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Nonlinear optical frequency conversion to & from the mid- infrared in Ti:PPLN waveguides for spectroscopy and free-space optical communication [Elektronische Ressource] / von Kai-Daniel Büchter

137 pages
Publié par :
Ajouté le : 01 janvier 2011
Lecture(s) : 29
Signaler un abus

Nonlinear Optical Frequency Conversion
to & from the Mid-Infrared in
Ti:PPLN Waveguides for Spectroscopy and
Free-Space Optical Communication
Thesis
Dem Department Physik,
Fakult¨at der Naturwissenschaften
der Universit¨at Paderborn vorgelegte
Dissertation
von
Kai-Daniel Frank Bu¨chter
zur Erlangung des akademischen Grades eines
Doktors der Naturwissenschaften (Dr. rer. nat.)
Erstgutachter: Professor Dr. W. Sohler
Zweitgutachter: Professor Dr. C. Meier
Tag der Einreichung: January 17th, 2011
Tag der mu¨ndlichen Pru¨fung: February 25th, 2011Contents
Introduction 1
1. Strip Waveguides for Nonlinear Frequency Conversion 7
1.1. Theoretical Treatment of Periodically Poled Waveguides . . . . . . . . . 8
1.1.1. Waveguide and Non-linear Optical Polarization Theory . . . . . . 8
1.1.2. Coupled Mode Theory . . . . . . . . . . . . . . . . . . . . . . . . 11
1.1.3. Quasi Phase-Matching . . . . . . . . . . . . . . . . . . . . . . . . 15
1.2. Waveguide Sample Fabrication . . . . . . . . . . . . . . . . . . . . . . . . 16
1.2.1. Waveguide Fabrication . . . . . . . . . . . . . . . . . . . . . . . . 17
1.2.2. Periodic Poling . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
1.3. Summary and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2. Mid-infrared Source based on Difference-Frequency Generation 21
2.1. Theoretical Modelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.2. Experimental Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2.3. Sample Characterization & Discussion of Results . . . . . . . . . . . . . 28
2.3.1. Mid-infrared Mode Distributions . . . . . . . . . . . . . . . . . . 28
2.3.2. Nonlinear Conversion Efficiency . . . . . . . . . . . . . . . . . . . 30
2.3.3. Wavelength Characteristics . . . . . . . . . . . . . . . . . . . . . 34
2.3.4. Output-Power Stability . . . . . . . . . . . . . . . . . . . . . . . . 35
2.4. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3. Hybrid Up-Conversion Detector 39
3.1. Theoretical Background . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
3.1.1. Basic Detector Figures of Merit . . . . . . . . . . . . . . . . . . . 40
3.1.2. Up-conversion Detector Performance Estimation . . . . . . . . . . 41
3.2. Up-Conversion Detector based on Sum-Frequency Generation . . . . . . 47
3.2.1. Experimental Setup . . . . . . . . . . . . . . . . . . . . . . . . . . 47
3.2.2. Results & Discussion of Detector Performance . . . . . . . . . . . 49
3.3. Up-conversion Detector based on Difference-Frequency Generation . . . . 55
3.3.1. Experimental Setup . . . . . . . . . . . . . . . . . . . . . . . . . . 55
3.3.2. Results & Discussion of Detector Performance . . . . . . . . . . . 56
3.4. Additional Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . 58
3.5. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
4. Absorption Spectroscopy using Frequency Conversion 63
4.1. Basics of Trace Gas Spectroscopy . . . . . . . . . . . . . . . . . . . . . . 64
i4.2. Absorption Spectroscopy using DFG-MIR Source . . . . . . . . . . . . . 66
4.3. Absorption Spectroscopy using DFG-MIR Source and SFG-UCD . . . . . 68
4.4. Frequency Modulation Spectroscopy using DFG Source and SFG-UCD . 70
4.5. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
5. Free-space Optical Transmission in the MIR using Wavelength Conversion 75
