Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
1998-05-26
2001-04-10
Ullah, Akm E. (Department: 2874)
Optical waveguides
With optical coupler
Input/output coupler
Reexamination Certificate
active
06215927
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates generally to optical waveguides and more specifically to optical fibers.
Optical fibers are used to guide light which might, typically, be an optical signal used in telecommunications or in sensing applications. Some optical fibers can be described as a thin strand of light-transmitting medium. In general, an optical fiber includes an inner core and an outer cladding having an effective index of refraction less than the inner core. Some optical fibers, however, have a complex structure made from an inner core surrounded by several outer cores, or claddings, each having different effective indices of refraction. The difference in the effective index of refraction creates internal reflections forcing the light to propagate along the inner core and preventing it from leaking out of the fiber.
Some optical fibers include Bragg gratings (BG). A Bragg grating is formed by producing a series of perturbations in the index of refraction of the inner core. Typically, the perturbations are formed by exposing the core through the cladding to an interference pattern of two ultraviolet beams directed against the optical fiber. The spacing of the perturbations creates a grating characterized by a center wavelength at which light will no longer propagate through the optical fiber. Bragg gratings with different perturbation spacings have different center wavelengths. In general, Bragg gratings are classified either as short period gratings or as long-period gratings. Long-period gratings are those in which the spacing of the perturbations is at least 10 times larger than the wavelength of input light. Typically, the period is in the range 15-1500 &mgr;m for center wavelengths between 700 and 1500 nm. In addition, long-period gratings can have a span of perturbations extending for a few cm. On the other hand, short period gratings have a span of a few 100 microns to several cm and a period in the range 0.2-0.7 &mgr;m for center wavelengths between 600 and 2100 nm.
Bragg gratings are used in optical fibers to filter out selected wavelengths from an optical signal, e.g., like a notch filter. As an optical signal propagates through the core and encounters a short period grating, specific wavelengths of light, which corresponds to the resonant or center wavelength of the grating, are reflected back along the inner core. When an optical signal encounters a long-period grating, the center wavelength of the grating is converted from a guided mode of the core to a non-guided mode of the cladding. A guided mode propagates through the core of the optical fiber. A non-guided mode of the cladding dissipates through the cladding and does not propagate through the optical fiber. The center wavelength reflection or conversion from a guided mode to a non-guided mode is a function of the perturbation spacing of the Bragg grating. The center wavelength of the Bragg grating is sensitive to strain and temperature. Strain and/or change in temperature causes the center wavelength to shift. Typically, for a long-period grating a central wavelength of 1550 nm shifts by about 1 to 1.5 nm per 100° C. change in temperature and by about 0.12 nm per 100 microstrain change in strain.
SUMMARY OF THE INVENTION
In general, in one aspect, the invention features a tape to be mounted on a workpiece. The tape includes an elongated ribbon and an optical waveguide (e.g. optical fiber) supported by the elongated ribbon.
The optical fiber can be attached along the elongated direction of the elongated ribbon. The optical fiber can include a Bragg grating and an outer coating. The outer coating can have a thickness and flexibility chosen to isolate substantially the optical fiber from the workpiece. The outer coating also can have a thickness and flexibility chosen to allow effective transfer of strain from the workpiece to the optical fiber. The outer coating can be a polyamide. The optical fiber also can include a plurality of Bragg gratings.
In another aspect, the invention features a tape to be mounted on a workpiece. The tape includes an elongated ribbon, a first optical fiber supported by the elongated ribbon, and a second optical fiber supported by the elongated ribbon.
The first and second optical fibers can be attached along the elongated direction of the elongated ribbon. The first and second optical fibers can include a Bragg grating. The first optical fiber also can include a first coating. The first coating can have a thickness and flexibility chosen to isolate substantially the first optical fiber from the workpiece. The second optical fiber also can include a second coating. The second coating can have a thickness and flexibility chosen to allow transfer of strain from the workpiece to the second optical fiber.
In another aspect, the invention features a method of producing a tape. The method includes providing a coated optical fiber and supporting the optical fiber with an elongated ribbon.
The step of supporting the optical fiber can include a step of attaching the optical fiber along the elongated direction of the elongated ribbon. The step of providing a coated optical fiber can include a step of coating an optical fiber with coating.
The invention provides a sensing tape by embedding a coated optical fiber into a support ribbon. The sensing tape is easily attached to a support structure to monitor strain and/or temperature. Also, the tape can be easily packaged by simply winding the tape onto a spool from which the desired amount of tape can be unwound at the time of installation and/or use.
REFERENCES:
patent: 4649529 (1987-03-01), Avicola
patent: 4806012 (1989-02-01), Meltz et al.
patent: 5351324 (1994-09-01), Forman
patent: 5355208 (1994-10-01), Crawford et al.
patent: 5723857 (1998-03-01), Underwood et al.
patent: 0 384 649 A2 (1990-08-01), None
patent: WO 98/12525 (1998-03-01), None
Claus et al., “Embedded Optical Fiber Sensors for Materials Evaluation”, Journal on Nondestructive Evaluation, Jun. 8, 1989, vol. 8, No. 2, New York, US, pp. 135-145.
A.M. Vengsarker et al., “Long-Period Fiber Gratings as Band-Rejection Filters”, IEEE Journal of Lightwave Technology, vol. 14, No. 1, Jan. 1996, pp. 58-65.
P. A. Robertson and B. P. Ludden, “A Fibre Optic Distributed Sensor System for Condition Monitoring of Synthetic Ropes”, Ref. No. 1997/033, IEE Colloquium on Optical Techniques for Smart Structures and Structural Monitoring, Feb. 17, 1997, pp. 12/1—12/6.
Fish & Richardson P.C.
Minnesota Mining & Maufacturing Company
Ullah Akm E.
LandOfFree
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