液晶闪耀光栅波前相位测量方法

电控液晶光栅在卫星激光通信、激光雷达的光束指向应用中具有体积小、光束灵活可控的优势。而获取电控液晶光栅对光波前的相位调制分布则是评价液晶光栅性能的关键。提出液晶光栅调制波前相位的共轭移相干涉测量技术,通过实验对比验证了实测远场分布与近场相位计算远场分布的一致性,由此可实现由近场相位测量的光束指向控制新方法。     

Infrared laser addressing of media for recording and displaying of high-resolution graphic information

Projection display systems which use a scanned infra-red laser beam to thermally record graphic information on different media may offer a useful alternative to CRT and other display systems. Three different types of thermal-recording projection display systems are reviewed. Laser micromachining of thin bismuth film has proved to be a very simple and efficient way to obtain instant high-quality images which are also permanent. Variable amplitude light pulses produced by an intracavity modulated laser beam were used to write these images. With an average laser power of 20 mW, 8×10 mm²facsimile type continuous-tone images, with a resolution of 1300×2000 resolvable elements, were recorded in 4 s. Thermal writing on liquid crystals offers a unique and simple way to record and display high-quality high-resolution graphic images with the capabilities of fast total or local erase. A CW Nd:YA1G laser was used to write graphic and alphanumeric-type information on cholesteric and smectic-type liquid-crystal light valves. High quality black and white images with a resolution of 2000×2000 picture elements were recorded within 30×30 mm²of liquid-crystal cell frames. With 4 mW of laser power, images were recorded at a rate of 10⁴resolvable elements per second. A contrast ratio of 7:1 was obtained with the cholesteric-type liquid-crystal light valve. The stored image was electrically erased in about 0.1 s. In smectic-type light valves, the contrast ratio was better than 10:1 and local erase was achieved by the application of an electric field while the laser beam locally heated the erased area.     

Electronically tunable liquid-crystal-etalon filter forhigh-density WDM systems

A 1.5-μm high-density wavelength-division-multiplexed (HD-WDM) system experiment is demonstrated using a novel Fabry-Perot etalon filter with a liquid-crystal electrical tuning element. The filter has a narrow passband (0.4 nm) and is continuously tunable over a wavelength range of >60 nm with a drive voltage from 1 to 5 V. Bit-error-rate measurements with an 8-channel (1539-1556 nm), 622 Mb/s WDM system confirms that the crosstalk penalty is negligible for an optical channel spacing of 2 nm     

A 2×2 fiber optic switch using chiral liquid crystals

A nonchemical 2×2 optical switch for fiber optic applications is described. Using a chiral-nematic liquid-crystal cell and switchable nematic liquid-crystal waveplates, the authors measured -26-dB crosstalk between unselected fibers, a fiber-to-fiber insertion losses of 1.4 dB, and switching times under 40 ms with operation at 1318 nm using 62.5/125-μm multimode fiber. The device features simple construction, low power requirements, and an optical bandwidth suitable for LED or laser sources, and it works equally well with multimode or single-mode fiber     

Electrically tunable narrowband optical filter

A narrowband optical filter of the Sole type is made from a twisted stack of birefringent plates between polarisers. If the plates are replaced by homogeneously aligned liquid-crystal cells whose retardation is controllable, the transmitted wavelength of the filter can be varied over the visible spectrum. The characteristics of a rudimentary device of this type agree with predictions.     

Analysis of a liquid crystal Fabry-Perot etalon filter: a novel model

The authors propose a novel analysis method to investigate the characteristics of an electrically tunable liquid-crystal Fabry-Perot interferometer (LC-FPI). Based on the solution of deformation analysis of the liquid crystal in an electric field and the assumption of small refractive index variation in the Fabry-Perot cavity, the voltage-dependent equivalent refractive index of the cavity has been derived. Tuning behaviors of the LC-FPI filter were simulated by means of the dependence. The calculated result and the experimental measured data agree well with each other.     

Polarisation independent tunable liquid-crystal Fabry-Perotinterferometer filter module with double-pass configuration

A novel tunable liquid-crystal Fabry-Perot interferometer (LC-FPI) filter module with a Faraday rotator and double-pass configuration has been fabricated. The filter module has a 3 dB bandwidth of ~0.4 nm, a 20 dB bandwidth of 1.5 nm, and a polarisation dependent loss (PDL) <0.8 dB over a tuning range of 56 nm. More than 49 dB isolation from the output port to the input port has been achieved     

Multicolor LCD for automotive applications

Segment-type, twisted nematic liquid-crystal panels with finely striped, two-color filters within the panel are discussed. The panel has a color filter-on-indium tin oxide structure. Two types of printed filter (an offset-printed (OP) filter and a screen-printed (SP) filter) were subjected to heat treatment and evaluated. It was found that an SP filter of about 0.3 μm has less effect on the operating voltage and availability for multiplexed drive than an OP filter of about 1 μm in thickness with the same color density. The test results for panel reliability for automotive use are given. The panels can digitally display a vehicle's speed, fuel level and engine revolutions in bargraph format with good legibility using three colors     

基于Mach-Zehnder滤波的可调谐光纤激光器

() ()基金项目: 。摘要:为了实现高稳定性的可调谐激光输出,提出并设计了一种基于Mach-Zehnder(M-Z)滤波结构,结合Fabry-Perot(F-P)滤波器的可调谐掺铒光纤激光器,并对激光器的原理及实现方案进行理论分析和实验验证。所设计激光器系统的泵浦源工作波长为976 nm;长度5 m的掺铒光纤作为增益介质;采用全光纤M-Z结构进行滤波,并结合F-P滤波器实现单波长激光可调谐输出。实验中,通过调节F-P滤波器,在泵浦功率为60 mW时,实现了1547～1568 nm范围内单波长激光的稳定可调谐输出,波长调谐间隔小于1.7 nm,每个输出波长的边模抑制比均大于55 dB,线宽均小于0.1 nm。     

