脉冲压缩在激光测距中的应用

脉冲式激光测距和相位式激光测距是目前主要的激光测距方法,但是在复杂噪声环境中,容易因回波信号湮没于噪声中而失效。针对微弱回波信号的提取难题,提出了脉冲压缩式激光测距法。通过发射线性调频的脉冲激光,接收时采用脉冲压缩技术提高脉冲峰值功率,改善信噪比,从而获得湮没于噪声中的回波信号。该方法对于提高测距距离和降低激光功率具有重要的研究意义和应用价值。建立了激光测距中脉冲压缩方法的数学模型,并针对典型高斯白噪声环境进行了仿真,分析了脉冲压缩参数对测距的影响,设计了线性调频的激光信号源并基于FPGA实现了脉冲压缩信号处理。     

激光测距机最大测程评估方法研究

最大测程是评估激光测距机测距性能的综合性指标,在实际应用过程中需要定期检验。目前采用的实际测距法受限于天气和目标条件难以实施,消光比法则因为难以实时设置或测量激光接收处理电路的增益也不易操作。而目前检验激光发射能量、光束发散角、光轴偏差角、最小可探测激光功率等关键参数的手段已经相当普及,可以恰当地应用这些检验结果来评估激光测距机的最大测程是否满足要求;如果能精确给出具体型号激光测距机激光能量分布的表达式,就可以给出精确评估最大测程的理论计算公式,从而通过测量激光测距机的关键参数来判定最大测程是否满足要求。     

远距离低盲区脉冲激光测距的实验系统

测距能力和测距盲区是脉冲激光测距系统中亟待解决的一对矛盾。本文介绍了远距离低盲区脉冲激光测距实验系统的基本组成和工作原理。通过对各种脉冲飞行时间测量方法的比较,确定采用延迟线数字插入法完成脉冲飞行时间的测量,从而保证系统的精度、测程和分辨率。同时,对测距盲区产生的原因进行了分析,提出了引入自动功率调节模块降低测距盲区的方法。系统利用雪崩光电二极管APD作为光电接收器件,采用软硬件结合的智能温度补偿方案对APD进行温度补偿。     

新型相位式激光测距系统电路的设计

为了提高相位式激光测距系统的精度和可靠性,设计了一种新型的相位式激光测距系统的发射和两路几乎一致的接收电路。通过采用具有微小频差的低抖动时钟发生技术,差频测相技术等原理,系统可以实现特定环境下的高精度测量。系统由级联式PLL可编程时钟信号源、激光发射与接收模块、自动增益控制、混频滤波及数据采集组成。利用时钟源产生调制信号,并对反馈信号和接收信号进行放大、混频滤波等信号调理,进而采集数据并对数据进行处理分析。在电路的设计中,优化了激光的调制发射电路,采用低回波损耗的尾纤式激光器,增加简单实用的自动增益模块等。实验观察的波形和数据结果分析表明,此相位式激光测距系统电路简单实用,并且具有较高的稳定性和较高的测量精度。     

手持激光测距仪及其发射电路

脉冲相位激光测距法是当前手持激光测距仪采用的一种新型测距方法,针对这种测距方法,设计了一种简易的产生测距激光信号的电路方案,其中包含频率合成方案、激光调制电路,并分析了设计对于测距的范围、精度、周期、能耗的影响,指出了提高测距指标的关键所在。另外,通过跨导运放的使能端实现了间歇发射激光脉冲串的目标,提高了发射激光的峰值功率,这有利于增加测距范围。电路设计方案简易,对手持激光测距技术研究有一定的参考意义。     

星间激光通信兼测距新技术研究

提出了一种用于小卫星编队飞行控制的星载激光通信兼测距机方案.该方案利用反馈式脉冲激光测距法,有效解决了传统脉冲激光测距法中存在的提高测距精度和缩短测量时间之间的矛盾.对该方案的原理进行了详细描述,给出了测距的误差分析,并提出了进一步提高测距精度的改进方法.     

机载远程激光测距机最大允许噪声仿真研究

为了提高机载远程激光测距机接收系统设计的可行性,从激光测距方程出发,分析了最小探测灵敏度与测程的关系。对回波频谱特性、探测模块带宽和放大器带宽进行了仿真,计算了回波信号的放大倍数,推算出主放大器输出信号的大小。依据高斯白噪声模型和主放大器输出信号值,推算了激光测距接收电路的最大允许输入噪声值。设计了电路并进行了试验测试。结果表明,激光接收灵敏度与理论值的偏差为5.7%,消光比法对应空中小目标最大测程与理论值的偏差仅为1.5%。该噪声分析方法对机载远程激光测距机的接收系统设计具有一定的指导意义。     

