Dr. Kathleen Richardson
Current Research Activities
HMO and ChG bulk glass/fiber for MIR applicationsCrystallization kinetics in MIR (Tellurite) glassesHigh Raman gain glasses – fibersExtrusion behavior of micro‐structured fibers
(NSF‐MWN, Universities of Bordeaux, Limoges and Torino, University of Adelaide)
Glasses for Precision Glass MoldingFundamental studies of glass‐mold interactionsCompositional engineering of glass workpiece and mold surface chemistry/microstructureModeling of workpiece material response via FEA
Final size/shapeStress relaxation measurements and modeling
(ARO, Edmund Optics, SCHOTT glass)Novel chalcogenide glass (ChG) bulk, films and fibers
Undoped and doped (NP and QD) ChG materials for magneto‐optic and active applications ChG metamaterials: device design and fabrication
(NSF, Raytheon and AFRL in collaboration with Penn St.)Chalcogenide glassy films for planar chemical sensors
(DTRA and DoE – NA‐22 in collaboration with MIT, Delaware)
Exploiting intrinsic material properties for improved integrated chalcogenide
waveguide resonators for mid‐IR sensingProf. Kathleen Richardson
J. Wilkinson, S. Novak, J. D. Musgraves, N. Carlie, B. Zdyrko, I. LuzinovSchool of Materials Science and Engineering, Clemson University
V. Singh, A. Agarwal, L. C. KimerlingMicro‐Photonics Center, Department of Materials Science and Engineering
Massachusetts Institute of TechnologyJ. J. Hu
Department of Materials Science and EngineeringUniversity of Delaware
A. Canciamilla, F. Morichetti, A. MelloniDipartimento di Elettronica e Informazione, Politecnico di Milano, Italy
Glass and Optical Materials Division MeetingPaper GOMD‐SIII‐035‐11
Glass Processing and Characterization Laboratory
Acknowledgments
Glass Processing and Characterization Laboratory 10
US Dept. of Energy (DoE) under contracts# DE‐SC52‐06NA27341 and DE‐NA000421DTRA under contract # HDTRA1‐10‐1‐0073
NSF – Materials World Network (MWN) program DMR‐0807016LasINOF program – Agence Nationale de la Recherche ANR (grant # ANR‐05‐BLAN‐0212‐01)
NSF INTL REU grant ENG‐0649230 & IGERT EEC‐0244109
Ongoing collaboration: Norm Anheier, Amy Qiao, Brad Johnson, John McCloy, Brian RileyPacific Northwest National Laboratory (PNNL)
Outline
Glass Processing and Characterization Laboratory
• Motivation – Sensing and chalcogenide glass (ChG) materials• Material selection, processing, manufacturing and applications
– Infrared spectroscopy– Chemical and biological molecular detection– Precision glass metrology
• Leveraging materials attributes to solve key device limitations– Loss reduction – thermal reflow
• Exploiting the glass’ low Tg– Loss reduction and compositional optimization – solution based glass processing
• Exploiting selective chemical durability– Device performance optimzation
• Exploiting photosensitivity• Future efforts
• MIR device integration via composition tailoring, and (hybrid) solution processing strategies
• enhancing device sensitivity via PTS (FOM optimization: dn/dT)“Integrated chalcogenide waveguide resonators for mid‐IR sensing: Leveraging material properties to meet fabrication challenges,” N. Carlie, J.D. Musgraves, B. Zdyrko, I. Luzinov, J. Hu, V. Singh, A. Agarwal, L. C. Kimerling, A. Canciamilla, F.
