Direct-detection optical receiver capable of signal-to-signal beat interference cancellation

An apparatus comprising a direct-detection optical data receiver that comprises:

• a single-ended photodiode to receive light combining an optical data signal and an optical frequency reference;
• an analog-to-digital converter to output digital intensity measurements of the light received by the single-ended photodiode at a sequence of times;
• and
• a digital signal processor connected to receive the digital intensity measurements, the digital signal processor being configured to recover a data stream carried by the optical data signal from the digital intensity measurements;
• wherein the digital signal processor comprises a first finite-impulse-response (FIR) filter and a digital circuit that comprises a second FIR filter, the second FIR filter being serially connected with the first FIR filter, the first FIR filter being configured to filter the digital intensity measurements, the digital circuit being configured to subtract estimates of signal-to-signal beat interference (SSBI) from the filtered digital intensity measurements generated by the first FIR filter;
• and
• wherein the digital signal processor is configured to update filter coefficients of both the first and second FIR filters based on a same feedback signal.