Joint Research on Gain-Coupled DFB Semiconductor Laser

增益耦合DFB半导体激光器联合研究

• 批准号: 06044060
• 负责人: TADA Kunio
• 金额: $ 4.35万
• 依托单位: University of Tokyo
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for international Scientific Research
• 财政年份: 1995
• 资助国家: 日本
• 起止时间: 1995 至 1996
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-06044060/
• 关键词: semiconductor laser; distributed-feedback laser; DFB laser; gain coupling; coupling coefficient; quantum well disordering; wavelength tunable; electro-absorption modulator

1. Measurement of gain coupling coefficient : Although the gain-coupling coefficient is the most imporant device parameter in the gain-coupled (GC) distributed-feedback (DFB) laser, there has been no measurement method for it. Here we studied, with the University of Gent, extraction of parameters including index and gain coupling coeffcients from DFB lasers by minimum-square-fitting theoretical subthreshold spectrum with the experimental one. As a result, it has become possible for the first time to measure and extract, for example, an index-coupling coefficient of 56.4cm_<-1> and a gain-coupling coefficient of 22.3cm_<-1> out of a complex-coupled DFB laser. Also, this method permits to determine the facet reflectivity and phase. Moreover, the linewidth enhancement factor can be extracted if the subthreshold spectrum is measured at different bias levels.2. Disordering of stratined InGaAs/InGaAIAs quantum wells on InP substrates : The above-mentioned quantum wells were grown by molecula … More r beam epitaxy at the University of California. The samples were next capped with SiO_2 and/or SiN films by plasma-assisted chemical vapor deposition (p-CVD) that were made into patterns later. Then, rapid thermal annealing (RTA) was applied to the whole sample to disorder the quantum wells. Photoluminescence (PL) from such samples was taken so that the degree of disordering could be evaluated by the PL wavelength shifts. Consequently, it was verified that the SiO_2 worked as a disordering promoter whereas the SiN worked as a protective cap which suppressed the disordering. The stress existing in the strained quantum wells was found to cause the disordering the RTA heating process regardless of whether the cap film was deposited or not. Finally, the in-plane spatial resolution of the selective disordering was evaluated through microscopic PL measurement. As a result, it turned out that microfabrication down to 2mum was possible by such processing.3. Analysis and fabrication of distributed forward-and backward-coupling wavelength-tunable laser : In wavelengthdivision multiplexed (WDM) optical communication systems, wide-range wavelength tunability is required in semiconductor lasers. However, in the GC DFB laser, tunable oscillation wavelength has not been possible so far. Here we proposed and studied, in collaboration with University of Gent, "distributed forward-and backward-coupling (DFBC) " structure that brings about wide-range wavelength tunability in the GC DFB laser. This structure has a sampled grating above the active layr, and a codirectional passive waveguide for shifting refractive index below the active layr. The sampled grating provides backward feedback necessary for laser oscillation, whereas the codirectional forward coupling between the active and the passive waveguides provides wavelength-filtering function. A small change in the index of the codirectional passive waveguide results in a large change in the wavelength selected by the filter, and thereby a wide-range tuning is made possible. Making use of the F-matrix analysis, we simulated wavelength tuning characteristics of a 1.55mum purely-gain-coupled DFBC laser, and found that index change as small as 0.03 in the codirectional passive waveguide could give rise to lasing wavelength shift as large as 100nm. Next, we designed a DFBC laser in 0.8mum wavelength region, and did preliminary fabrication experiment. After the first step MOCVD (organo-metallic vapor phase epitaxy), the sampled grating was formed by a newly-developed method of dual photoresist coating. Then, the second step MOCVD as well as a number of photolithography steps were carried out to complete the DFBC structure. We verified electrical diode characteristics and spontaneous emission in the fabricated sample, and thereby the fundamentals of the DFBC laser fabrication were established.4. Monolithic integration of a GC DFB laser and an external EA modulator : In collaboration with Tsinghua University, we fabricated a GC DFB laser integrated with an electro-absorption (EA) modulator. By detuning the DFB wavelength toward the longer side with respect to the gain profile peak, we could use identical quantum wells in both the laser and the modulator sections. As a result, whole structure was made by only two MOCVD growth steps. Due to the facet reflection insensitivity of the GC DFB,the laser oscillated in a single mode, and the modulator had sufficient extinction ratio.5. Analysis of analog modulation distortion in GC DFB lasers : The second-and third-order harmonic distortions which affect analog applications very much were analyzed in collaboration with University of Gent. Consequently, GC DFB lasers were found to generally possess a little smaller distortion than conventional DFB lasers due to smaller longitudinal spatial hole burning. The improvement could be as large as 10 dB in some cases. Less

