A focusing mechanism or module is designed to reduce the size of an optical lens-based focusing system that would be otherwise used in a portable device. According to one aspect of the present invention, the focusing mechanism includes a light guide with first and second sides. The light guide includes a plurality of light passages slanted inwardly formed evenly from the first side towards a center of the second side, wherein the light guide, disposed on top of the image sensor, collects a reflected light from a human body part and focuses the reflected light onto the image sensor, each of photosensors generates an proportional charge from the reflected light.