are beingincreasingly used in WDM systems forwavelength selection and dispersioncompensation. A European intercom-parison has been conducted build onwork carried out primarily in NorthAmerica to determine the industrialmetrology capability for spectral andgroup delay measurements of FBGs,which was co-ordinated by NIST [1].

Two chirped gratings were circulatedamongst several laboratories. The firstwas a commercial chirped grating(Bragg Photonics Inc.) mounted in anathermal package without any addi-tional temperature stabilization. Thesecond was a chirped broadbandgrating which was also athermallypackaged. Furthermore, its tempera-ture was controlled to better than 0.1

38

ºC using a thermo-electric cooler. Thisgrating was used in the North Ameri-can round robin.

An example of the measured groupdelay of the broadband chirped gratingis displayed in Figure 5.5.3-1. It showsthat the group delay measured with thephase-shift method agrees well. Thegroup delay measured with photoncounting deviates from the measure-ment conducted with the phase-shiftmethod.

-100

-50

0

50

100

1540 1545 1550 1555 1560

Wavelength (nm)

Gro

up d

elay

(ps)

Phase Shift @ 750 MHz

Photon Counting

Phase Shift @ 500 MHz

Figure 5.5.3-1. Group delay ofchirped grating.

The dispersion of the broadband grat-ing with different measurement meth-ods from both ends of the grating isgiven in Table 5.5.3-1.

Table 5.5.3-1. Summary of averagedispersion, D, of broadband grating.

Method D(ps/nm)Port A

D(ps/nm)Port B

Photon count-ing

5.71 -7.54

Phase shift @500 MHz

6.09 -7.23

Phase shift @750 MHz

6.24 -7.16

The European intercomparison wasco-ordinated by National PhysicalLaboratory. Preliminary results havebeen presented in a conference report[2] and further analysis is to be con-ducted.

This work has been conducted within theCOST Action 265.

[1] A. H. Rose, C.-M. Wang, and S. D.Dyer, “Round robin for optical fiberBragg gratings metrology,” J. Res.Nat. Inst. Stand. Technol. 105, 839-866(2000).

[2] M. Wicks, T. Niemi, H. Ludvigsen, M.Wegmuller, H. de Riedmatten, and N.Gisin, “Preliminary results of a Euro-pean intercomparison of group delaymeasurements of fiber Bragg gratings,”in OFMC’01, Conference Digest 2001,pp. 241-244.

39

5.6 Novel components for optical telecommunications

5.6.1 Supercontinuum generation in photonic crystal fibers

G. Genty, M. Lehtonen, M. Kaivola‡, J. R. Jensen*, and H. Ludvigsen

‡ Optics and Molecular Materials, HUT* Crystal Fiber A/S, Denmark

Photonic crystal fibers (PCFs) consistof a periodic array of air holes runningalongside the core of a silica fiber.This new type of optical waveguidestructure has proven to be particularlyefficient for supercontinuum lightgeneration due to the unique disper-sion properties and enhanced opticalnonlinearities. Such a continuumsource has led to numerous novel ap-plications in the field of optical me-trology and telecommunications.

400 600 800 1000 1200 1400 1600 1800-50

-40

-30

-20

-10

0

10

20

Inte

nsity

[dB

m]

Wavelength [nm]

λpump

=798 nm

Figure 5.6.1-1. Ultra-broad super-continuum.

We have generated supercontinua bylaunching femtosecond pulses from amode-locked Ti:Sapphire laser intovarious crystal fibers [1]. The linearlypolarized pulses from the pump lasercan be tuned in wavelength from 715

to 830 nm. The maximum peak powerof the 100 fs FWHM pulses is 170kW.

Figure 5.6.1-2. Pictures of the gen-erated supercontinua.

The evolution of the input pulse spec-trum into a supercontinuum was stud-ied by gradually increasing the powerof the pump laser. The influence of thepolarization and wavelength of thepump pulses on the generated contin-uum was also investigated. Variousnonlinear phenomena were found tocontribute to the formation of the con-tinuum, such as self-phase modula-tion, Raman scattering, four-wavemixing, and soliton decay, dependingon the type of fiber used to generatethe continuum. Different spectral fea-

40

tures of the supercontinuum can becontrolled by adjusting the parametersof the pump pulses. By optimizing theparameter of the input pulses, we areable to generate an ultra broad super-continuum that extends from 400 to1700 nm, as is shown in Figure5.6.1-1.

This work has been financially supported bythe Academy of Finland.

