Fiber lasers: A future technology for lasers in space

The constraints of operation in space have largely precluded the use of conventional solid-state laser systems for applications including remote sensing, communication relays, and active laser radars. A new technology, fiber lasers, may offer all of the needed features at an affordable price. An appealing aspect of the fiber laser is that it does not need a rigid optical bench. Only the output end of the fiber need be held in rigid reference to the optical tracking system. Design, fabrication, and testing of the laser resonator is generally the most expensive and longest lead part of the effort for conventional solid-state lasers. Advances in fiber optic technology and devices mean that the "fiber laser" need not be a simple device but may be a complex system employing sophisticated technology, such as wavelength selective Bragg reflectors and nonlinear optical frequency shifters. Three companies have obtained single-mode outputs of 35 - 40 watts single mode at 1.03 - 1.1 mu.     

谐振式光纤陀螺用激光器最优工作区间探究

激光器为谐振式光纤陀螺(R-FOG)的关键器件,根据R-FOG对激光器的要求,提出了一种R-FOG用激光器最佳工作点及最优工作区间的确立方法,制定了激光器性能自动化测试方案,得到激光器光功率、中心波长与电流、温度的变化关系。由此推导出2个激光器电流与温度的最佳工作点,并利用拍频检测原理确立2个激光器电流与温度的最优工作区域。激光器最优工作区域的掌握,为其应用于R-FOG提供了详实的参数指标。     

光电缆的分布式温度传感网络

提出增加一根光纤光栅与光电缆绕制在一起，用于监测电缆中的实时温度。采朋有限元分析方法，建立了光电缆温度场模型。使用可调谐脉冲激光作为系统光源，在一条光纤上刻制多个相同中心波长的布拉格光栅，即采用全同光栅作为系统的温度传感器，当光电缆线路中温度发生异常时，反射回来的光栅中心波长发生偏移，通过检测反射光中心波长发生的偏移量可以确定光栅温度变化的大小。不同位置的光栅返回光信号所需的时间不同，通过检测和计算光返回的不同时间，可以计算出发生温度变化的光栅位置。实验结果表明，光栅的温度敏感性可以达到11．4pm／℃，光栅的测量温度与实际温度的误差在3％范围内。     

Space power by ground-based laser illumination

Reducing energy storage requirements of space power systems by illuminating the photovoltaic arrays with a remotely located laser system is addressed. It is proposed that large lasers be located on cloud-free sites at one or more ground locations and that large lenses or mirrors with adaptive optical correction be used to reduce the beam spread due to diffraction or atmospheric turbulence. During the eclipse periods or lunar night, the lasers illuminate the solar arrays to a level sufficient to provide operating power. Two applications are discussed: illumination of geosynchronous orbit satellites and illumination of a moonbase power system. Issues for photovoltaic receivers for such a system are discussed     

Aeronautical use of semiconductor lasers for short optical pulses

In this paper, we investigate the feasible schemes to generate periodic optical pulses of width between several picoseconds (ps) and tens ps. Gain-switched semiconductor laser diodes are shown to be more suitable for avionics applications than mode-locked laser diodes. In the experiment, we use a low-cost Fabry-Perot laser diode to generate short optical pulse streams. A simple optical injection-locking scheme is then used to reduce the timing jitter and frequency chirp in such laser diodes, which in turn can improve the transmission performance of the generated optical pulses. It is expected that the use of gain-switched semiconductor lasers can meet the requirement of high-speed airborne communication networks or ground supporting systems at airports. Moreover, we discuss the possibility of using the pulsed semiconductor lasers to generate millimetre-wave (mm-wave) signals for future applications to airborne high-resolution, mm-wave radars.     

基于矩阵光学的多程激光放大器准直系统模型分析

多程放大技术成为高功率固体激光装置的主要发展方向,对激光光路进行调试和维护,建立光路准直的数学模型和调整方案很有必要,采用矩阵光学方法,建立了多程放大自动准直系统数学模型,得出了远、近场光斑偏移量与调整量的解析表达式,验证了该自动准直系统光路原理及调整方法的可行性.     

