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Proceedings Paper

2D CMOS image sensors for the rapid acquisition of modulated light and multi-parametric images
Author(s): Nicholas S. Johnston; Roger Light; Jing Zhang; Mike Somekh; Mark Pitter
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Paper Abstract

Many imaging techniques require highly sensitive optical systems including detectors capable of measuring extremely small fluctuations in the detected incident light. Such systems use a modulated light source (at frequencies up to 100's of kHz) in combination with optics that induce a change in the amplitude and/or phase of the modulation in response to changes in the sample being imaged. These signals are usually demodulated using a point detector and a lock-in amplifier. However, this technique is not suitable for the fast acquisition of 2D images. Using a modified active pixel sensor architecture, cameras with resolutions up to 256 x 256 pixels which are capable of demodulating optical signals with frequencies up to 1 MHz and have been designed and fabricated. Each demodulation pixel consists of a photodiode, a reset switch, four independently controlled shutter switches and four supplementary well-boosting capacitances that improve both linearity and signal to noise ratio. The reset and shutter switches are implemented with 5 V thick oxide transistors to maximize the dynamic range of the sensor. Demodulation is achieved by rapidly acquiring four images at 90 degree intervals of the modulation period, then applying simple post processing to extract the modulation amplitude, phase, and DC level of the optical signal. The camera outputs 16 parallel analogue channels and can deliver total pixel rates of up to 160 Mega pixels per second. In imaging systems where demodulation is not necessary, the camera can be clocked to behave as a conventional DC camera capable of taking four images with independent exposure periods allowing for advanced multi-parametric imaging.

Paper Details

Date Published: 6 May 2011
PDF: 8 pages
Proc. SPIE 8073, Optical Sensors 2011; and Photonic Crystal Fibers V, 807303 (6 May 2011); doi: 10.1117/12.886955
Show Author Affiliations
Nicholas S. Johnston, Univ. of Nottingham (United Kingdom)
Roger Light, Univ. of Nottingham (United Kingdom)
Jing Zhang, Univ. of Nottingham (United Kingdom)
Mike Somekh, Univ. of Nottingham (United Kingdom)
Mark Pitter, Univ. of Nottingham (United Kingdom)


Published in SPIE Proceedings Vol. 8073:
Optical Sensors 2011; and Photonic Crystal Fibers V
Kyriacos Kalli; Francesco Baldini; Jiri Homola; Robert A. Lieberman, Editor(s)

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