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We demonstrate the suppression of the bulk generation-recombination current in nBn devices based on an InAsSb active layer (AL) and a AlSbAs barrier layer (BL). This leads to much lower dark currents than in conventional InAsSb photodiodes operating at the same temperature. When the BL is p-type, very high doping must be used in the AL (nBpn⁺). This results in a significant shortening of the device cutoff wavelength due to the Moss-Burstein effect. For an n-type BL, low AL doping can be used (nB_nn), yielding a cutoff wavelength of ∼4.1 μm and a dark current close to ∼3 × 10−⁷ A/cm² at 150 K. Such a device with a 4-μm-thick AL will exhibit a quantum efficiency (QE) of 70% and background-limited performance operation up to 160 K at f/3. We have made nB_nn focal plane array detectors (FPAs) with a 320 × 256 format and a 1.3-μm-thick AL. These FPAs have a 35% QE and a noise equivalent temperature difference of 16 mK at 150 K and f/3. The high performance of our nB_nn detectors is closely related to the high quality of the molecular beam epitaxy grown InAsSb AL material. On the basis of the temperature dependence of the diffusion limited dark current, we estimate a minority carrier lifetime of ∼670 ns.

An enhanced original computer program is applied to explain in detail the influence of the photon recycling effect on carrier lifetime in a selected 3-μm n-on-p HgCdTe photodiode structure. The computer program is based on solution of carrier and photon transport equations for practical photodiode design. As a result, both distribution of thermal carrier generation and recombination rates and spatial photon density distribution in photodiode structures have been obtained. It is clearly shown that the photon recycling effect drastically limits the influence of radiative recombination on performance of HgCdTe photodiodes. A general conclusion confirms previous Humpreys' ascertainment that the radiative recombination, although of fundamental nature, does not limit the ultimate performance of HgCdTe photodiodes.

We report on a structure prepared by metalorganic chemical vapor deposition and molecular beam epitaxy techniques incorporated with a standard process of compound semiconductor to achieve In0.1Ga0.9As/InAs/In0.1Ga0.9As quantum dot infrared photodetector (QDIP)-based focal plane array. For investigating the mechanism of carrier transport and optoelectronic behavior, the photoresponse spectra and dark current were measured in agreement with the theoretical simulations. Furthermore, a model is proposed with the systematic analyses and explained for designing high-performance QDIPs based on the calculations of thermal activation energy and detectivity. For QDIP photoresponse measurements, the photovoltaic photoresponse is achieved, which can be attributed to the asymmetric morphology of quantum dot epitaxy. With increasing bias, the photoresponse spectra exhibit a redshift due to band bending that generates a thinner triangle barrier which increases the escape possibility of the excited carriers situated at lower excited-state levels. The trapezoid-edged scheme enhances infrared coupling and increases the photoresponse intensity. A single-sided gradient AlxGa1-xAs (x = 0.25→0) barrier can suppress the dark-current under bias efficiently. The infrared imaging performance of InGaAs QDIP based on 320×256 FPA is also demonstrated in this paper.

We have extended our investigation of corrugated quantum well infrared photodetector focal plane arrays (FPAs) into the far infrared regime. Specifically, we are developing the detectors for the thermal infrared sensor (TIRS) used in the Landsat Data Continuity Mission. To maintain a low dark current, we adopted a low doping density of 0.6×10¹⁸ cm⁻³ and a bound-to-bound state detector. The internal absorption quantum efficiency (QE) is calculated to be 25.4%. With a pixel fill factor of 80% and a substrate transmission of 70.9%, the external QE is 14.4%. To yield the theoretical conversion efficiency (CE), the photoconductive gain was measured and is 0.25 at 5 V, from which CE is predicted to be 3.6%. This value is in agreement with the 3.5% from the FPA measurement. Meanwhile, the dark current is measured to be 2.1×10⁻⁶ A/cm² at 43 K. For regular infrared imaging above 8 μm, the FPA will have an noise equivalent temperature difference (NETD) of 16 mK at 2 ms integration time in the presence of 260 read noise electrons. The highest operability of the tested FPAs is 99.967%. With the CE agreement, we project the FPA performance in the far infrared regime up to 30 μm cutoff.

The high level of accumulated expertise by ULIS and CEA/LETI on uncooled microbolometers made from amorphous silicon with 45, 35, and 25 μm enables ULIS to develop video graphics array (VGA) and extended graphics array (XGA) infrared focal plane array (IRFPA) formats with 17-μm pixel pitch to fulfill every application. These detectors keep all the recent innovations developed on the 25-μm pixel-pitch read out integrated circuit (ROIC) (detector configuration by serial link, low power consumption, and wide electrical dynamic range). The specific appeal of these units lies in the high spatial resolution it provides while keeping the small thermal time constant. The reduction of the pixel pitch turns the VGA array into a product well adapted for high-resolution and compact systems and the XGA a product well adapted for high-resolution imaging systems. High electro-optical performances have been demonstrated with noise equivalent temperature difference (NETD) < 50 mK. We insist on NETD and wide thermal dynamic range trade-off, and on the high characteristics uniformity achieved thanks to the mastering of the amorphous silicon technology as well as the ROIC design. This technology node paves the way to high-end products as well as low-end, compact, smaller formats, such as 320 × 240 and 160 × 120 or smaller.

