NEAR-INFRARED DUAL-COMB SPECTROSCOPY WITH A … · NEAR-INFRARED DUAL-COMB SPECTROSCOPY . WITH A...

NEAR-INFRARED DUAL-COMB SPECTROSCOPY WITH A CONTINUOUS-WAVE LASER

FRISNO 13 – Aussois, France – March 17 – March 22, 2015

Guy Millot, Stéphane Pitois Nathalie Picqué

1 - Motivation

2 – Experiment 3 - Results

Dual-Comb spectroscopy with a continuous-laser Generation of two mutually-coherent frequency combs

from a single continuous-wave tunable laser

2 2 DUAL COMB SPECTROSCOPY AUSSOIS – FRISNO13 2015

Outline

3

1 – Motivation : generalities on frequency combs

2 3

E(t) Pulse train

Spectrum FT

t

∆φ 2∆φ

1/frep

f

I(f) fo= ∆φ frep/2π

frep

fn= nfrep+ fo

DUAL COMB SPECTROSCOPY AUSSOIS – FRISNO13 2015

3

1 – Motivation : basic concept of dual-comb spectroscopy

2 4

12 repreprep fff −=∆

Comb 1

Comb 2

Gas sample

1/frep1

1/∆frep

Detector

No moving mechanical part !


Improvement up to six orders of magnitude in acquisition time, sensitivity, resolution and accuracy compared to Michelson-based Fourier transform spectroscopy

3

1 – Motivation : basic concept – Frequency domain

2 5

300 MHz 300,1 MHz λ0

Frequency (THz)

Comb 1 : frep1 = 300 MHz

Comb 2 : frep2 = frep1 + ∆frep= 300,1 MHz

Frequency (kHz) 100 kHz

200 kHz

N x 100 kHz

300 kHz

…

…

TeraHertz Domain

Down converted frequency factor 3000/1

1

=∆

=rep

rep

ff

Low frequency detection RadioFrequency domain

RF

∆frep (=100 kHz) << frep1 λ0 ∼ 1570 nm


We have thus achieved a down frequency conversion equivalent to a heterodyne detection

3

1 – Motivation : basic concept – Temporal domain

2 6

Period = 1 / ∆frep (10 µs)

Temporal Coincidence

Interferogram : Ι(t)

N pulses

N+1 pulses

T1=1/frep1 (3.3333 ns)

(N = 3 000)

T2=1/frep2 (3.3322 ns)

)11.1(21

psff

Trep

rep∆≅∆

ps50

Temporal Coincidence


3

1 – Motivation : state of the art


Principle of dual-comb spectroscopy firstly proposed by S. Schiller (Düsseldorf)

“Spectrometry with frequency combs,” Opt. Lett., vol. 27, no. 9, p. 766, 2002.

B. Bernhardt, PhD thesis Th. Hänsch & N. Picqué MPQ Garching

N. R. Newbury et al. NIST Boulder

The need to synchronize femtosecond lasers with an interferometric precision requires advanced experimental techniques of optical metrology

3

1 – Motivation : basic concept Difficulties and possible solutions

2 8

Dual-comb spectroscopy requires a high temporal stability

Possible solutions :

A: Use of an ultra-stable reference cavity and a fast locking system for stabilization of the two combs Pb : complex and expensive devices eg PRL 100, 013902 (2008)

B: Observation and recording of the time fluctuations, a posteriori mathematical correction of the interferograms Pb : costly time data analysis eg Opt. Express 18, 23358 (2010)

C: Use of an adaptive clock signal for data recording Pb : complex devices eg Nat. Comm. 5, 3375 (2014)

D: Design of a novel system with intrinsic mutual coherence between the two combs


3

2 – Experimental breakthrough : generation of two mutually-coherent combs with a single continuous laser

2 9

Laser Diode 1570 nm / 4 mW

Electrical Clock 300 MHz

Electrical Clock 300,1 MHz

Electrical Pulse Generator ( 50 ps)

Electrical Pulse Generator (50 ps)

