光反馈自混合干涉位移测量算法

为了实现光反馈机制下位移的测量,研究设计了基于非线性最小二乘法的位移测量算法.本文采用了光反馈自混合技术和梯度最优算法,可以达到数据理论的最佳拟合.同时给出了梯度迭代公式,参量迭代时引入了可变步长,从而实现位移的精密测量.针对不同情况,做了大量计算机仿真并给出仿真结果.结果表明该算法参数估计精度较高,不受参数初值选取的影响,且抗噪性能较好.     

Measurement of the linewidth enhancement factor of semiconductor lasers based on the optical feedback self-mixing effect

A new method for the measurement of the linewidth enhancement factor of semiconductor lasers is presented, based on the interferometric self-mixing effect. It is a fast and easy to perform method that does not require radio frequency nor optical spectrum measurements. A small fraction of the emitted light is backreflected into the laser cavity by a remote target driven by a sine waveform. The mixing of the returned and the lasing fields generates a modulation of the optical output power in the form of an interferometric waveform, with a shape that depends on the optical feedback strength and the linewidth enhancement factor /spl alpha/, according to the well-known Lang-Kobayashi theory. We show that the value of /spl alpha/ can be retrieved from a simple measurement of two characteristic time intervals of the interferometric waveform. Experimental results obtained on different laser diodes show an accuracy of /spl plusmn/6.5%.     

基于适度光反馈自混合干涉技术的微位移测量

光反馈自混合干涉技术是一种新出现的有别于传统双光束干涉的一类新的测试技术。为了在适度光反馈下进行位移的精密测量,提出了一种基于适度光反馈自混合干涉技术的位移测量方法。采用条纹记数法实现大范围位移粗测,具有半波长位移分辨力;然后基于适度光反馈下小数条纹的特点,给出了小于半波长位移测量的方法,从而提高位移测量的分辨力。用绝对精度达3nm的商用压电陶瓷驱动器比对实验,结果验证了这种三角波调制外反射体在普通实验室环境噪声中可以达到纳米级的位移测量精度。实验数据处理结果表明,对于3μm以下的位移,该算法位移测量相对误差约为1.20%。     

光反馈自混合干涉对称折叠算法的精度分析

为了提高对称折叠算法的精度,通过对仿真信号的测量,分析了影响算法精度的几种因素(光反馈水平因子,外腔的非线性运动,抽样速率和转折点的定位),并且给出了改进方法.仿真结果表明,在测量线宽展宽因子之前,需保证光反馈水平因子的准确测量,利用中间干涉条纹进行测量可以减少外腔非线性运动所带来的误差.这一结论对利用对称折叠算法处理实验信号有一定的帮助.     

光反馈自混合干涉对称折叠算法的精度分析

为了提高对称折叠算法的精度,通过对仿真信号的测量,分析了影响算法精度的几种因素(光反馈水平因子,外腔的非线性运动,抽样速率和转折点的定位),并且给出了改进方法。仿真结果表明,在测量线宽展宽因子之前,需保证光反馈水平因子的准确测量,利用中间干涉条纹进行测量可以减少外腔非线性运动所带来的误差。这一结论对利用对称折叠算法处理实验信号有一定的帮助。     

半导体激光自混合干涉的弱光反馈模型

文章针对弱光反馈情形，对基于光反馈效应的激光自混合干涉模型进行了探讨。采用双空模型，从增益阈值和振荡效率方面给出了理论模型。该模型很了地解释了激光自混合干涉现象。最后分析了一实用光纤自一干涉系统的数学模型。     

基于半导体环形激光器的光反馈动力学研究

为了研究半导体环形激光器在外部交叉光反馈情况下的非线性动力学特性, 基于环形激光器的速率方程, 采用数值仿真的方法, 得到了各种反馈参量下的时间序列及功率谱, 并研究了反馈系数对混沌带宽及时间延迟特性的影响。结果表明, 在各种不同外部反馈参量的情况下, 环形激光器展现了单周期、多周期、低频反相波动以及混沌态等丰富的动力学态; 在对称光反馈时, 可得到最大为3.7GHz的混沌带宽; 在时间不对称光反馈时, 产生的混沌信号的时延特征被很好地抑制。该研究结果可为环形激光器的实际应用提供一定的理论参考。     

光反馈自混合干涉系统反馈水平的研究与测量

为了能够较为准确地获得光反馈自混合干涉测量系统的反馈水平,采用仿真分析光反馈自混合干涉信号和求解Lang-Kobayashi方程的方法,得出反馈水平越高,光反馈自混合干涉信号上干涉条纹的谷值与下干涉条纹峰值之差越大,当反馈水平因子大于7.8时,一些干涉条纹将消失;同时由滞回现象可以推导出反馈水平因子的测量公式,建立了测量模型,并进行了仿真和实验验证。结果表明,光反馈自混合信号干涉条纹幅度受反馈水平影响;利用提出的测量模型可以判断光反馈自混合干涉实验信号的反馈水平机制,当光反馈水平因子介于1和7.8之间时可以测出具体的光反馈水平因子值。     

弱光反馈对半导体激光器AM和FM噪声谱的影响

一、引言 相干光通信系统具有灵敏度高,选择性好及可采用波分复用等优点。为了实现相干光通信系统,一个首要的问题便是抑制作为发射机振荡器与接收机本地振荡器的LD的噪声。光反馈是抑制LD噪声的有效手段,近年来人们对此进行了大量研究。然而,这些研究一般都局限于LD的线宽。由于LD的场功率谱通常不是洛伦兹型的,因此,必须研究LD的FM和AM噪声功率谱才有实际意义。     

Equivalent circuit of semiconductor lasers with weak coherentoptical feedback

The equivalent circuit modelling of semiconductor lasers makes simulation of direct modulation of semiconductor lasers extremely simple through the use of circuit simulators such as SPICE. The authors extend the circuit model to incorporate the effect of weak coherent optical feedback into the laser cavity. Results from circuit simulation of the model are compared with results reported earlier as well as results obtained from direct numerical analysis of rate equations     

Spectral linewidth reduction in semiconductor lasers by an external cavity with weak optical feedback

The linewidth narrowing of a semiconductor laser due to weak optical feedback is analysed, taking into account both phase condition and threshold change for the feedback-induced modes. The achievable linewidth reduction lies in between two limiting cases, 1/(1 + X ?(1 + ?2))2 and 1/(1 + X)2, where ? and X are the linewidth enhancement factor and the feedback parameter, respectively.     

