臺灣博碩士論文加值系統

週期性反轉式鈮酸鋰光波導(PPLN WG)在非線性頻率轉換的應用上，是相當受人注目的一種非線性積體光學元件。目前有很多方法可以在鈮酸鋰上製作光波導，例如液相質子交換法(LPE)、回火式液相質子交換法(APE)、反致換式質子交換法(RPE)、弱酸式質子交換法(SPE)和高溫式質子交換法(HTPE)。在這份研究中，我們介紹了氣相質子交換法(VPE)並將其應用在元件上。我們利用光菱鏡耦合器、X光繞射儀、光譜儀來精確分析氣相質子交換製作的平面光波導。並且，也分析在不同的實驗參數下的質子擴散特性，如溫度(260℃~325℃)、製程時間(3h~72h)、苯甲酸鋰混合質子酸的濃度。
經過實驗的驗證，我們相信折射率改變的增加是由於在氣相質子交換中，直接質子交換和回火效應平衡之後所造成對擴散速率改變的影響。利用氣相質子交換法可以直接得到單純κ2的晶相。比起液相質子交換法得到的β混合晶相，此κ2的晶相受到比較小的應力及擁有較少的折射率改變。質子交換後的回火過程，將使得κ2的晶相變成具有漸進式折射率的α晶相。這種晶相經過證實是具有低損耗、還原後的非線性係數。使用回火式氣相質子交換法(AVPE)得到的α晶相，比起回火式液相質子交換法(APE)得到的α晶相還要來的單一、純淨。(從X光峰谷值曲線比較而得) 實驗結果顯示出，我們有可能得到一個具有更低損耗、高效率的光波導元件。
我們已建立一個很好的電腦程式來模擬AVPE製程中的質子擴散行為。而我們可以從既有在波長範圍容許內修正過的Sellmeier方程式，來完整建立折射率分佈曲線。而且，這也是第一次有人展示和特性分析氣相質子交換法製作的PPLN WG。雖然有很多因素致使轉換效率很低，但我們相信可以利用現有成熟的技術來克服這些問題。無疑的是，這仍需要很多空間來思索解決之道，並改進及最佳化我們的製程。

Periodically-Poled LiNbO3 waveguide (PPLN WG) is an attractive integrated nonlinear device for high-efficient nonlinear frequency conversion applications. There are numerous competitive techniques to form the optical waveguide in LiNbO3, such as liquid-phase proton exchange (LPE), annealing liquid-phase proton exchange (APE), reverse proton exchange (RPE), soft proton exchange (SPE), and high-temperature proton exchange (HTPE). This work introduced the vapor phase proton exchange (VPE) process and applied it to fabricate the high-quality waveguide devices. The features of the planar waveguide by the VPE process have been accurately characterized using the prism coupler, x-ray diffractometer, and spectrophotometer. Also, the diffusions under various parameters such as temperature (260℃~325℃), process durations (3h~72h), and hydrogen concentration with lithium benzoate are analyzed.
It is believed that the diffusion rate balanced between the direct proton exchange and annealing leads to the index change and particular phase structure in the VPE process. A pure crystalline phase κ2 can be obtained directly via the VPE process. Theκ2 phase suffers smaller strains and lower refractive index change than the β mixture phases from the LPE. The post-exchange annealing will cause a phase transition from theκ2 phase toward the α phase with a graded index-like profile which is confirmed to have a low loss feature, and to include the recovered nonlinear coefficient. The α phase obtained using the annealing VPE (AVPE) procedure is even clearer and purer than that obtained using the APE procedure (from the comparison of the x-ray rocking curve peaks). That result indicates the possibility to fabricate even lower loss and high efficient waveguide devices.
The program for simulating the AVPE diffusion behavior is also established in this thesis. Index profile can be fully constructed within the wavelength range of the revised Sellmeier equation. Additionally, the first optical result of the PPLN WG fabricated by the AVPE method is demonstrated and characterized. Although the device suffers low conversion efficiency for various reasons, these problems can be overcome using the available techniques. Undoubtedly, considerable room remains for improvements and optimizations of the proposed procedure.