[1] G. Genty, M. Lehtonen, J. R. Jensen, M.Kaivola, and H. Ludvigsen, “Route tosupercontinuum in photonic crystal fi-bers,” in Conference on Lasers and Electro-Optics and Laser Science Conference(CLEO/QELS´02), Long Beach, CA,2002, paper CTuU1.

5.6.2 Fiber laser for L-band

G. Genty, T. Laukkanen, and H. Ludvigsen

Wavelength division multiplexing(DWDM) technique in the wavelengthwindow of 1535-1565 nm (C-band).To increase the transmission capacityof optical fibers in the future, thewavelength window will be extendedto the wavelength range from 1565 nm

to 1625 nm (L-band). Erbium-dopedfiber lasers have the potential to beused in the L-band as optical trans-mitters and in the characterization ofvarious types of fiber-optic compo-nents.

SF PC

OutputPump

WDM

EDF

I

MZM

RF

M

C/L Filter

Figure 5.6.2-1. Setup of the fiber laser for mode-locked operation.

We have constructed an Erbium-dopedfiber-ring laser, which operates in bothcontinuous wave and pulsed mode. Anoutline of the laser setup for pulsedoperation is presented in Figure5.6.2-1. The laser design is based on afiber-ring cavity where the erbium-doped fiber (EDF) is pumped by a di-ode laser at 980 nm. The pump light iscoupled into the cavity by a wave-

length division multiplexer (WDM).An optical isolator (I) determines thepropagation direction of the laserfield. The birefringence of the fiber iscompensated for with a polarizationcontroller (PC). Pulsed operation isachieved by introducing a Mach-Zehnder modulator (MZ) into the cav-ity. The modulator is driven with awide-bandwidth signal generator (RF)

41

which set the repetition rate of thepulse train. Ten percent of the opticalfield power is coupled to the laseroutput with a fiber coupler (FC). AC/L band reflecting filter and a mirror(M) allows the C-band ASE noise tobe re-utilized as pump.

The laser is temperature-stabilized anddelivers 1 mW output power. We have

obtained repetition rates of up to 6GHz and pulse widths of few ps [1].This work has been financially supported bythe Academy of Finland.

[1] G. Genty, T. Laukkanen, and H. Ludvig-sen, “Characterization of a harmonicallymode-locked fiber ring laser: modelingand experiments,” in 6th Optical FiberMeasurement Conference (OFMC’01),Conference Digest 2001, pp. 259-262.

5.6.3 Wavelength reference

J. Tuominen, T. Niemi, P. Heimala*, and H. Ludvigsen

* VTT, Information Technology

Modern WDM systems working overa broad wavelength range requiremeans to monitor and calibrate thechannel wavelengths with high accu-racy. Silicon Fabry-Perot etalon pro-vides a compact and flexible wave-length reference for these purposes.These references also find use in cali-bration of measurement devices andfrequency stabilization of lasers.

We have developed a wavelength ref-erence based on a tunable silicon eta-lon. The refractive index of silicon hasa temperature dependence that can beutilized to tune the transmission spec-trum of the etalon as shown in Figure5.6.3-1. By knowing the parameters ofthe etalon, the positions of the trans-mission fringes can be determined.Subsequently, a fringe can be tuned toany desired wavelength in the operat-ing range of the device with a changeof the temperature of the etalon. A

computer program has been written toautomate the calculations and thetuning procedure.

Figure 5.6.3-1. Tunable transmis-sion spectrum of the etalon.

The wavelength accuracy of the de-vice was determined at the 1.55-µmregion by measuring the beat fre-quency of two lasers. One laser waslocked to the center of a transmissionfringe of the etalon and another laserwas locked to an acetylene absorptionline for an accurate reference. The ac-curacy was measured against over 50

42

absorption lines. The measurementpoints indicate accuracy better than125 MHz.

Figure 5.6.3-2. Realized wavelengthreference.

The wavelength reference developedis found to be compact, robust, andcost-effective. Its operating range(1300-1700 nm) is superior comparedto molecular or atomic references,covering the whole wavelength rangeof interest for fiber-optic telecommu-nications. The accuracy is measured tobe ~1 pm. The realized device is pre-sented in Figure 5.6.3-2.

The work has been financially supported bythe Nordic Industrial Fund and the Centerfor Metrology and Accreditation.

