TRAVELING-WAVE PHOTODETECTOR THEORY

Photodetector efficiency decreases as bandwidth increases, Bandwidth-e fficiency limitations of traveling-ware photodetectors (TWPD's) are su bstantially greater than those of lumped-element photodetectors becaus e the velocity-mismatch bandwidth limitation is independent of device length, TWPD's can be long for high efficiency without significantly c ompromising bandwidth, The TWPD is modeled by a terminated section of transmission line with a position-dependent photocurrent source propag ating on it at the optical group velocity, A wave model fur the transm ission line confirms the accuracy of an equivalent-circuit model for e lectrical wave propagation, The velocity-mismatch impulse and frequenc y response are determined by absorption coefficient and wave velocitie s rather than junction capacitance and load resistance, The velocity-m ismatch bandwidth limitations can be written in a simple form which el ucidates the factors affecting device response, A discretized periodic TWPD is described by the same equations as the fully distributed vers ion, This more complicated device offers additional degrees of freedom in design and potentially improved performance.