Optical communications using multiplexed single sideband transmission and heterodyne detection
A transmitter subsystem generates an optical signal which contains multiple subbands of information. The subbands have different polarizations. For example, in one approach, two or more optical transmitters generate optical signals which have different polarizations. An optical combiner optically combines the optical signals into a composite optical signal for transmission across an optical fiber. In another approach, a single optical transmitter generates an optical signal with multiple subbands. The polarization of the subbands is varied, for example by using a birefringent crystal. In another aspect of the invention, each optical transmitter generates an optical signal containing both a lower optical sideband and an upper optical sideband (i.e., a double sideband optical signal). An optical filter selects the upper optical sideband of one optical signal and the lower optical sideband of another optical signal to produce a composite optical signal.
1 - 29 . (canceled)
30 . An optical communications system comprising:
a transmitter subsystem comprising:
an optical transmitter for generating an optical signal containing at least two subbands of information; and
a polarization controlling device coupled to the optical transmitter for varying a polarization of the subbands so that the subbands have different polarizations.
31 . The optical communications system of claim 30 wherein the polarization controlling device comprises a birefringent medium.
32 . The optical communications system of claim 30 wherein:
the optical transmitter comprises:
a wavelength-tunable optical source, whereby a wavelength of the optical signal can be tuned by tuning the wavelength-tunable optical source; and
the transmitter subsystem further comprises:
a comb filter having periodically spaced pass bands.
33 . The optical communications system of claim 30 wherein:
the optical signal has a lower optical sideband and an upper optical sideband; and
the transmitter subsystem further comprises:
an optical filter coupled to the polarization controlling device for selecting one optical sideband.
34 . The optical communications system of claim 33 wherein the optical filter comprises:
a comb filter having periodically spaced pass bands.
35 . The optical communications system of claim 33 wherein the optical filter attenuates out-of-band wavelengths.
36 . The optical communications system of claim 30 wherein the optical transmitter includes:
at least two electrical transmitters for generating electrical channels;
an FDM multiplexer coupled to the electrical transmitters for FDM multiplexing the electrical channels into an electrical high-speed channel, the electrical high-speed channel further including a tone; and
an E/O converter coupled to the FDM multiplexer for converting the electrical high-speed channel into the optical signal.
37 . The optical communications system of claim 30 further comprising:
a receiver subsystem coupled to the transmitter subsystem by an optical fiber for recovering the subbands from the optical signal.
38 - 54 . (canceled)
55 . A method for transmitting information across an optical fiber, the method comprising:
generating an optical signal containing at least two subbands of information;
varying a polarization of the subbands so that the subbands have different polarizations; and
transmitting the optical signal across an optical fiber.
56 . The method of claim 55 wherein:
the optical signal has a lower optical sideband and an upper optical sideband; and
the method further includes the step of optically filtering the optical signal to select one optical sideband.
57 . The method of claim 55 wherein the step of generating the optical signal comprises: generating electrical channels;
FDM multiplexing the electrical channels into an electrical high-speed channel, the electrical high-speed channel further including a tone; and
converting the electrical high-speed channel into the optical signal.
58 . The method of claim 55 further comprising:
receiving the optical signal; and
recovering the subbands using heterodyne detection.