Visible Light Swept-Source OCT Using Quasi-Phase Matching
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Solution Overview
Problem
Visible light optical coherence tomography (OCT) systems face limitations due to the lack of suitable broadband visible light swept-sources, leading to power-dependent noise, limited signal-to-noise ratio, and increased complexity, which negatively impact imaging quality and cost-effectiveness.
Innovation Solution
A method is developed to generate a broadband visible light swept-source using quasi-phase matching crystals, such as periodically poled lithium niobate, to convert near-infrared light into visible light, combined with coherent optical amplifiers to enhance power and bandwidth, and balanced photodetectors to mitigate noise and improve imaging depth and speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a nonlinearly generated supercontinuum laser is used as the light source for visible light OCT, then the system can achieve visible light imaging capability, but the system suffers from power-dependent noise (RIN) and limited signal-to-noise ratio
Solution Approach 1:
The patent introduces a swept-source laser as an intermediary device that converts near-infrared light to visible light through frequency conversion. This intermediary approach allows the system to use a stable NIR laser source while generating the required visible light output, thereby eliminating the RIN problem inherent in directly generating visible light from a supercontinuum laser.
Solution Approach 2:
The patent changes the operating wavelength parameter from visible light to near-infrared light for the laser source. By operating at NIR wavelengths where stable, high-power lasers are available, and then converting to visible light through frequency conversion, the system achieves both high power output and low noise performance.
2Reliability
If dual-spectrometer balanced detection is used to increase signal-to-noise ratio, then the SNR is improved, but the system complexity and cost increase
Solution Approach 1:
The patent extracts and eliminates the need for complex dual-spectrometer balanced detection by using a swept-source configuration with single-element photodetectors. The frequency sweeping mechanism inherently mitigates RIN effects, allowing simpler detection architecture while maintaining high SNR performance.
Solution Approach 2:
The patent introduces dynamic frequency sweeping of the laser source to transform the static RIN problem into a dynamic solution. By continuously sweeping the frequency, the system can distinguish between signal and noise components, enabling the use of simpler photodetector-based detection while maintaining high SNR.
3Productivity
If swept-source configuration is used to replace dual-spectrometers, then imaging speed and field of view are improved, but no visible light swept-source is available due to lack of broadband optical amplifiers
Solution Approach 1:
The patent changes the wavelength parameter from visible to near-infrared for the laser source, where broadband optical amplifiers are available. This parameter change enables the development of visible light swept-sources by using NIR amplification followed by frequency conversion to the visible range.
Solution Approach 2:
The patent uses frequency conversion as an intermediary process to bridge the gap between available NIR amplification technology and the required visible light output. This intermediary conversion enables the implementation of swept-source OCT in the visible range by leveraging existing NIR optical amplifier infrastructure.
4Measurement precision
If visible light OCT is used to achieve high spatial resolution, then imaging resolution is improved, but power-dependent noise limits the imaging depth
Solution Approach 1:
The patent changes the source wavelength from visible to near-infrared, where higher power and lower noise are achievable. This parameter change enables deeper penetration into tissue while maintaining the high spatial resolution capability through the swept-source frequency sweeping mechanism.
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 enables ultrafast visible light OCT with reduced motion artifacts, increased field of view, improved signal-to-noise ratio, and extended imaging depth, providing more accurate functional and structural imaging without sacrificing image quality.
Implementation Method 1
A method is developed to generate a broadband visible light swept-source using quasi-phase matching crystals, such as periodically poled lithium niobate, to convert near-infrared light into visible light
Implementation Method 2
combined with coherent optical amplifiers to enhance power and bandwidth
Implementation Method 3
balanced photodetectors to mitigate noise and improve imaging depth and speed
Data Source
AI summary
The present disclosure provides a new visible light swept source that enables ultrafast visible light OCT to operate at a faster rate to reduce the motion artifacts and increase the field of view without sacrificing image quality. The new visible light swept source further provides for improved roll-off performance and mitigation of influence of RIN and wash-out effect for wide-field imaging. With a much-improved increase in imaging speed, increased signal-to-noise ratio (SNR), and increased imaging depth, visible light swept-source OCT (vis-ss-OCT) has the capability to perform more accurate functional and structural imaging.