Broadly Tunable, Mode-Hop-Tuned cw Optical Parametric Oscillator Based on Periodically Poled Lithium Niobate

We describe a broadly tunable, cw optical parametric oscillator (OPO) based on periodically poled lithium niobate. The OPO can be tuned over a broad region in the mid IR (2900-3100 cm(-1)) covering the important C-H stretch region while a high spectral resolution (<0.1 cm(-1)) is maintained. The OPO is the light source for a field-portable photoacoustic spectrometer for gas-phase monitoring of volatile organic compounds.     

An Optical Thermometer Exploiting Periodically Poled Lithium Niobate for Monitoring the Pantographs of High-Speed Trains

Optical thermometers have been widely investigated. Here, the temperature behavior of second harmonic generation (SHG) in periodically poled lithium niobate (PPLN) substrates is analyzed; indeed, the QPM tuning in PPLN devices and the obtained SHG efficiency depend on the crystal thermal expansion and dispersion, particularly in the case of guided propagation. Therefore, such devices are suitable to realize optical thermometers for demanding applications. This investigation originated with the request of a thermometer to be installed on the pantographs of high-speed trains. Therefore, it must be sturdy and reliable, but it has even to work in an EMD environment. The temperature behavior of the SHG was theoretically modeled and experimentally validated at 1550 nm, in both bulk propagation and APE channel waveguides. In the first case, by using a 10-mW source, which was obtained from a laser diode and a fiber amplifier, an accuracy of 0.3 degC was found. The pump power was about three orders of magnitude smaller in guided propagation. In view of testing on the trains, our investigation resulted in the design of a device without mechanical contacts with the input and output fibers. Since it works in free propagation, there are no serious alignment and packaging problems. The performances, which are expected to be the same of our tests, widely satisfy all the requirements for working effectively in a strongly hostile and EMD environment and for giving accurate measurements on a wide range of temperatures     

Second Harmonic Generation in Ion Implanted Lithium Niobate Planar Waveguides

Abstract

We report the first demonstration of second harmonic generation (SHG) in ion implanted lithium niobate optical waveguides. For both ordinary and extraordinary index profiles a computer program was developed to simulate the positions of the modes within the optical well. With the help of this program the theoretical possibility of SHG using mode matching conditions within the guide was then studied as a function of the guide depth and temperature, and from these predictions, practical guides were constructed. Initially, SHG Cerenkov radiation was observed with leaky single implanted guides. Mode matched SHG from m = 0 to m = 2 was subsequently achieved by means of a multiple energy implant which was able to confine both fundamental and harmonic waves. Allowing for coupling and transmission losses, the corrected conversion efficiency is 0–018% W^?1 which compares favourably to a theoretical prediction for this guide of 0–020% W^?1. In this case a wide temperature tuning range was obtained.     

近化学计量比铌酸锂晶体的研究进展

介绍了近化学计量比铌酸锂晶体的主要生长方法及其特点,总结了近化学计量比铌酸锂晶体的主要性能,通过与同成分铌酸锂晶体的比较,指出了近化学计量比铌酸锂晶体的主要应用优势,明确了该类晶体今后的研究重点.     

Efficient Nd:YAG Laser Frequency Doubling with Periodically Poled KTP

Periodically poled flux-grown KTiOPO(4) was used for efficient extracavity 1064-nm Nd:YAG laser frequency doubling. A conversion efficiency exceeding 65% was obtained in Q-switched operation, and 1.34 W of average frequency-doubled power was generated with 2.2 W of mode-locked laser output. The conversion efficiency is approximately two times higher for periodically poled KTP than for conventional type II phase-matched KTP. The measurements indicate that periodically poled KTP is less susceptible to optical damage than type II KTP.     

Optical Properties of Copper-Doped Lithium Niobate Crystals

We have studied the optical properties of copper-doped lithium niobate crystals using semiconductor light-emitting diodes and lasers emitting in the visible and ultraviolet spectral regions as excitation sources. The results demonstrate that, at an excitation frequency approaching the frequency of electronic absorption in copper ions, there is discrete resonance Raman scattering in the form of a frequency comb. The observed Raman satellites of discrete light scattering are due to polar longitudinal A₁ optical modes of the lithium niobate single crystal. Under excitation by a light-emitting diode with a wavelength of 520 nm, we observe a sharp increase in discrete light scattering intensity in comparison with the photoluminescence excited by shorter wavelength excitation sources.     

