OCT Instrument Frequency Shifting for Extended Axial Depth Imaging
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Solution Overview
Problem
Conventional optical coherence tomography instruments are limited by detection bandwidth, restricting the axial imaging depth range and preventing the capture of a broader range of sample depths.
Innovation Solution
An OCT instrument utilizing an adjustable optical frequency shifter and frequency shift controller to generate sideband light and maintain optical frequency, enabling the detector to sample interference signals from both reference and signal light, allowing for the generation of multiple axial depth profiles covering different depth ranges without mechanical path length adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the coherence length of the measurement light is increased to extend the maximum imaging depth, then the axial depth range is improved, but the detection bandwidth limitation prevents recording of high frequency components, resulting in loss of information about deeper structures
Solution Approach 1:
The patent applies dynamic frequency shifting to the reference light using an acousto-optic modulator, where the frequency shift amount is dynamically adjusted based on the optical path length difference. This dynamic adjustment allows the system to capture interference signals from different depth ranges by varying the frequency shift, effectively extending the usable axial depth range beyond the detector bandwidth limitation while preserving information about deeper structures.
Solution Approach 2:
The patent changes the frequency parameter of the reference light dynamically. By applying a frequency shift to the reference light that varies with the optical path length difference, the system maps deep tissue reflection information to detectable frequency ranges. This parameter change enables the detector to capture signals from the full coherence length range, converting the limitation of fixed detection bandwidth into an extended imaging depth capability.
2Measurement precision
If the optical path length of the reference arm is adjusted to change the axial imaging position, then the imaging depth positioning is improved, but mechanical adjustment mechanisms increase device complexity and reduce measurement speed
Solution Approach 1:
The patent replaces mechanical path length adjustment mechanisms with optical frequency shifting. Instead of physically moving mirrors or adjusting optical paths mechanically, the system uses an acousto-optic modulator to dynamically shift the frequency of the reference light. This substitution eliminates complex mechanical components while achieving precise axial positioning through electronic control of the frequency shift amount, thereby reducing device complexity and increasing measurement speed.
3Measurement precision
If mechanical path length adjustment is used to optimize imaging depth, then the axial positioning is improved, but the measurement time increases due to mechanical movement limitations
Solution Approach 1:
The patent substitutes mechanical path length adjustment with optical frequency shifting using an acousto-optic modulator. The frequency shift can be changed electronically and instantaneously, allowing rapid optimization of imaging depth without the time delays inherent in mechanical movement. This enables the system to adapt to different imaging depths in real-time during scanning, significantly reducing measurement time while maintaining precise axial positioning.
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
Enables imaging over a broader axial depth range by adjusting optical frequencies, overcoming detection bandwidth limitations and preserving anatomical information across overlapping or non-overlapping depth ranges.
Implementation Method 1
The returning light from the sample arm and the reference arm are recombined by the coupler to generate an interference pattern
Implementation Method 2
swept narrowband light source arranged to provide measurement light, an optical frequency of which is periodically modulated in a controlled way across a defined source bandwidth
Implementation Method 3
an acousto-optic modulator arranged to generate sideband light by adjustably increasing, adjustably decreasing, or adjustably both increasing and decreasing an optical frequency of a part of one of the returned reference light or the returned signal light
Implementation Method 4
the detector unit samples a first time-varying interference signal resulting from an interference between the sideband light and the other of the returned reference light or the returned signal light
Data Source
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AI summary
An OCT instrument comprising: an optical coupler which generates signal light and reference light from a swept narrowband light source; a detector which samples a time-varying interference signal based on the reference light and signal light returned from a sample; an adjustable optical frequency shifter which: generates a first sideband light by adjusting an optical frequency of the reference light, such that the detector unit samples a first time-varying interference signal resulting from an interference between the sideband light and the returned signal light; and maintains the optical frequency of the reference light such that the detector unit samples a second time-varying interference signal resulting from an interference between the reference light and the returned signal light. The OCT instrument generates a respective axial depth profile of the sample based on each of the sampled first time-varying interference signal and the sampled second time-varying interference signal.