Spectral and spatial mode control in self-seeded semiconductor disk laser using optical feedback from fiber Bragg grating

Abstract

Semiconductor disk laser with mode control using the feedback from a partially reflecting fiber Bragg grating. With seed signal, the wavelength is locked to the Bragg wavelength and beam quality factor M 2 decreases from 1.6 to below 1.05. .Optically pumped semiconductor disk lasers (SEDLs), also known as vertical-external-cavity surface-emitting lasers, provide an attractive opportunity for producing tunable narrow-line radiation with diffraction-limited beam and output power scalable to multi-Watt level [1, 2]. SEDLs have low single-pass gain and, consequently, are very sensitive to cavity loss. Therefore, it is always desirable to minimize losses by reducing the number of cavity elements and mode control using means auxiliary to the laser cavity would be preferable.Here we report a narrow-linewidth self-seeded SEDL operating around 1-μm with spectral characteristics controlled using an optical feedback from fiber Bragg grating (FBG). The laser gain structure was designed for operation around 1050 nm and it comprises a 30.5-pair GaAs/AlGaAs distributed Bragg reflector and an amplifier section with 13 non-straincompensated Ga 0.74 In 0.26 As quantum-wells grown monolithically on a GaAs substrate by molecular beam epitaxy. In order to improve the heat transfer from the gain section, a transparent diamond heat spreader of 300-μm thickness was capillary bonded on the top of the 2.5×2.5 mm gain sample. The gain sample was mounted on a water-cooled copper heat sink. The diamond-air interface was coated with a two-layer TiO 2 -SiO 2 film to reduce pump and signal reflection. The laser cavity, shown in Fig. 1, had a V-shaped configuration consisting of the gain mirror, a folding mirror with radius of curvature RoC=200 mm and reflectivity R=99,5% and a plane output mirror with reflectivity R=95%. The gain structure was optically pumped with an ∼800-nm multimode fiber-coupled diode system at an angle of about 35°. The pump spot diameter on the gain media was about 180 µm, which matches the size of the fundamental cavity mode derived from numerical simulation. During all measurements, the temperature of the copper mounts was kept at 15°C. A fiber Bragg grating placed behind output mirror provides the seed signal to the laser cavity. The light transmitted through the fiber Bragg grating was monitored as a laser output. Fig. 1. Schematics of laser setup.5%-output coupler 808 nm pump Curved mirror Gain mirror Output Fiber Bragg grating 5%-output coupler 808 nm pump Curved mirror Gain mirror Output Fiber Bragg grating a2395_1.pdf JWA120.pdf ©OSA 1-55752-834-9