Optical System Centring for Accurate Interferometric Spacing Measurement
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Solution Overview
Problem
Existing methods for measuring spacings between optical surfaces in single-lens or multi-lens optical systems using short-coherence interferometers face challenges with tilted or decentred surfaces, leading to low signal-to-noise ratios and inaccurate measurements, as the measuring light does not impinge perpendicularly, resulting in unreliable and meaningless data.
Innovation Solution
A method and apparatus that detect the centring state of the optical system by directing a test-light ray along a reference axis and using a location-resolving optical sensor to adjust the system, ensuring the measuring-light ray passes through optical surfaces perpendicularly, thereby aligning the optical axis with the reference axis, ensuring accurate measurements along the optical axis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the measuring light is directed onto tilted optical surfaces, then the measurement can be performed, but the signal-to-noise ratio becomes very low and interference signals are barely detectable
Solution Approach 1:
The patent applies preliminary action by introducing a centring step before the actual spacing measurement. The optical system is first centred using a test-light ray and location-resolving optical sensor to ensure the measuring light impinges perpendicularly on all optical surfaces. This preliminary centring action prevents the signal-to-noise ratio degradation that would occur with tilted surfaces, allowing reliable interference signal detection during subsequent measurements.
2Ease of operation
If the measuring light impinges on optical surfaces at an angle, then the measurement can be performed along the measuring direction, but the measured values deviate from the actual spacings along the optical axis
Solution Approach 1:
The patent implements feedback by using a location-resolving optical sensor to detect the position where the test-light ray exits the optical system. This position information is fed back to determine whether centring is achieved, and the centring state is continuously monitored and adjusted until the measuring light impinges perpendicularly on all optical surfaces. This feedback mechanism ensures that spacing measurements are taken along the correct optical axis direction.
Solution Approach 2:
The patent applies preliminary action by introducing a centring step before the actual spacing measurement. The optical system is first centred using a test-light ray and location-resolving optical sensor to ensure the measuring light impinges perpendicularly on all optical surfaces. This preliminary centring action prevents the signal-to-noise ratio degradation that would occur with tilted surfaces, allowing reliable interference signal detection during subsequent measurements.
3Measurement precision
If a test-light ray and location-resolving optical sensor are used to detect and adjust the centring state, then the measuring light impinges perpendicularly on optical surfaces, but the device complexity increases
Solution Approach 1:
The patent applies universality by designing the test-light ray source and location-resolving optical sensor to serve multiple functions. The same optical components are used both for centring detection and for the subsequent spacing measurement process. This multi-functionality reduces the need for separate dedicated centring equipment, thereby limiting the increase in device complexity while still achieving accurate perpendicular incidence of measuring light on all optical surfaces.
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 enhances the reflection of measuring light into the interferometer, increases the signal-to-noise ratio, and ensures that spacings are measured accurately along the optical axis, minimizing measurement errors caused by tilting or decentring.
Implementation Method 1
measuring light reflected on the optical surfaces of the optical system is superimposed on a photodetector with the measuring light conducted in the reference arm. From interference phenomena detected by the photodetector, differences in the optical path length can be inferred
Implementation Method 2
directing a test-light ray, which propagates along a reference axis, onto the optical system
Implementation Method 3
detecting the location, at which the test-light ray impinges onto a location-resolving optical sensor, after it has passed completely through the optical system
Data Source
AI summary
A method for measuring spacings between optical surfaces of a multi-lens optical system includes detecting the centring state of the optical system by taking into consideration all optical surfaces of the optical system. Then the optical system is adjusted in such a way, taking the centring state into consideration, that the optical axis of the optical system is aligned as far as possible with a reference axis. In a next step the spacings between the optical surfaces are determined with the aid of a short-coherence interferometer. The measuring-light ray directed onto the optical system for this purpose runs likewise along the reference axis.