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Abstract

A method and apparatus for embedding control information in an optical signal transporting optical data, consisting of encoding the control information as a control signal having an amplitude proportional to a controllable modulation depth. The optical signal is then optically modulated in accordance with the amplitude of the control signal. The control signal is subsequently detected and the control information is decoded. A major feature of the invention lies in determining a level of similarity between the encoded and decoded control information and varying the modulation depth according to this level of similarity. Hence, the modulation depth yielding a given bit-error rate (BER) or signal-to-noise ration (SNR) can be minimized, in order to reduce the degradation of the optical channel data. The invention also provides a means for modulating the control information about a carrier frequency, and varying this carrier frequency if the SNR is below a certain tolerance value. This is useful in countering the periodic interference spectrum of framed data signals, which may be unknown or time-varying. Furthermore, the bit rate of the control signal can be adjusted to carry a required amount of information, so as to meet the system's evolving control requirements.

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First Claim