Table of Contents
Chapter 1 Introduction 1
1.1 Motivation 1
1.2 Reviews of the Nonlinear Optics 2
1.3 Quasi-phase Matching Structure 3
1.4 Reviews of the Proton Exchange Process 5
1.5 Dissertation Structure 6
Reference for Chapter 1 7
Chapter 2 Theory of Guided Wave Quasi-Phasematched Optical Frequency Conversion and Nonlinear Diffusion in Annealing Proton Exchanged Waveguide 9
2.1 Introduction 9
2.2 Coupled Mode Equations for Frequency Mixing 10
2.3 Nonlinear Diffusion in Annealing Proton Exchanged Waveguide 13
2.3-1 Diffusion of the Proton Exchange 13
2.3-2 Concentration Independent and Dependent Diffusion Process 14
2.4 Summary 18
Reference for Chapter 2 19
Chapter 3 Characterizations of the Planar Vapor-phase Proton-exchanged Waveguide 20
3.1 Introduction 20
3.2 Fabrication of the Planar Waveguide and Measuring Procedures. 21
3.2-1 Preparation of the Planar Waveguides by the VPE 21
3.2-2 Prism Coupler Measurement and Experimental Results 23
3.2-3 X-Ray Diffractometer Measurement and Experimental Results 26
3.2-4 Spectrophotometer Measurement and Experimental Results 29
3.3 Characterizations and Diffusion Modeling 31
3.3-1 Characterizations 31
3.3-2 Diffusion Modeling of the Annealing 36
3.4 Summary 40
Reference for Chapter 3 41
Chapter 4 PPLN Channel Waveguide by AVPE 42
4.1 Introduction 42
4.2 Fabrication of the PPLN Channel Waveguide 42
4.2-1 Fabrication of Periodically Poled Lithium Niobate 42
4.2-2 Design and Fabrication of the Channel Waveguide 43
4.3 Optical Testing on PPLN WG 45
4.3-1 Optical Measurement Setup 45
4.3-2 Optical Result and Discussion 47
4.4 Summary 49
Reference for Chapter 4 50
Chapter 5 Conclusions 51
5.1 Summary of Research Contributions 51
5.2 Future Research 51
Appendix A Characterizations of 5% MgO Doped Lithium Niobate 53
A.1 Experiment and Characterization 53
Appendix B Sellmeier Equation for the Index of Refraction, ne, in Congruent Lithium Niobate 57
List of Illustrations
1.1 Schematic of the critical and non-critical phase matching.......................................5
2.1 Index profile of the APE and AVPE……………………………………………...14
2.2 Simulation of the constant diffusion……………..................................................16
2.3 Simulation of the nonlinear diffusion equation…………………………………..17
2.4 Simulation of the concentration-dependent diffusion……………………………18
3.1 Design of the glass tube for VPE………………...…………................................21
3.2 Planar waveguide fabrication flowchart…………………………….....................22
3.3 Schematic of the prism coupler………….…………………………….........……24
3.4 Index profile of the VPE under different durations……………………..…….….25
3.5 Schematic diagram of the x-ray diffractometer…………..……………...……….27
3.6 Schematic of the cell expansion and the Bragg diffraction………………………27
3.7 Structure phase diagram of the x-ray rocking curve..............................................28
3.8 Characterization results from the x-ray rocking curve………………………..….29
3.9 Possible OH- bond locations in the LiNbO3...…………………………………...30
3.10 Absorption peaks from a spectrophotometer…………...……………………….30
3.11 The diffusion relations of the samples with different exchange duration………32
3.12 The effects of exchange durations, temperature, and hydrogen concentration....33
3.13 The hypothesis of the diffusion behaviors………………………………………35
3.14 The Sellmeier equation for the CLN and the VPE……………………………...36
