Recovery of second-order optical nonlinearity in annealedproton-exchanged LiNbOx

The second-order nonlinear coefficients measured in proton-exchanged LiNbO₃ as a function of annealing time are discussed. Measurements of reflected second-harmonic power indicate that the second-order nonlinear coefficient d₃₃ is reduced to 60% of the bulk value as a result of proton exchange in pure benzoic acid. It is also shown that annealing restores the d-coefficients to almost the original value of the virgin crystal. For example, recovery to ~90% of the bulk value was obtained for a sample with a 0.3-μm-bulk proton-exchanged layer, annealed for 10 h at 350°C     

缓冲质子源LiNbO3波导折射率计算及实验

为实现铌酸锂退火质子交换(APE)波导折射率分布的准确计算,选择含苯甲酸锂的苯甲酸缓冲液作为质子交换质子源,高温退火制作了波导样本.针对该工艺过程建立退火质子交换波导模型,包括非线性扩散模块和光学数值仿真模块,分别计算APE波导折射率及其模式有效折射率.以测得的样本波导模式有效折射率和计算的有效折射率差的均方根构建评价函数(FOM),结合遗传算法提取该工艺条件下质子扩散参数,实现了不同交换深度和退火时间波导折射率分布及其光学特性的一体化计算.实验表明:FOM小于0.001,计算折射率分布同IWKB方法测得结果吻合较好,最大偏差约0.002.     

Characterization of annealed proton exchanged LiNbO3waveguides for nonlinear frequency conversion

A thorough and detailed characterization of annealed proton-exchanged (APE) waveguides in Z-cut LiNbO₃ is described. The mode index measurements in planar waveguides as a function of wavelength and annealing time are reported, including useful analytical relations for the refractive index change, its dispersion, and the depth profile as a function of annealing parameters. Analytical expressions for the mode propagation characteristics are presented and experimentally verified with reasonable accuracy. It is shown that the planar waveguide characterization results can be used to model the channel waveguide characteristics accurately. The model provides closed-form expressions for the mode index and the mode field profile, and the theoretical results are in excellent agreement with the measured data. The technique is used to accurately predict the phase mismatch between the fundamental and second harmonic modes in frequency-doubling experiments using APE channel waveguides. An optimum waveguide geometry for which the phase mismatch is relatively insensitive to the waveguide nonuniformity was predicted and verified experimentally     

Crystalline and optical quality of proton exchanged waveguides

In this paper we demonstrate the possibility of obtaining high-quality proton-exchanged (PE) lithium niobate guides by performing the exchange at high temperatures (300°C) in benzoic acid diluted with lithium benzoate. Rutherford backscattering studies suggest that the higher exchange temperatures avoid the production of niobium dislocations, and, IR absorption measurements suggest that the use of lithium benzoate diluted melts prevents the creation of interstitial hydrogen.     

Acoustooptic interaction at 520 MHz in proton-exchangedY-lithium niobate waveguides

Experimental results are reported on acoustooptic interaction at 520 MHz in proton-exchange waveguides in Y-lithium niobate. The acoustooptic diffraction efficiency for an electrical input of 300 mW is 39% in proton-exchanged devices as compared to 22% in titanium-indiffused ones. The dynamic range observed in proton-exchanged and Ti-indiffused acoustooptic devices is 22 and 25 dB, respectively     

Proton-exchanged optical waveguides in Z-cut LiNbO3 using phosphoric acid

Proton-exchanged Z-cut LiNbO₃ planar waveguides formed using phosphoric acid were characterized optically. The refractive index profile and the diffusion parameters were studied systematically. These waveguides have propagation losses of less than 1 dB/cm and exhibit properties that are different from those obtained using benzoic acid. The index profile is not a simple step function and can be modeled accurately by a polynomial expression. A maximum surface index increase of 0.145 was measured at a 0.633-μm wavelength. The diffusion constant D₀ and the activation energy Q for the proton-exchange process using this acid were found to be 6.43×10⁸ μm²/h and 82.91 kJ/mol, respectively. The annealing properties of these waveguides were also established, and the effects of annealing on surface index change and waveguide depth increase were found to follow a power-law relationship     

