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/NXOR) and OR logic, shift registers, and pseudo-random binary sequence (PRBS) generators.
1. An all-optical pseudo-random binary sequence (PRBS) generator comprising:
an on-off-keying (OOK) to phase-shift-keying (PSK) converter;
a delay interferometer;
a wavelength conversion block, the wavelength conversion block arranged between the delay interferometer and the OOK-to-PSK converter; and
a feedback loop, the feedback loop coupling an output of the OOK-to-PSK converter to an input of the delay interferometer.
2. The PRBS generator of claim 1 wherein the OOK-to-PSK converter includes:
a first delay element, the first delay element delaying a first signal to generate a delayed first signal;
a second delay element, the second delay element delaying a second signal to generate a delayed second signal, wherein the second signal is an inverse of the first signal so that when the first signal is in a first state, the second signal is in a second state and when the first signal is in the second state, the second signal is in the first state;
a first nonlinear element, the first nonlinear element receiving the first signal, the delayed second signal, and a periodic optical signal;
a second nonlinear element, the second nonlinear element receiving the second signal, the delayed first signal, and the periodic optical signal;
a phase shifter, the phase shifter introducing a phase offset between the output signals of the first and second nonlinear elements, the phase offset being substantially equal to π radians; and
a combiner, the combiner combining the phase-offset output signals of the first and second nonlinear elements.
3. The PRBS generator of claim 1 comprising:
an optical bandpass filter, the optical bandpass filter being arranged in the feedback loop between the output of the OOK-to-PSK converter and the input of the delay interferometer.
4. The PRBS generator of claim 1 comprising an OOK output.
5. The PRBS generator of claim 1 comprising a PSK output.
6. The PRBS generator of claim 1 , wherein the delay interferometer includes a tap delay and a directional coupler, and wherein an XOR operation between an output of the feedback loop and a tap point of the tap delay is performed at the directional coupler.
7. The PRBS generator of claim 1 , wherein the wavelength conversion block includes:
a first wavelength converter coupled to a non-inverted output of the delay interferometer;
a second wavelength converter coupled to an inverted output of the delay interferometer;
a first optical band pass filter coupled to an output of the first wavelength converter; and
a second optical band pass filter coupled to an output of the second wavelength converter,
wherein the first and second wavelength converters convert signals to a first wavelength from a second wavelength and the first and second optical band pass filters pass signals of the first wavelength and block signals of the second wavelength.
8. The PRBS generator of claim 7 , wherein the OOK-to-PSK converter generates PSK signals of the second wavelength based on OOK signals of the first wavelength.
9. The PRBS generator of claim 2 , wherein at least one of the first and second nonlinear elements includes a semiconductor optical amplifier.