3.15 Index profile of the VPE under varied annealing durations….............................37
3.16 Simulation results from the origin program…………………………………….38
3.17 Analyzing proton numbers from the integrations and OH- absorption peak…...39
3.18 Simulation results from the modified program…………………………………40
4.1 Fabrication process of the PPLN…………………………………………………43
4.2 Non-critical phase matching diagram…………………………………………….43
4.3 Fabrication process of the PPLN WG by the VPE……………………………….44
4.4 Index profile of the APE and AVPE waveguide……………………………...…..44
4.5 Schematic of the optical measuring system...……………………………………45
4.6 The view of the alignment from the vertical microscope………………………...46
4.7 The wavelength tuning curve of the PPLN WG by the AVPE...............................47
4.8 The micro-view of the channel waveguide and the beam profile of the harmonic wave………………………………………………………………………………….48
A.1 Index Profile of the 5% MgO-LN……………………………………………….53
A.2 Schematic of the diffusion relation between CLN and 5% MgO-LN…………...54
A.3 X-ray rocking curve of 5% MgO-LN by LPE, VPE, APE, AVPE……………....55
List of Tables
3.1 Fabrication condition of the VPE………………………………………………...23
3.2 External CW light sources used in prism coupler………………………………..24
3.3 Index and thickness from the measurement of the prism coupler………………..25
3.4 Absorption peaks………………………………………………………………....30
3.5 Correlations of the phase and index from the reference..………………………...31
3.6 Correlations of the phase and index from the experiment………………………..31 3.7 Index reference table from the measurement…………………………………….36
4.1 Spec. list of optical testing system instrument……………………...……………46
A.1 Fabrication Conditions for 5% MgO-LN samples………………………………53
A.2 Measured Index and Thickness for 5% MgO-LN samples….…………………..54
A.3 Experimental Conditions………………………………………………………...55
B.1 Fitted Parameters for Eqn. B.1…………………………………………………..57

REFERENCE FOR CHAPTER 1
[1] E. J. Lim, M. M. Fejer, and R. L. Byer, “Second harmonic generation of green light in periodically poled lithium niobate waveguide”, Electron Lett. 25, 174-175, 1989.
[2] Kawanishi S, Chou MH, Fujiura K, et al, “All-optical modulation and time-division-multiplexing of 100Gbit/s signal using quasi-phasematched mixing in LiNbO3 waveguides”, Electron. Lett. 36, 1568-1569, 2000.
[3] Parameswaran KR, Fujimura M, Chou MH, et al, “Low-power all-optical gate based on sum frequency mixing in APE waveguides in PPLN”, IEEE Photonic Tech. Lett. 12, 654-656, 2000.
[4] P. A. Franken, A. E. Hill, C. W. Peters, and G. Weinreich, “Generation of optical harmonics”, Phys. Rev. Lett. 7, 118-119, 1961.
[5] J. L. Jackel, C. E. Rice, and J. J. Veselka, “Proton exchange for high-index waveguide in LiNbO3“, Appl. Phys. Lett. 41, 607-608, 1982.
[6] D. Hofmann. G. Shreiber, C. Hasse, H. Herrmann, R. Ricken, and W. Sohler, “Continuous-wave mid-infrared optical parametric oscillators with periodically poled Ti: LiNbO3 channel waveguides”, Opt. Lett. 24, 896-898, 1999.
[7] T. Fujiwara, R. Srivastava, X. Cao, and R. V. Ramasway, “Comparison of photorefractive index change in proton-exchanged and Ti-diffused LiNbO3 waveguides”, Opt. Lett. 18, 346-348, 1993.
[8] M. L. Bortz and M. M. Fejer, “Annealed proton-exchanged LiNbO3 waveguides”, Opt. Lett. 16, 1844-1846, 1991.
[9] X. Cao, R. Srivastava, R. V. Ramaswamy, and J. Natour, “Recovery of second-order optical nonlinearity in annealed proton-exchanged LiNbO3”, IEEE Photonic Tech. Lett. 3, 25-27, 1991.
