Semiconductor optical amplifier array coupled to uncoated flat-end fibers with integrated beam expanders and TiO2 antireflection coatings

We present a novel coupling scheme consisting of an integrated beam expander, a specifically tailored TiO₂ antireflection coating, optical index matching gel, and uncoated flat-end single-mode fiber (SMF). This scheme was used to package four-channel semiconductor optical amplifier arrays. Far-field profiles for each discrete amplifier in the array are typically 80 and 150 FWHM, perpendicular and parallel to the junction plane, respectively. The TiO₂ AR coating overcomes the indices mismatching of fiber glass and InP based device, and reduce optical reflection to 0.002% at 1.55 μm. Misalignment tolerance in the l-dB excess loss range, for a discrete channel, is typically 5 μm vertically and 8 μm laterally. The average coupling loss is 4.3 dB per facet for the devices measured. Fiber coupled small signal gain for the amplifiers is typically 11.6 dB and a saturation output power of 3.0 dBm. The method of characterization and optimization of the TiO₂ coating is discussed