Optical waveguide with diffraction grating and method of forming

Details Optical waveguide with diffraction grating and method of forming Optical waveguide with diffraction grating and method of forming

1995-04-17

1997-02-18

Bovernick, Rodney B.

Optical waveguides

With optical coupler

Input/output coupler

359569, G02B 634

Patent

active

056048297

ABSTRACT:
A method for forming an index grating in an optical waveguide, such as an optical fiber, with precise control over the grating's period, cross-sectional shape and length. A single writing beam is passed through an optical grating mask, such as a phase mask. A photosensitive waveguide is spaced from the optical grating by a distance that corresponds to an integer fraction of the Talbot self-imaging distance, so that the optical grating (or a desired transformation of it) is imaged in the waveguide core. The grating image has substantially the same cross-sectional shape, period and length as the portion of the optical grating that is illuminated by the writing beam. Thus, an index grating that substantially replicates the cross-sectional shape, period and length of the optical grating mask, which preferably has a substantially square-wave shaped cross-section, is written in the waveguide core. The substantially square-wave shaped cross-section results in higher reflectivity per unit length than prior waveguide gratings with sinusoidal cross-sections. As a result, a high order waveguide index grating may be formed over a waveguide length that is shorter than would previously be required. Alternatively, a low order grating may be formed that has higher reflectivity than a low order sinusoidal grating.

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