Spectral characteristics of semiconductor lasers with optical feedback

Optical feedback-induced changes in the output spectra of several GaAlAs lasers operating at 0.83 μm are described. The feedback radiation obtained from a mirror 60 cm away from the laser is controlled in intensity and phase. Spectral line narrowing or broadening is observed in each laser depending on the feedback conditions. Minimum linewidths observed with feedback are less than 100 kHz. Improved wavelength stability is also obtained with optical feedback resulting in 15 dB less phase noise. An analytical model for the three-mirror cavity is developed to explain these observations.     

Modeling of distributed feedback semiconductor lasers withaxially-varying parameters

A numerical model that is capable of predicting important laser characteristics such as the threshold gain and the gain margin between the main and side modes for a distributed-feedback (DFB) semiconductor laser of arbitrary complexity is described. The method consists of solving the coupled-mode equations with axially varying parameters iteratively until the boundary conditions at the two facets are satisfied. The numerical model is applied to two DFB laser structures. In the case of a multiple-phase-shift DFB laser the results show that such devices can have a more uniform axial distribution than that of a conventional quarter-wave-shifted DFB laser while maintaining sufficient gain margin between the main and side modes. In the case of a dual-pitch DFB laser it is shown that the incorporation of a slightly different grating period (~0.1%) over a small section can provide a gain margin that is comparable to that achieved in quarter-wave-shifted DFB lasers     

Mode partition in semiconductor lasers with optical feedback

The authors point out that random noise processes induce mode partition fluctuations in semiconductor lasers. Mode partition depends on laser parameters and modulation current. However, external optical feedback can also increase mode partition noise. Here, a numerical solution of multimode noise-driven rate equations with time-delayed terms is utilized to investigate mode partition in semiconductor lasers with reflecting feedback. Photon statistics of the main and side modes in semiconductor lasers under both CW operation and dynamic operation are considered. Probability-density curves for the main and side modes are shown. The feedback-induced change of photon statistics of the main and side modes is clearly seen. Numerical results indicate that, if the laser used is exposed to reflections, a more stringent mode discrimination requirement for suppressing the buildup of laser-cavity longitudinal side modes may result. If mode discrimination is insufficient for avoiding the excitation of side modes, the feedback-induced power penalty depends on the fiber dispersion     

Theoretical analysis of external optical feedback on DFB semiconductor lasers

The effect of external optical feedback on resonant frequency, threshold gain, and spectral linewidth of distributed feedback (DFB) semiconductor lasers is theoretically analyzed. The analysis applies to any type of laser cavity formed by a corrugated waveguide limited by partially reflecting facets. It is shown that the sensitivity to optical feedback on a facet is closely related to the power emitted through this facet. Numerical results on wavelength selectivity and on sensitivity to optical feedback are given for conventional DFB lasers having an AR-coated facet and for quarter-wave-shifted (QWS) DFB lasers with AR-coatings on both facets. Both laser types are found to be more sensitive to optical feedback on their AR-coated facet than Fabry-Perot lasers for lowkL. On the other hand, QWS-DFB lasers are found to be relatively insensitive to optical feedback for largekL.     

Multiwavelength lasers based on semiconductor optical amplifiers

Stable multiwavelength lasing is demonstrated with a novel laser, in which a semiconductor optical amplifier offers optical gain and cascaded sampled fiber gratings serve as a comb filter. Five lasing lines are obtained with a fixed wavelength spacing of 0.8 nm. Optical power fluctuations among the lasing lines are improved by adjusting the reflectivity profile through the cascade of two sampled gratings     

一种半导体激光自混合效应模型参数的测量方法

从半导体激光自混合干涉系统的一般模型公式出发,建立了一个非线性函数模型,利用非线性最小二乘法的曲线拟合,来估计半导体激光自混合效应的模型参数——线宽展宽因数和光反馈因数。经计算仿真分析表明,该算法有较好的收敛性,迭代次数少且参数估计精度高,是半导体激光自混合效应参数测量的一种有效方法。     

Analysis of DFB semiconductor lasers with external optical feedback

A theoretical analysis of the sensitivity of DFB semiconductor lasers to external optical feedback is presented. Numerical simulations allow the authors to determine the optimum facet reflectivity, for a given κL value, to minimise the sensitivity to external optical feedback     

Noise properties of semiconductor lasers due to optical feedback

It has been recognized for some time that reflections back into the cavity of an injection laser from a mechanically unstable external mirror cause noise in the output of the laser (reflection noise). In this paper, noise measurements are presented for index-guided lasers as functions of the output power, the degree of optical isolation and external cavity length (5-15 cm), while current modulation (using 2-4 mA at 50-200 MHz) has been used to reduce the noise levels by as much as 20 dB. It is demonstrated that the mechanism of noise reduction by modulation is the frequency modulation of the laser's spectrum and its interaction with the modes of the external cavity. It is shown that using an optical isolator can give a relative intensity noise of -110 dB while using modulation in addition can reduce this to -125 dB; the bandwidth performance of optical storage systems is discussed in terms of these two schemes.