Abstract: A relative-motion cursor control device configured as a pen permits fine control of the cursor. Optical fibers are employed to reduce to nib-size the active, sensory surface of an optical mouse. In the preferred embodiment, two bundles of optical fibers are orthogonally arrayed with hexagonal packing against a passive referent image. Quadrature logic translates edge crossings into unambiguous motion in an X-Y plane. Each fiber in the bundles acts as both source and receptor of light to and from the spot under it in the referent image. Light is directionally injected into each fiber with simple, bent-fiber coupling. Hexagonal packing automatically adjusts for the fiber's inactive cladding thus permitting a larger diameter and maximum light transmission. Contrast enhancement compensates for optical losses and noise.