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Bias Control of the IQ Optical Modulator Using Side Pilot-Tone in Optical OFDM Transmitters

Among several advantages of inserting a side pilot-tone (SPT) in optical orthogonal frequency-division multiplexing (OFDM) systems, bias control of the IQ optical modulator (IQOM) is presented in this letter. It is shown that a SPT with a small frequency gap and limited power can be employed to generate powerful error signals for phase and amplitude offsets of the IQOM without ambiguity. These error signals are exploited for bias drift correction using a suggested low-cost automatic bias controller with a fast correction algorithm. Insertion of the SPT is further justified as it can also be used for coherent detection purposes.