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The focal point of a lens written onto a spatial light modulator can be translated laterally by displacement of the central location of the encoded lens function. We show that the beam can be translated by a fraction of a pixel, in contrast to the expected single-pixel limitation. This increases the positional sensitivity obtainable with this technique. Experimental results are presented. Key words: Fresnel lenses, diffractive optical elements, spatial light modulators, binary optical elements.

Binary Fresnel lenses produce focused spots at subharmonics of the principal focal length of the lens. The intensities of these focal spots can be controlled by variation of the relative widths of the rings of the Fresnel lens compared with the spacings between the rings. Theory is presented and experimental verification is provided with Fresnel lenses written onto the magneto-optic spatial light modulator. Key words: Fresnel lenses, diffractive optical elements, spatial light modulators, binary optical elements.