Angled-facet S-bend semiconductor optical amplifiers for high-gain and large-extinction ratio

The extinction ratio of an optical gate with a spot-size-converter-integrated semiconductor optical amplifier (SSC-SOA) is deteriorated following the direct coupling of unguided light between the input and output fibers, In this letter, an S-bend waveguide structure is introduced into an active waveguide to suppress such direct coupling. Angled facet structures are also introduced for obtaining low facet reflectivity. The fabricated SSC-SOA operating at 1.55-mu m wavelength achieves an extinction ratio up to 70 dB and a fiber-to-fiber gain of 20 dB.