We discuss the current performance of long-wavelength infrared photodetectors based on type-II superlattices, and the projected characteristics for diffusion-limited operation. For optimized architectures such as graded-gap and abrupt-heterojunction designs, the dark currents are strongly dominated by Shockley-Read (SR) rather than Auger processes. A factor of 10 improvement over the demonstrated SR lifetimes would lead to a factor of 4 lower dark current than state-of-the-art HgCdTe devices.

Since the late 1990s Semiconductor devices (SCDs) has developed and manufactured a variety of InSb two-dimensional (2D) focal plane arrays (FPAs) that were implemented in many infrared (IR) systems and applications. SCD routinely manufactures both analog and digital InSb FPAs with array formats of 320×256, 480×384, and 640×512 elements, and pitch size in the range 15 to 30 µm. These FPAs are available in many packaging configurations, including fully integrated detector-Dewarcooler-assembly, with either closed-cycle Stirling or open-loop Joule-Thomson coolers. In response to a need for very high resolution midwave IR (MWIR) detectors and systems, SCD has developed a large format 2D InSb detector with 1280×1024 elements and pixel size of 15 µm. The ROIC is fabricated in CMOS 0.18-µm technology, that enables the small pixel circuitry and relatively low power generation at the focal plane. The digital ROIC has an analog to digital (A/D) converter per-channel and allows for full frame readout at a rate of 100 Hz. Such on-chip A/D conversion eliminates the need for several A/D converters with fairly high power consumption at the system level. The digital readout, together with the InSb detector technology, lead to a wide linear dynamic range and low residual nonuniformity, which is stable over a long period of time following a nonuniformity correction procedure. A special Dewar was designed to withstand harsh environmental conditions while minimizing the contribution to the heat load of the detector. The Dewar together with the low power ROIC, enable a megapixel detector with overall low size, weight, and power with respect to comparable large format detectors. A variety of applications with this detector make use of different cold shields with different f-number and spectral filters. In this paper we present actual performance characteristics of the megapixel InSb detector and demonstrate its high manufacturability.

Application requirements driving present IR technology development activities are improved capability to detect and identify a threat as well as the need to reduce size weight and power consumption (SWaP) of thermal sights. In addition to the development of 3rd Gen IR modules providing dual-band or dual-color capability, AIM is focused on IR FPAs with reduced pitch and high operating temperature for SWaP reduction. State-of-the-art MCT technology allows AIM the production of mid-wave infrared (MWIR) detectors operating at temperatures exceeding 120 K without any need to sacrifice the 5-µm cut-off wavelength. These FPAs allow manufacturing of low cost IR modules with minimum size, weight, and power for state-of-the-art high performance IR systems. AIM has realized full TV format MCT 640×512 mid-wave and long-wave IR detection modules with a 15-µm pitch to meet the requirements of critical military applications like thermal weapon sights or thermal imagers in unmanned aerial vehicles applications. In typical configurations like an F/4.6 cold shield for the 640×512 MWIR module an noise equivalent temperature difference (NETD) <25 mK @ 5 ms integration time is achieved, while the long-wavelength infrared (LWIR) modules achieve an NETD <38 mK @ F/2 and 180 µs integration time. For the LWIR modules, FPAs with a cut-off up to 10 µm have been realized. The modules are available either with different integral rotary cooler configurations for portable applications that require minimum cooling power or a new split linear cooler providing long lifetime with a mean time to failure (MTTF) > 20000, e.g., for warning sensors in 24/7 operation. The modules are available with optional image processing electronics providing nonuniformity correction and further image processing for a complete IR imaging solution. The latest results and performance of those modules and their applications are presented.

We describe the factors that go into the component choices for a short wavelength IR (SWIR) imager, which include the SWIR sensor, the lens, and the illuminator. We have shown the factors for reducing dark current, and shown that we can achieve well below 1.5 nA/cm² for 15 μm devices at 7 °C. In addition, we have mated our InGaAs detector arrays to 640×512 readout integrated integrated circuits to make focal plane arrays (FPAs). The resulting FPAs are capable of imaging photon fluxes with wavelengths between 1 and 1.6 μm at low light levels. The dark current associated with these FPAs is extremely low, exhibiting a mean dark current density of 0.26 nA/cm² at 0 °C. Noise due to the readout can be reduced from 95 to 57 electrons by using off-chip correlated double sampling. In addition, Aerius has developed laser arrays that provide flat illumination in scenes that are normally light-starved. The illuminators have 40% wall-plug efficiency and provide low-speckle illumination, and provide artifact-free imagery versus conventional laser illuminators.

An evolving combat arena poses an ever-growing hostile fire threat for various ground and airborne targets. Protecting both static posts and moving military platforms against these threats require high performance and affordable solutions, favoring uncooled sensing alert technologies. By analyzing accumulated target and clutter data using new algorithmic and hardware building blocks we establish improved hostile fire indication system configurations. The paper will review new system demonstrations harnessing uncooled IR sensors technology alongside empirical field testing results.

A review of the III-V Lab activities in the field of quantum well infrared photodetectors (QWIPs) is presented. We discuss the specific advantages of this type of detector and present the production facilities and status. A large section is dedicated to broadband QWIPs for space applications and to QWIPs on InP for mid-wavelength infrared detection. We review the progress of QWIP technology for the next generation (dual band, polarimetric, and multispectral) of thermal imagers. Finally, the state-of-the-art of very long wavelength QWIPs is discussed.

