SS-OCT Reference Arm Delay Line for Coherence Revival Suppression
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Solution Overview
Problem
Swept-source optical coherence tomography (SS-OCT) systems face challenges due to coherence revival artifacts caused by stray light in the reference arm, leading to image artifacts and limited adoption due to high cost and complexity, especially when the cavity length of the swept-source laser is short.
Innovation Solution
The design includes a Mach-Zehnder interferometer with a specific configuration of fiber couplers and a delay line that increases the optical path length difference between the reference arm and the sample arm beyond 8 times the cavity length of the swept-source laser, effectively suppressing coherence revival artifacts by managing parasitic reflections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the cavity length of the swept-source laser is short, then the device complexity and cost are reduced, but coherence revival artifacts increase due to parasitic reflections in the reference arm
Solution Approach 1:
The patent introduces an optical isolator as an intermediary component in the reference arm to block parasitic reflections from returning to the swept-source laser. This isolator acts as a mediator that allows the laser to maintain a short cavity length while preventing the harmful feedback that causes coherence revival artifacts.
Solution Approach 2:
The patent extracts and isolates the parasitic reflection problem by placing an optical isolator specifically in the reference arm path. This separates the harmful reflected light from the main optical path, allowing the system to use a shorter laser cavity without suffering from coherence revival artifacts caused by reference arm reflections.
2Measurement precision
If optical isolators are added to suppress coherence revival artifacts, then image quality improves, but additional optical losses and polarization mode dispersion occur
Solution Approach 1:
The patent applies partial action by using optical isolators with sufficient isolation performance to suppress coherence revival artifacts to acceptable levels, rather than using perfect isolation. This partial approach achieves the necessary image quality improvement while minimizing the associated optical losses and polarization mode dispersion effects.
3Object-generated harmful factors
If optical path length difference is increased beyond 8 times the cavity length, then coherence revival artifacts are suppressed, but the optical path length adjustment complexity increases
Solution Approach 1:
The patent changes the critical parameter from optical path length difference to laser cavity length. By increasing the laser cavity length to be greater than 35mm, the system achieves suppression of coherence revival artifacts without requiring complex optical path length adjustments beyond 8 times the cavity length, thereby simplifying the overall system configuration.
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 configuration reduces coherence revival artifacts, maintains system sensitivity, and avoids additional optical losses or polarization mode dispersion, making the SS-OCT system more practical and cost-effective.
Implementation Method 1
a swept-source laser, wherein the laser cavity length of the swept-source laser is greater than 35 mm
Implementation Method 2
Both SD-OCT and SS-OCT are based on an optical interference system, which includes a sample arm and a reference arm, and detects the interference in the frequency domain
Implementation Method 3
the reference arm includes an adjustable optical delay line for adjusting the optical path length of the reference arm to match the optical path length of the sample arm
Implementation Method 4
SS-OCT uses a swept-source laser and a high-speed photodetector to acquire the interference spectral signals
Data Source
AI summary
An optical coherence tomography system, includes a swept-source laser, a Mach-Zehnder interferometer and a balanced detector. The interferometer includes a first fiber coupler, a second fiber coupler, a sample arm and a reference arm. The reference arm includes a reference arm front section, a reference arm rear section and a delay line. A tail end of the reference arm front section is connected to the reference arm rear section through the delay line. The first fiber coupler is configured to split the output light of the swept-source into a sample light and a reference light and distribute the returned sample light to the second fiber coupler. A difference between the optical path length of a parasitic reflected signal of the delay line reaching the second fiber coupler and the optical path length of the sample light is greater than 8 times the cavity length of the swept-source laser.