Method and system for the monolithic integration of circuits for monitoring and control of RF signals
A method of operating a BPSK modulator includes receiving an RF signal at the BPSK modulator and splitting the RF signal into a first portion and a second portion that is inverted with respect to the first portion. The method also includes receiving the first portion at a first arm of the BPSK modulator, receiving the second portion at a second arm of the BPSK modulator, applying a first tone to the first arm of the BPSK modulator, and applying a second tone to the second arm of the BPSK modulator. The method further includes measuring a power associated with an output of the BPSK modulator and adjusting a phase applied to at least one of the first arm of the BPSK modulator or the second arm of the BPSK modulator in response to the measured power.
1. An apparatus for monitoring and controlling an RF signal that is provided by a transmitter into an optical communication channel, the apparatus comprising:
an input waveguide;
a receiver; and
a feedback path; wherein:
the input waveguide operably couples a portion of the RF signal in the optical communications channel to the receiver;
the receiver comprises:
a photodiode that generates an electronic output in response to the portion of the RF signal, and
an analog spectral monitoring unit that generates feedback, from the portion of the RF signal, on channel distortion within the optical communication channel;
the feedback path provides the feedback on channel distortion within the optical communication channel to the transmitter; and
the input waveguide, the receiver and the feedback path are integrated within a silicon photonics chip.
2. The apparatus of claim 1 , wherein the analog spectral monitoring unit comprises a plurality of spectral filters.
3. The apparatus of claim 2 , wherein the plurality of spectral filters include:
a low pass filter that provides a low frequency passband, bounded by an low pass cutoff frequency;
a high pass filter that provides a high frequency passband, bounded by a high pass cutoff frequency; and
a bandpass filter that provides a center passband, bounded by the low pass cutoff frequency and the high pass cutoff frequency.
4. The apparatus of claim 2 , further comprising a plurality of RMS detectors equal in number to the plurality of spectral filters, wherein:
each of the plurality of spectral filters provides an output passband to a corresponding one of the RMS detectors; and
each of the RMS detectors provides an output that indicates distortion present in the corresponding output passband.
5. The apparatus of claim 1 , wherein the receiver further comprises a splitter and rotator that receive the portion of the RF signal from the input waveguide, the splitter and rotator being coupled with two output waveguides, wherein:
the splitter and rotator couple TE polarized light from the input waveguide into a first one of the output waveguides; and
the splitter and rotator couple TM polarized light from the input waveguide into a second one of the output waveguides.
6. The apparatus of claim 5 , further comprising a WDM filter, and wherein the TE polarized light and the TM polarized light from the respective first and second output waveguides are filtered by the WDM filter before passing to the photodiode and the spectral monitoring unit.
7. The apparatus of claim 6 , wherein the photodiode is one of a plurality of photodiodes, and the WDM filter directs input light of a different wavelength to each of the plurality of photodiodes.
8. The apparatus of claim 1 , further comprising the transmitter, and wherein the transmitter is integrated with the input waveguide, the receiver and the feedback path within the silicon photonics chip.
9. The apparatus of claim 8 , the transmitter comprising a BPSK modulator, and wherein the receiver measures power associated with an output of the BPSK modulator by spectrally filtering the output of the BPSK modulator.
10. A method for monitoring and controlling an RF signal that is provided by a transmitter into an optical communication channel, the method comprising:
operably coupling the RF signal, through an input waveguide that carries the optical communications channel, to a receiver;
generating, with a photodiode in the receiver, an electronic output in response to the RF signal;
generating, with an analog spectral monitoring unit, feedback on channel distortion within the optical communication channel; and
providing the feedback on channel distortion to the transmitter through a feedback path;
wherein the steps of operably coupling the RF signal, generating the high speed electronic output, generating the feedback on channel distortion within the optical communication channel, and providing the feedback on channel distortion are performed with the input waveguide, the receiver and the feedback path integrated within a silicon photonics chip.
11. The method of claim 10 , wherein generating the feedback on channel distortion within the optical communication channel comprises coupling the RF signal into a plurality of spectral filters.
12. The method of claim 11 , wherein coupling the RF signal into the plurality of spectral filters include coupling the RF signal into:
a low pass filter that provides a low frequency passband, bounded by an low pass cutoff frequency;
a high pass filter that provides a high frequency passband, bounded by a high pass cutoff frequency; and
a bandpass filter that provides a center passband, bounded by the low pass cutoff frequency and the high pass cutoff frequency.
13. The method of claim 11 , wherein:
the analog spectral monitoring unit includes a plurality of RMS detectors equal in number to the plurality of spectral filters;
each of the plurality of spectral filters provides an output passband to a corresponding one of the RMS detectors; and
generating the feedback on the channel distortion within the optical communication channel comprises providing an output from each of the RMS detectors, that indicates distortion present in the corresponding output passband.
14. The method of claim 10 , wherein the receiver further comprises a splitter and rotator that receive the portion of the RF signal from the input waveguide, and wherein:
the splitter and rotator couple TE polarized light from the input waveguide into a first output waveguide; and
the splitter and rotator couple TM polarized light from the input waveguide into a second output waveguide.
15. The method of claim 14 , wherein the receiver further comprises a WDM filter, and wherein:
the WDM filter filters the TE polarized light and the TM polarized light from the respective first and second output waveguides before passing the TE polarized light and the TM polarized light to the photodiode and the spectral monitoring unit.
16. The method of claim 15 , wherein the photodiode is one of a plurality of photodiodes, and further comprising directing input light of a different wavelength to each of the plurality of photodiodes, by the WDM filter.
17. The method of claim 10 , wherein the steps of operably coupling the RF signal, generating the high speed electronic output, generating the feedback on channel distortion within the optical communication channel, and providing the feedback on channel distortion are performed with the transmitter integrated with the input waveguide, the receiver and the feedback path in the silicon photonics chip.
18. The method of claim 17 , wherein generating the feedback on channel distortion within the optical communications channel comprises measuring power associated with an output of a BPSK modulator within the transmitter by spectrally filtering the output of the BPSK modulator.