Photonic integrated circuit optical phase lock loop tuneable active filter

We report the first foundry-fabricated photonic integrated circuit (PIC) optical phase lock loop (OPLL) tuneable active optical filter for optical frequency comb line selection and amplification. The PIC containing DBR lasers and photodiodes is integrated with low frequency electronics to create an OPLL, which functions as a highly selective optical filter with sub-GHz bandwidth and 50dB out-of-band suppression. The OPLL output is a single tone coherent with the comb line, whose optical power is 6dB higher than the selected input line, and whose frequency can be offset from the input line by an agile and precisely defined frequency.