Optical waveguides – Optical waveguide sensor – Including physical deformation or movement of waveguide
Reexamination Certificate
1998-07-29
2001-05-29
Spyrou, Cassandra (Department: 2872)
Optical waveguides
Optical waveguide sensor
Including physical deformation or movement of waveguide
C385S012000
Reexamination Certificate
active
06240220
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is related to the field of fiber optic devices and networks, and in one embodiment provides a mechanism which varies a wavelength response of one or more fiber Bragg gratings by producing a strain in an optical fiber.
Modern fiber optic communication systems often have the ability to simultaneously transfer light signals having differing wavelengths over a single optical fiber.
Fiber Bragg gratings (FBG) are a particularly advantageous structure for differentiating and manipulating optical signals based on their wavelength. Fiber Bragg gratings are often formed by selectively exposing photosensitive fiber to light, thereby creating a permanent refractive-index grating along the core of the fiber. The resulting sharp reflection resonances can be used as demultiplexers, dispersion compensators, and the like. Fiber Bragg gratings also have applications in communications and sensor areas, operating as resonators, filters, pressure sensing elements, etc. Therefore, fiber Bragg gratings are expected to be important components in many optical communication systems, particularly in the dense wavelength division multiplex systems now being developed.
In operation, a grating is written into a fiber to reflect light of a particular wavelength or band of wavelengths, while other wavelengths of light are transmitted through the grating. Each grating is a wavelength-selective reflector having a reflectance response curve with at least one well-defined peak. If the fiber in which the gratings are written is subjected to a strain, the reflectance peak of the grating shifts. Shifts in the wavelength response may result from changes in environmental temperature, mechanical tension, or vibration.
It has been proposed to make use of the variable wavelength response of fiber Bragg gratings to produce novel optical devices. One proposed tunable fiber bandpass filter is achieved by controlling the strain distribution along the length of a linearly chirped fiber Bragg grating by affixing the grating to each element of a piezoelectric stack. This structure can provide complex filter characteristics such as multiple bandpass peaks, comb filtering, and the like. Unfortunately, this proposed structure will also involve a complex controller, and may result in inconsistent filtering if the coupling between the grating and each piezoelectric element is not tightly controlled. As a result, this phase shift structure appears to be quite difficult to fabricate.
In light of the above, there is a significant need for a fiber optic package that provides a new, yet simple and low cost technique for inducing a phase-shift in a fiber Bragg grating. Therefore, a fiber optic package that subjects a fiber Bragg grating to a controlled strain to produce a desired and predetermined change in a grating wavelength is desired.
SUMMARY OF THE INVENTION
The present invention provides a fiber optic package which can cause a change in the center wavelength of a fiber Bragg grating. The package provides a controlled and predetermined change in wavelength response by subjecting a fiber, having a fiber Bragg grating written therein, to a controlled strain. The strain in the fiber Bragg grating causes a wavelength or phase shift of the optical signal, attributable to the controlled optical grating strains.
In some embodiments, a uniform strain in the fiber is induced by varying a longitudinal displacement of a fiber support member supporting the fiber, thereby causing the fiber to stretch. Optionally, the fiber may be fixed at both ends and supported therebetween by the fiber support member. A control actuator is normally used to linearly displace the fiber support member. As the support member is displaced, the fiber is uniformly stretched. By varying the magnitude of the displacement of the fiber support member, and consequently the strain in the fiber, the user can vary the optical characteristics of the package so as to provide the desired optical characteristics throughout a wide range of strain deformation in the fiber.
In one embodiment, an optical fiber package is provided. The package has an optical fiber having at least one grating with an optical characteristic which varies with strain. At least a portion of the optical fiber is received by a fiber support member. The package also includes a control actuator which is coupled to the fiber support member to cause a displacement of the fiber support member. The displacement of the fiber support member creates a uniform strain along the grating.
In yet another embodiment, a tunable optical fiber package is provided which has at least one fiber support member. The fiber support member has a convex surface with a channel formed into the convex surface extending along the convex surface. The package also has an optical fiber which includes optical characteristics which can vary with strain. The optical fiber rides in the channel to correlate changes in the displacement of the fiber support member with changes in the strain of the optical fiber. A control actuator is also provided which has an axis. The displacement of the fiber support member is in the direction of the axis and normal to a portion of the optical fiber in the channel.
Another aspect of the invention relates to a method which includes actuating a control actuator to cause a displacement of a fiber support member, and deforming a span of an optical fiber supported by the fiber support member to induce a uniform strain throughout the span. The optical fiber has an optical characteristic which varies with strain. The strain in the fiber causes a uniform change in a wavelength response of the fiber throughout the span.
In yet another aspect, a method for tuning a fiber Bragg grating package is provided. The method includes introducing an optical fiber into a channel of a fiber support member; and activating a plurality of piezoelectric segments formed into a stack, such that a change in the length of the stack induces an elongation of the control actuator so as to move the fiber support member. The method also includes deforming the optical fiber with the elongation to induce a strain thereby causing a change in a resonant wavelength, such that the resonant wavelength of the fiber is made variable throughout a predetermined range of strain.
In another embodiment, an adjustable optical device is provided which includes an optical fiber having a first portion, a second portion, and a fiber Bragg grating therebetween. The device also includes a first fiber support member, which supports the first portion of the optical fiber; a second fiber support member, which supports the second portion of the optical fiber; and a control actuator, coupled to the first fiber support member and to the second fiber support member. The actuator controllably displaces the first member relative to the second member so as to vary a strain of the fiber such that the strain in the fiber remains substantially uniform between the first portion and the second portion of the fiber.
In yet another aspect, a package for an optical fiber is provided which includes an optical fiber having at least one grating with an optical characteristic which varies with strain. The package also contains a tuning structure for receiving at least a portion of the optical fiber. A control actuator is coupled to the tuning structure and elongates to move at least a portion of the tuning structure. The elongation of the control actuator provides a predetermined correlation between the optical characteristics of the fiber and the elongation.
In yet another embodiment, a variable wavelength optical device is provided which includes an optical fiber having a first end, a second end, and a fiber Bragg grating therebetween. The device also includes a piezoelectric actuator movable throughout an actuator stroke, and a mechanical advantage mechanism coupling the piezoelectric actuator to the optical fiber so that an optical fiber elongation between the first end and the second end is larger than the actuator stroke.
Other f
Pan Jing-Jong
Zhou Feng-Qing
Barrish, Esq. Mark D.
E-Tek Dynamics, Inc.
Spyrou Cassandra
Townsend and Townsend / and Crew LLP
Treas Jared
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