Short-wavelength infrared image sensors based on p-i-n photodiode arrays present a tremendous interest in applications such as passive and active imagery for laser detection/warning, hot spot or detection for lasers sensors, enhanced vision systems or low light level sensors. The capability to work at room temperature with dark current equivalent to silicon-based devices is another motivation for the fast development of this technology. This paper presents several modules and camera based on InGaAs photodiode arrays from the III-VLab. First, we describe the electro-optics performance in terms of dark signal, sensitivity, and particularly the visible extension capability. We also present a nucless logarithmic sensor based on a 1/2 video graphics array (VGA) format at a pitch of 25 μm initially designed for visible CMOS camera chip. We will also present the next generation of focal plane arrays based on a VGA format of 640×512 pixels with a pitch of 15 μm. This array will be associated to a CTIA readout circuit and also to an innovative CMOS logarithmic wide dynamic range ROIC, developed by New Imaging Technologies. This VGA logarithmic device developed for automotive safety will involve visible extension capability in a European project named 2Wide_sense.

Theoretical modeling and experimental evidence show that the dark currents of antimonide (Sb)-based Type-II Superlattice (T2SL) detectors sensitive to long-wavelength infrared (LWIR) radiation are limited by the minority carrier lifetimes associated with the Shockley Read-Hall (SRH) generation-recombination process. Despite the low minority carrier lifetimes, the present photodiode dark current performance is achieved by increasing the background doping density of the absorber layers to N_A ~ 2×10¹⁶ cm^-3. This paper will discuss the measured minority carrier lifetimes of T2SL LWIR detectors with various background doping densities. To make comparisons, we designed several T2SL absorber layers sensitive in the LWIR range and p-type doped up to various densities. We find the minority carrier lifetimes are dominated by the SRH generation-recombination process. By analyzing minority carrier lifetime data as a function of excess carrier densities, we estimate SRH lifetimes and actual ionized acceptor densities of the absorber layers. The data are compared with the measured impurity doping densities of the detectors. In addition, we predict the type of flaws responsible for the SRH recombination process and narrow down the flaw energy level relative to the Fermi energy.

Large format infrared imaging sensors are required to achieve simultaneously high resolution and wide field of view image data. Infrared sensors are generally required to be cooled from room temperature to cryogenic temperatures in less than 10 min thousands of times during their lifetime. The challenge is to remove mechanical stress, which is due to different materials with different coefficients of expansion, over a very wide temperature range and at the same time, provide a high sensitivity and high resolution image data. These challenges are met by developing a hybrid where the indium antimonide detector elements (pixels) are unconnected islands that essentially float on a silicon substrate and form a near perfect match to the silicon read-out circuit. Since the pixels are unconnected and isolated from each other, the array is reticulated. This paper shows that the front side illuminated and reticulated element indium antimonide focal plane developed at L-3 Cincinnati Electronics are robust, approach background limited sensitivity limit, and provide the resolution expected of the reticulated pixel array.

Significant progress has been made over the past decade on uncooled focal plane array technologies and production capabilities. The detector pixel dimensions have continually decreased with an increase in pixel performance making large format, high-density array products affordable. In turn, this has resulted in the proliferation of uncooled IR detectors in commercial and military markets. Presently, uncooled detectors are widely used in firefighting, surveillance, industrial process monitoring, machine vision, and medical applications. Within the military arena, uncooled detectors are ubiquitous in Army soldier systems such as weapon sights, driver's viewers, and helmet-mounted sights. Uncooled detectors are also employed in airborne and ground surveillance sensors including unmanned aerial vehicles and robot vehicles.

An axicon structured lens is designed and its properties of long focal depth is demonstrated. The phase function of the axicon structured lens is constructed according to the properties of nondiffractive Bessel beam with uniform-intensity. Based on the relationship of the side length of the square hole and the phase retardation, the required phase distribution of the axicon structured lens with a long focal depth in a metallic film can be determined. To verify the feasibility of the method, an axicon structured lens with focal length 1000 mm, a focal depth larger than 20 mm was designed and the intensity distribution of far field was calculated. The results show that the focal depth is 25 mm which is nearly 7 times extended with nearly diffraction-limited image quality.

In order for the Czerny-Turner spectrometer to be utilized in the imaging spectrometer for far-ultraviolet waveband, we describe the elimination of the principal aberration coma and astigmatism for the arrangement by light-path function analysis. The modified structure is built by a spherical mirror, a toroidal mirror, and a fixed plane grating. Starting with coma and astigmatism corrected by adjusting the incident angle to the collimating mirror and using a toroidal mirror, we obtain the optimized distances between the grating to the focusing mirror and the focusing mirror to the image plane by geometric analysis and first order differential calculation, in order to acquire high imaging quality in broad waveband. The design result shows a simple optical imaging structure that can be used in the ionosphere detection (120 to 180 nm) that is superior and convenient.

Lightweight, active, silicon carbide mirrors have the potential to enable larger primary aperture, space-based optical systems, hence improving the resolution and sensitivity of such systems. However, due to the lack of design heritage, the best mirror designs are not yet known. Therefore, an integrated model of the lightweight mirrors is created in order to explore the design space. The model determines the achievable radius of curvature change within wavefront error limits, the peak launch stress, and the mass of a mirror segment. However, designing a mirror to meet any of these individual objectives results in a system that performs poorly in terms of the other objectives. Therefore, a full trade space analysis is run to determine the portions of the design space that best balance the trade-offs between metrics. These results are used to determine designs that perform well with respect to specific missions and can be used for future mirror designs.

