激光多脉冲探测的计算机模拟与实验研究

对激光多脉冲探测理论进行了分析,在考虑了影响探测的各种噪声及其分布特性的基础上,得到了激光多脉冲探测信噪比与脉冲积累次数的定量关系。利用计算机仿真模拟多脉冲探测,其结果与理论分析相符;在实验室条件下对多脉冲探测进行了研究,实验结果表明,在脉冲叠加数较少时,实验与理论符合得很好,当脉冲叠加数较多时,实验数据明显小于理想的数值,分析了出现这种偏差的原因及解决方案。激光多脉冲积累探测可以有效地提高激光探测的信噪比,应用积累探测的方式能有效地将激光探测的弱信号从强噪声背景中检测出来。     

Computer simulation of laser photon fluctuations: Single-cavity laser results

In this second paper of a series I present statistical results obtained from computer simulated experiments in single-cavity semiconductor lasers and show that the probability distribution for realistic lasers are much broader than the Poisson distribution. When the gain saturation parameter is properly chosen, the computer simulated probability distributions agree very well with published experimental results. The following is a summary of the results. 1) Only the longitudinal laser mode at the center of the gain peak shows a probability distribution whose peak coincides with the average photon number. The modes to either side of the central mode have noise-like character with probability maxima at zero photon number. 2) The photon probability distribution narrows with increasing power output, increasing cavity mirror reflectivity and decreasing cavity length. 3) For the photon probability distribution to approach the Poisson limit, the cavity mirrors must have reflectivity near unity and the cavity losses must be very low. 4) Two modes symmetrically located at either side of the gain peak have a probability distribution that is constant from zero photon number to a cutoff value, because the modes compete for power and fluctuate widely. 5) Pulsed single-cavity lasers do not turn on consistently in the same longitudinal mode even if they are biased above threshold. 6) The performance of coupled-cavity (C³) and distributed feedback lasers (to be discussed in a subsequent paper) is much better than that of single-cavity lasers.     

Computer simulation of laser photon fluctuations: Theory of single-cavity laser

This paper is the first of a series devoted to theoretical studies of photon fluctuations in the light output of semiconductor injection lasers. Statistics on laser photon fluctuations are collected by means of a simulation of the dynamic behavior of the laser based on numerical solutions of noise driven laser rate equations. This first paper in the series introduces the noise driven rate equations for a single-cavity laser, explains the method used for their numerical solution, and discusses some approximate analytical results. The second paper presents results of photon counting statistics for the single-cavity laser collected from numerical solutions of the time dependent equations. Additional papers in this series will concentrate on coupled-cavity and distributed feedback lasers. Comparison of these statistical results will show clearly the advantage of coupled-cavity and distributed feedback laser designs over conventional single (Fabry-Perot) cavity injection lasers.     

Computer simulation of laser photon fluctuations: Coupled-cavity lasers

This third paper of the series deals with photon fluctuations in the light output of coupled-cavity lasers. As before, statistics on laser photon fluctuations are collected from numerical solutions of noise driven rate equations. Compared to the single-cavity injection laser, the coupled-cavity laser is found to have the following advantages. 1) The coupled-cavity laser can be made to operate in a single mode by driving one of its sections above and the other below threshold. For a given amount of output power from the high-current end, fewer photon fluctuations occur if it is the longer laser section that is driven above threshold. 2) The order of magnitude of the photon fluctuations of the single lasing mode of a coupled-cavity laser is comparable to the fluctuations of the total power output of a single-cavity laser. 3) Contrary to single-cavity lasers, which cannot be made to operate in a single mode if they are driven by short current pulses, coupled-cavity lasers will readily deliver a single, pulsed mode. Thus, if thermal effects and backreflection of scattered light (for example, from an attached fiber) can be ignored, mode jumping need not occur.     

