Correlation-control QPSK transmitter
An optical transmitter utilizing a multi-level data modulator to produce a PDM-QPSK signal, a one-bit delay interferometer configured to correlate the multi-level data modulated signal and an optical filter configured to combine the correlated multi-level data modulated signal with one or more neighboring signals prior to transmitting over one of a plurality of optical channels. The PDM-QPSK correlated signal is configured to reduce the signal spectrum thereby increasing spectral efficiency of the transmitted signal.
1. A method for correlation-control of a quadrature phase-shift keying signal, comprising:
receiving a polarization division multiplexed quadrature phase-shift keying (PDM-QPSK) signal;
correlating the PDM-QPSK signal using a delay line interferometer to provide a reduced signal spectrum as compared to a non-correlated modulated signal; and
transmitting the correlated PDM-QPSK signal over an optical medium.
2. The method of claim 1 wherein the delay line interferometer is a first delay line interferometer to create a two-tap correlation PDM-QPSK signal.
3. The method of claim 1 wherein the a delay line interferometer is a first delay line interferometer, the method further comprising further correlating the transmitted correlated PDM-QPSK signal utilizing a second delay line interferometer to correlate the PDM-QPSK.
4. The method of claim 1 wherein the delay line interferometer comprises a Mach-Zehnder interferometer to correlate the PDM-QPSK signal.
5. The method of claim 1 , further comprising:
using an optical filter to combine the correlated PDM-QPSK signal with at least one neighboring signal prior to transmitting the correlated PDM-QPSK signal over a channel.
6. The method of claim 5 , further comprising using an optical filter to maintain a short inter-symbol interference length by adding a correlation property into the transmitted correlated PDM-QPSK signal after sending the correlated PDM-QPSK signal over the channel.
7. The method of claim 1 , further comprising:
receiving the correlated QPSK signal, wherein the correlated QPSK signal has a short inter-symbol interference length; and
using multi-symbol detection to interpret the correlated QPSK signal.
8. An optical communication system configured to transmit a modulated optical signal having a plurality of optical channels, each of said channels at a particular wavelength, said system comprising:
an optical transmitter configured to modulate data on an optical signal using a multi-level data modulation format, said optical transmitter comprising:
a delay line interferometer configured to correlate the multi-level data modulated signal; and
an optical filter configured to combine the correlated multi-level data modulated signal with one or more neighboring optical signals prior to transmitting over one of said plurality of channels;
an optical transmission path coupled to said transmitter; and
a receiver coupled to the optical transmission path to receive said multi-level data modulated optical signal.
9. The optical communication system of claim 8 wherein said transmitter further comprises a PDM-QPSK modulator coupled to said delay line interferometer and configured to generate said multi-level data modulated signal.
10. The optical communication system of claim 8 wherein said optical filter combines the correlated PDM-QPSK modulated signal with the one or more neighboring optical signals prior to transmitting over the one of said plurality of channels.
11. The optical communication system of claim 8 wherein the delay line interferometer is a DPSK demodulator.
12. An optical transmitter comprising:
a modulator configured to generate a multi-level data modulated signal;
a delay line interferometer configured to correlate the multi-level data modulated signal; and
an optical filter configured to combine the correlated multi-level data modulated signal with one or more neighboring signals prior to transmitting over one of a plurality of optical channels.
13. The optical transmitter of claim 12 wherein said modulator is a PDM-QPSK modulator.
14. The optical transmitter of claim 13 wherein said modulator is a first PDM-QPSK modulator, said transmitter further comprising a second PDM-QPSK modulator.
15. The optical transmitter of claim 14 further comprising a polarization beam splitter for combining a first output signal from said first PDM-QPSK modulator and a second output signal from said second PDM-QPSK modulator, said combined signal supplied to said delay line interferometer.
16. The optical transmitter of claim 12 wherein said multi-level data modulated signal is a PDM-QPSK modulated signal.
17. The optical transmitter of claim 16 wherein said a delay line interferometer is configured to correlate the QPSK signal is a first delay line interferometer, said transmitter further comprising a second delay line interferometer coupled to a constructive port of the first delay line interferometer to produce a three-tap correlated signal.
18. The optical transmitter of claim 17 wherein said first and second delay line interferometers are a first DPSK demodulator and a second DPSK demodulator respectively.
19. The optical transmitter of claim 12 wherein the optical filter is further configured to generate a short inter-symbol interference length.
20. The optical transmitter of claim 12 wherein said delay line interferometer is a DPSK demodulator.