Electrooptic coefficient measurements in LiTaO3 andLiNbO3 waveguides

The magnitudes of linear electrooptic coefficients r₁₃ and r₃₃ in Zn:LiTaO₃ repoled channel waveguides are reported. The measurements were made at 0.633-μm wavelength using a Fabry-Perot interferometer. The waveguides were produced by diffusion from the vapor phase at a temperature above the Curie temperature. For full recovery of the Pockels effect, an electric field of 200 V/cm is needed during repoling. The measured values of r₁₃ and r₃₃ at 32-MHz modulation frequency are 7.2 and 30.3 pm/V, respectively. The difference between unclamped and clamped coefficients is comparable to that from bulk crystals. Measurements were also made on Ti:LiNbO₃ waveguides that did not require repoling, and good agreement with bulk crystal values was obtained     

LiNbO3质子交换波导性能不稳定性的研究

对在不同条件下ｘ切ＬｉＮｂＯ３与纯苯甲酸进行质子交换所得波导的模析射率随时间变化的观测结果表明，质子交换波导中存在着性能不稳定性，这种不稳定性与波导的制作条件、工作（或存放）环境温度等有关，对造成这种不稳定现象的原因进行了讨论，并提出了克服不稳定性的一些措施，红外吸收与二次离子质谱测试结果与分析论点吻合。     

利用缓冲质子源制作LiNbO3光波导:光学特性及稳定性研究

利用缓冲质子源(苯甲酸中掺入一定量的苯甲酸锂)在Z切LiNbO3基底上制作了质子交换平面光波导，得到了不同掺杂摩尔分数(0．5％，1．0％和1．5％)的缓冲质子源质子交换波导的有效扩散系数及折射率分布。随着质子源中苯甲酸锂的摩尔含量逐渐增加，质子交换的有效扩散系数呈指数衰减，同时波导表面折射率增量线性递减。研究了有效折射率的稳定性特征，并与用纯苯甲酸制作的光波导进行了比较，发现利用缓冲质子源制作的LiNbO3光波导的稳定性明显优于纯苯甲酸制作的光波导。     

Singlemode channel waveguides and electrooptic modulators in KTiOPO4 for the short visible wavelength region

Single-mode channel waveguides at short visible wavelengths have been fabricated in KTiOPO₄ by Rb&rlhar2;K ion exchange in mixed melts of RbNO₃-KNO₃-Ba(NO₃)₂ . The technological parameters have been chosen by means of theoretical WKB- and “effective index” calculations concerning the singlemode region of the effective channel waveguide index N₀₀ at the given wavelength. Great diffusion anisotropy and small dispersion of the surface refractive index change guarantee singlemode operation of the very same channel waveguide from the blue up to the red. Typical attenuation of about 2.0 dB/cm for TM- and 1.5 dB/cm for TE polarization was obtained at λ=0.5145 μm. Light-induced refractive index changes (photorefractive effect) have been determined as a function of time, wavelength, guided optical mode intensity and temperature. The light-induced effects in Rb&rlhar2;K ion-exchanged channel waveguides in KTiOPO₄ are about two orders of magnitude smaller than those in annealed proton-exchanged channel waveguides in LiNbO₃. Electrooptic phase modulators have been successfully investigated concerning dynamic V_π measurements, the electric-optical field overlap and dc-drift phenomena. Design, fabrication and experimental results of integrated-optic Mach-Zehnder-interferometer modulators for short visible wavelengths are presented     

