Phototransistors based on InP HEMTs and their applications to millimeter-wave radio-on-fiber systems

Phototransistors based on InP high electron-mobility transistors (HEMTs) are investigated for millimeter-wave radio-on-fiber system applications. By clarifying the photodetection mechanism in InP HEMTs, the phototransistor internal gain is determined. We present their use as millimeter-wave harmonic optoelectronic mixers and characterize them at the 60-GHz band. In order to evaluate the InP HEMT optoelectronic mixer performance, internal conversion gain is introduced and a maximum of 17 dB is obtained for 60-GHz harmonic optoelectronic up-conversion. Utilizing them, we construct a 60-GHz radio-on-fiber system and demonstrate 622-Mb/s data transmission over 30-km single-mode fiber and 3-m free space at 60-GHz band.