Receivers and method for detecting a non-persistent communication superimposed on an overt communication channel
Aspects are generally directed to optical receivers and methods for detecting a non-persistent communication superimposed on an overt communication channel. In one example, an optical receiver includes an optical resonator to receive an optical signal having one or more symbols encoded thereon at a modulated symbol repetition rate, the modulated symbol repetition rate being modulated relative to a nominal symbol repetition rate. The optical resonator is configured to emit an intensity-modulated output optical signal that has a variation in an intensity thereof corresponding to a symbol transition in the optical signal. The optical receiver further includes signal processing circuitry including a clock configured to generate a reference signal, a photodetector configured to generate a trigger signal, and a non-persistent communication decoder configured to determine a temporal misalignment between the symbol transition and the nominal symbol repetition rate based on the reference signal and the trigger signal.
1. An optical receiver comprising:
an optical resonator positioned to receive an optical signal having one or more symbols encoded thereon at a modulated symbol repetition rate, the modulated symbol repetition rate being modulated relative to a nominal symbol repetition rate of the optical signal, wherein the optical resonator is configured to emit an intensity-modulated output optical signal, the intensity-modulated output optical signal having a variation in an intensity thereof corresponding to a symbol transition in the one or more symbols encoded on the optical signal; and
signal processing circuitry coupled to the optical resonator, the signal processing circuitry including:
a clock configured to generate a reference signal, the reference signal having a reference repetition rate that corresponds to the nominal symbol repetition rate of the optical signal,
a photodetector configured to generate a trigger signal having a pulse temporally aligned to the variation in the intensity-modulated output optical signal, and
a non-persistent communication decoder configured to determine a temporal misalignment between the symbol transition and the nominal symbol repetition rate based at least in part on the reference repetition rate of the reference signal and the trigger signal, the temporal misalignment being representative of a non-persistent communication.
2. The optical receiver of claim 1 , wherein the temporal misalignment is a jitter of a source of the optical signal.
3. The optical receiver of claim 2 , wherein the optical signal is a phase-modulated optical signal, and wherein the symbol transition corresponds to a phase change in the optical signal.
4. The optical receiver of claim 3 , wherein the non-persistent communication decoder is configured to mix the reference signal and the trigger signal to generate a mixed signal, and wherein a magnitude of the mixed signal is proportional to the temporal misalignment.
5. The optical receiver of claim 4 , wherein the pulse of the trigger signal is shorter in duration than the nominal symbol repetition rate.
6. The optical receiver of claim 4 , further comprising a low-pass filter coupled to non-persistent communication decoder and configured to filter the mixed signal.
7. The optical receiver of claim 1 , wherein the clock is configured to generate at least one of a saw clock signal and a square-wave clock signal as the reference signal, and the reference repetition rate of the reference signal is temporally aligned with the nominal symbol repetition rate.
8. An optical receiver comprising:
an optical resonator having a pair of semi-reflective surfaces positioned to receive an optical signal having one or more symbols encoded thereon at a modulated symbol repetition rate, the modulated symbol repetition rate being modulated relative to a nominal symbol repetition rate of the optical signal, wherein the optical resonator is configured to resonate the optical signal between the pair of semi-reflective surfaces and emit an intensity modulated output optical signal, and wherein the intensity-modulated output optical signal has a variation in an intensity thereof corresponding to a symbol transition in the one or more symbols encoded on the optical signal; and
signal processing circuitry coupled to the optical resonator, the signal processing circuitry including:
a clock configured to generate a reference signal, the reference signal having a reference repetition rate that corresponds to the nominal symbol repetition rate of the optical signal, and
a non-persistent communication decoder configured to determine a temporal misalignment between the symbol transition and the nominal symbol repetition rate based at least in part on the reference repetition rate of the reference signal and the intensity-modulated output optical signal, the temporal misalignment being representative of a non-persistent communication.
9. The optical receiver of claim 8 , wherein the temporal misalignment is a jitter of a source of the optical signal.
10. The optical receiver of claim 9 , wherein the optical signal is a phase-modulated optical signal, and wherein the symbol transition corresponds to a phase change in the optical signal.
11. The optical receiver of claim 10 , wherein the non-persistent communication decoder is configured to mix the reference signal and the intensity-modulated output optical signal to generate a mixed signal, and wherein a magnitude of the mixed signal is proportional to the temporal misalignment.
12. The optical receiver of claim 11 , further comprising a low-pass filter coupled to non-persistent communication decoder and configured to filter the mixed signal.
13. The optical receiver of claim 8 , wherein the clock is configured to generate at least one of a saw clock signal and a square-wave clock signal as the reference signal, and the reference repetition rate of the reference signal is temporally aligned with the nominal symbol repetition rate.
14. A method of detecting a communication superimposed on an overt communication channel, the method comprising:
receiving an optical signal having one or more symbols encoded thereon at a modulated symbol repetition rate, the modulated symbol repetition rate being modulated relative to a nominal symbol repetition rate of the optical signal;
resonating the optical signal within an optical resonator;
emitting an intensity-modulated output optical signal from the optical resonator, the intensity-modulated output optical signal having a variation in an intensity thereof corresponding to a symbol transition in the one or more symbols encoded on the optical signal;
receiving a reference signal, the reference signal having a reference repetition rate that corresponds to the nominal symbol repetition rate of the optical signal; and
determining, based on the reference signal and the intensity-modulated output optical signal, a temporal misalignment between the symbol transition and the nominal symbol repetition rate, the temporal misalignment being representative of a non-persistent communication.
15. The method of claim 14 , wherein resonating the optical signal within the optical resonator includes trapping the optical signal between a pair of semi-reflective surfaces by reflecting at least a portion of the optical signal between the pair of semi-reflective surfaces.
16. The method of claim 15 , wherein determining the temporal misalignment includes mixing the reference signal and the intensity-modulated output optical signal to generate a mixed signal, wherein a magnitude of the mixed signal is proportional to the temporal misalignment.
17. The method of claim 14 , further comprising generating a trigger signal, the trigger signal having a pulse temporally aligned to the variation in the intensity-modulated output optical signal.
18. The method of claim 17 , wherein determining the temporal misalignment includes mixing the reference signal and the trigger signal to generate a mixed signal, and wherein a magnitude of the mixed signal is proportional to the temporal misalignment.
19. The method of claim 18 , further comprising low-pass filtering the mixed signal.
20. The method of claim 14 , further comprising generating at least one of a saw clock signal and a square-wave clock signal as the reference signal, wherein the reference repetition rate of the reference signal is temporally aligned with the nominal symbol repetition rate.