Optical waveguide fabrication in neodymium-doped lithium niobate

Reports the realisation of high-quality, proton-exchanged optical waveguide structures in neodymium-doped lithium niobate. Measurements indicate that the presence of the neodymium does not alter the proton exchange rate, and the presence of the protons does not affect the emission and absorption spectra of the bulk material significantly. Such waveguides will permit the realisation of highly efficient semiconductor laser pumped amplifiers and laser structures integrated with electro-optic and/or acousto-optic elements     

Elastic constants and thermal fracture of AgGaSe2 andd-LAP

The elastic constants and thermoelastic coefficients of silver gallium selenide and deuterated l-arginine phosphate (d-LAP) are reported. Their fracture strength as measured by indentation tests is also reported. These data are used to calculate their thermal fracture resistance, a parameter which is important in high-average-power laser systems. Their thermal fracture resistance is then compared to that of other nonlinear crystals. To the extent that the damage threshold increases with fracture temperature, the data on AgGaSe₂ and d-LAP are favorable indicators of a higher damage threshold. In particular, the data suggest that d-LAP should compare favorably with other solution-grown materials such as lithium iodate and KDP. Preliminary data on the damage threshold of d-LAP appear to confirm that it is indeed more damage resistant than comparably prepared samples of these other solution-grown materials     

Decrease of gate oxide dielectric constant in tungsten polycidegate processes

The gate oxide thickness for tungsten (W) polycide gate processes is studied, with tungsten silicide (WSi_x) deposited either by chemical vapor deposition (CVD) or sputtering. For WSi_x deposited by CVD, it is found that the effective thickness of gate oxide as determined by CV measurement increases in all cases if the annealing temperature is 900°C or higher. However, high-resolution transmission electron microscopy (TEM) measurement indicates that the physical thickness does not change after a 900°C anneal. In this case, the dielectric constant of the gate oxide decreases by 7%. As the annealing temperature increases to 1000°C, CV and TEM measurements give the same thickness and the decrease of the dielectric constant disappears. In contrast, for WSi_x film deposited by sputtering, annealing at 900°C has no effect on the gate oxide thickness as measured by CV and TEM     

Technological implementation of Bragg grating reflectors in Ti:LiNbO/sub 3/ waveguides by proton exchange

The authors propose and demonstrate a simple and novel method for fabrication of efficient Bragg grating reflectors at telecommunication wavelengths in titanium-indiffused lithium niobate single-mode channel waveguides. This technique is based on the patterned proton-exchanged process. The validity of the method is verified by the good agreement of the spectral responses and the Bragg phase-matching condition. Reflectivity as high as 94% at 1546 nm was measured with 4-mm distributed parameter waveguides in z-cut lithium niobate.     

A comprehensive study on p+ polysilicon-gate MOSFET'sinstability with fluorine incorporation

It is reported that fluorine can jeopardize p⁺-gate devices under moderate annealing temperatures. MOSFETs with BF₂ or boron-implanted polysilicon gates were processed identically except at gate implantation. Evidence of boron penetration through 12.5-nm oxide and a large quantity of negative charge penetration (10 ¹² cm^-2) by fluorine even at moderate annealing conditions is reported. The degree of degradation is aggravated as fluorine dose increases. A detailed examination of the I-V characteristics of PMOSFET with fluorine incorporated p⁺-gate revealed that the long gate-length device had abnormal abrupt turn-on I_d-V_g characteristics, while the submicrometer-gate-length devices appeared to be normal. The abnormal turn-on I_d-V_g characteristics associated with long-gate-length p⁺-gate devices vanished when the device was subjected to X-ray irradiation and/or to a high-voltage DC stressing at the source/drain. The C-V characteristics of MOS structures of various gate dopants, processing ambients, doping concentrations, and annealing conditions were studied. Based on all experimental results, the degradation model of p⁺-gate devices is presented. The incorporation of fluorine in the p⁺ gate enhances boron penetration through the thin gate oxide into the silicon substrate and creates negative-charge interface states. The addition of H/OH species into F-rich gate oxide will further aggravate the extent of F-enhanced boron penetration by annealing out the negative-charge interface states     

