Embedded Grating ${\hbox {n}}^{+}{\hbox {-i-}}{\hbox {n}}^{+}$ Traveling-Wave Photodetectors

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 layer´s 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.