Optical modulation system

An optical signal modulation system, comprising:

• an input optical light guide;
• an optical signal source coupled to the input optical light guide for supplying the input optical light guide with a carrier optical signal;
• an output optical light guide;
• a source of a first modulation signal to be transmitted along the output optical light guide;
• means for generating a second modulation signal as the Hilbert transform of the first modulation signal;
• a dual arm drive Mach-Zehnder modulator connected between the input optical light guide and the output optical light guide for modulating the first and second modulation signals onto the carrier optical signal, such that an output optical signal transmitted along the output optical light guide from the modulator has the form of a vestigial sideband signal;
• and
• means for adding DC bias to one or both arms of said Mach Zehnder modulator in order to create an optical phase difference of 90 degrees between carrier optical signal in each arm of said Mach Zehnder modulator.

An optical signal modulation system, comprising:

• an input optical light guide;
• an optical signal source coupled to the input optical light guide for supplying the input optical light guide with a carrier optical signal;
• an output optical light guide;
• a source of a first modulation signal to be transmitted along the output optical light guide;
• means for generating a second modulation signal as the Hilbert transform of the first modulation signal;
• means for forming a first linear combination of the first modulation signal and its Hilbert transform;
• means for forming a second linear combination of the first modulation signal and its Hilbert transform;
• a modulator connected between the input optical light guide and the output optical light guide for modulating the first and second modulation signals onto the carrier optical signal, such that an output optical signal transmitted along the output optical light guide from the modulator has a single or vestigial sideband;
• and
• the first and second linear combinations being selected such that modulation of the carrier optical signal with the first linear combination and with the second linear combination results in an output optical signal that includes part of the carrier optical signal.

An optical signal modulation system, comprising:

• an input optical light guide;
• an optical signal source coupled to the input optical light guide for supplying the input optical light guide with a carrier optical signal;
• an output optical light guide that forms part of a transmission system in which the output optical light guide induces phase distortion of transmitted signals;
• a photodetector coupled to the output optical light guide;
• an electrical equalizer located after the photodetector to remove phase distortion of the transmitted signals induced by the output optical light guide;
• a source of a first modulation signal to be transmitted along the output optical light guide;
• means for generating a second modulation signal as the Hilbert transform of the first modulation signal;
• and
• a modulator connected between the input optical light guide and the output optical light guide for modulating the first and second modulation signals onto the carrier optical signal, such that an output optical signal transmitted along the output optical light guide from the modulator has the form of a vestigial sideband signal.

An optical signal modulation system, comprising:

• an input optical light guide;
• an optical signal source coupled to the input optical light guide for supplying the input optical light guide with a carrier optical signal;
• an output optical light guide;
• a source of a first modulation signal to be transmitted along the output optical light guide;
• means, including a tapped delay element, for generating a second modulation signal as the Hilbert transform of the first modulation signal, said tapped delay element having symmetrical tap weighting amplitudes about a center tap;
• and
• a modulator connected between the input optical light guide and the output optical light guide for modulating the first and second modulation signals onto the carrier optical signal, such that an output optical signal transmitted along the output optical light guide from the modulator has the form of a vestigial sideband signal.

An optical signal modulation system, comprising:

• an input optical light guide;
• an optical signal source coupled to the input optical light guide for supplying the input optical light guide with a carrier optical signal;
• an output optical light guide;
• a source of a first modulation signal to be transmitted along the output optical light guide;
• means for generating a second modulation signal as the Hilbert transform of the first modulation signal;
• means for forming a first linear combination of the first modulation signal and the second modulation signal;
• means for forming a second linear combination of the first modulation signal and the second modulation signal, the first and second linear combinations being selected such that modulation of the carrier optical signal with the first linear combination and with the second linear combination results in an output optical signal that includes part of the carrier optical signal;
• and
• a modulator connected between the input optical light guide and the output optical light guide for modulating the first and second modulation signals onto the carrier optical signal, such that an output optical signal transmitted along the output optical light guide from the modulator has the form of a vestigial sideband signal.