Coherent light generators – Particular beam control device – Tuning
Reexamination Certificate
1999-12-06
2001-05-08
Scott, Jr., Leon (Department: 2881)
Coherent light generators
Particular beam control device
Tuning
C372S006000, C372S064000
Reexamination Certificate
active
06229827
ABSTRACT:
TECHNICAL FIELD
This invention relates to fiber gratings, and more particularly to a compression-tuned Bragg grating and laser.
BACKGROUND ART
It is known in the art of fiber optics that Bragg gratings embedded in the fiber may be used in compression to act as a tunable filter or tunable fiber laser, as is described in U.S. Pat. No. 5,469,520, entitled “Compression Tuned Fiber Grating” to Morey, et al and U.S. Pat. No. 5,691,999, entitled “Compression Tuned Fiber Laser” to Ball et al., respectively, which are hereby incorporated herein by reference.
To avoid fiber buckling under compression, the technique described in the aforementioned U.S. Pat. Nos. 5,469,520 and 5,691,999 uses sliding ferrules around the fiber and grating and places the ferrules in a mechanical structure to guide, align and confine the ferrules and the fiber. However, it would be desirable to obtain a configuration that allows a fiber grating to be compressed without buckling and without sliding ferrules and without requiring such a mechanical structure.
Also, it is known to attach an optical fiber grating to within a glass tube to avoid buckling under compression for providing a wavelength-stable temperature compensated fiber Bragg grating as is described in U.S. Pat. No. 5,042,898, entitled “Incorporated Bragg Filter Temperature Compensated Optical Waveguide Device”, to Morey et al. However, such a technique exhibits creep between the fiber and the tube over time, or at high temperatures, or over large compression ranges.
SUMMARY OF THE INVENTION
Objects of the present invention include provision of a fiber grating configuration that allows the grating to be compression-tuned without creep and without requiring sliding ferrules or a mechanical supporting structure for the ferrules.
According to the present invention, a compression-tuned optical device, comprises; a tunable optical element, having outer dimensions along perpendicular axial and transverse directions, the outer dimension being at least 0.3 mm along the transverse direction; the tunable optical element receiving and propagating input light and having at least one reflective element disposed therein along the axial direction, the reflective element reflecting a reflection wavelength of the input light; at least a portion of the tunable element having a transverse cross-section which is contiguous and comprises a substantially homogeneous material; and the reflective element being axially strain compressed so as to change the reflection wavelength without buckling the tunable element in the transverse direction.
According further to the present invention, the tunable element comprises an optical fiber, having the reflective element embedded therein; and a tube, having the optical fiber and the reflective element encased therein along a longitudinal axis of the tube, the tube being fused to at least a portion of the fiber. According further to the present invention the tunable element comprises a large diameter optical waveguide having an outer cladding and an inner core disposed therein and an outer waveguide diameter of at least 0.3 mm.
According still further to the present invention the material is a glass material. According still further to the present invention the tube is fused to the optical fiber where the reflective element is located. According still further to the present invention the a plurality of the optical fibers or cores disposed in the tunable element. According still further to the present invention, the tunable element has a plurality of reflective elements encased in the tube. According still further to the present invention, the tunable element has at least one pair of reflective elements disposed therein and at least a portion of the tunable element is doped with a rare-earth dopant between the pair of elements to form a laser. According still further to the present invention, the laser lases at a lasing wavelength which changes as force on the tube changes.
The present invention provides a Bragg grating disposed in a tunable optical element which includes either an optical fiber fused to at least a portion of a glass capillary tube (“tube encased grating”) or a large diameter waveguide grating having an optical core and a wide cladding. The tunable element is placed in compression to tune the reflection wavelength of the grating without buckling the element.
The element may be made of a glass material, such as silica or other glasses. The tunable element may have alternative geometries, e.g., a dogbone shape, that provides enhanced force to wavelength shift sensitivity and is easily scalable for the desired sensitivity. The present invention allows a fiber grating or laser to be wavelength tuned with very high repeatability, low creep and low hysteresis. Also, one or more gratings, fiber lasers, or a plurality of fibers or optical cores may be disposed in the tunable element.
The grating(s) or laser(s) may be “encased” in the tube by having the tube fused to the fiber on the grating area and/or on opposite axial ends of the grating area adjacent to or a predetermined distance from the grating. The grating(s) or laser(s) may be fused within the tube or partially within or to the outer surface of the tube. Also, one or more wavguides and/or the tube encased fiber/gratings may be axially fused and optically coupled to form the tunable element.
The foregoing and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of exemplary embodiments thereof.
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Bailey Timothy J.
Brucato Robert N.
Davis Michael A.
Fernald Mark R.
Kersey Alan D.
CiDRA Corporation
Jr. Leon Scott
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