Transmission Formats for High Bit-Rate Systems

Abstract

An apparatus, system and method wherein a multi-level data modulation format, such as DQPSK, is combined with symbol rate synchronous amplitude, phase, and/or polarization modulation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

Reference should be made to the following detailed description which should be read in conjunction with the following figures, wherein like numerals represent like parts:

FIG. 1 is a simplified block diagram of one exemplary embodiment of a system consistent with the present disclosure;

FIG. 2 shows a simplified block diagram of one exemplary embodiment of a transmitter consistent with the present disclosure.

FIG. 2A shows a simplified block diagram of another exemplary embodiment of a transmitter consistent with the present disclosure.

FIG. 3 shows waveforms associated with one exemplary embodiment of a transmitter consistent with the present disclosure.

FIG. 4 includes plots of Q-factor vs. power illustrating transmission performance of an embodiment consistent with the present disclosure.

FIG. 5 shows eye diagrams for the amplitude characteristic of an embodiment consistent with the present disclosure with varying amounts of symbol rate synchronous AM modulation.

FIG. 6 shows eye diagrams for the amplitude characteristic of an embodiment consistent with the present disclosure with varying amounts relative timing shift between the data and symbol rate synchronous AM modulation.

Claims

1. An apparatus for transmitting an optical signal comprising: a data modulator configured to modulate data on an optical signal using a multi-level data modulation format to provide a data modulated signal comprising multiple bits of said data encoded in each of a plurality of output symbols provided at a symbol rate; andat least one overhead modulator configured to impart a periodic modulation at said symbol rate of at least one characteristic selected from the group consisting of: an amplitude of said optical signal, a phase of said optical signal and a polarization of said optical signal.

2. An apparatus according to claim 1, wherein said periodic modulation at said symbol rate comprises periodic modulation of at least two characteristics selected from the group consisting of: said amplitude of said optical signal, said phase of said optical signal and said polarization of said optical signal.

3. An apparatus according to claim 1, wherein said periodic modulation at said symbol rate comprises periodic modulation of each of said amplitude of said optical signal, said phase of said optical signal and said polarization of said optical signal.

4. An apparatus according to claim 1, said apparatus further comprising at least one amplitude adjustment mechanism for selectively varying a level of said periodic modulation.

5. An apparatus according to claim 1, said apparatus further comprising at least one variable delay mechanism for selectively varying the timing of said periodic modulation relative said output symbols.

6. An apparatus according to claim 1, wherein said multi-level data modulation format is a differential quadrature phase shift keying (DQPSK) modulation format.

7. An apparatus according to claim 1, wherein said multi-level data modulation format is a quadrature phase shift keying (QPSK) modulation format.

8. An apparatus according to claim 1, wherein said data modulated signal comprises forward error correction (FEC) coding

9. An apparatus according to claim 1, wherein said periodic modulation at said symbol rate is established by a clock coupled to said data modulator.

10. An apparatus according to claim 1, wherein said at least one overhead modulator is coupled to an output of said data modulator.

11. An apparatus according to claim 1, wherein said data modulator is coupled to an output of said at least one overhead modulator.

12. An apparatus according to claim 1, wherein said data is received by said apparatus in a modulation format different from said multi-level data modulation format.

13. A transmission system comprising: a transmitter comprising: a data modulator configured to modulate data on an optical signal using a multi-level data modulation format to provide a data modulated signal comprising multiple bits of said data encoded in each of a plurality of output symbols provided at a symbol rate; andat least one overhead modulator configured to impart a periodic modulation at said symbol rate of at least one characteristic selected from the group consisting of: an amplitude of said optical signal, a phase of said optical signal and a polarization of said optical signal.an optical transmission path coupled to said transmitter; anda receiver coupled to the optical transmission path.

14. A system according to claim 13, wherein said periodic modulation at said symbol rate comprises periodic modulation of at least two characteristics selected from the group consisting of: said amplitude of said optical signal, said phase of said optical signal and said polarization of said optical signal.

15. A system according to claim 13, wherein said periodic modulation at said symbol rate comprises periodic modulation of each of said amplitude of said optical signal, said phase of said optical signal and said polarization of said optical signal.

16. A system according to claim 13, said apparatus further comprising at least one amplitude adjustment mechanism for selectively varying a level of said periodic modulation.

17. A system according to claim 13, said apparatus further comprising at least one variable delay mechanism for selectively varying the timing of said periodic modulation relative said output symbols.

18. A system according to claim 13, wherein said multi-level data modulation format is a differential quadrature phase shift keying (DQPSK) modulation format.

19. A system according to claim 13, wherein said multi-level data modulation format is a quadrature phase shift keying (QPSK) modulation format.

20. A system according to claim 13, wherein said data modulated signal comprises forward error correction (FEC) coding

21. A system according to claim 13, wherein said periodic modulation at said symbol rate is established by a clock coupled to said data modulator.

22. A system according to claim 13, wherein said at least one overhead modulator is coupled to an output of said data modulator.

23. A system according to claim 13, wherein said data modulator is coupled to an output of said at least one overhead modulator.

24. A system according to claim 13, wherein said data is received by said transmitter in a modulation format different from said multi-level data modulation format.

25. A method of modulating an optical signal for transmission on an optical communication system, said method comprising: modulating data on said optical signal using a multi-level modulation format to encode multiple bits of said data in each of a plurality of output symbols provided at a symbol rate; andimparting a periodic modulation at said symbol rate of at least one characteristic selected from the group consisting of: an amplitude of said optical signal, a phase of said optical signal and a polarization of said optical signal.

26. A method according to claim 25, said method further comprising selectively adjusting a level of said periodic modulation at said symbol rate.

27. A method according to claim 25, said method further comprising selectively varying the timing of said periodic modulation of said amplitude of said optical signal relative said output symbols.