Toward Complex GaAs PIC-Based Laser Sources

Diode lasers (DLs) based on gallium arsenide (GaAs) enable direct emission from 630 nm up to 1180 nm [1], a wavelength range that is of interest for a wide range of applications in metrology, spectroscopy [2], and quantum photonics [1]. However, most of these applications require tailored lasers beyond standard Fabry-Pérot cavities to achieve e.g. narrow linewidths [1], multiple wavelengths [2], [4], and tunable wavelength emission [3]. These demands can only be met by the integration of functional elements such as i) gratings (either in distributed feedback (DFB) or in distributed Bragg reflector (DBR) configuration [3]–[5]), ii) passive and active waveguide bends and couplers [4], and iii) thermo-or electro-optic phase shifters [3]. Even though most of the required functional elements have already been integrated into GaAs DLs, the complexity and functionality of the devices have not yet reached the level of InP photonic integrated circuits (PIC). This is mainly due to the more complicated multi-step epitaxy for the GaAs material system, with a high susceptibility to oxygen at the regrowth interface and a high growth velocity of crystalline defects. However, in recent years we made considerable progress in the integration of several functional elements into GaAs lasers. Here, we present two novel devices that exemplify this progression: a widely-tunable sampled-grating DBR (SGDBR) laser emitting around 970 nm [3] and a dual-wavelength (DW) laser emitting at two wavelengths around 784 nm out of a single aperture [4].