InP Photonic Integrated Circuit for 6.7GHz Spaced Optical Frequency Comb Generator

We have demonstrated a novel approach to photonically integrated optical frequency comb generation on Indium Phosphide (InP) using generic foundry platforms. The optical comb utilized a recirculating loop technique to generate 59 comb lines (within a 20 dB power envelope) which are separated by 6.7 GHz frequency spacing. All comb lines exhibit strong phase coherence as characterized by low phase noise measurements of −105 dBc/Hz at 100 kHz. The choice of InP as an integration platform allowed for an immediate optical amplification of the modulated sideband tones. This approach reduced the requirement for external high-power RF amplifiers and therefore made the entire system more compact and power efficient. The amplified recirculating loop comb occupied 6 x 0.7 mm
²
area of InP chip and consisted of electro-optic phase modulator (EOPM) and semiconductor optical amplifier (SOA) components embedded within a short (12 mm long) waveguide loop, such that the round-trip loop frequency corresponding to the loop optical length equated to 6.7 GHz. Modulation frequencies equal to the round-trip loop frequency were used to generate broad comb spans.