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Fundamental amplifying characteristics of 1.55-mum semiconductor optical amplifiers (SOAs) that contain multiquantum well (MQW) active layers with an optimized tensile strain or bulk active layers with various tensile strains were investigated. Both types of SOAs have their own merits and demerits. For device application in networks, driving current and wavelength in the low-polarization-sensitivity condition are very important, but they have not been clarified yet. The results of the present investigation clarify the driving current and wavelength characteristics of low-polarization-sensitivity SOAs with MQW and strained-bulk active layers. The low-polarization-sensitivity condition of SOAs with a strained-bulk active layer is shown to have a very wide range of driving current and wavelength for network-device application. These results, with other requirements taken into account, provide guidelines for choosing the type of SOA most suitable for a given application [ABSTRACT FROM PUBLISHER]

An efficient spotsize converter (SSC) is necessary for directly coupling an InP-based deep-ridge waveguide structure to a fiber. We have already proposed an SSC that uses a laterally buried taper, selectively grown over a thick cladding layer and an optimized deep-ridge-buried waveguide junction. The experimentally obtained converter loss was less than 2 dB, which is still large. Further optimization is possible by introducing a short taper waveguide for the deep-ridge-buried waveguide junctions and improving the taper shape by using a two-step linear taper with a short narrow waveguide. A simulation result shows that we can achieve a converter loss of less than 1 dB with a converter length of only 200 μm. [ABSTRACT FROM PUBLISHER]