Uni-traveling-carrier photodiodes for high-speed detection and broadband sensing

The uni-traveling-carrier photodiode (UTC-PD) is a novel photodiode that utilizes only electrons as the active carriers. This unique feature is the key to realize its excellent high-speed and high-output characteristics simultaneously. To date, a record 3-dB bandwidth (f_3dB) of 310 GHz and a very high millimeter (mm)-wave output power of over 17 mW at 120 GHz have been achieved. These superior characteristics are essential for the detection of high-bit-rate optical signal in communications systems and for the generation of high-frequency electro-magnetic waves in measurement and sensing systems. For optical communications, we have realized a photoreceiver operating at up to 160 Gbit/s and an avalanche photodiode with a record f_3dB of 40 GHz. For generating mm-/sub-mm-wave signals, we have developed a compact UTC-PD module with a rectangular waveguide output port for operation at up to 325 GHz. We have also fabricated a quasi-optical module for operation at higher frequencies integrating a UTC-PDs and a planar log-periodic antenna. This module can be operated at up to 1.6 THz with a maximum output-power of 2.6 μW at 1.04 THz. The UTC-PD has been used successfully for several applications, such as mm-wave imaging and photonic local signal supply for radio telescopes, demonstrating its feasibility for high-frequency measurement and sensing systems. As a challenge for future high-sensitivity sensing systems, the possibility of UTC-PD modules operating at a very low temperature of 15 K has also been demonstrated.