High-speed and high-gain optical amplifying photodetection in a semiconductor laser amplifier

A high-speed and high-gain photodetection was experimentally demonstrated in a distributed feedback semiconductor laser amplifier by detecting its forward voltage changes induced by the injection of weak intensity modulated light. Physical phenomenon involved in the photodetection stems from the reduction of quasi-Fermi level separation through the depletion of carrier density by optical amplification. A bandwidth as wide as 500 MHz was measured together with a narrowband spectral selectivity for the amplifier biased just below the lasing threshold. The responsivity and the noise equivalent power were found to be comparable with those of the conventional detection scheme using a similar optical preamplifier and a Ge avalanche photodetector.