System, method and fiber-optic transceiver module for bandwidth efficient distortion-tolerant transmissions for high-bit rate fiber optic communications

1. A fiber optic communications system that comprises:

a receiver having a photo-sensor that provides a receive signal representing intensity of light received from an optical fiber; and

a transmitter that transmits a channel characterization signal over the optical fiber, said characterization signal covering a frequency range between a minimum frequency and a maximum frequency,

wherein the receiver determines from the receive signal a frequency position for each null in said frequency range based, at least in part, on a length and a distortion coefficient of the optical fiber.

2. The system of claim 1 , wherein the receiver determines the frequency position for each null in accordance with a type of optical fiber that exceeds 200 kilometers in length.

3. The system of claim 2 , wherein the transmitter employs an orthogonal frequency division multiplexing (OFDM) modulator with frequency bins corresponding to said null frequency positions being zeroed out.

4. The system of claim 2 , wherein the receiver assembles a data stream for a host by collecting data from blocks, each block corresponding to a channel and having a size based at least in part on a bandwidth of said channel.

5. The system of claim 4 , wherein each of the parallel demodulators have independent timing recovery modules.

6. The system of claim 4 , wherein each of the parallel demodulators have independent equalization modules.

7. The system of claim 4 , wherein each of the parallel demodulators have independent M-TCM decoders.

8. The system of claim 2 , wherein the receiver divides the receive signal using a set of bandpass filters each having a programmable center frequency and bandwidth that are set based on the null frequency positions, wherein the filtered receive signals are processed by a set of parallel demodulators.

9. The system of claim 1 , wherein, based on the null frequency positions, the transmitter divided said frequency range into channels and spreads data from a host into blocks, each block corresponding to a channel and having a size corresponding to a capacity of that channel.

10. The system of claim 1 , wherein, based on the null frequency positions, the transmitter divides said frequency range into channels and spreads data from a host across a set of parallel modulators, each modulator generating a signal for a corresponding channel.

11. The system of claim 10 , wherein each modulator signal is filtered by a respective bandpass filter having a programmable center frequency and bandwidth, said center frequency and bandwidth being set based on the null frequency positions.

12. The system of claim 10 , wherein the transmitter includes an RF combiner that combines the modulator signals to form a transmit signal, and wherein the transmitter further includes an optical modulator that communicates the transmit signal over the optical fiber.

13. The system of claim 10 , wherein the set of parallel modulators include at least one multi-dimensional Trellis-coded modulator (M-TCM).

14. The system of claim 13 , wherein the M-TCM modulator employs a PSK or QAM signal constellation that carries more than 2 bits per symbol.

15. The system of claim 13 , wherein a partial-response precoder and modulator are used with the M-TCM modulator to further increase the bits-per-symbol rate.

16. The system of claim 13 , wherein each M-TCM modulator is coupled to a signal conditioner that at least partly compensates for expected channel effects.

17. The system of claim 10 , wherein the set of parallel modulators include at least one orthogonal frequency division multiplexing (OFDM) modulator.

18. The system of claim 1 , wherein the receiver determines the frequency position for each null in said frequency range based, at least in part, on the length and the distortion coefficient of the optical fiber in accordance with an equation

f

=

1

2

⁢

⁢

π

⁢

(

2

⁢

k

+

1

)

⁢

π

β

2

⁢

z

,

where “z” constitutes the length and β 2 constitutes the distortion coefficient.

19. A fiber optic communications method comprising:

dynamically identifying frequencies at which spectral nulls occur in a signal received via an optical fiber, the frequencies at which the spectral nulls occur are estimated based, at least in part, on a length and a distortion coefficient of the optical fiber; and

segregating communications over the optical fiber into a set of inter-null bands defined by the spectral nulls.

20. The method of claim 19 , wherein said segregating includes using, for each inter-null band, a respective modulator to generate an analog transmit signal and a respective demodulator to process an analog receive signal, said analog signals being frequency-limited to that inter-null band.

21. The method of claim 19 , further comprising setting center frequencies and bandwidths for a set of bandpass filters that conduct frequency limiting of analog transmit signals for the inter-null bands.

22. The method of claim 19 , further comprising setting center frequencies and bandwidths for a set of bandpass filters that conduct frequency limiting of analog receive signals for the inter-null bands.

23. The method of claim 19 , wherein the frequencies at which the spectral nulls occur are estimated in accordance with a type of optical fiber that exceeds 200 kilometers in length.

24. A method comprising:

dynamically identifying frequencies at which spectral nulls occur in a signal received via a single-mode optical fiber that corresponds to a long-haul optical communication link, the frequencies at which the spectral nulls occur are identified based, at least in part, on a length and a distortion coefficient of the optical fiber; and

segregating communications over the optical fiber into a set of inter-null bands each associated with an optical carrier, the optical carriers each being separated from each other by twice a frequency of a first channel null for a first inter-null band of the set of inter-null bands.