Intensity Modulators

Optical Comb 300 MHz

Optical Comb 300,1 MHz

EDFA


As both combs are generated from the same initial laser, they have very good mutual coherence, so there is no need to synchronize them

3

2 – Experiment : need for optical spectral filtering

2 10

300 MHz 300,1 MHz

λ0

Frequency (THz)

… …

Optical spectrum

Problem of optical spectral overlapping : double contribution of the optical lines


200 kHz N x 100 kHz

Low frequency detection ( RF domain)

300 kHz

… Down converted spectrum


3


2 11

λ0

Frequency (THz)

… …


200 kHz

N x 100 kHz

Low frequency detection ( RF domain )

300 kHz

…

Solving the problem of spectral overlapping with an optical filter

Optical filter

Down converted spectrum


3

2 – Experiment : spectral detection limit

2 12

λ0

Frequence (THz)

…

Frequency (MHz) 100 kHz

N x 100 kHz

Low frequency detection ( RF domain ) … … … … …

300 MHz 600 MHz 0 MHz Useful

domain

Limitation of the number of lines : N x ∆frep < frep2 / 2 = 150 MHz

Optical spectrum

Frequency domain of the down converted spectrum

frep2/2

Order 0

Order 1 Order 2


3

2 – Experiment : frequency comb characterization

2 13

Temporal pulse profile

directly measured

with an ultrafast oscilloscope (33 GHz)

Characterization with an

optical spectrum analyzer (OSA)

Characterization of the optical pulses generated at the output of the intensity modulators

∼ 50 ps

50 100 150 200 250

Time (ps)

Inte

nsity

(arb

. uni

ts)

1

2

3

4

5

6


∼ 0.2 nm @ -10dB

3

2 – Experiment : spectral broadening of the two frequency combs by wave-breaking

2 14

Principle of Wave Breaking

Normal dispersion leads to flat-top spectrum and maintains high level of spectral coherence


t

P

oω−ω=δω

•

•

t

chirp •

•

Numerical simulation of the NLSE

Intensity Modulator

EDFA PC Dispersion Compensated Fiber (DCF)

FC

3


2 15

Dispersion Compensated Fiber with normal dispersion @ 1569 nm L = 1.38 km γ= 3 W-1 km-1

α= 1 dB/km D = -94 ps/nm/km

S = -0,12 ps/nm2/km

Spectral broadening versus power at the DCF input


∼ 3 nm (400 GHz) @ -10dB

• Wave-breaking leads to flat-top spectra with low amplitude noise which span up to about 3 nm (400 GHz) when input power reaches 24 dBm • The 3-nm spectrum is composed of 1350 individual lines with a power of 0.18 mW per comb line

3



Spectral broadening of the two combs in a single DCF with counter-propagating beams

narrows the comb spectrum to avoid aliasing around the carrier line and to reject spontaneous emission generated by the different amplifiers

Intensity Modulator

EDFA

1.378 km DCF

Intensity Modulator

EDFA

50/50

PC

PC

Circulator

Circulator

Comb 1

Comb 2

Tunable Optical Filter

Filter

3

2 – Experiment : comb coherence measurement

2 17

Mutual coherence between the two combs - Characterization with a RF spectrum analyzer

Interference line between the two combs at 3 MHz

2.5 Hz 2.5 Hz


2.5 Hz corresponds to a relative coherence time of 400 ms. Such coherence time appears unaffected by the kilometric length of the nonlinear fiber, partly due to the use of a single fiber for the broadening of the two combs

The counter-propagation of the two combs in the same nonlinear fiber is highly suitable for generating a coherent dual-comb

after spectral broadening before spectral broadening

3

2 – Experiment : use of a Hollow-Core Photonic Crystal Fiber

2 18

Physical properties Core diameter 10 ± 1 μm Cladding pitch 3.8 ± 0.1 μm PCF domain diameter 70 ± 5 μ Cladding diameter 120 ± 2 μm

