Deterministic stabilization of eight-way 2D diffractive beam combining using pattern recognition

Abstract

We demonstrate a new method for controlling diffractive, high power beam combination, sensing phase errors by analyzing the intensity pattern of uncombined side beams at the output. A square array of eight beams is combined with <0.3% stability and 84.6% efficiency. As channel count is increased, so does the usable information, enabling scaling to large channel counts without significant slowing of control loop response time, an advantage over single-input algorithms.

Fiber laser development enabled by machine learning: review and prospect

“…Phase detection in classic active phase-locking can be divided into two categories: direct and indirect detection. Direct ones yield high accuracy while requiring complex experimental structures, such as the heterodyne detection method [144,145], interferometric phase measurement method [146], phase-intensity mapping method [147], and pattern recognition method [148]. Indirect detection techniques utilize electrical modulation and demodulation to find phase information, typically dithering techniques [149][150][151][152] and stochastic parallel gradient descent (SPGD) algorithm [153].…”

Machine Learning Pattern Recognition Algorithm With Applications to Coherent Laser Combination

“…Control challenges in complex CBC lasers include large dimensionality in the control parameters. For example in a two-dimensional, N×M beam combination system with a diffractive optical element [8], [12], the number of input phase control variables is N×M, and the output/observable variables include (2N-1)×(2M-1) beams in an interference pattern. Optical coherence stabilization requires fast control to suppress noise from the environment with high bandwidth [12].…”

“…For example in a two-dimensional, N×M beam combination system with a diffractive optical element [8], [12], the number of input phase control variables is N×M, and the output/observable variables include (2N-1)×(2M-1) beams in an interference pattern. Optical coherence stabilization requires fast control to suppress noise from the environment with high bandwidth [12]. Also, measurement of laser intensity loses phase information when using an optical power measurement from cameras or This work is supported by the Office of Science, Office of High Energy Physics, of the U.S. Department of Energy under contract no.…”

Towards Ultimate High-Power Scaling: Coherent Beam Combining of Fiber Lasers

“…They theoretically showed that, by implementing two DOEs, combining pulses with widths down to 30 fs can be achieved without the significant combining loss, while 300 fs is the onset of remarkable combining loss for combining with a single DOE. There have been significant advancements in CBC of high-power fiber lasers via DOEs in both pulsed and CW fiber lasers in recent years, leading to multi kW output power in the CW regime and CBC of eight femtosecond laser in 2D [181,[183][184][185][186][187][188][189][190].…”

“…In 2019, Du et al demonstrated a new version of the PIM-based phase-locking algorithm based on intensity pattern recognition of the uncombined beams [190]. One year later, they managed to produce 81 independently controllable beams and then coherently combined them via DOE [153].…”