Morichetti, A. Melloni, and K. Richardson Optics Express 18 25 (2010) 26728‐26743
Glass Processing and Characterization Laboratory 12
Cl
F
At
Br
I
Ar
Ne
Rn
Kr
Xe
P
N
Bi
As
Sb
S
O
Po
Se
Te
He
Al
B
Tl
Ga
In
Si
C
Pb
Ge
Sn
Compositional development: Chalcogenide Glasses (ChGs)
Bulk Glass (Target) Preparation
SiO2
ZBLAN (Fluoride)
Ge‐Sb‐S/Se/Te
As‐Te‐I Te‐I
Composition dependent properties‐Refractive index: 2‐3Thermal stability: Tg ~ 100‐500 °CAbsorption band gap: 500‐2000 nmIR cut‐off: 10 ‐20 μm
Planar chem‐bio sensors for MIR work are based on As‐Ge‐Sb‐S‐Se system
Glass Processing and Characterization Laboratory
Wide transparency windows make ChGsideal for biological & chemical sensing
Visible NIR Mid‐IR Far‐IRUV
m)
S=OO‐HO‐H
water transparency
N‐O N‐O
C‐H fingerprint region
functional group region
silicasilicon
chalcogenidesheavy‐metal oxides
germanium
Glass Processing and Characterization Laboratory
Material choices for planar ChG sensors
Planar devices based on thin films tend to undergo more rapid cooling compared to bulk materials during deposition
MUST have understanding of bulk/film property differences (refractive index, dispersion, dn/dT, chemical stability and compatibility)
Linear and nonlinear properties (low TPA)Low optical loss (dB’s/m) ‐ purificationHigh index contrast compact devices
MUST be compatible with deposition and further back‐end fab process for complex device layouts
system compatibility, preferential material response and interaction, functionalization with ChG compatible polymers
KNOWN photo response – thermal and optical stability during fabrication and post‐fab
Need to measure refractive index in spectral range of use to ±0.001 GOAL: low loss, HIC, CMOS‐compatible ChG film optimized for MIR spectral window (MIR)
Schematic of a second order filter made by two directly coupled micro‐ring
resonators
CO2laser
QCL
IR He‐Ne
Vis. He‐Ne (632.8 nm)
Fiber laser
Interchangeable detectors• Ge photodiode (Vis‐NIR) • un‐cooled MCZT
GaP prismZnSe 2.5:1 telescope Ge window
2kHz chopper
• Four (4) lasers added and aligned collinear to reference He-Ne using an IR camera• Tunable CO2 waveguide laser: 9.2 – 10.6 μm• Maxion distributed feedback (DFB) quantum cascade laser (QCL): 5.348 μm• IR HeNe gas laser: 3.391 μm• Agilent Telecom DFB fiber laser 1.547 μm
• HeCdZnTe IR detector added: Vigo Systems, Model PVM-10.6 un-cooled due to tight workspace low SNR due to thermal background. IR lasers chopped at 2kHz, signal recovery with current preamp. and lock-in amplifier Modified detector mount allows placement near prism surface (<1mm) for expanded scan angle range
•SiO2/Rutile prisms replaced by GaP/Ge• Transmission from 0.6 to 20 μm• Better index match to chalcogenide glasses (ChG)• Refractive index of prism was calibrated against ZnSe primary reference material
• Sample/prism heater added to stabilize temperature • High dn/dT of IR prism materials (4x10-4 for Ge) is significant compared to instrument resolution
PNNL Metricon for MIR/LWIR index measurement (2009)
PNNL Modified Prism Coupler(2011)
16
-N. Carlie, et al., Rev. Sci. Inst., 82 5 (2011) 053102-A. Qiao et al., Proc. SPIE 8016-13 (2011)
Available Prisms
wavelength(µm)
Ge Prism (40o)
Si Prism (55o)
GaP Prism (50o)
Rutile Prism (60o)
GGG Prism (50o)
high low High low High low high low high low
0.6328 2.90 2.01 2.69 1.95 1.84 1.00
1.547 3.14 2.32 2.70 1.81 2.54 1.80 1.81 1.00
3.391 3.14 2.12 3.10 2.28 2.68 1.78 2.54 1.79 1.79 1.00
5.348 3.14 2.11 3.09 2.28 2.67 1.77 2.54 1.79 1.75 1.00
10.591 3.13 2.11 2.63 1.73
11.5 3.13 2.11 2.61 1.71Transparency*
(µm) 1.8-17 1.2-10 0.6-13 0.45-5.7 0.36-6.0
dn/dt* (ppm/oC) 400 150 130 -95 20
17
The current measurement accuracy is ±1x10‐3 and is expected to improve to ±1x10‐4 after obtaining calibration standards and implementing thermal control of the prism and the measured samples.
