Balanced Detection in Optical Coherence Tomography
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Solution Overview
Problem
Swept-source Optical Coherence Tomography (SS-OCT) systems with high relative intensity noise (RIN) suffer from reduced sensitivity performance due to incomplete RIN suppression, primarily caused by non-uniform wavelength-dependent splitting ratios of fiber optic couplers, which limits their sensitivity to 10-12 dB less than theoretical shot-noise limited sensitivity.
Innovation Solution
The implementation of both optical hardware and electronic based solutions to spectrally filter and attenuate the source reference light, optimizing the matching of spectral and power characteristics in balanced detection systems, either within the interferometer or at the balanced detection input ports, or a combination of both, to compensate for the non-uniform splitting ratios, allowing for single channel detection and reduced noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional fiber optic couplers are used in SS-OCT systems, then the system structure is simple, but the non-uniform wavelength-dependent splitting ratios cause incomplete RIN suppression and reduce sensitivity performance
Solution Approach 1:
The patent applies parameter changes by modifying the splitting ratios of fiber optic couplers to be wavelength-dependent in a controlled manner. Specifically, the first coupler has a splitting ratio that varies with wavelength to compensate for the non-uniform response of the second coupler, thereby achieving uniform RIN suppression across the spectral range while maintaining simple hardware structure
Solution Approach 2:
The patent introduces asymmetry by using two fiber optic couplers with different, non-uniform splitting ratio characteristics. The first coupler is deliberately designed with asymmetric wavelength-dependent splitting behavior that complements the second coupler's characteristics, creating a balanced overall system that suppresses RIN uniformly across wavelengths
2Reliability
If dual-channel acquisition spectral balanced detection is implemented, then RIN noise suppression is improved, but data bandwidth requirements and system complexity increase
Solution Approach 1:
The patent extracts and corrects the spectral imbalance problem at the optical level using wavelength-dependent couplers before the light reaches the detector. By addressing the root cause in the optical path rather than requiring complex post-detection processing, the system achieves RIN suppression with simple single-channel hardware
Solution Approach 2:
The patent replaces the need for complex dual-channel electronic balanced detection with a simplified optical solution using specially designed fiber optic couplers. The optical components perform the balancing function that would otherwise require complex electronic processing and dual-channel acquisition systems
3Measurement precision
If spectral filtering and attenuation are applied to match spectral characteristics, then sensitivity is enhanced and shot-noise limited performance is achieved, but additional optical components are required
Solution Approach 1:
The patent makes the fiber optic couplers multi-functional by designing them to simultaneously perform signal splitting and spectral balancing. These same couplers achieve both the beam division required for interferometry and the wavelength-dependent attenuation needed for RIN suppression, eliminating the need for separate spectral filtering components
Solution Approach 2:
The patent merges the functions of spectral filtering and beam splitting into the fiber optic couplers themselves. By combining these functions in single components rather than using separate elements, the system achieves shot-noise limited sensitivity performance without adding significant optical complexity
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 sensitivity of SS-OCT systems by up to 6 dB, achieving shot-noise limited performance while reducing data bandwidth requirements and eliminating the need for post-processing corrections, thus improving RIN and fixed pattern noise suppression.
Implementation Method 1
the returned light from the sample is recombined with the source reference light at a 50/50 fiber optic coupler and the resulting interference signal
Implementation Method 2
The light incident on each of the photodiodes PD1 and PD2 generates photocurrents
Implementation Method 3
The implementation of both optical hardware and electronic based solutions to spectrally filter and attenuate the source reference light
Data Source
AI summary
Systems and methods for reducing noise in balanced detection based optical coherence tomography (OCT) systems are described. Embodiments including both optical hardware and electronic based solutions to spectrally filter and attenuate the source reference light in optical coherence tomography in an effort to reduce RIN and FPN noise in OCT systems are presented. A novel application to electronic balanced detection schemes in which a single source of reference detection is balanced against the interferometric signals from multiple interferometers is also presented.