Realization of High Power Narrow Beam Divergence in Photonic-Crystal Surface-Emitting Laser

The photonic-crystal surface-emitting laser (PCSEL) is an attractive semiconductor laser in which a thin two-dimensional photonic-crystal (2D-PC) layer is incorporated into the ordinary broad area edge-emitting laser structure to control the longitudinal-transverse mode owing to diffraction. In principle, the zero group velocity effect at the band edge of the 2D-PC is utilized as a resonator and can be used for the unique properties including large-area coherent oscillation as well as arbitrary beam controlling, which includes the polarization, beam patterns, directions, and generation of vector beams. We investigated the PCSEL toward realizing a practical device that has high power and high beam quality. Here, we show our recent progress. The device structure, which consists of an InGaAs/AlGaAs material system on n-GaAs substrates, is based on an ordinary broad area edge-emitting laser structure except it has a thin 2D-PC layer. The 2D-PC layer is placed near the active layer, and both are embedded between the p and n cladding layers. It is fabricated by using EB lithography, dry etching, and regrowth or MOCVD. The square emitting area has side of 200 micrometers, and transverse modes are well controlled in the entire region. The output power is more than 0.75 W with a single wavelength of 966 nm, and the narrow beam divergence is as narrow as 1 degrees under continuous wave (CW) operation at room temperature. The beam quality is superior with an M-2 of 1.1, which is almost the same as that of the ideal Gaussian beam.