Traveling-wave photodetector theory

Photodetector efficiency decreases as bandwidth increases, Bandwidth-efficiency limitations of traveling-ware photodetectors (TWPD's) are substantially greater than those of lumped-element photodetectors because the velocity-mismatch bandwidth limitation is independent of device length, TWPD's can be long for high efficiency without significantly compromising bandwidth, The TWPD is modeled by a terminated section of transmission line with a position-dependent photocurrent source propagating on it at the optical group velocity, A wave model fur the transmission line confirms the accuracy of an equivalent-circuit model for electrical wave propagation, The velocity-mismatch impulse and frequency response are determined by absorption coefficient and wave velocities rather than junction capacitance and load resistance, The velocity-mismatch bandwidth limitations can be written in a simple form which elucidates the factors affecting device response, A discretized periodic TWPD is described by the same equations as the fully distributed version, This more complicated device offers additional degrees of freedom in design and potentially improved performance.