For a number of different security and industrial applications, there is the need for reliable person identification methods. Among these methods, face recognition has a number of advantages such as being noninvasive and potentially covert. Other advantages of conventional two-dimensional face recognition, in particular, are its low data capture duration and its low cost. However, the recent introduction of fast and comparatively inexpensive time-of-flight cameras for the recording of 2.5D range data in real time calls for a closer look at three-dimentional face recognition in this context. One major disadvantage, however, is the low quality of the data acquired with this type of camera. In this paper, we investigate the feasibility of face recognition systems based on such range images.

Problems of efficiency and quality improvement of diamond-abrasive finishing of optical materials by tools with bounded polishing powders, including diamond powder, are considered. The dependences of the particle number on the diffusion angle and coordinate of the contact have been derived in the studies of the dynamics of collision and diffusion of slime particles. The coordinate dependence of the flat surface roughness of glass K8 optics in fine diamond grinding has been described. Interaction and dispersion of deterioration particles in a contact zone of the tool and the processed sample in the course of polishing is described and the dispersion structure of deterioration particles of the tool on slime particles and on deterioration particles is explained oscillatory. It is shown a that differential dispersion section of deterioration particles on slime particles is not less than on deterioration particles and is maximum at corners of dispersion close to 0° and 180° on the central sites of a contact zone. Coordinate dependence of the full dispersion section of deterioration particles of the tool and dependence of microprofile height of the processed surface on circular zones radius are calculated.

The error in three-dimensional (3-D) scans by a 3-D measurement system based upon fringe projection on translucent objects is presented. The dependencies on different material parameters are shown. A model describing the cause of the measurement error is introduced and the possibility of error compensation by shifting measurement points in a normal direction is demonstrated.

Accurate and robust phase unwrapping is an important procedure for three dimensional (3D) profilometry measurement. The mask cut phase-unwrapping algorithm merges the characteristics of Goldstein's branch cut and reliability-guided path-following algorithms, so that it has higher accuracy and stability. However, it cannot handle discontinuous phase regions because it completely relies on the phase quality map to guide the placement of mask cuts, thereby easily causing phase error propagation. To overcome these drawbacks, we propose a new phase-unwrapping method that merges the residue check principle and a Laplace phase derivative variance quality map that we developed. First, the entire phase was divided into several isolated regions in accordance with the quality map. Then, each pixel of the absolute phase marker line was taken as the starting point to unwrap the discontinuous phase regions based on reliability guidance. In addition, a new list-trimming algorithm was employed to guarantee a speedy phase-unwrapping procedure. The entire phase unwrapping and accurate 3D measurement of discontinuous objects was successfully completed. The simulated and experimental data both demonstrate the validity of the proposed phase-unwrapping algorithm.

A detector consisting of two biased microchannel plates and a P20 or P43 phosphor screen was illuminated with 500-eV electrons in order to characterize the size and amplitude of individual microchannel plate (MCP) firings as a function of phosphor-to-MCP distance d and voltage V_acc. The P43 phosphor was significantly brighter (71%) than P20 at V_acc = 4250 V, and brighter but less so (4%) at V_acc = 8000 V. Events were Gaussian-shaped with full widths at half maximum of order 0.27 mm for V_acc = 4250 V and d = 2 mm. Widths decreased by 23% to 28% when V_acc was increased to 8000 V, and increased between 9 to 34% when doubling d, depending on Vacc and phosphor type.

A simple setup for radially polarized beam generation based on the reflecting volume phase grating is proposed to enhance the converting efficiency. The radially polarized beam is obtained by coherently combining the two orthogonally polarized Hermite-Gaussian HG0₁ and HG₁₀ beams. By using the plane wave decomposition and the three-dimensional rigorous coupled wave analysis approaches, the intensity distribution of the diffracted beam is compared with the respective incident beam. The intensity and the polarization angle divergence of the combined beam are analyzed. The results show that the intensity profile of the diffracted beam is not changed remarkably compared to that of the input beam. The radially polarized beam can be obtained with a converting efficiency of 99.93% and the degree of radial polarization approaches a unit at a given polarization angle divergence value of 1 deg when the central alignment divergence is smaller than 0.025 mm.

Local decolorizing of gamma-ray irradiated silicate glasses has been studied under thermal annealing by a laser beam. The influence of the beam's exposure time was studied, showing that an increase of the glass temperature on the irradiated areas can locally induce complete decolorizing (bleaching) of glass. In this work, the heat conduction differential equation is solved by numerical approach using the finite element method and results are compared by experimental analysis. Although much work is being developed in the fields of color centers creation and its decay by heat, this work presents the first systematic study on near-infrared decolorizing of gamma-irradiated float silicate glasses.

A novel hydraulic pressure sensor based on fiber Bragg grating and elastic metal film is proposed in this paper. Pressure sensing experiments are conducted after the finite element analysis of the sensor probe's structure. The experiments demonstrate that this kind of pressure sensor possesses good linearity and repeatability in its large measurement range with the sensitivity about 23.8 pm/MPa.

We present a low crosstalk, low losses crossings for silicon-on-insulator waveguides by choosing the optimum crossing angle. The waveguides are broadened using a 3 μm parabolic taper in each arm. It is obtained that by using the crossing angles of 60 deg instead of the conventional 90 deg crossing angle, crosstalk losses are improved by more than 3.7 dB without degrading transmission losses. The transmission behavior of the crossing waveguides are illustrated by numerical simulations through the finite difference time domain method. The proposed crossing structure has a high compactness, a broad bandwidth with almost flat transmission losses, and constant crosstalk losses.

