Stabilization and Noise Reduction of DFB Laser by Incoherent Optical Feedback using FP-Resonator

在相干光通信系统中，半导体激光器必须达到稳频和窄化的目的。在我们的研究计划中，这旨在通过加载一个具有高精细度的FP谐振器并通过将其波长控制在FP谐振器反射曲线的正斜率的部分来实现。该方法的优点在于，负反馈的量仅通过由于载流子效应而改变有源层的折射率来确定。但是，上述方案存在以下缺点：a)FP腔的高灵敏度与相应的带宽窄化之间存在折衷；b)FP腔的输入端存在大量的光反射；c)FP腔的偶数阶光反射存在残余相干光反馈。此外，实验证实，与迈克尔逊干涉仪相比，使用高精细度的FP谐振器并没有显示出明显的优势。另一方面，有报道称，一些研究正在利用TM光注入的效应来确定半导体激光器的动态参数、波长转换方案、皮秒脉冲产生和偏振双稳。针对这些情况，我们将研究问题转向TM光注入的基本性质。作为结果，我们实现了一种在TM光影响下测量增益压缩因子的实验方法，以及对DFB激光器偏振双稳的分析研究，这两种方法分别发表在IEEE光子学技术快报和IEEE光波技术杂志上。

For the purpose of coherent optical communication system, semiconductor lasers should be frequency stabilized and its spectral linewidth should be narrowed. In our research plan, this is intended to achieve by loading a FP resonator having a high finess and by controlling its wavelength at a portion on the positve slope of the reflection curve of the FP resonator. This method has an advantage that amount of negative feedback is determined only by changing the refractive index of the active layer due to the carrier effect. So the system is free from the roll-off attributable to the parasitic capacitance and inductance.However, it has been found that the above scheme has the following drawbacks ; a) there exists a tradeoff between a high sensitivity of FP resonator and the corresponding bandwidth narrowing, b) there exists a considerable amount of light reflection from the input facit of FP resonator, and c) there exists a residual coherent light feedback due to the even order light reflections from FP resonator. In addition to these, it has been experimentally confirmed that employment of a FP resonator having a high finess does not exhibit a remarkable advantage as compared with other interferometer such as Michelson's.On the other hand, it has been reported that a number of studies are taking advantage of the effects of TM light injection in determining the dynamic parameters of semiconductor lasers, wavelength conversion scheme, picosecond pulse generation and polarization bistability. In relation to these circumstances, we turned our research issue to the fundamental properties of TM light injection. As results of that we have achieved a new method for experimental determination of gain compression factors in the presence of TM light infection, and analytical study of polarization bistability of DFB laser, which were accepted for publication in IEEE Photonics Technology Letters, and IEEE J. of Lightwave Technology, respectively.