2000 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.

IEEE Journal of Lightwave Technology
Volume 18 Number 3, March 2000

Propagation of the Fundamental Mode in Curved Graded Index Multimode Fiber and Its Application in Sensor Systems

Page 334.

Abstract:

A novel principle of light transmission through very small radius bend in optical fibers is presented. The potential applications of the proposed structure are fiber optic sensors and other fiber optic systems. The design makes use of graded index multimode fiber as transmission medium. However,the feed to the multimode fiber is through a single mode fiber to ensure that only the lowest order spatial mode is launched. Similarly the receiver is also coupled to the sensing element through a single mode fiber. The fundamental mode within graded index multimode fiber proves to be very insensitive to macrobends if bend radius is larger than certain critical value. If bend radius is reduced below critical value the loss increases very rapidly and this allows for construction of relatively sensitive macrobend fiber optic sensor. This work presents a quantitative theoretical model of the proposed structure and a detailed experimental investigation of structure with possibilities for its practical applications.

References

1. D. Marcuse, "Curvature loss formula for optical fibers", J. Opt. Soc. Amer., vol. 66, no. 3, pp.  216-220, 1976.
2. D. Marcuse, "Field deformation and loss caused by curvature of optical fibers", J. Opt. Soc. Amer., vol. 66, no. 4, pp.  311-320, 1976.
3. J. A. Buck, Fundamentals of Optical Fibers, Wiley Series in Pure and Applied Optics, New York: Wiley, 1995.
4. R. C. Gauthier and C. Ross, "Theoretical and experimental consideration for single-mode fiber optic bend-type sensors", Appl. Opt., vol. 36, no.  25, pp.  6264-6273, 1997.
5. W. A. Gambling, H. Matsumura, C. M. Ragdale and R. A. Sammut, "Measurement of radiation loss in curved singlemode fibers", Microwaves, Opt. Acoust., vol. 2, no.  4, pp.  134-140, 1978.
6. A. B. Sharma, A.-H. Al-Ani and S. J. Halme, "Constant-curvature loss in monomode fibers: An experimental investigation", Appl. Opt., vol. 23, no.  19, pp.  3297-3301, 1984.
7. A. J. Harris and P. F. Castle, "Bend loss measurements on high numerical aperture single-mode fibers as a function of wavelength and bend radius", J. Lightwave Technol., vol. 4, pp.  34-40, Jan.  1986.
8. E. G. Neumann and W. Richter, "Sharp bends with low losses in dielectric optical waveguides", Appl. Opt., vol. 22, no. 7, pp.  1016 -1022, 1983.
9. D. Donalgic and B. Culshaw, "Microbend sensor structure for use in distributed and quasi distributed sensor systems based on selective launching and filtering of the modes in graded index multimode fiber", J. Lightwave Technol., vol. 17, pp.  1856-1869, Oct.  1999.
10. D. Marcuse, "Gaussian approximation of the fundamental modes of graded-index fibers", J. Opt. Soc. Amer., vol.  68, no. 1, 1978.