Visible light propagation inside free-standing InGaN/GaN quantum-well rib waveguides

This paper describes a double-side process to fabricate free-standing InGaN/GaN multiple quantum wells (MQWs) rib waveguides on a GaN-on-silicon platform. The large index contrast between GaN and air imposes a strong optical confinement of the rib waveguide structures. When the light is generated from InGaN/GaN MQWs, part of the excited light is guided and propagates within the rib waveguide. Experimental and simulation results show that multiple light losses will reduce the light propagation distance, and back wafer etching of free-standing membrane is an effective way to decrease the light loss and to increase the light propagation distance. The performance of the light propagating inside the orthogonal waveguides illustrates that the rib waveguide structures can be utilized to control the light propagation direction inside the waveguide, which is promising for the development of diverse beam splitters for further integrated photonic circuit in the visible wavelength range.