Optical Measurement Device Using Circulating Reference Light for Temperature Compensation
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Solution Overview
Problem
The measurement device disclosed in Patent Literature 1 is affected by temperature changes due to the temperature-dependent refractive index of optical fibers, leading to fluctuations in light speed and measurement accuracy.
Innovation Solution
An optical measurement device that includes a wavelength sweeping light source, an irradiation optical system, a circulating light path, a measurement signal acquirer, and a signal processor. The device uses a low coherence light source and a circulating reference light path to expand the measurement range and reduce temperature-related fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If a wavelength scanning interference method is used to expand measurement range, then measurement range is expanded, but measurement accuracy is affected by temperature changes due to refractive index fluctuations in optical fibers
Solution Approach 1:
The patent applies feedback by measuring the light path length of the reference light path and using this measurement to correct the light path length measurement of the measurement light path. The control unit receives the light path length of the reference light path, calculates the difference between reference and measurement light paths, and uses this difference to determine the distance to the measurement object, thereby compensating for temperature-induced refractive index changes.
Solution Approach 2:
The patent uses the reference light path as an intermediary to indirectly measure and compensate for environmental temperature effects. By introducing a reference light path that experiences similar temperature conditions but does not interact with the measurement object, the system can isolate and correct for temperature-induced refractive index changes in the optical fibers.
2Length of stationary object
If optical fibers are used in the reference light path to enable circulating reference light, then measurement range is expanded through multiple circulations, but light path length fluctuates with temperature changes
Solution Approach 1:
The system continuously monitors the light path length of the reference light path and feeds this information back to the control unit. The control unit uses this feedback to calculate the actual light path length difference, compensating for temperature-induced fluctuations and maintaining stable measurements despite environmental changes.
Solution Approach 2:
The patent creates a copy of the optical fiber path in the reference light path that mirrors the measurement light path's environmental conditions. By circulating reference light through identical or similar optical fibers, the system creates a reference that replicates temperature effects, allowing for accurate compensation of refractive index changes.
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
The device achieves high-accuracy distance measurements with expanded measurement ranges, while being resistant to environmental temperature changes, even when using low coherence light sources.
Implementation Method 1
a wavelength sweeping light source that outputs swept light having a wavelength continuously changing with time
Implementation Method 2
receives reflected light obtained by the measurement object reflecting the measurement light
Implementation Method 3
combines the measurement reflected light from the irradiation optical system and the circulating reference light from the circulating light path, outputs an accurate measurement signal obtained by photoelectrically converting the combined interference light
Implementation Method 4
a refractive index of an optical fiber has temperature dependency. Therefore, a light speed in the optical fiber fluctuates
Data Source
AI summary
An optical measurement device includes: a wavelength sweeping light source that outputs swept light having a wavelength continuously changing with time; an irradiation optical system that emits measurement output light toward a measurement object, receives reflected light from the measurement object, and outputs the reflected light as measurement reflected light; a circulating light path that includes a loop portion and outputs circulating reference light for each circulation, in which reference output light caused by the swept light circulates through the loop portion N (an integer equal to or more than 0) times; a measurement signal acquisition unit that combines the measurement reflected light from the irradiation optical system and the circulating reference light from the circulating light path, outputs an accurate measurement signal, and rough measurement signals; and a signal processor unit that identifies the number of circulations in the circulating light path of the circulating reference light.