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

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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.