Juha-Pekka J. Laine

Characterization of a compressive imaging system using laboratory and natural light scenes

Compressive imagers acquire images, or other optical scene information, by a series of spatially filtered intensity measurements, where the total number of measurements required depends on the desired image quality. Compressive imaging (CI) offers a versatile approach to optical sensing which can improve size, weight, and performance (SWaP) for multispectral imaging or feature-based optical sensing. Here we report the first (to our knowledge) systematic performance comparison of a CI system to a conventional focal plane imager for binary, grayscale, and natural light (visible color and infrared) scenes. We generate 1024×1024 images from a range of measurements (0.1%-100%) acquired using digital (Hadamard), grayscale (discrete cosine transform), and random (Noiselet) CI basis sets. Comparing the outcome of the compressive images to conventionally acquired images, each made using 1% of full sampling, we conclude that the Hadamard Transform offered the best performance and yielded images with comparable aesthetic quality and slightly higher spatial resolution than conventionally acquired images.

Pixel response function experimental techniques and analysis of active pixel sensor star cameras

Abstract. The pixel response function (PRF) of a pixel within a focal plane is defined as the pixel intensity with respect to the position of a point source within the pixel. One of its main applications is in the field of astrometry, which is a branch of astronomy that deals with positioning data of a celestial body for tracking movement or adjusting the attitude of a spacecraft. Complementary metal oxide semiconductor (CMOS) image sensors generally offer better radiation tolerance to protons and heavy ions than CCDs making them ideal candidates for space applications aboard satellites, but like all image sensors they are limited by their spatial frequency response, better known as the modulation transfer function. Having a well-calibrated PRF allows us to eliminate some of the uncertainty in the spatial response of the system providing better resolution and a more accurate centroid estimation. This paper describes the experimental setup for determining the PRF of a CMOS image sensor and analyzes the effect on the oversampled point spread function (PSF) of an image intensifier, as well as the effects due to the wavelength of light used as a point source. It was found that using electron bombarded active pixel sensor (EBAPS) intensification technology had a significant impact on the PRF of the camera being tested as a result of an increase in the amount of carrier diffusion between collection sites generated by the intensification process. Taking the full width at half maximum (FWHM) of the resulting data, it was found that the intensified version of a CMOS camera exhibited a PSF roughly 16.42% larger than its nonintensified counterpart.

Prototype development and field-test results of an adaptive multiresolution PANOPTES imaging architecture

The design, development, and field-test results of a visible-band, folded, multiresolution, adaptive computational imaging system based on the Processing Arrays of Nyquist-limited Observations to Produce a Thin Electro-optic Sensor (PANOPTES) concept is presented. The architectural layout that enables this imager to be adaptive is described, and the control system that ensures reliable field-of-view steering for precision and accuracy in subpixel target registration is explained. A digital superresolution algorithm introduced to obtain high-resolution imagery from field tests conducted in both nighttime and daytime imaging conditions is discussed. The digital superresolution capability of this adaptive PANOPTES architecture is demonstrated via results in which resolution enhancement by a factor of 4 over the detector Nyquist limit is achieved.

Field Test of PANOPTES-Based Adaptive Computational Imaging System Prototype

We describe the design and prototype development of a visible-band, multi-resolution, steerable computational imager in a flat profile, based on the PANOPTES architecture. We present this imager’s superresolution capabilities via field test results.

High-Q silica microsphere optical resonator sensors using stripline-pedestal antiresonant reflecting optical waveguide couplers

There is currently a significant amount of interest in the development of integrated optical sensors for a variety of applications. Attractive features of these types of sensors include miniature size and low operating powers. We have demonstrated a novel integrated optical sensor platform based on high-Q silica microsphere resonators and stripline-pedestal anti-resonant reflecting optical waveguide (SPARROW) optical couplers. Advantages of the planar SPARROW coupler include high light coupling efficiency, robust planar structure, and standard optical chip processing/fabrication techniques. High light coupling efficiencies (approaching 100%) have been observed using this sensor platform. Several sensor configurations are presented here, including one designed to reduce input optical power requirements. High resolution flexured-mass-based sensors which have been demonstrated include acceleration and seismic sensors. Proposed sensor concepts based on thermo-optic effects are also discussed.