Effects of growth interruption on the properties of InGaN/GaN MQWs grown by MOCVD

These applications normally employ an InGaN/GaN mul- tiple quantum wells (MQWs) as the active layer. But the growth of high quality MQWs is very difficult. Firstly, the growth condition is strict due to the high volatility of InN and the low thermal pyrol…     

Low-insertion-loss, tunable wavelength multiplexer on lithium niobate

Integrated-optical dual-channel multi/demultiplexers with a wavelength periodic transmission characteristic are fabricated on X-cut LiNbO3. The devices are designed for the wavelength range ? = 1300-1600nm. Channel separations as low as 30nm, far-end crosstalk attenuation up to 40dB and an insertion loss of fibre-coupled devices below 3dB are achieved. The transmission characteristic can be tuned electro-optically at a rate of 2.5 nm/V.     

An electrically controlled tunable photonic crystal filter based on thin-film lithium niobate

In this paper, we present an electrically controlled tunable narrowband filter based on a thin-film lithium niobate two-dimensional(2D) photonic crystal. The filter incorporates a photonic crystal microcavity structure within the straight waveguide, enabling electronic tuning of the transmitted wavelength through added electrode structures. The optimized microcavity filter design achieves a balance between high transmission rate and quality factor, with a transmission center wavelength of 1 551....     

Low-voltage tunable TE/TM converter on ion-sliced lithium niobate thin film

Lift-off of a prefabricated thin-film lithium niobate device using ion slicing has been demonstrated. The device is a low-voltage electro-optically tunable TE/TM mode converter, which is fabricated on a sliced 10 /spl mu/m-thick film. A new electrode configuration allows this thin-film device low-voltage tuning of the mode conversion wavelength at 0.26 nm/V. The high tuning per volt is attributed to an improved overlap integral in the thin-film form of the device.     

基于Talbot效应的电光调制位相阵列器

利用周期极化反转的铌酸锂晶体设计与制备圆形周期单元六角结构排列的可调位相阵列器,对位相阵列器的Talbot效应光衍射成像进行理论和实验研究,得到了不同位相差和不同分数Talbot距离条件下阵列器近场衍射的理论仿真和实验观测图像,实验结果与理论研究相符.计算衍射场取样区域内平均强度,获得取样区内强度随位相差和Talbot距离变化的曲线,揭示了位相差和衍射位置对阵列器衍射强度分布的影响.     

高性能硅和铌酸锂异质集成薄膜电光调制器 （特邀）

硅基光子集成平台因其高集成度、CMOS工艺兼容性等特点在光通信领域受到了广泛的关注,而电光调制器作为光通信系统中最为重要的器件之一,承担着将电信号加载至光信号上的关键作用,为打破硅基调制器的性能限制,可利用硅和铌酸锂的大面积键合技术以及铌酸锂低损耗波导刻蚀技术实现高性能硅和铌酸锂异质集成薄膜电光调制器,目前该类调制器的性能可达半波电压3 V,3 dB电光带宽超过70 GHz,插入损耗小于1.8 dB, 消光比大于40 dB。文中对比了硅和铌酸锂异质集成调制器的研究现状并介绍了该异质集成薄膜调制器的结构设计与工艺实现方法。     

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.<>     

Growth of thin-film lithium niobate by molecular beam epitaxy

Lithium niobate has been grown in single-crystal thin-film form by molecular beam epitaxy. Single-crystal films were grown on bulk-crystal LiNbO3 and on sapphire (?-Al2O3). The layers have been excited as optical waveguides, and the refractive indices and optical propagation loss were measured.     

Formation of a bidomain structure in lithium niobate wafers for beta-voltaic alternators

The possibility of increasing the efficiency of a beta-voltaic generator due to using a single-crystal bimorph element made of lithium niobate as a piezoelectric converter. The known beta voltaic alternators consist of a piezoelectric cantilever and a source of β-electrons. The cantilever represents a resilient member made, for example, of silicon, on which a piezoelectric element made of PZT piezoceramics is mounted. It is proposed to replace the silicon cantilever structure with a piezoelectric element by a uniform cantilever that represents a thin wafer made of a bidomain single-crystal lithium niobate. Due to this, the efficiency of the mechanical oscillation conversion into electrical power, the system Q-factor, and the stability of the operating parameters simultaneously increase; and the operation temperature range also significantly increases (by several hundred degrees). The solution of the main problem—the formation of a bidomain structure in a thin wafer of lithium niobate—is considered in detail. A method for the high-temperature annealing of samples in a nonuniform electric field is proposed. It is demonstrated that one can predict the domain structure based on the developed model. Samples are obtained having the occurrence depth of the interdomain boundary ranging from 120 to 150 μm. At the same time, it is shown that the sharpness of the boundary depends on the potential difference between the striated electrodes of the technological cell and the external electrode. The method is efficient for manufacturing a bidomain structure in a wafer up to 300 μm thick.     

