Photonic Filter Bank System and Method of Use

• US 20190331912A1
• Filed: 04/04/2019
• Published: 10/31/2019
• Est. Priority Date: 04/30/2018
• Status: Active Grant

• Current Assignee: The Trustees of Princeton University (Princeton University)
• Original Assignee: The Trustees of Princeton University (Princeton University)
• Inventors: Tait, Alexander N., Wu, Allie X., de Lima, Thomas Ferreira, Nahmias, Mitchell A., Shastri, Bhavin J., Prucnal, Paul R.
• Granted Patent: US 10,670,860 B2
• Time in Patent Office: Days
• CPC Class Codes: G02B 27/0012 Optical design, e.g. procedures, algorithms, optimisation routines
• CPC Class Codes: G02F 1/225 in an optical waveguide structure

Abstract

A system for photonic computing, preferably including: an input module, computation module, and/or control module, wherein the computation module preferably includes one or more filter banks and/or detectors. A photonic filter bank system, preferably including two waveguides and a plurality of optical filters arranged between the waveguides. A method for photonic computing, preferably including: controlling a computation module; controlling an input module; and/or receiving outputs from the computation module.

Claims

1. A method for optical computation comprising:

throughout a time period, controlling a filter bank based on a plurality of weights, comprising;

based on a first weight of the plurality, determining a first control signal;

based on a second weight of the plurality, determining a second control signal;

providing the first control signal to a first optical filter of the filter bank, wherein the first optical filter is associated with a first optical characteristic; and

providing the second control signal to a second optical filter of the filter bank, wherein the second optical filter is associated with a second optical characteristic different from the first optical characteristic;

during the time period, receiving an optical input signal at an input waveguide of the filter bank, wherein the optical input signal comprises;

a first portion having the first optical characteristic; and

a second portion having the second optical characteristic; and

during the time period, in response to receiving the optical input signal at the input waveguide;

at the first optical filter, based on the first control signal, coupling a first signal subportion of the first portion from the input waveguide to an output waveguide of the filter bank;

at the second optical filter, based on the second control signal, coupling a second signal subportion of the second portion from the input waveguide to the output waveguide;

at the second optical filter, coupling a first leakage subportion of the first portion from the input waveguide to the output waveguide; and

at the output waveguide, outputting the first signal subportion, the second signal subportion, and the first leakage subportion, wherein the first signal subportion is phase-shifted with respect to the first leakage subportion.

2. The method of claim 1, wherein:

the first optical characteristic is a first optical wavelength;

the second optical characteristic is a second optical wavelength;

the first optical filter comprises a first wavelength-selective filter; and

the second optical filter comprises a second wavelength-selective filter.

3. The method of claim 2, wherein:

the first wavelength-selective filter comprises a first microresonator;

the second wavelength-selective filter comprises a second microresonator;

providing the first control signal to the first optical filter alters a first resonance wavelength of the first microresonator; and

providing the second control signal to second first optical filter alters a second resonance wavelength of the second microresonator.

4. The method of claim 3, wherein:

the first wavelength-selective filter is a first even-pole filter; and

the second wavelength-selective filter is a second even-pole filter.

5. The method of claim 1, wherein the first signal subportion and the first leakage subportion define a phase difference, wherein a magnitude of the phase difference is between π

/4 radians and 3π

/4 radians.

6. The method of claim 5, wherein the phase difference is substantially equal to ±

π

/2 radians.

7. The method of claim 1, further comprising:

throughout a second time period after the time period, controlling the filter bank based on a second plurality of weights, comprising;

based on a third weight of the second plurality, determining a third control signal;

based on a fourth weight of the second plurality, determining a fourth control signal;

providing the third control signal to the first optical filter; and

providing the fourth control signal to the second optical filter;

during the second time period, receiving a second optical input signal at the input waveguide, wherein the second optical input comprises;

a third portion having the first optical characteristic; and

a fourth portion having the second optical characteristic; and

during the second time period, in response to receiving the second optical input signal at the input waveguide;

at the first optical filter, based on the third control signal, coupling a third signal subportion of the third portion from the input waveguide to the output waveguide;

at the second optical filter, based on the fourth control signal, coupling a fourth signal subportion of the fourth portion from the input waveguide to the output waveguide;

at the second optical filter, coupling a third leakage subportion of the third portion from the input waveguide to the output waveguide; and

at the output waveguide, outputting the third signal subportion, the fourth signal subportion, and the third leakage subportion, wherein the third signal subportion is phase-shifted with respect to the third leakage subportion by a phase difference;

wherein the first signal subportion is phase-shifted with respect to the first leakage subportion substantially by the phase difference.

8. The method of claim 7, wherein:

a first amplitude ratio of the first signal subportion to the first portion is substantially equal to the first weight; and

a third amplitude ratio of the third signal subportion to the third portion is substantially equal to the third weight.

