Guido Torrese

An analytical small-signal bias-dependent nonuniform model for p-i-n traveling-wave photodetectors

A fully analytical small-signal model is developed for the frequency response of traveling-wave photodetectors. It takes into account the dependence of the equivalent transmission-line admittance on the position, induced by the nonuniform distribution of the optical beam along the traveling direction. Moreover, the influence of the bias voltage on the transit time has been accurately investigated. The model is applied to the design of an InAlAs-InGaAs p-i-n photodetector. Its performances are investigated in term of electrical bandwidth.

Embedded Grating

This paper describes the design of embedded-grating n+-i-n+ traveling-wave photodetectors (TWPDs). In the ideal case of perfect electrically matched photodetectors, the TWPD bandwidth is determined by the velocity mismatch between the group velocity of the optical beam and the phase velocity of the electrical photogenerated signal, as well as by the attenuation of the RF signal propagating along the electrodes. Since the group velocity is determined once the layers thickness is selected, which, in turn, is optimized for coupling the light into the photodetector, only an accurate electrode design allows for the velocity matching. In this paper, we propose a new structure that utilizes a grating integrated within a single-mode waveguide in order to tailor the optical group velocity and match it to the phase velocity of the photogenerated signal.