Near-field imaging of fiber Bragg gratings

Mills, J.D., Hillman, C.W.J., Blott, B.H. and Brocklesby, W.S. (1999) Near-field imaging of fiber Bragg gratings. MRS 1999 Spring Meeting, San Francisco, United States. 04 - 08 Apr 1999.

Abstract

Fiber Bragg gratings are an important component of modern telecommunications systems. Characterisation of gratings is usually performed by interrogating the whole grating in either reflection or transmission along the fiber, and there is considerable interest in possible errors and defects in the gratings. In these experiments we have used near-field optical techniques to characterise Bragg gratings on a microscopic scale. Using D-fibers in order to access the evanescent fields normally within the cladding of the fiber, direct imaging of the standing wave patterns formed when the propagating laser is on resonance with the grating has been performed. Changes in patterns with laser wavelength can be observed, and compared with theories of grating reflectivity which predict superstructure on the standing wave patterns.
The SNOM tip can also be used to study the free-space patterns formed by the phase masks used to write the gratings into the core of the fiber. Our images of the patterns agree well with theoretical predictions developed from earlier work, and clearly show the effect of errors in writing wavelength on the visibility of fringes.

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Contributors

Author: W.S. Brocklesby

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