Analog intersatellite communication with frequency-modulated light. Part 1. Noise theory

A detailed analysis of the noise properties of wideband optical FM systems is presented. The equations, which are extensions of the results derived by Middleton [Q. Appl. Math. 7, 129 (1949)] and Rice [Bell Syst. Tech. J. 27, 109 (1948)] over 50 years ago, can be used to determine the final noise spectral density for all degrees of limiting, with and without sinusoidal frequency modulation. These results are perfectly general and can be used for any FM system (radio, microwave, or optical) having the particular type of limiter described herein.     

Spatial correlation and irradiance statistics in a multiple-beam terrestrial free-space optical communication link

By means of numerical simulations we analyze the statistical properties of the power fluctuations induced by the incoherent superposition of multiple transmitted laser beams in a terrestrial free-space optical communication link. The measured signals arising from different transmitted optical beams are found to be statistically correlated. This channel correlation increases with receiver aperture and propagation distance. We find a simple scaling rule for the spatial correlation coefficient in terms of the propagation distance and we are able to predict the scintillation reduction in previously reported experiments with good accuracy. We propose an approximation to the probability density function of the received power of a spatially correlated multiple-beam system in terms of the parameters of the single-channel gamma-gamma function. A bit-error-rate evaluation is also presented to demonstrate the improvement of a multibeam system over its single-beam counterpart.     

Semiconductor lasers for optical communication

Recent progress in the development of semiconductor lasers for optical-fibre communication is reviewed. GaInAsP buried heterostructure and distributed feedback structure, are described in some detail. An overview of the novel GaInAsSb mid-infrared (2–4 microns) lasers is also presented.     

通信用聚合物光纤放大器

通过对掺杂有机燃料聚合物光纤放大器、掺杂稀土螯合物聚合物光纤放大器、聚合物光纤拉曼放大器以及半导体聚合物光纤放大器的基本原理和特点以及近期新发展的介绍,指出了几种聚合物光纤放大器的研究方向.     

Atmospheric-turbulence-induced power-fade statistics for a multiaperture optical receiver

To estimate the probability distributions of power fades, we consider two basic types of disturbance in electromagnetic wave propagation through atmospheric turbulence: wave-front intensity fluctuations and wave-front distortion. We assess the reduction in the cumulative probability of losses caused by these two effects through spatial diversity by using a multiaperture receiver configuration. Degradations in receiver performance are determined with fractal techniques used to simulate the turbulence-induced wave-front phase distortion, and a log normal model is assumed for the collected power fluctuations.     

大气激光通信机的设计

光束发散角和接收口径是大气激光通信机设计的主要参数。根据高斯光束的光强分布特性,分析激光大气通信中主要的几何扩展损耗,并提出了基于该损耗的光端机设计新方法。通过对几何扩展损耗与发散角、接收口径的相互关系数值分析,确定出适合于数公里级大气激光通信机的主要参数:光束发散角可取0.8mrad～1.2mrad,接收口径为120mm。研制了155Mbps,4km大气激光通信机,初步实验结果表明在能见度大于4km的情况下,系统性能满足误码率低于10-9要求。     

Speckle statistics in optical coherence tomography

The two previously reported calculations of the amplitude distribution of speckles in optical coherence tomography, each based on a different mathematical formulation, yield different results. We show that a modification of an initial assumption in one of the formulations leads to equivalent results.     

空间光通信系统的设计及实现

提出一种较全面的空间光通信系统结构。该系统的光发射接收子系统采用三发三收的设计方法,以增大光的发射功率和接收功率;APT子系统采用望远镜进行粗瞄准,音频调制光标信号进行精瞄准;控制子系统采用Ethernet接口,远程通过Internet对系统进行测量和控制的设计方法。给出一个近地大气空间光通信系统的设计实例, 其信号传输速率为155Mbps,传输距离为4km,在误码率不大于10-9条件下,系统接收灵敏度达到-52dBm。     

光通信系统中一种新颖的级联码型

基于级联码对光通信系统中级联码特性和ITU-T G.975.1中两种超强前向纠错(SFEC)码型进行分析和研究后,提出了一种新颖的RS(255,239) BCH(1023,963)级联码型.仿真表明,该码型与ITU-T G.975.1中RS(255,239) CSOC(k0/n0=6/7,J=8)码相比较,具有更低的冗余度和更好的纠错性能,并且在经过三次迭代且误码率(BER)为10-12时其净编码增益(NCG)比ITU-T G.975.1中RS(255,239) CSOC(k0/n0=6/7,J=8)码和BCH(3860,3824) BCH(2040,1930)码要分别大0.60 dB和0.57 dB.因而,它更适用于超长距离、超大容量和超高速的光通信系统中,并可以作为SFEC码的一种候选码型.     

