Method and apparatus for interleaved optical single sideband modulation

An optical carrier notch filter, comprising:

• a multiple port circulator including at least a first, a second and a third port;
• an optical bandpass filter coupled to the second port of the multiple port circulator, the optical bandpass filter separating an output received from the circulator into a transmitted signal that contains an optical carrier and a reflected signal that includes interleaved optical single sideband signals and is reflected from the optical bandpass filter to the third port of the circulator;
• and
• a modulator coupled to the optical bandpass filter to receive the optical carrier, a modulating signal is applied to the electrodes of the modulator modulating the carrier to form a modulated optical carrier.

An interleaved optical single sideband communications system comprising:

• an optical modulator, constructed and arranged to accept an incoming optical carrier and including:
• a splitter which splits the incoming optical signal into a first optical carrier and a second optical carrier;
• a first AC phase modulator to apply a first electrical signal carrying a plurality of first channels to modulate the first optical signal;
• a second AC phase modulator to apply a second electrical signal carrying a plurality of second channels to modulate the second optical signal, each first channel corresponding to one of the second channels, and each first channel being phase shifted 90° relative to each corresponding second channel;
• a first DC phase modulator to modulate the first optical signal;
• a second DC phase modulator to modulate the second optical signal, the first and second DC phase modulators constructed and arranged to modulate an optical carrier component of the first optical signal to be phase shifted 90° relative to an optical carrier component of the second optical signal, the optical carrier component of the second optical signal having a frequency substantially equal to the optical carrier component of the first optical signal;
• a directional coupler that coupled to the optical modulator and combines the modulated first and second optical signals to form a combined optical signal having an optical carrier component, such that alternate channels of the combined optical signal are substantially cancelled;
• and
• wherein the optical modulator creating a plurality of first single side bands on a side of the optical carrier frequency, a plurality of first residual images on the opposite side of the optical carrier frequency, a second side bands on a side of the optical carrier frequency, and a plurality of second residual images on the opposite side of the optical carrier frequency.

An interleaved optical single sideband communications system comprising:

• an optical modulator, constructed and arranged to accept an incoming optical carrier, the optical modulator comprising:
• a splitter which splits the incoming optical signal into a first optical carrier and a second optical carrier;
• a first AC phase modulator to apply a first electrical signal carrying a plurality of first channels to modulate the first optical signal;
• a second AC phase modulator to apply a second electrical signal carrying a plurality of second channels to modulate the second optical signal, each first channel corresponding to one of the second channels, and each first channel being phase shifted 90° relative to each corresponding second channel;
• a first DC phase modulator to modulate the first optical signal;
• a second DC phase modulator to modulate the second optical signal, the first and second DC phase modulators constructed and arranged to modulate an optical carrier component of the first optical signal to be phase shifted 90° relative to an optical carrier component of the second optical signal, the optical carrier component of the second optical signal having a frequency substantially equal to the optical carrier component of the first optical signal;
• a combiner which combines the modulated first and second optical signals to form a combined optical signal having an optical carrier component, such that alternate channels of the combined optical signal are substantially cancelled;
• and
• a notch filter coupled to the optical modulator, the notch filter including, an optical coupler including at least a first, a second and a third port, the first port being configured to receive an output that includes an optical carrier and interleaved optical single sideband signals, and an optical bandpass filter coupled to a second port of the optical coupler, the optical bandpass filter separating the output into a transmitted signal that contains the optical carrier and a reflected signal that includes the interleaved optical single sideband signals that are reflected from the optical bandpass filter to the third port of the optical coupler.

An interleaved optical single sideband communications system comprising:

• an optical modulator, constructed and arranged to accept an incoming optical carrier, the optical modulator comprising:
• a splitter which splits the incoming optical signal into a first optical carrier and a second optical carrier;
• a first AC phase modulator to apply a first electrical signal carrying a plurality of first channels to modulate the first optical signal;
• a second AC phase modulator to apply a second electrical signal carrying a plurality of second channels to modulate the second optical signal, each first channel corresponding to one of the second channels, and each first channel being phase shifted 90° relative to each corresponding second channel;
• a first DC phase modulator to modulate the first optical signal;
• a second DC phase modulator to modulate the second optical signal, the first and second DC phase modulators constructed and arranged to modulate an optical carrier component of the first optical signal to be phase shifted 90° relative to an optical carrier component of the second optical signal, the optical carrier component of the second optical signal having a frequency substantially equal to the optical carrier component of the first optical signal;
• a combiner which combines the modulated first and second optical signals to form a combined optical signal having an optical carrier component, such that alternate channels of the combined optical signal are substantially cancelled;
• and
• a notch filter coupled to the optical modulator, the notch filter including, an optical coupler including at least a first, a second and a third port, the first port being configured to receive an output that includes an optical carrier and interleaved optical single sideband signals, and an optical bandpass filter coupled to a second port of the optical coupler, the optical bandpass filter separating the output into a reflected signal that contains the optical carrier and a transmitted signal that includes the interleaved optical single sideband signals that are transmitted through the optical bandpass filter.

