Optical Sample Clock Phase Shifting for Equal-Interval OCT Sampling
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Solution Overview
Problem
In optical coherence tomography (OCT) systems, particularly swept-source OCT (SS-OCT), generating a high-frequency sample clock with equal optical frequency intervals is challenging due to the influence of the wavelength-swept light source on the interference pattern amplitude, leading to distortion and reduced resolution.
Innovation Solution
A sample clock generator is designed using an interference optical system with an optical phase shifter to shift the phase of the input light by 1/4 or 1/8 wavelength, independent of the input light frequency, allowing for frequency multiplication of the sample clock signal while minimizing noise and frequency-dependent phase shifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the optical path length difference in the interferometer is increased to generate high-frequency k-clock, then the sampling frequency is improved, but the amplitude of the interference pattern becomes smaller making generation difficult
Solution Approach 1:
The patent replaces the conventional electrical phase shifter with an optical phase shifter that uses optical feedback. The optical phase shifter includes a photodetector that detects the interference signal and feeds it back to control the phase modulation, thereby generating the k-clock signal optically rather than electrically. This substitution resolves the contradiction by maintaining adequate interference pattern amplitude while achieving high-frequency sampling through optical path length control.
2Speed
If an electrical phase shifter is used to double the k-clock frequency, then the frequency multiplication is achieved, but the phase shift amount becomes frequency-dependent causing unequal frequency intervals
Solution Approach 1:
The patent substitutes the electrical phase shifter with an optical phase shifter that uses optical feedback through a photodetector. The photodetector detects the interference signal and feeds it back to control the phase modulation, ensuring that the phase shift amount remains consistent across different frequency components. This optical feedback mechanism resolves the frequency-dependent phase shift issue and maintains equal frequency intervals in the multiplied k-clock signal.
3Productivity
If the sampling is performed at even frequency intervals with respect to optical frequency, then the sampling rate is improved, but distortion is generated in the A-scan OCT signal deteriorating resolution
Solution Approach 1:
The patent implements feedback by using a photodetector to detect the interference signal from the interferometer and feeding it back to control the optical phase shifter. This feedback mechanism ensures that the phase modulation accurately follows the interference signal, enabling sampling at equal optical frequency intervals without distortion. The feedback loop maintains the correct phase relationship between successive samples, thereby preserving resolution while achieving high sampling rates.
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 enables the generation of high-frequency sample clocks with equal intervals, improving the resolution and reducing noise in OCT imaging by isolating the sample clock signal from frequency variations in the input light, thus enhancing the quality of tomographic images.
Implementation Method 1
an optical phase shifter to shift a phase of the input light guided through the first optical path by 1/4 or 1/8 wavelength
Implementation Method 2
an interference optical system at least includes a first optical path through which part of an input light emitted from a light source is guided; a second optical path through which other part of the input light is guided
Data Source
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AI summary
A sample clock generator includes a first optical path and a second optical path through which input lights are guided, an optical phase shifter to shift a phase of the input light guided through the first optical path, an interference-light generating unit to combine a phase-shifted input light and the input light guided through the second optical path to thereby generate an interference light for sample clock, a splitting unit to split the interference light for sample clock into two split lights having different phases, one light receiving unit to at least receive one split light from among the two split lights having different phases, the other light receiving unit to at least receive the other split light, a signal generating unit to generate a sample clock signal based on signals outputted from the one light receiving unit and the other light receiving unit.