The transmission of both optical code division multiple-access (OCDMA) and wavelength division multiplexing (WDM) users on the same band is investigated. Code pulses of spectral amplitude coding (SAC)/optical code division multiple-access (CDMA) are overlaid onto a multichannel WDM system. Notch filters are utilized in order to suppress the WDM interference signals for detection of optical broadband CDMA signals. Modified quadratic congruence (MQC) codes are used as the signature codes for the SAC/OCDMA system. The proposed system is simulated and its performance in terms of both the bit-error rate and Q-factor are determined. In addition, eavesdropper probability of error-free code detection is evaluated. Our results are compared to traditional nonhybrid systems. It is concluded that the proposed hybrid scheme still achieves acceptable performance. In addition, it provides enhanced data confidentiality as compared to the scheme with SAC/OCDMA only. It is also shown that the performance of the proposed system is limited by the interference of the WDM signals. Furthermore, the simulation illustrates the tradeoff between the performance and confidentiality for authorized users.

The optical cryptosystem based on phase-shifting interferometry (PSI) is one of the most interesting optical cryptographic schemes in recent years. However, we find that the PSI technique provides an attractive method to record the ciphertext, but contributes little to the security level of the cryptosystem. From the cryptanalysis point of view, in a certain simplified case, an attacker is only required to crack two equivalent decryption keys instead of the original random phase keys and geometric key. Moreover, a chosen-plaintext attack method is proposed, in which an impulse function is chosen as a known plaintext. By using this attack, the attacker can effectively recover any plaintext from the corresponding ciphertext. The validity of the attack is verified by computer simulations.

We propose the use of polyvinyl alcohol photosensitized with copper chloride dihydrated CuCl₂(2H₂O) as a photosensitive material for recording holographic gratings. We obtained different dissolutions changing concentration of photosensitive agent and varying their pH factor, refraction index, and optical density for each sample. We registered diffraction gratings by holographic methods. The behaviors of diffraction efficiency parameters of holographic gratings regarding the concentration of a photosensitive agent were analyzed. We show there exists a correspondence between the diffraction efficiency parameter with concentration change of CuCl₂(2H₂O). The low toxicity of this holographic recording material as well as its peculiar behavior, photosensitivity, and ability to conduct electricity, makes it attractive for production diffractive optical elements with bio-polymers.

A simple and rugged optical hardware configuration for digital holography of microscopic reflecting structures is presented. The proposed technique employs a cube beam splitter, oriented as in the Gates interferometer, for recording a hologram. The experimental results for the United States Air Force resolution target and the reflection coating of a compact disk are presented. The salient features of the proposed configuration for reflection digital holography are its simplicity and low sensitivity to ambient vibrations.

Realization of distortion invariant correlation filters in optical image correlators open possibilities for object identification with remarkably high computational capabilities. Application of the linear phase coefficient composite filter (LPCCF) is attractive for recognition of binary edged images. We use methods of digital holographic synthesis to realize LPCCF in a coherent 4-F correlator as a computer-generated amplitude holographic filter. A high resolution spatial light modulator (SLM) has to be implemented for such a filter representation. Transparency limitations of high frame rate and high resolution SLM's and its effect on recognition performance of holographic filter in the 4-F correlator are discussed in the given paper.

Theory and simulations of a novel hyperspectral imaging polarimeter for remote sensing are presented. The spectropolarimeter is formed by cascading two laser servocontrol modified wave plates (MWP) and a polarization interference imaging spectrometer (PIIS). Using the phase modulation of the MWPs, this setup enables PIIS, originally developed by C. Zhang, to be extended for full polarization detection without dividing the interference fringes into channels as that in Oka's original channeled polarimeter. In this way, we can get the polarization information with higher spectral resolution. Besides, the data can be acquired with simpler operation. Aside from this feature, the configuration retains the advantages of both elements: the high precision phase modulation of the MWPs and the high spectral, spatial resolution, and higher throughput of the PIIS. A design example with spectral resolution 100 cm^-1 and range 0.4-1.0 µm is given.

This paper concerns the application of an iterated extended risk sensitive filter (IERSF) to target tracking problems. The relative merits of IERSF vis-à-vis the extended risk sensitive filter (ERSF) for a bearings-only tracking problem using root mean square error (RMSE) and robustness with uncertainty in initial condition are explored. An ERSF weakness, specifically an accumulation error in the computation of innovation steps due to approximating nonlinear functions at a recently available prior estimate, is presented. By using the IERSF with proper tuning of risk factor and local iteration, the filtering divergence may be overcome, and a stable, robust, and unbiased estimation is satisfactorily obtained. With numerical simulation results, the tracking performance of IERSF is compared with the performance of ERSF and extended Kalman filter. The IERSF results in reduced estimation error without much of an increase in burden of the associated computational algorithm.

We report on a theoretical study of free-standing phase transmission gratings for high-resolution extreme ultraviolet (EUV) and soft x-ray spectroscopy and investigate their properties. Designed for wavelengths between about 2 and 40 nm, the devices may provide a first order diffraction efficiency beyond 30%. We use rigorous coupled wave analysis methods in order to optimize the grating design parameters and discuss features of segmented grating arrays. Elemental, as well as compound, materials such as Be, Mo, LiF, and poly-(methylmethacrylate) are considered with respect to their potential and practical limitations in terms of feasibility and sensitivity to radiation damage. Simulations are performed for several samples on the radiation produced by a table-top EUV plasma source and applications to astrophysical problems are considered.

