铌酸锂集成光学基片折射率的测量

在2″精度的测角仪上,用棱镜耦合法,以0.6μm的准直He-Ne激光束(直径1mm)实现了铌酸锂(LN)晶片折射率的高精度测量。实验中使用了差分技术与液晶旋光器,结果表明折射率测量精度达到1×10~(-4),系统重复性误差小于5×10~(-5)。     

Transducer and multistrip-coupler performance for leaky surface waves on lithium niobate

Measurements are reported of the properties of leaky surface waves propagating on 41° and 64° rotated cuts of LiNbO3 both on the free surface and under metal. Transducer and multistrip-coupler performance are consistent with piezo electric-coupling constants of 18° and 12%, respectively. Insertion-loss and spurious-signal-level results show that the interdigital transducer with few finger pairs is better matched to a metallised propagation path than to a free surface path for leaky waves.     

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.<>     

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.     

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.     

A polarization-independent 1 × 16 guided-wave optical switch integrated on lithium niobate

We report the fabrication and testing of several models of a complex integrated Ti : LiNbO3switch array, a one-input-to-sixteen-output switch that is polarization independent for use with standard single-mode fibers. The switch array has 15 directional couplers arranged in a binary tree with four ranks. The device is fitted with connectorized single-mode fiber pigtails and housed in a package that permits convenient transport and use. The best measured losses (fiber-waveguide-fiber) are 3.0 dB for the TE polarization and 3.6 dB for the TM. Permanent attachment of the pigtails adds 0.65-dB loss. Crosstalk suppression averages 10 dB below the transmitted signal for the brightest unwanted path.     

Spatial optical solitons in nonlinearly coupled lithium niobate waveguides

We numerically investigate a novel type of quadratic spatial solitons in the system of surface and buried planar waveguides obtained via direct- and reverse-proton exchange in z-cut lithium niobate, respectively, and coupled by the second-order susceptibility. Through frequency doubling, transverse-electric and transverse-magnetic modes lock into a 1+1D solitary wave encompassing orthogonal field components at the two harmonic wavelengths. The phase matching scheme leads to a wavelength-comb filter with adjustable linewidths.     

Quasi-polarization-independent Mach-Zehnder coherencemodulator/demodulator integrated in Z-propagating lithium niobate

We present in this paper recent results obtained in the area of coherence multiplexing and integrated optics. It is well known that coherence multiplexing requires two-wave interferometric modulators featuring large optical delays. We report a system formed by a pair of Mach-Zehnder interferometers integrated in a Z-propagating lithium niobate crystal, suitable for quasi-polarization-independent transmissions of signals by coherence modulation. The behavior and the working conditions are presented for the TE and TM polarization states of the light     

Features of propagation of surface acoustic waves in two-dimensional phononic crystals on the surface of a lithium niobate crystal

Two-dimensional phononic crystals are fabricated on the surface of a lithium niobate crystal. A numerical method is developed for calculating the frequency dependences of the transmission and reflection coefficients of a surface acoustic wave for a rectangular region with two-dimensional periodic structure on the surface of an elastic body. Measurements of the frequency dependences of the reflection and transmission coefficients are performed for propagation in the part of the lithium niobate crystal surface on which two-dimensional phononic crystals were fabricated. Forbidden zones are found in the transmission spectra of the waves transmitted through phononic crystals. It is shown that, if the width of the incident wave beam is less than the width of the region with the two-dimensional periodic structure (the two-dimensional phononic crystal), then a resonant increase in the transmission coefficient arises near the center of the rejection band.     

Analysis of titanium diffused planar optical waveguides in lithium niobate

Characteristics of titanium indiffused waveguides in lithium niobate have been investigated. The effects of diffusion time, temperature, and ambient atmosphere on mode structure, surface refractive index, and profile, waveguide depth, surface morphology, and composition are described. Similarities and discrepancies between these and any previously published results are discussed and mechanisms for new features proposed. The necessity for fabrication in an oxygen atmosphere at elevated temperatures is demonstrated, and directions for further investigation indicated.     

