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OPTICAL-FREQUENCY MIXERS IN PERIODICALLY POLED nlo. · PDF file 2020. 10. 9. · optical-frequency mixers in periodically poled lithium niobate: materials, modeling and characterization

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  • OPTICAL-FREQUENCY MIXERS IN PERIODICALLY POLED LITHIUM

    NIOBATE: MATERIALS, MODELING AND CHARACTERIZATION

    A DISSERTATION

    SUBMITTED TO THE DEPARTMENT OF APPLIED PHYSICS

    AND THE COMMITTEE ON GRADUATE STUDIES

    OF STANFORD UNIVERSITY

    IN PARTIAL FULFILLMENT OF THE REQUIREMENTS

    FOR THE DEGREE OF

    DOCTOR OF PHILOSOPHY

    Rostislav Vatchev Roussev

    December 2006

  • c© Copyright by Rostislav Vatchev Roussev 2007 All Rights Reserved

    ii

  • I certify that I have read this dissertation and that, in my opinion, it is fully

    adequate in scope and quality as a dissertation for the degree of Doctor of

    Philosophy.

    Martin M. Fejer Principal Adviser

    I certify that I have read this dissertation and that, in my opinion, it is fully

    adequate in scope and quality as a dissertation for the degree of Doctor of

    Philosophy.

    Robert L. Byer

    I certify that I have read this dissertation and that, in my opinion, it is fully

    adequate in scope and quality as a dissertation for the degree of Doctor of

    Philosophy.

    Stephen E. Harris

    Approved for the University Committee on Graduate Studies.

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  • iv

  • Abstract

    Efficient wavelength conversion is an attractive approach for obtaining coherent radiation in

    regions of the spectrum where lasers are unavailable or impractical. Optical signal process-

    ing in WDM networks, optical-CDMA communications, and quantum communication are

    examples of applications that can utilize efficient nonlinear frequency conversion at low

    power levels. Lithium niobate (LN) is a very promising material for the purpose, because it

    has a mature crystal-growth process, wide transparency range, large second-order nonlinear

    coefficient, and allows quasi-phasematching via periodic poling (PP). Waveguides enable

    efficient conversion at low powers and can be formed via reverse proton-exchange. Precise

    modeling of both the fabrication process and the properties of the resulting waveguides is

    thus necessary for the demonstration of high-density optical integrated circuits.

    This dissertation presents a complete fabrication model that accurately predicts the

    nonlinear diffusion of protons in PPLN as well as the dispersion of the waveguides between

    450 and 4000 nm. Using this model, waveguides are fabricated for two experiments: efficient

    generation of 3–4-µm radiation for spectroscopy via difference frequency generation using

    two near-IR lasers; and parametric amplification of 1.57-µm seed signal radiation for remote

    wind sensing using a 1.064-µm pump laser.

    The waveguides are fabricated in conventional congruent-composition LN. Photorefrac-

    tive damage (PRD) and green-induced infrared absorption (GRIIRA) limit the generated

    output power in these devices at room temperature due to the presence of high-intensity

    visible light. Resistance to PRD and GRIIRA can be achieved by heavy doping with Mg2+,

    or by using crystals with stoichiometric composition.

    PRD-resistant, bulk near-stoichiometric lithium niobate (SLN) was fabricated by vapor-

    transport equilibration (VTE) of originally congruent lithium niobate wafers with light MgO

    (0.3–1 mol%) doping. Details of the poling process and the dependence of photorefractive

    properties on crystal composition are presented. We obtained periodic poling down to a

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  • period of 7 µm and achieved 2 W at 532 nm via second harmonic generation in a 0.3 mol-

    % VTE-MgO:LiNbO3 bulk crystal at room-temperature. These breakthroughs will enable

    efficient tunable radiation from the visible to the mid-IR for a variety of applications.

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  • Acknowledgements

    I have been very fortunate to pursue my advanced degree at the Stanford University depart-

    ment of Applied Physics, where I had the opportunity to interact with many extraordinary

    people. They have contributed significantly to my growth as a scientist and as a person. I

    would like to acknowledge their support.

