Wideband and high efficiency AlInAs/GaInAs waveguide photodetectors for 40-Gbps receivers

Two types of waveguide photodiodes (WG-PD) - an evanescently coupled photodiode (EC-WG-PD) and a separated-absorption-and-multiplication avalanche photodiode (SAM-WG-APD) - have been developed for use in 40-Gbps receivers. The EC-PD is much more robust than a conventional WG-PD under high optical input operation because of its distributed absorbed optical power density along the light propagation in the waveguide. The EC-WG-PD simultaneously exhibited a high external responsivity of 0.96 A/W, a wide bandwidth of >40 GHz, and as high as 10-mA photocurrent operation. On the other hand, the SAM-WG-APD has a wide bandwidth of 30-35 GHz and a gain-bandwidth product of 140-180 GHz as a result of its small waveguide mesa structure and a thin multiplication layer. Record highest receiver sensitivities of -28.8 dBm at 10 Gbps and -19.6 dBm at 40 Gbps have been achieved for the first time.