An interleaved optical single sideband communications system comprising:

• an optical modulator, constructed and arranged to accept an incoming optical carrier, the optical modulator comprising:
• a splitter which splits the incoming optical signal into a first optical carrier and a second optical carrier;
• a first AC phase modulator to apply a first electrical signal carrying a plurality of first channels to modulate the first optical signal;
• a second AC phase modulator to apply a second electrical signal carrying a plurality of second channels to modulate the second optical signal, each first channel corresponding to one of the second channels, and each first channel being phase shifted 90° relative to each corresponding second channel;
• a first DC phase modulator to modulate the first optical signal;
• a second DC phase modulator to modulate the second optical signal, the first and second DC phase modulators constructed and arranged to modulate an optical carrier component of the first optical signal to be phase shifted 90° relative to an optical carrier component of the second optical signal, the optical carrier component of the second optical signal having a frequency substantially equal to the optical carrier component of the first optical signal;
• a combiner which combines the modulated first and second optical signals to form a combined optical signal having an optical carrier component, such that alternate channels of the combined optical signal are substantially cancelled;
• and
• wherein the optical modulator creates a first single side band on a side of the optical carrier frequency with a first residual image on a side of the optical carrier frequency, a second side band on a side of the optical carrier frequency with a second residual image on a side of the optical carrier frequency;
• and a frequency of the first side band is offset from the second residual image, and a frequency of the second side band is offset from the first residual image.

A method of modulating an optical carrier, comprising:

• receiving an output that includes an optical carrier and interleaved sideband signals;
• separating the interleaved sideband signals from the optical carrier;
• modulating the optical carrier to create a modulated optical carrier;
• and
• combining the interleaved sideband signals with the modulated optical carrier.

A method of modulating an optical carrier frequency in an optical modulator that includes a first phase modulator and a second phase modulator, comprising:

• splitting a power of the optical carrier frequency into a first portion and a second portion;
• introducing the first portion of the carrier signal frequency to the first phase modulator and the second portion of the carrier signal frequency to the second phase modulator;
• applying a first signal to the first phase modulator at a first phase and to the second phase modulator at a second phase;
• creating a first single side band on a side of the optical carrier frequency, and a first residual image on a side of the optical carrier frequency;
• applying a second signal to the first phase modulator at a first phase and to the second phase modulator at a second phase
• creating a second side band on a side of the optical carrier frequency, and a second residual image on a side of the optical carrier frequency;
• and
• wherein a frequency of the first side band is offset from the second residual image, and a frequency of the second side band is offset from the first residual image.

A method of transmitting a plurality of channels, comprising:

• providing a plurality of electrical signals with adjustable powers and frequencies, each electrical signal corresponding to a channel;
• producing a first and a second split signal corresponding to each of the plurality of signals, each first split signal being substantially at quadrature with a corresponding second split signal;
• providing an optical carrier signal;
• multiplexing the optical carrier signal with the split signals to produce a multiplexed optical signal such that alternate channels are substantially cancelled and residual images of upper side band channels do not substantially overlap channels carried on a lower side band;
• interleaving the at least one multiplexed optical signal to reverse positive and negative frequencies of adjacent wavelengths are reversed.

An optical communication system, comprising at least one optical transmitter which comprises:

• an electrical modulation control unit to produce a first modulation control signal comprising a plurality of first channel signals at different and equally spaced channel frequencies and a second modulation control signal comprising a plurality of second channel signals that are respectively at the different channel frequencies of the first channel signals and respectively carry the same channel information as the first channel signals, wherein two adjacent channel signals in each of the first and the second modulation control signals have a relative phase shift of 90 degrees, and wherein each channel signal in the first modulation control signal has a relative phase shift of 90 degrees with respect to a corresponding channel signal at the same channel frequency in the second modulation control signal;
• and
• a Mach-Zehnder optical modulator comprising an input port to receive an optical carrier at an optical carrier frequency, a first optical path and a second optical path which receive a first portion of the optical carrier as a first optical carrier and a second portion of the optical carrier as a second optical carrier, respectively, and an output port to combine light from the first and second optical paths to produce an optical output signal which carries output channel signals having the same channel information of the first and second channel signals and a frequency spacing between two adjacent output channel signals being twice a frequency spacing between two adjacent channel signals in the first and second modulation control signals,
• wherein the first optical path receives and responds to the first modulation control signal to modulate the first optical carrier to carry the first channel signals on both sides of the optical carrier frequency, and the second optical path receives and responds to the second modulation control signal to modulate the second optical carrier to carry the second channel signals on both sides of the optical carrier frequency and to produce a phase shift of 90 degrees in light in the second optical path relative to light in the first optical path.

A method for modulating a plurality of channels at different channel frequencies onto an optical carrier at an optical carrier frequency, comprising:

• electronically producing a first modulation control signal which comprises a plurality of first channel signals at different and equally spaced channel frequencies and a second modulation control signal which comprises a plurality of second channel signals that are respectively at the different channel frequencies of the first channel signals and respectively carry the same channel information as the first channel signals, wherein two adjacent channel signals in each of the first and the second modulation control signals have a relative phase shift of 90 degrees, and wherein each channel signal in the first modulation control signal has a relative phase shift of 90 degrees with respect to a corresponding channel signal at the same channel frequency in the second modulation control signal;
• applying the first modulation control signal to a first optical path of a Mach-Zehnder optical modulator to module a first portion of the optical carrier in the first optical path to carry the first channel signals on both sides of the optical carrier frequency;
• applying the second modulation control signal to a second optical path of the Mach-Zehnder optical modulator to module a second portion of the optical carrier in the second optical path to carry the second channel signals on both sides of the optical carrier frequency;
• biasing a relative phase between the first and the second optical path to produce a phase shift of 90 degrees in light in the second optical path relative to light in the first optical path;
• and
• combining light from the first and second optical paths to produce an optical output signal which carries the first channel signals.