Passive integrated optical polarisation mode-splitter in lithium niobate employing a resonant metal-loaded structure

A passive polarisation mode-splitter has been demonstrated in Z-cut Y-propagating LiNbO/sub 3/ which achieves polarisation crosstalk better than -30 dB and excess loss of less than 1 dB in both polarisation states at lambda =1.52 mu m. The technique employed simplifies the design of polarisation mode splitters for arbitrary operating wavelengths and LiNbO/sub 3/ wafer orientations.<>     

铌酸锂光波导制作工艺进展

文章综述了几种常用的铌酸锂波导的制作工艺,包括表面外扩散、金属内扩散、离子交换和质子交换,并分析、比较和总结了在不同工艺制作的条件下对铌酸锂光波导的性能造成的不同影响。目前,获得高质量光波导的主要途径是Ti扩散和质子交换。同时,文章对逐渐建立起的铌酸锂波导光学特性和结构特性之间的理论关系也进行了介绍。     

Acoustoelectric amplification of surface waves in structure of cadmium-selenide film on lithium niobate

Electronic gain of 38 dB/mm at 170 MHz has been observed in a dispersive surface-wave delay line consisting of a cadmium-selenide film on a lithium-niobate substrate.     

Rotating-waveplate optical-frequency shifting in lithium niobate

A rotating-waveplate optical frequency shifter using lithium niobate (LiNbO3) has been constructed and fully evaluated. The experimental modulator frequency shifts the incoming 6328-Å light by 110 MHz, requires 15 W of drive power, and has an inherent 12-MHz bandwidth. The output beam has high spectral purity with very little power in unwanted sidebands and closely matches the TEM00mode of the input beam. An analysis of the effects of electrical and optical maladjustments on modulator performance shows only moderate requirements on optical and electrical alignment. Heating due to the absorbed drive power slightly degrades the modulator in agreement with a temperature analysis of the modulator. An increase in insertion loss due to diffraction of the light by acoustic waves in the LiNbO3crystal was observed.     

Optimum second-harmonic generation in lithium niobate

An experimental study of noncritically phase-matched (theta_{m} = 90deg) second-harmonic generation is described, in which the theoretical predictions of Boyd and Kleinman with regard to strength of focusing and effect of mismatch are closely verified. Radiation at 1.084 μ from a He-Ne laser was employed to generate light at 542 nm in LiNbO3.     

Novel ion-assisted antireflection coatings for lithium niobate devices

A technique for producing single-layer antireflection coatings on lithium niobate is described, based on ion-assisted deposition of magnesium fluoride and silicon dioxide. Measurements show a lowest device reflectivity of -42 dB, at 1.55 mu m, using a silicon dioxide coating.<>     

Test structures for characterization of electrooptic waveguidemodulators in lithium niobate

A method of determining the critical parameters of waveguide modulators, using a set of test devices fabricated on a single chip, is presented. The five parameters are the depth and lateral Ti diffusion lengths, the peak index change in the waveguides, the electrooptic coefficient, and the buffer layer dielectric constant. The finite element method is used for calculation of optical modes in waveguides with graded refractive index profiles. The integral equation method is used for calculation of the static electric field due to electrodes in a three-layer structure of air, buffer layer, and LiNbO₃. The test set includes a planar waveguide, Mach-Zehnder modulators, symmetrically perturbed directional couplers, and widened X modulators. Several test chips have been fabricated using different fabrication conditions. The parameter values determined using this method are compared with those reported by other authors     

Voltage-induced optical waveguide modulator in lithium niobate

A type of optical modulator first proposed by D.J. Channin (1971) in which an optical waveguide is induced in an electrooptic substrate by applying voltage between two parallel coplanar electrodes is reinvestigated. It is found that such devices will work for voltages much smaller than those used by Channin. The devices are fabricated with much smaller gaps between the electrodes and have an optical buffer layer to isolate the optical field from the electrodes. The theory of operation is developed and the device is modeled mathematically. The theory predicts that the optical field distributions of the modes of these devices become more highly confined with increasing voltage     

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.     

Proton-exchanged optical waveguides in Y-cut lithium niobate

The fabrication of proton exchanged monomode optical waveguides on Y-cut lithium niobate is reported. Molten benzoic acid is used, but damage of the crystal surface is avoided.     