18
Mid‐IR ChG Characterization
C1 As(36) Sb(6) S(58)
C2 As(42) S(58)
C3 As(36) Ge(6) S(58)
C4 Ge(23) Sb(7) S(70)
15,5
16,0
16,5
2,1
2,2
2,3
2,4
2,5
C1 C2 C3 C4
mol
ar v
olum
e (c
m3/
mol
)
refr
activ
e in
dex
refractive index at 5.3 ummolar volume
2,02,12,22,32,42,52,62,7
0 2 4 6 8 10 12
refra
ctiv
e in
dex
wavelength (µm)
Clemson bulk glass dn/dC1C2C3C4
Vm=M/ρ
Bulk – film propertiesAs2Se3 glass
Glass Processing and Characterization Laboratory
0 2 4 6 8 10 12
2.66
2.68
2.70
2.72
2.74
2.76
2.78
2.80
2.82
2.84
2.86
2.88
Ref
ract
ive
inde
x
Wavelength (m)
Bulk glass As-deposited film Annealed film (170oC - 3hrs)
Other key data:‐Material dn/dT (system capability to 200°C)‐Optical homogeneity (to ±1x10-4 )
Mid-IR metrology tools include a Twyyman-Green interferometer (bulk optics), amodified Metricon prism coupler (thinfilms), and a custom waveguide lossmeasurement system (waveguides andfibers)
Planar integration: key to miniaturization, mass production, and cost & power consumptionreduction
Source, resonator, detector,signal read-out & processingcircuitry, fluidic system …
The OLD way:discrete devices
Planar integration
The NEW way:integrated chips
Smaller, better cheaper & greener
Waveguide integrated detector (Si‐Ge, PbSe/PbTe)
Compact and robust device structure Evanescent coupling efficiency > 90% Reduced dark noise and improved SNR
Molecular imprinted artificial antibody
Combined chemical & geometrical recognition for high specificity Superior durability and robustness compared to their natural counterparts
Ultra‐high‐Q resonator sensorDoped glass ring laser
Monolithic structure on Si Co‐planar coupling with low‐loss glass waveguides
Atomically smooth surface for reduced scattering loss Enhanced photon‐molecule interaction for high sensitivity
CMOS circuitry
Microfluidic channel
Source
DetectorMicrofluidicchannel
CMOS circuitry
22
Surface‐functionalized ‘lab‐on‐chip’ optical sensor systems
• IR transparency for detection of absorption signatures• High refractive index for small feature sizes• Low optical loss for high sensitivity resonators• Amenable to surface functionalization for selectivity
• Stable in chemical environment to be sensed• Able to be fabricated into waveguides/resonators
Glass for this application must be/have:
Two sensing regimes
Refractive index sensing
Shift of resonant wavelength
Absorption feature sensing
Decrease of effective transparency
As2S3: a model system for studying structural modificationsGe23Sb7S70: a stable glass ideal for sensing applications
As2S3 Ge23Sb7S70
Refractive index @ 1550 nm 2.37 – 2.42 2.15 – 2.33
Glass transition temperature 210 ºC 310 ºC
Stability against oxidation in an ambient environment
Blanket film: ok Patterned film: poor Excellent
• Film deposition– Thermal evaporation– Pulsed laser deposition– Magnetron sputtering– Spin‐coating
• Device fabrication– Waveguide– Bragg gratings– Photonic crystal
• Device integration
R. P. Wang et al., J. Appl. Phys. 100, 063524 (2006)
V. Ushanov et al., Semicond. Sci. Technol. 19, 787 (2004)**S. Song, et al., J. Non. Cryst. Sol. 355 (2009) 2272‐2278
N. Hô et al., Opt. Lett. 31, 1860 (2006)
M. Lee et al., Opt. Express 15, 1277 (2007)
**A. Saliminia et al., J. Opt. Soc. Am. B 17, 1343 (2000)
** all loss data is for unpurified bulk glass materials: < ~5 dB/cm @ 1550nm
**T.V. Galstian, et al., J. of Lightwave Technol., 15 8 1343 (1997)
B. Eggleton et al., Nature Photonics, 5 (2011) 141‐148
Requirement Material choicesSubstrate Large area (low cost), good mechanical properties
(robustness)Si, glass or metal acceptable: Si is
