Passive active resonant coupler (PARC) platform with mode expander

We have developed a monolithic integration platform where three waveguides of different characteristics are using a single epitaxial growth. This is achieved by having three waveguides in the growth direction and by coupling the mode between them by resonance over compact tapers. The top waveguide is an active waveguide optimized for gain at 1.55 μm. The middle waveguide is a confined passive waveguide optimized for passive devices such as splitters and filters, etc. The bottom waveguide is a large loosely confined passive waveguide optimized for a high coupling efficiency to a single-mode fiber. The mode is coupled from the active waveguide to the confined passive waveguide over a 120-μm-long taper with less than 0.1-dB coupling loss. To couple the mode from the confined passive waveguide to the large-mode passive waveguide, a 270-μm-long taper is used with less than 0.25-dB coupling loss. Lasers have been fabricated to test the platform and have a butt-coupling loss of 3.5 dB to a standard cleaved single-mode fiber.