oe 16 24 20047 Essay - 6385 Words

Sensor modulation transfer function measurement using band-limited laser speckle
Xi Chen,1* Nicholas George,2 Gennadiy Agranov,1 Changmeng Liu1 and Bob Gravelle1
1
Aptina Imaging, 3080 N. First Street, San Jose, CA, 95124, USA
The Institute of Optics, University of Rochester, Rochester, NY, 14627, USA
*
Corresponding author: xchen@aptina.com

2

Abstract: A new methodology for image sensor modulation transfer function measurement using band-limited laser speckle is presented. We use a circular opal milk glass diffuser illuminated by a 5mW He-Ne laser and a linear polarizer to generate band-limited speckle on the sensor. The power spectral density cut-off frequency of the speckle is chosen to be twice that of the sensor Nyquist frequency by placing the sensor at the specific Z location along the optical axis. For the speckle input, we calculate the power spectral density at the sensor using the Rayleigh-Sommerfeld integral and then measure the output power spectral density for the speckle pattern captured by the sensor. With these data, the two-dimensional image sensor modulation transfer function (MTF) is calculated.
©2008 Optical Society of America
OCIS codes: (130.6010) Sensors; (030.6140) Speckle; (120.0120) Instrumentation, measurement, and metrology

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1. Introduction
CMOS image sensors are widely used on digital imaging devices. The modulation transfer function (MTF) of the image sensors is an important characteristic to evaluate the overall imaging system quality. The image sensor MTF reflects the spatial frequency response of the sensor. It is determined by the spatial structure and optical and electrical cross-talk of the pixels. There have been several techniques widely used for measuring sensor MTF. For example, the sensor MTF is measured with bar targets [1], slanted edge technique [2], random targets
[3], self-calibrating fringe pattern [4], and laser speckle modulated with a double-slit aperture
#102216 - $15.00 USD Received 30 Sep 2008; revised 10 Nov 2008; accepted 14 Nov 2008; published 20 Nov 2008

(C) 2008 OSA

24 November 2008 / Vol. 16, No. 24 / OPTICS EXPRESS 20047

[5]. Among these methods, the slanted edge method is commonly applied in industry. A super resolution scan can be created with a slanted edge [2], which solves the sample-scene phase problem [6]. The

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