High accuracy frequency response measurements of mm-wave photodiodes using a DFB heterodyne system with a novel detection scheme

If the optical frequencies of two lasers can be accurately controlled then the response of the photodetector can be determined by measuring the heterodyne RF power and the photocurrents. The distributed feedback laser (DFB) incorporates a grating within the laser cavity to reduce the linewidth and give single frequency operation. A DFB heterodyne system operating at 1.53 μm is described. The system uses a novel detection scheme to overcome problems caused by the laser linewidth. The errors introduced by electrical reflections between the photodiode and the measurement system are discussed. Measurements of two research photodiodes at frequencies of up to 40 GHz are presented. The 3 dB frequencies of the diodes are 30.8±0.5 GHz and 26.9±0.5 GHz