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

为了实现相干光通信系统，需要对半导体激光器进行频率稳定和谱线宽度的收窄。在我们的研究计划中，我们打算通过加载一个高光洁度的FP谐振器，并通过控制其波长在FP谐振器反射曲线的正斜率上的一部分来实现这一点。该方法的优点是，由于载流子效应，仅通过改变有源层的折射率来确定负反馈的量。因此，系统不受寄生电容和电感引起的滚降的影响。然而，我们发现上述方案存在以下缺陷：a)在FP谐振器的高灵敏度和相应的带宽收窄之间存在权衡，b) FP谐振器的输入面存在相当数量的光反射，c)由于FP谐振器的偶阶光反射，存在残留的相干光反馈。除此之外，实验证实，与其他干涉仪（如迈克尔逊干涉仪）相比，使用高精密度的FP谐振器并不具有显着的优势。另一方面，据报道，许多研究正在利用TM光注入的影响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性。针对这些情况，我们的研究课题转向了TM光注入的基本特性。在此基础上，我们实现了一种新的TM光感染下增益压缩因子的实验测定方法，以及DFB激光器偏振双稳性的分析研究，分别被IEEE Photonics Technology Letters和IEEE J. of light wave Technology接受发表。

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.