# US 10,767,973 B2 · Dual-edge sampling with k-clock to avoid aliasing in optical coherence tomography

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- Number: US 10,767,973 B2
- Document ID: US10767973B2
- Status: Granted
- Kind: B2
- Application number: 16/173,146
- Filed: 2018-10-29
- Published: 2019-05-02
- Granted: 2020-09-08
- Earliest claimed: 2017-11-02
- Assignees: Alcon Inc.
- Applicants: Alcon Inc.
- Inventors: Bing Wang; Muhammad K. Al-Qaisi; Hugang Ren
- Web page: https://patentgrep.com/patent/US10767973B2

## CPC

- G01B 9/02084: {Processing in the Fourier or frequency domain when not imaged in the frequency domain}
- A61B 3/102: {for optical coherence tomography [OCT]}
- A61B 5/0066: {Optical coherence imaging}
- A61B 5/7257: {using Fourier transforms}
- G01B 9/02004: using frequency scans
- G01B 9/02091: Tomographic interferometers, e.g. based on optical coherence
- A61B 5/725: {using specific filters therefor, e.g. Kalman or adaptive filters (specific diagnostics methods using using bioelectric or biomagnetic signals A61B5/316)}
- G01B: MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D)

## Abstract

Techniques and apparatus for producing sampled Optical Coherence Tomography (OCT) interference signals without aliasing, based on a swept-source OCT interference signal. An example apparatus comprises a k-clock circuit configured to selectively output a k-clock signal at any of a plurality of k-clock frequencies ranging from a minimum k-clock frequency to a maximum k-clock frequency, and an anti-aliasing filter configured to filter a swept-source OCT interference signal, to produce a filtered OCT interference signal, where the anti-aliasing filter has a cut-off frequency greater than one-half the minimum k-clock frequency but less than the minimum k-clock frequency. The apparatus further comprises an analog-to-digital (A/D) converter circuit configured to sample the filtered OCT interference signal at twice the k-clock frequency, to produce a sampled OCT interference signal. In some embodiments, the A/D converter circuit samples the filtered OCT interference signal at both rising and falling edges of the k-clock signal.

## Claims

### Claim 1

An Optical Coherence Tomography (OCT) data acquisition and processing circuit for use in producing an OCT image based on a swept-source OCT interference signal, the OCT data acquisition and processing circuit comprising:
a k-clock configured to selectively output a k-clock signal at any of a plurality of k-clock frequencies ranging from a minimum k-clock frequency to a maximum k-clock frequency;
an anti-aliasing filter configured to filter the swept-source OCT interference signal, to produce a filtered OCT interference signal, the anti-aliasing filter having a cut-off frequency greater than one-half the minimum k-clock frequency but less than the minimum k-clock frequency; and
an analog-to-digital (A/D) converter circuit coupled to an output of the anti-aliasing filter and configured to sample the filtered OCT interference signal at twice the k-clock frequency, to produce a sampled OCT interference signal;
wherein the A/D converter circuit comprises first and second A/D converters, the first A/D converter being configured to sample the filtered OCT interference signal at the k-clock frequency, using the k-clock signal, and the second A/D converter being configured to separately sample the filtered OCT interference signal at the k-clock frequency, using a phase-shifted replica of the k-clock signal, the A/D converter circuit further comprising a multiplexer to combine the sampled outputs from the first and second A/D converters to obtain the sampled OCT interference signal.

### Claim 2 (depends on 1)

An OCT system comprising the OCT data acquisition and processing circuit of claim 1, and further comprising:
a swept optical source; and
an interferometer coupled to an output of the swept optical source, the interferometer comprising a detector circuit configured to generate the swept-source OCT interference signal from an optical interference signal produced by the interferometer.

### Claim 3 (depends on 1)

An OCT system comprising the OCT data acquisition and processing circuit of claim 1, and further comprising:
a digital signal processing circuit configured to process the sampled OCT interference signal to obtain an OCT image; and
a display configured to display the OCT image.

### Claim 4 (depends on 1)

The OCT data acquisition and processing circuit of claim 1, further comprising:
a k-clock doubler configured to produce the phase-shifted replica of the k-clock signal.

### Claim 5

An Optical Coherence Tomography (OCT) data acquisition and processing circuit comprising:
a k-clock configured to selectively output a k-clock signal at any of a plurality of k-clock frequencies ranging from a minimum k-clock frequency to a maximum k-clock frequency;
a k-clock doubler configured to produce a phase-shifted replica of the k-clock signal;
an anti-aliasing filter configured to filter the swept-source OCT interference signal, to produce a filtered OCT interference signal, the anti-aliasing filter having a cut-off frequency greater than one-half the minimum k-clock frequency but less than the minimum k-clock frequency;
first and second A/D converters, the first A/D converter being configured to sample the filtered OCT interference signal at the k-clock frequency, using the k-clock signal, and the second A/D converter being configured to separately sample the filtered OCT interference signal at the k-clock frequency, using the phase-shifted replica of the k-clock signal, the A/D converter circuit further comprising a multiplexer to combine the sampled outputs from the first and second A/D converters to obtain the sampled OCT interference signal;
a digital signal processor, an input of the digital signal processor coupled to an output of the analog-to-digital (A/D) converter circuit;
the multiplexer coupled to an output of the first A/D converter and to an output of the second A/D converter; and
the digital signal processor coupled to an output of the multiplexer.

### Claim 6 (depends on 5)

An OCT system comprising the OCT data acquisition and processing circuit of claim 5, and further comprising:
a swept optical source; and
an interferometer coupled to an output of the swept optical source, the interferometer comprising a detector circuit configured to generate the swept-source OCT interference signal from an optical interference signal produced by the interferometer.

### Claim 7 (depends on 5)

An OCT system comprising the OCT data acquisition and processing circuit of claim 5, and further comprising:
a digital signal processing circuit configured to process the sampled OCT interference signal to obtain an OCT image; and
a display configured to display the OCT image.