All-optical methods and systems
View Patent ↗An all-optical modulation format converter for converting optical data signals modulated in an on-off-keying (OOK) format to a phase-shift-keying (PSK) format. The OOK-to-PSK converter can be coupled to a delay-line interferometer to provide an all-optical wavelength converter for differential PSK (DPSK). The OOK-to-PSK converter can also be used in all-optical implementations of various functions, including, for example, exclusive-OR (XOR) logic, shift registers, and pseudo-random binary sequence (PRBS) generators.
1. An all-optical signal processing method comprising:
delaying a first on-off-keying (OOK) signal by a delay that is substantially the same as a pulse width of the first OOK signal to generate a delayed first signal;
delaying a second OOK signal by a delay that is substantially the same as a pulse width of the second OOK signal to generate a delayed second signal, wherein the first and second OOK signals are complementary is an inverse of the first signal so that when the first OOK signal is in a first state, the second OOK signal is in a second state and when the first OOK signal is in the second state, the second OOK signal is in the first state;
modulating with a first nonlinear element a periodic optical signal with the first OOK signal when the first OOK signal is in the first state and with the delayed second signal when the first OOK signal is in the second state to generate a first modulated signal;
modulating with a second nonlinear element the periodic optical signal with the second OOK signal when the first OOK signal is in the second state and with the delayed first signal when the first OOK signal is in the first state to generate a second modulated signal;
phase shifting the second modulated signal π radians relative to the first modulated signal; and
combining the first and second modulated signals to generate a-n a phase-shift-keying (PSK) output signal.
2. The method of claim 1 , wherein the periodic optical signal has a wavelength that is different from the first and second OOK signals.
3. The method of claim 2 , comprising passing the output signal and attenuating the first and second OOK signals.
4. The method of claim 1 , wherein the first and second OOK signals have different wavelengths.
5. The method of claim 1 , comprising generating the first and second OOK signals from a differential PSK (DPSK) input signal.
6. The method of claim 1 , wherein the periodic optical signal includes a continuous wave signal.
7. The method of claim 1 , wherein at least one of the first and second nonlinear elements comprises a semiconductor optical amplifier.
8. The method of claim 1 , wherein the first and second OOK signals have substantially the same wavelength.
9. The method of claim 1 , wherein the periodic optical signal has a wavelength substantially the same as at least one of the first and second OOK signals.
10. The method of claim 5 , wherein a current data content of the PSK output signal is equivalent to an exclusive OR of a current data content of the DPSK input signal and a previous data content of the DPSK input signal.
11. The method of claim 10 , wherein the encoding P n of the DPSK input signal is related to a data sequence D n to be sent according to P n =D n ⊕P n−N−1 , wherein n and N are integers.