Active coherent beam combining of diode lasers

Abstract

We have demonstrated active coherent beam combination (CBC) of up to 218 semiconductor amplifiers with 38.5 W cw output using up to eleven one-dimensional 21-element individually addressable diode amplifier arrays operating at 960 nm. The amplifier array elements are slab-coupled-optical-waveguide semiconductor amplifiers (SCOWAs) set up in a master-oscillator-power-amplifier configuration. Diffractive optical elements divide the master-oscillator beam to seed multiple arrays of SCOWAs. A SCOWA was phase actuated by adjusting the drive current to each element and controlled using a stochastic-parallel-gradient-descent (SPGD) algorithm for the active CBC. The SPGD is a hill-climbing algorithm that maximizes on-axis intensity in the far field, providing phase locking without needing a reference beam.

Separate phase-locking and coherent combining of two laser diodes in a Michelson cavity

“…The minimization algorithm uses a random exploration of the currents around its nominal value, with a 0.5 mA maximum amplitude. Due to the highly non-linear behavior of the laser cavity, it is noteworthy that the currents are not optimized, strictly speaking -as opposed to the SPGD protocol used in MOPA configurations [3]. Instead, they are corrected in order to ensure the proper phase relationship on the front side, while the external cavity self-adjusts to maintain the phase-locking.…”

“…The feasibility of such architectures has been brilliantly demonstrated with fiber and solid state lasers, showing impressive performance in the past few years. With diode lasers and amplifiers, the highest output power and the largest number of phase-locked semiconductor amplifiers (respectively 40 W and 218) have been demonstrated in the Master-Oscillator Power-Amplifier (MOPA) configuration by Creedon, Redmond and their co-workers at MIT Lincoln Laboratory [3] [4]. They have used arrays of individually-addressed slab-coupled waveguide amplifiers (SCOWA), which typically provide an output power of 1 W per device in a diffraction-limited profile.…”

Integrated phase-locked laser diodes at 1.55μm

“…Recently techniques have been developed based on seeding arrays of semiconductor optical amplifiers (SOAs) from a single laser, to generate output beams that can be combined coherently [2].…”

Dielectric Coating Thermal Stabilization During GaAs-Based Laser Fabrication for Improved Device Yield

“…[1][2][3][4][5] The most recently fabricated devices have been slabcoupled optical waveguide (SCOW) lasers and amplifiers. The SCOW device is fabricated with an epitaxially grown, multiple-quantum-well active region, which emits a large, nearly circular, neardiffraction-limited beam.…”