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.<>     

Operation of a lithium niobate electrooptic Q switch at 1.06 µ

The performance of an electroopticQswitch using lithium niobate as the electrooptic material is described and compared with that of a conventional device using potassium di-deuterium phosphate.     

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.     

Mach-Zehnder modulators with lithium niobate ridge waveguidesfabricated by proton-exchange wet etch and nickel indiffusion

Mach-Zehnder ridge waveguide modulators on c⁺-LiNbO₃ by proton-exchange wet etch and nickel indiffusion are fabricated for the first time. Modulators operating at 0.633 μm and 1.31 μm are both produced, and the half-wave voltages are measured to be 4 V and 22.5 V, respectively, for an electrode length of 6 mm. The extinction ratios are 14 dB and 13.2 db, respectively, and can be improved by forming the ridge structure only at the electrode interaction region instead. These results make the wet-etched LiNbO₃ optical devices promising to take over the dry-etched ones in the near future     

应用于相控阵天线系统的C波段6位移相器设计

A C-band 6-bit digital phase shifter is presented.The phase shifter is based on the synthetic design of a high-pass/low-pass network and the all-pass network.The series scatter restrain method is also discussed.The phase shifter is fabricated in 0.25μm GaAs PHEMT technology and developed for C-band phased arrays,and the relative phase shift varies from 0 to 360 in step of 5.625°.The phase shifter,with a chip size of 4×1.95 mm~2,has achieved an insertion loss better than 6.4 dB,RMS phase error of less than 1.73°,and an input and output VSWR less than 1.6 at all conditions.     

Linear tunable phase shifter using a left-handed transmission line

We demonstrate a compact, linear, and low loss variation hybrid phase shifter using a left-handed (LH) transmission line. For frequencies from 4.3 to 5.6 GHz, this phase shifter gives a nearly linear phase variation with voltage, with a maximum deviation of /spl plusmn/7.5/spl deg/. Within this frequency range, the maximum insertion loss is 3.6 dB, and the minimum insertion loss is 1.8 dB over a continuously adjustable phase range of more than 125/spl deg/, while minimum return loss is only 10.2 dB. Furthermore, this phase shifter requires only one control line, and it consumes almost no power.     

Analytical investigation to achieve the highest phase difference between two orthogonal components of light in lithium niobate based electro-optic system

Electro-optic Pockels cell are important opto-electronic devices for conduction of optical switching, optical modulation, where an electrical biasing signal acts on a polarized light passing through the system. Since last few decades lots of works are reported in this area. Again, it is observed that a good switching or modulation becomes realized if the depth of modulation is increased by increasing more phase difference between two orthogonal polarized components of light passing through the material against a biasing signal. Here in this paper the authors propose a new scheme, where multi-passing technique is used to create a high degree of phase difference between those two orthogonal polarized components of light against the biasing signal. The multi-passing of light through the material enables more and more optical path length for the light. So, more and more phase difference between the components of light beams, one passing outside the material and other passing through the material multiple times is created. This method ultimately generates a high degree of depth of modulation in optical switching.     

Blue light generated by frequency doubling of laser diode light ina lithium niobate channel waveguide

Blue light was generated in a LiNbO₃ channel waveguide by frequency doubling radiation from a laser diode in a guided to guided wave interaction, utilizing first-order quasi-phase-matching in a periodically domain inverted structure. A fabrication method that does not depend on the use of titanium was used. A periodic pattern of silicon oxide on the positive c-face of LiNbO₃ was used in combination with a heat treatment to achieve a periodic outdiffusion and domain reversal in the surface layer. A channel guide was subsequently formed by proton exchange     

铌酸锂晶片的键合减薄及热释电性能研究

铌酸锂(LN)作为一种热释电材料,可以被用于制作光电探测器敏感单元的敏感层,但通常LN晶片厚度为0.5 mm,远大于光电敏感单元厚度的要求,所以需要用键合减薄及抛光技术对LN晶片进行加工处理。本研究所用键合减薄技术主要包含:RZJ-304光刻胶键合、铣磨、抛光、剥离液剥离和丙酮清洗RZJ-304胶。利用该技术加工得到了面积为10 mm×10 mm,厚度为50μm,表面比较光滑,表面粗糙度为1.63 nm的LN晶片。LN晶片的热释电信号峰峰值在减薄抛光后为176 mV,是未经处理时的4倍,满足了热释电探测器敏感层的要求。     

Analysis of a FBG sensing system with transverse uniform press by using genetic algorithm

An analytical method in a quasi-static fiber grating sensing system under transverse uniform press is proposed based on genetic algorithm The effect of population size, generations, crossover ratio and mutation ratio to genetic algorithm, and the optimization parameters of genetic algorithm were given. The relevant experimental system is constructed. The simulation and experiments show that the analytical method proposed can be applied to analyze the reflective spectra of the quasistatic FBG sensing system at transverse uniform press, the strain measurement with high-precision of 0.91% can be realized