A method for conveying signaling information through an optical fiber link between a transmitter and a receiver of an optical communication system, the method comprising: generating, by the transmitter, a predetermined spectral change in an optical signal, and transmitting the optical signal including the predetermined spectral change through an optical fiber link to the receiver, the predetermined spectral change being indicative of the signaling information; and detecting, by a detector associated with the receiver, the predetermined spectral change in the optical signal received through the optical fiber link, and generating a detection signal in accordance with the detection result; wherein the detecting is performed independently of demodulation of the optical signal by the receiver; wherein generating the predetermined spectral change in the optical signal comprises: generating a tone signa using an electrical oscillator signal at a predetermined frequency; and inserting the tone signal into the optical fiber link; and wherein detecting the tone signal comprises: tapping a photodetector signal generated by a photodetector of the receiver in response to the optical signal received through the optical fiber link; mixing the tapped photodetector signal with an electrical oscillator signal having a second predetermined frequency to generate a combined signal; filtering the combined signal using a filter characteristic having a pass band corresponding to the tone signal, to generate a filtered signal; and comparing the filtered signal to a predetermined threshold, and generating the detection signal based on the comparison result. generating, by the transmitter, a predetermined spectral change in an optical signal, and transmitting the optical signal including the predetermined spectral change through an optical fiber link to the receiver, the predetermined spectral change being indicative of the signaling information; and detecting, by a detector associated with the receiver, the predetermined spectral change in the optical signal received through the optical fiber link, and generating a detection signal in accordance with the detection result; wherein the detecting is performed independently of demodulation of the optical signal by the receiver; wherein generating the predetermined spectral change in the optical signal comprises: generating a tone signa using an electrical oscillator signal at a predetermined frequency; and inserting the tone signal into the optical fiber link; and wherein detecting the tone signal comprises: tapping a photodetector signal generated by a photodetector of the receiver in response to the optical signal received through the optical fiber link; mixing the tapped photodetector signal with an electrical oscillator signal having a second predetermined frequency to generate a combined signal; filtering the combined signal using a filter characteristic having a pass band corresponding to the tone signal, to generate a filtered signal; and comparing the filtered signal to a predetermined threshold, and generating the detection signal based on the comparison result. tapping a photodetector signal generated by a photodetector of the receiver in response to the optical signal received through the optical fiber link; mixing the tapped photodetector signal with an electrical oscillator signal having a second predetermined frequency to generate a combined signal; filtering the combined signal using a filter characteristic having a pass band corresponding to the tone signal, to generate a filtered signal; and comparing the filtered signal to a predetermined threshold, and generating the detection signal based on the comparison result.