Apparatus for and methods of sensing evanescent events in a fluid field
First Claim
1. A system for sensing variations in flow field intensity of a fluid flowing in a boundary layer adjacent to a body exposed to the fluid, the system comprising:
- an optical fiber in or on the body, the optical fiber having at least an input face and an output face and a core covered by cladding;
the optical fiber having D-shaped cross-section defining a planar surface adjacent to the core, the planar surface having an optical grating thereon;
a tunable laser for producing an initial laser beam;
a beam splitter disposed between the turnable laser and an input end of the optical fiber for providing a probing beam and a reference beam, wherein the probing beam passes through the optical fiber for interaction with the optical grating;
at least a first detector for receiving the reference beam and producing an output indicative of the amplitude of the the reference beam;
a second sensor receiving the probe beam as modulated by variations in flow field intensity for producing a modulated output indicative of the amplitude of the probe beam as modulated by the grating; and
a comparator connected to the first and second sensors for receiving the reference output and the modulated output and for producing a differential signal indicative of flow field intensity in the boundary layer adjacent to the body.
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Accused Products
Abstract
An evanescent filed based sensor uses a detector for sensing variations in properties of a fluid flowing in a boundary layer adjacent to the detector. The detector comprises an optical waveguide in the form of an optical fiber having a core layer covered by a cladding layer and having a substantially D-shaped cross section defining a planar surface with an optical grating pattern thereon. When a beam of laser light is directed through the detector as an input, variations in an output of the beam of laser light are indicative of changes in fluid pressure or density in the boundary layer or immediate region adjacent to the grating of the optical waveguide.
40 Citations
14 Claims
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1. A system for sensing variations in flow field intensity of a fluid flowing in a boundary layer adjacent to a body exposed to the fluid, the system comprising:
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an optical fiber in or on the body, the optical fiber having at least an input face and an output face and a core covered by cladding;
the optical fiber having D-shaped cross-section defining a planar surface adjacent to the core, the planar surface having an optical grating thereon;
a tunable laser for producing an initial laser beam;
a beam splitter disposed between the turnable laser and an input end of the optical fiber for providing a probing beam and a reference beam, wherein the probing beam passes through the optical fiber for interaction with the optical grating;
at least a first detector for receiving the reference beam and producing an output indicative of the amplitude of the the reference beam;
a second sensor receiving the probe beam as modulated by variations in flow field intensity for producing a modulated output indicative of the amplitude of the probe beam as modulated by the grating; and
a comparator connected to the first and second sensors for receiving the reference output and the modulated output and for producing a differential signal indicative of flow field intensity in the boundary layer adjacent to the body. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method of using an optical fiber for sensing variations in flow field intensity of a fluid flowing in a boundary layer adjacent to a body exposed to the fluid, the method comprising:
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producing an initial laser beam with a tunable laser;
splitting the laser beam with beam splitter disposed between the turnable laser and an input end of an optical fiber for providing a probing beam and a reference beam;
directing the probing beam through an optical fiber in or on the body, the optical fiber having at least an input face, an output face, a core covered by cladding and a D-shaped cross-section defining a planar surface adjacent to the core, the planar surface having an optical grating thereon;
detecting the reference beam and producing a reference output indicative of the amplitude thereof;
detecting the probe beam as modulated by the conditions in the boundary layer for producing a modulated output indicative of the amplitude of the probe beam as modulated by the grating; and
comparing the reference output and the modulated output to produce a differential signal indicative of flow field intensity in the boundary layer adjacent to the body. - View Dependent Claims (9, 10, 11, 12, 13, 14)
forward coupling the initial laser beam through the first portion of the optical grating into the second portion of the optical grating;
using the second portion of the grating to reverse couple the laser beam into the cladding adjacent to the boundary layer and sending a reverse laser beam back to the first portion of the grating;
through reciprocity, coupling the reverse laser beam back into the core and out of the inlet face to provide the reference beam for signal detection by the first sensor, while minimally forward coupling a forward laser beam back to the core for transmission out of the optical fiber to provide a modulated probe beam for signal detection by the second sensor.
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14. The method of claim 13 comprising minimizing unwanted front end reflections not associated with the modulated signals of interest by disposing the input end face of the optical fiber at an angle with respect to the longitudinal axis of the optical fiber.
Specification