5.6.4 Measurements of thermally poled waveguides with Bragg gratings

G. Genty, C. J. Marckmann*, Y. Ren*, J. Arentoft*, and M. Kristensen*

*Research Center COM, Technical University of Denmark

Due to its centrosymmetric nature,silica does not exhibit second-ordernonlinear optical properties. This hasprevented fabrication of silica-basedelectro-optic devices such as switches,modulators or wavelength converters.By poling silica-based optical wave-guides it is possible to induce second-order nonlinear optical properties insilica. Electric field poling is per-formed by applying a large electricfield across the sample while excitingit by either heat or radiation.

We have performed measurements onthermally poled UV-writtenwaveguides with Bragg gratings. Us-ing the charge separation model andfitting the shift of the wavelength of

the reflection peaks as function of anexternally applied field to a parabolicprofile, we were able to extract the in-duced second and third-order nonline-arities as well as the poling induced dcelectric field. The linear electro-opticcoefficient, the quadratic coefficientand the poling induced internal dcelectric field were deduced from theshift of the reflection peak of thegratings when increasing the voltage[1].

These values are consistent with theresults obtained by other groups thathave performed interferometric meas-urements on samples similar to thesample used in this work and are wellexplained by the charge separation

43

model.This research has been conducted at Re-search Center COM and it has been fundedby the Nordic Academy for Advanced study(NorFA) and the GETA Graduate School.

[1] C. J. Marckmann, G. Genty, Y. Ren, J.

Arentoft, and M. Kristensen, “Bragggratings as probes to determine non-linearities induced by thermal poling,”in Bragg Gratings, Photosensitivity,and Poling in Glass Waveguides,Stresa, Italy, July 4-6, 2001, paperBFC3.

44

6 INTERNATIONAL CO-OPERATION

6.1 International Comparison Measurements

Bilateral comparison of spectral irradiance with NIST, USA

The spectral irradiance scales of NIST and HUT were compared in the 290 –900 nm region. The comparison indicates an agreement except in the UVB re-gion, where the discrepancies are slightly higher than the uncertainty of thecomparison. During 2001, the comparison report has been prepared to be sub-mitted to Metrologia.

Bilateral comparison of illuminance with NIST, USA

The illuminance scales of NIST and HUT were compared in summer 2000. Thecomparison indicates an excellent agreement within the uncertainty of the com-parison. The results have been accepted to be published in Metrologia.

Bilateral comparison of luminous flux with NIST, USA

The new luminous flux scale of HUT was compared with the scale of NIST insummer 2000. The comparison indicates an excellent agreement within the un-certainty of the comparison. The results have been accepted to be published inMetrologia.

Improving the accuracy of ultraviolet radiation measurement

In this project funded by the SMT-program of the EU, novel filter radiometertechniques developed by HUT were used to compare various ultraviolet cali-bration facilities in France (BNM), Finland and UK (NPL). In 2001, HUT pre-pared the final report on the measurements [Petri Kärhä, Neil Harrison, SauliusNevas and Issam Abu-Kassem, Improving the Accuracy of Ultraviolet Radia-tion Measurement, Report on the filter radiometer measurements in WorkPackage 1, February 2001]. The results indicate an agreement between thespectral responsivity and spectral irradiance scales of NPL and HUT in theUVA region within the uncertainties of the comparison.

International comparison of fiber Bragg grating group delay (COST-project)

A comparison was carried out for measurements of group delay, bandwidth andrelative transmittance for a fiber Bragg grating with several European partici-

45

pants in 2000. The results showing excellent agreement between HUT, NPL andUniversity of Geneva were published in OFMC’01.

Bilateral comparison of spectral diffuse reflectance with MSL, New Zea-land

The new diffuse reflectance scale of HUT was compared with the scale of MSL.In 2001, HUT conducted their part of the measurements. The results are not yetavailable.

6.2 Thematic Networks

6.2.1 Thematic network for ultraviolet measurements

HUT is the co-ordinator of the Thematic Network for Ultraviolet Measure-ments, which has continued its activities after the EU-funded period. During2001, preparations for the 5th workshop were carried out.

6.2.2 Fiber Optics Technology Network

HUT is a member in the Fiber Optics Technology Network -(FOToN)- (SMT4-CT98-7523) co-ordinated by the National Physical Laboratory (NPL) in UnitedKingdom. FOToN is an interactive information network for the optical fiberuser community. It is sponsored by the European Commission under the Stan-dards Measurement and Testing Program.

