broad band mid-ir transmitting single mode fibers (smfs) and integrated optical circuits (iocs) -...
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Broad Band Mid-IR Broad Band Mid-IR Transmitting Transmitting
Single Mode Fibers (SMFs) Single Mode Fibers (SMFs) and Integrated Optical and Integrated Optical
Circuits (IOCs) - Circuits (IOCs) - Spatial Filters for the ESASpatial Filters for the ESA
DARWIN ProjectDARWIN ProjectAbraham KatzirAbraham Katzir
Tel Aviv University, Tel Aviv, Tel Aviv University, Tel Aviv, ISRAEL ISRAEL
www.tau.ac.il/[email protected]@post.tau.ac.il
• The TPF and the Darwin projectsThe TPF and the Darwin projects• Nulling interferometryNulling interferometry• Spatial & modal filteringSpatial & modal filtering• Single mode fiber as a modal filterSingle mode fiber as a modal filter• Silver halide material and fibersSilver halide material and fibers• Single mode silver halide fiber Single mode silver halide fiber • Measurements & resultsMeasurements & results• Micro-structured fibersMicro-structured fibers• Single mode flat waveguide (for Integrated Single mode flat waveguide (for Integrated
Optics Circuits)Optics Circuits)• ConclusionsConclusions• SummarySummary
Lecture OutlineLecture Outline
Performing Performing atmosphere atmosphere spectroscopy in the 8-spectroscopy in the 8-2020μμm mid-IR spectral m mid-IR spectral range for planets near range for planets near stars. stars. Indications for the Indications for the presence of life?presence of life?
TargeTargett::
A star “masks” the A star “masks” the radiation from a radiation from a neighboring planetneighboring planet
ProblemProblem::
DARWIN and TPF DARWIN and TPF projectsprojects
Nulling interferometryNulling interferometrySolutiSolution:on:
Selecting Selecting the the
operating operating region region
4µm - 20µm4µm - 20µm
NullingNullingInterferomInterferom
etryetry
TPF and DARWIN basic ideaTPF and DARWIN basic idea
Darwin - Alain Leger, ParisDarwin - Alain Leger, Paris Pierre Kern, GrenoblePierre Kern, Grenoble
TPF – Peter Lawson, Alex Ksendzov JPLTPF – Peter Lawson, Alex Ksendzov JPL
Collaboration & FundingCollaboration & Funding
ResulResult:t:
Phase deviations caused by:Phase deviations caused by:
Wave front (phase) deviationsWave front (phase) deviations
A. DustA. Dust
B. Telescope imperfectionsB. Telescope imperfections
C. Telescope pupilC. Telescope pupil
Destroying the interference patternDestroying the interference pattern
Proposed Solutions:Proposed Solutions:
A. Spatial filtering (Pinhole)A. Spatial filtering (Pinhole)
B. Modal filtering (Single mode fibers B. Modal filtering (Single mode fibers or waveguidesor waveguides ))
d
2ρ
z0
ReflectingReflectingsurfacessurfaces
Modal filteringModal filtering using Single Mode using Single Mode FibersFibers
IR TransmittingSingle Mode Fibers
Beam splitter
Fold Mirror
Fold Mirrors
Compensation Plate
( phase shift)
Space Telescope
Spatial Filter for the Nulling Interferometer
Spatial Filter for the Nulling Interferometer
IRDetector
Theoretical evaluation Theoretical evaluation of of
the modal filtering by the modal filtering by a step a step
index single mode index single mode fiber fiber **
*O. Wallner *O. Wallner et. al.et. al.
Step index fiber configurationStep index fiber configuration
r
n
1n
2n a
b13n
Theoretical model:Theoretical model:
b → b → ∞∞
Real fibers:Real fibers:
b - finiteb - finite
Single Mode Conditions Single Mode Conditions
2122
21
0
nnλ
a2πV
2
VN
2
Single mode condition (LP01)V<2.405
Waveguide parameter Waveguide parameter - -
Number of modesNumber of modes --
Small difference between indices of refractionSmall difference between indices of refraction Small coreSmall core diameter diameter
*Theoretical evaluation of *Theoretical evaluation of
the minimal filter length the minimal filter length -- z z00
Modal filtering Modal filtering
is length dependent !!is length dependent !!
