FBG Wavelength Interrogation for OCT Start Timing
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Solution Overview
Problem
Current optical coherence tomography (OCT) systems face challenges in accurately determining the start wavelength during scanning due to mechanical variations, amplitude fluctuations, and thermal drift, leading to uncertainty in positioning sampling times, which increases complexity and cost while reducing image quality.
Innovation Solution
A wavelength interrogation apparatus comprising an optical fiber with a fiber Bragg grating and an electrical circuit including a transimpedance amplifier, differentiator, comparator, and multivibrator, which converts optical power into electrical signals to generate a pulse with a predetermined duration, eliminating the need for optic circulators and reducing mechanical and thermal sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If amplitude based threshold from light source output spectrum is used to determine start of scan, then the method is simple to implement, but it is prone to amplitude light source long term and short term power output variations, spectrum variation, and temperature stability issues
Solution Approach 1:
The patent replaces amplitude-based detection with wavelength-based detection using an FBG sensor. Instead of monitoring amplitude fluctuations that are sensitive to power variations and temperature, the system uses wavelength discrimination through the FBG's resonant reflection characteristics, substituting a mechanical/optical resonance mechanism for an amplitude-threshold mechanism.
Solution Approach 2:
The patent changes the detection parameter from amplitude to wavelength. By using an FBG with a specific resonant wavelength, the system monitors wavelength changes rather than amplitude variations, fundamentally changing the parameter being measured to achieve better stability against power fluctuations and temperature effects.
2Measurement precision
If FBG with circulator or coupler is used to capture start wavelength, then wavelength based detection is achieved, but it uses more fiber optical components and more light for triggering hence less light for imaging
Solution Approach 1:
The patent extracts and removes the circulator or coupler components from the FBG wavelength detection system. By directly monitoring the reflected light from the FBG without requiring these additional optical components, the system achieves the same wavelength detection function with simpler architecture and fewer components.
Solution Approach 2:
The patent eliminates the need for circulators or couplers as intermediary components. The FBG itself serves as both the wavelength-selective element and the triggering mechanism, directly converting wavelength information into an electrical signal without requiring additional optical intermediaries.
3Measurement precision
If FBG is used for wavelength interrogation, then wavelength based detection is achieved, but it causes high cost and complexity to setup, and bandwidth reduction due to power fluctuation over time
Solution Approach 1:
The patent removes the circulator or coupler components that contribute to high cost and complexity. By directly monitoring the FBG reflection without these additional components, the system maintains wavelength detection accuracy while reducing setup complexity and cost.
Solution Approach 2:
The FBG serves multiple functions simultaneously: it acts as the wavelength-selective filter, the triggering mechanism, and the sensor element. This self-service approach eliminates the need for separate components, reducing overall system complexity and cost while maintaining detection precision.
4Measurement precision
If increase of input power is required to compensate for power loss in FBG, then wavelength detection is maintained, but it results in lower power for sample interrogation and causes artifact(s) in the image
Solution Approach 1:
The patent removes the circulator or coupler components that cause significant power loss. By eliminating these components, the system reduces the overall power consumption of the wavelength detection mechanism, leaving more power available for sample interrogation without compromising detection capability.
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 solution provides accurate start wavelength image acquisition, reducing wavelength complexity and cost, and mitigating uncertainty in sampling times, resulting in more precise and repeatable OCT imaging with reduced electromagnetic interference and thermal drift.
Implementation Method 1
A fiber Bragg grating (FBG), for example, can be used in reflection mode with a circulator or coupler to capture a narrow peak for start of wavelength
Implementation Method 2
Today's wavelength interrogation is based on converting laser power via a photodiode to an amplitude power monitor signal with respect to time
Data Source
AI summary
A wavelength interrogation apparatus includes an optical fiber with a fiber core and an interference pattern in the fiber core, one or more photodiodes or photo-sensors to convert from a transmittance light of the optical fiber to an electrical signal, and an electrical circuit to generate a pulse with a predetermined duration, wherein the apparatus provides image acquisition at accurate start wavelength. The electrical circuit can include a first amplifier, a first differentiator or high-pass filter, a comparator, and a multivibrator, and can include other components.