Coherence Length Controller for Interferometer Spurious Fringe Reduction
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Solution Overview
Problem
Interferometer systems face challenges in reducing spurious interference fringes due to the long coherence length of electromagnetic sources, which can lead to extraneous interference patterns that complicate data processing and reduce effectiveness.
Innovation Solution
A system and method for controlling the coherence length of electromagnetic beams by applying a modulating signal to a phase modulator, adjusting the bandwidth of the signal to reduce the coherence length, and introducing a phase delay to position the coherence plane within the interferometer system, thereby reducing spurious interference fringes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If a long coherence length electromagnetic source is used in an interferometer system, then the interference pattern can be observed over larger path differences, but spurious interference fringes appear that complicate data processing
Solution Approach 1:
The patent applies spectral broadening to change the frequency parameters of the electromagnetic source, transforming it from a narrowband source with long coherence length to a broadband source with reduced coherence length. This parameter change in the frequency domain directly reduces the coherence length while maintaining the ability to observe interference patterns over useful path differences, thereby eliminating spurious fringes without completely losing the interference signal.
2Object-generated harmful factors
If the coherence length is reduced to remove spurious fringes, then extraneous interference patterns are minimized, but the ability to observe interference over larger path differences is reduced
Solution Approach 1:
The patent introduces dynamic control of the coherence length through adjustable spectral broadening. The system can dynamically adjust the degree of spectral broadening to optimize the coherence length for different measurement requirements. This dynamic adjustment allows the system to adapt between needing longer coherence length for large path differences and shorter coherence length for eliminating spurious fringes, providing flexibility to balance both requirements.
3Object-generated harmful factors
If spectral broadening is applied to reduce coherence length, then spurious fringes are eliminated, but the bandwidth of the electromagnetic source increases
Solution Approach 1:
The patent converts the harmful effect of long coherence length (which causes spurious fringes) into a beneficial controlled parameter. By intentionally broadening the spectrum, the patent transforms the source characteristics to achieve the desired reduction in coherence length. The increased bandwidth, while appearing as a negative parameter, is actually the mechanism used to control and reduce coherence length, converting what could be seen as a harmful expansion of spectral content into a useful control parameter for eliminating spurious interference.
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 effectively reduces the coherence length of electromagnetic beams, enhancing the contrast of desired interference patterns while minimizing extraneous fringes, allowing for more precise measurement and data extraction in interferometer systems.
Implementation Method 1
A phase modulator is then applied to modulate the coherent radiation beam using the broadband signal to reduce the coherence length of the coherent radiation beam
Data Source
AI summary
Techniques for producing higher fidelity interferometer measurements by reducing sensitivity to spurious sources include reducing the coherence length of an electromagnetic beam. In addition, multiple surfaces within an optical system may be measured by electronically tuning the position of a coherence plane along the optical paths of an interferometer. A phase modulator is used in conjunction with a long coherence length electromagnetic source to generate beams for each leg of an interferometer. Providing a controlled broadband RF signal to the phase modulator increases the bandwidth of the beam and thereby reduces the coherence length of the beam. This reduces the spurious contributions to the output interference fringes from undesired surfaces along the beam path.