Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
1999-10-12
2001-08-21
Font, Frank G. (Department: 2877)
Optical waveguides
With optical coupler
Input/output coupler
Reexamination Certificate
active
06278819
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
The present invention relates to relates generally to the manufacturing of optical fiber components and particularly to a method and apparatus for precisely controlling the optical path length of an optical fiber component.
2. Technical Background
Optical fiber based devices are widely utilized as components for optical communications due to their relatively low insertion loss and low cost. Foremost of optical fiber components are fiber Bragg gratings (FBG) which are typically made by ultraviolet (UV) wavelength energy exposure. Once an FBG is mounted to a substrate and annealed, it is no longer photosensitive and cannot be further tuned. Thus, it is necessary to empirically predict the final frequency of such a grating which can lead to a significant error resulting in gratings which are not within specifications. Due to the uncertainty of the wavelength shift resulting from the attachment process and annealing, the center wavelength (CWL) of a packaged fiber Bragg grating can vary as much as +/−60 picometers from the desired CWL. Such a wavelength error combined with a wavelength drift of, for example, distributed feedback lasers, which may be from +/−50 picometers, and the residual temperature dependence of +/−20 picometers imposes a highly stringent requirement on the design of, for example, 50 GHz fiber Bragg gratings.
A typical attachment process for a fiber Bragg grating is to bond one end of the fiber to a substrate, tension the fiber by an empirically determined amount, and bonding the opposite end of the fiber.
FIG. 1
shows the distribution of the CWL for samples manufactured by this process. Since the total available margin is only +/−40 picometers, only a fraction (20% to 30%) of the gratings can be employed.
Precise control of optically tuned fiber-optic devices with a CWL within less than +/−15 picometers is desired to minimize cross-talk between adjacent communication channels of a system. In order to maintain the CWL of a tuned fiber-optic device, such as a fiber Bragg grating, a &bgr;-eucryptite substrate has been employed having a coefficient of temperature expansion of −7.5 ppm/° C. to compensate for the refractive index change of the fiber with temperature variations. With such substrates, the CWL shift due to temperature changes over a range of from
0
° C. to 70° C. has been reduced to +/−15 pm. Thus, although the substrate selection has improved the stability of the device once manufactured, there remains a need to manufacture devices such as fiber Bragg gratings or other optically tuned components to a CWL that produces a yield rate for precise CWL devices higher than that previously available with existing manufacturing techniques.
It has been discovered that the variability of the CWL of fiber-optic devices is not a function of the laser power employed in the manufacturing of the devices nor is it a result of the substrate material. Instead, it appears that the variability is inherent in the attachment process and there remains a need, therefore, for a process and system for manufacturing precisely tuned fiber-optic devices.
SUMMARY OF THE INVENTION
The method and apparatus of the present invention achieves the manufacturing of fiber-optic devices to precise CWL specifications by plasticizing one attachment end of a mounted fiber-optic device and finely adjusting the fiber tension while monitoring the CWL.
A method of manufacturing an optical fiber component to a precise CWL includes the step of affixing the ends of a fiber component under tension to a substrate to approximate a desired CWL. Subsequently, one end of the fiber is gripped with a movable clamp and the adjacent attachment plasticized while the tension on the fiber is adjusted until the CWL is within a desired range. The attachment is rehardened while the tension on the fiber is maintained by the movable clamp.
In one embodiment, one end of a fiber is bonded to a negative coefficient of expansion substrate using a glass frit and the opposite end gripped under tension by a movable clamp while the CWL is monitored. The fiber tension is adjusted by moving the clamp until the CWL is about 0.35 nm below the target CWL for 70 mm substrates. Next, a second frit bonds the fiber to the substrate at an opposite end adjacent the movable clamp. The CWL is again checked and, if off more than 10 picometers, the fiber is retensioned by moving the clamp to the previous position, reheating and plasticizing the second frit, and adjusting the clamp while monitoring the CWL until the CWL change equals an amount corresponding to the difference between the first measured CWL and the target CWL. Once cooled, the clamp is released and the final CWL is measured and recorded.
The result of this process produces precisely tuned fiber-optic devices, such as a fiber Bragg grating. Although particularly suitable for manufacturing fiber Bragg gratings, other tunable fiber-optic components likewise can be manufactured using such technique, to precisely control the optical path length of the optical fiber device during manufacturing.
Additional features and advantages of the invention will be set forth in the detailed description which follows and will be apparent to those skilled in the art from the description or recognized by practicing the invention as described in the description which follows together with the claims and appended drawings.
It is to be understood that the foregoing description is exemplary of the invention only and is intended to provide an overview for the understanding of the nature and character of the invention as it is defined by the claims. The accompanying drawings are included to provide a further understanding of the invention and are incorporated and constitute part of this specification. The drawings illustrate various features and embodiments of the invention which, together with their description serve to explain the principals and operation of the invention.
REFERENCES:
patent: 5218655 (1993-06-01), Mizrahi
patent: 5841920 (1998-11-01), Lemaire et al.
patent: 5949934 (1999-09-01), Shima et al.
patent: 6137932 (2000-10-01), Kim et al.
Corning Incorporated
Font Frank G.
Mooney Michael P.
Price Heneveld Cooper DeWitt & Litton
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