Optical properties @ 1550 nm Design wavelength 1550 nm Attenuation < 30 dB/km Typical GVD 90 ps/nm/km Spectral range of use 1490-1680 nm Mode diameter 9 ± 1 μm

Cross section Intensity profile

Hollow Core photonic bandgap fiber

NKT Photonics HC-1550-02 L = 48 m


2 – Experiment : overview of the experimental setup

HzWNEP /10 15−=

Laser diode (1569 nm)

EDFA

Electrical Pulse Generator 300 MHz

Intensity Modulators

Electrical Pulse Generator 300,1 MHz

EDFA

EDFA

Polarization Controler

Polarization Controler 1,38 km DCF

(D =- 94 ps/nm/km)

Circulator Circulator

Optical filter

Reference Coupler 99/1

Coupler 50/50

Collimator MO x20 MO x20

Micro Lens

Photodiode

Ampli / Electrical Filter (32 MHz)

16 bits Oscilloscope Picoscope 5444B

16 bits with 60 MHz bandwidth 62.5 MS/s

48 m - HC Fiber

Gas cell

19 DUAL COMB SPECTROSCOPY AUSSOIS – FRISNO13 2015

3

3 – Results : carbon dioxide absorption at telecommunication wavelengths

2 20

Absorption in the mid-infrared

Absorption in the

near-infrared (telecom)

~ 100 000 times weaker


3

3 – Results : carbon dioxide absorption at telecommunication wavelengths

2 21

Absorption in the L-band

12CO2

13CO2 X 100

1569 nm

P R

P R

Band 30012–00001


3

3 – Results : carbon dioxide absorption

2 22

Spectrum with a mixture C12/C13 90% - 10 %

Total pressure 200 mBar – Carrier wavelength : 1569 nm

frep = 300 MHz ; ∆frep = 103 kHz

A total optical span exceeding 400 GHz without aliasing

is possible.

Recording time 52.4 ms SNR > 500


FT

Interferogram

λo = 1569.00 nm

9.7 µs

The noise-equivalent-absorption (NEA) coefficient

at 1s-time-averaging, defined as (Labs SNR)-1 (T/M)1/2,

is 8.5 x 10-9 cm-1 Hz-1/2.

The long optical path within the hollow core fiber leads to high sensitivity without multi-pass cell

Time window = 524 µs Average over 100 spectra

35 GHz (115 lines)

3

3 – Results : carbon dioxide absorption

2 23

1 : 13C16O2 30011-00001 band R(10) line λ=1569.419 nm S=4.4 10-25 cm.molecule-1

2 : 12C16O2 31112-01101 band R(21) line λ=1569.486 nm S=5.8 10-25 cm.molecule-1 3 : 12C16O2 30012-01101 band R(36) line λ=1569,494 nm S=5.0 10-24 cm.molecule-1 4 : 12C16O2 31112-01101 band R(20) line λ=1569,544 nm S=6.0 10-25 cm.molecule-1

λo = 1569.00 nm


Reference spectrum

1 2 3 4

v1v2l2v3n

Normalization

Computed spectrum with the line parameters of the HITRAN 2012 database assuming Lorentzian profiles

3

3 – Results : carbon dioxide absorption Linewidth of spectral modes

2 24

Zoom on a line

12 Hz !

Temporal window = 134.2 ms

No averaging

RF spectrum (down converted frequencies)


36 kHz in the optical domain

For comparison, the width of an individual comb line from free-running mode-locked erbium-doped fiber lasers was found to be 260 kHz over an integration time of 1.3 s

Ideguchi T., Poisson A., Guelachvili G., Picqué N, Hänsch T.W., Nature Communications 5, 3375 (2014)

3

3 – Results : carbon dioxide absorption Wavelength tunability


1 12C16O2, 31112-01101 band R(16) line

2 12C16O2, 30012-00001 band R(30) line

3 12C16O2, 31112-01101 band R(15) line

4 12C16O2, 31112-01101 band R(14) line

5 12C16O2, 30012-00001 band R(28) line

The frequency agility of the laser diode allows us to readily probe other spectral regions or other molecules

Frequency agility is mainly limited by the bandwidth of the amplifiers

Use of optical amplifiers at other telecom bands access to a wide spectral range

3

4- Conclusions and perspectives

2 26

Original method using a single continuous diode laser with standard linewidth. No need to synchronize the two combs and low phase noise. The set-up only harnesses standard optoelectronic devices at telecom wavelengths and adapted fibers. This dramatically simplifies the implementation of a dual-comb spectrometer.