The three-year project was launched in November 1998 and it co-ordinates thework of thirteen Regional Groups. Hanne Ludvigsen acts as the regional co-ordinator of the Finnish participants in the network. The Regional Groups areresponsible for identifying common issues and concerns relating to fiber indus-try and for co-ordinating collaborative research. They also provide a nationalforum for the transfer of technology relating to standardization issues.

The FOToN network has prepared web pages for the promotion of regionalgroup activities and to provide an interactive source of information on fiber op-tics.

In year 2001, the 4th regional FOToN meeting was held in connection with Op-tics Days 2001 in Tampere. Furthermore, the 3rd steering group meeting was ar-ranged on 16 May 2001 in connection with the COST Action 265 meeting inHelsinki. On national level the activity has been organized within an OpticalFiber Measurement Club (OFMeC) which currently has 46 members. OFMeC

46

has been established as a sub-activity within the Finnish Optical Society (FOS).

A link to the Finnish OFMeC and the FOToN network can be found from theFiber-Optics Group’s web pages: metrology.hut.fi/fiberopticsgroup.

This project ended on November 31, 2001.

6.3 Conferences and Meetings

The personnel participated in the following conferences and meetings:

CIE Uncertainty Workshop, Vienna, Austria, January 22 – 24, 2001; PetriKärhä

EUROMET CC/Rapporteur meeting, Vienna, Austria, January 23 – 24, 2001;Erkki Ikonen

EUROMET Contact persons meeting, Vienna, Austria, January 24 – 25, 2001;Erkki Ikonen and Petri Kärhä

Optical Communication Wavelength References – 1st steering group meeting,Helsinki, Finland, February 9, 2001, Hanne Ludvigsen

Fourth International Conference on Modeling and Simulation of Microsystems(MSM’2001), Hilton Head, USA, March 19 – 21, 2001; Tuomas Lamminmäkiand Pekka Rantakari

OFC 2001 Conference, Anaheim, California, USA, March 17 – 23, 2001;Hanne Ludvigsen

XXXV Annual Conference of the Finnish Physical Society, Jyväskylä, Finland,March 22 – 24, 2001; Tero Ahola, Miika Heiliö, Ossi Kimmelma, Mika Kosken-vuori, Kristian Lahti, Thomas Lindvall, Mikko Merimaa, Kaisa Nera, LauraNiinikoski, Kaj Nyholm, Ilkka Tittonen, Eero Vahala, and Markku Vainio

FOToN - 4th Regional Meeting, Tampere, Finland, April 19, 2001; Hanne Lud-vigsen, Goëry Genty, Tommi Laukkanen, and Petri Kärhä

Optics Days 2001, Tampere, Finland, April 20 – 21, 2001; Tero Ahola, JouniEnvall, Goëry Genty, Ossi Hahtela, Jari Hovila, Erkki Ikonen, Kristian Lahti,Tommi Laukkanen, Mikko Merimaa, Ilkka Tittonen, Pasi Toivanen, Jesse Tuo-minen, and Markku Vainio

47

Work Package Manager Meeting for the EU-project “Improving the Accuracyof Ultraviolet Radiation Measurement,” Espoo, Finland, April 23, 2001; PetriKärhä

CCPR Key Comparison Working Group Meeting, Paris, France, April 23, 2001;Erkki Ikonen

CCPR meeting, Paris, France, April 23 – 26, 2001; Erkki Ikonen

2nd CIE LED Symposium 2001 and CIE LED Tutorial Workshop 2001,Gaithersburg, MD, USA, May 10 – 12, 2001; Pasi Toivanen

CORM 2001, Gaithersburg, MD, USA, May 13 – 16, 2001; Pasi Toivanen

COST Action 265 – 5th meeting, Helsinki, Finland, May 14 – 15, 2001; HanneLudvigsen, Goëry Genty, and Tapio Niemi

COST Action 265 – 5th MC Meeting Helsinki, Finland, May 14 – 15, 2001;Hanne Ludvigsen

FOToN – 3rd Steering Group meeting, Espoo, Finland, May 16, 2001; HanneLudvigsen

EUROMET General Assembly, Bern, Switzerland, May 14 – 17, 2001; ErkkiIkonen

Nordic School on Atomic Quantum Gases and Matter Wave Optics, Turku,Finland, May 22 – 31, 2001; Thomas Lindvall

11th International Conference on Solid-State Sensors and Actuators, Munich,Germany, June 10 – 14, 2001; Tuomas Lamminmäki, Pekka Rantakari, andMika Koskenvuori

