Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
2000-03-20
2002-11-05
Ullah, Akm E. (Department: 2874)
Optical waveguides
With optical coupler
Input/output coupler
C385S014000, C385S123000, C385S141000
Reexamination Certificate
active
06477299
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to optical waveguide devices, and particularly to optical waveguide devices that include negative thermal expansion substrates which athermalize an optical waveguide. The substrate is made from a material having a negative thermal expansion so that the substrate shrinks with a rise in temperature, which compensates for thermally varying optical properties of the optical waveguide device.
2. Technical Background
This invention relates to a temperature compensated, athermal optical device and, in particular, to an environmentally stabilized device with a stabilized negative expansion substrate for utilization in an optical fiber reflective Bragg grating optical waveguide device and to a method of stabilizing the optical waveguide device.
Index of refraction changes induced by UV light are useful in producing complex, narrow-band optical components such as filters and channel add/drop devices. These devices can be an important part of multiple-wavelength telecommunication systems. A popular photosensitive optical fiber device is a reflective grating (Bragg grating), which reflects light over a narrow wavelength band. Typically, these devices have channel spacings measured in nanometers.
There are already known various constructions of optical filters, among them such which utilize the Bragg effect for wavelength selective filtering. U.S. Pat. No. 4,725,110 discloses one method for constructing a filter which involves imprinting at least one periodic grating in the core of the optical fiber by exposing the core through the cladding to the interference pattern of two ultraviolet beams that are directed against the optical fiber at two angles relative to the fiber axis that complement each other to 180° C. This results in a reflective grating that is oriented normal to the fiber axis. The wavelength of the light reflected by such an optical fiber with the incorporated grating filter is related to the spacing of the grating which varies either with the strain to which the grating region is subjected, or with the temperature of the grating region, in a clearly defined relationship, which is substantially linear to either one of these parameters.
For a uniform grating with spacing L, in a fiber with an effective index of refraction n and expansion a, the variation of center reflective wavelength, l
r
is given by
dl
r
/dT=
2
L[dn/dT+na]
In silica and germania-silica fiber reflective gratings the variation in center wavelength is dominated by the first term in the brackets, the change of index of refraction with temperature. The expansion term contributes less than ten percent of the total variability. The ratio dl
r
/dT is typically 0.01 nm°C. for a grating with a peak reflectance at 1550 nm.
One practical difficulty in the use of these gratings is their variation with temperature. In as much as the wavelength of the light reflected by the fiber grating varies with the temperature of the grating region this basic filter cannot be used in applications where the reflected light wavelength is to be independent of temperature. Methods of reliably and stably athermalizing the fiber reflective grating are needed to meet the rigorous and always growing optical telecommunications application demands and requirements for such gratings.
One method of athermalizing a fiber reflective grating is to thermally control the environment of the grating with an actively controlled thermal stabilization system. Such thermal stabilization is costly to implement and power, and its complexity leads to reliability concerns.
A second athermalization approach is to create a negative expansion that compensates the dn/dT. Devices which employ materials with dissimilar positive thermal expansions to achieve the required negative expansion are known.
U.S. Pat. No. 5,042,898 discloses a temperature compensated, embedded grating, optical waveguide light filtering device having an optical fiber grating. Each end of the fiber is attached to a different one of two compensating members made of materials with such coefficients of thermal expansion relative to one another and to that of the fiber material as to apply to the fiber longitudinal strains, the magnitude of which varies with temperature in such a manner that the changes in the longitudinal strains substantially compensate for these attributable to the changes in the temperature of the grating.
Yoffe, G. W. et al in “Temperature-Compensated Optical-Fiber Bragg Gratings” OFC95 Technical Digest, paper WI4, discloses a device with a mechanical arrangement of metals with dissimilar thermal expansions which causes the distance between the mounting points of an optical fiber to decrease as the temperature rises and reduce the strain in a grating.
Another method of athermalizing optical waveguide devices utilizes a substrate for attachment with the optical fiber grating with the substrate fabricated from a material with an intrinsic negative coefficient of expansion.
SUMMARY OF THE INVENTION
One aspect of the present invention is an environmentally stable athermalized optical fiber grating waveguide device for use in an optical waveguide deployment environment, which includes an optical fiber grating which reflects light centered about a wavelength &lgr;, an environmentally stable (stabilization treated) negative thermal expansion beta-eucryptite glass-ceramic substrate with the fiber grating attached under tension to the substrate with an environmentally durable lead zinc boron glass frit fusion seal wherein the substrate compensates for thermally induced wavelength shifts in the fiber grating and the wavelength &lgr; varies less than +/−0.015 nm when exposed to a humid environment.
According to an embodiment of the present invention an environmentally stable athermalized optical fiber Bragg grating waveguide filter device for use in an optical waveguide deployment environment, includes an optical fiber Bragg grating which reflects light centered about a wavelength &lgr;, a stabilized treated environmentally stable negative thermal expansion microcracked beta-eucryptite glass-ceramic substrate, with the fiber grating being attached under tension to the substrate wherein the substrate compensates for thermally induced wavelength shifts in the fiber grating and the wavelength &lgr; varies less than +/−0.015 nm when exposed to a humid environment.
According to one embodiment of the present invention a method of making an environmentally stable athermalized fiber grating waveguide device for use in an optical waveguide deployment environment, includes the steps of providing an optical fiber grating which operates on light centered about a wavelength &lgr;, environmentally stabilizing a negative thermal expansion beta-eucryptite glass-ceramic substrate, attaching the optical fiber grating to the environmentally stabilized glass-ceramic substrate with a lead zinc borate glass frit fusion seal wherein the substrate athermalizes thermally induced wavelength shifts in the fiber grating and the wavelength &lgr; varies less than +/−0.015 nm when exposed to a humid environment.
An embodiment of the present invention also includes a method of making an environmentally stable athermalized fiber grating waveguide device for use in an optical waveguide deployment environment. The method includes the steps of providing an optical fiber Bragg grating which reflects light centered about a wavelength &lgr;, environmentally stabilizing a negative thermal expansion microcracked beta-eucryptite glass-ceramic substrate, attaching the optical fiber grating under tension to the environmentally stabilized glass-ceramic substrate wherein the substrate compensates for thermally induced wavelength shifts in the fiber grating and the center wavelength &lgr; varies less than +/−0.010 nm when exposed to a humid environment which has a relative humidity of at least 80 %.
An embodiment of the invention also includes a method of making an environ
Beall George H.
Carberry Joel P.
Chyung Kenneth
Pierson Joseph E.
Reddy Kamjula P.
Corning Incorporated
Doan Jennifer
Short Svetlana
Ullah Akm E.
LandOfFree
Environmentally stable athermalizes optical fiber grating... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Environmentally stable athermalizes optical fiber grating..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Environmentally stable athermalizes optical fiber grating... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2920399