Locking a polarization-insensitive optical receiver

Patent metadata

Field	Value
Publication number	US-9832552-B2
Application number	US-201615013857-A
Country	US
Kind code	B2
Filing date	Feb 2, 2016
Priority date	Feb 2, 2016
Publication date	Nov 28, 2017
Grant date	Nov 28, 2017

Abstract

An optical receiver is described. Using silicon-photonic components that support a single polarization, the output of an optical receiver is independent of the polarization of an optical signal. In particular, using a polarization-diversity technique, the two orthogonal polarizations in a single-mode optical fiber are split in two and processed independently. For example, the two optical signals may be provided by a polarization-splitting grating coupler. Subsequently, a redistribution element provides mixtures of the two optical signals. Next, a wavelength channel in the two mixed optical signals is selected using a wavelength-selective filter (for example, using ring-resonator drop filters or an echelle grating) and converted into an electrical signal at an optical detector (such as a photodetector) to achieve polarization-independent operation.

First claim

What is claimed is:

1. An optical receiver, comprising:
a polarization-splitting grating coupler (PSGC) having an input port, a first output port and a second output port, wherein, during operation:
the input port receives an input optical signal having two orthogonal polarization components and multiple wavelengths;
the first output port provides a first optical signal having a type of transverse mode corresponding to one of the two polarization components; and
the second output port provides a second optical signal having the type of transverse mode corresponding to the other of the two polarization components;
a redistribution element, optically coupled to the first output port and the second output port, having a third output port and a fourth output port, wherein, during operation, the third output port and the fourth output ports provide mixtures of the first optical signal and the second optical signal;

a first optical waveguide optically coupled to the third output port;
a second optical waveguide optically coupled to the fourth output port;
a wavelength-selective filter, optically coupled to the first optical waveguide and the second optical waveguide, having output ports that, during operation, provide output optical signals having the wavelengths in the first optical signal and the second optical signal, wherein a given output port provides a given output optical signal having a given wavelength in the first optical signal and the second optical signal, wherein the wavelength-selective filter includes pairs of ring-resonator drop filters optically coupled to the first optical waveguide and the second optical waveguide, and optically coupled to the optical detectors, wherein a first ring-resonator drop filter in a given pair of ring-resonator drop filters includes one of the output ports and, during operation, outputs a first output optical signal having a first wavelength in the first optical signal and the second optical signal, and wherein a second ring-resonator drop filter in the given pair of ring-resonator drop filters includes another of the output ports and, during operation, outputs a second output optical signal having the first wavelength in the first optical signal and the second optical signal; and
optical detectors, optically coupled to the wavelength-selective filter, that, during operation, provide electrical signals corresponding to the output optical signals, wherein a given optical detector is optically coupled to at least the given output port and provides a given electrical signal corresponding to at least the given output optical signal.

2. The optical receiver of claim 1 , wherein, during operation, the PSGC projects the two orthogonal polarization components into the first optical signal on the first output port having the type of transverse mode and the second optical signal on the second output port having a second type of transverse mode.

3. The optical receiver of claim 1 , wherein the redistribution element includes one of: a directional coupler, and a multi-mode interferometer.

4. The optical receiver of claim 1 , wherein the given optical detector is optically coupled to the first ring-resonator drop filter and the second ring-resonator drop filter.

5. The optical receiver of claim 1 , wherein the wavelength-selective filter includes:
input ports that, during operation, optically couple to the first optical waveguide and the second optical waveguide;
a propagation region that, during operation, conveys the first optical signal and the second optical signal;
an optical device that, during operation, images and diffracts the first optical signal and the second optical signal using a reflective geometry; and
the output ports, optically coupled to diffraction orders of the optical device, that, during operation, provide the output optical signals having the wavelengths in the first optical signal and the second optical signal.

6. The optical receiver of claim 5 , wherein an incidence angle associated with a given diffraction order of the optical device is different than a diffraction angle associated with the given diffraction order.

7. The optical receiver of claim 5 , wherein the optical device includes a diffraction grating on a curved surface.

8. The optical receiver of claim 5 , wherein the optical device includes an echelle grating.

9. The optical receiver of claim 1 , further comprising:
a substrate;
a buried-oxide layer disposed on the substrate; and
a semiconductor layer disposed on the buried-oxide layer, wherein the first optical waveguide and the second optical waveguide are included in the semiconductor layer.

10. The optical receiver of claim 9 , wherein the substrate includes a semiconductor.

11. The optical receiver of claim 9 , wherein the wavelength-selective filter is included in the semiconductor layer.

12. The optical receiver of claim 1 , wherein the wavelength-selective filter includes first pairs of ring-resonator drop filters optically coupled to the first optical waveguide, and the optical detectors, and second pairs of ring-resonator drop filters optically coupled to the optical detectors and the second optical waveguide; and
wherein the optical receiver further comprises control logic that, during operation, locks a given first pair of ring-resonator drop filters to a first wavelength on the first optical waveguide and a given second pair of ring-resonator drop filters to the first wavelength on the second optical waveguide by:
applying a dithering electrical signal to a thermal-tuning mechanism that is thermally coupled to a given pair of ring-resonator drop filters in the given first pair of ring-resonator drop filters and the given second pair of ring-resonator drop filters in order to thermally modulate resonance wavelengths of the given pair of ring-resonator drop filters thereby creating a dithered optical signal associated with the given pair of ring-resonator drop filters;
detecting the dithered optical signal using a given optical detector;
determining an error signal based on the dithered optical signal and a threshold value; and
adjusting, based on the error signal, the dithering electrical signal applied to the thermal-tuning mechanism.

13. The optical receiver of claim 1 , wherein the wavelength-selective filter includes pairs of ring-resonator drop filters optically coupled to the first optical waveguide and the second optical waveguide, and optically coupled to the optical detectors; and
wherein the optical receiver further comprises control logic that, during operation, locks a given pair of ring-resonator drop filters by:
determining a polarity of an error signal by comparing a given electrical signal output by a given optical detector with a threshold value; and
reversing, based on a sign of the error signal, a sign of an amount of an increment that is applied to a thermal-tuning mechanism that is thermally coupled to the given pair of ring-resonator drop filters.

14. The optical receiver of claim 13 , wherein the threshold value is modified after a time interval.

15. The optical receiver of claim 1 , wherein one or more of the optical detectors are shared by different output ports in the wavelength-selective filter using time-division multiplexing.

16. A system, comprising:
a processor;
a non-transitory computer-readable medium having computer-readable instructions executable by the processor; and
an optical receiver, wherein the optical receiver includes:
a polarization-splitting grating coupler (PSGC) having an input port, a first output port and a second output port, wherein, dur

Assignees

• Oracle Int Corp

Inventors

• Lee Daniel Y
• Zheng Xuezhe
• Krishnamoorthy Ashok V

Classifications

• H04J14/06 Primary

  Polarisation multiplex systems · CPC title

• H04Q2011/0016

  using wavelength multiplexing or demultiplexing · CPC title

• H04J14/0212

  using optical switches or wavelength selective switches [WSS] · CPC title

• H04Q11/0005 Primary

  Switch and router aspects · CPC title

• H04Q2011/0009

  using wavelength filters · CPC title