Intersatellite laser crosslinks

Intersatellite laser crosslinks (ISL) provide a method of communication that has significantly increased the data throughput that can be managed over typical RF communication systems, and has significant growth potential. Optical communications offer very wide bandwidths which can be effectively utilized with wavelength division multiplexing techniques. The data rate growth potential is well beyond the few gigabit per second range of RF technology. The use of lasers in transmitting optical data takes advantage of its small wavelength and low beam divergence to send highly directed signals over significant distances with controlled losses in intensity. The high directivity of the laser aids in resistance to jamming communications between satellites, or between satellites and ground stations. Various intersatellite laser optical crosslink system are discussed including the Massachusetts Institute of Technology's Laser Intersatellite Transmission Experiment (LITE), the McDonnell Douglas Electronic Systems Company Laser Crosslink System, and The Ball Aerospace Optical Intersatellite Link,in order to display the various subsystem and their implementations. Link budget calculations are performed on the most commonly used modulation formats to determine system parameters necessary to close the crosslink. Background is provided on primal system architectures and methods of laser communication, as well as presently implemented systems. The authors provide some insights on where ISL systems have opportunity to increase their data throughput and reduce acquisition time     

Surface emitting lasers for avionics applications

Vertical cavity surface emitting lasers offer many features that are suitable for applications in optical interconnect, optical data bus, optical backplane, and optical signal processing. The authors describe basic device structure and fabrication techniques of GaAs-based vertical cavity surface emitting lasers and discuss key laser performance characteristics such as emission wavelength, beam pattern, threshold current, power output, quantum efficiency, and modulation response that are important to these potential applications. Results on monolithic integration of the laser with an n-channel MESFET driver are described     

Optical communication systems for avionics

Avionic information processing and transmission requirements are increasing geometrically, with no end in sight, The only feasible way to meet them is to incorporate fiber-optic communication systems into avionic platforms, Such systems can be employed to replace standard electronic components, to augment existing systems, or to enable new technologies. In this paper, we survey the field of low-power communication systems from the avionics engineering perspective. We review the fundamental merits of optical fiber for information transmission and discuss various information modulation schemes. These modulation techniques determine the performance requirements for laser transmitters, We describe the horizontal- and vertical-cavity semiconductor lasers currently available for these systems, and measure their performance against the additional environmental constraints of avionics platforms. Finally, we outline expected near- and far-term trends in system and device development     

轻质刚性纳米隔热材料的制备与性能

针对高马赫数飞行器局部位置对刚性隔热材料的迫切需求,开展了轻质刚性纳米孔隔热材料的制备和性能研究。通过纤维分散、模压成型和纳米颗粒复合技术,成功制备出力学性能优良的刚性纳米孔隔热材料。研究了材料组成与力学性能、隔热性能和微观结构的关系。结果表明,采用刚性骨架增强的纳米孔隔热材料是相同密度下纤维毡增强隔热材料压缩强度的两倍;温度越高,隔热材料的压缩强度变化就越大。     

基于PD-MSM-Lyot 滤波器的多波长掺铒光纤激光器

提出了一种基于偏振依赖多模- 单模- 多模光纤Lyot (PD-MSM-Lyot) 滤波器的 多波长掺铒光纤激光器。PD-MSM-Lyot 光纤滤波器由一个PD-MSM 滤波器和一段保偏光 纤构成,其相邻滤波通带具有相同波长间隔。充分利用偏振依赖MSM 光纤滤波器的起 偏作用并结合腔内色散位移光纤中的非线性偏振旋转效应, 构成了强度相关损耗机 制, 从而抑制掺铒光纤中的增益竞争作用, 获得了室温下19 个波长间隔为0.2 nm 的密 集多波长激光输出。通过对比可得, 输出激光光谱随泵浦功率增大而变的更平坦, 且 波长数更多。     

2 μm LIDAR for laser-based remote sensing: flight demonstrationand application survey

A flight test of a diode-pumped solid-state 2 μm Doppler Light Detection And Ranging (LIDAR) system was conducted on-board the NASA Ames DC-8 Airborne Laboratory. This was the first ever airborne demonstration of a 2 μm diode-pumped solid-state Doppler LIDAR. The LIDAR performance was verified by comparing the true-airspeed (TAS) estimate with that found using the pneumatic air data system; excellent agreement was found. The capabilities of this pulsed 2 μm Doppler LIDAR system include high bandwidth air data determination without the need for extensive forebody calibration, remote wind profiling as far as several kilometers away from the aircraft, eye-safe laser transmission at 2 μm, and diode-pumped solid-state design for compact construction and reliable performance     

Military avionics optical fiber data buses with active-couplerconfigurations

Military avionics optical fiber data buses of high reliability are discussed. Because Light Emitting Diodes (LED's) have better temperature performance and require less complex driver circuits than laser diodes, the former is normally chosen as an optical source in the severe aircraft environment at present. In this case, optical power budget becomes a critical factor which can significantly limit the number of terminals in a data bus. To effectively solve this problem while maintaining a high reliability, we present several configurations of all-active couplers and hybrid passive/active couplers for avionics optical fiber data buses using PIN photodiodes and LED's. The system design is also described, which incorporates a modulation scheme called partial trilevel Manchester II bi-phase coding     

