Direct optical injection locking of a 52-GHz InP-InGaAs HPT oscillator IC for over-100-Gb/s half- or fullrate optoelectronic clock recovery

We present a fully monolithic 52-GHz oscillator integrated circuit (IC) that uses a back-illuminated InP-InGaAs heterojunction phototransistor (HPT). The HPT with an emitter size of 5 /(mu)m(phi), where the whole emitter area can be illuminated from the back side of the substrate, exhibits a maximum oscillation frequency of 135 GHz, thus enabling us to achieve a 52-GHz oscillator with a wide margin. Optical injection locking was evaluated by using two laser diodes with a frequency difference of around 104 GHz, which corresponds to the oscillatorʹs second-harmonic frequency. Injection locking is successfully achieved for the second harmonic as well as for the fundamental spectrum. The oscillator IC promises to achieve a half- or full-rate optoelectronic clock extraction from over-100-Gb/s optical data streams.