HETERODYNE LASER EYE ATTITUDE SENSOR WITH RAPID RESPONSE

AN IMPROVED LASER DOPPLER TECHNIQUE TO MONITOR EYE ATTITUDE USING AN OPTRA DEVELOPED 2-FREQUENCY HE NE LASER IS PROPOSED. THE HETERODYNE APPROACH MAKES IT POSSIBLE TO UNAMBIGUOUSLY MEASURE EYE ATTITUDE BY INTEGRATING THE DOPPLER SHIFT OF LIGHT SCATTERED OFF THE CORNEA OR SCLERA. THE HIGH SENSITIVITY OF THIS METHOD MAKES IT POSSIBLE TO OPERATE A LOW LIGHT LEVELS--WELL BELOW THE EYE SAFETY EXPOSURE LIMITS.SINCE THE MEASUREMENT SAMPLING RATE IS AT THE HETERODYNE FREQUENCY (TYPICALLY 250 KHZ), THE SYSTEM RESPONSE IS FAST, E.G. LESS THAN 1 MSEC, MAKING THIS METHOD WELL-SUITED FOR MONITORING RAPID SACCADIC EYE MOTIONS AND FOR COUPLING WITH STIMULUS-BASED DISPLAY SYSTEMS. THE RESOLUTION IS HIGH, SINCE THE MEASUREMENT IS PERFORMED AT OPTICAL WAVELENGTHS. MOREOVER, THE METHOD IS CAPABLE OF FOLLOWING LARGE EYE EXCURSIONS. WE PROPOSE, IN ORDER TO MINIMIZE WEIGHT AND HEAD RESTRAINTS, TO USE FIBER OPTICS BOTH TO BRING ILLUMINATION TO THE EYE, AND TO COLLECT THE SCATTERED LIGHT. WHILE THE PHASE I EFFORT INVOLVES ONLY ANALYSIS OF A SINGLE AXIS, THE APPROACH IS INHERENTLY CAPABLE OF MONITORING MULTI-AXIAL MOTIONS.