Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
1998-05-01
2001-01-30
Sanghavi, Hemang (Department: 2874)
Optical waveguides
With optical coupler
Input/output coupler
C385S031000, C385S015000
Reexamination Certificate
active
06181851
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is related to the field of fiberoptic devices and networks, and more particularly, provides optical fiber packages which vary tension in an optical fiber, particularly for compensating for temperature induced wavelength variations in fiber Bragg gratings.
Modern fiberoptic communication systems often have the ability to simultaneously transfer light signals having differing wavelengths over a single optical fiber.
Fiber Bragg gratings 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. Sharp reflection resonances can be used as demultiplexers, laser diode wavelength stabilizers, external laser mirrors, 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.
Unfortunately, fiber Bragg gratings often have a significant temperature sensitivity. For example, the resonant wavelength of a fiber Bragg grating may vary as much as 0.01 nm per degree centigrade. This temperature sensitivity is significantly higher than the sensitivity of resonators and/or filters formed using thin-film coating techniques, which typically provide resonant frequencies which vary about 0.003 nm per degree centigrade. Their large temperature sensitivity mitigates the cost advantages and precise wavelength control otherwise provided by fiber Bragg gratings, thereby limiting their acceptability.
To overcome the disadvantageous sensitivity of fiber Bragg gratings to changes in temperature, a variety of temperature compensation packages have been proposed. Known compensation packages generally rely on fiber support structures having one or more materials which are affixed to the fiber so as to compensate for the thermal expansion of the fiber material. Unfortunately, to overcome the disadvantageous increase in length of the fiber Bragg grating, these known compensation packages generally requires identification of a material (or combination of materials) which provides an exactly compensating effective thermal coefficient of expansion throughout the entire wavelength range.
Although known temperature compensation packages have decreased the sensitivity of the packaged fiber Bragg grating, these known structures suffer from certain disadvantages. For example, these known structures are often difficult to mass produce, and also tend to retain a significant amount of temperature sensitivity. While the remaining temperature sensitivity variation of known compensated fiber Bragg gratings is acceptable for some uses, it may be unacceptable for use in some dense wave division multiplex systems.
SUMMARY OF THE INVENTION
The present invention substantially mitigates or overcomes the above disadvantages, generally by providing additional mechanisms for varying the tension within a fiber Bragg grating or other fiber-based optical device. In some embodiments, the fiber tension/temperature correlation may be tailored using not only the linear coefficient of expansion of two different materials, but also by varying the resilient flexibility of a yieldable member supporting the fiber. In the exemplary embodiment, the temperature/tension correlation may be established during the package design process by varying a length of an arm extending from the beam to the fiber, by varying the resilient strength of the arm, and the like, thereby allowing the temperature compensation characteristics of the package to be tailored so as to provide the desired optical characteristics throughout a wide temperature range. By relying on the resilient deformation of a flexible fiber support member, the present invention provides a much greater number of degrees of freedom within the temperature compensation design parameters. This provides temperature compensated packages which precisely compensate for changes in wavelengths of fiber Bragg gratings with significantly greater precision than known temperature compensation packages. Where such precise control over the temperature/tension correlation is not required, the present invention provides alternative compensation packages which can be mass-produced at significantly lower cost than known package structures.
In a first aspect, the present invention provides a temperature-adjusting optical fiber package comprising a first member having a first thermal coefficient of expansion. A second member has a second thermal coefficient of expansion which is different than the first coefficient. The second member is coupled to the first member to impose a resilient deflection in the first member which varies with temperature. An optical fiber is supported by the first member, and has an optical characteristic which varies with tension. The first member supports the fiber under a tension which varies with the resilient deflection of the first member.
In another aspect, the invention provides a temperature compensated optical fiber package comprising a first member having a first thermal coefficient of expansion, a first end, a second end, and an axis between the first end and the second end. A second member is affixed axially along the first member. The second member has a second thermal coefficient of expansion which is different than the first coefficient so that a resilient lateral deflection of the first and second members varies in response to a temperature of the package. An optical fiber has an optical characteristic which varies with temperature and with tension. The fiber is attached to the first and second ends of the first member by first and second attachment structures, respectively. The attachment structures impose a tension on the fiber which varies in response to the lateral deflection of the first and second members, so that the tension compensates for temperature-induced variations in the optical characteristic.
In yet another aspect, the present invention provides a temperature compensated fiber Bragg grating package, the package comprising a first member comprising a first material and having a first thermal coefficient of expansion. A second member engages the first member, and comprises a second material having a second thermal coefficient of expansion. An optical fiber has a Bragg grating with a resonant frequency which varies with temperature when the fiber is at rest. The fiber is coupled to the members so that the members impose a varying tension in the fiber while a temperature of the package changes within a range of between about −20 and 80 degrees centigrade. The varying tension is tailored throughout the temperature range to compensate for temperature induced resonant frequency variations of the Bragg grating, so that the resonant frequency of the packaged Bragg grating remains within a range of about 0.001 nm throughout the temperature range.
In yet another aspect, the present invention provides a temperature compensated fiber package comprising a member having a first end, a second end, and a channel which extends therebetween. The channel is open laterally, and the member comprises a material having a negative thermal coefficient of expansion. A fiber with an optical characteristic which varies with both temperature and tension is disposed within the laterally open channel of the member. The fiber is attached adjacent to the first and second ends of the member by first and second attachment structures, respectively. The member imposes a tension on the fiber which increases with decreasing temperature to compensate for temperature induced variation in the optical characteristic.
In a method provided by the invention, a tension is imposed on an optical fiber
Chen Jian
Ma Pan
Pan Jing-Jong
Barrish, Esq. Mark D.
E-Tek Dynamics, Inc.
Kim Ellen E.
Sanghavi Hemang
Townsend & Townsend & Crew LLP
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