1.增益耦合系数的测量：增益耦合系数是分布反馈（DFB）激光器中最重要的器件参数，但目前还没有一种测量方法，本文与英国Gent大学合作，研究了用最小平方拟合理论亚阈值谱与实验亚阈值谱的方法提取DFB激光器的折射率和增益耦合系数等参数。结果，第一次有可能测量和提取例如复合耦合DFB激光器的56.4cm-1的折射率耦合系数<-1>和22.3cm-1的增益耦合系数<-1>。此外，该方法允许确定小面反射率和相位。此外，在不同偏压下测量亚阈值谱，可以提取线宽增强因子. InP衬底上InGaAs/InGaAlAs分层量子威尔斯阱的无序化：采用分子束外延生长了上述量子威尔斯阱， ...更多信息 在加州大学的r束外延。然后用等离子体辅助化学气相沉积（p-CVD）法在样品上覆盖SiO_2和/或SiN薄膜，并制成图案。然后，对整个样品进行快速热退火（RTA）以使量子威尔斯阱无序化。从这样的样品的光致发光（PL），以便无序的程度可以通过PL波长偏移进行评估。结果表明，SiO_2作为无序化促进剂，SiN作为抑制无序化的保护帽。发现应变量子威尔斯中存在的应力会导致RTA加热过程的无序化，而不管盖膜是否沉积。最后，面内空间分辨率的选择性无序进行了评估，通过显微PL测量。结果，事实证明，通过这种处理，可以进行低至2 μ m的微细加工。分布式前向和后向耦合波长可调谐激光器的分析和制作：在波分复用（WDM）光通信系统中，要求半导体激光器具有宽范围的波长可调谐性。然而，在GC DFB激光器中，迄今为止，振荡波长可调谐是不可能的。在这里，我们提出并研究，与根特大学合作，“分布式前向和后向耦合（DFBC）”的结构，带来了宽范围的波长调谐的GC DFB激光器。该结构在有源层上方有一个取样光栅，在有源层下方有一个同向无源波导用于改变折射率。取样光栅提供激光振荡所需的后向反馈，而有源和无源波导之间的同向前向耦合提供波长滤波功能。同向无源波导的折射率的小变化导致滤波器选择的波长的大变化，从而使得宽范围调谐成为可能。利用F矩阵分析方法，模拟了1.55 μ m纯增益耦合DFBC激光器的波长调谐特性，发现同向无源波导中折射率变化小至0.03，就能引起100 nm的激射波长漂移。其次，我们设计了一台0.8 μ m波长的DFBC激光器，并进行了初步的制作实验。在第一步MOCVD（有机金属气相外延）之后，采用一种新的双光刻胶涂敷方法形成取样光栅。然后，进行第二步MOCVD以及若干光刻步骤以完成DFBC结构。验证了所制备样品的电学特性和自发辐射特性，为DFBC激光器的制备奠定了基础. GC DFB激光器和外部EA调制器的单片集成：与清华大学合作，我们制作了一个集成了电吸收（EA）调制器的GC DFB激光器。通过相对于增益分布峰值向较长侧失谐DFB波长，我们可以在激光器和调制器部分中使用相同的量子威尔斯。结果，整个结构仅由两个MOCVD生长步骤制成。由于GCDFB的端面反射不敏感性，激光器在单模振荡，调制器有足够的消光比. GC DFB激光器中模拟调制失真的分析：与根特大学合作，分析了对模拟应用影响很大的二阶和三阶谐波失真。因此，发现GC DFB激光器通常具有比常规DFB激光器小一点的失真，这是由于较小的纵向空间烧孔。在某些情况下，改善可能高达10 dB。少

项目成果

戸田知朗: "吸収性回折格子型利得結合DFBレーザの高周波小信号変調特性" 電子情報通信学会総合大会へ投稿済. (1996)

Tomoaki Toda：“吸收光栅型增益耦合DFB激光器的高频小信号调制特性”提交给IEICE大会（1996年）。

Weimin Si: "Theoretical analysis of DFB laser integrated with EA modulator" Extended Abstracts of the Int.Conf.on SSDM'94. PB-4-8. 247-249 (1994)

斯伟民：“与 EA 调制器集成的 DFB 激光器的理论分析”SSDM94 Int.Conf.的扩展摘要。

Kenji Sato: "Wavelength Tuning Simulation of Widely Tunable Distributed Forward-Backward Coupling (DFBC) Simiconductor Laser" Extended Abstracts of 55th Autumn Meeting, Japan Society of Applied Physics. 22-S-8. (1994)

Kenji Sato：“宽可调分布式前向-后向耦合 (DFBC) 半导体激光器的波长调谐仿真”日本应用物理学会第 55 届秋季会议的扩展摘要。

Kenji Sato: "Analysis of distributed forward-and backward-coupling lasers by using mode expansion method" Extended Abstracts of 42nd Spring Meeting, Japan Society of Applied Physics. 30a-ZG-2. (1995)

Kenji Sato：“使用模式展开法分析分布式前向和后向耦合激光器”日本应用物理学会第 42 届春季会议扩展摘要。

江口匡史: "吸収性回折格子に端子を設けた利得結合DFBレーザトライオードの試作" 第42回応用物理学関係連合講演会予稿集. 30a-ZG-5. (1995)

Tadashi Eguchi：“在吸收衍射光栅上提供终端的增益耦合 DFB 激光三极管的原型”第 42 届应用物理协会会议记录（30a-ZG-5）。