*O. Wallner *O. Wallner et. al.et. al.
A= PA= PLPLP0 1 0 1 (z(z00))
/ /
PPLM LM (z(z00))For modal filteringFor modal filtering::
A= 10A= 1066 Filter losses Filter losses ~ ~ 1-2 1-2 dB/mdB/m
DefinitionDefinition::
Attenuation Factor – Model Attenuation Factor – Model
2ρ
z0
Theoretical Estimates - O. Theoretical Estimates - O.
Wallner et. al.Wallner et. al.
IR Transmitting MaterialsIR Transmitting Materials
0.10.1 11 1100WavelengthWavelength[ [ mm]]
Silica Glasses
Sapphire
Fluoride Glasses
Silver Halide CrystalsSilver Halide Crystals
Chalcogenide Glasses
Most Most SuitaSuitableble
Candidates for Single mode fibersCandidates for Single mode fibers((Other than Silver HalidesOther than Silver Halides))
Chalcogenides* glasses seems to haveChalcogenides* glasses seems to have the most promising performancethe most promising performance
* Proc. SPIE * Proc. SPIE 5905 5905, 447, 2005, 447, 2005* J. Opt. Adv. Mat. 4, 665, 2002* J. Opt. Adv. Mat. 4, 665, 2002
Developed by the Developed by the University of Rennes FranceUniversity of Rennes France
Under DARWIN contract Under DARWIN contract
FluoridesFluoridesChalcogenidesChalcogenides
Silver HalideSilver Halide
Crystals and Crystals and
FibersFibers
at Tel Aviv University at Tel Aviv University
(TAU)(TAU)
Silver Halides CrystalsSilver Halides Crystals - -Optical PropertiesOptical Properties- -
Transmission RangeTransmission Range
AgClAgCl
AgBrAgBr
0.4 to 250.4 to 25mm
0.45 to 350.45 to 35mm
Crystal Growing SystemCrystal Growing System
cm
AgClBr CrystalsAgClBr Crystals
Typical DimensionsTypical Dimensions
Heaters
Crystal
Upper & LowerPlates
Fiber
Rod
Die
Press
Extrusion of a Silver Halide FiberExtrusion of a Silver Halide Fiber
Polycrystalline Structure – Typical Grain Polycrystalline Structure – Typical Grain Size Size ~~ 1µm 1µm
Silver Halide Unclad Fibers – Properties Silver Halide Unclad Fibers – Properties
Transmission Range & Loss Coefficient*Transmission Range & Loss Coefficient*
Silver Halide Unclad Fibers – Properties Silver Halide Unclad Fibers – Properties
Rayleigh Gans scattering Rayleigh Gans scattering λλ≈D≈Dscatscat ; I ; Iscat scat αα λλ22 * Measured by * Measured by
FTIRFTIR
* Measured at TAU where x – the molar fraction of * Measured at TAU where x – the molar fraction of chlorine in the compound.chlorine in the compound.