[10] Michael L. Bortz, Quasi-phasematched optical frequency conversion in lithium niobate waveguides, Ph.D. Dissertation, Department of Electrical Engineering, Stanford University, Stanford, CA(1992).
[11] Yu. N. Korkishko, V. A. Fedorov, and T. M. Morozova, “Reverse proton exchange for buried waveguides in LiNbO3”, J. Opt. Soc. Am. A 15, 1838-1842, 1998.
[12] K. R. Parameswaran, R. K. Route, et al, “Highly efficient second-harmonic generation in buried waveguides formed by annealed and reverse proton exchange in periodically poled lithium niobate”, Opt. Lett. 27, 179-181, 2002.
[13] L. Chanvillard, P. Aschieri, P. Baldi, et al, “Soft proton exchange on periodically poled LiNbO3: A simple waveguide fabrication process for highly efficient nonlinear interactions”, Appl. Phys. Lett. 76, 1089-1091, 2000.
[14] Yu. N. Korkishko, V. A. Fedorov, and O. Y. Feoktistova, “LiNbO3 optical waveguide fabrication by high-temperature proton exchange”, J. Lightwave Tech.18, 562-568, 2000.
[15] J. Rams and J. M. Cabrera, “Preparation of proton-exchange LiNbO3 waveguide in benzoic acid vapor”, J. Opt. Soc. Am. B 16, 401-406, 1999.
REFERENCE FOR CHAPTER 2
[1] K. R. Parameswaran, J. R. Kurz, R. V. Roussev, and M. M. Fejer, “Observation of 99% pump depletion in single-pass second-harmonic generation in a periodicalliy poled lithium niobate waveguide,” Opt. Lett. 27, 43 (2002).
[2] R. W. Boyd, Nonlinear Optics, Academic Press, 1992.
[3] P. G. Suchoski, T. K. Frindakly, and F. J. Leonberger, “Stable, low-loss proton exchanged LiNbO3 waveguide devices with no electro-optic degradation”, Opt. Lett. 13, 1050-1052, 1988.
[4] M. M. Howerton, W. K. Burns, P. R. Skeath, and A. S. Greenblatt, “Dependence of refractive index on hydrogen concentration in proton exchanged LiNbO3”, IEEE J. Quantum Electronics 27, 593-601, 1991.
[5] J. M. Zavada, H. C. Casey, S. W. Novak, and A. Loni, “Correlation of substitutional hydrogen refractive index profiles in annealed proton-exchanged z- and x-cut LiNbO3”, J. Appl. Phys. 77, 2697-2708, 1994.
[6] D. F. Clark, A.C. G. Nutt, K. K. Wong, P. J. R. Laybourn, and R. M. De La Rue, “Characterization of proton exchange slab optical waveguides in z-cut LiNbO3” J. Appl. Phys. 54, 6218-6220, 1983.
[7] T. Maciak and M. Sokolowski, “Fabrication of proton exchange optical waveguides in x-cut LiNbO3”, Optica Applicata 19, 423-428, 1989.
[8] J. Crank, Mathematics of Diffusion, Charlendon Press, 1975.
[9] Dieter H. Jundt, “Temperature-dependent Sellmeier equation for the index of refraction, ne, in congruent lithium niobate”, Opt. Lett. 22, 1553-1555, 1997.
[10] Michael L. Bortz, Quasi-phasematched optical frequency conversion in lithium niobate waveguides, Ph.D. Dissertation, Department of Electrical Engineering, Stanford University, Stanford, CA(1992).
REFERENCE FOR CHAPTER 3
[1] T. Fujiwara, X. Cao, R. Sricastava, and R. V. Ramaswamy, “Photorefractive effect in annealed proton-exchanged LiNbO3 waveguides”, Appl. Phys. Lett. 61, 743-745, 1992.
[2] T. R. Volk and N. M. Rubinina, “Nonphotorefractive impurities in lithium niobate: magnesium and zinc”, Sov. Phys. Solid State 33, 674-680, 1991.
