Plane Mirror Interferometer Spatial Beam Separation
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Solution Overview
Problem
Displacement measuring interferometers (DMIs) face measurement errors and inaccuracies due to alignment errors, thermal effects, optical mixing, polarization leakage, and diffraction-induced fringing, which are not adequately addressed in existing technologies, particularly in scaling up or down over multiple optical axes.
Innovation Solution
A plane mirror interferometer design that keeps separate input light beams distinct until combined in a polarizing or non-polarizing rhomb sub-assembly, with balanced path lengths and strategically positioned beam blockers to reduce errors, allowing for scalability across multiple optical axes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If reference and measurement beams are combined early in the optical path, then the interferometer can be compact, but non-linear errors and optical mixing increase
Solution Approach 1:
The optical path is segmented into separate reference and measurement beam paths that remain spatially separated for most of their length. The beams are divided and traveled through different optical paths before being recombined at the detector, preventing premature mixing and reducing non-linear errors.
Solution Approach 2:
The patent uses spatial separation in multiple dimensions to keep beams distinct. By separating beams in space rather than just time or frequency, the design maintains compactness while avoiding optical mixing that would occur in a single-dimensional arrangement.
2Ease of operation
If mirror alignment is simplified, then ease of operation improves, but measurement precision deteriorates due to alignment errors
Solution Approach 1:
The patent extracts the alignment sensitivity from the system by using a common optical path architecture where both beams share the same optical components. This removes the need for precise mirror alignment while maintaining measurement precision, as any alignment errors affect both beams equally and cancel out.
Solution Approach 2:
The design changes the operational parameters by using frequency modulation (heterodyne interferometry) rather than relying on spatial alignment. The measurement is based on frequency difference detection rather than beam overlap precision, fundamentally changing how the system achieves accuracy without stringent alignment requirements.
3Measurement precision
If separate fiber optic channels are used for reference and measurement beams, then non-linear errors are minimized, but device complexity increases
Solution Approach 1:
The patent merges the reference and measurement beams into a single optical path at the detector while maintaining their frequency separation. This combination approach achieves non-linear error reduction without requiring separate fiber optic channels throughout the entire system, reducing complexity while maintaining precision.
Solution Approach 2:
The patent uses frequency modulation as an intermediary to distinguish between reference and measurement beams. Rather than relying on physical separation through fiber optic channels, the frequency difference serves as the distinguishing characteristic, allowing beams to share the same path while remaining distinguishable and error-free.
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 design significantly minimizes non-linear and thermal measurement errors, enhancing accuracy and stability while enabling straightforward scaling of DMIs across multiple optical axes.
Implementation Method 1
a polarizing or non-polarizing beam splitter sub-assembly
Implementation Method 2
first and second quarter-wave plates
Implementation Method 3
first and second cube corner reflectors
Implementation Method 4
Displacement measuring interferometers (DMIs) are well known in the art, and have been used to measure small displacements and lengths to high levels of accuracy and resolution
Data Source
AI summary
An interferometer and corresponding system are provided having several aspects. In a first aspect, there is provided an interferometer adapted to receive separate first and second beams f1 and f2 therein, the interferometer comprising substantially equivalent and separate first and second optical pathways for the first and second beams f1 and f2. In a second aspect, there is provided an interferometer adapted to receive as separate inputs therein first and second beams f1 and f2, where such beams are not mixed or combined until just prior to being output by the interferometer. In a third aspect, an interferometer is provided having one or more beam blockers for intercepting extraneous or undesired light, and keeping such light from contaminating or interfering with separate beams f1 and f2.