Low-Bulk Interferometric Sensor With Coaxial Beam Splitters
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Solution Overview
Problem
Conventional interferometric measurement probes have a large bulk due to the need for a reference surface close to the output of the light beam, limiting their use on samples with unsuitable size or shape, and cannot be bent for radial measurements without increasing bulk, compromising confocal measurement signals.
Innovation Solution
A confocal system with coaxial beam splitters and lenses in the objective, where the optical axes are coincident, allowing a compact design and enabling radial measurements by positioning the reference surface within the objective, maintaining a sufficient numerical aperture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a reference surface is placed close to the output of the light beam to achieve confocal measurements, then measurement precision is improved, but the bulk of the probe increases
Solution Approach 1:
The reference surface is nested within the objective structure itself, specifically formed on the first beam splitter, rather than being a separate external component. This integration allows the reference surface to be positioned close to the light beam output without increasing the overall probe bulk, as it utilizes the existing optical path components.
Solution Approach 2:
The reference surface function is merged with the first beam splitter component. The beam splitter serves dual purposes: dividing the light beam and providing the reference surface for interference measurements. This combination eliminates the need for a separate reference surface component, reducing probe bulk while maintaining measurement precision.
2Adaptability or versatility
If the probe is bent to carry out radial measurements, then adaptability to different measurement configurations is improved, but the bulk increases due to insufficient working distance
Solution Approach 1:
The reference surface is nested within the compact objective structure, enabling the probe to maintain sufficient working distance even when bent for radial measurements. The integrated design allows the optical path to accommodate angular configurations without requiring additional bulk.
Solution Approach 2:
The probe design allows bending in radial directions (changing the spatial dimension of deployment) while maintaining the confocal measurement capability. The compact internal arrangement of beam splitters and the nested reference surface enable the probe to adapt to different measurement geometries including radial configurations without proportionally increasing bulk.
3Device complexity
If beam splitters and lenses are arranged non-coaxially to simplify structure, then device complexity is reduced, but measurement precision deteriorates due to loss of confocal signal
Solution Approach 1:
The coaxial arrangement serves multiple functions simultaneously: it maintains confocal measurement signal integrity, provides a compact structure, and enables the reference surface to be positioned optimally within the objective. The first and second beam splitters, along with lenses, are arranged coaxially with coincident optical axes, ensuring that the confocal condition is maintained while the system remains relatively simple.
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
Achieves precise nanometre-level measurements with reduced bulk, facilitating use on various sample sizes and shapes, and enabling radial measurements without compromising signal quality.
Implementation Method 1
The spectral analysis system then generates a band spectrum comprising fringes resulting from the interference of the recombined beams
Implementation Method 2
One of these beams is reflected by the sample that it is desired to characterise; the other of the beams is reflected on a reference surface placed in the measurement probe
Implementation Method 3
a white light is focused by an objective
Implementation Method 4
lenses
Data Source
AI summary
The present invention relates to an objective (3) for a confocal system (1) of spectral interferometric measurement, comprising: —a source hole (14); —a second beam splitter (12) having a partially reflective face (12a), —a first beam splitter (10) having a face which is configured to form a reference surface (6) and being located between the source hole (14) and the second beam splitter (12); and—lenses (11, 13). The first and second beam splitters are positioned in the objective (3) such that an optical distance (dref) between the reference surface (6) and the partially reflective surface (12a) is substantially equal to an optical distance (dm) between the partially reflective surface (12a) and a focal plane of the objective (3).