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 a chieved by having three waveguides in the growth direction and by coupling the mode between them by resonance over compact tapers. The top waveguide i s an active waveguide optimized for gain at 1.55 mu m, The middle waveguide is a confined passive waveguide optimized for passive devices such as spli tters and filters, etc. The bottom waveguide is a large loosely confined pa ssive waveguide optimized for a high coupling efficiency to a single-mode f iber. The mode is coupled from the active waveguide to the confined passive waveguide over a 120-mu m-long taper with less than 0.1-dB coupling loss. To couple the mode from the confined passive waveguide to the large-mode pa ssive waveguide, a 270-mu m-long taper is used with less than 0.25-dB coupl ing 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.