Michelson Interferometer Reference Beam Lateral Offset
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Solution Overview
Problem
In free-beam Michelson interferometers used for full-field optical coherence tomography, the lateral offset of the reference beam relative to the sample beam on the detector is problematic, especially when there is limited installation space or long interferometer arm lengths, leading to reduced contrast and sensitivity of the interference signal due to non-central detection and further offset changes with reference mirror movement.
Innovation Solution
The reference light beam is laterally offset relative to itself through an odd number of reflections in the reference arm section, allowing it to be guided in opposite parallel directions, and then deflected by a fixed light-deflecting element such as a prism or diffraction grating to intersect the sample light beam on the detector without lateral offset, maintaining interference across the detector surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the reference beam is tilted onto the light detector to generate interference fringes, then the interference pattern can be detected, but the reference beam becomes laterally offset from the sample beam, causing reduced contrast and sensitivity
Solution Approach 1:
The patent introduces a third dimension (lateral offset) to separate the reference and sample beams on the detector surface. By allowing the beams to overlap in the optical path while maintaining lateral separation, the system achieves both interference capability and beam distinction without requiring beam tilting that would cause misalignment.
Solution Approach 2:
The patent uses an optical element (such as a beam splitter or dichroic mirror) as an intermediary to combine the reference and sample beams. This intermediary allows the beams to be superimposed on the detector while maintaining their respective optical paths, enabling interference without lateral offset that would reduce contrast.
2Adaptability or versatility
If the reference arm length is changed by displacing the reference mirror, then different sample depths can be scanned, but the lateral offset of the reference beam on the detector changes further, reducing measurement precision
Solution Approach 1:
The patent decouples the longitudinal adjustment (for depth scanning) from the lateral position on the detector. By using a three-dimensional beam arrangement where the reference and sample beams can be laterally separated yet optically combined, the system allows reference mirror displacement for depth scanning without affecting beam overlap quality on the detector.
Solution Approach 2:
The patent separates the functions of beam combination and beam position adjustment. The optical intermediary handles beam combination for interference, while the lateral offset arrangement handles position stability. This segmentation allows independent optimization of depth scanning capability and beam position stability.
3Area of stationary object
If the beam diameter is increased to accommodate lateral offset, then more installation space is required, but the system can maintain beam overlap, however this increases device complexity and reduces space efficiency
Solution Approach 1:
The patent utilizes the lateral dimension to achieve beam overlap without requiring increased beam diameter. By arranging beams to overlap in the optical path while maintaining lateral separation, the system achieves effective beam area utilization within a compact footprint, avoiding the need for larger beam diameters that would increase installation space requirements.
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 configuration ensures that sample and reference light can be superimposed on the detector without lateral offset, maintaining high contrast and sensitivity of the interference signal, even with extended, spatially partially coherent light sources, and allows for variable reference arm lengths without affecting the beam's position on the detector.
Implementation Method 1
a beam splitter with a semi-transparent beam splitter mirror (70)
Implementation Method 2
the reference light beam is laterally offset relative to itself by means of an odd number of reflections in each reflection plane in at least one reference arm section
Implementation Method 3
deflecting light by means of diffraction or refraction
Implementation Method 4
deflecting light by means of diffraction or refraction
Implementation Method 5
Interference on the two-dimensional light detector - e.g. a CCD or CMOS camera - at the output of the interferometer
Data Source
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AI summary
The invention relates to a method for generating a two-dimensional interferogram using a Michelson-type open-jet interferometer comprising an expanded, spatially partially coherent light source and a two-dimensional light detector, wherein light of the light source is split into a sample light beam and a reference light beam by a beam splitter with a semi-transparent beam splitter mirror and supplied to a sample branch and a reference branch, wherein the sample light beam returning from a sample is guided onto the light detector via the beam splitter mirror, wherein the reference light beam coming from the reference branch encloses a predetermined angle greater than zero with the sample light beam on the light detector, and wherein the length of the reference branch is changeable, characterised in that the reference light beam is laterally offset in relation to itself by means of an odd number of reflections in each reflection plane in at least one reference branch section, and running in parallel in the opposite direction, same is guided through an element which is fixed to the outlet of the reference branch and deflects light by means of diffraction or refraction.