Microresonator Frequency Comb OCT for Deep, High-Resolution Imaging
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Solution Overview
Problem
Current optical coherence tomography (OCT) systems struggle to simultaneously achieve deep signal penetration and ultra-high resolution due to limitations in available light sources, particularly in clinical settings, as conventional sources like superluminescent diodes (SLDs) suffer from a trade-off between bandwidth and output power, and supercontinuum sources face high optical powers and instability issues.
Innovation Solution
A microresonator-frequency-comb-based platform using high-Q silicon nitride resonators and a single or multiple distributed feedback lasers generates frequency combs with broad bandwidth and small line spacing, compatible with standard OCT systems, enabling sub-micrometer axial resolution and deeper penetration by overcoming the limitations of traditional SLDs and supercontinuum sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If superluminescent diodes (SLDs) are used as light sources in OCT systems, then the system is compact and cost-effective, but the bandwidth is limited and axial resolution cannot achieve ultra-high resolution
Solution Approach 1:
The patent changes the fundamental parameters of the light source by using microresonator-based frequency combs instead of conventional SLDs. This enables broadband operation ( exceeding 100 nm FWHM bandwidth) while maintaining compactness, thereby achieving ultra-high axial resolution below 5 μm without sacrificing the compact and cost-effective advantages of integrated sources
Solution Approach 2:
The patent employs composite microresonator structures combining high-Q silicon nitride resonators with distributed feedback lasers. This composite approach enables simultaneous achievement of narrow linewidth (for high resolution) and broad bandwidth (for deep penetration), resolving the contradiction between resolution and bandwidth that plagues conventional SLDs
2Length of stationary object
If the wavelength is increased above 1 μm to reduce Rayleigh scattering and achieve deeper signal penetration, then penetration depth improves, but axial resolution deteriorates due to the need for broader bandwidth
Solution Approach 1:
The patent operates in the long-wavelength regime (above 1 μm) to minimize Rayleigh scattering and maximize penetration depth, while simultaneously achieving ultra-broad bandwidth through microresonator frequency combs. This resolves the contradiction by enabling both deep penetration and high resolution at long wavelengths, where conventional sources fail to provide sufficient bandwidth
Solution Approach 2:
The patent uses tunable microresonator frequency combs that can dynamically adjust their spectral characteristics. This enables optimization of both penetration depth (by operating at longer wavelengths) and axial resolution (by ensuring sufficient bandwidth is available), allowing the system to adapt to different imaging requirements
3Manufacturing precision
If supercontinuum sources are used to achieve high resolution with broad bandwidth, then axial resolution improves, but the system requires high peak power pulsed lasers and becomes unstable due to nonlinear processes
Solution Approach 1:
The patent replaces expensive, complex, and unstable supercontinuum generation systems with simpler, more reliable microresonator frequency combs. The microresonator approach uses continuous-wave or low-power pulsed pumping instead of high-peak-power ultrafast lasers, eliminating the instability caused by nonlinear processes while maintaining ultra-broad bandwidth and high resolution
Solution Approach 2:
The patent extracts the essential function of broadband light generation from the complex supercontinuum process and implements it through a simpler microresonator frequency comb mechanism. This removes the harmful nonlinear effects (dispersive wave generation, stimulated Raman scattering, self-phase modulation, four-wave mixing) while preserving the beneficial broadband spectrum for high-resolution OCT
4Length of stationary object
If SLDs are used to achieve deep signal penetration at long wavelengths, then penetration depth improves, but axial resolution is limited by bandwidth narrowing due to optical back reflections
Solution Approach 1:
The patent introduces microresonator frequency combs as an intermediary light source that decouples the relationship between wavelength and bandwidth. Unlike SLDs where bandwidth is inherently limited by gain narrowing and back reflections, the frequency comb provides ultra-broad bandwidth at long wavelengths through resonant enhancement, enabling both deep penetration and high resolution simultaneously
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
The platform achieves sub-micrometer axial resolution and deeper tissue penetration with clinically safe power levels, reducing setup costs and size, and is compatible with commercial SD-OCT systems, demonstrating improved image quality in human tissue imaging.
Implementation Method 1
measured frequency comb spectrum generated using the silicon nitride on-chip microresonator
Implementation Method 2
A method of providing a microresonator frequency comb includes generating a frequency comb spectrum from a continuous wave laser source using a high-Q silicon nitride resonator
Implementation Method 3
a single or multiple distributed feedback lasers generates frequency combs
Implementation Method 4
distributed feedback lasers provides coherent continuous wave laser light
Implementation Method 5
Optical coherence tomography (OCT) is a non-invasive interferometric imaging modality
Implementation Method 6
Real-time spectral domain optical coherence tomography (SD-OCT) imaging of human tissue
Implementation Method 7
Axial resolutions below 5 μm require sources with a full-width half-maximum (FWHM) bandwidths of more than 100 nm
Implementation Method 8
working at longer wavelengths (above 1 μm) provide deeper signal penetration due to reduced Rayleigh scattering inside the biological tissue
Data Source
AI summary
A method of providing optical coherence tomography (OCT) imaging may comprise using an on-chip frequency comb source interfaced with an OCT system by a circulator as an imaging source and reconstructing OCT images from resulting spectral data from target tissue illuminated by the imaging source.