DFB半导体激光器自注入锁定失稳因素分析

分布反馈(Distributed Feedback, DFB)半导体激光器具有体积小、成本低和工艺成熟等优势,但兆赫兹量级的线宽使其应用范围受限。采用环形谐振器对其进行自注入锁定,可将线宽压窄到千赫兹量级,但仍存在锁定不稳定的问题。文章采用四只不同的环形谐振器对DFB半导体激光器进行自注入锁定,通过实验监测自注入锁定时多个端口的光功率、偏振态和光波长的变化,揭示影响DFB半导体激光器自注入锁定稳定性的因素有谐振模式跳变、偏振态跳变,以及外界温度和振动引起的锁定环路的相位变化,且使用不同类型的环形谐振器进行锁定时,主导的影响因素不同。控制这些影响因素可以改善DFB半导体激光器自注入锁定的稳定性,使DFB半导体激光器自注入锁定技术有更好的应用效果。     

半导体激光器的电噪声

通过测量激光器的电噪声,可以用来在线监测器件的诸多特性,如阈值电流的大小,是否有模式跳变发生,以及谱线宽窄等.另外,根据电噪声的大小,还可以对器件的质量和可靠性作出评价,具有快速、方便、无损等优点.文章概述了半导体激光器的电噪声,对其主要应用进行了综合和讨论,概括性评述了该领域目前的研究进展.     

全内腔He-Ne激光器开机光强调谐曲线及激光器性能

虽然固体激光器和半导体激光器有很多优势,但在精密测量领域,He-Ne激光器仍然是制造高精度仪器最常用的激光器。在开始的升温过程中,He-Ne激光器经历了一段功率、频率、横向模式等不稳定的时间。文中全面、综合地报导了长期实验中得到的丰富的He-Ne激光器（一般和双折射双频激光器）开机光强调谐曲线,并以此作为判断激光器性能的依据,研究如何从曲线对激光器的参数做出推断。包括推断:激光纵模间隔,激光出光带宽,激光单、双纵模区宽度,子腔效应的程度等。     

Synchronized chaotic mode hopping in DBR lasers with delayedopto-electric feedback

We propose and demonstrate a scheme for generating synchronized chaotic mode hopping in two wavelength-tunable lasers. Chaotic mode hopping resulting in large hops in wavelength is induced by delayed feedback of an electrical signal proportional to the intensity of the laser output which passes through an optical filter. Mode hopping among up to 11 modes was experimentally observed and optical signals in each wavelength band show a different on-off modulation time series. Analysis of the time series indicates high dimensionality. By using a unidirectional coupling method that injects part of the output of one laser into another, we can synchronize the chaotic mode hopping of two separate lasers and obtain synchronized chaotic on-off modulation patterns in multiple corresponding wavelength bands. The robustness of the synchronization with respect to the parameter mismatch and the effects of the coupling strength are investigated. The chaotic mode hopping dynamics and synchronization are well described with a numerical model that includes the characteristics of the laser tuning and the filter transmission. A multiplexed data transmission scheme using chaotic carriers is proposed and experiments demonstrate that multiple messages can be simultaneously recovered when chaos synchronization is achieved     

Characteristics of chaos synchronization in semiconductor lasers subject to polarization-rotated optical feedback

We numerically investigate the detailed characteristics of chaos synchronization in semiconductor lasers subject to polarization-rotated optical feedback. The emission of the dominant TE mode of a drive laser is rotated 90 deg and fed back to the laser with time delay. The polarization-rotated TE mode is also injected with time delay into the TM mode of a second laser. Two types of synchronization with different time-lags are found, as in the case for synchronization in semiconductor lasers with nonrotated optical feedback. However, a significant difference to the nonrotated optical feedback case is that neither of the two types of synchronization requires matching of optical carrier frequency between the two lasers.     

