System, apparatus, and architecture for migrating an optical communication network
Coherent optical communications technology for recovery of 1D and 2D formatted optical signals. For example, 1D or 2D formatted signals that travel through fiber optic media may be recovered by separating the light into X- and Y-polarization components, rotating one polarization component (e.g., Y-component) into the polarization space of the other component (e.g., Y-component into the X-polarization space), delaying the rotated component enough to avoid destructive interference and combining the delayed component with the undelayed component to form a folded optical signal, which may then be processed as a X-polarized signal.
1. An optical transmission system, comprising:
an optical transmitter configured to generate a four dimensional optical signal, the optical transmitter having:
a laser;
a first Mach-Zehnder modulator optically coupled to the laser;
a second Mach-Zehnder modulator optically coupled to the laser;
a first multiplexer optically coupled directly to the first Mach-Zehnder modulator;
a second multiplexer;
a time delay module optically coupling the second Mach-Zehnder modulator and the second multiplexer; and
a polarization beam combiner coupled to the first and second multiplexers and configured to output an encoded optical signal received from the first and second multiplexers onto an optical fiber; and
a two dimensional coherent optical receiver, comprising:
a polarization beam splitter configured to receive an encoded optical signal and output a first output signal and a second output signal;
a delay unit configured to receive the second output signal and produce a delayed second output signal;
at least one of an optical coupler or a Mach-Zehnder interferometer optically coupled to the polarization beam splitter and the delay unit, the optical coupler or Mach-Zehnder interferometer each having a first input and a second input and a first output, the first input receiving the first output signal and the second input receiving the delayed second output signal, the first output comprising a folded optical signal formed by combining the first output signal and the delayed second output signal, wherein the delayed second output signal is rotated into a polarization space corresponding to the first output signal so that the first output signal and the delayed second output signal are in the same polarization space and wherein the delayed second output signal of the folded optical signal is delayed relative to the first output signal of the folded optical signal; and
a de-multiplexer optically coupled to the at least one of the optical coupler or the Mach-Zehnder interferometer to receive the folded optical signal from the first output of the optical coupler or the Mach-Zehnder interferometer.
2. The optical transmission system of claim 1 , wherein the first output signal includes a first polarization component and the second output signal includes a second polarization component.
3. The optical transmission system of claim 2 , wherein a polarization rotator is configured to rotate the second polarization component of the second output signal into a polarization state corresponding to the first polarization component of the first output signal.
4. The optical transmission system of claim 3 , wherein the polarization beam splitter includes the polarization rotator.
5. The optical transmission system of claim 1 wherein the at least one of the optical coupler or the Mach-Zehnder interferometer is the Mach-Zehnder interferometer.
6. The optical transmission system of claim 1 , wherein the delay unit comprises a time delay module that introduces a time delay proportional to a symbol period T in the delayed second output signal.
7. The optical transmission system of claim 1 , wherein the first output signal comprises a X-polarized signal and the second output signal comprises a Y-polarized signal and the folded optical signal comprises an optical signal where polarization components of the Y-polarized signals and the X-polarized signals occur in either a X-polarization plane or a Y-polarization plane.
8. The optical transmission system of claim 7 , comprising a 90-degree hybrid wherein the 90-degree hybrid outputs X-polarized light which contains information about both the X-polarized signal and the Y-polarized signals and both I and Q components.
9. The optical transmission system of claim 8 , comprising a pair of optoelectronic converters coupled to the 90-degree hybrid and configured to convert the I and Q components of each of the X-polarized and Y-polarized signals to respective electrical signals.
10. The optical transmission system of claim 9 , wherein each of the optoelectronic converters comprise a photodiode and a transimpedance amplifier.
11. An optical transmission system, comprising:
an optical transmitter configured to generate a four dimensional optical signal, the optical transmitter having:
a laser;
a first Mach-Zehnder modulator optically coupled to the laser;
a second Mach-Zehnder modulator optically coupled to the laser;
a first multiplexer optically coupled directly to the first Mach-Zehnder modulator;
a second multiplexer;
a time delay module optically coupling the second Mach-Zehnder modulator and the second multiplexer; and
a polarization beam combiner coupled to the first and second multiplexers and configured to output an encoded optical signal received from the first and second multiplexers onto an optical fiber; and
a two dimensional coherent optical receiver having:
a polarization beam splitter configured to receive the encoded optical signal and output a first output signal and a second output signal;
a delay unit configured to receive the second output signal and produce a delayed second output signal;
at least one of an optical coupler or a Mach-Zehnder interferometer optically coupled to the polarization beam splitter and the delay unit, the optical coupler or Mach-Zehnder interferometer each having a first input and a second input and a first output, the first input receiving the first output signal and the second input received the delayed second output signal, the first output comprising a folded optical signal generated from the first output signal and the delayed second output signal; and
a de-multiplexer optically coupled to the at least one of the optical coupler or the Mach-Zehnder interferometer to receive the folded optical signal from the first output of the optical coupler or the Mach-Zehnder interferometer.
12. The optical transmission system of claim 11 , wherein the first output signal includes a first polarization component and the second output signal includes a second polarization component.
13. The optical transmission system of claim 12 , wherein a polarization rotator is configured to rotate the second polarization component of the second output signal into a polarization state corresponding to the first polarization component of the first output signal.
14. The optical transmission system of claim 13 , wherein the polarization beam splitter includes the polarization rotator.
15. The optical transmission system of claim 11 , wherein the at least one of the optical coupler or the Mach-Zehnder interferometer is the Mach-Zehnder interferometer.
16. The optical transmission system of claim 11 , wherein the delay unit comprises a time delay module that introduces a time delay proportional to a symbol period T in the delayed second output signal.
17. The optical transmission system of claim 11 , wherein the first output signal comprises a X-polarized signal and the second output signal comprises a Y-polarized signal and the folded optical signal comprises an optical signal where polarization components of the Y-polarized signal and the X-polarized signals occur in either a X-polarization plane or a Y-polarization plane.
18. The optical transmission system of claim 17 , comprising a 90-degree hybrid wherein the 90-degree hybrid outputs X-polarized light which contains information about both the X-polarized signal and the Y-polarized signal and both I and Q components.