Planar Fresnel lens photoimprinted in a germanium-doped silica optical waveguide

A gradient-thickness Fresnel lens was photoimprinted in the germanium-doped core layer of a single-mode planar waveguide on silica by exposure to ultraviolet light through a mask, which increases the refractive index in the lens region by ≈5 × 10−3. The lens is used to collimate the output of a standard single-mode optical fiber butt coupled to the waveguide at a wavelength of 1.3 μm. The method is applicable to the mass production of complex diffractive elements in a planar waveguide geometry.

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