Contents I. Introduction
The performance of microwave and millimeter-wave photonic systems would benefit from the use of photodiodes (PDs) with high saturation power, high-speed and high responsivity performance. There has been a great deal of interest demonstrated in photodiodes with side-illuminated evanescently coupled waveguides (ECPD) [1] because not only do they allow one to overcome the well-known compromise between responsivity and electrical bandwidth, but they also offer an excellent high power capability. Recently, several research groups have demonstrated the state-of-the-art performance of an evanescently-coupled PD with a short coupling length and multi-mode waveguides [1]. Unfortunately, the responsivity of this kind of ECPD is usually very sensitive to the cleaved waveguide length [1] and the tolerance of the cleaving process is thus very small (less than ). In the first part of this paper, we review our recent work about dual-steps ECPDs [2], which can overcome the above-mentioned problems, and achieve excellent high-speed/power performance at V-band (60GHz). Furthermore, the performance of such device, which is monolithic integrated with a passive wavelength de-multiplexer, for the application of CWDM transmission will also be reviewed [3]. Regarding with the photodiodes for the application of W-band microwave photonic system, the most important issue of them is the maximum output power instead of responsivity due to that in such high-frequency regime, the millimeter wave (MMW) output power from device is limited. In the second part of this paper, we also review our work about near-ballistic uni-traveling carrier photodiode [4] with vertical-illuminated structure and very high output power at W-band.