preferable for ease of integration other electronic and photonic devices on-chip
Under cladding
Excellent transparency at working wavelength, process compatibility, sufficient thickness (prevent
optical leakage)
Silicon oxide (for biosensing-NIR applications), ChG glasses (for chemical
sensing for NIR, MIR and LWIR)Buried bus waveguide
Index matching with resonator material, good optical transparency in wavelength range of choice
Silicon nitride, ChG glasses
Resonator Excellent transparency at working wavelength, preferably good chemical stability, amenable to
sidewall smoothing process (including reflow & solvent treatment), low photosensitivity & small or no aging
(for index sensing), possibility of athermal design (for index sensing), relatively high refractive index (> 1.8)
ChG glasses or other high-index glasses
Surface coating
Specificity, sensitivity enhancement without compromising optical loss or environmental stability
(Artificial) antibodies, polymers
Gas/liquid channels
Mechanical robustness, good chemical stability, process compatibility with WGs, wettability with liquid (in particular for sensing in an aqueous environment), biocompatibility (for certain biosensing applications)
Glass, polymer (e.g. PDMS, SU8)
Substrate
Under claddingBuried bus WG
Gas/liquid channel
Selective surface coating –functionalized polymer Resonator
Glass resonators are fabricated on silicon via a CMOS‐backend compatible lift‐off process
Lift‐off process flow
Resist coating
Development
UV exposure on a 500 nm i‐line stepper
Glass thermal evaporation
Lift‐off
Single‐source evaporation
Target heaters
Bulk glasses
Silicon substrate
~10-7 Torr
Tantalum boats
Ge23Sb7S70/As2S3
“Si‐CMOS‐compatible lift‐off fabrication of low‐loss planar chalcogenide waveguides,” Optics Express 15, 11798 (2007)
Wafer‐scale, parallel process Leverage on standard silicon‐
CMOS tools Non‐composition specific
As2S3Microdisk
Optical resonators can enhance photon‐matter interactions by orders of magnitude
Resonator
Light
Enhanced optical fieldEnhanced optical field
Long optical path lengthLong optical path lengthDetection limit: 0.02 cm‐1
Corresponding to ppmlevel sensitivity
and 3x more sensitive!
Further optimization: use of purified raw materials, enhanced resonator device designs and materials for ultra‐low loss components, is ongoing
Goal: surpass ppb sensitivity with superb selectivity to mixed streams withoutpre‐concentration
High‐Q ChG resonator sensor is capable of detecting refractive index (RI) changes as small as 8× 10‐7
Refractive index limit of detection 8× 10‐7 RIU (Refractive Index Unit) Demonstrated 10x improvement over commercial SPR sensors ! An additional 10x improvement expected by changing wavelength to near‐
infrared (e.g. 1.06 m) to minimize water absorption
RI sensitivity: 182 nm/RIU
Solution index increase
“Planar waveguide‐coupled, high‐index‐contrast, high‐Q resonators in chalcogenide glass for sensing,” Opt. Lett. 33, 2500‐2502 (2008)
= 1550 nm
The strong photon‐matter interactionin integrated high‐Q optical resonatorsmake them ideal for rapid sensing
Detection of refractive index change induced by surface binding of chemical orbiological molecular species:KEY ISSUES time constant of response to binding event, vapor/liquid analyteform, concentration of analyte within mixed stream of species
Specific surface binding
Low optical loss(High‐Q)
Strong molecule‐photon interaction
Sharp resonant peak & high sensitivity
“Design guidelines for optical resonator biochemical sensors,” J. Opt. Soc. Am. B. 26, 1032‐1041 (2009).