Summer School on Advanced Photonics, Copenhagen, Denmark, August 17 –25, 2001; Hanne Ludvigsen, Goëry Genty, and Tommi Laukkanen

International Summer School on Advanced Topics on Fiber Optic Communica-tions, Tampere, Finland, August 20 – 24, 2001; Tapio Niemi

6th Symposium of Frequency Standards and Metrology, University of St. An-drews, Scotland, September 9 – 15, 2001; Thomas Lindvall and Mikko Merimaa

48

6th Optical Fibre Measurement Conference OFMC 2001, Girton College Cam-bridge, United Kingdom, September 26 – 28, 2001; Hanne Ludvigsen andGoëry Genty

COST Action 265 - 6th MC Meeting, Girton College Cambridge, Cambridge,United Kingdom, September 28, 2001; Hanne Ludvigsen

Optical Communication Wavelength References – 2nd Steering Group meeting,Girton College Cambridge, Cambridge, United Kingdom, September 28, 2001;Hanne Ludvigsen

27th European Conference on Optical Communication ECOC’01, Amsterdam,The Netherlands, September 30 – October 4, 2001; Hanne Ludvigsen and TapioNiemi

Quantum Optics Euroconference 2001, San Feliu de Guixols, Spain, October6 – 11, 2001; Ilkka Tittonen and Thomas Lindvall

6.4 Visits by the Laboratory Personnel

Ilkka Tittonen and Thomas Lindvall, University of Heidelberg, Germany, Janu-ary 30 – February 2, 2001

The personnel of the laboratory, The Royal Institute of Technology and Univer-sity of Stockholm, Sweden, June 7, 2001

6.5 Research Work Abroad

Farshid Manoocheri, National Institute of Standards and Technology (NIST),USA, January 1 – April 30, 2001

Goëry Genty, Technical University of Denmark, Lyngby, Denmark, January 1 –31, 2001

Mikko Merimaa, Kaj Nyholm, and Tero Ahola, Bureau International des Poidset Mesures (BIPM), Paris, France, May 7 – 23, 2001

Petri Kärhä, Ulusal Metroloji Enstitüsü (UME), Turkey, August 26 – Septem-ber 3, 2001

Markku Vainio, HELP Institute, Kuala Lumpur, Malesia, September 1 – De-cember 31, 2001

49

6.6 Guest Researchers

Benoit Sabys, SupOptique, Paris, France, June 1 – August 31, 2001

Diego Beltrami, Politecnico di Milano, Milan, Italy, June 1 – August 31, 2001

Toomas Kübarsepp, Metrosert Ltd., Tartu, Estonia, August 15 – 31, 2001 andOctober 1 – 5, 2001

Robert Mosig, University of Chemnitz, Chemnitz, Germany, August 1 – Sep-tember 30, 2001

Kamel Bencheikh, Laboratoire de Photonique et de Nanostructures (LPN), Paris,France, August 16 – 26, 2001

6.7 Visits to the Laboratory

Anne Andersson-Fäldt, SP Swedish National Testing and Research Institute,Sweden, February 8 – 9, 2001

Jan C. Petersen, DFM, Denmark, Per Anell, Frederik Brandt, Adel Asseh,Proximion, Sweden, Hasse Ekengren, Nordisk Industrifond, Norway, February9, 2001

Toomas Kübarsepp, Metrosert Ltd., Tartu, Estonia, March 20, 2001

Jeevek M. Parpia, Cornell University, Ithaca, NY, USA, April 5, 2001

Hans Rabus, PTB, Germany, April 23, 2001

Neil Harrison and Hannah Oliver, NPL, United Kingdom, April 23 – 25, 2001

Tibor Berceli, Technical University of Budapest, Hungary, May 4, 2001

Anne Andersson-Fäldt, SP, Sweden, Jan C. Petersen, DFM, Denmark, OttokarLeminger and Werner Weierhausen, T Nova, Germany, May 15, 2001

Hadi Damirji, Optitune PLC, London, United Kingdom, August 13, 2001

Masami Kihara, NTT Network Innovation Laboratories, Kanagawa, Japan,August 17, 2001

Chris Chunnilall, NPL, United Kingdom, August 29, 2001

50

Toomas Kübarsepp and Juhan Tuppits, Metrosert Ltd., Tartu, Estonia, Septem-ber 18, 2001

Daniel Bos, NMi-VSL, The Netherlands, November 19, 2001

Mackillo Kira, KTH Stockholm, Sweden, November 29 – 30, 2001

Vahid Sandoghdar, ETH Zurich, Switzerland, December 6 – 8, 2001

Lennart Robertsson, BIPM, Paris, France, December 9 – 11, 2001

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7 PUBLICATIONS

7.1 Articles in International Journals

T. Niemi, M. Uusimaa, S. Tammela, P. Heimala, T. Kajava, M. Kaivola, and H.Ludvigsen, “Tunable silicon etalon for simultaneous spectral filtering andwavelength monitoring of a DWDM transmitter,” Photon. Technol. Lett. 13,58-60 (2001).

