Optical Coherence Tomography Frequency Shifter for Axial Depth Adjustment
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Solution Overview
Problem
Conventional optical coherence tomography instruments face challenges in achieving fast, reliable, and precise adjustment of the axial position for obtaining axial depth profiles, as they rely on either fixed or mechanically adjustable reference arm optical path lengths, which are inflexible, insufficiently fast, or imprecise.
Innovation Solution
The introduction of an adjustable optical frequency shifter, such as an acousto-optic or electro-optic modulator, between the optical coupler and the reference or sample optical systems, allows for controlled optical frequency shifts, effectively adjusting the optical path length without moving parts, ensuring high-frequency interference components fall within the detector's bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the optical path length of the reference arm is fixed, then the system structure is simple, but the system becomes inflexible and cannot adjust axial position
Solution Approach 1:
The patent replaces the mechanical mirror adjustment system with an acousto-optic modulator (AOM) that uses acoustic waves to diffract and frequency-shift light. This substitutes mechanical movement with an acoustic field-based optical modulation, enabling electronic control of optical path length without physical moving parts in the optical path.
Solution Approach 2:
The patent changes the optical frequency parameter of the reference light using the AOM. By modulating the acoustic frequency applied to the AOM, the optical frequency of the reference beam is shifted, which effectively changes the optical path length difference between reference and sample arms, enabling dynamic adjustment of the imaging depth without mechanical movement.
2Measurement precision
If a movable mirror is used to adjust the optical path length, then the axial position can be adjusted, but the adjustment is insufficiently fast, reliable or precise
Solution Approach 1:
The patent eliminates the movable mirror entirely and replaces it with an acousto-optic modulator. The AOM responds to electrical signals with sub-microsecond response times, providing adjustment speeds orders of magnitude faster than mechanical mirrors. The precision is enhanced by the ability to control the acoustic drive frequency with high stability, enabling precise control of the optical frequency shift and thus the effective optical path length.
Solution Approach 2:
The patent introduces the AOM as an intermediary device between the electrical control signal and the optical path. The AOM converts electrical signals into acoustic waves that modulate the optical frequency, serving as a precise mediator that translates electronic control into optical path length adjustment without the inertia and friction limitations of mechanical systems.
3Reliability
If mechanical adjustment is used for optical path length, then some flexibility is achieved, but the system lacks reliability and precision
Solution Approach 1:
The patent replaces the mechanical adjustment system with an electronically-controlled AOM. This eliminates mechanical wear, friction, and positioning errors, significantly improving reliability. The electronic control interface simplifies operation, allowing precise adjustment through voltage or frequency control signals without complex mechanical interfaces or manual alignment procedures.
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 enables precise and flexible adjustment of the axial position, allowing for accurate imaging of retinal structures without the need for mechanical adjustments, thereby enhancing the system's reliability and precision in obtaining axial depth profiles.
Implementation Method 1
an adjustable optical frequency shifter, such as an acousto-optic or electro-optic modulator
Implementation Method 2
an adjustable optical frequency shifter, such as an acousto-optic or electro-optic modulator
Implementation Method 3
The returning light from the sample arm and the reference arm are recombined by the coupler to generate an interference pattern
Data Source
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AI summary
An optical coherence tomography instrument suitable for imaging a retina is disclosed. In the instrument, an adjustable optical frequency shifter, which can be or include an acousto-optic modulator or electro-optic modulator, is arranged either (i) between a coupler and a reference optical system, (ii) in a reference optical system, (iii) between the coupler and a front-end optical system, or (iv) in a front-end optical system. The optical frequency of reference light or signal light may adjustably be increased or decreased. In operation, a subject is arranged such that its retina is in the focal depth of the front-end optical system. The increase or decrease in the optical frequency of the reference light or the sample light can be adjusted. Thereby, an interferogram representing a depth structure at the retina obtained between returning signal light and returning reference light may be brought to lie within a detection bandwidth of the instrument.