液晶光栅相控阵偏转波前测量方法研究

为了测试相控阵激光雷达的关键器件液晶光栅相控阵的偏转光束波前,以监控和评价雷达扫描光束的质量,采用带有光束变向功能的径向剪切干涉测量方法,进行了理论分析和实验验证,取得了口径为10mm×10mm的偏转波前测试系统与商用WYKO干涉仪的比对测试数据。两种仪器对同一块平面样板测出的波前之差的峰谷值小于λ/20,均方根值小于λ/200,还取得了实测液晶光栅相控阵不同偏转光束的波前数据。结果表明,该方法可以对液晶光栅相控阵的偏转波前进行高精度测试。     

Tunable liquid-crystal Fabry-Perot interferometer filter forwavelength-division multiplexing communication systems

We explain how to obtain the bandwidth and tunable range required for wavelength-division multiplexing communication systems and how to design tunable liquid-crystal Fabry-Perot interferometer filters. The main factors determining the performance are liquid-crystal loss, mirror loss, surface roughness, and parallelism, as well as mirror reflectivity and cavity gap. Experimental results closely agree with the designed performance. Temperature dependence, response time, acceptable input power, and reliability are investigated. Pigtailed polarization-independent filter modules with a Peltier controller are made and are shown to have low polarization dependence (<0.3 dB), low driving voltage (<15 V), and compact size, as well as a narrow bandwidth (0.3 nm), high finesse of 189, and large tunable range (50 nm)     

Tunable light source using a liquid-crystal Fabry-Perot interferometer

A tunable light source with a liquid-crystal Fabry-Perot interferometer (LC-FPI) tuning element that emits a laser beam with a tuning range of 41 nm has been constructed. Incorporating a multiple quantum well (MQW) laser diode with a phase control (PC) section enables the selection of almost all external modes. Stable single-mode emission is obtained for the region, except where the slope of the lasing wavelength versus applied voltage to the liquid crystal is quite large.<>     

Varistor-controlled liquid-crystal displays

A new method of constructing multiplexed reflective liquid-crystal displays is described. A passive nonlinear control layer is formed by applying appropriate conductor and insulator layers to a slab of ZnO varistor material which forms the rear wall of the liquid-crystal cell, thereby, placing a varistor in series with each display element. The sharp nonlinearity of the varistor I-V characteristics allows matrix displays with a very large number of lines (∼ 1000), while achieving the same optical performance as a nonmultiplexed display. Resolution limits and drive requirements are also discussed.     

Formation of synthetic images on a laser-beam-adressed smectic liquid-crystal display

The reproduction and the storage of synthetic images on a smectic liquid-crystal display is described. The `write? is obtained by an infrared laser beam. A spatial modulation of the cell transmission is obtained with a variable alternating voltage applied to the cell. A high-resolution display with high contrast and continuous gray scale was realised.     

Star-coupler-based optical cross-connect switch experiments withtunable receivers

An optical cross-connect switch using the star-coupler-based frequency-division-multiplex technique are discussed. Two specific tunable receivers have been implanted. The first is a heterodyne receiver with a tunable laser as the local oscillator (LO) and the second is a tunable filter followed by a direct-detection receiver. In the heterodyne receiver, the tunable LO was a monolithic three-section multiple-quantum-well distributed Bragg laser capable of a 1000-GHz tuning range. Receiver sensitivity was measured to be -38 dBm at 1 Gb/s (BER=10^-10). The power margin in the system substantiated feasibility for a 400×400 switch. In the tunable-filter receiver, the tunable filter is a tunable two-stage optical fiber Fabry-Perot filter design consisting of a narrowband filter followed by a wideband filter. The tuning of the filters is computer controlled, and the combined filter has a tuning range of 15000 GHz with a finesse of ≈5170. Therefore, it is capable of covering over 1000 channels of 2.9 GHz each     

超窄带滤光技术研究进展

对自适应光学中激光导星的基本原理及系统中所需的超窄带滤光技术作了简单的介绍.重点介绍了一些有望应用于激光导星系统上的滤光技术,如:原子共振光学滤光器、双折射滤光器、法拉第反常色散滤光器、法布里-珀罗滤光器等.针对以上滤光技术各自的特点,阐明了它们的基本原理,给出了部分主要参数,并且对各滤光技术的发展现状和不足作了简要阐述.     

Multiwavelength tunable liquid-crystal etalon filter

Using a liquid-crystal Fabry-Perot etalon with multielement electrodes, the authors demonstrated a tunable filter capable of simultaneously filtering many wavelengths in the 1.2-1.6 mu m wavelength region. The configuration is demonstrated by tuning two wavelengths independently by applying different voltages to two electrodes. Each of the passbands could be tuned over the free spectral range (65 nm) with an applied voltage of 1 to 3 V.<>     

Smectic liquid-crystal flat display with light-pen and readout functions

A thermally addressed smectic liquid-crystal flat display is described, which is addressed by a laser-diode light pen as well as by the usual heating electrodes. Information can be written manually on the display panel using a laser diode or information generated by external equipment can be displayed by resistive heating in a line-at-a-time sequence. The manually written information can also be read out electrically by detecting the capacitance of each pixel. To detect the pixel's capacitances arranged in X-Y matrix form, we describe a scheme to prevent crosstalk and to avoid the influence of the electrodes' resistance. By using these techniques, we constructed an experimental display, It has a 30 × 40 mm²display area and a resolution of 4 lines/mm.