Polarization-Folding Coherent Optical Technology for Short Reach Optical Communication

A method for transmission of optical signals comprising:

• deriving for output, from an encoded optical signal received at a polarization beamsplitter (PBS), a first optical signal at a first output port of the PBS and a second optical signal at a second output port of the PBS, the first optical signal having a first polarization component and the second optical signal having a second polarization component;
• delaying, using a delay element, the second optical signal by a pre-determined time period to produce a delayed second optical signal;
• receiving, directly at an optical coupler, the first optical signal;
• combining the first optical signal and the delayed optical signal at an optical coupler;
• and
• rotating, using a polarization rotator, a polarization component of either the second optical signal or the delayed second optical signal.

An optical transmission system, comprising:

• a polarization beam splitter having an input port, a first optical output port and a second optical output port, the input port coupled to an optical communication channel, the first optical output port providing a first optical signal derived from an encoded optical signal received over the optical communication channel and the second optical output port providing a second optical signal derived from the encoded optical signal, the first optical signal having a first polarization component and the second optical signal having a second polarization component;
• a delay element coupled to the second optical output port of the polarization beam splitter and configured to delay the second optical signal by a pre-determined time period to produce a delayed second optical signal;
• an optical coupler that includes a first input directly coupled to the first optical output of the polarization beam splitter and a second input coupled to the delay element so as to receive the delayed second optical signal, the optical coupler combining the first optical signal and the delayed second optical signal to form a combined optical signal;
• and
• a polarization rotator configured to rotate a polarization component of either the second optical signal or the delayed second optical signal into a polarization state corresponding to the first polarization component,
• wherein the combined optical signal comprises a folded optical signal in which the first optical signal being a first X-polarized signal and the delayed second optical signal being a second X-polarized signal delayed by a predetermined time period.

An optical transmission system, comprising:

• a polarization beam splitter having an input port, a first optical output port and a second optical output port, the input port coupled to an optical communication channel, the first optical output port providing a first optical signal derived from an encoded optical signal received over the optical communication channel and the second optical output port providing a second optical signal derived from the encoded optical signal, the first optical signal having a first polarization component and the second optical signal having a second polarization component;
• a delay element coupled to the second optical output port of the polarization beam splitter and configured to delay the second optical signal by a pre-determined time period to produce a delayed second optical signal;
• a polarization rotator coupled to the delay element and configured to rotate the delayed second optical signal into a polarization state corresponding to the first polarization component;
• an optical coupler that includes a first input directly coupled to the first optical output of the polarization beam splitter and a second input coupled to the delay element so as to receive the delayed second optical signal, the optical coupler combining the first optical signal and the delayed second optical signal to form a combined optical signal, wherein the combined optical signal comprises a folded optical signal in which the first optical signal comprises a first X-polarized signal and the delayed second optical signal comprises a second X-polarized signal delayed by a predetermined time period;
• and
• an X-polarized hybrid element for recovering respective in-phase (I) and quadrature phase (Q) optical signals from the folded optical signal.