Computer simulation of laser photon fluctuations: DFB lasers

This fourth paper of the Series is devoted to photon fluctuations in the light output of distributed feedback (DFB) lasers. Statistics on laser photon fluctuations are collected from numerical solutions of noise driven rate equations. The approximate formula for the variance of the photon fluctuations, presented earlier [1], is also applicable to the DFB laser. Compared to the single-cavity injection laser, the DFB laser has the following features. 1) The order of magnitude of the photon fluctuations of the single lasing mode of a DFB laser is comparable to the fluctuations of the total power output of a single-cavity laser. 2) Contrary to single-cavity lasers, which cannot be made to Operate in a single longitudinal mode even under idealized conditions if they are driven by short current pulses, DFB lasers will readily deliver a single, pulsed mode. Thus, if thermal effects and backreflection of scattered light can be controlled, there will be no mode jumping during pulsed operation.     

Optical FSK modulation using injection-locked laser diodes

A FSK (frequency shift keying) modulator based on the α-parameter induced frequency shift in injection-locked laser diodes is studied. The attainable frequency deviations can easily be set up to several gigahertz by acting on the injected power. A major limitation is found in the switching time which, in some anomalous cases, can become as large as 10 ns     

Semiconductor laser FSK modulation and optical direct discrimination detection

FSK signals are generated in an AlGaAs double heterostructure laser by employing an electrical equalising circuit to compensate for its nonuniform FM modulation characteristics. A 10?9 bit error rate is achieved at a 100 Mbit/s data rate in the optical direct discrimination detection with a Michelson interferometer. The optical FSK discrimination detection performance is studied in terms of receiving signal power level and laser spectral linewidth.     

半导体激光器光束特性的计算机模拟与实验研究

为建立一套快速、准确的测量系统以适用于半导体激光器中、大规模生产的测试要求,利用有限元差分数值模拟方法对半导体激光器光束的近、远场分布,发散角等作理论模拟,利用测量系统对其光束的近远场分布、发散角等进行测量。最后提出相应方案处理测量结果以减小误差。与一般测量光束参数的系统相比,该测量系统具有兼顾简单快速与准确的优点。     

激光腔模形成过程的计算机图形模拟

本文依据菲涅耳-基尔霍夫衍射积分方程,在IBM-PC机上用数值计算方法计算出激光谐振腔(条状腔)光场的振幅分布和相位分布,并将计算结果用三维图形模拟展示出自再现模形成的动态过程,其数值计算及三维绘图的结果与福克斯和厉鼎毅的结果相符,因而提供了一种用计算机图形技术辅助设计激光腔的新方法.     

Adaptive quantized feedback equalization of laser FM-response foroptical FSK transmission

Using a mathematical model for nonuniform FM-response DFB lasers, the authors calculated the influence of thermal and carrier-density effects on an adaptive quantized feedback equalization circuit (AQFE). A linear networks is introduced which allows the calculation of an equivalent overall system bandwidth. The equalizer circuit is tolerant to dip frequency variations f_min of the laser's frequency response from 0 to >10 MHz and amplitude variations A between 0.1 and 0.5 for f≫f_min. Hence, lasers can be equalized independent of their individual FM-response. It is calculated that an equivalent bandwidth f _c of more than 1 GHz can achieved     

基于SystemView的2FSK信号相干解调系统仿真

移动通信是一个十分复杂的工程系统,移动通信设计的EDA技术在研发阶段实现软件仿真已成为时尚。通过2FSK信号相干解调系统的仿真介绍了通信仿真软件SystemView的使用方法。     

Analysis of delay-and-multiply optical FSK receivers withline-coding and non-flat laser FM response

