Method and apparatus for demodulating an optical differential phase-shift keying signal

1. An apparatus for demodulating an optical Differential Phase-Shift Keying (DPSK) signal, comprising:

a self-homodyne receiver for receiving the optical signal;

a converter for converting the optical signal received by the self-homodyne receiver into a representative electrical signal; and

a processor that processes the representative electrical signal using decision feedback multi-symbol detection in order to obtain a decision variable that indicates a differential phase-shift in the optical signal, the decision feedback multi-symbol detection utilized by the processor being implemented according to the following equation:

x ( nT+{tilde over (t)} )= u ( nT+{tilde over (t)} )+ w·u ( nT+{tilde over (t)} )· x [( n− 1) T+{tilde over (t)} ]·exp[− jc ( n− 1)],

wherein the complex number u(t) is representative of the electrical signal converted by the converter, the real number w is a weighting factor, the complex number exp[−jc(n−1)] is representative of the estimated phase of the previous data symbol and the complex number x(t) is the decision variable.

2. The apparatus of claim 1 , wherein the self-homodyne receiver consists of a pair of interferometers for receiving in-phase and quadrature components of the optical signal.

3. The apparatus of claim 1 , wherein binary DPSK is adopted and the decision feedback multi-symbol detection simplifies into:

x ( nT+{tilde over (t)} )= u ( nT+{tilde over (t)} )+ w·u ( nT+{tilde over (t)} )· x [( n− 1) T+{tilde over (t)}]·c ( n− 1),

wherein the complex number u(t) is representative of the electrical signal converted by the converter, the real number w is a weighting factor, the real number c(n−1) is representative of the estimated previous data symbol and the real part of the complex number x(t) is the decision variable.

4. The apparatus of claim 1 , wherein quaternary DPSK is adopted and the decision feedback multi-symbol detection simplifies into:

x ( nT+{tilde over (t)} )= u ( nT+{tilde over (t)} )+ w·u ( nT+{tilde over (t)} )· x [( n− 1) T+{tilde over (t)}]·c *( n− 1),

wherein the complex number u(t) is representative of the electrical signal converted by the converter, the real number w is a weighting factor, the complex number c(n−1) is representative of the estimated previous data symbol, the complex number x(t) is the decision variable, and * denotes complex conjugation.

5. The apparatus of claim 1 , wherein further comprising a sampler for sampling the electrical signal converted by the converter and wherein the decision feedback multi-symbol detection is implemented in digital form.

6. A method for demodulating an optical Differential Phase-Shift Keying (DPSK) signal, comprising the steps of:

receiving the optical signal using a self-homodyne receiver;

converting the optical signal received by the self-homodyne receiver into a representative electrical signal; and

processing the representative electrical signal using decision feedback multi-symbol detection in order to obtain a decision variable that indicates a differential phase-shift in the optical signal, wherein the decision feedback multi-symbol detection utilized in the step of processing follows the following equation:

x ( nT+{tilde over (t)} )= u ( nT+{tilde over (t)} )+ w·u ( nT+{tilde over (t)} )· x [( n− 1) T+{tilde over (t)} ]·exp[− jc ( n− 1)],

wherein the complex number u(t) is representative of the electrical signal converted by the converter, the real number w is a weighting factor, the complex number exp[jc(n−1)] is representative of the estimated phase of the previous data symbol and the complex number x(t) is the decision variable.

7. The method of claim 6 , wherein the adopted modulation is differential binary phase-shift keying.

8. The method of claim 6 , wherein the adopted modulation is quaternary differential phase-shift keying.