High butt-coupling efficiency to single mode fibers using a 1.55 μm InGaAsP laser integrated with a tapered ridge mode transformer

The 1.55 μm wavelength window is important for future WDM systems, and hence there has been considerable interest in realizing mode expanded lasers at this wavelength. Here, we present a mode expanded laser based on a tapered ridge design, which was grown in a single epitaxial step, and required only conventional lithography and etching techniques. This device showed reduced far-field divergence angles and high coupling efficiencies to a standard cleaved single mode fiber (3.7 dB loss). To our knowledge, this is the lowest loss demonstrated in longer wavelength devices fabricated without using regrowth