Guided-wave acousto-optic diffraction in Zn:LiNbO3

The acousto-optic control of light in Zn-diffused LiNbO₃ optical waveguides is demonstrated. The guided optical mode diffraction by the surface acoustic waves is consistent with the Klein and Cook model for the intermediate diffraction regime. The SAW induced refractive index change is 1.5times10^-4 at acoustic power 130 mW. The Zn-diffused lithium niobate waveguides appear to be good candidates for integrated light-control devices based on acousto-optic interaction     

Electric-field-assisted proton-exchanged optical waveguides in lithium niobate

We describe the fabrication of a broad stripe optical wave-guide in z-cut lithium niobate by electric-field-assisted thermal proton exchange in a benzoic acid melt. Electric fields of 5 × 104V/m to 105V/m were laterally applied by means of in-contact gold thin-film electrodes 1 mm apart, producing an asymmetric depth across the width of the stripe. Similar vertical fields, applied across the thickness of the wafer, increased the stripe depth in the region of applied field. Refractive index profiles are given for both cases.     

钽酸锂晶体宽带滤波器

本文简要介绍钽酸锂晶体及器件的一些特性,对用该材料制作的21.4MHz宽带滤波器的设计、制作和测试结果作了较详细的介绍,滤波器的带宽达225kHz,矩形系数(BW_(?0dB)/BW_(3dB)为2.66,带外衰减在50dB以上。该材料在做宽带滤波器和压控振荡器方面具有优越性。     

Intermodulation in X-cut lithium tantalate resonators

The analysis of intermodulation in X-cut lithium tantalate resonators is performed and applied to the evaluation of the fourth-order nonlinear elastic coefficient. A comparison with an AT-cut quartz resonator indicates that lithium tantalate nonlinearities are much lower.     

Wet etching of proton-exchanged lithium niobate-a novel processingtechnique

A novel and simple method to etch lithium niobate is reported. It was found that proton exchanged areas on the c⁺-face of the crystal can be etched away using a mixture of HF:HNO₃ while the unexchanged regions are left untouched. The method can be used as a tool for studies of the proton exchange process, as well as to form three-dimensional structures     

Radiation effects on a lithium tantalate optical waveguide structure

The effects of X- and gamma radiation on an optical waveguide, fabricated in lithium tantalate, are described and discussed. The measurements indicate that quite severe radiation environments would be necessary to produce significant problems with LiTaO/sub 3/ devices. However, the level of the radiation effects may depend, like those in semiconductor devices and fibre optics, on the details of the composition of the material and the constructional methods employed. Because there appear to be effects due to a radiation-induced, internal, electric field, there will be a dependence on the cut of the crystal used.<>     

Multistrip coupler performance for surface-skimming bulk waves on lithium tantalate

Measurements are presented of the performance of the multi-strip coupler for X-direction propagating acoustic waves on 36° rotated Y-cut lithium tantalate. The predominant launched and coupled mode is the surface-skimming bulk wave. The coupler shows excellent discrimination against other modes. The maximum power transfer ratio is limited to approximately 4:1 and the strengths of transmitted symmetric and antisymmetric modes are found to be unequal.     

近化学计量比LiTaO_3反转畴运动特性研究

通过添加助熔剂,生长了掺Mg近化学计量比LiTaO3(SLT)晶体,晶体的居里温度为684±1℃。对厚度1.8 mm的晶片进行外加单脉冲电场室温极化,得到了完全反转的畴结构。利用化学腐蚀的方法,观察极化过程中反转畴成核、运动及合并的过程。结果表明,室温极化时,反转畴的运动是非匀速的,实现完全反转至多需要50 s,极化初始阶段反转畴的平均横向扩展速率为0.012 mm/s。     

Characterization of in-situ terahertz detection by optical interaction in a periodically poled stoichiometric lithium tantalate nonlinear crystal

Terahertz waves are generated using a femtosecond laser pulse in a periodically poled stoichiometric lithium tantalate crystal and simultaneously detected via a non-collinear optical parametric interaction inside the same crystal. Real time up-conversion signal between the generated THz and an optic probe pulses is measured depending on the beam overlapped conditions using a general silicon-photodiode for the THz detection. The non-collinear geometry is to facilitate manipulated property of the position-dependent bandwidth at narrow and broad bandwidths of 45 GHz and 3.3 THz, respectively at the one crystal. Furthermore, an aperture effect at the detection part is characterized as the function of size and position owing to the spatial distribution of the frequency conversion signal and it is applied in optimization of the in-situ detection scheme.     

Thin-film acousto-optic interaction in LiNbO3

100% Bragg diffraction of guided optical waves by surface acoustic waves in metal-diffused layers in LiNbO3 substrates has been observed. The predicted efficiency, which compares favourably with experimental measurement, is shown to arise mainly from the electro-optic contribution of the electric field associated with the yz acoustic surface waves instead of the clasto-optic contribution due to the strain or from the surface ripple components.     