发展光通信的某些关键技术

信息业务持续呈爆炸式的增长 ,光纤通信容量相应依指数递增 .为此 ,与光纤通信相关的技术和支持它发展的器件以越来越快的速度推陈出新 .任何一篇巨作均不可能全面概括该领域的发展 ,本文仅就发展光纤通信的某些关键技术作粗浅论述 .     

Graded-index polymer optical fiber for high-speed data communication

We successfully obtained a high-bandwidth (1 GHz km) and low-loss (90 dB/km at 0.572 μm of wavelength) graded-index polymer optical fiber by using the interfacial-gel polymerization technique, in which we used an unreactive component to obtain the quadratic refractive-index distribution. This high-bandwidth graded-index polymer optical fiber makes it possible to transmit a high-speed optical signal in a short-range network, which is not possible when we use the step-index type of polymer optical fiber commercially available.     

High bandwidth underwater optical communication

We report error-free underwater optical transmission measurements at 1 Gbit/s (10(9) bits/s) over a 2 m path in a laboratory water pipe with up to 36 dB of extinction. The source at 532 nm was derived from a 1064 nm continuous-wave laser diode that was intensity modulated, amplified, and frequency doubled in periodically poled lithium niobate. Measurements were made over a range of extinction by the addition of a Mg(OH)(2) and Al(OH)(3) suspension to the water path, and we were not able to observe any evidence of temporal pulse broadening. Results of Monte Carlo simulations over ocean water paths of several tens of meters indicate that optical communication data rates >1 Gbit/s can be supported and are compatible with high-capacity data transfer applications that require no physical contact.     

自由空间光通信的最大后验概率检测

为了减小大气闪烁对自由空间光通信的通信性能的影响,基于光信号的对数振幅序列服从联合高斯分布特性,提出了一种最大后验概率算法,给出了随时间变化的判决阈值.模拟结果表明,此算法可以有效减小大气闪烁对通信性能的影响,降低其误码率.     

Fabrication of silicon based glass fibres for optical communication

Silicon based glass fibres are fabricated by conventional fibre drawing process. First, preform fabrication is carried out by means of conventional MCVD technique by using various dopants such as SiCl₄, GeCl₄, POCl₃, and FeCl₃. The chemicals are used in such a way that step index single mode fibre can be drawn. The fibre drawing process consists of various steps such as heating the preform at elevated temperature, diameter monitor, primary and secondary coating, and ultra violet radiation curing. The fibres are then characterized for their geometrical and optical properties. The drawn fibre has diameter of core and cladding to be 8.3 μm and 124.31 μm, respectively whereas non-circularity is found to be 4.17% for core and 0.26% for cladding as seen from phase plot. Mode field diameter is found to be 8.9 μm and 9.2 μm using Peterman II and Gaussian method, respectively. The fabricated fibres showed the signal attenuation of 0.35 dB/km and 0.20 dB/km for 1310 nm and 1550 nm, respectively as measured by the optical time domain reflectometer (OTDR).     

深空光通信中导航星表的构造

提出一种导航星表的构建方法，该方法以星跟踪器视场内最亮恒星作为信标，把信标锁定在视场中心，测量视场内其他恒星到信标的角间隔，把测量的所有恒星角间隔和信标的赤经、赤纬存储到导航星表中。基于该方法，利用史密森天文观测台恒星星表（SAO），选择星等小于6等的恒星，建立起导航星表，该星表仅包括5103颗星，其容量仅为1.2兆。相对三角形算法，该星表容量更小，可节省星载系统的存储空间，减少识别时间，提高跟踪速率。蒙特-卡诺仿真结果表明，利用该导航星表识别信标具有较好的抗干扰性，且当星跟踪器测角误差（30σ）在1μrad以内时，信标正确识别概率几乎为100％。     

Wide-beam atmospheric optical communication for aircraft application using semiconductor diodes

Design considerations for atmospheric optical communication systems using wide divergent beams are described. This new approach can eliminate the need for complex gimbaled pointing and tracking mountings. Communicating systems have been designed and built using both infrared LED and cw and pulsed laser diodes operating in the wavelength range of lambda = 0.8-0.9 microm. Both single-channel and multichannel receivers were designed with fields of view (FOVs) ranging from 0.4 to 24 degrees. Receiver performances were compared for a range close to 1 km under various ambient conditions. Laboratory simulation experiments were used to determine the operating margin and expected SNRs resulting from various design considerations. The need for narrow spectral bandwidth and wide-angle FOV interference filters is pointed out. The systems designed in the present work were low data rate (a few kbit/sec) communication systems and are suitable for aircraft-to-aircraft data exchange or voice communication.     

Fundamental approach to failure statistics of optical glass fibres

Tensile strength data of fused silica optical fibres was analysed without making any a priori assumptions regarding the flaw density distribution. Based on the strength data of short length specimens (0.05 to 0.6 m), predictions of the strengths of long length specimens (500 to 1100 m) were in good agreement with actual data. The advantages of a fundamental approach to the statistical analysis of failure of optical glass fibres compared with the more widely used Weibull statistics are discussed.