Frequency response of an MQW DFB laser injected with intensity-modulated TM-polarized light

The frequency response of a multiquantum-well (MQW) distributed-feedback (DFB) laser was measured by injecting intensity-modulated transverse-magnetic (TM)-polarized light. With low bias currents, the 3-dB bandwidth of the MQW DFB laser's frequency response was anomalously enhanced by injection of intensity-modulated TM-polarized light. The maximum 3-dB bandwidth, 16 GHz, was observed when the normalized bias current (I/I/sub th/-1) was 1. The 3-dB bandwidth behavior of the MQW DFB laser with TM-polarized light injection looks promising for high-speed lasing mode control of semiconductor 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     

Computer simulation of FSK laser spectra and of FSK-to-ASKconversion

The performance of binary frequency shift keyed (FSK) modulated two-segment semiconductor injection lasers is simulated by generating a 64-b pseudorandom step-function bit pattern. This signal, superimposed on a DC bias, is used to drive a two-segment distributed feedback (DFB) laser. To obtain the optical laser spectrum, the input signal is passed through the laser's small-signal transfer function. The resulting spectrum is passed through a Fabry-Perot filter that rejects one of the two principal peaks of the wide-deviation optical spectrum and converts the FSK modulation to amplitude shift keying (ASK) modulation. This simulation determines how different system parameters influence the performance of a laser system used for signal transmission by means of FSK-to-ASK conversion     

Couplage phase-amplitude et taux d’émission spontanée dans les lasers à semiconducteur à contre-réaction distribuée ou à cavité composite

This article presents a formalism which describes the noise and modulation properties of a complex structure semiconductor laser. As an example, the distributed feedback lasers and the distributed Bragg reflector lasers are examined. The rate of the spontaneous emission coupled to the lasing mode and the phase-amplitude coupling factor are discussed. The obtained results show particularly the influence of both the materials properties and the structure. The interactions between these two factors should be controlled to develop high performance laser diodes.     

Global excess spontaneous emission factor of semiconductor laserswith axially varying characteristics

An expression of the excess spontaneous emission factor of semiconductor lasers having axially varying characteristics has been derived, using a classical treatment for the contribution of spontaneous emission to the laser's noise figure. Although the analysis is focused on semiconductor laser structures, including DFB lasers, the expression obtained can be applied with minor changes to other standing-wave laser geometries. This global excess spontaneous emission factor, accounting for transverse as well as longitudinal effects, is relevant even for laser structures wherein the longitudinal and lateral field distributions are mutually coupled. In this situation, this factor is not equivalent to the product of Petermann's excess noise factor and a longitudinal correction factor accounting for outcoupling losses     

Mid-range coherent optical frequency domain reflectometry with aDFB laser diode coupled to an external cavity

The optical frequency of an external double cavity coupled laser diode was controlled via the phase of the feedback light. Strong linewidth and mode hopping reductions were obtained, extending coherent reflectometry with semiconductor sources to the range of hundreds of meters     

Coherent transmission using an external waveguide Bragg reflector laser with direct frequency modulation

Single-frequency l.5?m semiconductor lasers, formed by butt-coupling of a regular Fabry?Perot laser to an external waveguide Bragg reflector, are shown to have very uniform frequency modulation characteristics under direct current modulation. The laser's frequency modulation characteristics, together with its narrow linewidth (? 1 MHz), make coherent transmission possible without external modulators. The laser performance was evaluated in a 417Mbit/s, 102 km, frequency-shift-keying coherent transmission experiment.     

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.     

Detecting mode hopping in semiconductor lasers by monitoringintensity noise

Mode-hopping semiconductor lasers exhibit intensity fluctuations which are correlated to the level of mode-hopping activity. It is shown that these fluctuations occur at a level that is easily measured and that mode hopping can be detected with a p-i-n photodiode and an AC voltmeter having microvolt sensitivity. A plot of intensity fluctuations versus laser case temperature and injection current displays periodicities in the conditions under which mode hopping occurs. These regularities are explained in terms of the peak gain wavelength passing the longitudinal mode wavelength as temperature changes. The occurrence of mode hopping is determined by junction temperature (which determines the relationship of the gain peak with longitudinal mode structure) and injection current (which determines mode-hopping frequency). The junction temperature is itself a function of case temperature and injection current. The stability map shows that precise control of the operating parameters is not sufficient to avoid mode hopping. It is necessary to have these parameters set properly     