5.1. Atmospheric Transmission Impairments . . . . . . . . . . . . . . . . . . . 77
5.2. Down- and Up-Conversion for Free-Space Optical Transmission. . . . . . 79
5.2.1. Experimental Setup . . . . . . . . . . . . . . . . . . . . . . . . . . 80
5.2.2. Free-Space Transmission-Line Characteristics. . . . . . . . . . . . 81
5.3. Evaluation of Free-Space Data-Transmission . . . . . . . . . . . . . . . . 87
5.4. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
Conclusions 91
A. Waveguide and Poling Mask Design 97
B. Modeling of Lens Dispersion 101
C. Waveguide Inhomogeneity Calculations 103
D. Reference HgCdTe Detector Characterization 105
E. Atmospheric Transmission Impairments 107
E.1. Atmospheric Scattering and Absorption . . . . . . . . . . . . . . . . . . . 107
E.2. Beam Divergence and Spreading . . . . . . . . . . . . . . . . . . . . . . . 110
E.3. Scintillation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
iiList of Figures
0.1. SFG / DFG energy level diagram. . . . . . . . . . . . . . . . . . . . . . . 2
0.2. Overview of MIR lasers. . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
0.3. Free-space transmission using frequency conversion. . . . . . . . . . . . . 5
1.1. Illustration of Ti-indiffused waveguide in LiNbO . . . . . . . . . . . . . . 83
1.2. Fundamental electric field distributions in an MIR-waveguide. . . . . . . 11
1.3. SFG and DFG efficiency calculations. . . . . . . . . . . . . . . . . . . . . 14
1.4. Nonlinear-optic generation of radiation over short interaction lengths. . . 16
1.5. Waveguide fabrication steps. . . . . . . . . . . . . . . . . . . . . . . . . . 17
1.6. Periodic poling steps. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.1. Calculated idler power dependence on pump and signal powers. . . . . . 23
2.2. DFG-MIR source scheme and photo. . . . . . . . . . . . . . . . . . . . . 25
2.3. Illustration of lens dispersion. . . . . . . . . . . . . . . . . . . . . . . . . 25
2.4. DFG setup and fiber coupling details. . . . . . . . . . . . . . . . . . . . . 26
2.5. Transmission properties of input anti-reflection coating. . . . . . . . . . . 27
2.6. MIR waveguide modes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.7. Measured and calculated Ti-waveguide MIR mode profiles. . . . . . . . . 29
2.8. DFG tuning characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . 30
2.9. DFG power characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . 32
2.10.Senza pump laser. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
2.11.Two-dimensional DFG power plot. . . . . . . . . . . . . . . . . . . . . . 33
2.12.DFG phase-matching temperature dependence. . . . . . . . . . . . . . . 34
2.13.DFG stability measurements. . . . . . . . . . . . . . . . . . . . . . . . . 36
3.1. Principle of SFG and DFG up-conversion detectors. . . . . . . . . . . . . 39
3.2. Ideal detectivity of photo-conductive / photo-voltaic detectors. . . . . . . 43
3.3. NEP of shot-noise / background limited detectors. . . . . . . . . . . . . . 46
3.4. Calculated UCD conversion efficiencies, including losses. . . . . . . . . . 47
3.5. Experimental setup for UCD characterization. . . . . . . . . . . . . . . . 48
3.6. SFG up-conversion detector scheme. . . . . . . . . . . . . . . . . . . . . . 49
3.7. Femto OEC-200-IN2 noise characteristics. . . . . . . . . . . . . . . . . . 50
3.8. SFG up-conversion detector characterization setup. . . . . . . . . . . . . 51
3.9. Up-conversion detector pump reflection mirror characteristics. . . . . . . 52
3.10.SFG up-conversion detector power characteristics. . . . . . . . . . . . . . 52
3.11.Direct comparison of MCT and SFG-UCD. . . . . . . . . . . . . . . . . . 53
