Swept-Source OCT Clock Generation for Stable High-Speed Imaging
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Solution Overview
Problem
Current swept-source optical coherence tomography (OCT) systems face limitations in scan speed, noise performance, and image resolution, particularly at large optical scan depths, due to mechanical constraints, spectral power density, and mode-hopping issues with short-cavity lasers, which hinder real-time imaging of rapidly moving or large structures like the beating heart.
Innovation Solution
The implementation of a Fourier-Domain Mode Locking (FDML) based SS-OCT system with a clock generator and digital control system that stabilizes the drive frequency of the laser, uses gain elements with different polarization dependencies, and incorporates optical delay elements to reduce polarization mode dispersion, enabling efficient and stable operation with continuous real-time image display.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If time-domain OCT systems use mechanically actuated reference arms for path-length scanning, then image quality can be maintained, but scan speed is limited to approximately 15 images/sec due to dynamic mechanical constraints
Solution Approach 1:
The patent replaces the mechanically actuated reference arm with a swept-frequency laser source that performs optical frequency discrimination. Instead of using mechanical actuators to scan the reference path length, the system uses a tunable laser that sweeps through a range of frequencies, eliminating the need for long-range mechanical actuators and enabling much higher scan speeds while maintaining image quality.
Solution Approach 2:
The patent changes the fundamental operating parameter from mechanical displacement to optical frequency modulation. By using a swept-frequency laser that modulates its output frequency over time, the system achieves path-length scanning without mechanical movement, thereby increasing scan speed from 15 images/sec to potentially 1000 images/sec or higher.
2Length of moving object
If short-cavity lasers are used for swept-source OCT, then device size is reduced, but mode-hopping occurs which degrades signal-to-noise ratio and image resolution at optical scan depths exceeding 2-3 mm
Solution Approach 1:
The patent implements feedback control mechanisms to stabilize the laser operation and prevent mode-hopping. By monitoring the laser output and adjusting operating parameters in real-time, the system maintains stable frequency sweeping without mode-hopping, thereby preserving signal-to-noise ratio and image resolution even with compact short-cavity laser designs.
Solution Approach 2:
The patent optimizes the dynamic characteristics of the short-cavity laser to enable rapid frequency sweeping without mode-hopping. By carefully controlling the sweep rate and using appropriate modulation techniques, the system achieves high-speed operation with compact lasers, overcoming the traditional limitation that short-cavity lasers are prone to mode-hopping.
3Productivity
If image acquisition rate is increased by at least an order of magnitude, then real-time visualization of rapidly moving structures like the beating heart becomes possible, but maintaining adequate signal-to-noise ratio becomes more difficult
Solution Approach 1:
The patent uses swept-frequency OCT with Fourier transformation to achieve high-speed imaging without the mechanical scanning limitations. By collecting information from multiple depths simultaneously through optical frequency discrimination, the system achieves image acquisition rates an order of magnitude higher than time-domain OCT while maintaining adequate signal-to-noise ratio through efficient use of available source power.
Solution Approach 2:
The patent performs Fourier transformation of the recorded interference signals to obtain depth profiles, which allows post-processing enhancement of signal-to-noise ratio. By acquiring all depth information simultaneously during the wavelength sweep and then applying mathematical transformation, the system achieves both high speed and high signal quality.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the scan speed, reduces noise, and improves image resolution, allowing for higher acquisition rates without significant loss of image quality, thus facilitating real-time imaging of extended structures like coronary arteries.
Implementation Method 1
The interference signals generated by reflections from structures at different depths are measured point-by-point as the reference path length changes
Implementation Method 2
the light reflected during a wavelength sweep collected with a single photodetector
Implementation Method 3
a profile of reflections from different depths is obtained by Fourier transformation of the recorded interference signals
Data Source
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AI summary
The invention relates to an optical coherence tomography data collection apparatus. The apparatus can include a sample clock generator, where the sample clock generator can be configured to clock an analog-to-digital converter. The analog-to-digital converter can be configured to sample interference signals at an output of a main interferometer. The sample clock generator comprises an interferometer having an input and an output, the interferometer being in electrical or optical communication with the laser and configured to receive the laser light, a balanced photoreceiver having an input in optical or electrical communication with the output of the interferometer, the photoreceiver having an output, a frequency multiplier having an input in optical or electrical communication with the output of the photoreceiver, the frequency multiplier having an output and a zero-cross detector having an input in optical or electrical communication with the output of the frequency multiplier, the output of the zero-crossing detector being the generated clock.