基于周期性极化钽酸锂晶体的连续激光倍频技术研究

针对连续激光倍频的需求,对比分析了周期性极化钽酸锂晶体和铌酸锂晶体的非线性光学特性,从技术研究角度确定了周期性极化钽酸锂晶体更适合用于连续激光倍频。依据非线性转换效率和晶体结构安装尺寸,确定了基频激光压缩及倍频激光准直的参数,从保证工程应用的角度选择了81μm极化周期的钽酸锂晶体,设计并实现了双光路倍频,获得了超过5W的540nm连续倍频激光输出。     

多级声光衍射相互作用长度的实验研究

实验研究了多级声光衍射条件下的最佳声光相互作用长度与声波和光波之间的定量关系。测量结果表明最佳声光相互作用长度与声频紧密相关而几乎与入射光波长及强度无关。实验结果发现当声频低时,相互作用长度短,声频在9 MHz左右,相互作用长度约为8 mm,当声频降低为6 MHz左右时,相互作用长度约为4 mm。设计了以纯水为介质的声光Q开关器件,在超声频率9 MHz,声功率3.4 W的条件下实现了约98%的总衍射效率。     

Periodic domain inversion and generation of blue light in lithium tantalate waveguides

Generation of blue light from small solid-state light sources is a technological challenge with applications in many areas, among others optical data storage. The authors report frequency doubling using third-order quasi-phase matching in periodically domain-inverted lithium tantalate waveguides. Periodic proton exchange followed by heat treatment caused periodic domain inversion and waveguide formation in a single step. Infrared radiation from a dye laser was coupled through the waveguides and second-harmonic generation corresponding to third-order quasi-phase-matching was observed.<>     

Guided-wave acoustooptic interaction with phase modulation in a ZnOthin-film transducer on an Si-based integrated Mach-Zehnderinterferometer

This paper presents the design and the realization of a novel integrated Mach-Zehnder interferometer (MZI) with heterodyne scheme. Well-controlled machining as well as ZnO thin-film transducer integration on the same Si substrate permits to transform an optically passive device to an active device with sinusoidal phase modulation. Theoretical and experimental results are presented, demonstrating that an efficient sensor can be designed and fabricated     

Temperature dependence of permittivity and loss tangent of lithium tantalate at microwave frequencies

Lithium tantalate (LiTaO/sub 3/) exhibits excellent electro-optical, piezoelectric, and pyroelectric properties and a very low thermal expansion. In this paper, we report measurements of loss tangent and the real part of the relative permittivity /spl epsiv//sub r/spl perp// measured in c-axis LiTaO/sub 3/ crystals in the temperature range from 14 K to 295 K at a frequency of 11.4 and 10 GHz. Microwave properties of LiTaO/sub 3/ were determined by measurements of the resonance frequency and the unloaded Q/sub o/ factor of a TE/sub 011/ mode cylindrical cavity containing the sample under test and accounting for uncalibrated cables and adaptors inside the cryocooler. The permittivity of LiTaO/sub 3/ was found to increase from 38.9 to 41.1 and the loss tangent to change from 1.1/spl times/10/sup -4/ to 6.5/spl times/10/sup -4/ over the full temperature range. Due to its low loss and relatively high permittivity, LiTaO/sub 3/ is suitable for microwave applications.     

Integrated optic a.d. convertor based on bulk acousto-optic interaction

A method is described using integrated optics to perform high data rate a.d. conversion. The approach uses the bulk acousto-optic interaction in optical waveguides, with a segmented transducer array to deflect light in response to an analogue signal applied to phase-shifting elements at the transducer.     

Measurement of acousto-optic interaction in Germanium in the far infrared

Acousto-optic interaction in a Germanium Bragg cell, which was operated as acoustic resonator, was measured at 119 μm relative to 10.6 μm. The figure of merit of the material was found to be approximately 20% higher in the far infrared. The performance of various acousto-optic materials in the far infrared is briefly discussed.     

Polarisation-independent low-power integrated acousto-optic tunable filter/switch using APE/Ti polarisation splitters on lithium niobate

A new polarisation-diversity integrated acousto-optic tunable filter/switch, incorporating passive Ti-indiffused waveguides and annealed proton-exchanged adiabatic X-junction polarisation splitters on XY lithium niobate, is demonstrated. The device requires only 11.2 dBm/channel of driving RF power. Switching characteristics at four 4 nm-spaced wavelengths are reported.<>     

Guided-wave laser based on erbium-doped silica planar lightwave circuit

The Er-doped silica guided-wave laser operating around 1.6 mu m was realised using a low-scattering-loss planar lightwave circuit with an Er-doped silica core which was fabricated by flame hydrolysis deposition and reactive ion etching techniques on an Si substrate. CW lasing was achieved successfully with an incident threshold power of 49 mW for pumping at 0.98 mu m.<>     

Control of the instrument function of acousto-optic cells with a noncollinear interaction geometry

A possibility of controlling the instrument function of acousto-optic devices with a noncollinear interaction geometry by using split piezotransducers is shown. A device’s instrument function can be corrected by modifying the distribution of the ultrasonic amplitude in an acousto-optic cell along the direction of propagation of optic beams. Optimum distributions of acoustic-deformation amplitudes are found, thus enabling reduction of the sidelobes of the device’s instrument function. The level of sidelobes is shown to depend both on the distribution of voltage amplitudes over sections of an acoustic transducer and on the width of the gap between these sections. An acousto-optic cell is developed and tested experimentally. It contains a piezotransducer consisting of eight sections that are power-supplied through a capacitance divider.