Elucidation of polarization maintaining mechanism and Establishment of suppressing techniques of polarization fluctuation in fibers

近年来，光纤传输系统、光纤传感器等光纤系统的研究与发展取得了长足的进展。这些光纤系统通常采用普通单模光纤。在通常的光纤传输系统中，当使用普通单模光纤时，发射器和接收器中的光器件必须是与偏振无关的。所以系统变得复杂了。随着比特率的提高，极化模态色散对传输中比特率的限制不容忽视。为了实现简单、低成本的光纤传输系统，采用保偏光纤是有效的。然而，使用保偏光纤的光纤传输系统还没有得到充分的研究。在光纤陀螺中，采用保偏光纤可以提高陀螺的精度。在这些光纤系统的构建中，通常采用热扩散扩展芯（TEC）技术来降低损耗和器件集成。然而，在传统保偏光纤中应用TEC技术时，由于模式场呈椭圆形，模式场不容易扩展。本文研究了基于保偏光纤的偏振光基波波分复用传输系统。在该系统的各个部分，对发射功率和极化串串进行了澄清。测量了光脉冲模式传输过程中的误码率。设计了适合TEC技术的保偏光纤。理论上表明，在几百米光纤系统中，极化得到了充分的维持，并可推导出较大的模场扩展。此外，在TEC技术应用中考虑了掺杂物扩散引起的折射率分布。

Recently, researches and developments of optical fiber systems, such as optical fiber transmission systems and optical fiber sensors, are progressed. Normal single mode fibers are often used in these optical fiber systems. In usual optical fiber transmission systems, optical devices in transmitters and receivers are necessary to be polarization-independent when normal single mode fibers are used. So the systems become complex. The limitation of bit-rate in transmission caused by polarization modal dispersion cannot be neglected as the bit-rate becomes higher. To realize simple and low-cost optical fiber transmission systems, it is effective to use polarization maintaining fibers. However, optical fiber transmission systems using polarization maintaining fibers have not been sufficiently investigated. In optical fiber gyros, the accuracy of the gyros can be improved using polarization maintaining fibers. In constructions of those optical fiber systems, thermally-diffused expanded core (TEC) techniques are often used to decrease losses and device integration. However, the mode fields cannot be easily expanded in TEC techniques application to conventional polarization maintaining fibers since the mode fields become elliptical.In this research, the basic WDM transmission system using polarized lightwave with polarization maintaining fiber was investigated. In the various part of this system, transmitted powers and polarization crosstalks were clarified. The bit error rate was also measured in the transmission of optical pulse patterns. The polarization maintaining fibers suitable for TEC techniques were designed. It was theoretically shown that the polarization is sufficiently maintained in several hundred meter fiber system and that large mode field expansion can be derived. Moreover, the mode field considering refractive index distribution caused by dopant diffusion in TEC technique application.