Optical Interference Measurement Device Using Frequency Comb for Extended Range
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Solution Overview
Problem
Conventional optical coherence tomography (OCT) devices are limited in their ability to measure targets positioned farther than a certain measurable range, due to the optical frequency resolution of the spectrometer, which restricts the distance between the measurement target and the branching portion of the reference and measurement lights.
Innovation Solution
The optical interference measurement device employs an optical frequency comb light source with an optical comb generation filter that adjusts the low coherence light to equal frequency intervals, allowing the light to be divided into measurement and reference lights by a reference surface positioned away from the measurement head, enabling measurement of targets at distances beyond the conventional measurable range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the branching portion is positioned close to the measurement target to achieve common path optical system, then measurement precision is improved, but the measurable range is limited to a short distance
Solution Approach 1:
The patent introduces an optical frequency comb light source that operates in the frequency domain, transforming the measurement approach from spatial domain (where path length difference limits range) to frequency domain (where spectral resolution determines range). This dimensional transformation allows the system to measure targets at distances exceeding the conventional path length difference limitation while maintaining common path optical system advantages.
Solution Approach 2:
The patent changes the key parameter from optical path length difference to optical frequency resolution. By using a spectrometer with sufficient frequency resolution to distinguish comb modes, the system can measure targets at distances L > c/(2Δν) where Δν is the frequency resolution, thereby extending the measurable range beyond conventional limits while preserving measurement precision through the common path configuration.
2Adaptability or versatility
If the distance to measurement target exceeds the measurable range, then the measurement cannot be performed, but extending the distance is required for practical applications
Solution Approach 1:
The optical frequency comb light source emits light with periodic frequency components (comb modes) at intervals of FSR. This periodic frequency structure allows the spectrometer to distinguish between different path length differences by identifying the specific comb mode pattern, enabling reliable measurement of targets at extended distances through the periodic revival of interference signals at multiples of the coherence length.
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 allows for accurate measurement of targets positioned farther than the conventional measurable range, while maintaining high accuracy and signal quality by adjusting the optical path lengths and using a common path optical system.
Implementation Method 1
Both of them divide light emitted from a light source into measurement light and reference light, then multiplex the measurement light and the reference light reflected from a measurement target, and acquire an optical tomographic image based on a beat frequency of interference light between the measurement light and the reference light
Implementation Method 2
an optical frequency comb light source that causes the low coherence light to have equal frequency intervals by an optical comb generation filter
Implementation Method 3
In spectroscopic device 40, the measurement light and the reference light interfere with each other in the spectral region, and as a result, interference fringes are measured as interference signals
Data Source
AI summary
When light adjusted at equal frequency intervals by optical comb generation filter 205 is incident and emitted from measurement head 207 to measurement target W, the light adjusted at equal frequency intervals by optical comb generation filter 205 is divided into measurement light and reference light by light division unit 208, and interference light in which reflected light of the measurement light from measurement target W and the reference light are multiplexed is detected by interference light detection unit 210.