< 15 min
Objectives:Enhance evanescent wave sensor response to analyte of interest
Strategy:Create a polymer layer on top of chalcogenide glass waveguide with the ability to selectively bind analyte of interest
Approach:Grafting of a compatible polymer layer bearing chemical moieties able to react reversibly with the analyte
Polymer grafting
Analyte
ChG waveguide Change of the enrichment layerthickness and/or refractive index
Polymer coatings for chalcogenide glasses
Developing a selectivepolymer layer system
0 500 1000 1500 2000 2500 3000 35000.00
0.05
0.10
0.15
0.20
0.25
0.30
Time [s]
Hexane Acetone Chloroform Isopropanol Ethanol
0 500 1000 1500 2000 2500 3000 35000.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
Time [s]
Hexane Acetone Chloroform Isopropanol Ethanol
30
Per
cent
age
of th
ickn
ess
chan
ge
Detection by Infrared
• Spectra of analyte vapors in multi layer system have distinguishable peaks that can be used for detection.
3500 3000 2500 2000 1500 1000 500
0.000.01
0.000.020.04
0.00
0.01
0.00
0.01
0.000.010.02
Wavenumbers [cm-1]
Hexane
Acetic acid Abs
orba
nce
Ethanol
Isopropanol
Methanol
31
Signal strength by analyte flow and concentration
• Analyte is acetone, peak used is carbonyl b/w 1652‐1839cm‐1
• Signal strength increases with increasing flow rate.
20 to 80
50 to 50
70 to 30
100 to 0
0
0,2
0,4
0,6
0,8
1
1,2
1,4
Area
Multi‐layer concentration variable
10 to 1030 to 30 50 to 50
100 to 100
0
0,2
0,4
0,6
0,8
1
1,2
Area
Multi‐layer flow variable
• Analyte is acetone, peak used is carbonyl b/w 1652‐1839cm‐1
• Signal strength increases with increasing concentration.
32
Outline
• Motivation – Sensing and chalcogenide glass (ChG) materials• Material selection, processing, manufacturing and applications
– Infrared spectroscopy– Biological molecular detection– Precision glass metrology
• Leveraging materials attributes to solve key device limitations– Loss reduction – thermal reflow
• Exploiting the glass’ low Tg– Loss reduction and compositional optimization – solution based glass processing
• Exploiting selective chemical durability
– Device performance optimization • Exploiting photosensitivity
– Future efforts • MIR device integration via composition tailoring, and (hybrid) solution processing strategies • enhancing device sensitivity via PTS (FOM optimization: dn/dT)
“Integrated chalcogenide waveguide resonators for mid‐IR sensing: Leveraging material properties to meet fabrication challenges,” N. Carlie, et al., Optics Express 18 25 (2010) 26728‐26743
Thermal reflow successfully eliminates sidewall roughness and associated scattering loss: Ge‐Sb‐S
Viscous flow driven by surface tension removes roughness 50% optical loss reduction achieved via thermal reflow Magnitude of glass volatilization is small but measurable
“Optical loss reduction in HIC chalcogenide glass waveguides via thermal reflow,” J. Hu, N. Feng, A. Agarwal, L. Kimerling, N. Carlie, L. Petit and K. Richardson, Optics Express, 18 (2010) 1469–1478
35
Ground glass
Liquid solvent
Glass solution /Suspension
Optimization of glass‐solution spin‐coating conditions
Dissolution Spin‐coating Heat Treatment
Effect of: • Glass/solvent ratio• Dissolution time
On: • Film composition
Effect of: • Initial hold time• Spin speed • Spin time• Acceleration/Deceleration• Final hold time
On: •Film thickness•Uniformity/Coverage•RMS roughness