Silver Halides CrystalsSilver Halides Crystals - -Optical PropertiesOptical Properties- -
Refractive Indices of AgClRefractive Indices of AgClxxBrBr1-x1-x Solid Solutions * Solid Solutions *
Summary of silver halide fiber Summary of silver halide fiber parametersparameters
Spectral rangeSpectral range
2 - 25 μm2 - 25 μm
Optical losses at 10 μmOptical losses at 10 μm
uncladunclad
0.2 dB/m0.2 dB/m (or 95%* per meter)
core/cladcore/clad
~~1 dB/m1 dB/m (or 93%* per meter)
core diametercore diameter
uncladunclad
0.7 - 0.9 mm0.7 - 0.9 mm
core/cladcore/clad
0.3 - 0.6 mm0.3 - 0.6 mm LengthLength
2 - 10 m2 - 10 m
Field of view Field of view ~ 45º~ 45º
Flexible, Non toxic, Non-hygroscopic, BiocompatibleFlexible, Non toxic, Non-hygroscopic, Biocompatible
Single Mode Fibers (SMFs)Single Mode Fibers (SMFs)
- Basic “theoretical” demands -- Basic “theoretical” demands -
212
2
2
10
2nn
aV
B. Small coreB. Small core
A. Small difference between indices of refraction A. Small difference between indices of refraction
≤ ≤ 2.4052.405
Predicted Region for Single Predicted Region for Single Mode Operation @ 10.6Mode Operation @ 10.6mm
AgClBr single mode fibers AgClBr single mode fibers applicable for nulling applicable for nulling
interferometer missioninterferometer mission
Silver halide Silver halide AgClAgClxxBrBr1-x1-x Single Single Mode Fiber (SMF) Mode Fiber (SMF)
configurationconfiguration
r
n1n
2na
bxx
x+x+0.020.02
60µm>2a>50µm60µm>2a>50µm 2b=900µm2b=900µm
Improvement of the core-clad interface:Improvement of the core-clad interface:- Reducing the roughness- Reducing the roughness- Reducing the impurities- Reducing the impurities
Solving the problem of cracksSolving the problem of cracks
Small core = Extrusion process:Small core = Extrusion process:
Small Small ΔΔn = Homogeneous crystals:n = Homogeneous crystals:
Reduction of core diameter to 2a Reduction of core diameter to 2a ~~ 60 - 3060 - 30mm
Reduction of Reduction of n=nn=n11-n-n2 2 to to nn ~~ 0.005 0.005
Silver Halide SMFSilver Halide SMF
- Practical demands for single mode operation -- Practical demands for single mode operation -
Crystal Homogeneity:Crystal Homogeneity:
Crystal Growing Crystal Growing
Crystal Composition Crystal Composition
MeasurementsMeasurements
The Composition as a Function of The Composition as a Function of Position in Various Cross Sections Position in Various Cross Sections
Along a Vertical LineAlong a Vertical LineFOR EXAMPLEFOR EXAMPLE
Nominal composition: 83% BrNominal composition: 83% Br
83.5 ± 0.883.5 ± 0.8
84.084.0
84.084.084.084.0
84.584.5
84.584.5
83.083.0
82.582.5
82.582.5
Lower Lower layerlayer
181
181
4141
5252
6565
1010
66
[mm][mm]
Reduction of Core DiameterReduction of Core Diameter
αα [dB/m][dB/m] = 0.5 = 0.5 (2a=350µm)(2a=350µm), 1, 1((140µm)140µm), 4 - 5, 4 - 5(6(60µm)0µm)
Measurements at Measurements at =10.6=10.6mm
Smooth Smooth Interface;Interface;
Round (±5%) and homogeneous Round (±5%) and homogeneous corescores
60 60 m core m core fiberfiber
900 900 mm
MM5050 MM500500
60 60 mm
Core :Core :AgClAgCl4040BrBr6060
Clad :Clad : AgClAgCl9595BrBr55
RRzz~~200-250nm200-250nm ( ( Former RFormer Rzz~~1 to 2µm1 to 2µm))
IR IR
Problem: Clad modes Problem: Clad modes interfere interfere
with core radiation with core radiation
Output end of the Step Index (SI) core-clad Output end of the Step Index (SI) core-clad silver halide fiber of length silver halide fiber of length L=50 cm and core L=50 cm and core
diameter 2a = 60diameter 2a = 60mm Significant total energy in the cladSignificant total energy in the clad
Removal of Removal of Clad ModesClad Modes
Goal:Goal:
Attenuation of clad modes Attenuation of clad modes 40dB 40dB
Method:Method:Adding an absorbing layer onAdding an absorbing layer on the external surface of the fiberthe external surface of the fiber
Clad mode attenuation by Clad mode attenuation by Application of an Application of an absorbing layerabsorbing layer
r
n1n
2na
bAbsorbing layerAbsorbing layer