A clutter-adaptive target-detection method is proposed to detect small moving targets in midwave infrared maritime scenarios. In particular, we focus our attention on the sea-sky background and targets of interest are ships along the horizontal sea-sky line. In the distant sea-sky background infrared imagery, small targets frequently appear as weak intensity and do not have enough structure information in the vicinity of horizontal sea-sky-line, that is sea-sky region, and the complexity of background clutters has direct impact on the target detection performance. Thus, a fuzzy system constructed by the extracted image-based features is designed for the clutter classification. And then, based on the determined clutter type, low clutter or high clutter, the horizontal sea-sky line can be detected successfully. In the target detection stage, under the guidance of the sea-sky line, a modified multilevel filter method is applied to enhance the target in the sea-sky region. Finally, the recursive segmentation method and the target validation technique are adopted for the target extraction and validation. In the experiments, the target detection performance of proposed method is validated by extensive experiments on infrared images taken in different imaging conditions. It achieves high accuracy with a low false alarm rate.

Imaging systems are progressing in both accuracy and robustness, and their use in precision agriculture is increasing accordingly. One application of imaging systems is to understand and control the centrifugal fertilizing spreading process. Predicting the spreading pattern on the ground relies on an estimation of the trajectories and velocities of ejected granules. The algorithms proposed to date have shown low accuracy, with an error rate of a few pixels. But a more accurate estimation of the motion of the granules can be achieved. Our new two-step cross-correlation-based algorithm is based on the technique used in particle image velocimetry (PIV), which has yielded highly accurate results in the field of fluid mechanics. In order to characterize and evaluate our new algorithm, we develop a simulator for fertilizer granule images that obtained a high correlation with the real fertilizer images. The results of our tests show a deviation of <0.2 pixels for 90% of estimated velocities. This subpixel accuracy allows for use of a smaller camera sensor, which decreases the acquisition and processing time and also lowers the cost. These advantages make it more feasible to install this system on existing centrifugal spreaders for real-time control and adjustment.

Home automation is being implemented into more and more domiciles of the elderly and disabled in order to maintain their independence and safety. For that purpose, we propose and validate a surveillance video system, which detects various posture-based events. One of the novel points of this system is to use adapted Vander-Lugt correlator (VLC) and joint-transfer correlator (JTC) techniques to make decisions on the identity of a patient and his three-dimensional (3-D) positions in order to overcome the problem of crowd environment. We propose a fuzzy logic technique to get decisions on the subject's behavior. Our system is focused on the goals of accuracy, convenience, and cost, which in addition does not require any devices attached to the subject. The system permits one to study and model subject responses to behavioral change intervention because several levels of alarm can be incorporated according different situations considered. Our algorithm performs a fast 3-D recovery of the subject's head position by locating eyes within the face image and involves a model-based prediction and optical correlation techniques to guide the tracking procedure. The object detection is based on (hue, saturation, value) color space. The system also involves an adapted fuzzy logic control algorithm to make a decision based on information given to the system. Furthermore, the principles described here are applicable to a very wide range of situations and robust enough to be implementable in ongoing experiments.

We propose an approach to automatically extracting foreground regions. This is a novel method for segmenting salient objects from still images by background elimination. To extract foreground regions, a new method of background elimination based on multiscale segmentation is proposed to detect candidate object regions. To this end, we use a trimap consisting of foreground, background, and undefined regions and a region adjacency graph. A graph-cut technique is finally used to extract exact foreground regions from the candidates. Experimental results have shown that the proposed method yields a better foreground extraction than Kim's method under various environments containing multiple objects and clutter backgrounds in natural images.

This study is to investigate a new representation of a partition of an image domain into a fixed but arbitrary number of regions via active contours and level sets. The proposed algorithm is composed of simple closed evolving planar curves by an explicit correspondence to minimize the energy functional containing three terms: multiregion fitting energy, regularization related to the length of the curve, and the distance regularizing term to penalize the deviation of the level set function from a signed distance function. This formulation leads to a system of coupled curve evolution equations, which is easily amenable to a level set implementation, and an unambiguous segmentation because the evolving regions form a partition of the image domain at all times during curve evolution. In order to increase the robustness of the method to noise and to reduce the computational cost, a multiresolution level set schema is proposed, which can perform the evolution curves of the partitioned image at a different resolution. Given these advantages, the proposed method can get good performance and experiments show promising segmentation results on both synthetic and real images.

The existing fusion methods cannot adjust fused images, adaptively according to the requirements of follow-up image processing steps, as well as the merits of different fusion methods, and are not easy to be integrated. Since a data assimilation system can integrate the advantage of a model operator and observer operator, a fusion framework based on the data assimilation concept is proposed, which can adaptively fuse different remote sensing images. Under this framework, a fusion method based on an independent component analysis and àtrous wavelet transform is used as a model operator, and another fusion method based on nonsubsampled contourlet transform is used as an observation operator. Meanwhile, image quantitative evaluation indicators are used as an objective function. Then, the genetic particle swarm algorithm is employed to optimize the objective function in order to gain a more suitable image. Finally, three sets of panchromatic images and multispectral images are used in experiments. The results show that the proposed algorithm can adjust fusion results adaptively, according to a particular objective function.

