基于表面曲线光栅的高功率窄线宽半导体激光器

随着智能感知技术的快速发展，高功率、窄线宽的半导体激光光源成为研究热点。通过在边发射半导体激光器件表面引入高阶曲线光栅，设计了一种独特的非稳谐振腔结构，可实现高功率和窄线宽。采用紫外光刻和电感耦合等离子体（ICP）刻蚀技术，制备了周期为6.09μm、占空比为0.66、刻蚀深度为500 nm的曲线光栅。在室温条件下，测得腔长为2 mm的器件的阈值电流为220 mA，连续输出功率为1.48 W，斜率效率为0.63 W/A。比较了法布里-珀罗激光器、直线光栅分布式反馈（DFB）激光器和曲线光栅DFB激光器的光谱，结果表明，曲线光栅对半导体激光器的模式选择起到了关键作用，有利于实现高功率DFB激光器的窄线宽单模输出。该器件具有制作工艺相对简单、性能优异、可靠性高等特点，具有广阔的应用前景。     

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。     

基于片上微腔自反馈注入锁定的窄线宽激光器

对半导体激光器外腔自反馈注入锁定进行了理论分析,研究了片上微腔的自反馈注入锁定对于分布反馈(DFB)激光器输出线宽的影响,分析了决定锁定带宽及线宽压缩系数的关键参数。基于Q值为2.4×10⁶的片上Si₃N₄微腔的后向瑞利散射实现了DFB激光器的自反馈注入锁定,将其输出线宽由自由运转时的556.71 kHz压窄到了92.28 kHz,锁定带宽达到425 MHz。研究结果有助于理解半导体激光器自反馈注入锁定机理,并为实现窄线宽激光器提供了新的结构更简单、集成化潜力更高的方案。     

外腔半导体激光器的设计与高次谐波稳频

首先讨论了半导体激光器外腔结构参量对激光连续可调范围影响的理论计算方法，给出了Littrow结构外腔半导体激光器调谐范围的计算结果。然后介绍了半导体激光器外腔结构参量的具体设计，利用该设计得到了出射激光线宽小于1 MHz、连续可调谐范围可达3 GHz的780 nm波段外腔半导体激光器。接着讨论了利用腔外饱和吸收谱的三次谐波稳频方法对半导体激光器进行稳频，优化激光频率短期稳定度的方法。最后根据该优化方法设计出稳频系统对半导体激光器进行稳频，得到了稳定度达到10-12量级的半导体激光输出。     

半导体激光器波导结构对线宽影响的理论修正

从质子轰击条形半导体激光器线宽的实验测量，发现半导体激光器线宽与谐振腔结构有关。通过对Ｃ．Ｈ．Ｈｅｎｒｙ给出的半导体激光器线宽的理论公式进行分析，认为半导体激光器腔结构不同会引起激光器线宽的不同，并从理论上分析与推导了波导结构对激光器线宽的影响，定义了结构线宽△ｖｓ１／２概念及其表达式。修正了的线宽理论公式具有更广泛的适用范围。     

405nm波段光栅外腔窄线宽蓝紫光半导体激光器

自由运行的半导体激光器由于谱线较宽而无法满足如拉曼散射等对线宽有要求的应用需求,因此获得线宽较窄、波长稳定的半导体激光器十分必要。采用反射式全息光栅作为谱线窄化元件,研究了在Littrow布局下的405 nm外腔半导体激光器。反射式全息光栅的加入,使得光栅面和半导体激光器的输出面组成耦合外腔,这在很大程度上改善了405 nm半导体激光器的线宽性能。实验结果表明,通过加入2400 line/mm的反射式全息光栅形成外腔反馈,半导体激光器的阈值电流由31 m A下降到22 m A,谱线宽度从自由运行时的1 nm减小到0.03 nm以下,实现了窄线宽输出,并且在工作电流为100 m A时,得到窄线宽半导体激光器的输出功率为28 m W,为自由运行半导体激光器输出功率的31.7%。此外,通过调节反馈光栅的角度,实现了较大电流范围的激光波长的连续调谐,最大调谐范围达3.5 nm。     

外腔半导体激光器动态模稳定性的研究

为了研究调谐过程中外腔半导体激光器的模稳定性,采用多光束干涉理论推导Littrow结构外腔半导体激光器的腔增益,并模拟其模结构。分析了光栅面和转臂不在同一平面的情形下,在光栅转动调谐时,通过匹配光栅的反馈波长变化率与外腔波长变化率,推导出最佳的初始外腔长度,并研究了动态模稳定（无跳模调谐）的范围;采用严格的耦合理论和光线变换矩阵分析了准直（耦合）透镜的位置对系统后向耦合效率的影响。结果表明,系统后向耦合效率最大可达99%,极大地压窄了中心波长为780nm半导体激光器的线宽,外腔半导体激光器的理论线宽为未加外腔时的0.96%,动态模稳定范围可达6.8nm。     

准直透镜失调对Littman-Metcalf光栅外腔激光器线宽的影响

以光栅外腔半导体激光器的理论知识为基础,对Littman-Metcalf型外腔半导体激光器的工作原理进行了说明,并详细地讨论了外腔半导体激光器的线宽压窄以及模式选择机制,采用严格的耦合理论和光线变换矩阵推导了系统结构参数对光场耦合效率影响的计算公式。同时,对影响Littman-Metcalf外腔激光器输出激光线宽的几个重要因素进行了分析,重点讨论了系统中准直透镜位置失调导致的线宽变化规律。计算结果表明:合理地控制Littman-Metcalf光栅外腔半导体激光器的外腔参数可以将中心波长为785 nm半导体激光器的本征线宽压窄四个数量级,该外腔系统中准直透镜位置失调会影响系统出射光场与经外腔反馈光场之间的耦合效率,进而影响光栅外腔半导体激光器的输出线宽。     

半导体激光器等效电路模型及其参数提取

从半导体激光器的速率方程出发,讨论了DFB半导体激光器的等效模型以及模型中各个参数的提取方法.分析表明该等效电路模型可以与后端封装设计级联,从而得到端到端的仿真结果,有助于提升工程上光电模块的设计效率.     