[3] I. W. Kim, B. C. Park, B.M. Jin, A.S. Bhalla, and J. W. Kim, “Characteristics of MgO-doped LiNbO3 crystals”, Materials Lett. 24, 157-160, 1995.
[4] P. K. Tien and R. Ulrich, “Theory of prism-film coupler and thin-film light guides”, J. Opt. Soc. Am. 60, 1325-1337, 1970.
[5] J. M. White and P. F. Heidrich, “Optical waveguide refractive index profiles determined from measurement of mode indices: a simple analysis”, Appl. Opt. 15, 151-155, 1976.
[6] Dieter H. Jundt, “Temperature-dependent Sellmeier equation for the index of refraction, ne, in congruent lithium niobate”, Opt. Lett. 22, 1553-1555, 1997.
[7] Shen Hy, Xu H, Zeng Zd, Lin Wx, and Wu Rf, Xu Gf, “Measurement of refractive-indexes and thermal refractive-index coefficients of LiNbO3 crystal doped with 5 mol percent MgO”, Appl. Opt. 31, 6695-6697, 1992.
[8] Yu. N. Korkishko, and V. A. Fedorov, “Structure phase diagram of HxLi1-xNbO3 waveguides: The correlation between optical and structural properties”, IEEE J. Sele. Top. Quantum Electronics 2, 187-196, 1996.
[9] Yu. N. Korkishko, V. A. Fedorov, et al, “Relationships between structural and optical properties of proton-exchanged waveguides on z-cut lithium niobate”, Appl. Opt. 35, 7056-7060, 1996.
[10] J.M. Cabrera, J. Olivares, M. Carrascosa, J. Rams, et al, “Hydrogen in lithium niobate”, Adv. in Phys. 45, 349-392, 1996.
[11] Y. Kong, J. Xu, W. Zhang, and G. Zhang, “The site occupation of protons in lithium niobate crystals”, J. Phys. and Chem. Solid. 61, 1331-1335, 2000.
[12] Yu. N. Korkishko, and V. A. Fedorov, “Relationship between refractive index and hydrogen concentration in proton exchanged LiNbO3 waveguides”, J. Appl. Phys. 82, 1010-1017, 1997.
[13] Yu. N. Korkishko, V. A. Fedorov and F. Laurell, ”The SHG-response of different phases in proton exchanged lithium niobate waveguide”, IEEE J. Sele. Top. Quantum Electronics 6, 132-142, 2000.
[14] J. Rams, F. Agullo-Rueda, and J. M. Cabrera, “Structure of high index proton exchange LiNbO3 waveguides with undegraded nonlinear optical coefficients”, Appl. Phys. Lett. 71, 3356-3358, 1997.
REFERENCE FOR CHAPTER 4
[1] G. D. Miller, Periodically poled lithium niobate: modeling, fabrication, and nonlinear optical performance, Ph.D. Dissertation, Department of Electrical Engineering, Stanford University, Stanford, CA (1998).
[2] Ming-Hsien Chou, Optical frequency mixers using three-wave mixing for optical fiber communications, Ph.D. Dissertation, Department of Applied Physics, Stanford University, Stanford, CA (1999).
[3] E. J. Lim, S. Matsumoto, and M. M. Fejer, “Noncritical phase matching for guided-wave frequency conversion”, Appl. Phys. 57, 2294-2296, 1990.
[4] M. L. Bortz, S. J. Field, M. M. Fejer, D. W. Nam, R. G. Waarts and D. F. Welch, “Noncritical quasi-phasematched second harmonic generation in an annealed proton exchanged LiNbO3 waveguides”, Trans. on Quantum Electron. 30, 2953, 1994.
[5] Michael L. Bortz, Quasi-phasematched optical frequency conversion in lithium niobate waveguides, Ph.D. Dissertation, Department of Electrical Engineering, Stanford University, Stanford, CA(1992).