M. Merimaa, P. Kokkonen, K. Nyholm, and E. Ikonen, “A portable laser fre-quency standard at 633 nm with a compact external-cavity diode laser,” Me-trologia 38, 311-318 (2001).

T. Niemi, J-G. Zhang, and H. Ludvigsen, “Effect of optical filtering on pulsesgenerated with a gain-switched DFB laser,” Opt. Commun. 192, 339-345(2001).

K. Ylä-Jarkko, S. Tammela, T. Niemi, A. Tervonen, and M. Leppihalme, “Scal-ability of a metropolitan bidirectional multifiber WDM-ring network,” Photon-ics Network Communications 3, 349-362 (2001).

T. Niemi, M. Uusimaa, and H. Ludvigsen, “Limitations of phase-shift method inmeasuring dense group delay ripple of fiber Bragg gratings,” IEEE PhotonicsTechnol. Lett. 13, 1334-1336 (2001).

T. Niemi, S. Tammela, and H. Ludvigsen, “Device for frequency chirp meas-urements of optical transmitters in real time,” Rev. Sci. Instrum. (in press).

G. Genty, M. Kaivola, and H. Ludvigsen “Linewidth variations of a grating-cavity laser measured within one external cavity mode,” (accepted).

P. Helistö and I. Tittonen, “Experiments with Coherent Fields: Gamma Echoand Related Phenomena,” Hyperfine Interactions (in press).

T. Mattila, O. Jaakkola, J. Kiihamäki, J. Karttunen, T. Lamminmäki, P. Ranta-kari, A. Oja, H. Seppä, H. Kattelus, and I. Tittonen, “14 MHz micromechanicaloscillator,” Sensors and Actuators (in press).

J. Hovila, P. Toivanen, E. Ikonen, and Y. Ohno, “Intercomparison of the illumi-nance responsivity and luminous flux units between HUT (Finland) and NIST(USA),” Metrologia (in press).

52

T. Kübarsepp, H. W. Yoon, S. Nevas, P. Kärhä, and E. Ikonen, “Comparison ofspectral irradiance scales between NIST and HUT,” Metrologia (in press).

7.2 International Conference Presentations

P. Kärhä, “Uncertainties for measurements on sources using broad band detec-tors,” Abstracts of the CIE Expert Symposium on Uncertainty Evaluation, Vi-enna, Austria, January 22-24 (invited talk).

T. Mattila, O. Jaakkola, J. Kiihamäki, J. Karttunen, T. Lamminmäki, P. Ranta-kari, A. Oja, H. Seppä, H. Kattelus, and I. Tittonen, “14 MHz MicromechanicalOscillator,” Proceedings of Transducers ’01 Eurosensors XV, Digest of Techni-cal Papers, Volume 2, 2001, pp. 1102-1105 (talk).

P. Rantakari, J. Kiihamäki, M. Koskenvuori, T. Lamminmäki, and I. Tittonen,“Reducing the Effect of Parasitic Capacitance on MEMS Measurements,” Pro-ceedings of Transducers ’01 Eurosensors XV, Digest of Technical Papers, Vol-ume 2, 2001, p. 1556-1559 (poster).

M. Merimaa, T. Lindvall, I. Tittonen, and E. Ikonen, “All-optical atomic clockbased on dark states of 85Rb,” Symposium Digest of the 6th Symposium on Fre-quency Standards and Metrology 2001 (talk).

T. Lindvall, M. Merimaa, and I. Tittonen, “Studies of the linewidth of darkresonances,” Symposium Digest of the 6th Symposium on Frequency Standardsand Metrology 2001 (poster).

T. Lindvall, M. Merimaa, I. Tittonen, and E. Ikonen, “All-optical atomic clockbased on dark states of 85Rb,” Proceedings of the 6th Symposium on FrequencyStandards and Metrology 2001 (in press).

