Ultrafast applications of uni-traveling-carrier photodiodes from measurement to signal processing

Ultrafast photodiode is a key device, which links electronics and photonics technologies, especially in measurement, sensing and communications systems. Uni-traveling-carrier photodiode (UTC-PD) is unique in that it provides both a large bandwidth and a high-saturation output current at 1.55-mum wavelength. In this paper, we describe recent progress in UTC-PD technologies and their analog and digital applications in the frequency regions from giga-hertz to tera-hertz. First, operation principle and characteristics of InP/InGaAs UTC-PDs are shown: Time-domain response exhibited <1-ps pulse width, which corresponds to the 3-dB bandwidth of over 300 GHz. To enhance the output power, resonant-operation of the UTC-PD integrated with a matching circuit is proposed. The CW output power exceeds 20 mW at 100 GHz. Photonically-generated electrical signals are applied as stimulus to ultrafast measurement systems such as IC testers and network analyzers. By integrating PDs with planar antennas in monolithic as well as hybrid fashions, millimeter and submillimeter-wave emitters are developed. These photonic emitters are used as signals sources for transmitters in millimeter-wave wireless links, imaging applications, and local oscillators in radio-astronomy receivers. Finally, a novel functional device, in which an electro-absorption modulator is integrated with the PD, is demonstrated as a demultiplexer for over 300-Gb/s optical communications systems.