Adjustable gain and bandwidth light amplifiers in terms of distributed-feedback structures

Three different types of distributed-feedback semiconductor optical amplifier (DFB-SOA) are studied: periodic, linearly tapered, and linearly chirped DFB-SOA’s. The features of these amplifiers are as follows: because of weak distributed-feedback structures caused by corrugations, wide bandwidth and high gain can be realized, i.e., higher gain than for traveling-wave-type amplifiers and wider bandwidth than for Fabry–Perot-type amplifiers. Two different applications for these three different types of DFB-SOA can be considered, viz., as transmission and as reflection structures; however, one transmission structure is better than the other. To reduce reflections from the amplifiers to the input side, either linearly tapered coefficients with negative taper or linearly chirped DFB-SOA’s are useful. The noise level (caused by spontaneous emissions) of the proposed amplifiers can be lower than for traveling-wave-type amplifiers because here a lower injection current is required for the same level of amplification to be obtained.