Birefringent-biased sensor having temperature compensation
AssigneeAlliedSignal Inc.
InventorsDevlin M. Gualtieri, Janpu Hou, William R. Rapoport, Herman Van de Vaart
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Abstract
A birefringent bias is provided to an optical sensor by the addition of one or more single birefringent elements where the total birefringence-length product remains within the accepted tolerances of current devices. The bias provided by two or more elements is such that where each element has a birefringence, a dB/dT and a coefficient of thermal expansion term, the elements are arranged in tandem so that the combined birefringence terms equal the required birefringence bias and the dB/dT and coefficient of thermal expansion terms effectively cancel.
Claims8
A photoelastic sensor comprising a sensing element that exhibits birefringence in the presence of external pressure applied to said sensing element in combination with a first and second biasing element that exhibit birefringence in the absence of said external pressure applied to said biasing element and said biasing elements further selected and aligned with respect to each other so that the sum of the dB/dT terms of said first and second biasing elements are substantially zero where B is the birefringence terms of said first and second biasing elements and T is the temperature experienced by said first and second biasing elements.
A pressure sensor system for providing a frequency signal indicative of an environmental pressure comprising a sensor for receiving a linearly polarized light source and further comprising a sensing element that exhibits birefringence in the presence of said external pressure applied to said sensing element in combination with a first and second biasing element that exhibit birefringence in the absence of said external pressure and said biasing elements further selected and aligned with respect to each other so that the sum of the dB/dT terms of said first and second biasing elements are substantially zero where B is the birefringence terms of said first and second biasing elements and T is the external temperature experienced by said first and second biasing elements;
- whereby said linearly polarized wave decomposes into first and second orthogonally polarized waves, and an application of force to said sensing element causes a stress-induced birefringence resulting in said first and second orthogonally polarized waves to experience a further phase difference on propagating through said sensing element proportional to said force.
Dependencies are inferred from the claim text.