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 8 degrees and 15 degrees 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 mu m. Misalignment tolerance in the 1-dB excess loss range, for a discrete channel, is typically 5 mu m vertically and 8 mu m 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.