Output end of a coated SIOutput end of a coated SIcore-clad silver halide core-clad silver halide
fiber (comment: fiber (comment: photograph overexposed)photograph overexposed)
Core diameter = 60Core diameter = 60mm
IRIR
900 900 mm
Optical Optical
Properties of Properties of
Silver Halide Silver Halide
Single Mode Single Mode
Fibers Fibers
SMF With Core Diameter = SMF With Core Diameter = 5050µmµm
- Typical Losses- Typical Losses 15-20 dB/m15-20 dB/m
“ “Smooth” far field Smooth” far field patternpattern
Composition:Composition:
Core:Core: AgClAgCl0.30.3BrBr0.70.7
Inner clad:Inner clad: AgClAgCl0.320.32BrBr0.680.68
Far field Far field distributiondistribution
))L=50cmL=50cm((
RadialRadial far field far field distributiondistribution
Typical far field pattern of a 50µm coreTypical far field pattern of a 50µm coreSilver halide SMF, L=50cmSilver halide SMF, L=50cm
V# =2.1033V# =2.1033
CO2 laser
Demonstration of modal filteringDemonstration of modal filtering
SMF SMF L=50L=50µmµm
LensLensSilicon Silicon windowswindows
SpiricoSpiriconnIR IR
cameracamera
Microstructured Optical FibersMicrostructured Optical FibersJ. C. Flanagan J. C. Flanagan et al.et al.
Microstructured fibers are Microstructured fibers are potentially better suited potentially better suited for modal filtering than for modal filtering than step index (SI) step index (SI) fibersfibers
Main claim:Main claim:
April 19, 2023 Applied Physics Group 41
A schematic drawing of a configuration of a TIR - PCF
Photonic Crystal Fibers - PCFsPhotonic Crystal Fibers - PCFs
Transmission via Total Internal Transmission via Total Internal Reflection - TIRReflection - TIR
C
B
D
n1
n2
n2<n1
April 19, 2023 Applied Physics Group 42
A Thermal Image of a COA Thermal Image of a CO22 Laser Beam Laser Beam
Transmitted through a large core PCFTransmitted through a large core PCF Laser CO2
PCF
Thermal
Camera
Input
Output
Beam confined to the core Beam confined to the core areaarea
nnnnV coclco 222 22
Flat Flat WaveguideWaveguideY coupled waveguides Y coupled waveguides will be thewill be thebasis of integrated basis of integrated optical circuitsoptical circuits
> 20> 20mm core thickness core thicknessxx~~5%5%
* Radiation was coupled directly to the flat guide, using a F= 36cm * Radiation was coupled directly to the flat guide, using a F= 36cm lens (D=2.54cm).lens (D=2.54cm).
Thermal image of the output end of the Thermal image of the output end of the waveguide waveguide
The input end was illuminated by a COThe input end was illuminated by a CO22 Laser radiation*Laser radiation*
Single Mode Flat WaveguideSingle Mode Flat Waveguide
We have developed a new crystal growing We have developed a new crystal growing technique ensuring composition technique ensuring composition
homogeneityhomogeneity of about ±1%of about ±1%
DiscussionDiscussion
We have developed an absorbing coating We have developed an absorbing coating that is useful for stripping of cladding modes.that is useful for stripping of cladding modes.
We established special extrusion conditions We established special extrusion conditions needed for the extrusion of core-clad fibers of needed for the extrusion of core-clad fibers of extremely small cores.extremely small cores.
We have developed and fabricated fibers We have developed and fabricated fibers having small core and small having small core and small n that exhibit n that exhibit Single Mode properties.Single Mode properties.
The extrusion process has been improved The extrusion process has been improved
We have developed a new single mode flat We have developed a new single mode flat waveguide which can be used for fabrication waveguide which can be used for fabrication of integrated optical circuit. of integrated optical circuit.
DiscussionDiscussion
We have developed microstcutured fiber and We have developed microstcutured fiber and demonstrated transmission through its core. demonstrated transmission through its core.
ConclusionsConclusions