铌酸钾锂晶体的生长技术

铌酸钾锂被认为是目前综合性能指数最高的非线性光学晶体,在半导体二极管蓝激光倍频方面有广阔的应用前景。本文综述了用于蓝光倍频的铌酸钾锂晶体生长研究进展,比较了不同生长方法的优缺点,报道了我们在该晶体坩埚下降法生长研究方面的最新成果。     

铌酸钾锂晶体的生长研究

首次使用坩埚下降法生长了蓝光掊频晶体铌酸钾锂K₃Li_2-xNb_5＋xO_15＋2_x（0＜x＜0．5）,探讨了该晶体的最佳生长条件,包括组份选择、原料处理、炉温控制、温场设计等,成功地生长出直径10mm、长度25mm的透明KLN晶体．     

Structural Defects and Photoluminescence in Zinc-Doped Lithium Niobate Crystals

Inorganic Materials - We demonstrate that increasing the zinc concentration in Zn-doped lithium niobate crystals to their first concentration threshold (~3.0 mol % ZnO) leads to a decrease in...     

Photoelectric Fields and Band Gap in Doped Lithium Niobate Crystals

Photoinduced light scattering and optical spectroscopy have been used to study the photorefractive effect and determine the band gap in nominally undoped congruent and stoichiometric lithium niobate crystals, as well as in a series of congruent LiNbO₃ crystals doped with Mg, Zn, B, Gd, Y, and Er cations and LiNbO₃ single crystals codoped with Mg:Gd, Mg:Fe, Mg:Y, and Mg:Ta.     

铌酸钾锂晶体的生长与性能

使用坩埚下降法成功生长了尺寸为φ10mm50mm、四方钨青铜结构、透明铌酸钾锂晶体,讨论了引起晶体开裂的主要原因,研究了该晶体的光透过性能和介电性能,室温下该晶体的介电常数ε33=127,ε11=376,居里温度为380°     

Improved Long-Term DC Drift in OH-Reduced Lithium Niobate Optical Intensity Modulators

Long-term dc drift of lithium niobate optical intensity modulators is successfully reduced by exclusion of OH(-)ions from the lithium niobate substrate. In this regard, the titanium-indiffused waveguide is prepared on a commercial OH-free substrate under a dry gas atmosphere.The dc drift measured for these hermetically sealed modulators indicates a possibility for continuous operation over 20 years at 50°C.     

LiNbO3晶体点缺陷形成能的经验途径计算

基于通过经验参数化方法确定的铌酸锂晶体内离子间互作用势参数，计算了该晶体中点缺陷的形成能，由此判断锂Frenkel对是化学计量比铌酸锂晶体中的本征缺陷，锂空位模型为描述一致熔化组分铌酸锂晶体中点缺陷的主导类型。     

Defect Complexes and Optical Properties of Doubly Doped Lithium Niobate Crystals

The effect of defect complexes related to the presence of protons on the optical properties of LiNbO₃:Y(0.24):Mg(0.63) and LiNbO₃:Gd(0.25):Mg(0.75) (wt %) crystals has been studied using IR absorption spectroscopy, photoinduced light scattering, and laser conoscopy. The results indicate that the absorption bands at frequencies of 3483 and 3486 cm^–1 correspond to vibrations of a V _Li ^- –OH^? defect complex. To a Mg _Li ⁺ - Mg _Nb ^3- –OH^?defect complex in the LiNbO₃:Gd(0.25):Mg(0.75) crystal correspond bands at frequencies of 3526 and 3535 cm^–1. In the LiNbO₃:Y(0.24):Mg(0.63) crystal, we have detected an anomalous opening of the speckle structure of the photoinduced light scattering indicatrix.     

铌酸锂晶片抛光的主要物理及化学因素分析

光学器件的飞速发展对基体材料铌酸锂不断提出更高要求。为获得满足器件使用要求的超光滑、高平整晶片表面,采用化学机械抛光方法对铌酸锂进行加工。研究过程中,对负载压力、抛光布表面结构、抛光液流量、p H值等工艺参数进行了优化调整,最终制备出平整度较高、表面粗糙度较小的铌酸锂抛光片。实验结果表明,选取Suba 600抛光布、液流量3 m L/s、p H值为10、底盘转速60 r/min、压力为0.16 MPa作为抛光工艺参数可获得高平整、超光滑的铌酸锂抛光片。平面度测量仪与原子力显微镜测试结果表明,所制备LN抛光片的总厚度变化(TTV)为6.398μm,粗糙度(Ra)为0.196 nm。     

利用新设计磨具对铌酸锂晶片的减薄及减薄后的测试

铌酸锂晶体具有较强的热释电效应,由铌酸锂制作的红外传感器敏感头受到科研人员的广泛关注。将晶片与硅衬底在200°C和压力100N的条件下键合,利用自行设计的磨具将铌酸锂减薄到40微米,磨料由水与刚玉以1∶1的比例制成。本文讨论了铌酸锂键合的过程,减薄的过程及厚度测试,通过拉曼光谱分析残余应力,通过原子力显微镜测试样品表面粗糙度。研究结果表明,通过自行设计的磨具研磨的晶片厚度最大差值7微米,较为均匀;研磨后晶片表面粗糙度为118纳米,较为粗糙;键合后存在一定的残余应力。制作好的铌酸锂晶片符合制作红外传感器敏感头的要求。