Coherent polarization beam combining of three lasers using phase-to-amplitude modulated optical heterodyne phase-locking technique

Abstract

Coherent polarization beam combining （CPBC） is an effective method to obtain a high-brightness laser with linear polarization state. In this paper, we propose a method to apply optical heterodyne detection to CPBC. An optical phase modulation is implemented to transform the phase difference of two beams to amplitude modulation for polarization state detection. The CPBC of two lasers with the same frequency is realized by linear proportional-integral-derivative (PID) phase-locked control. Based on this principle, a three-channel CPBC system is realized to obtain a linearly polarized output beam with a high PER. The PER obtained in the experiment reached 17.44 dB with the output power of 431 mW, while the control bandwidth is 66.1 kHz. The residual phase noise of the first-stage CPBC system achieved to 1×10-4 rad/ √Hz at 1 Hz and 4×10-6 rad/ √Hz for more than 100 Hz.Compared with other CPBC phase-locking methods, this method can effectively suppress phase noise and has a significant improvement in control bandwidth and polarization extinction ratio.