Sensitivity and power penalty considerations for laser preamplified direct detection optical receivers

Abstract

The paper presents a theoretical analysis of the performance of direct detection optical receivers incorporating semiconductor laser amplifiers (SLAs) prior to the photodetector, and places an emphasis on achievable sensitivity, considering in particular the influence of various system impairments. Illustrative results are included based on amplifier material and device structural parameters. Important specific issues addressed in detail include the influence of residual facet reflectivity, the extinction ratio associated with the incoming optical signal, input and output laser amplifier coupling losses, and the frequency mismatch between the signal and the amplifier peak gain. The results show that little further improvement in receiver sensitivity can be obtained by reducing facet reflectivity below 0.1%, or by inserting an optical filter with bandwidth greater than 50 nm. The authors found that these new laser preamplifier receivers can be more sensitive to the input signal extinction ratio compared with conventional pin or APD receivers, especially when a narrow bandwidth filter is used. In addition, any deviation in the signal frequency from the amplifier central mode frequency will significantly degrade receiver performance, especially when the amplifier gain is high, as one would expect. The analyses presented in the paper aim to provide useful guidelines for the design of wideband high sensitivity optical receivers.