Optical transmission system

Claim 2

A receiver for a CPFSK optical transmission system, said receiver comprising: an optical coupler, a local oscillator controlled by an integrater based frequency control signal for producing a local signal which is coupled with a received optical signal by the coupler for producing IF signals, balanced photodetectors which detect the IF signals and produce electrical signals responsive thereto, a receiver amplifier which amplifies said electrical signals, and a demodulator/discriminator arrangement including an AGC circuit, an IF discriminator and a multiplier, wherein the AGC circuit receives an input from the amplifier and outputs a data signal to the IF discriminator and a feedback signal, and the IF discrimininator produces an output data signal and a second, baseband output which is multiplied by the multiplier with the AGC feedback signal, whereby the multiplier outputs to said integrator based control circuit a signal which determines the frequency of the local oscillator laser which reduces any frequency error between a nominal data IF frequency and the IF discriminator frequency characteristic.

Claim 3

An optical transmission system utilising at a transmitter, continuous phase frequency shift keyed modulation of a laser and a coherent heterodyne receiver therefor, the system including at the transmitter means for imposing a low-frequency modulation on the transmitter optical power, wherein the receiver comprises: an optical coupler, a local oscillator controlled by an integrater based frequency control signal for producing a local signal which is coupled with a received optical signal via the coupler for producing IF signals, balanced photodetectors which detect the IF signals and produce electrical signals responsive thereto, a receiver amplifier which amplifies said electrical signals, and a demodulator/discriminator arrangement including an AGC circuit, an IF discriminator and a multiplier, wherein the AGC circuit receives an input from the amplifier and outputs a data signal to the IF discriminator and a feedback signal, and the IF discrimininator produces an output data signal and a second, baseband output which is multiplied by the multiplier with the AGC feedback signal, whereby the multiplier outputs to said integrator based control circuit a signal which determines the frequency of the local oscillator laser which reduces any frequency error between a nominal data IF frequency and the IF discriminator frequency characteristic.

Claim 4

An optical transmission system utilising at a transmitter, continuous phase frequency shift keyed modulation of a laser and a coherent heterodyne receiver therefor, the system including at the transmitter means for imposing a low-frequency modulation on the transmitter optical power, wherein the receiver comprises: an optical coupler, a local oscillator controlled by an integrater based frequency control signal for producing a local signal which is coupled with a received optical signal via the coupler for producing IF signals, balanced photodetectors which detect the IF signals and produce electrical signals responsive thereto, a receiver amplifier which amplifies said electrical signals, and a demodulator/discriminator arrangement including an AGC circuit, an IF discriminator and a multiplier, wherein the AGC circuit receives an input from the amplifier and outputs a data signal to the IF discriminator and a feedback signal, and the IF discrimininator produces an output data signal and a second, baseband output which is multiplied by the multiplier with the AGC feedback signal, whereby the multiplier outputs to said integrator based control circuit a signal which determines the frequency of the local oscillator laser which reduces any frequency error between a nominal data IF frequency and the IF discriminator frequency characteristic.