We present a theoretical analysis of the performance of coherent optical FSK systems when the driving laser signal is AMI or Manchester (biphase) line-coded to counteract the nonideal FM characteristic of the transmit laser diode, and the received signal is heterodyned and detected by a delay-and-multiply demodulator. The analysis takes into account IF filtering by assuming linear filtering of the noisy signal phase, accounting, for small linewidths, for laser phase noise in a straightforward and accurate manner. A simple equivalent baseband model of the system is derived for performance evaluation, applicable to both cases of large demodulator delay and when the delay tends to zero (ideal discriminator). Noise statistics include the clicks due to both signal and phase noise. The problem of performance evaluation is reduced to a classical intersymbol interference problem which is solved by mead of the method of Gauss quadrature rules. The analysis accurately predicts the effectiveness of AMI and Manchester line coding, depending on several system parameters such as linewidth, modulation index, IF bandwidth and laser FM response, and can be easily extended to other line coding techniques     

Fast wavelength switching and simultaneous FSK modulation using tunable DBR laser

The authors describe the operation of a tunable three-section DBR laser for multiwavelength switching with up to 48 resolvable wavelengths. Fast switching among wavelengths that are spaced over a 2.2 nm continuous tuning range and simultaneous FSK data modulation of each channel are demonstrated. A novel wide-deviation FSK modulation scheme to reduce temperature induced wavelength drifts is also described.<>     

Coherent FSK transmitter using a negative feedback stabilised semiconductor laser

An electrical negative frequency feedback scheme is applied to a semiconductor laser to improve its direct frequency modulation performance in an FSK transmitter. An error signal caused by imperfect FM response is extracted through heterodyne discrimination detection with a stable master laser and fed back to the FM semiconductor laser.     

Frequency stabilisation of semiconductor laser using atomicabsorption line under direct FSK

The oscillation frequency of an AlGaAs laser diode is stabilised using the Rb-D2 absorption line (780 nm) under the direct frequency shift keying (FSK) condition. Only one side (mark or space) frequency signal is used to obtain the feedback signal for stabilisation in this system. The stability obtained is almost the same as that of the case without FSK     

Performance of linecoded optical heterodyne FSK systems withnonuniform laser FM response

A simple theoretical analysis for evaluating the performance of linecoded optical frequency shift keying (FSK) systems is presented. It accounts for the combined effects of laser phase noise, receiver noise, and nonuniform BM response of distributed feedback lasers. A close form expression for the random frequency noise due to the combined effect of laser nonuniform FM response and phase noise is developed. The analysis is carried out for three different linecoding schemes, i.e., alternate mark inversion, Miller code or delay modulation, and Manchester coding, to investigate the efficacy of the line coding schemes in counteracting the effect of nonflat FM response. Theoretical and simulation results show that the sensitivities of linecoded FSK systems are within 0.7 and 0.4 dB for single-branch and dual-branch detection, respectively, at a bit error probability of 10^-9 relative to the random non-return to zero FSK with flat FM response     

人工神经网络在激光加工温度场模拟中应用

研究了人工神经网络在激光加工温度场模拟用参数推算中的应用方法;并设计了相应的BP神经网络模型及软件;研究表明BP神经网络适用于对激光加工模拟的参数推算,其准确性优于回归分析不和函数插值法.     

Optical FSK heterodyne detection experiments using semiconductor laser transmitter and local oscillator

Frequency modulated semiconductor laser signals are demodulated by optical heterodyne detection using an independently temperature stabilized semiconductor laser local oscillator and a square-law detector followed by electrical frequency discrimination circuitry. Short-term and long-term beat frequency stability of the free-running laser transmitter and the local oscillator are delineated. Direct frequency modulation characteristics of the laser transmitter are studied by observing the intermediate frequency spectra. Frequency modulation-demodulation of pulse pattern signals at 100-200 Mbit/s is demonstrated. Reduction of the intermediate frequency fluctuation to less than 5 MHz is realized by employing a feedback of the RF frequency discriminator output to the local oscillator injection current.     

1.55 ?m narrow-linewidth multielectrode DFB laser for coherent FSK transmission

A 1.55?m multielectrode DFB laser, with both flat FM response characteristic and spectral linewidth as narrow as 4.5 MHz, has been fabricated by an MOVPE/LPE hybrid growth method. Since this device is relatively easy to fabricate, the multielectrode DFB laser is most promising as a coherent FSK transmission light source