掺铁铌酸锂晶体中光损伤的暗衰减效应

为了研究铌酸锂晶体中的光损伤,着重对掺铁铌酸锂晶体中光损伤的暗衰减效应进行研究,发现在薄样品中光损伤的暗衰减时间远大于在厚样品中的暗衰减时间,利用红外吸收光谱和喇曼光谱对这个现象的潜在机理进行了初步分析,综合几个实验结果发现,晶体厚度对光损伤的暗衰减是一个重要的影响因素.     

Low-sidelobe weighted-coupled integrated acoustooptic tunablefilter using focused surface acoustic waves

A single-stage low-sidelobe weighted-coupled integrated acoustooptic tunable filter (IAOTF) operating at the optical wavelength of 1.31 μm has been realized on a Y-cut X-propagating LiNbO₃ substrate for the first time. The weighted-coupling, which enabled the achievement of low-sidelobe levels, was facilitated by focused surface acoustic waves generated by a curved interdigital transducer. First sidelobe levels as low as -17.6 dB have been obtained. Optical bandwidth of 4 nm and tuning range of 170 nm for an interaction length of 6 mm were also accomplished     

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.<>     

Generation of Rayleigh and bulk waves by interdigital transducers on y-cut z-propagating lithium niobate

Theoretical predictions are made of the generation of Rayleigh bulk-shear and bulk-longitudinal waves by interdigital transducers on y-cut z-propagating lithium niobate. Frequency response and bulk-wave radiation patterns are compared with experimental evidence, and the proportions of input power converted to the three modes are shown as functions of both frequency and number of finger pairs.     

PMOS integrated circuit fabrication using BF3 plasma immersion ion implantation

The feasibility of plasma immersion ion implantation (PHI) for multi-implant integrated circuit fabrication is demonstrated. Patterned Si wafers were immersed in a BF₃ plasma forp-type doping steps. Boron implants of up to 3 × 10¹⁵ atoms/cm² were achieved by applying microsecond negative voltage (-2 to -30 kV) pulses to the wafers at a frequency of 100 Hz to 1 kHz. After implantation the wafers were annealed using rapid thermal annealing (RTA) at 1060° C for 20 sec to activate the dopants and to recrystallize the implant damaged Si. For the PMOS process sequence both the Si source-drain and polycrystalline Si (poly-Si) gate doping steps were performed using PIII. The functionality of several types of devices, including diodes, capacitors, and transistors, were electrically measured to evaluate the compatibility of PIII with MOS process integration.     

Pulsed optical parametric generation, amplification, and oscillation in monolithic periodically poled lithium niobate crystals

We conducted a series of passively Q-switched Nd:YAG laser pumped optical parametric generation, amplification, and oscillation experiments in monolithic periodically poled lithium niobate (PPLN) crystals. Double-pass optical parametric generation with an effective gain length of 10 cm in a PPLN crystal was performed in comparison with single-pass operation in the same crystal. By seeding a PPLN optical parametric amplifier with a distributed feedback (DFB) diode laser, we produced 200-ps transform-limited laser pulses at 1549.6 nm and observed parametric gain competition at different pump levels. For optical parametric oscillations, we first demonstrated 22% power efficiency from a 2.4-cm intrinsic-cavity PPLN optical parametric oscillator pumped by a 4.2-ns, 10-kW passively Q-switched Nd:YAG laser. Preliminary studies on DFB optical parametric oscillators in PPLN are mentioned. The temporal and spectral properties of these optical parametric generators, amplifiers, and oscillators are characterized and discussed.     

Graphical illustration of the phase-matching condition in an optical-frequency convertor using lithium niobate

A graphical illustration is given of the phase-matching condition in optical parametric oscillators and frequency multipliers using lithium niobate. It clearly shows the importance of index matching in such a process. The authors explain why, at a given frequency, the working temperature varies from one lithium niobate monocrystal to another. One can thus obtain the relation giving the frequency of a parametric oscillator versus the temperature.