Modal S-matrix design of metal finned waveguide componentsand its application to transformers and filters

Optimized all-metal E-plane finned waveguide components are designed with the rigorous method of modal field expansion into the ridged eigenmodes, which includes both the higher order mode interaction between the step discontinuities and the finite thickness of the fins. The design, which combines the advantage of constant fin thickness with that of the optimum matching potential of different waveguide inner cross-section dimensions and fin heights, achieves very broadband transformers and evanescent-mode filters with improved performance. Computer optimized data demonstrate the efficiency of the method by typical design examples: compact transformers for WR112, WR42, WR15, and WR12 input waveguides to E-plane finned waveguides, corrugated lowpass filters designed for a cutoff frequency in the waveguide Ku and U bands, and an evanescent-mode bandpass filter with unequal fin heights. The theory is verified by available measurements     

LiNbO3质子交换光波导退火特性的研究

本文报道ＬｉＮｂＯ３质子交换波导的退火特性。用ＩＷＫＢ法计算了热退火前后的折射率分布，并采用广义高斯函数对计算出的折射率分布曲线进行了拟合，反映出该函数能准确而灵活地描述退火质子交换光波导的折射率分布及其变化。在实验中发现，高温下较长时间退火，导模消失。     

质子交换LiNbO3波导表面裂纹的研究

为了研究x切铌酸锂波导表面裂纹的产生机理及对波导性能的影响,采用对比实验、波导表面观察、XRD晶相分析、红外吸收谱分析等方法,比较了退火后波导的微观结构、表面情况、波导中H+存在形式和浓度变化特征.结果表明,质子交换铌酸锂波导表面裂纹是波导层应力顺晶体主解理面释放而产生的,具有4个特点:裂纹是交换过程造成的,裂纹间相互平行,裂纹程度与交换时间成正比,退火工艺对裂纹程度有所改善;裂纹是波导层应力大小的宏观体现;退火工艺可以调整波导层中H+的存在形式及其浓度,调整波导层晶相和应力大小,从而改善波导性能.可见纯质子交换波导层中多相并存,各晶相晶格常数差异较大造成应力,导致裂纹产生.提出α相波导的晶格变形小,引起的应力也小,可以减少裂纹产生,有助于提高波导质量.     

Electro-optic effect in proton exchanged LiNbO3 andLiTaO3 waveguides

Electro-optic properties of proton-exchanged (PE) waveguide layers in LiTaO₃ and LiNbO₃ are studied and related to their optical characteristics. The proton-exchange process induces a degradation of the electro-optic activity in both types of waveguides, PE LiNbO₃ and PE LiTaO₃. The measured electro-optic effect is close to the detection sensitivity even when the exchange regime is performed at low temperatures for short periods of time. The PE samples have been annealed (APE waveguides) and the changes of their r₃₃ electro-optic coefficient has been followed at successively higher temperatures and periods of time. Subjected to annealing at temperatures between 265-420°C, the LiTaO₃ layers show a partially recovered r₃₃ coefficient, the recovering being different for quick and slow cooling of the samples. In thin APE LiNbO₃ waveguiding layers a restoration of r₃₃ up to 75% of the bulk value is observed due to the annealing at temperatures between 200-340°C     

Novel hydrogen annealing for forming SiO2 film by rapidthermal processing

Hydrogen annealing at 700-1100°C for 0-300 s has been combined with SiO₂ formation by rapid thermal processing (RTP). The SiO₂ films formed with the above processes were evaluated by C-V and I-V measurements and by time-dependent dielectric breakdown (TDDB) tests. These films provide longer time to breakdown andless positive charge generation than SiO₂ films formed without H₂ annealing. In particular, the SiO₂ formation-H₂ annealing SiO ₂ formation process is quite effective in improving the dielectric strength of the thin RTP-SiO₂ film