Dark-field laser mouse works on transparent surfaces

Standard optical mice use either an LED or a laser source to illuminate the surface beneath the mouse.

Dec 1st, 2009

Standard optical mice use either an LED or a laser source to illuminate the surface beneath the mouse. A lens captures the diffused light and an onboard processor uses the information from a tiny image sensor to look for minute differences that it can use to determine the direction and speed of motion. If a surface has many irregularities, it is easier for the sensor to identify reference points for accurate motion measurement. And because laser light illuminates surfaces in far greater detail than LED light, traditional laser mice are superior to standard optical mice at tracking on smooth, glossy surfaces such as ceramic tile, metal, and polished wood. Unfortunately, transparent surfaces (such as glass) transmit much of the incident light, and have minimal irregularities with poor contrast.

Borrowing dark-field illumination techniques used in microscopy to increase contrast of tiny particulates like dust and surface imperfections such as grease and scratches, Logitech (Fremont, CA) developed a new optical mouse that uses a technique called dark-field laser tracking. Using two lasers and avoiding their reflected light while collecting light that scatters from an object at an angle, dust spots appear as bright lights against a black background for improved tracking. A Logitech study showed that 40% of laptop users own a glass table, and 47% of them use their notebook computer on it at least once a week, making the dark-field laser mouse an appealing alternative. Contact Sarah Youngbauer at sarah_youngbauer@logitech.com.

More in Research