A Detector array for direct control of a deformable mirror

A wavefront sensing detector array is presented with capabilities suited towards high-order adaptive optics systems. The phase of the wavefront is sensed by modulating and synchronously sampling the fringes of a white light interferogram imaged onto the array. The nature of the modulation is characterized by a voltage signal, which is delivered as an input to the array. As a fringe moves across an individual detector, the null is sensed, triggering a sampling of the modulation signal. The sampled signal represents the phase of the wavefront and is held until the next null is sensed. The signal makes it possible to directly send commands to a deformable mirror to correct the phasefront. This chip is optically mapped such that each pixel in the array corresponds to an actuator on the deformable mirror. The array outputs both the photodetector current and the sampled modulation signal voltage from individual pixels by means of bit parallel row and column inputs. A prototype of this array has been fabricated in a 0.5μm CMOS process with 21 × 21 detectors, suitable for (circular) deformable mirrors with up to 349 actuators. Experimental results suggest refresh rates in excess of 3kHz are attainable. This wavefront sensor could greatly simplify the process of controlling a deformable mirror for many applications, thereby increasing refresh rates and improving sensitivity.