Measurement of Laser Phase Noise for Ultra-Long Period of 0.8 Seconds With 800-ps Temporal Resolution Using Optical Coherent Detection With FPGA-Implemented Data Acquisition

In this study, we demonstrate laser phase noise measurement with a 0.8-s period and an 800-ps temporal resolution. An optical carrier is received by heterodyne detection, and the detected electrical signals are acquired using field programmable gate array circuits with 1.25-GSample/s analog-to-digital converters and 1-GByte memory. The laser phase noise is visualized using a field spectrogram and a very wide FM noise spectrum from near the DC, which is constructed using our proposed phase-compensating interleaved fast Fourier transformation. We compare the phase noise characteristics of an external cavity laser with those of a distributed feedback semiconductor laser.