Image fusion combines multiple images of the same scene into a single image which is suitable for human perception and practical applications. Different images of the same scene can be viewed as an ensemble of intercorrelated images. This paper proposes a novel multimodal image fusion scheme based on the joint sparsity model which is derived from the distributed compressed sensing. First, the source images are jointly sparsely represented as common and innovation components using an over-complete dictionary. Second, the common and innovations sparse coefficients are combined as the jointly sparse coefficients of the fused image. Finally, the fused result is reconstructed from the obtained sparse coefficients. Furthermore, the proposed method is compared with some popular image fusion methods, such as multiscale transform-based methods and simultaneous orthogonal matching pursuit-based method. The experimental results demonstrate the effectiveness of the proposed method in terms of visual effect and quantitative fusion evaluation indexes.

This paper proposes an efficient deinterlacing algorithm using the approximated sinc interpolator and adaptive distance weighting scheme that is suitable for real-time applications. The conventional edge-based deinterlacing algorithms provide poor image quality due to the limitation of the number of edge directions considered; moreover, the existing algorithms which consider many edge directions have high computational burden while still producing the staircase artifacts at the complex region. To overcome these problems, the proposed algorithm adopts an approximated sinc interpolator and adaptive distance weighting scheme which utilizes the pixel correlation. Simulation results show that the proposed algorithm provides outstanding performances in terms of both the objective and subjective image qualities, and it has lower computational complexity than the existing algorithms.

In this paper, a novel region-based active contour model is proposed. Unlike the Chan-Vese model, the energy function of our model only uses information outside the evolving curve. A restriction matrix is introduced for restricting the curve to evolve in the desired region. By minimizing the proposed energy function, the corresponding level set function is obtained. The proposed method has four advantages over the traditional region-based level set methods. First, the level set function is no longer required to be initialized as a sign distance function. Second, due to the simplified level set formulation and its fast curve evolution speed, the level set function does not need to be re-initialized and the computational cost is low. Third, our model is applicable to multiobject images since it can segment objects by separating background from an image. Finally, the proposed model has the property of selective local or global segmentation; it can segment not only the desired object but also the other objects in an image. The advantages of our model are demonstrated using synthetic and real images.

No-reference image quality assessment (NRIQA) is to be used when a reference image may not be available. The existing well-known NRIQA algorithms are those that use natural scene statistics (NSS), such as NSS model in wavelet domain (WNSS) and NSS model in contourlet domain (CNSS). WNSS is only applicable to evaluate JPEG2000 compressed images, while CNSS can be used to evaluate five different distortion types of image sets such as JPEG, JPEG2000, white noise, Gaussian blur, and fast fading. However, due to the downsamplers and upsamplers, the contourlet transform is not shift-invariant and may cause pseudo-Gibbs phenomena. In this paper, we propose an improved NRIQA based on the nonsubsampled contourlet transform (NSCT) which has shift-invariant characteristics, multiscale, and multidirection expansion. The basic observation of the proposed algorithm is that in the nonsubsampled contourlet domain natural images exhibit certain common joint statistical characteristics which can be represented by a mathematical model and disturbed by a wide variety of distortions. Performance evaluation tests show that the predicted quality scores obtained by the proposed algorithm are more effective and consistent with visual quality than those by WNSS or CNSS-based NRIQA on four distortion types of image sets in the LIVE image database except for JPEG2000 compressed images.

In this paper, we propose a wave leader pyramids based Visual Information Fidelity method for image quality assessment. Motivated by the observations that the human vision systems (HVS) are more sensitive to edge and contour regions and that the human visual sensitivity varies with spatial frequency, we first introduce the two-dimensional wavelet leader pyramids to robustly extract the multiscale information of edges. Based on the wavelet leader pyramids, we further propose a visual information fidelity metric to evaluate the quality of images by quantifying the information loss between the original and the distorted images. Experimental results show that our method outperforms many state-of-the-art image quality metrics.

In this paper, we present a hybrid system for time delay and integration (TDI) image restoration. Images are degraded by residual motion, which distorts and blurs the TDI images during exposures and excludes the along-track scanning motion. The motion trajectory is estimated from the image sequence captured by an auxiliary high-speed camera. In order to make the estimated results less sensitive to the imaging conditions and noise, a new method based on cross-correlation is introduced for motion estimation. Then geometric distortion of the TDI image is removed by choosing the correct blurred block according to the central of the corresponding motion trajectory and the final image is restored row by row with the Richardson-Lucy algorithm. Simulated and experimental results are given to prove the effectiveness of our system.

The purpose of this study is to propose a novel method of a partition of an image domain into an adaptive number of regions using a multilayer foreground-filled method. First, two coupled curves based on a three-region Chan-Vese model, which is built based on the techniques of evolving simple closed planar curves by an explicit correspondence to minimize energy functional containing a fitting term and a regularization term, evolve simultaneously to segment images containing two objects and one background region in each image layer. Second, a foreground-filled technique is used to generate a new image and the three-region Chan-Vese model is repeated to segment the new image for the next image layer. To avoid the long iteration process for level set evolution, an efficient termination criterion is presented on the basis on the length change of an evolving curve. This iterative process is repeated until the background image layer is detected. Numerical experiments on some synthetic and real images have demonstrated the efficiency and robustness of our method.

