SBS suppression and electronic path length matching in coherent beam combining

US11831123B2 · kind B2 · utility

Assignee

• Massachusetts Institute of Technology · US

Inventors

• Jason E. Langseth · Malden, US
• Andrew Benedick · Stow, US
• Seth Trotz · Acton, US

Key dates

• Filing date: Mar 8, 2021
• Grant date: Nov 28, 2023
• Expiry date: Jan 28, 2042

Classification

• Technology area (CPC H): Electricity
• CPC primary: H01S2301/03
• WIPO field: Optics
• WIPO sector: Instruments

Abstract

In coherent beam combining, the beams can be phase-modulated with a pseudo-random bit sequence (PRBS) to prevent stimulated Brillouin scattering (SBS) downstream. To coherently combine the phase-modulated beams, however, the PRBS waveforms should be true-time-delayed to within a small fraction of the bit duration. Traditionally, this true time delay is achieved by cutting optical fibers to length or with optical trombones. But trimming fibers is hard to do precisely, and optical trombones have large insertion loss. In addition, the path length mismatch varies as the fibers heat up and/or vibrate. Here, the beams are generated from a kilohertz linewidth seed split among N>1 (e.g., N=100) arms. Each arm is phase-modulated with a separate copy of the unique PRBS pattern. The relative phase of the PRBS patterns is stabilized by phase-locking the master oscillators used to read out the PRBS patterns. The PRBS patterns can be phase shifted with respect to one another to compensate for physical path length mismatches of the optical fibers. Scanning the relative phase of the PRBS pattern used to modulate different arms yields a cross-correlation peak in combined power when the phases are m…