Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
2000-03-08
2002-11-05
Ullah, Akm E. (Department: 2874)
Optical waveguides
With optical coupler
Input/output coupler
C359S333000, C359S337000
Reexamination Certificate
active
06477297
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to bent optical fibers, to optical systems such as optical amplifiers incorporating such fibers and, to a method of assembling such optical systems.
2. Technical Background
It is well known, throughout the photonics industry, that insertion loss due to macrobending in single-mode fiber increases with smaller radius of curvature and with longer wavelength of the transmitted light. This knowledge has led to standard practices for the deployment of optical fiber in spliced concatenations of pigtailed components such as Erbium doped fiber amplifiers (EDFAs) and Multiplexing/Demultiplexing assemblies. Macrobending is typically controlled in the design of optical systems by ensuring that the fiber is bend around large radii such as 25 mm or greater. This approach, however, works in direct opposition to the requirement of reducing the size of the optical systems. Furthermore, the macrobend losses become larger when the signal wavelength is longer, which is required in long-band (L-band) amplifiers. A long band amplifier is an amplifier that operates in an approximately 1560 nm to approximately 1625 nm wavelength range. Sometimes the bent optical pigtails are utilized in optical systems that operate at even longer wavelengths, for example about 1650 nm.
As we seek to reduce the overall size of optical systems comprising concatenated optical components, we need to be able to bend or coil the pigtails more tightly and simultaneously avoid increase in bend losses.
SUMMARY OF THE INVENTION.
According to one aspect of the present invention a method of assembling an optical system includes the steps of:
(i) selecting, from a plurality of optical fibers characterized by a common nominal cut-off wavelength &lgr;
cn
and an actual cut-off wavelength &lgr;
c
such that the cut-off wavelength &lgr;
c
of each one of this plurality of fibers is the same as the nominal cut-off wavelength &lgr;
cn
or differs slightly from the nominal cut-off wavelength due to manufacturing tolerances, only fibers with &lgr;
c
>&lgr;
min
, where &lgr;
min
is a predetermined minimum acceptable cut-off wavelength of the selected fibers; and
(ii) bending at least one section of at least one of these selected fibers such that this bent section has a bend radius R, where 12 mm<R<18 mm.
According to one embodiment of the present invention, the method of assembling an optical amplifier comprises the steps of: (i) manufacturing a plurality of optical fibers, the fibers being single-mode fibers that have a common nominal cut-off wavelength &lgr;
cn
≧1290 nm; (ii) and bending at least one section of at least one of these fibers such that this bent section has a bend radius R, where 12 mm<R<18 mm.
According to an embodiment of the present invention an optical system is selected from at least 10 optical systems which are identical except for differences due to manufacturing tolerances. Each of these optical systems includes bent optical fiber pigtails having: (i) a bend radius R, such that 12 mm<R<18 mm; (ii) a common design cut-off wavelength &lgr;
cn
, and (iii) an actual cut-off wavelength &lgr;
c
, such that the cut-off wavelength &lgr;
c
of each of the optical fibers of these pigtails is larger than the same or larger than &lgr;
cn
−1.5 &Dgr;, where &Dgr; is a standard deviation of &lgr;
c
distribution.
According to an embodiment of the present invention, a method of assembling an optical amplifier comprises the steps of:
(i) manufacturing a plurality of optical fibers, the optical fibers being single-mode fibers that are characterized by a common nominal Mac number MAC
n
, such that the Mac number MAC of each of the optical fibers is the same as the nominal Mac number MAC
n
or differs slightly from the nominal Mac number due to manufacturing tolerances;
(ii) selecting from these optical fibers only fibers that satisfy the following equation MAC<MAC
n
+&Dgr;, where &Dgr; is a standard deviation of Mac number distribution of said plurality of optical fibers; and
(iii) bending at least one section of at least one of these selected fibers such that this bent section has a bend radius R, where 12 mm<R<18 mm.
According to an embodiment of the present invention a method of assembling an optical amplifier comprises the steps of: (i) selecting from a plurality of optical fibers only fibers that satisfy the following equation MAC<7.0, where MAC is a Mac number of each of the selected fibers; the plurality of optical fibers being single-mode fibers; (ii) and bending at least one section of at least one of the selected fibers such that this bent section has a bend radius R, where 12 mm<R<18 mm.
According to one embodiment of the present invention an optical system selected from at least 10 optical systems which are identical except for differences due to manufacturing tolerances, each of the optical systems including optical fiber pigtails having: (i) a bend radius R, such that 12 mm<R<18 mm; (ii) a common design Mac number MAC
n
; and (iii) an actual Mac number MAC, such that the actual Mac number MAC of each of the fibers is the same or smaller than said common design Mac number MAC
n
.
It is an advantage of this invention that optical amplifiers and other optical devices of the present invention can utilize strongly bent optical fiber (with bend radius of 12 to 18 mm) without suffering from extensive macrobend losses and, thus, can be more compact and operate at longer wavelengths.
For a more complete understanding of the invention, its objects and advantages refer to the following specification and to the accompanying drawings. Additional features and advantages of the invention are set forth in the detailed description, which follows.
It should be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various features and embodiments of the invention, and together with the description serve to explain the principles and operation of the invention.
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patent: 5544272 (1996-08-01), Carratt et al.
patent: 0 334 247 (1989-09-01), None
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Unger, C. et al, “Characterization of the Bending Sensitivity of Fibers by the MAC-Value”, Optics Communications 107, May 1, 1994, pp. 361-364.
Arnaud, J. A., “Transverse Coupling in Fiber Optics Part III: Bending Losses”, The Bell System Technical Journal, vol. 53, No. 7, Sep. 1974, pp. 1379-1394.
Faustini, Luca et al, “Bend Loss in Single-Mode Fibers”, Journal of Lightwave Technology, vol. 15, No. 4, Apr. 1997, pp. 671-679.
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Tangonan, G.L. et al, “Bend Loss Measurements for Small Mode Field Diameter Fibres”, Electronic Letters, vol. 25, No. 2, Jan. 19, 1989, pp. 142-143.
Marcuse, D., “Influence of Curvature on the Losses of Doulby Clad Fibers”, Applied Optics, vol. 21, No. 23, Dec. 1, 1982, pp. 4208-4213.
Marcuse, D., “Field Deformation and Loss Caused by Curvature of Optical Fibers”, Optical Society of America, vol. 66, No. 4, Apr. 1976, pp. 311-320.
Marcuse, D., “Curvature Loss Formula for Optical Fibers”, Optical Society of America, vol. 66, No. 3, Mar. 1976, pp. 216-220.
DeMeritt Jeffery A.
Gaeta Zagorka D.
Wigley Peter G.
Corning Incorporated
Rahll Jerry T
Short Svetlana
Ullah Akm E.
LandOfFree
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