On evolution of CMOS image sensors

CMOS Image Sensors have become the principal technology in majority of digital cameras. They started replacing the film and Charge Coupled Devices in the last decade with the promise of lower cost, lower power requirement, higher integration and the potential of focal plane processing. However, the principal factor behind their success has been the ability to utilise the shrinkage in CMOS technology to make smaller pixels, and thereby have more resolution without increasing the cost. With the market of image sensors exploding courtesy their inte- gration with communication and computation devices, technology developers improved the CMOS processes to have better optical performance. Nevertheless, the promises of focal plane processing as well as on-chip integration have not been fulfilled. The market is still being pushed by the desire of having higher number of pixels and better image quality, however, differentiation is being difficult for any image sensor manufacturer. In the paper, we will explore potential disruptive growth directions for CMOS Image sensors and ways to achieve the same

Laser space rendezvous and docking tradeoff

A spaceborne laser radar (LADAR) was configured to meet the requirements for rendezvous and docking with a cooperative object in synchronous orbit. The LADAR, configurated using existing pulsed CO2 laser technology and a 1980 system technology baseline, is well suited for the envisioned space tug missions. The performance of a family of candidate LADARS was analyzed. Tradeoff studies as a function of size, weight, and power consumption were carried out for maximum ranges of 50, 100, 200, and 300 nautical miles. The investigation supports the original contention that a rendezvous and docking LADAR can be constructed to offer a cost effective and reliable solution to the envisioned space missions. In fact, the CO2 ladar system offers distinct advantages over other candidate systems

Optically resonant structures for the enhancement of polycrystalline PbSe photoconductors

The mid-wave infrared (MWIR) regime of the electromagnetic spectrum is attractive for long-range imaging systems due to the atmospheric window between 3 and 5 [mu]m. Due to ambient thermal background, it is often necessary to operate sensor systems below room temperature to achieve an adequate signal-to-noise ratio (SNR). This cooling requirement adds size, weight, and complexity to systems in which these parameters are at a premium. In this work I investigated two methods for optically enhancing the absorptive properties of lead selenide (PbSe) photoconductive films to increase the operating temperature up to 290 K, thereby mitigating system cooling requirements. By employing surface plasmon resonant (SPR) and embedded reflective structures, we were able to demonstrate enhanced responsivity and raise the operating temperature to room-temperature. Sensitivity was observed to increase by a factor of three for SPR enhanced detectors, and up to two-times at room temperature in detectors with an embedded Pt back reflector. Moreover, PbSe detectors with SPR discs operating at room temperature were observed to have responsivity comparable to reference detectors at 230 K. Photoconductors with the embedded Pt back reflector had a performance at room temperature that was similar to the reference detector at 250 K. Herein, I discuss my design process, as well as the fabrication of these resonant structures. Also discussed are the measurement and test results I obtained from surface plasmon and embedded reflector enhanced PbSe detectors. In this dissertation, I present results that demonstrate the viability of SPR and interference structures as mechanisms for increasing the operating temperature of PbSe MWIR photodetectors up to 290 KIncludes bibliographical reference

Optical Yagi-Uda nanoantennas

Conventional antennas, which are widely employed to transmit radio and TV signals, can be used at optical frequencies as long as they are shrunk to nanometer-size dimensions. Optical nanoantennas made of metallic or high-permittivity dielectric nanoparticles allow for enhancing and manipulating light on the scale much smaller than wavelength of light. Based on this ability, optical nanoantennas offer unique opportunities regarding key applications such as optical communications, photovoltaics, non-classical light emission, and sensing. From a multitude of suggested nanoantenna concepts the Yagi-Uda nanoantenna, an optical analogue of the well-established radio-frequency Yagi-Uda antenna, stands out by its efficient unidirectional light emission and enhancement. Following a brief introduction to the emerging field of optical nanoantennas, here we review recent theoretical and experimental activities on optical Yagi-Uda nanoantennas, including their design, fabrication, and applications. We also discuss several extensions of the conventional Yagi-Uda antenna design for broadband and tunable operation, for applications in nanophotonic circuits and photovoltaic devices

