Method and apparatus for the generation and detection of optical differential varied-multilevel phase-shift keying with pulse amplitude modulation (ODVMPSK/PAM) signals
View Patent ↗Methods and apparatus are described for generating and receiving amplitude and differential-phase encoded signals in which the number of phase states at a given amplitude level is always less than or equal to that at a higher amplitude level and at least two amplitude levels have different numbers of phase states.
1. A method of generating amplitude and differential-phase encoded optical signals comprising the steps of:
amplitude-modulating an optical carrier to produce an amplitude-modulated optical signal having a plurality of amplitude levels; and
phase-modulating the amplitude-modulated optical signal to produce an optical differential varied-multilevel phase-shift keying with pulse amplitude modulation (ODVMPSK/PAM) signal in which the number of phase states at a given amplitude level of the plurality of amplitude levels is less than or equal to the number of phase states at a higher amplitude level of the plurality of amplitude levels and at least two of the plurality of amplitude levels have different numbers of phase states.
2. The method of claim 1 , comprising phase-modulating the optical carrier using differential quadrature phase shift keying (DQPSK) before the amplitude-modulating step.
3. The method of claim 1 , wherein the phase-modulating step includes phase-modulating the amplitude-modulated optical signal depending on an amplitude level of a current symbol and an amplitude level of a preceding symbol.
4. The method of claim 1 , wherein the number of allowed phase states of a current symbol equals that of a preceding symbol when an amplitude of the current symbol is larger than an amplitude of the preceding symbol.
5. The method of claim 1 , wherein the phase-modulating step is synchronized to the amplitude-modulating step.
6. The method of claim 1 , wherein the amplitude-modulating step includes:
splitting the optical carrier into a number of optical signals, wherein each one of the number of optical signals has a different optical power;
phase-modulating at least one of the number of optical signals; and
combining the phase-modulated optical signals.
7. The method of claim 6 , wherein the optical carrier is split into log 2 (m)+1 optical signals having a respective power splitting distribution of (0.4+m/2), (m/4), (m/8), . . . , (1), and (1/2), wherein m is the number of amplitude levels.
8. The method of claim 6 , wherein the amplitude-modulating step includes aligning the phase-modulated optical signals before they are combined.
9. The method of claim 6 , wherein the step of phase-modulating the at least one of the number of optical signals is performed in accordance with a data tributary.
10. The method of claim 9 , wherein a phase of the at least one of the number of optical signals is modulated by an amount approximately equal to π.
11. The method of claim 1 , wherein the number of phase states at each of the plurality of amplitude levels is approximately proportional to a magnitude of an amplitude of each of the plurality of amplitude levels.
12. The method of claim 11 , wherein the number of phase states at each of the plurality of amplitude levels is approximately four times an order of each of the plurality of amplitude levels.
13. The method of claim 1 wherein the ODVMPSK/PAM signal is formatted with return-to-zero pulse formatting.
14. A method of generating amplitude and differential-phase encoded optical signals comprising the steps of:
phase-modulating an optical carrier to produce a phase-modulated optical signal; and
amplitude-modulating the phase-modulated optical signal with a plurality of amplitude levels to produce an optical differential varied-multilevel phase-shift keying with pulse amplitude modulation (ODVMPSK/PAM) signal in which the number of phase states at a given amplitude level of the plurality of amplitude levels is less than or equal to the number of phase states at a higher amplitude level of the plurality of amplitude levels and at least two of the plurality of amplitude levels have different numbers of phase states.
15. The method of claim 14 , wherein the phase-modulating step includes phase-modulating the optical carrier using differential quadrature phase shift keying (DQPSK).
16. An apparatus for generating amplitude and differential-phase encoded optical signals comprising:
an amplitude modulator, the amplitude modulator amplitude-modulating an optical carrier to produce an amplitude-modulated optical signal having a plurality of amplitude levels; and
a phase modulator, the phase modulator phase-modulating the amplitude-modulated optical signal to produce an optical differential varied-multilevel phase-shift keying with pulse amplitude modulation (ODVMPSK/PAM) signal in which the number of phase states at a given amplitude level of the plurality of amplitude levels is less than or equal to the number of phase states at a higher amplitude level of the plurality of amplitude levels and at least two of the plurality of amplitude levels have different numbers of phase states.
17. The apparatus of claim 16 , comprising a differential quadrature phase shift keying (DQPSK) modulator for modulating the optical carrier before it is amplitude-modulated.
18. The apparatus of claim 16 , wherein the phase modulator phase-modulates the amplitude-modulated optical signal depending on an amplitude level of a current symbol and an amplitude level of a preceding symbol.
19. The apparatus of claim 16 , wherein the number of allowed phase states of a current symbol equals that of a preceding symbol when an amplitude of the current symbol is larger than an amplitude of the preceding symbol.
20. The apparatus of claim 16 , wherein the amplitude modulator includes:
a splitter for splitting the optical carrier into a number of optical signals, wherein each one of the number of optical signals has a different optical power;
a further phase modulator for phase-modulating at least one of the number of optical signals; and
a combiner for combining the phase-modulated optical signals.
21. The apparatus of claim 20 , wherein the further phase modulator includes a Mach-Zehnder modulator biased at null.
22. The apparatus of claim 20 , wherein the optical carrier is split into log 2 (m)+1 optical signals having a respective power splitting distribution of (0.4+m/2), (m/4), (m/8), . . . , (1), and (1/2), wherein m is the number of amplitude levels.
23. The apparatus of claim 20 , wherein the further phase modulator phase-modulates the at least one of the number of optical signals in accordance with a data tributary.
24. The apparatus of claim 23 , wherein a phase of the at least one of the number of optical signals is modulated by an amount approximately equal to π.
25. The apparatus of claim 20 , wherein the amplitude modulator includes a phase controller for aligning the phase-modulated optical signals before they are combined.
26. The apparatus of claim 16 , wherein the number of phase states at each of the plurality of amplitude levels is approximately proportional to a magnitude of an amplitude of each of the plurality of amplitude levels.
27. The apparatus of claim 26 , wherein the number of phase states at each of the plurality of amplitude levels is approximately four times an order of each of the plurality of amplitude levels.
28. The apparatus of claim 16 , wherein the ODVMPSK/PAM signal is formatted with return-to-zero pulse formatting.
29. An apparatus for generating multilevel amplitude and phase encoded optical signals comprising:
a phase modulator, the phase modulator phase-modulating an optical carrier to produce a phase-modulated optical signal; and
an amplitude modulator, the amplitude modulator amplitude-modulating the phase-modulated optical signal with a plurality of amplitude levels to produce an optical differential varied-multilevel phase-shift keying with pulse amplitude modulation (ODVMPSK/PAM) signal in which the number of phase states at a given amplitude level of the plurality of amplitude levels is less than or equal to the number of phase states at a higher amplitude level of the plurality of amplitude levels and at least two of the plurality of amplitude levels have different numbers of phase states.
30. The apparatus of claim 29 , wherein the phase modulator includes a differential quadrature phase shift keying (DQPSK) modulator.