Optical waveguides – With optical coupler – Particular coupling function
Reexamination Certificate
2000-02-01
2001-08-28
Ullah, Akm E. (Department: 2874)
Optical waveguides
With optical coupler
Particular coupling function
C385S037000
Reexamination Certificate
active
06282338
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable
FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
FIELD OF THE INVENTION
The present invention relates generally to the propagation of light in optical waveguides and more particularly to an interfacial propagating mode in an optical fiber waveguide.
BACKGROUND OF THE INVENTION
Optical fiber waveguides are being used with increasing regularity for the transmission and processing of optical signals. In addition to telecommunications applications, fiber optic sensors are used for measuring parameters such as temperature, pressure, radiation levels, chemical concentrations and the like. In an optical fiber sensor, for example, having a core and a surrounding cladding, the presence of chemical analytes can produce a change in the refractive indices of the cladding and core and consequently in the optical output of the fiber. A need exists, however, for improved optical fiber sensors that are more sensitive and that can produce greater variations in optical output.
BRIEF SUMMARY OF THE INVENTION
The present invention comprises an optical fiber waveguide for generating a new type of light propagating mode, an interfacial propagating mode (IPM), where a substantial portion of light energy transmitted through the waveguide is propagated in the cladding region of the fiber. Furthermore, by increasing the amount of light transmitted through the cladding, higher amounts of fluorescence in the cladding can be excited and more light absorption can be achieved to produce more sensitive active cladding-based and absorption-based fiber sensors.
The IPM technology incorporates a specific type of grating structure within a waveguide structure to couple bound modes into interfacial propagating modes. As is known to those skilled in the art, a Bragg grating couples light signals in an optical fiber, from a forward propagating mode to a backward propagating mode, by reflecting a specific wavelength of light depending on the spatial periodicity structure of the grating as described, for example, in U.S. Pat. No. 5,563,967.
To produce PM's in an optical waveguide, the initial forward propagating bound mode can be coupled into a backward propagating interfacial mode with an effective index of refraction greater than the fiber core refractive index, i.e., n
f
>n
core
. This condition is satisfied whenever the Bragg grating period (&Lgr;) is very short, typically less than 200 nm. In this region, up to half of the total IPM energy may be propagated in the fiber cladding.
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Intelligent Optical Systems, Inc.
Shapiro Herbert M.
Ullah Akm E.
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