Pressure sensor having an optical waveguide and method for pressure detection
First Claim
1. A pressure sensor, comprising:
- an optical waveguide having;
a cladding-free optical fiber with a given refractive index;
a flexible, tube-shaped, extruded sheath having locally limited support points;
said optical fiber being disposed in said sheath and supporting said sheath thereon only at said locally limited support points to define an intermediate space therebetween surrounding said optical fiber;
said optical fiber being disposed in said sheath surrounded by said intermediate space in an unloaded state of said sheath when no pressure is applied to said optical waveguide;
a medium filling said intermediate space and surrounding said optical fiber, said medium having a refractive index less than said given refractive index; and
said sheath being elastic and resting at least at a local point on said optical fiber when pressure is applied to said optical waveguide such that propagation of light in said optical waveguide is attenuated even without deformation of said optical fiber.
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Abstract
A pressure sensor includes an optical waveguide having an optical fiber with a refractive index n1, located in a fiber guide with a refractive index n3, forming an intermediate region. A medium with a refractive index n2 is located in the intermediate region. The refractive indices correspond to the relation n3>n1>n2. When subjected to a pressure, the fiber guide is pressed against the optical fiber such that the condition for the total reflection required for the normal optical waveguidance in the optical waveguide is no longer fulfilled, and attenuation takes place. The attenuation is evaluated in a corresponding control unit. The pressure sensor is especially provided for an anti-pinch device in the motor vehicle industry.
21 Citations
27 Claims
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1. A pressure sensor, comprising:
an optical waveguide having;
a cladding-free optical fiber with a given refractive index;
a flexible, tube-shaped, extruded sheath having locally limited support points;
said optical fiber being disposed in said sheath and supporting said sheath thereon only at said locally limited support points to define an intermediate space therebetween surrounding said optical fiber;
said optical fiber being disposed in said sheath surrounded by said intermediate space in an unloaded state of said sheath when no pressure is applied to said optical waveguide;
a medium filling said intermediate space and surrounding said optical fiber, said medium having a refractive index less than said given refractive index; and
said sheath being elastic and resting at least at a local point on said optical fiber when pressure is applied to said optical waveguide such that propagation of light in said optical waveguide is attenuated even without deformation of said optical fiber. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
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22. A pressure sensor, comprising:
an optical waveguide having;
a loaded state and an unloaded state;
a cladding-free optical fiber with a given refractive index;
a flexible, tube-shaped, extruded sheath having support points;
said fiber being disposed in said sheath to surround said fiber by an intermediate space in said unloaded state and to support said fiber in a locally limited manner only at said support points;
said intermediate space containing a medium surrounding said fiber and having a refractive index less than said given refractive index; and
said sheath being sufficiently elastic to rest on said optical fiber when pressure is applied in said loaded state and to attenuate light propagating through said fiber.
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23. In combination with a motor vehicle, a pressure sensor, comprising:
an optical waveguide having;
a cladding-free optical fiber with a given refractive index;
a flexible, tube-shaped, extruded sheath having locally limited support points;
said optical fiber being disposed in said sheath and supporting said sheath thereon only at said locally limited support points to define an intermediate space therebetween surrounding said optical fiber;
said optical fiber being disposed in said sheath surrounded by said intermediate space in an unloaded state of said sheath when no pressure is applied to said optical waveguide;
a medium filling said intermediate space and surrounding said optical fiber, said medium having a refractive index less than said given refractive index; and
said sheath being elastic and resting at least at a local point on said optical fiber when pressure is applied to said optical waveguide such that propagation of light in said optical waveguide is attenuated even without deformation of said optical fiber. - View Dependent Claims (24, 25)
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26. A method for detecting pressure, comprising:
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extruding a sheath into a flexible tube shape, the sheath having support points;
creating an optical waveguide by;
placing a cladding-free optical fiber with a given refractive index into the sheath to create an intermediate space between the fiber and the sheath surrounding the fiber in an unloaded state of the waveguide; and
supporting the fiber in the sheath in a locally limited manner only on the support points with the intermediate space being filled with a medium surrounding the fiber and having a refractive index less than the given refractive index;
injecting light into the fiber to form an evanescent field within the intermediate space in an outer area of the fiber directly adjacent the fiber;
when pressure is applied to the waveguide, moving the sheath into the outer area of the fiber to attenuate the evanescent field and, thereby, the light propagating in the fiber even without any deformation of the fiber; and
detecting the attenuation of the light propagating in the fiber.
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27. A method for pressure detection, which comprises:
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providing an optical waveguide with a cladding-free optical fiber having a given refractive index;
surrounding the fiber on all sides in a flexible, tube-shaped, extruded sheath and an intermediate space existing in an unloaded state of the waveguide and supporting the sheath on the fiber only at locally limited support points;
surrounding the fiber in the intermediate space with a medium having a refractive index less than the given refractive index;
injecting light into the fiber to form an evanescent field within the intermediate space in an outer area of the fiber directly adjacent the fiber;
when pressure is applied to the waveguide, moving the sheath into the outer area of the fiber to attenuate the evanescent field and, thereby, the light propagating in the fiber even without any deformation of the fiber; and
detecting the attenuation of the light propagating in the fiber.
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Specification