F. Manoocheri, S. W. Brown, and Y. Ohno, “NIST Colorimetric Calibration Fa-cility for Displays,” Proceedings of the 2001 SID International Symposium Di-gest of Technical Papers 2001, pp. 330 –333.

C. J. Marckmann, G. Genty, Y. Ren, J. Arentoft, and M. Kristensen, “Bragggratings as probes to determine nonlinearities induced by thermal poling,” inBragg Gratings, Photosensitivity, and Poling in Glass Waveguides, in Stresa,Italy, July 4-6 2001, paper BFC3 (talk).

M. Wicks, T. Niemi, H. Ludvigsen, M. Wegmüller, H. de Riedmatten, and N.Gisin, “Preliminary results of a European intercomparison of group delay meas-

53

urements of fiber Bragg gratings,” in 6th Optical Fiber Measurement Confer-ence (OFMC’01), Conference Digest 2001, pp. 241-244 (talk).

G. Genty, T. Laukkanen, and H. Ludvigsen, “Characterization of a harmonicallymode-locked fiber ring laser: modeling and experiments,” in 6th Optical FiberMeasurement Conference (OFMC’01), Conference Digest 2001, pp. 259-262(talk).

T. Niemi, G. Genty, and H. Ludvigsen, “Group-delay measurements usingphase-shift method: Improvement on the accuracy,” in Proceedings of 27th

European Conference on Optical Communication (ECOC’01) in Amsterdam,The Netherlands, 2001, paper Th.M.1.5 (talk).

T. Lindvall, M. Merimaa, and I. Tittonen, “Coherent population trapping in ru-bidium vapor,” Quantum Optics Euroconference 2001, San Feliu de Guixols,Spain, October 6 – 11, 2001 (poster).

A. Huttunen, M. Rodriguez, P. Törmä, T. Lindvall, I. Tittonen, A. Shevchenko,and M. Kaivola, “Coherence in an Atomic Beam Splitter,” Quantum OpticsEuroconference 2001, San Feliu de Guixols, Spain, October 6 – 11, 2001(poster).

7.3 National Conference Presentations

K. Lahti and I. Tittonen, “Coupling of coherent optical fields in the process ofsecond harmonic generation,” in Proceedings of the XXXV Annual Conferenceof the Finnish Physical Society, Research Report No. 5/2001, University ofJyväskylä, 2001, p. 51 (talk).

M. Merimaa, P. Kokkonen, K. Nyholm, and E. Ikonen, “A portable laser fre-quency standard at 633 nm with a compact external-cavity diode laser,” in Pro-ceedings of the XXXV Annual Conference of the Finnish Physical Society, Re-search Report No. 5/2001, University of Jyväskylä, 2001, p. 55 (talk).

K. Nera, O. Hahtela, K. Lahti, T. Lamminmäki, K. Ruokonen, and I. Tittonen,“Micromechanical HIGH-Q oscillators for the detection of weak forces,” inProceedings of the XXXV Annual Conference of the Finnish Physical Society,Research Report No. 5/2001, University of Jyväskylä, 2001, p. 107 (talk).

T. Lindvall, M. Merimaa, and I. Tittonen, “Coherent population trapping,” inProceedings of the XXXV Annual Conference of the Finnish Physical Society,Research Report No. 5/2001, University of Jyväskylä, 2001, p. 58 (poster).

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T. Lindvall, A. Huttunen, M. Rodriquez, A. Shevchenko, M. Kaivola, P. Törmä,and I. Tittonen , “Microtraps for neutral atoms,” in Proceedings of the XXXVAnnual Conference of the Finnish Physical Society, Research Report No.5/2001, University of Jyväskylä, 2001, p. 57 (poster).

T. E. Ahola, M. Merimaa, and K. Nyholm, “Iodine-stabilized frequency-doubled Nd:YAG laser for length metrology,” in Proceedings of the XXXV An-nual Conference of the Finnish Physical Society, Research Report No. 5/2001,University of Jyväskylä, 2001, p. 62 (poster).

M. Koskenvuori, T. Lamminmäki, P. Rantakari, I. Tittonen, V. Ermolov, O.Jaakkola, H. Kattelus, J. Kiihamäki, H. Kuisma, T. Mattila, A. Oja, T. Ryhänen,and H. Seppä, “Mechanical silicon resonators for RF electronics,” in Proceed-ings of the XXXV Annual Conference of the Finnish Physical Society, ResearchReport No. 5/2001, University of Jyväskylä, 2001, p. 111 (poster).

