A CMOS active-pixel image sharpness sensor

The technique of maximizing image sharpness is a powerful means of adaptively correcting phase aberrations in wavefronts. Crucial to this correction is a sensor that provides an accurate real-time estimate of image sharpness. In this paper, we introduce a novel image sharpness sensor using CMOS active pixel technology that computes image sharpness at a sample rate of 7.8 kHz. The sharpness sensor contains a 40×40 pixel array and is fabricated in a 0.5-μm CMOS process through MOSIS. Power consumption is 12 mW. Each pixel is 24.5 × 24.5 μm² with a fill factor of 20%. Experimental results obtained under open-loop static conditions show that the output value changes by 87.5% when the sensor is moved 1 cm away from the 50-cm focal point. This sensor finds potential applications in closed-loop adaptive optics systems.