广义两段式半导体激光器的特性研究

利用由射线法导出的两段式半导体激光器(2SLD)的端面输出谱的表达式,研究了两电极半导体激光器(2ELD)和外腔式半导体激光器(ECLD).结果表明;2ELD的振荡波长并非始终都与腔的共振波长相同;在ECLD上实现准连续调谐的关键是使激光器能被调谐在二极管的反共振波长处振荡,因此,我们求得了ECLD实现反共振激射的阈值载流子数密度以及对界面反射率的要求的表达式。     

实现外腔半导体激光器连续调谐的两个基本要求

定量讨论了实现外腔式半导体激光器连续调谐的两个基本要求:同时改变外腔长度及光栅反射波长,半导体激光器(LD)端面镀减反膜。分析表明:前人给出外腔的可调整范围并非是实现最大调谐范围的必要条件,而是实现调谐连续性的一种可行选择。针对具体的减反射膜,对在ECLD上可能实现的连续调谐范围进行了研究。     

调谐外腔半导体激光器输出双稳环的确定

在考察了外腔半导体激光器(ECLD)的振荡频率ν与激光二极管(LD)中载流子密度N(或增益g)、介质的折射率n以及LD第m个模式的共振频率νm间的关系之后,利用微扰法对LD的N-ν曲线上被前人错判为不稳定的两个关键区段重新进行了分析,结果表明这两个区段是稳定区段,据此,可以确定在对ECLD进行调频的过程中其增益介质的N-ν曲线上出现的双稳环.     

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。     

外腔半导体激光器激射波长温度稳定性的研究

在考虑了光纤光栅(FG)的相位分布之后,根据光纤光栅外腔半导体激光器(FGESL)所满足的阈值条件,从理论上研究了前端面反射率对光纤光栅长外腔半导体激光器(LECFGSL)激射波长温度稳定性的影响.数值模拟的结果表明:随着温度的变化,LECFGSL的激射波长围绕光栅布拉格反射波长上下波动,激光器前端面反射率对激射波长波动幅度有较大的影响,当前端面反射率＜10-4时,激射波长与光栅布拉格反射波长基本一致,其温度稳定性较好.     

光反馈对光纤光栅外腔半导体激光器特性的影响

主要研究了外加光反馈对光纤布拉格光栅外腔半导体窄线宽激光器特性的影响。在研究温度对光纤光栅外腔半导体激光器激射波长影响的基础上,设计了强度可调的外加光反馈系统,并利用延时自外差法测试外腔半导体激光器的线宽,从实验上分析了不同强度的外加光反馈对外腔半导体激光器线宽和噪声的影响。实验结果表明,在外加光反馈强度逐渐增强的过程中,激光器线宽逐渐变窄。当反馈比为-22dB时,激光器线宽被压窄至原始线宽的15%。与此同时,在相同的反馈变化下,激光器的相对强度噪声开始无明显变化,直到反馈比达到-27dB。再继续增大反馈强度,相对强度噪声显著增大,激光器内部发生相干崩塌。     

液晶可调谐VCSEL中高对比光栅结构的设计

基于严格耦合波理论设计了一种以液晶为低折射率材料的Si-SiO2复合高对比光栅,该光栅适合用于实现液晶可调谐功能的垂直腔面发射半导体激光器件。当940nm的TM偏振光入射时,通过优化参数可得到宽带(Δλ=256nm)高反射率(R>99%)且具有偏振稳定性的光栅结构,满足垂直腔面发射半导体激光器顶部腔面反射镜要求。液晶折射率的改变不会影响光栅的性能,未来有望将高对比光栅或混合光栅与液晶可调谐垂直腔面发射半导体激光器相结合,实现可调谐半导体激光器。     

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。     

光纤光栅外腔半导体激光器输出特性耦合效率的研究

本文采用射线追踪法,导出了光纤光栅外腔半导体激光器(FGESL)的连续输出谱P(λ)及输出功率的隐函表达式.在此基础上,结合载流子速率方程,对外腔半导体激光器的P(λ)及P-I特性进行了研究.结果表明:光纤光栅外腔的输出谱在反射带宽内呈现出多峰结构,峰值与耦合效率有关;随着祸合效率的增大,输出功率整体上呈现上升的趋势,并在上升过程中出现的抖动越来越小.     