Effect of: • Soft‐bake time/temperature•Hard‐bake time/temperature
On: Refractive index Raman spectra (glass structure)IR spectra (residual solvent)
Three Stage Process
The following process variables were examined and optimized:
Goal: bulk composition = film composition
Goal: lowest roughness for highest thickness
Goal: film properties = bulk properties
Nathan Carlie, “A solution‐based approach to the fabrication of novel chalcogenide glass materials and structures,” PhD thesis, Clemson University (2010)
36
Infrared transparency of heat treated films
As42S58 derived from propylamine solution: 60°C ‐ 1hr soft‐bake + 90‐180°C – 1 hr hard‐bake
Solution derived films can be engineered for applications in infrared sensing
*Corrected for Fresnel loss
3 4 5 6 7 8 910
Wavelength (m)
4000 3500 3000 2500 2000 1500 1000
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Abso
rban
ce
Wavenumber (cm-1)
Propylamine 90 oC 120 oC 150 oC 180 oC
80 100 120 140 160 180
0.0
0.2
0.4
0.6
0.8
1.0
2900 cm-1
1600 cm-1
Abso
rban
ce
Heat Treatment Temperature (oC)
Absorption features near 2900 cm‐1 (N‐H) and 1600 cm‐1 (C‐N) decrease at higher temperatures.
N‐H bonds lost at a faster rate than C‐N bonds Probably through conversion of –NH2 to H2S
Absorbance near 3μm decreased 0.87 (90 °C) to 0.015 (180 °C) – (reduction of 98%)
37
Solution‐derived optical coatings Sources of optical loss: Typical solutions employed:
Roughness scattering is the dominant source of loss for most waveguide systems.
CU/MIT Provisional Patent issued
Material absorption Material purificationSubstrate leakage Geometry optimizationRoughness scattering Surface smoothing
AFM line‐scan along waveguide
• Waveguide RMS roughness reduced from 19 nm to 1.4 nm• Optical loss reduces by up to 50%• Cladding layer can be the same material as the waveguide
Index match to “sub‐layer/substrate”No adverse effect on the overall index profile
• Cladding layer can be different material (glass or hybrid coating)Allows creation of tailored or graded index profile
• Cladding layer is thin compared to waveguideMinimal effect on optical geometry/performanceSuitable for additional surface functionalization
Glass loading (mg/ml) / spin speed / Temperature
Waveguide surface cladding
Control of film thickness and quality with glass loading and water content
• Controlled by glass loading level, spin speed: target at = 3.4m, t =1m• Glass type (As‐S, GeSbS) does not have a noticeable effect on quality• Water content impacts quality; less of an effect on thickness (rms < 10 nm)
Amount of Glass in 10 mL of PA Spin Speed Thickness
0.2 g4000 rpm ~100‐150 nm
3000 rpm ~150 nm
0.5 g4000 rpm ~300‐350 nm
3000 rpm ~400‐450 nm
0.7 g
4000 rpm ~650‐700 nm
3000 rpm ~685‐715 nm
2500 rpm ~785‐815 nm
0.9 g4000 rpm ~800‐850 nm
3000 rpm ~830‐900 nm
Trimming of a coupled ring structure
Simulated transmission
In
Out
second order optical filter
flat‐top pass band…
R2
R1
Wavelength [nm]
Tran
smission
[dB]
1521.5 1522 1522.5 1523-20
-15
-10
-5
0 R2 R1
… provided that R2 R1
R2 ≠ R1
“Resonant cavity enhanced photosensitivity in As2S3 chalcogenide glass at 1550 nm telecommunication wavelength,” J. Hu, et al., Opt. Letters 35 6 (2010) 874‐876
Compensation of fabrication imperfections
Visible light trimming(halogen lamp)
Permanent compensation of fabrication imperfections
In
OutR1
nm .35012 RR
maskR2R1