月地及月地以远测控通信与若干关键技术发展趋势

通过研究国内外主要测控通信技术现状与发展动态,梳理出了目前我国在月地及月地以远距离测控通信技术遇到的挑战:面临测量精度尚不能满足科学探测更高的要求,数据传输能力难以满足更高的数据传输速率需求,关键器件自主可控较为薄弱,激光通信高精度快速捕获手段单一,以及星载终端设计与关键技术在轨验证较少等。针对这些问题,提出了对天线组阵、激光测控通信技术、Ka波段及毫米波低温接收机、超导纳米线单光子探测器、深空光学跟瞄系统、窄线宽激光光源的产生技术、光通信调制技术和高功率低噪声放大器的迫切需求,并介绍了国外最新的用于深空测控通信的新概念与前沿技术,即一体化微波/光学混合通信系统与微波光子射频信号稳相传输技术。最后,结合我国现状,讨论了我国测控通信重点发展方向及其关键技术的建议,可供构建月地及月地以远测控通信系统参考。     

High speed plastic networks (HSPN): a new technology for today'sapplications

Decades ago, glass fiber promised to be the future of communications offering large bandwidth, low attenuation, and electromagnetic compatibility. For the long haul applications, this promise has been fulfilled. Today, glass fibers have yielded simple, reliable, and economic means of communicating worldwide. However, when it comes to shorter distances and rugged environments, glass fiber optics has not been the answer. Unforeseen rapid developments in software and display technology have enabled communications in the form of multimedia, E-mail, web pages, and video conferencing. These developments are pushing data rates higher and higher in application environments that are more severe, uncontrolled and require shorter connected intensive links. To achieve desired data rates and electromagnetic compatibility (EMC) using copper systems, shielded cable and connectors or parallel links are necessary, driving up cost and complexity. Glass fiber optic systems provide more than adequate bandwidth and superior EMC but cannot offer a cost effective, robust, user-friendly system. Recent developments have poised plastic optical fiber (POF) to fill the physical layer gap. This paper will discuss the recent developments in plastic fiber including appropriate application space, types of plastic optical fiber, ARPA-funded HSPN team, and recent POF developments     

精密加工表面粗糙度在线检测系统的研究

介绍一个高精度的激光光纤传感式精密加工表面粗糙度在线检测系统。系统的工作原理基于表面散射理论,综合采用了光强补偿、调制、单通道信号处理以及互补采样等一系列技术,确保了测量的高精度。系统使用了单片微机,包括信号切换、互补采样、运算处理及显示打印等测量全过程,均由单片机控制     

光纤F—P腔压力传感器的研究进展

光纤F—P腔压力传感器因其独有的优点广泛应用于军事、民用领域。国内外诸多高校、科研院所都在对其进行研究。本文介绍了光纤F—P腔压力传感器的研究进展,对全光纤结构F-P压力传感器、激光加工微型光纤压力传感器、二氧化硅膜片压力传感器的结构和制作过程进行了总结,并对利用MEMS制作压力传感器的工艺进行了详述,对比分析了不同加工工艺下传感器的性能及其优缺点。     

Pointing grade fiber optic gyroscope

Fiber optic gyroscopes (FOG) are solid-state rotation sensors that are appropriate for a wide variety of applications. In addition to becoming competitive with ring laser gyroscopes on new programs, FOGs are being manufactured to replace spinning wheel gyro technology in existing programs. The FOG brings with it the advantages of long life, high reliability, input axis stability, and low acceleration sensitivity. The AlliedSignal pointing grade fiber gyroscope was designed to replace a high-performance mechanical gyroscope currently made by AlliedSignal. Detailed passive thermal design, gyro assembly techniques, methods for rejecting light source intensity noise, and light source wavelength control are critical features that have been developed to produce a FOG with low noise, stable bias, and a stable and linear scale factor. Results of performance tests and error models indicate that these gyros have a capability for random walk of 0.0002 degrees/≠ hour and bias stability of 0.001 degrees/hour     

Reduced minimum configuration fiber optic gyro for land navigationapplications

Further cost reduction of the fiber optic gyroscope is necessary to meet the economic requirements of land navigation systems. Previous concentration was on the reduction of the number of splices and component improvements in the open-loop minimum configuration. Now non-essential components and splices are eliminated. The source-detector coupler is not part of the Sagnac interferometer, and serves solely to direct light from the interferometer into the output photodetector. Many commercial laser diodes incorporate a back-facet photodetector to monitor laser intensity. The signal returned from the Sagnac traverses the laser, and can be detected at this photodetector. The gyro signal can be distinguished from the laser signal by the bias modulation applied in the interferometer. Configuring a gyro in this manner eliminates a directional coupler and the separate photodetector, as well as up to two fiber splices in an all-fiber gyroscope. A production, open-loop fiber optic gyroscope has been modified to demonstrate this principle. The gyroscope exhibits performance comparable to the conventional minimum configuration