Optical Measurement Apparatus Coherence Length Control
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Solution Overview
Problem
Existing optical coherence tomography (OCT) apparatuses face challenges with high-speed mechanical scanning requirements, optical axis shifts leading to decreased signal intensity, and the need for expensive wavelength scanning type light sources or spectrometers, which result in image deterioration due to optical interference like inter-layer crosstalk and speckle.
Innovation Solution
Incorporating a high-frequency superimposing unit to adjust the coherence length of laser light by branching it into signal and reference light, scanning the condensing position with a high NA objective lens, and using a light path length adjusting unit to minimize interference, allowing for interference phase differences and reducing optical interference effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a laser light source with long coherence length is used to enable three-dimensional measurement by scanning condensing position, then the apparatus becomes compact and cost-effective without requiring wavelength scanning light source or spectroscope, but image deterioration due to optical interference such as inter-layer crosstalk or speckle occurs
Solution Approach 1:
The patent changes the coherence length parameter of the light source by switching between two light sources: one with long coherence length for light path adjustment and one with short coherence length for measurement. This parameter change allows the system to achieve both compact design and reduced optical interference effects.
Solution Approach 2:
The patent performs preliminary light path length adjustment using a long coherence length light source before the actual measurement. This preliminary action ensures that the light paths are properly aligned, and then switches to short coherence length light source for measurement to avoid interference during the actual imaging process.
2Object-affected harmful factors
If high frequency is superimposed on driving current to shorten coherence length and reduce optical interference, then image quality improves, but light path length difference between signal light and reference light must be precisely adjusted
Solution Approach 1:
The system performs preliminary light path length adjustment using a long coherence length light source before switching to the short coherence length light source for measurement. This preliminary adjustment ensures that the light paths are properly aligned, making the subsequent high-precision measurement feasible.
Solution Approach 2:
The long coherence length light source acts as an intermediary tool to facilitate the light path length adjustment. It enables precise alignment of optical paths before the actual measurement with the short coherence length light source, serving as a preparatory mediator in the measurement process.
3Measurement precision
If condensing position is scanned by scanning objective lens to achieve three-dimensional measurement, then spatial resolution is improved, but alignment between signal light and reference light becomes more difficult
Solution Approach 1:
The patent uses a long coherence length light source during the light path adjustment phase to enable precise alignment of the optical paths. The long coherence length provides a larger interference signal, making it easier to detect and adjust the alignment between signal light and reference light before scanning measurements are performed.
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 enables a compact, cost-effective OCT apparatus with improved spatial resolution and reduced image deterioration from optical interference, preventing SN ratio decreases and allowing for accurate tomographic imaging without the need for expensive equipment.
Implementation Method 1
a signal is obtained by combining and interfering the signal light reflected from the measurement object and the reference light
Implementation Method 2
high frequency is superimposed on the driving current by a high-frequency superimposing unit
Implementation Method 3
laser light (signal light) is condensed and irradiated on a measurement object by using a high NA objective lens
Data Source
AI summary
A small and inexpensive optical measurement apparatus is provided in which noise due to optical interference such as inter-layer crosstalk or speckle is suppressed. The optical measurement apparatus includes a light source to emit laser light, a high-frequency superimposing unit to superimpose a high-frequency current on a driving current to drive the light source, a light branching element to branch the laser light into signal light and reference light, an objective lens to condense and irradiate the signal light on a measurement object, a condensing position scanning unit to scan a condensing position of the signal light, a light path length adjusting unit to adjust a light path length difference between the signal light and the reference light, an interference optical system which combines the signal light reflected or scattered by the measurement object and the reference light, and generates a plurality of interference lights different from each other in phase relation, and a photodetector to detect the interference lights.