# US 12,191,870 B2 · Clock jitter and spurious tone cancellation system using optical delay

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- Number: US 12,191,870 B2
- Document ID: US12191870B2
- Status: Granted
- Kind: B2
- Application number: 18/162,091
- Filed: 2023-01-31
- Published: 2024-08-01
- Granted: 2025-01-07
- Earliest claimed: 2023-01-31
- Assignees: Cisco Technology, Inc.
- Applicants: Cisco Technology, Inc.
- Inventors: Abhishek Bhat; Sujit Handanhal Ramachandra
- Web page: https://patentgrep.com/patent/US12191870B2

## CPC

- H03L 7/1075: {by changing characteristics of the loop filter, e.g. changing the gain, changing the bandwidth (H03L7/1072 takes precedence)}
- H01S 3/13: Stabilisation of laser output parameters, e.g. frequency or amplitude
- H03L 7/0818: {the controlled phase shifter comprising coarse and fine delay or phase-shifting means}
- H03L: AUTOMATIC CONTROL, STARTING, SYNCHRONISATION OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES (generation of oscillations H03B)
- H01S: DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL

## Abstract

Techniques to reduce or eliminate phase noise and jitter from a noisy clock signal. A method includes generating an electrical clock signal, generating a delayed optical clock signal based on the electrical clock signal, detecting a phase difference between the electrical clock signal and the delayed optical clock signal, and processing, based on the phase difference, the electrical clock signal to obtain a reduced phase noise version of the electrical clock signal.

## Claims

### Claim 1

A method comprising:
generating an electrical clock signal;
generating, using a photonic crystal resonator in a photonics integrated circuit, a delayed optical clock signal based on the electrical clock signal;
detecting a phase difference between the electrical clock signal and the delayed optical clock signal; and
processing, based on the phase difference, the electrical clock signal to obtain a reduced phase noise version of the electrical clock signal.

### Claim 2 (depends on 1)

The method of claim 1, wherein generating the delayed optical clock signal comprises passing an optical signal, generated based on the electrical clock signal, through the photonic crystal resonator.

### Claim 3 (depends on 2)

The method of claim 2, wherein generating the delayed optical clock signal comprises passing the optical signal through a cascaded add-drop filter based on the photonic crystal resonator.

### Claim 4 (depends on 2)

The method of claim 2, wherein generating the delayed optical clock signal comprises modulating the optical signal using a resonant driver and a Mach-Zehnder Interferometer.

### Claim 5 (depends on 4)

The method of claim 4, further comprising tapping a laser light source as an input to the Mach-Zehnder Interferometer.

### Claim 6 (depends on 1)

The method of claim 1, further comprising detecting the phase difference between the electrical clock signal and the delayed optical clock signal using an XOR-based phase detector.

### Claim 7 (depends on 6)

The method of claim 6, further comprising calibrating the XOR-based phase detector with a calibration loop.

### Claim 8 (depends on 1)

The method of claim 1, wherein processing the electrical clock signal to obtain a reduced noise version of the electrical clock signal comprises controlling a voltage-controlled delay line based on a signal representative of the phase difference.

### Claim 9 (depends on 1)

The method of claim 1, wherein the reduced phase noise version of the electrical clock signal comprises reduced spurious tones compared to the electrical clock signal.

### Claim 10

A method comprising:
generating a clock signal;
modulating an optical signal based on the clock signal to obtain a modulated optical signal;
delaying, using a photonic crystal resonator in a photonics integrated circuit, the modulated optical signal to obtain a delayed modulated optical signal;
converting the delayed modulated optical signal to an electrical signal;
detecting a phase difference between the electrical signal and the clock signal; and
processing, based on the phase difference, the clock signal to obtain a reduced phase noise version of the clock signal.

### Claim 11 (depends on 10)

The method of claim 10, further comprising filtering a signal representative of the phase difference.

### Claim 12 (depends on 10)

The method of claim 10, wherein delaying the modulated optical signal to obtain a delayed modulated optical signal comprises passing a modulated optical signal through the photonic crystal resonator.

### Claim 13

A device comprising:
a clock configured to generate a clock signal;
an optical modulator configured to modulate an optical signal based on the clock signal to obtain a modulated optical signal;
an optical delay comprising a photonic crystal resonator disposed in a photonics integrated circuit, configured to delay the modulated optical signal to obtain a delayed modulated optical signal;
a photo detector configured to convert the delayed modulated optical signal to an electrical signal;
a phase detector configured to detect a phase difference between the electrical signal and the clock signal; and
a voltage controlled delay line configured to process, based on the phase difference, the clock signal to obtain a reduced phase noise version of the clock signal.

### Claim 14 (depends on 13)

The device of claim 13, further comprising a filter configured to filter a signal representative of the phase difference.

### Claim 15 (depends on 13)

The device of claim 13, wherein the optical modulator comprises a Mach-Zehnder Interferometer, and the device further comprises a resonant driver configured to drive the Mach-Zehnder Interferometer.

### Claim 16 (depends on 15)

The device of claim 15, further comprising an optical tap configured to tap a laser light source as an input to the Mach-Zehnder Interferometer.

### Claim 17 (depends on 13)

The device of claim 13, wherein the phase detector comprises a phase-frequency-detector or a down-conversion mixer.

### Claim 18 (depends on 13)

The device of claim 13, wherein the optical delay is implemented as a cascaded add-drop filter based on the photonic crystal resonator.

### Claim 19 (depends on 13)

The device of claim 13, wherein the phase detector comprises an XOR-based phase detector.

### Claim 20 (depends on 19)

The device of claim 19, further comprising a calibration loop to calibrate the XOR-based phase detector.