    My research adviser, Prof. Martin Fejer, has helped me not only with difficulties in

    research, but also in my personal life. Without his support, I would not have gotten this

    far. I have been amazed at how he always found time to check if students had any difficulties,

    and to offer very helpful advice. He has done that for me throughout my Stanford years,

    and I am very grateful to him for that. I have learned a lot from him not only about science,

    but also about responsibility and devotion. I enjoyed many technical discussions with my

    adviser, which were both helpful and stimulating. I learned a large fraction of my technical

    knowledge through direct interactions with him. I would also like to thank him for making

    time to read and correct my dissertation according to my schedule.

    Prof. Robert Byer has been very supportive of my collaborations with members of his

    group. He has made me believe that a person can be great at many things and need not

    worry about it. I would also like to thank Prof. Byer for the wonderful presentations about

    beautiful places around the globe, for reading my dissertation during the only time interval

    in which I could deliver it and for the encouraging final remarks.

    I would like to thank Prof. Stephen Harris for the very stimulating and inspirational

    presentations that he and his students have given at local symposia. In addition, I would

    like to thank him for the great care taken in the teaching of the Nonlinear Optics class that

    I took in my first year. Taking the class was a pleasant learning experience for me. Finally,

    I would like to thank Prof. Harris for the great support during his reading of my thesis and

    for the remarks of approval.

    I would like to thank the other two members of my thesis defense committee - Prof.

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  • Robert Feigelson and Prof. James Harris, for accepting the responsibility on a short notice,

    and for making my defense a memorable experience in a good way. I would also like to

    thank Prof. Feigelson for helpful discussions about lithium niobate and vapor-transport

    equilibration.

    I would not be writing acknowledgements today if it were not for the support of my

    reading committee and two of my student colleagues – Arun Sridharan and Carsten Lan-

    grock. Carsten helped me a lot by proof-reading chapters of my dissertation and providing

    helpful suggestions. I would like to also thank him for his perseverance throughout our

    collaborations in the past, which helped us achieve remarkable results, as well as for being

    a great friend. Arun has been a friend of mine since the beginning of my Ph.D. study. He

    has helped me many times. We have had a significant amount of joint work and achieved

    great results together. In addition, I would like to thank him for the superior technical and

    logistical support related to the writing and submission of my dissertation over the past

    several weeks.

    I would like to thank Roger Route for getting me up to speed on the VTE process, as

    well as for many thoughtful discussions about materials, processes, and furnace building.

    In addition, I would like to thank Roger for quality advice about life.

    I have been very fortunate to start my Ph.D. studies in the Fejer group under the direct

    guidance of Krishnan Parameswaran. He spent a long time teaching me everything that

    he knew about photolithography, periodic poling, waveguide fabrication, waveguide testing,

    and testing equipment. In addition, he gave me a lot of helpful advice about living in the

    Stanford area.

    I would like to thank Andrew Schober for always showing interest in discussions about

    physics and optics, and sharing his knowledge. I am also thankful to him for boosting my

    self-confidence and optimism during hard times. I would like to thank Genady Imeshev for

    providing me with a good background on short-pulse QPM theory, for our collaboration on

    MgO-doped LiNbO3, and for helpful discussions about career paths after Stanford.

    I am thankful to Jonathan Kurz for taking the initiative to pursue a more repeatable

    fabrication process, and for the collaborative work during my early years at Stanford, when

    we helped each other solve many technical problems. I would like to thank David Hum for

    many helpful discussions about near-stoichiometric materials, periodic poling, and many

    aspects of engineering in general. In addition, I am thankful to Xiuping Xie for developing

    the code for two-dimensional modeling simulations, as well as for many discussions of the

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  • fabrication process. I would like to acknowledge the significant contributions of Joseph

    Schaar to the automation of the short-pulse poling process. I am thankful to Paulina Kuo

    for taking time to satisfy my curiosity about orientation-patterned GaAs, and to Jie Huang

    for sharing his device fabrication and testing experience.

    Besides Arun, other members of the Byer group with whom I have had significant col-

    laboration were Karel Urbanek and Supriyo Sinha. Karel has contributed very significantly

    in the OPA experiments in Chapter 3 which would not