Coherent beam combining technology is a high output method of laser systems [1,2]. However, such technology is complicated because light has a wave nature. Achieving coherent addition using optical fibers is also difficult with conventional technology because the optical phase in an optical fiber fluctuates due to such disturbance as temperature drift in the ambient condition. In this study, we attempted accurate control of optical phases with aluminum coated fibers (ACF) to which electricity power was applied and developed a coherent addition fiber amplifier system using the technology of optical phase control with ACF. Besides, we composed a coherent addition fiber amplifier system with Faraday rotator mirrors (FRM) to compensate polarization changes due to the birefringence in optical fibers.
We experimented about coherent addition of amplified spontaneous emission (ASE) to examine whether our coherent addition amplifier system can combine very low coherent lights. We achieved a maximum coherent addition efficiency of almost 98% and succeeded in suppressing the coherent addition output changes to less than 0.1dB using ACF. Our coherent addition amplifier system with FRM permitted stable and high-efficient coherent addition without relying on the state-of-polarization.