9. The method of claim 1, wherein:

the filter bank further comprises a third optical filter associated with a third optical characteristic different from the first and second optical characteristics;

the optical input signal further comprises a third portion having the third optical characteristic;

controlling the filter bank based on the plurality of weights further comprises;

based on a third weight of the plurality, determining a third control signal; and

providing the third control signal to the third optical filter; and

the method further comprises, during the time period, in response to receiving the optical input signal at the input waveguide;

at the third optical filter, based on the third control signal, coupling a third signal subportion of the third portion from the input waveguide to the output waveguide;

at the third optical filter, coupling a second leakage subportion of the second portion from the input waveguide to the output waveguide; and

at the output waveguide, outputting the third signal subportion and the second leakage subportion, wherein the second signal subportion is phase-shifted with respect to the second leakage subportion.

10. The method of claim 9, further comprising, during the time period, in response to receiving the optical input signal at the input waveguide:

at the first optical filter, coupling a fourth leakage subportion of the second portion from the input waveguide to the output waveguide; and

at the output waveguide, outputting the fourth leakage subportion, wherein the second signal subportion is phase-shifted with respect to the fourth leakage subportion.

11. The method of claim 1, wherein:

the input waveguide defines a first propagation vector, wherein the optical input signal propagates along the first propagation vector;

the output waveguide defines a second propagation vector, wherein the first signal subportion and the second signal subportion propagate along the second propagation vector; and

a dot product of the first and second propagation vectors is greater than zero.

12. The method of claim 1, wherein:

the first optical filter couples the first signal subportion from a first point of the input waveguide to a second point of the output waveguide;

the second optical filter couples the second signal subportion and the first leakage subportion from a third point of the input waveguide to a fourth point of the output waveguide;

the first signal subportion propagates along a first input waveguide section from the third point to the first point;

the second signal subportion and the first leakage subportion propagate along a second input waveguide section from the fourth point to the second point; and

an optical path length difference between the first input waveguide section and the second input waveguide section is substantially non-zero.

13. A system comprising a spectral filter bank, the spectral filter bank comprising:

a first waveguide;

a second waveguide;

a first wavelength-selective optical filter arranged between a first point of the first waveguide and a second point of the second waveguide, wherein the first wavelength-selective optical filter is configured to couple light of a first wavelength between the first point and the second point;

a second wavelength-selective optical filter arranged between a third point of the first waveguide and a fourth point of the second waveguide, wherein the second wavelength-selective optical filter is configured to couple light of a second wavelength between the third point and the fourth point;

wherein;

the spectral filter bank defines a first path between the first and fourth points via the first wavelength-selective optical filter;

the spectral filter bank defines a second path between the first and fourth points via the second wavelength-selective optical filter; and

an optical path length difference between the first path and the second path is substantially non-zero.

14. The system of claim 13, wherein:

the first wavelength-selective optical filter comprises a first tunable filter; and

the second wavelength-selective optical filter comprises a second tunable filter.

15. The system of claim 14, wherein:

the first tunable filter is a first microresonator; and

the second tunable filter is a second microresonator.

16. The system of claim 15, wherein:

the first wavelength-selective optical filter is a first even-pole filter; and

the second wavelength-selective optical filter is a second even-pole filter.

17. The system of claim 13, wherein:

the spectral filter bank further comprises;

a third waveguide;

a third wavelength-selective optical filter arranged between a fifth point of the first waveguide and a sixth point of the second waveguide, wherein the third wavelength-selective optical filter is configured to couple light of a third wavelength between the fifth point and the sixth point;

the spectral filter bank defines a third path between the first and sixth points via the third wavelength-selective optical filter;

the spectral filter bank defines a fourth path between the first and sixth points via the second wavelength-selective optical filter; and

a second optical path length difference between the third path and the fourth path is substantially non-zero.

18. The system of claim 17, wherein the optical path length difference is substantially equal to the second optical path length difference.

19. The system of claim 18, wherein the optical path length difference is within λ

/8n of λ

/n (k±

¼

), wherein λ

is the first wavelength, n is an index of refraction of the spectral filter bank, and k is an integer.

20. The system of claim 19, wherein the optical path length difference is substantially equal to λ

/4n.

21. The system of claim 13, wherein:

the first waveguide defines a substantially linear optical path between the first point and the third point; and

the second waveguide defines a substantially non-linear optical path between the second point and the fourth point.

22. A method for spectral filtering, the method comprising, at a spectral filter bank comprising an input waveguide, an output waveguide, a first optical filter, and a second optical filter:

at the input waveguide, receiving an optical signal comprising;

a first portion within a first wavelength band; and

a second portion within a second wavelength band, wherein the first and second wavelength bands do not overlap;

at the first optical filter, coupling a first signal subportion of the first portion from the input waveguide to the output waveguide;

at the second optical filter, coupling a second signal subportion of the second portion from the input waveguide to the output waveguide;

at the second optical filter, coupling a first leakage subportion of the first portion from the input waveguide to the output waveguide; and

at the output waveguide, outputting the first signal subportion, the second signal subportion, and the first leakage subportion, wherein the first signal subportion is phase-shifted with respect to the first leakage subportion.