T. Laukkanen, G. Genty, and H. Ludvigsen, “Erbium-doped fiber-ring laser op-erating in the L-band,” in Proceedings of Optics Days 2001, Physics Series Re-port 2-01, Tampere University of Technology, 2001, p. O1 (talk).

M. Merimaa, T. Lindvall, I. Tittonen, and E. Ikonen, “An all-optical atomicclock based on dark states of Rb,” in Proceedings of Optics Days 2001, PhysicsSeries Report 2-01, Tampere University of Technology, 2001, p. O5 (talk).

J. Hovila, P. Toivanen, and E. Ikonen, “HUT/NIST intercomparison of the unitsof illuminance responsivity and luminous flux,” in Proceedings of Optics Days2001, Physics Series Report 2-01, Tampere University of Technology, 2001, p.P1 (poster).

J. Envall, P. Kärhä, and E. Ikonen, “Development of a national standard for fi-ber optic power,” in Proceedings of Optics Days 2001, Physics Series Report 2-01, Tampere University of Technology, 2001, p. P3 (poster).

T. E. Ahola, M. Merimaa, and K. Nyholm, “Frequency stabilization of a diode-pumped Nd:YAG laser at 532 nm to iodine by using third-harmonic technique,”in Proceedings of Optics Days 2001, Physics Series Report 2-01, Tampere Uni-versity of Technology, 2001, p. P5 (poster).

O. Hahtela, K. Lahti, K. Nera, E. Vahala, and I. Tittonen, “Interferometric de-termination of mechanical susceptibility of a silicon oscillator,” in Proceedingsof Optics Days 2001, Physics Series Report 2-01, Tampere University of Tech-nology, 2001, p. P6 (poster).

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K. Lahti and I. Tittonen, “Higher-order Hermite-Gaussian modes in the opticalprocess of second harmonic generation,” in Proceedings of Optics Days 2001,Physics Series Report 2-01, Tampere University of Technology, 2001, p. P22(poster).

M. Vainio, M. Merimaa, T. Kübarsepp, and E. Ikonen, “Second harmonic gen-eration with a transmission grating laser,” in Proceedings of Optics Days 2001,Physics Series Report 2-01, Tampere University of Technology, 2001, p. P23(poster).

7.4 Patents

S. Metsälä, Patent n:o US 6,317,278 B1, Precision-mechanical transverse posi-tioning device (Hienomekaaninen poikittaisasemointilaite) 2001, 16 p.

7.5 Other Publications

P. Kärhä (editor), Annual report 2000, Metrology Research Institute, HelsinkiUniversity of Technology, Espoo 2000, Metrology Research Institute Report18/2001, 64 p.

M. Merimaa, T. Lindvall, I. Tittonen, and E. Ikonen, All-optical atomic clockbased on coherent population trapping in 85Rb, Metrology Research InstituteReport 19/2001, 17 p.

A. Pietiläinen and M. Merimaa, Mittaustekniikan perusteiden laboratoriotyöt,8th edition, Espoo 2001, 105 p. (in Finnish)

56

HELSINKI UNIVERSITY OF TECHNOLOGY METROLOGY RESEARCH

INSTITUTE REPORT SERIES

HUT-MRI-R10/1997 A. Pietiläinen, M. Kujala and E. Ikonen,

Investigation of trapped rubidium atoms through frequency-modulation-

induced coherent transient effects.

HUT-MRI-R11/1998 I. Tittonen (editor),

Annual report 1997.

HUT-MRI-R12/1998 P. Toivanen, A. Lassila, F. Manoocheri, P. Kärhä and E. Ikonen,

A new method for characterization of filter radiometers. 1998


Annual report 1998.

HUT-MRI-R14/1999 T. Kübarsepp, P. Kärhä, F. Manoocheri, S. Nevas, L. Ylianttila and E. Ikonen,

Absolute spectral irradiance measurements of quartz-halogen tungsten lamps

in the spectral range 290-900 nm.

HUT-MRI-R15/1999 T. Kübarsepp,

Optical radiometry using silicon photodetectors.


Annual report 1999.

HUT-MRI-R17/2000 P. Toivanen,

Detector based realisation of units of photometric and radiometric quantities.

HUT-MRI-R18/2001 P. Kärhä (editor),Annual report 2000.

HUT-MRI-R19/2001 M. Merimaa, T. Lindvall, I. Tittonen, and E. Ikonen,All-optical atomic clock based on coherent population trapping in 85Rb.

ISSN 1237-3281

Picaset Oy, Helsinki 2002

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