No resonant cavity : variable repetition rate ( from 100 to 500 MHz ) and subsequent resolution.

Spectral broadening by wave breaking : flatness of the spectrum and low time and amplitude jitters. First use of a Hollow Core fiber in dual-comb spectroscopy: high sensitivity, measurement of weak absorption lines (almost a billion times less intense than absorption lines in the mid- infrared).

Easy self-calibration spectra. Small spectral window, but significant power per comb line and wavelength agility by using a tunable continuous laser.

Work in progress : increase the signal to noise ratio, access to other wavelengths


3 2 27

and for financial supports :

• IXCORE Research Foundation

• PARI PHOTCOM Regional Council of Burgundy

• Labex ACTION

and THANKS :

to Julien Fatome, Bertrand Kibler, Christophe Finot, Gil Fanjoux, Vincent Tissot, Philippe Morin

THANKS FOR YOUR ATTENTION


3

2 – Experimental breakthrough : generation of two mutually-coherent combs with a single continuous laser

2 9

Laser Diode 1570 nm / 4 mW

Electrical Clock - 300 MHz

Electrical Clock - 300,1 MHz

Electrical Pulse Generato ( 50 ps)

Electrical Pulse Generator (50 ps)

Intensity Modulator

Electrical Comb 300 MHz

Electrical Comb 300,1 MHz

Optical Comb 300 MHz

Optical Comb 300,1 MHz

EDFA

OSICS TLS-50 YENISTA 1568,77 nm - 1607,47 nm 4mW - 10 mW Linewidth ∼1 MHz typical

PPG50 PHOTLINE Gaussian to super-Gaussian Pulse Width: 50 ps Repetition rate : 100 MHz to 500 MHz Rise time: 15 ps RMS jitter < 2 ps

MODBOX PHOTLINE Signal wavelength tunable from 1520 to 1600 nm Maximum input power : 100 mW (20 dBm) Optical modulator : bandwidth 18 GHz Extension rate : 30 dB Optical pulse duration : 50 ps

AGILENT MGX N5181A-501 Sinusoidal electrical wave : tunable frequency from 100 kHz to 1 GHz by step of 1 Hz Temporal jitter < 1ps at 100 MHz and < 500 fs at 500 MHz Output power > 13 dBm

MANLIGHT L Band - 20 dBm


As both combs are generated from the same initial laser, we will see later that they have very good mutual coherence, so there is no need to synchronize them

3


2 11

λ0

Frequency (THz)

… …


200 kHz

N x 100 kHz

Low frequency detection ( RF domain )

300 kHz

…

Solving the problem of spectral overlapping with an optical filter

Optical filter

Filter YENISTA : Spectral range : 1480 nm to 1620 nm Spectral bandwidth : 32 pm to 650 pm Filtering slope : 800 dB/nm

∼ 4 to 80 GHz @ 1570 nm that to say

∼ 1 to 26 MHz for the down converted spectrum

Down converted spectrum


3

2 – Experiment : frequency comb characterization

2 14

Direct measurement of the temporal profile of an optical pulse with the ultrafast oscilloscope (33 GHz)

RF comb with frep= 300 MHz Zoom on the peak at 300 MHz

∼ 2 Hz

Characterization of the electrical combs with the RF spectrum analyzer

Characterization with the optical spectrum analyzer (OSA)

Characterization of the optical pulses generated at the output of the intensity modulators

∼ 50 ps

50 100 150 200 250

Time (ps)

