Optical Interference Measurement with Overlapping Scan Ranges
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Solution Overview
Problem
Conventional optical coherence tomography (OCT) devices are limited by the measurable size of the measurement object in the scanning direction due to the limited measurement range in the depth direction, restricting the ability to measure larger changes in distance to the object during scanning.
Innovation Solution
An optical interference measurement method using an optical frequency comb light source with an optical comb generation filter to adjust light into equal frequency intervals, combined with a scanning mechanism, allows for the detection of interference light over extended ranges by overlapping measurement and reference light paths, enabling continuous measurement beyond the conventional limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the measurement range in the depth direction is limited by conventional OCT devices, then the device complexity is reduced, but the measurable size of the measurement object in the scanning direction is limited
Solution Approach 1:
The patent transitions from measuring only in the depth direction to measuring in both depth and scanning directions by utilizing the overlap between consecutive measurement ranges. This dimensional extension allows the measurement object to be measured in a larger area without increasing device complexity, as the scanning mechanism naturally provides the additional measurement dimension.
Solution Approach 2:
The patent performs preliminary positioning by setting the start position of scanning so that the first measurement range overlaps with the second measurement range. This preliminary action ensures continuous measurement coverage without gaps, allowing the measurable size to be extended beyond the single measurement range limit.
2Area of stationary object
If the scanning mechanism moves the measurement light over a large distance, then the measurable area is increased, but the change in distance exceeds the measurement range causing measurement discontinuity
Solution Approach 1:
The patent divides the total measurement area into multiple overlapping measurement ranges. Each range is measured separately by the scanning mechanism, and the overlap between consecutive ranges ensures continuous measurement. This segmentation allows large areas to be measured reliably without exceeding the measurement range limit in any single measurement.
Solution Approach 2:
The patent dynamically adjusts the scanning position and overlap between measurement ranges to maintain measurement continuity. By controlling the scanning mechanism to move through multiple positions with appropriate overlap, the system maintains reliable continuous measurement across the entire measurable area.
3Length of moving object
If the measurement range is extended to cover larger distance changes, then the measurable size is increased, but the measurement precision may be degraded
Solution Approach 1:
The patent maintains high measurement precision by dividing the total measurement into multiple smaller segments, each within the optimal measurement range. Each segment is measured with full precision, and the overlap ensures continuous coverage. This segmentation approach preserves measurement precision while extending the total measurable size.
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 continuous measurement of the surface shape of an object even when the change in distance during scanning exceeds the conventional measurement range, allowing for wide-range and long-distance surface shape profiling.
Implementation Method 1
optical coherence tomography (that is, OCT) is a tomographic imaging method for a structure such as a coating film or a living body using a light interference phenomenon
Implementation Method 2
In low coherence interferometer 3 in the device illustrated in FIG. 5, light emitted from broadband light source 2 is divided into reference light and measurement light by beam splitter 5
Implementation Method 3
An optical interference measurement method using an optical frequency comb light source with an optical comb generation filter to adjust light into equal frequency intervals
Implementation Method 4
the measurement light passes through lens 6 and galvanometer mirror 7 to reach measurement object 8
Data Source
AI summary
When measurement light enters measurement object W, a range obtained by adding measurement range LD determined by an interference light detection unit from a zero point overlaps with the range obtained by subtracting measurement range LD from distance LC(=c/2FSR) from the zero point. The zero point is a point at which a signal optical path length of signal light that is the measurement light matches a reference optical path length of the reference light. The distance is a distance of a half of the value obtained by multiplying the reciprocal of mode interval FSR of optical comb generation filter 205 by light speed c. The change amount L(1-1/cos θ) of distance (L/cos θ) between scanning mechanism and measurement object W generated when scanning with scanning mechanism 211 is performed is caused to exceed twice measurement range LD determined by the interference light detection unit, that is, 2LD.