基于光栅光阀可调谐半导体激光器外腔结构的设计研究

目的:提出利用光栅光阀(GLV)来精密调节光栅外腔半导体激光器输出波束的新方法。方法:这种基于光栅光阀的可调谐外腔半导体激光器的结构使光栅光阀与闪耀光栅形成了共焦结构,便于使被选择的波束可以原路返回,经过在谐振腔中振荡,最后输出。结果:这种基于光栅光阀结构的可调谐外腔半导体激光器可以任意控制输出或者被过滤掉的相应波束的数量。结论:利用光栅光阀的特性,这种可调谐外腔半导体激光器能有效地实现激光输出波束的精密调谐,同时也降低了调谐的机械难度。     

Maximum and Continuous Wavelength Tuning Ranges of a Grating External—cavity Laser Diode

The wavelength tuning rages of a grating external-cavity laser diode(ECLD)have been studied by the equivalent avity method.The maximum tuning range(MTR)and the continuous tunding range(CTR),which are related to the maximum and the minimum threshold carrier densities,are deduced from the threshold condition.We define a ratio of the CTR to the MRT.This ratio is only determined by the reflectivities of the external and internal facets of the ECLD.The analysis shows that there is an appropriate combination of the external and internalcavity reflectivites to obtain a given CTR in the design of an ECLD.     

Uncooled 1.3-/spl mu/m complex-coupled DFB BH laser diodes with the Fe-doped InGaAsP-InP hybrid current-blocking grating

In this letter, we proposed an alternate method by using the Fe-doped InGaAsP-InP hybrid grating layers to fabricate the 1.3-/spl mu/m current-blocking-grating complex-coupled distributed-feedback (CBG CC-DFB) laser diodes (LDs) grown by metal-organic chemical vapor deposition (MOCVD). By combining the Fe-doped InGaAsP-InP grating layers, the CBG CC-DFB LDs can provide high optical DFB coupling coefficient and high current confining ability. Moreover, the current aperture in the lateral direction can be easily controlled by the self-aligned MOCVD regrowth process. Therefore, the manufacture of CBG CC-DFB buried heterostructure LDs is easy as the ridge-waveguide LDs. The LDs exhibit a low threshold current of 5.3 mA, a high slope efficiency of 0.42 mW/mA, and a stable single mode with a high sidemode suppression ratio of /spl sim/42 dB at two times the threshold (10.5 mA). Even at high temperatures, these LDs still have an extremely low threshold current of 15.8 mA at 90/spl deg/ and a small variation in slope efficient of only -1 dB at the temperatures between 20/spl deg/ and 80/spl deg/. Furthermore, these LDs show a high-speed characteristic of more than 11.8 GHz at 20/spl deg/, which are suitable for 10-Gb/s Ethernet and OC-192 applications.     

解析式表示外腔半导体激光器的特征参量

用射线法研究了强反馈可调谐外腔式半导体激光器的阈值行为，导出了ＥＣＬＤ被财在不同波长振荡所需的阈值载流子数密度外腔长度及阈值电流的解析表达式，也得到了不同电流ＥＣＬＤ的调谐输出功率及载流子密度的表达式。     

DFB LD manufactured by nanoimprint lithography

Gratings of distributed feedback laser diodes (DFB LDs) have been successfully manufactured by nanoimprint lithography (NIL). Uniform gratings with periods of about 240 nm and phase-shifted in the center have been fabricated by a soft press NIL employing a polymer stamp technology. Moreover, the shape of the grating is rectangle, rather than sinusoidal by holography.The test results show good characteristics of the electrical and spectral output. The results of this study indicate that NIL has high potential for the manufacture of DFB LDs.     

