Optical Interface Measurement via Low-Coherence Interferometry
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Solution Overview
Problem
Current methods for measuring geometric parameters of optical elements, such as lenses in optical assemblies, face challenges in precision, particularly in positioning and resolving distances between closely spaced interfaces, often requiring accurate alignment with the optical axis and struggling with resolutions below the coherence length of the light source.
Innovation Solution
A method and device using low-coherence interferometry with an optical sensor and positioning means to selectively detect interference signals from interfaces, allowing for the construction of a mathematical interface and determination of geometric information, including positions, tilts, and distances, without needing direct alignment with the optical axis, and enabling resolutions better than the coherence length limit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If retro-reflection measurement technique with normal incidence is used, then measurement accuracy is improved, but alignment complexity and difficulty increase
Solution Approach 1:
The patent introduces a reference interface as an intermediary element that facilitates measurement. By creating a reference interface with known geometric properties and using it as a mediator between the measurement beam and the target interface, the system achieves accurate measurements without requiring complex alignment procedures. The reference interface serves as an intermediate reference frame that simplifies the measurement process.
Solution Approach 2:
The patent replaces the mechanical alignment system with an optical reference system. Instead of mechanically aligning the measurement beam with the optical axis of the assembly (which requires high precision mechanical positioning), the system uses optical reference interfaces and interferometric measurement to achieve accurate measurements. This substitution of mechanical alignment with optical reference methods resolves the contradiction between measurement accuracy and alignment complexity.
2Measurement precision
If retro-reflection measurement technique is used, then measurement accuracy is improved, but measurement time increases
Solution Approach 1:
The patent performs preliminary actions by pre-establishing reference interfaces with known geometric properties before the actual measurement process. By preparing the reference measurement data in advance and creating a reference model of the optical assembly, the system reduces the time required during actual measurements. The reference interfaces are set up once and reused for multiple measurements, eliminating the need for repeated complex alignment procedures.
Solution Approach 2:
The patent introduces dynamic scanning capability that allows the measurement beam to rapidly scan multiple interfaces in sequence. The system dynamically adjusts the measurement beam position and automatically processes measurements from multiple interfaces, reducing manual intervention time. The dynamic measurement approach, combined with automated data processing, achieves high measurement accuracy while minimizing measurement time through efficient sequential scanning and parallel data processing.
3Measurement precision
If measurement beam is aligned with optical axis, then measurement accuracy is improved, but adaptability decreases
Solution Approach 1:
The patent creates a universal measurement system that can measure multiple types of interfaces (planar, curved, tilted) and multiple optical parameters (positions, orientations, distances) using the same reference interface methodology. The reference interface approach is universally applicable to different optical assembly configurations and interface types, making the measurement system highly adaptable. The system can measure interfaces in various orientations and positions without requiring specific alignment procedures for each case, achieving both accuracy and versatility.
Solution Approach 2:
The patent changes the measurement parameters by using optical path difference and interferometric phase information instead of direct geometric measurement. By measuring optical path differences relative to the reference interface, the system can accurately determine positions and orientations of interfaces regardless of their spatial configuration. This parameter transformation enables the measurement system to adapt to different interface geometries and positions while maintaining high measurement accuracy through interferometric detection.
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 precise measurement of geometric parameters and relative positions of optical elements, improving manufacturing accuracy and resolving capabilities for closely spaced interfaces, allowing for better validation of optical components during production.
Implementation Method 1
A measurement optical beam originating from a broad-spectrum optical source is propagated through the surfaces of the optical element. The reflections of the beam on these surfaces are collected and analyzed, making them interfere with one another and/or with a reference beam in order to determine the differences in the optical paths between interfering beams
Data Source
AI summary
A method for measuring an item of geometric information of an interface of an optical element including interfaces, with a device configured to direct a measurement beam towards the optical element so as to pass through at least one of the interfaces and be reflected by the interface and generate a reflected beam, to selectively detect an interference signal between the reflected beam and a reference beam, the method including positioning a coherence area at an interface; measuring the interface so as to produce interference signals; and processing the signals including constructing a mathematical interface based on a sub-set of interference signals, determining, based on the mathematical interface and an expected shape of the interface, an item of geometric information of the interface.