Retrieving the full information carried by phase shift keyed (PSK) data streams requires a reference local oscillator (LO). If the receiver utilizes digital signal processing (DSP), a free-running LO can be used, although several benefits can be derived from generating an optical LO that is locked in frequency and phase to the original signal carrier (which is unfortunately suppressed in the PSK data modulation process). Here, we present a new concept of carrier recovery. Using nonlinear optics, we strip the data modulation and derive an error signal proportional to the phase/frequency difference between a free running intradyne LO and the data-stripped signal. After extracting this frequency difference (using slow electronics), we frequency shift the free running LO by this amount, effectively obtaining a homodyne LO. The carrier is recovered to a precision of better than ±0.5 Hz and the method is tested by performing homodyne detection of a 20 Gbaud binary PSK signal.
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