Seed Sources for Spectral Beam Combining via Brillouin De-Interleaving of 1 μm Frequency Combs

Abstract

Spectral Beam Combining (SBC) of multiple fiber laser modules enables high power scaling with applications in material processing and defense. However, it requires multiple laser diodes as seed sources, and each source needs an individual control unit, increasing the system cost and complexity. In contrast, de-multiplexed Optical Frequency Comb (OFC) lines can serve as efficient seed sources for SBC, requiring only a small number of laser diodes to begin with. Owing to the availability of highly efficient gain media such as Yb-doped Fiber Amplifiers (YDFA) for generating high-power laser sources, power scaling using SBC is favorable in the $1~\mu $ m wavelength band. However, due to a dearth of components such as phase modulators and high-resolution de-multiplexers, implementing SBC using frequency combs at this wavelength becomes challenging. In this work, we solve this problem by generating a frequency comb-based seed source with a large channel spacing by de-interleaving a low repetition rate comb using the Vernier effect in Brillouin amplification process. We have obtained a frequency comb with a repetition rate of 34 GHz by selectively amplifying a few lines of an 8.5 GHz repetition rate seed comb using a pump comb with a slightly higher rep-rate (~11.3 GHz). The de-interleaved comb lines are de-multiplexed with a grating-based de-multiplexer, providing ~20 dB of inter-channel suppression and delivering a few mWs of power per channel. This promises to be a compact, easy-to-integrate replacement for multiple seed sources in SBC systems at $1~\mu $ m.