Multi-stage coherent beam combination of semiconductor optical amplifiers in ready-made fiber couplers

Abstract

We report on multi-stage coherent beam combination (CBC) of continuous-wave (CW) outputs from semiconductor optical amplifiers (SOAs) in ready-made fiber couplers. The first CBC stage combines two 120-mW outputs from SOAs seeded by an extended-cavity diode laser (ECDL) at 1458 nm in a 2×2 50%:50% fiber coupler. Two beams generated by two such CBC setups are then combined in the second stage. By concatenating three stages we obtained an output power of 723 mW at 1458 nm from eight SOAs with a total combining efficiency of 75.3%. Stable power generation without interrupts nor degradation over three days was successfully implemented using a simple low-bandwidth servo system. An averaged single-stage combining efficiency of 89.5% deduced from seven CBC setups constituting the three-stage CBC is used to estimate scaling to further stages. As a practical application the output is used to second harmonic generation (SHG) in a nonlinear crystal to achieve an output power of 239 mW at 729 nm.