CMB Telescopes and Optical Systems

The cosmic microwave background radiation (CMB) is now firmly established as a fundamental and essential probe of the geometry, constituents, and birth of the Universe. The CMB is a potent observable because it can be measured with precision and accuracy. Just as importantly, theoretical models of the Universe can predict the characteristics of the CMB to high accuracy, and those predictions can be directly compared to observations. There are multiple aspects associated with making a precise measurement. In this review, we focus on optical components for the instrumentation used to measure the CMB polarization and temperature anisotropy. We begin with an overview of general considerations for CMB observations and discuss common concepts used in the community. We next consider a variety of alternatives available for a designer of a CMB telescope. Our discussion is guided by the ground and balloon-based instruments that have been implemented over the years. In the same vein, we compare the arc-minute resolution Atacama Cosmology Telescope (ACT) and the South Pole Telescope (SPT). CMB interferometers are presented briefly. We conclude with a comparison of the four CMB satellites, Relikt, COBE, WMAP, and Planck, to demonstrate a remarkable evolution in design, sensitivity, resolution, and complexity over the past thirty years.Comment: To appear in: Planets, Stars and Stellar Systems (PSSS), Volume 1: Telescopes and Instrumentatio

Imaging by Detection of Infrared Photons Using Arrays of Uncooled Micromechanical Detectors

The objective of this dissertation was to investigate the possibility of uncooled infrared imaging using arrays of optically-probed micromechanical detectors. This approach offered simplified design, improved reliability and lower cost, while attaining the performance approaching that contemporary uncooled imagers. Micromechanical infrared detectors undergo deformation due to the bimetallic effect when they absorb infrared photons. The performance improvements were sought through changes in structural design such as modification and simplification of detector geometry as well as changes in the choice of materials. Detector arrays were designed, fabricated and subsequently integrated into the imaging system and relevant parameters, describing the sensitivity and signal-to-noise ratio, were characterized. The values of these parameters were compared to values published for other uncooled micromechanical detectors and commercial uncooled detectors. Several designs have been investigated. The first design was made of standard materials for this type of detectors - silicon nitride and gold. The design utilized changes in detector geometry such as reduction in size and featured an optical resonant cavity between the detector and the substrate on which arrays were built. This design provided decrease in levels of noise equivalent temperature difference (NETD) to as low as 500 mK. The NETD parameter limits the lowest temperature gradient on the imaged object that can be resolved by the imaging device. The second design used silicon dioxide and aluminum, materials not yet fully investigated. It featured a removed substrate beneath each detector in the array, to allow unobstructed transmission of incoming IR radiation and improve the thermal isolation of the detector. Second design also featured an amorphous silicon layer between silicon dioxide and aluminum layers, to serve as an optical resonant cavity. The NETD levels as low as 120 mK have been achieved. The only difference between the third and the second design was the modification of the geometry to minimize the noise. Successfully obtained thermal images and improved NETD values, approaching those of modern uncooled imagers (20 mK for commercial bolometer-based detectors), confirm the viability of this approach. With further improvements, this approach has a potential of becoming a lowcost alternative for uncooled infrared imaging

Spaceborne sensors (1983-2000 AD): A forecast of technology

A technical review and forecast of space technology as it applies to spaceborne sensors for future NASA missions is presented. A format for categorization of sensor systems covering the entire electromagnetic spectrum, including particles and fields is developed. Major generic sensor systems are related to their subsystems, components, and to basic research and development. General supporting technologies such as cryogenics, optical design, and data processing electronics are addressed where appropriate. The dependence of many classes of instruments on common components, basic R&D and support technologies is also illustrated. A forecast of important system designs and instrument and component performance parameters is provided for the 1983-2000 AD time frame. Some insight into the scientific and applications capabilities and goals of the sensor systems is also given

Angular and Polarization Response of Multimode Sensors with Resistive-Grid Absorbers

High sensitivity receiver systems with near ideal polarization sensitivity are highly desirable for development of millimeter and sub-millimeter radio astronomy. Multimoded bolometers provide a unique solution to achieve such sensitivity, for which hundreds of single-mode sensors would otherwise be required. The primary concern in employing such multimoded sensors for polarimetery is the control of the polarization systematics. In this paper, we examine the angular- and polarization- dependent absorption pattern of a thin resistive grid or membrane, which models an absorber used for a multimoded bolometer. The result shows that a freestanding thin resistive absorber with a surface resistivity of \eta/2, where \eta\ is the impedance of free space, attains a beam pattern with equal E- and H-plane responses, leading to zero cross polarization. For a resistive-grid absorber, the condition is met when a pair of grids is positioned orthogonal to each other and both have a resistivity of \eta/2. When a reflective backshort termination is employed to improve absorption efficiency, the cross-polar level can be suppressed below -30 dB if acceptance angle of the sensor is limited to <60degrees. The small cross-polar systematics have even-parity patterns and do not contaminate the measurements of odd-parity polarization patterns, for which many of recent instruments for cosmic microwave background are designed. Underlying symmetry that suppresses these cross-polar systematics is discussed in detail. The estimates and formalism provided in this paper offer key tools in the design consideration of the instruments using the multimoded polarimeters.Comment: 22 pages, 15 figure