Optical design of evanescently coupled, waveguide-fed photodiodes for ultrawide-band applications

Beam propagation method simulation shows that evanescently coupled waveguide/photodiodes can be optimized to have absorption lengths as short as butt-coupled photodiodes. Efficient focalization of optical power in the absorber is achievable by appropriate choice of layer geometry and refractive index. Two AlGaInAs-GaInAs structures have been designed for ultrawide-band operation at 60 and 100 GHz: these devices exhibit internal quantum efficiency as high as 94% and 75%, respectively, at 1.55-μm wavelength. Such promising performances are suitable for the realization of high-speed high-efficiency integrated photoreceivers with applications to millimeter-wave optical fiber links.