Velocity-matched distributed photodetectors with high saturation power and large bandwidth

High power, high frequency photodetectors are the key components for high performance RF fiber optic links and coherent receivers with high LO power. Conventional high speed photodetectors have poor saturation power because of their small absorption volume. High bandwidth and high efficiency have been demonstrated by the traveling-wave photodetector. However, its absorption volume remains very small. An attempt has been made to increase the saturation power by employing large-core waveguide photodetectors. Previously, we have proposed a velocity-matched distributed photodetector (VMDP) which consists of an array of high speed photodiodes serially connected by a passive optical waveguide, and a separate microwave output transmission line. By matching the velocities of the microwave transmission line and the optical waveguide, very large absorption volume, and hence high saturation power, can be achieved without sacrificing the bandwidth. In this paper, we report on the first demonstration of the VMDP. High peak saturation photocurrent (56 mA at l-dB compression) and high bandwidth of 49 GHz are demonstrated.