Beam combining techniques for high-power high-brightness diode lasers

Abstract

Laser diodes are efficient and compact devices operating in a wide range of wavelengths. Boosting power by beam combining while maintaining good beam quality has been a long-standing challenge.We discuss various approaches for beam combining with emphasis on solutions pursued at DirectPhotonics. Our design employs single emitter diodes as they exhibit highest brightness and excellent reliability. In a first step, after fast axis collimation, all single emitter diodes on one subunit are stacked side-by-side by a monolithic slow-axis-collimator thus scaling the power without enhancing the brightness.The emissions of all diodes on a subunit are locked by a common Volume Bragg grating (VBG), resulting in a bandwidth < 0.5nm and high wavelength stability. Second, two subunits with identical wavelength are polarization coupled forming one wavelength channel with doubled power and brightness. Third, up to five channels are serially spectrally combined using dichroic filters. The stabilized wavelengths enable dense spectral combining, i.e. narrow channel spacing. This module features over 500W output power within 20nm bandwidth and a beam parameter product better than 3.5mm*mrad x 5mm*mrad (FA x SA) allowing for a 100µm, 0.15NA delivery fiber [1].The small bandwidth of a 500-W-module enables subsequent coarse spectral combining by thin film filters, thus further enhancing the brightness.This potential can only be fully utilized by automated manufacturing ensuring reproducibility and high yield. A precision robotic system handles and aligns the individual fast axis lenses. Similar technologies are deployed for aligning the VBGs and dichroic filters.

High-power broad-area buried-mesa lasers

“…in air), enabling the realization of the direct diode lasers for industrial applications, i.e. lasers where the output emission comes directly from the diodes and not from an optically pumped active medium [5].…”

Energy Efficient Laser Beam Welding of Metals with a Ultra-High Brightness Direct-Diode Laser System

“…Nevertheless, direct diode lasers having enough laser power and beam quality for remote welding were not available. Recently, more energy efficient ultra-high brightness direct diode lasers with comparable beam quality to conventional beam sources are available [10,11,12,13] but not yet investigated for welding. In this project, first investigations on welding with such beam sources in conjunction with fixed optics took place to evaluate the application of ultra-high brightness direct diode lasers in laser beam welding.…”

High Coupling Efficiency of the Fiber-Coupled Module Based on Photonic-Band-Crystal Laser Diodes

“…[11] In 2015, direct photonics industries (Germany) developed a continuous wave (CW) 500 W with the beam quality of 5 mm•mrad and the brightness of 41.19 MW/(cm 2 •sr) in a fiber core of 100 µm and NA of 0.22 based on beam shaping, wavelength and polarization beam combination. [12,13] BWT Beijing Ltd. developed a module based on 18 single-emitter laser diodes, providing more than 140 W output power from a fiber with core diameter of 105 µm and NA of 0.15 at the wavelength of 915 nm. The coupling efficiency was over 90% within NA of 0.13.…”