Designed semiconductor network random lasers

Abstract

Conventional lasers typically support a well-defined comb of modes. Coupling many resonators together to form larger complex cavities enables the design of the spatial and spectral distribution of modes, for sensitive and controllable on-chip light sources. Network lasers, formed from a mesh of dye-doped polymer interconnecting waveguides, have shown great potential for random lasing with a highly sensitive and customizable lasing spectrum albeit suffering from gain bleaching. Here on-chip semiconductor network lasers are introduced, and fabricated by etching an InP epilayer bonded onto a SiO2∕Si wafer, as a reproducible, stable and designable random laser with a rich multimodal spectrum and low room temperature lasing threshold. Thresholds are observed as low as 60 𝛍Jcm−2 pulse−1 for InP networks with an optimum link width of 450 nm and thickness of 120 nm. It is further shown, both experimentally and numerically, that the network density directly affects the mode spatial distribution, and lasing modes are spatially localized over only 10–20 connected links in large dense networks. The InP network lasers are also stable to pump illumination and sensitive to small variations in the pump pattern. These studies lay the ground for the future design of random lasers tailored to the application in robust semiconductor platforms with impact for sensing, signal processing, cryptography and machine learning.