Radius = 100 mFSR = 130 GHzBandwidth = 32.5 GHz
As2S3 double‐ring filter
Moving R1 only
light
R2
0.32 MW/cm2
Visible light trimming(microscope halogen lamp)
Trimming time ≈ 1 nm / 4 min
“Rigid” frequency shift of the filter response
As2S3 double‐ring filter
Moving R1 and R2
Correction/adjustment of theworking wavelength
Radius = 100 mFSR = 130 GHzBandwidth = 32.5 GHz
In
OutR1
mask
light
R2
0.32 MW/cm2
1520 1520.5 1521 1521.5 1522 1522.5
-20
-15
-10
-5
0
As2S3 double‐ring filter
Photosensitivity relaxation
Wavelength [nm]
Tran
smission
[dB]
after 2° exposureafter 1 week
No relaxation effects
No bandwidth changes
After one week…
Radius = 100 mFSR = 130 GHzBandwidth = 32.5 GHz
Top flatness preserved
In
OutR1
R2
• Shifting from NIR MIR ( – 3.25 m)– Device component geometries change
• Integration with source and detectors– Alignment– Packaging– New components and/or materials
• Isolators, lenses, filters
• New geometries of sensing regions to enhance further sensitivity– Photo‐thermal spectroscopy: exploiting dn/dT
Moving forward
Glass Processing and Characterization Laboratory
Integration challenges
From C. Tsay, et al., “Chalcogenide glass waveguides integrated with quantumcascade lasers for on chip mid‐IR photonic circuits,” Opt. Lett. 35, 3324‐3326 (2010)
Further enhancing sensitivityPhotoThermal Spectroscopy (PTS)
Incident IR radiation Transmission
Medium
Scattering
Scatterers
Heat
Temperature change
Refractive index change
Key advantages:• Photothermal enhancement• Immunity to scattering interference
Spe
ctro
met
er
J. Hu, Opt. Express 18, 22174‐22186 (2010)
Cavity‐enhanced absorption
Cavity‐enhanced absorption
Resonator temperature
change
Resonator temperature
change
Resonant wavelength shift
Resonant wavelength shift
Localized heat generation
Light
Light circulation in cavity
Light Cavity
Simultaneous optical & thermal confinement in nano‐cavity PTS
Chipscale Optical Nano‐Cavity Enhanced Photo‐Thermal Spectroscopy (CONCEPTS)
PT enhancement factor > 104
Chalcogenide glasses (ChG) are ideal for nano‐cavity PTS
Material Refractive index
Thermal conductivity
(W/mK)
Thermo-optic coefficient (/K)
Figure-of-Merit (m/W)
ChG 2.81 0.22 1.4 × 10-4 /K 1.8 × 10-3
Silicon 3.45 149 2.3 × 10-4 /K 5.2 × 10-6
SiO2 1.45 1.38 1.0 × 10-5 /K 1.0 × 10-5
n: refractive indexα: thermo‐optic coefficient (dn/dT)σ: thermal conductivity
FOM n
J. Hu, “Ultra‐sensitive chemical vapor detection using micro‐cavity photothermal spectroscopy”, Opt. Express 18, 22174‐22186 (2010).
Goal: need precise material properties at wavelengths of interest/use
J. Hu, Opt. Express 18, 22174‐22186 (2010).
42 10~32
33 PQdVEGnnE
e Np
c Absorption cross‐section detection
limit: 10‐17 cm2 (a single molecule)
Potential of single, small molecule detection using chalcogenide glass nano‐cavities
• Chalcogenide glasses (ChGs) offer a blend of compositional‐tailoring opportunities and processing‐compatible strategies for optical components and devices for sensing in the MIR and LWIR.
• Traditionally considered “limitations” associated with ChG materials can be utilized to enhance component optical properties and device performance.
• Interfacing attributes of inorganic and organic materials and creative device designs can lead to novel glassy structures with unique functionality that will continue to enhance sensor specificity and selectivity to low ppb ppt levels.
Conclusions