Broad aperture semiconductor lasers usually suffer from low spatial quality of the emitted beams. Due to the highly compact character of such lasers the use of a conventional intra-cavity spatial filters is problematic. We demonstrate that extremely compact Photonic Crystal spatial filters, incorporated into the laser resonator, can improve the beam spatial quality, and correspondingly, increase the brightness of the emitted radiation. We report the decrease of the M 2 from 47 down to 28 due to Photonic Crystal spatial intra-cavity filtering, and the increase of the brightness by a factor of 1.5, giving a proof of principle of intra-cavity Photonic Crystal spatial filtering in broad area semiconductor lasers.

In this work, we report an experimental and numerical study of the intracavity spatial filtering in edge-emitting lasers using a chirped photonic crystal (PhC) as the filtering element in the near-field domain. We provide a comprehensive analysis of the near-field PhC filtering scheme and compare it to conventional spatial filtering using a variable width slit in the far-field domain. Using a two-dimensional chirped PhC as a spatial filter, we experimentally demonstrate a brightness enhancement by a factor of 1.3, considering an edge-emitting laser with a 1.5 mm cavity length, consistent with a numerical prediction of brightness enhanced by a factor of 1.7. The experimental results are theoretically confirmed by numerical integration of a spatio-temporal model of the edge-emitting laser. Furthermore, numerical results show that brightness can be further increased over a factor of 2, applying optimized spatial-filtering elements at both the front and rear facets of the lasers.

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A brightness-and power-scalable polarization beam combining scheme for high-power, broadarea semiconductor laser diodes is investigated numerically and experimentally. To achieve the beam combining, we employ Lyot-filtered optical reinjection from an external cavity, which forces lasing of the individual diodes on interleaved frequency combs with overlapping envelopes and enables a high optical coupling efficiency. Unlike conventional spectral beam combining schemes with diffraction gratings, the optical coupling efficiency is insensitive to thermal drifts of laser wavelengths. This scheme can be used for efficient coupling of a large number of laser diodes and paves the way towards using broad-area laser diode arrays for cost-efficient material processing, which requires high-brilliance emission and optical powers in the kW-regime.

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