A two-step laterally tapered 1.55-/spl mu/m SSC DFB laser fabricated by using a nonselective grating process

We demonstrate a two-step laterally tapered 1.55-/spl mu/m spot size converter distributed feedback laser diode (SSC DFB LD) having a planar buried heterostructure-type active waveguide and a ridge-type passive waveguide fabricated by using a nonselective grating process. Unlike conventional SSC DFB LDs, where a selective grating is employed, this SSC DFB LD employed a nonselective grating over the entire device region in order to make its fabrication much simpler than that of the conventional SSC DFB LDs. The two-step laterally tapered SSC is effective in removing an unwanted wavelength peak originating from the SSC section having a multiquantum well and a grating under it. The fabricated SSC DFB LD operates at 1.553-/spl mu/m wavelength and shows a far field pattern in horizontal and vertical directions of 13.4/spl deg/ and 19.5/spl deg/, respectively.     

H表达的ECLD双稳环环宽的研究

采用H参量简化模型研究光栅调谐外腔半导体激光器的双稳特性,导出以H参量表达的双稳环环宽解析式,给出了其适用范围,得到剩余反射率减小时导致双稳环消失的临界值,然后数值模拟了光栅反射率、谱线展宽因子、H参量、剩余反射率对载流子密度与频率关系曲线的影响,从中发现了剩余反射率增大时也存在双稳环环宽为零的情况,数值计算了剩余反射率极限值,并指出了环宽极大值的位置。     

1.5μm波段乙炔气体稳频光纤光栅外腔半导体激光器

为了提高1.5μm波段激光器的频率稳定性,利用乙炔分子饱和吸收稳频,设计了一种稳频的光纤光栅外腔半导体激光器。其通过步进电机对光纤光栅进行拉伸调节波长,实现了激光频率调谐。结果表明,所研制的激光器拥有较高的频率稳定度。     

Wideband frequency-response measurement of optical receivers usingoptical heterodyne detection

Measurements have been carried out using 1.3-μm distributed-feedback laser diodes (DFB-LDs). The frequency difference of the LDs is continuously varied with temperature changes of a few degrees and the spectral linewidth of one of the LDs is narrowed by optical feedback using a grating. Wideband, highly sensitive measurement has been achieved for a p-i-n photodiode and a Ge avalanche photodiode from DC to 20 GHz. The result is compared with that of the pulse spectrum analysis (PSA) method. Although the finite pulsewidth in the PSA method causes roll-off in the frequency response, the optical heterodyne method has the advantage for very wideband frequency response measurement. The S/N ratio in the optical heterodyne method can be made as high (~40 dB) as that of the PSA method by narrowing the spectral linewidth of DFB-LDs     

Low threshold operation of 1.55 μm GaInAsP/InP DFB-BH LDsentirely grown by MOVPE on InP gratings

1.55 μm GaInAsP/InP DFB-BH LDs on corrugated InP substrates were fabricated by only two-stage MOVPE including burying layer growth. The 9 mA minimum threshold current was achieved with both facets cleaved, which the authors believe is the lowest among MOVPE grown DFB LDs with InP grating. Up to 20 mW maximum output power and 0.21 W/A differential quantum efficiency were also attained under single longitudinal mode operation     

Nanosecond Switching and Wavelength Tuning of External-Cavity Laser Diode Using a Reflective Electroabsorption Modulator

We present a novel technique for ultrafast on-off switching and wavelength tuning of an external-cavity laser diode (ECLD) using an intracavity reflective electroabsorption modulator array as the end mirror. on-off and wavelength switching of the ECLD are based upon the electrically induced control of the modulator's reflectivity yielding a modulation of the cavity losses and hence a modulation of the lasing threshold. We experimentally demonstrate on-off switching of selected wavelengths with a contrast in excess of 40 dB. Ultrafast modulation in the nanosecond-regime has been achieved which is close to the fundamental physical speed limit of the ECLD.