Facet reflectivity of a spot-size-converter integrated semiconductor optical amplifier

Traveling-wave type, semiconductor optical amplifiers (SOAs) integrated with a spot-size-converter (SSC) are extensively studied for the improvement of coupling efficiency with single-mode fiber and for cost reduction in packaging. In this paper, the structural dependence of the SSC on the effective facet reflectivity R-eff is investigated theoretically as well as experimentally. It is shown that not only a sufficient mode-conversion in a SSC region, but also an introduction of angled facets, are essential for reducing R-eff. A small gain ripple (less than 0.1 dB) in an amplified spontaneous emission (ASE) spectrum, fiber-to-fiber gain of 26 dB, and saturation output power of 7 dBm are observed at the fabricated SOA, which consists of a window length of 20 gm, facet angle of 7degrees, and anti-reflection coated facet of less than 1% reflectivity.