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     

Wet-etched ridge waveguides in y-cut lithium niobate

By the technique of nickel indiffusion proton exchange (NIPE) and the technique of buffered proton exchange (PE) melt, wet-etched ridge waveguides in y-cut LiNbO₃ are fabricated for the first time. The fabricated ridge waveguides have smooth surfaces and are good enough for low-loss waveguides. Moreover, a ridge waveguide Mach-Zehnder modulator in y-cut LiNbO₃ is fabricated. The measured half-wave voltage is about 30% lower than that of a conventional modulator. The wet-etched ridge waveguides in y-cut and z-cut substrates are also characterized for comparison     

Photolithography by a tunable electro-optical lithium niobate phase array

Photolithography experiments are performed by means of an optical phase mask with electrooptically tunable phase step. The phase mask consists of a 2-dimensional hexagonal lattice of inverted ferroelectric domains fabricated on a z-cut lithium niobate substrate. The electro-optically tunable phase step, between inverted domain, is obtained by the application of an external electric field along the z axis of the crystal via transparent electrodes. The collimated beam of an argon laser passes through the phase mask and the near field intensity patterns, at different planes of the Talbot length and for different values of the applied voltage, are used for photolithographic experiments. Preliminary results are shown and further applications are discussed.     

A lithium niobate light modulator for fiber optical communications

An electrooptic intensity modulator using lithium niobate has been developed for applications in binary fiber optical digital communications at the wavelength of 1.06 µm. We have shown that many shortcomings generally associated with electro-optic modulators can be surmounted. The modulator was driven by a compact transistor amplifier, temperature dependence of the static birefringence was minimized, and the optical bias was made adjustable by a dc voltage superposed on the signal. The modulator has been operated at 70-Mb/s pulse rate and 100-percent modulation, its extinction ratio is better than 40 to 1 and the optical insertion loss is about 1 dB.     

铌酸锂晶体结构对电场传感器灵敏度影响分析

铌酸锂晶体光学电场传感器为全介质结构,具有宽带宽、对被测电场干扰小的优点,但其灵敏度较低。因此,分析了晶体几何尺寸对传感器灵敏度的影响机理,得出通过增加沿外加电场方向的晶体尺寸同时减少晶体横截面上沿外加电场垂直方向的晶体尺寸来提高传感器的灵敏度。使用COMSOL仿真分析了铌酸锂晶体不同厚度、宽度、长度对晶体内部电场强度的影响,得出晶体厚度从15 mm减小到3 mm和宽度从3 mm增加到22 mm时,晶体内部电场强度分别提高约5.1倍和12.3倍;晶体长度从15 mm变化到55 mm时,晶体内部的电场强度变化仅约为5%。设计并研制出晶体尺寸分别为3 mm×3 mm×42.2 mm (x×y×z),3 mm×6 mm×42.2 mm (x×y×z),6 mm×6 mm×42.2 mm(x×y×z)的三只铌酸锂晶体电场传感器,并搭建工频电场测试平台,测试得出三只电场传感器的灵敏度分别为0.243 mV/(kV·m^-1)、0.758 mV/(kV·m^-1)、0.150 mV/(kV·m^-1)。当晶体厚度和长度一定且晶体宽度从3 ...     

铌酸锂量子器件研究进展

量子信息科技的进步, 在很大程度上依赖于传统材料的成熟与发展。近年来, 铌酸锂成为量子器件的重要基础材料, 在量子科技领域具有巨大的应用潜力。梳理了基于铌酸锂材料制备的量子光源、量子中继器件、单光子探测器件等各类铌酸锂量子器件的技术进展, 总结了它们的优缺点并展望了其未来主要的发展趋势, 对基于铌酸锂材料制备的量子器件在量子信息科技的实用化具有很好的指导作用。     

Calculated wavelength sensitivity of lithium niobate switches

A method is presented for calculating the wavelength sensitivity for electrooptic guided-wave stitches that work by mode interference, including directional-coupler and balanced-bridge switches. The method relies on a coupled-mode theory, using measured wavelength sensitivity of the coupling. Crosstalk is taken as the bandwidth-limiting property and is calculated by expanding in bandwidth. It is found that the wavelength sensitivity depends on the coupler gap, the amount of coupling, and the electrode configuration. Numerical examples show that switches with proper design can exhibit better than 25 dB of crosstalk with a 100-μm bandwidth. Modulators have a still wider bandwidth     

Use of lithium niobate detector for measuring X-ray intensity in mammographic range

A detector system that can measure X-ray intensity in the mammographic range of 22 to 36 kVp (equivalent photon energies of the beam between 11 and 15 keV) is presented. It consists of a lithium niobate detector and a high-sensitivity current-to-voltage converter.