Ultrasound modulated tomography using a CMOS modulated light lock-in pixel

There are many situations in optics (such as heterodyne microscopy and some biomedical imaging applications) where the required information is carried on a modulated component of the received image. When, as frequently is the case, the frequency of modulation exceeds the frame rate of conventional imagers (i.e. CCD or CMOS charge integrating active pixel sensor cameras) this modulated component must be detected by a single detector rather than imaged in parallel by and array or camera. It is for these reasons that there is a pressing need for the development of new imaging technologies. In this paper we present a lock-in pixel for a CMOS modulated light camera (MLC) capable of detecting modulated components in the incident light. The detected frequency is independent of, and is much higher than the frame rate of any conventional commercial camera. The pixel presented here is capable of narrow band lock-in detection of light modulated between 10MHz and 75MHz even when superimposed on a large ambient background. We present the design of this pixel and experimental results that optically image the ultrasound field using a pixel fabricated in a standard 0.35μm CMOS process. We also discuss the current work increasing the frequency response, providing phase sensitive (I and Q) detection and the development of an imaging array leading to a full field modulated light camera.