Mode-Locked 1.33 µm Semiconductor Disk Laser with a Bismuth-Doped Fiber Amplifier

This paper demonstrates a picosecond mode-locked SDL emitting at 1.33 μm with a bismuth-doped fiber amplifier. The 1.33 μm SDL gain chip consisted of an InP-based active region and a GaAs-based distributed Bragg reflector (DBR). Both structures are grown by solid source molecular beam epitaxy (MBE). The active region comprised 10 compressively strained (1%) AlGaInAs quantum wells (QWs). The QWs are placed in a 3-3-2-2 sequence on the antinodes of the optical field. They are sandwiched by AlGaInAs strain compensation layers and the QW groups are separated by lattice matched AlGaInAs spacers. The DBR comprised 25.5 pairs of quarter wave thick GaAs and AlAs layers. The active region and the DBR are bonded together at 200 °C using a monolayer of (3-Mercaptopropyl)trimethoxysilane (MPTMS). The InP substrate is then removed by wet etching and a 2 × 2 mm2 chip is capillary bonded onto a 2° wedged 300 μm thick chemical vapor deposition (CVD) diamond. The top surface of the diamond is antireflection coated with TiO₂/SiO₂ layers at the signal wavelength. The SESAM used for the mode-locking is similar to the gain element and is irradiated with heavy ions to shorten the recovery time of the absorption.