On-die optics have been proposed for stand-alone image sensors. Previous works by the authors have proposed fabricating diffractive optical elements using the upper metal layers in a commercial CMOS process. This avoids the cost associated with process steps associated with microlens fabrication, but results in a point spread function that varies with the wavelength, angle, and polarization of incident light. Wavelength and angle sensitivities have been addressed by previous works. This paper models the effects of polarization on the point spread function of the imaging system, and proposes optical and algorithmic methods for compensating for these effects. The imaging behaviors of the resulting systems are evaluated. Simulations indicate that the uncorrected system can locate point sources to within +/-0.1 radian, and polarized point sources to within +/-0.05 radian along the axis of polarization. A system is described that uses a polarization-insensitive optical element and a deconvolution filter to achieve a corrected resolution pf +/-0.05 radian, with the ability to perform imaging of non-point sources with white light illumination.
On-die optics have been proposed for imaging, spectral analysis, and
communications applications. These systems typically require extra process
steps to fabricate on-die optics. Fabrication of diffractive optics using
the metal layers in commercial CMOS processes circumvents this
requirement, but produces optical elements with poor imaging behavior.
This paper discusses the application of Wiener filtering to reconstruction
of images suffering from blurring and chromatic aberration, and to
identification of the position and wavelength of point sources. Adaptation
of this approach to analog and digital FIR implementations are discussed,
and the design of a multispectral imaging sensor using analog FIR
filtering is presented. Simulations indicate that off-die post-processing
can determine point source wavelength to within 5% and position to
within ±0.05 radian, and resolve features 0.4 radian in size in
images illuminated by white light. The analog hardware implementation is simulated to resolve
features 0.4 radian in size illuminated by monochromatic light, and 0.7
radian with white light.
On-die optics are an attractive way of reducing package size for imaging and non-imaging optical sensors. While systems incorporating on-die optics have been built for imaging and spectral analysis applications, these have required specialized fabrication processes and additional off-die components. This paper discusses the fabrication of an image sensor with neither of these limitations. Through careful design, an image sensor is implemented that uses on-die diffractive optics fabricated using a standard 0.18 micron bulk CMOS process, with simulations indicating that the resulting die is capable of acting as a standalone imaging system resolving spatial features to within ±0.15 radian and spectral features to within ±40 nm wavelength accuracy.
A pixel-parallel image sensor readout technique is demonstrated for CMOS active pixel sensors to facilitate a range of applications where the high-speed detection of the presence of an object, such as a laser spot, is required. Information concerning the object’s location and size is more relevant that a captured image for such applications. A sensor for which the output comprises the numbers of pixels above a global threshold in both rows and columns is demonstrated in 0.18 μm CMOS technology. The factors limiting the ultimate performance of such a system are discussed. Subsequently, techniques for enhancing information retrieval from the sensor are introduced,including centroid calculations using multiple thresholds, multi-axis readout, and run-length encoding.