3.12.Spectrum of SFG up-conversion detector output. . . . . . . . . . . . . . . 54
3.13.DFG up-conversion detector scheme. . . . . . . . . . . . . . . . . . . . . 56
iii3.14.DFG up-conversion detector characterization setup. . . . . . . . . . . . . 56
3.15.DFG up-conversion detector power characteristics. . . . . . . . . . . . . . 57
3.16.Parametric gain in DFG up-conversion detector. . . . . . . . . . . . . . . 58
3.17.Parametric fluorescence spectrum of the DFG-UCD at 1550 nm. . . . . . 59
4.1. Absorption spectroscopy setup using conventional detection. . . . . . . . 65
4.2. Absorption measurement using DFG-MIR source and a MCT detector. . 66
4.3. Normalized absorption measurement using DFG source. . . . . . . . . . . 67
4.4. Absorption spectroscopy using SFG-UCD. . . . . . . . . . . . . . . . . . 68
4.5. Photo of DFG-SFG absorption setup. . . . . . . . . . . . . . . . . . . . . 69
4.6. Methane absorption measurement using DFG and SFG. . . . . . . . . . . 69
4.7. FM spectroscopy using SFG-UCD. . . . . . . . . . . . . . . . . . . . . . 71
4.8. Frequency modulation spectrum of methane. . . . . . . . . . . . . . . . . 71
5.1. Illustration of free-space optical links. . . . . . . . . . . . . . . . . . . . . 75
5.2. Wavelength dependence of atmospheric attenuation. . . . . . . . . . . . . 78
5.3. Free-space transmission using frequency conversion. . . . . . . . . . . . . 79
5.4. Power characteristics of the FSO transmitter module. . . . . . . . . . . . 80
5.5. DFG power characterization setup for FSO transmission modules. . . . . 81
5.6. FSO transmission experiment using nonlinear wavelength conversion. . . 82
5.7. Pump-reflection mirror of the receiver sample. . . . . . . . . . . . . . . . 82
5.8. Photo of Transmitter module. . . . . . . . . . . . . . . . . . . . . . . . . 83
5.9. Transmitter and Receiver tuning characteristics. . . . . . . . . . . . . . . 84
5.10.Transmitter power characteristics. . . . . . . . . . . . . . . . . . . . . . . 85
5.11.FSO-transmission line characteristics. . . . . . . . . . . . . . . . . . . . . 86
5.12.Losses in the FSO transmission line. . . . . . . . . . . . . . . . . . . . . 86
5.13.FSO data transmission setup. . . . . . . . . . . . . . . . . . . . . . . . . 88
5.14.BER impairment with wavelength converters. . . . . . . . . . . . . . . . 89
5.15.Free-space transmission line through a wind tunnel. . . . . . . . . . . . . 90
A.1. Waveguide group layout. . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
A.2. Nonlinear efficiency (DFG) as function of strip width and thickness. . . . 98
A.3. Mask layout with six poling groups. . . . . . . . . . . . . . . . . . . . . . 99
B.1. Gaussian beam modeling of lens dispersion. . . . . . . . . . . . . . . . . 102
C.1. Phase-matching chirp assumed for modeling. . . . . . . . . . . . . . . . . 104
D.1. MCT detector characterization. . . . . . . . . . . . . . . . . . . . . . . . 105
E.1. Molecular and Aerosol scattering and absorption coefficients. . . . . . . . 108
E.2. Atmospheric transmission considering absorption losses. . . . . . . . . . . 109
E.3. High resolution atmospheric transmission spectra. . . . . . . . . . . . . . 111
E.4. Atmospheric transmission considering scattering and absorption losses. . 112
E.5. Scintillation index for weak, moderate, and strong turbulence conditions [1].114
ivList of Tables
2.1. Effect of waveguide inhomogeneities on Δβ. . . . . . . . . . . . . . . . . 31
3.1. Comparison of theoretical detectivities at different wavelengths. . . . . . 45
E.1. Transmission bands in the near- to mid-infrared range. . . . . . . . . . . 110
v