1．3μm外腔粘接型窄线宽InGaAsP单模半导体激光器

外腔半导体激光器具有一些令人瞩目的优点，其中最突出的是它可以提供线宽很窄的单模激光，而且价格低廉。这一特点暂时还不易被其它形式的半导体激光器（如单模的激光二极管，DFB半导体激光器）所取代，因而还有一定的发展前途，这也是现今世界上有不少国家、大学和研究机构积极从事外腔半导体激光器研制的原因。     

Linewidth enhancement for DFB lasers due to longitudinal field dependence in the laser cavity

To calculate the linewidth for an index-guided semiconductor laser, one usually neglects a correction factor for the spontaneous emission rate, which is introduced by the longitudinal field distribution within the laser cavity. For FabryPerot lasers with cleaved facets the correction factor is small. However, for DFB lasers this correction factor may become quite significant, yielding a linewidth enhancement for DFB laser diodes.     

The optical gain coupling saturation effect on the linewidthproperty of complex coupled DFB lasers

The cavity length dependence of the linewidth property of complex coupled (CC) DFB lasers is investigated. In CC-DFB lasers with a fixed geometrical structure of the active region, the cavity length strongly affects the ratio of index coupling strength to the gain coupling one, which results in the variation of the effective linewidth enhancement factor α_eff. It is also found that pure gain coupled (GC) DFB lasers have the saturation characteristic in the linewidth power product, with the extension of the cavity length, These results indicate the importance of the selection of the cavity length in CC-DFB lasers     

Analysis of the phase-amplitude coupling factor and spectrallinewidth of distributed feedback and composite-cavity semiconductorlasers

A Green's function approach to the analysis of semiconductor lasers is formulated in a form suitable for complex cavity structures. Both the spontaneous emission rate and the effective phase-amplitude coupling factor can be accurately evaluated. For distributed-feedback (DFB) lasers, the spontaneous emission rate is strongly dependent on both the facet reflectivities and the grating coupling coefficients. The effective phase-amplitude coupling factor depends on the wavelength detuning from the gain maximum. The calculated linewidth of DFB lasers differs considerably from previous calculated results and gives better agreement with experimental results. For composite-cavity lasers, the frequency dependence of the equivalent reflectivity has a strong impact on the phase-amplitude coupling factor and the spontaneous emission rate. Distributed Bragg reflector (DBR) lasers are investigated as an example of a composite-cavity structure     

Dynamic and noise properties of tunable multielectrodesemiconductor lasers including spatial hole burning and nonlinear gain

A general formalism based on the Green's function method is given for multielectrode semiconductor lasers. The effects of both spatial hole burning and nonlinear gain are included in this formalism. An effective nonlinear gain is introduced by taking into account the influence of the laser structure and the associated distribution of the mode intensity along the cavity length and the frequency and intensity modulation properties of multielectrode semiconductor lasers are studied. A general linewidth expression which includes contributions from spontaneous emission and carrier shot noise is given. It is found that the effective α-factor affecting the linewidth is in general different from its counterpart affecting modulation and injection locking properties due to spatial hole burning and nonlinear gain. The linewidth due to various contributions is calculated for both uniform intensity distributed lasers and phase-shifted distributed feedback (DFB) lasers     

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.     

Analysis of the spectral linewidth of distributed feedback laser diodes

The spectral linewidth of distributed feedback (DFB) laser diodes is theoretically studied. Numerical calculation shows that DFB lasers with long cavity lengths and large coupling coefficients have very narrow spectral linewidth less than 1 MHz, The effects of the phase shift and mirror facets on the spectral characteristics of DFB lasers are also analyzed, It is shown that the phase-shifter further narrows the spectral linewidth of DFB lasers. Its numerical result and physical meaning are also shown.     

Five wavelength DFB fibre laser source for WDM systems

Singlemode UV-induced distributed feedback (DFB) fibre lasers with a linewidth of <15 kHz and a sidemode suppression better than 61 dB are presented. The stability of the lasers is verified by a 10 Gbit/s transmission experiment. Five DFB fibre lasers are cascaded and pumped by a single semiconductor laser, thereby forming a multiwavelength source for WDM systems     

Extremely narrow linewidth ( approximately 1 MHz) and high-power DFB lasers grown by MOVPE

A suitable structure of narrow linewidth DFB laser is studied experimentally. By thinning the active layer to around 0.07 mu m, controlling kappa L to 1.0, and improving the geometrical uniformity of active region, the linewidth less than 1 MHz is achieved at an output power of around 20 mW in 1.55 mu m DFB lasers with 1.2 mm long cavity length.<>