Inte

nsity

(arb

. uni

ts)

1

2

3

4

5

6


∼ 0.2 nm @ -10dB

3

2 – Experiment : comb characterization

2 13

Electrical Spectrum Analyzer

Optical Spectrum Analyzer

OSA

YOKOGAWA AQ6370 Resolution : 20 pm -> 2 nm Dynamical range : 45 dB -> 57 dB

AGILENT N9010A Range : 9kHz – 26,5 GHz Resolution : 2 Hz

Ultrafast Oscilloscope

DSO

AGILENT Infiniium DSO-X 93304Q Bandwidth : 33 GHz 80 GSa/s


3

2 – Experiment : spectral broadening of the two frequency combs by self-phase modulation

2 15

High NonLinear Fiber with anomalous dispersion @ 1569 nm L = 1000 m γ= 10 W-1 km-1

α= 0,4 dB/km D = 0,2 ps/nm/km

S = 0,045 ps/nm2/km

Spectral broadening versus power at the HNLF input


Intensity Modulator

EDFA PC High Nonlinear Fiber

Frequency Comb

∼ 15 nm @ -10dB

3


2 13

Spectro-temporal representation of a pulse at different propagation distances Fig.2 from : C. Finot et al., JOSAB 25, p. 1938 (2008).

Flat-top spectrum High degree of coherence

ξ=z/LD τ=t/To


3

2 – Experiment : spectral characterization examples

2 20

After the DCF After the optical filter After absoption in CO2

Optical spectra directly measured with the OSA


3

2 – Experiment : jitters of the two combs

2 20

Direct observation of the timing and amplitude jitters with the 33 GHz oscilloscope

10 000 optical pulses – Trigger by the electrical pulse (data b)

50 ps Before spectral broadening

162 ps

After

100 ps

100 ps


3

2 – Experiment : jitters of the two combs

2 21

Histogram obtained with the 33 GHz oscilloscope

8417 optical pulses – Trigger by the electrical pulse

100 ps

After spectral broadening


3

2 – Experiment : comb coherence measurement

2 17

Comb coherence after spectral broadening - Characterization with the RF spectrum analyzer

Interference line between the two combs at 3 MHz at the DCF

input 2.5 Hz output 2.5 Hz


Comb at the DCF input ( peak at 300 MHz ) Comb at the DCF output ( peak at 300 MHz )

1 Hz 1 Hz

The nonlinear fiber does not induce any additional jitter on each comb

The counter-propagation of the two combs in the same nonlinear fiber is highly suitable for generating a coherent dual-comb

Coherence of each Comb

Mutual coherence

between the two Combs

3

3 – Results : carbon dioxide absorption Different pressure and different C12/C13 ratios

2 27

Spectrum 100 mBar / natural CO2 (1 % C13)

Carrier wavelength : 1569 nm

frep = 300 MHz ; ∆frep = 103 kHz

Temporal window = 525 µs

Average over 100 spectra

C12 : R36 1569,494 nm

C12 : R20 1569,544 nm

Reference

C12 : R38 1569,250 nm

λo = 1569,00 nm

Recording time ∼ 50 ms


3


2 29

Spectrum with a mixture C12/C13 90% - 10 % Total pressure 200 mBar – Carrier wavelength : 1572,45 nm frep = 300 MHz ; ∆frep = 103 kHz Temporal window = 525 µs Average over 100 spectra

C12 : R14 1572,66 nm

λo = 1572,45 nm

Reference



3


2 30

C12 : R6 1574,034 nm


λo = 1573,90 nm

Reference



3


2 31


C12 : 1569,25 nm

C12 :R40 1569,012 nm

C12 : 1569,19 nm

C12 :R38 1569,228 nm

C13 : 1569,075 nm

λo = 1568,80 nm

Reference



3



frep1

frep2

Absorption line

Elec

tric

fiel

d

Optical frequency (THz)

∆frep Radio frequency (MHz)

3

3 – Biomedical application : diagnosis of air breathing


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