Gennadiy Agranov

Sensor modulation transfer function measurement using band-limited laser speckle

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 5 mW 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.

Challenges and opportunities in small pixel development for novel CMOS image sensors

As pixels continue to shrink, increasingly complicated structures are being used to maintain performance. Some of these involve novel processes like wafer thinning and bonding, while others involve novel device or optical structures like light-pipes. The development of 3D interconnect and packaging technologies has also allowed new sensor structures to be developed that allow further customization to imaging. Whether these will be commercially viable, will depend on the cost-effectiveness of developing and manufacturing such structures. Despite the fact that increasingly complicated structures are being used, as we reach pixels with sizes 1.1um and below, system MTF does not continue to scale in performance with the increased pixel sampling frequency. However, the increased pixel sampling frequency can be used to support novel functionality such as High Dynamic Range Imaging or time-interleaved sampling for other applications like depth sensing and stereo vision.