基于模拟自相关方法的微弱激光脉冲信号检测

激光测距以其高空间分辨率、高灵敏度、全天候等优良特性在主动遥感领域倍受青睐。激光测距仪的灵敏度(最大测程)主要取决于激光发射能量、有效接收光学孔径和系统信噪比。在激光发射能量和有效接收光学孔径受到限制的情况下,如何降低系统噪声,将微弱的激光脉冲信号从噪声中提取出来,成为至关重要的问题。从激光测距的原理出发,分析了各种微弱信号的检测方法,得出相关法是一种简单实用的方法。通过自相关与互相关的对比,决定采用模拟自相关法来进行微弱激光脉冲信号的检测。给出模拟自相关法检测电路并对其进行了试验。试验结果表明,使用模拟自相关法的最小信噪改善比为4.5,灵敏度为未经过模拟自相关检测的3.16倍。     

改进型相位式激光测距电路的设计

为了提高无合作目标的相位式激光测距系统的稳定性和精度,并简化测距系统,设计了一种相位式激光测距系统的发射和接收电路.采用了双频调制、直接数字频率合成器(DDS)、差频测相技术等原理.进行了理论的研究、分析和实际的电路实验.利用DDS产生的正弦波信号进行调制发射,并且对非合作目标反射回来的激光信号进行接收、调理,并进行数据处理.在设计中,优化了系统的调制发射电路,采用新的光电探测器和高压偏置电路,增加简单实用的自动增益控制(AGC)模块等.实验结果表明,该测距系统简单有效,具有较高的测量精度和稳定性.     

激光飞行时间测距关键技术进展

文中扼要介绍了激光飞行时间测距的若干关键技术研究进展。主要包括；脉冲激光测距的时间间隔测量技术和时刻鉴别技术，激光相位测距的相位调制技术及其调制噪声问题，调频连续波测距技术和半导体激光自混合干涉测距技术等。     

脉冲激光测距仪雪崩光电探测器最佳工作状态和接收灵敏度研究

根据脉冲激光测距仪目前广泛应用的达通型硅雪崩光电二极管（Si-APD)的噪声谱密度,从理论和实验结果分析各种测距精度的脉冲激光测距仪,在不同脉冲宽度条件下,Si-APD的负载电阻、接收放大器带宽、噪声等效功率,最小可探测功率以及信噪比等数据,并将其进行比较。说明保持Si-APD器件的最佳工作状态是提高激光测距仪的探测灵敏度和测量数据的稳定性、可靠性的重要条件。     

脉冲激光测距仪光电探测器最佳工作状态下的接收灵敏度研究

本文根据脉冲激光测距仪和目前广泛应用的达通型硅雪崩光电二极管（Ｓｉ－ＡＰＤ）的噪声谱密度，从理论和实验结果计算、分析出各类测距精度的脉冲激光测距仪在相同脉冲宽度条件下，Ｓｉ－ＡＰＤ的负载电阻、接收器带宽、噪声等效功率、最小可探测功率和信噪比的数据并进行了比较。说明保持Ｓｉ－ＡＰＤ处于最佳工作状态是提高仪器的探测灵敏度和测量数据的稳定性、可靠性的重要条件。     

Tunable Chirp Managed Laser

We demonstrate a compact tunable chirp managed laser (CML) comprising a radio-frequency switch, a directly modulated distributed feedback laser array, a microelectromechanical systems mirror, and an optical filter and obtain error-free transmission performance over 30 nm at 10.7 Gb/s up to 200 km without electrical dispersion compensation (EDC) or optical dispersion compensation. Transmission distance is stretched to 300 km over the same wavelength range by adding a standard EDC to the receiver.     

Optical beat noise suppression and power equalization in subcarrier multiple access passive optical networks by downstream feedback

This paper describes a cost-effective method of suppressing optical beat noise in subcarrier multiple access passive optical networks. The method is based on initial power equalization followed by automatic fine tuning of laser wavelengths, via downstream feedback control of their mean powers, so that the receiver noise floor level is continuously minimized. Application and performance of the method is demonstrated for a low-cost 16-channel system with uncooled Fabry-Perot lasers, utilizing narrow-band QPSK modulated subcarrier frequencies over more than one octave. In static and dynamic temperature worst-case situations a considerable reduction in the number of transmission errors caused by optical beat noise is observed, depending on the temperature change rate.     

