High brilliance photonic band crystal lasers

Abstract

High concentration of optical power in a narrow exit angle is extremely important for numerous applications of laser diodes, for example, for low-cost fiber pumping and coupling, material processing, direct frequency conversion, etc. Lasers based on the longitudinal photonic band crystal (PBC) concept allow a robust and controllable extension of the fundamental mode over a thick multi-layer waveguide region to achieve a very large vertical optical mode spot size and, consequently, a very narrow vertical beam divergence. Many undesirable effects like beam filamentation, lateral multimode operation and catastrophic optical mirror damage (COMD) are strongly reduced. 650 nm GaInP/GaAlInP PBC lasers show narrow far field pattern (FWHM~7º) stable up to the highest output powers. Differential efficiency up to 85% is demonstrated. Total single mode output power as high as 150 mW is achieved in 4 µm-wide stripes in continuous wave operation, being limited by COMD due to not passivated facets. The lateral far field FWHM is 4 degrees. 840 nm GaAs/GaAlAs PBC lasers show a vertical beam divergence of 8 o (FWHM) and a high differential efficiency up to 95% (L=500 µm). A total single mode CW power approaches 500 mW for 1 mm-long 4 µm-wide stripes devices at ~500 mA current, being COMD-limited. The lateral far field FWHM is 5 degrees. Another realization of a longitudinal PBC laser allows lasing in a single high-order vertical mode, a so-called tilted mode, which provides wavelength selectivity and substantially extends the possibility to control the thermal shift of the lasing wavelength. In a multilayer laser structure, where the refractive index of each layer increases upon temperature, it is possible to reach both a red shift of the lasing wavelength for some realizations of the structures, and a blue shift for some others. Most important, the absolute thermal stabilization of the lasing wavelength of a semiconductor laser can be realized.