Optical waveguides – Accessories – External retainer/clamp
Reexamination Certificate
2001-02-01
2003-03-04
Font, Frank G. (Department: 2877)
Optical waveguides
Accessories
External retainer/clamp
C385S037000
Reexamination Certificate
active
06529671
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to optical fibers and long-period gratings.
Optical fibers are used to guide light which might, typically, be an optical signal used in telecommunications. In general, an optical fiber includes an inner core and an outer clad having an index of refraction less than the inner core. The difference in the index of refraction creates internal reflections forcing the light to propagate along the inner core and preventing it from leaking out of the fiber.
Some optical fibers include long-period gratings (LPG). A long period grating is formed by producing a series of perturbations in the index of refraction of the inner core. It is well known in the art how to produce optical fibers having long-period gratings, e.g., as described in U.S. Pat. No. 5,430,817. In general, the optical fibers are made from high purity SiO
2
or other optical materials, e.g., germanosilicate. The long-period gratings can be made by first loading the fibers with hydrogen or deuterium and then selectively exposing the core of an optical fiber to ultra-violet light. Typically, the perturbations are formed by exposing the core through the cladding to an intensity pattern which is produced by transmitting an ultra-violet beam directed through an amplitude mask. The spacing of the perturbations creates a grating characterized by a center wavelength at which light will no longer propagate through the optical fiber. Long-period gratings with different perturbation spacings have different center wavelengths. In general, long-period gratings are those in which the spacing of the perturbations is at least 10 times larger than the wavelength of input light. Typically, the period is in the range 15-1500 &mgr;m for center wavelengths between 700 and 1500 nm. In addition, long-period gratings can have a span of perturbations extending for a few cm.
Long-period gratings are used in optical fibers to filter out selected wavelengths from an optical signal, e.g., like a notch filter. As an optical signal propagates through the core and encounters a long-period grating, specific wavelengths of light, i.e., the center wavelength of the grating, are converted from a guided mode of the core to a non-guided mode of the cladding. A guided mode propagates through the core of the optical fiber. A non-guided mode of the cladding dissipates through the cladding and does not propagate through the optical fiber. The center wavelength conversion from a guided mode to a non-guided mode is a function of the perturbation spacing and the difference in the effective index of refraction between the guided and non-guided mode. Typically, for a single mode optical fiber, there is only one core guided mode, but several cladding non-guided modes. In addition, each non-guided mode of cladding is characterized by an unique effective index of refraction. Therefore, for a given perturbation spacing, there are several non-guided cladding modes, and thus, several center wavelengths at which light is converted from a guided mode to non-guided modes. In addition, for a given center wavelength, there are several perturbation spacings at which light is converted from a guided mode to non-guided mode.
Optical fibers having long-period gratings are useful as amplified spontaneous emission (ASE) filters, erbium-doped fiber amplifier (EDFA) gain equalizers and sensors. The use of optical fibers having long-period gratings continues to increase. Long-period gratings, however, are sensitive to changes in temperature. Typically, a central wavelength of 1550 nm shifts by 2 to 30 nm per 100° C. change in temperature. It is important, for instance, in telecommunication applications that the central wavelength of the long-period grating be constant over temperature ranges of 100° C.
SUMMARY OF THE INVENTION
In general, in one aspect, the invention features a passively compensated optical fiber having an optical fiber and a support member. The support member is attached to the optical fiber at a first attachment point and at a second attachment point. The distance between the first attachment point and the second attachment point increases with increasing temperature due to expansion of the support member.
The passively compensated optical fiber includes a stainless steel, aluminum, or copper support attached with an epoxy to the optical fiber at two points. The epoxy can be ultra-violet curable. The passively compensated optical fiber also includes a coating, an outer core, and an inner core. The inner core includes a long-period grating between the first attachment point and the second attachment point.
In another aspect, the invention features a method of fabricating a passively compensated optical fiber. The method includes identifying the strain response and thermal response for a long-period grating having a central wavelength, choosing a support member having a coefficient of linear expansion which compensates the optical fiber, and attaching the optical fiber to the support member at a first attachment point and at a second attachment point.
In another aspect, the invention features a method of fabricating a passively compensated optical fiber. The method includes calculating an optical fiber design for compensating an optical fiber having a center wavelength and a substrate having a coefficient of thermal expansion, manufacturing an optical fiber having a long-period grating fabricated using the calculated optical fiber design, and attaching the fabricated optical fiber to a support member at a first attachment point and at a second attachment point.
In another aspect, the invention features a method of compensating an optical fiber. The method includes providing an optical fiber, attaching the optical fiber at a first attachment point and at a second attachment point, and increasing the distance between the first attachment point and the second attachment point in response to an increase in temperature.
Preferably, the method of compensation is done passively.
The invention provides a passively compensated LPG device by attaching an optical fiber having a LPG to a thermally expanding support.
REFERENCES:
patent: 4593969 (1986-06-01), Goodman et al.
patent: 4636031 (1987-01-01), Schmadel, Jr. et al.
patent: 5042898 (1991-08-01), Morey et al.
patent: 5367589 (1994-11-01), MacDonald et al.
patent: 5430817 (1995-07-01), Vengsarkar
patent: 5469520 (1995-11-01), Morey et al.
patent: 5641956 (1997-06-01), Vengsarkar et al.
patent: 5694503 (1997-12-01), Fleming et al.
patent: 5703978 (1997-12-01), DiGiovanni et al.
patent: 5757540 (1998-05-01), Judkins et al.
patent: 5841920 (1998-11-01), Lemaire et al.
patent: 5926599 (1999-07-01), Bookbinder et al.
patent: 5987200 (1999-11-01), Fleming et al.
patent: 5991483 (1999-11-01), Engelberth
patent: 5999671 (1999-12-01), Jin et al.
patent: 6055348 (2000-04-01), Jin et al.
patent: 6128424 (2000-10-01), Espindola et al.
patent: 6137932 (2000-10-01), Kim et al.
patent: 6181852 (2001-01-01), Adams et al.
patent: 6266462 (2001-07-01), Kim et al.
patent: 6278819 (2001-08-01), Reddy
patent: 0 767 391 (1996-09-01), None
patent: WO 97/28480 (1997-07-01), None
A.M. Vengsarkar, “Long-Period Fiber Gratings”, Optical Society of America Technical Digest, Bragg Gratings, Photosensitivity and Poling in Glass Fibers and Waveguides: Applications and Fundamentals, Oct. 26-28, 1997, pp. 12/BsuB1-1—BsuBl-4/15.
H.J. Patrick et al., “Hybrid Fiber Bragg Grating/Long Period Fiber Grating . . . Strain/Temperature Discrimination”, IEEE Photonics Technology Letters, vol. 8, No. 9, Sep. 1996, pp. 1223-1225.
A.M. Vengsarkar et al., “Long-Period Fiber Gratings as Band-Rejection Filters”, IEEE Journal of Lightwave Technology, vol. 14, No. 1, Jan. 1996, pp. 58-65.
V. Bhatia et al., “Standard Optical Fiber Long-Period Gratings . . . and Refractive Index Sensing”, Proceedings of the 1997 Conference on Optical Fiber Communications, Feb. 1997, pp. 346-347.
3M Innovative Properties Company
Font Frank G.
Ho Nestor F.
Mooney Michael P
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