锑化物中红外单模半导体激光器研究进展

锑化物材料因为其天然的禁带宽度较小的优势,是2~4 m波段半导体光电材料和器件研究的理想体系。近年来,国内外在锑化物大功率半导体激光器方面的研究取得了很大的进展,实现了大功率单管、阵列激光器的室温工作。然而,由于锑化物材料与常见的半导体单模激光器制备工艺的不兼容性,只有少数几个研究单位和公司掌握了锑化物单模激光器的制备技术。文中介绍了锑化物单模激光器常用的侧向耦合分布反馈激光器的基本原理,分析了其设计的关键技术,回顾了锑化物单模激光器的设计方案和制备技术,并针对国内外锑化物单模激光器主要研究内容进行了总结。     

外部光反馈对强耦合外腔半导体激光器特性影响的理论分析

本文从理论上分析了外部光反馈对强耦合外腔半导体激光器特性的影响，对相干外部光反馈和非相干外部光反馈两种情形的分析结果均表明强耦合外腔半导体激光器可将半导体激光器所能容忍的临界光反馈强度提高大约２０ｄＢ以上，同时得出了长外腔和强耦合有利于提高外腔半导体激光器抗反馈能力的结论。     

External optical feedback effects on semiconductor injection laser properties

Influences on the semiconductor laser properties of external optical feedback, i.e., return of a portion of the laser output from a reflector external to the laser cavity, have been examined. Experimental observations with a single mode laser is presented with analysis based on a compound cavity laser model, which has been found to explain essential features of the experimental results. In particular, it has been demonstrated that a laser with external feedback can be multistable and show hysteresis phenomena, analogous to those of non-linear Fabry-Perot resonator. It has also been shown that the dynamic properties of injection lasers are significantly affected by external feedback, depending on interference conditions between returned light and the field inside the laser diode.     

Effective nonlinear gain in semiconductor lasers

An effective nonlinear gain is introduced for semiconductor lasers by taking into account the effect of laser structure and the associated distribution of the mode intensity along the cavity length. It should be used in the analysis of laser dynamics and noise in place of the material nonlinear gain parameter. A general expression for the effective nonlinear gain is given by using the Green's function method. The results obtained for Fabry-Perot and distributed feedback lasers show that the effective nonlinear gain could be considerably enhanced. The exact value of the enhancement factor depends on cavity parameters. Affected by the laser structure, the nonlinear gain has a different power dependence than expected from material considerations alone     

Spatial feedback effects in narrow-stripe index-guidedsemiconductor lasers

We demonstrate experimentally that spatial effects of feedback are important in determining the operating characteristics of index-guided semiconductor lasers. It is in fact the inflexibility of the index-guided mode that makes the laser susceptible to small misalignments of the external cavity, which can induce power variations of nearly 40% of the solitary laser power with feedback levels of less than 2%.(-17 dB). With a simple model, we calculate the modification of the feedback wavefront as a function of the external cavity length and show that the power variations are induced through changes in the cavity loss brought on by the interference of the feedback field with the field reflected off the laser facet. By experimental comparison to a partly gain-guided laser, we conclude that these large-scale variations will be significantly reduced or absent in purely gain-guided lasers     

Theoretical analysis of longitudinal mode coupling in external cavity semiconductor lasers

The single longitudinal mode behavior in long external cavity semiconductor lasers is discussed. Experimentally, the laser exhibits a single frequency oscillation even for an external cavity length of 100 cm. The mode selectivity of a composite cavity is shown to be insufficient to explain the experiments. Longitudinal mode coupling in semiconductor lasers is found to arise from an interference effect between the modes on the interband transition probability of electrons. Mode coupling equations are derived, which indicates that the single mode oscillation in long external cavity semiconductor lasers is brought about when the coupling strength goes beyond a critical value. It is shown that the effect of the hole burning in the external cavity semiconductor lasers is similar to that in the solitary laser.