Ultra-broadband depolarization based on directly-coupled quantum wire-to-well modulation and their aliasing effect...

Nowadays, strained quantum structures have been widely used in various light-emitting devices with a variety of compounds for progressive applications. However, the lattice-mismatch-induced strains in the materials would cause a problem of polarization dependence for polarization-independent optical applications. To address this issue, in this paper we propose a novel ultra-broadband depolarization mechanism and approach based on a directly-coupled well-wire-hybrid nanostructure. It contains quantum wire-to-well modulation and their aliasing effects on strain, energy-band structure and optical gain to obtain independent and comparable bipolarization of optical signals. The material structure involves a special well and on-well quantum wires with gradually-changing band-gaps, which are formed by utilizing the indium (In)-segregation effect and the growth-orientation-dependent multi-atomic step effect. With this special hybrid nanostructure, the depolarization efficiency can be 95% higher than that of a single compressive-strained quantum well. A low polarization degree of 0.05 and a very small gain difference of |G_TE - G_TM| < 1.3 cm^-1 in different polarizations are achieved over a very broad gain bandwidth (870-950 nm) for an InGaAs material system. Therefore, this is a new chance for the development of ultra-broadband and polarization-insensitive optical applications.