High-speed, burst-mode, packet-capable optical receiver andinstantaneous clock recovery for optical bus operation

This paper describes an enhanced performance version of a high-speed burst-mode compatible optical receiver and its application to 622-Mb/s optical bus operation in conjunction with an instantaneous clock recovery scheme. The receiver is fabricated in a 12 GHz f_t silicon bipolar technology and consists of a differential transimpedance amplifier with an auto-threshold level controller and a high-speed quantizer. Using an InGaAs avalanche photodiode, the typical burst mode sensitivity is around -34 dBm (10^-9 BER) at bit rates up to 1.5 Gb/s with a dynamic range of 26 db for both pseudorandom and burst signals. The results using a laser beam modulated by a high-speed external modulator indicate that the receiver can be operated at bit rates higher than 2 Gb/s. With a worst-case self-resetting time <50 ns for the threshold control circuit, the receiver is usable for optical packet communication where data signals with varying optical power are employed. This receiver was demonstrated in a 622-Mb/s optical bus application where the clock signal was recovered from the packet data signal using a novel high-speed CMOS instantaneous clock recovery IC     

The effect of laser chirping on lightwave system performance

Directly modulated semiconductor lasers exhibit a dynamic wavelength shift (chirping) arising from gain-induced variations of the laser refractive index. The effect of laser chirping on the performance of multi-Gb/s lightwave systems operating at a wavelength of 1550 nm is investigated. Models suitable for computer-aided analysis are used to describe the dynamic response of the laser and the propagation of chirped optical pulses through a step-index single-mode optical fibre. A truncated pulse train, Gauss quadrature rule method is used to evaluate the average bit error rate of the receiver. This permits pattern effects in the transmitted optical waveform due to the laser dynamics and nonlinear optical power transmission properties of optical fibers to be included in the system model. The influence that modulation and device parameters have on the receiver sensitivity is assessed     

Etude des performances ďun récepteur homodyne à laser local synchronisé pour la détection de signaux optiques modulés en phase

An injection-locked DFB semiconductor laser can be used as a local oscillator in a receiver for phase modulated optical signals. The receiver performances are affected by phase noise of the emitter and local lasers, shot noise and the noise resulting from the local laser locking by a modulated carrier. The performances are shown to be slightly better than those of the phase-locked loop for laser linewidths below one megahertz. A design procedure for the receiver is given.     

Linewidth-insensitive coherent AM optical links: design,performance, and potential applications

The use of coherent detection in analog optical links offers several advantages over direct detection: improved receiver sensitivity, inherent frequency translation, and the ability to utilize angle modulation and separate wavelength division multiplexed (WDM) signals. In this paper, we investigate an externally modulated coherent AM optical link. We study the dynamic range of the coherent AM link, considering receiver noise, laser phase noise, laser relative intensity noise (RIN), and system nonlinearities. With proper selection of the receiver's IF bandwidth, the coherent AM link can be made insensitive to the laser linewidth. For optical powers less than 5 mW, RIN of less than -160 dB/Hz reduces the spurious-free dynamic range (SFDR) by less than 3 db with the use of a balanced receiver. The external modulator nonlinearity is the dominant nonideal effect; it reduces the SFDR by 5-19 dB from the theoretical limit for 100% modulation index. We compare the performance of the coherent AM link with that of a conventional direct detection link for two applications: point-to-point links and distribution networks. When the received optical power is less than 1 mW, the coherent link can provide higher SFDR than the direct detection link. Thus, coherent links are well-suited for long distance point-to-point links and FM video distribution systems     

Improved Automatic Filtered Power Control Pumping Method for Uniform Shortpass Band in Optical Fiber Communications

To form a low noise figure and uniform shortpass band in optical fiber communications an improved automatic filtered power control (AFPC) pumping method is proposed here. A modulated single laser signal was entered in a closed feedback loop, in which the erbium-doped fiber amplifier (EDFA) was used as a part of the AFPC loop. Owing to the constant filtered signal and the quadrature phase shift delay inside the feedback loop, an optical pass band was uniformly formed. This EDFA attains high performance with a low noise figure simultaneously. The method was successfully applied to the fabrication of practical 12.0 m length of erbium-doped fiber pumped at 980 nm wavelength and 20 dBm power. Experiments prove that the signal gain of the loop remain flat in the range of 18.2 to 22.4 dB with a worst case error of ±0.5 dB and the noise figure was reduced by 2.2 dB at optimal, which correspond to a shortpass range of 40 nm band pass from 1525 nm to 1565 nm in wavelength. Of course, it should be possible to extent the system performance to all pumping configurations for semiconductor optical amplifiers. This provides the simplest and most economical way to transmit a well-defined band of modulated laser signal and to reject all other unwanted radiation.     

A novel resonance-type optical receiver for high-speed opticalheterodyne transmission systems

A wideband resonance-type optical receiver (WROR) is proposed. It is based on inserting inductance in the feedback path of transistors to improve the frequency bandwidth and noise characteristics of the ROR in the high-frequency range. The noise characteristics of conventional and resonance-type optical receivers are evaluated by considering the series resistance of photodiodes. The double-balanced wideband resonance-type optical receiver is also evaluated. Its frequency bandwidth is 5-12 GHz. Finally, a 5-Gb/s optical CPFSK modulation and demodulation experiment is carried out using this optical receiver