In this paper, we introduce a direction-oriented covariance-based adaptive deinterlacing (CAD) method. The conventional CAD method preserves edge direction; however, it does not consider the local edge direction, which makes it unsuitable for real-time applications. The proposed method only utilizes the neighbor pixels aligned in the local edge direction to obtain optimal coefficients, with less processing time than the aforementioned CAD. First, the local edge direction is determined using the modified edge-based line average method. Then, based on direction-oriented geometric duality, the optimal interpolation coefficients for the neighbor pixels in the corresponding direction are estimated using the Wiener filter. Furthermore, we present inverse-free least squares approximations using orthogonal-triangular decomposition based on the Gram-Schmidt process. This technique's performance improves as the size of the image becomes larger. The experimental results prove that the proposed method provides a significant improvement over other deinterlacing methods.

A source coding distortion estimation scheme using one-pass encoding is proposed to predict the distortion in the next frame based on the distortion of the last coded frames. Motion-compensated prediction is analyzed first, in the case that quantization step sizes used for different video frames may be different due to bit-rate constraint in constant bit-rate real-time applications. Second, the proposed scheme uses a linear prediction model to compute the variances of the discrete cosine transform (DCT) coefficients. Third, the DCT coefficients are assumed to follow a Laplacian distribution and the distortion model of the Laplacian source is used to compute the coding distortions of the DCT coefficients. Fourth, the proposed scheme calculates a distortion error which appears because of assuming the direct current coefficient to be Laplacian distributed instead of Gaussian distributed. Finally, the source coding distortion in the frame is predicted using the coding distortions in the DCT coefficients and the calculated distortion error. The proposed scheme does not need trial encoding and can be applied to real-time video coding. When compared to the other five existing schemes, experimental results show that the proposed scheme can estimate source coding distortion more accurately than the five schemes.

AVC/H.264 supports the use of multiple reference frames (e.g., 5 frames in AVC/H.264) for motion estimation (ME), which demands a huge computational complexity in ME. We propose an adaptive search range adjustment scheme to reduce the computational complexity of ME by reducing the search range of each reference frame-from the (t-1)'th frame to the (t-5)'th frame-for each macroblock. Based on the statistical analysis that the 16×16 mode type is dominantly selected rather than the other block partition mode types, the proposed method reduces the search range of the remaining ME process in the given reference frame according to the motion vector (MV) position of the 16×16 block ME. In the case of the (t-1)'th frame, the MV position of the 8×8 block ME-in addition to that of 16×16 block ME-is also used for the search range reduction to sub-block partition mode types of the 8×8 block. The experimental results show that the proposed method reduces about 50% and 65% of the total encoding time over CIF/SIF and full HD test sequences, respectively, without any noticeable visual degradation, compared to the full search method of the AVC/H.264 encoder.

As more multimedia services have become increasingly available over networks where bandwidth is not always guaranteed, quality monitoring has become an important issue. For instance, quality of experience and quality monitoring have become important problems in internet protocol television applications, since transmission errors may introduce all kinds of additional video quality degradations. In this paper, we present a reduced-reference objective model for video quality measurements in multimedia applications. The proposed method first measures edge degradations that are critical for perceptual video quality and then considers transmission error effects. We compared the proposed method with some existing methods. Independent verifications confirmed that the proposed method showed good performance and consequently it was included in an International Telecommunication Union recommendation. The proposed method can be used to monitor video quality at receivers while requiring minimum usage of additional bandwidth.

This paper presents an objective video quality evaluation method for quantifying the subjective quality of digital mobile video. The proposed method aims to objectify the subjective quality by extracting edgeness and blockiness parameters. To evaluate the performance of the proposed algorithms, we carried out subjective video quality tests with the double-stimulus continuous quality scale method and obtained differential mean opinion score values for 120 mobile video clips. We then compared the performance of the proposed methods with that of existing methods in terms of the differential mean opinion score with 120 mobile video clips. Experimental results showed that the proposed methods were approximately 10% better than the edge peak signal-to-noise ratio of the J.247 method in terms of the Pearson correlation.

In this paper, we developed a novel photon sieve consisting of a large number of precisely positioned holes distributed according to an underlying Fresnel zone plate (FZP) geometry, while the holes at transparent and opaque circular rings of the FZP have a π phase shift. Compared to a conventional photon sieve which we call an amplitude-photon sieve (PS), the binary photon sieve has a transmission two times more amplitude-PS and a diffractive efficiency approximately four times than amplitude-PS. A 70-mm diameter, f/10 binary photon sieve has been fabricated for operation at visible light. Details of design, fabrication, and performance of the binary photon sieve are presented.

In this paper, an optical color image encryption/decryption technology based on joint fractional Fourier transform correlator and double random phase encoding (DRPE) is developed. In this method, the joint fractional power spectrum of the image to be encrypted and the key codes is recorded as the encrypted data. Different from the case with classical DRPE, the same key code was used both in the encryption and decryption. The security of the system is enhanced because of the fractional order as a new added key. This method takes full advantage of the parallel processing features of the optical system, and could optically realize single-channel color image encryption. The experimental results indicate that the new method is feasible.

An optical joint transform correlation-based cryptographic system is a used to feed multiple phase-shifted encryption keys into four parallel channels along with a to-be-encrypted signal in the form of an image. The resulting joint power spectra (JPS) signals are phase-shifted and then combined to yield a modified JPS signal. Inverse Fourier transformation of the modified JPS signal yields the secured encrypted image. For decryption purpose, the received encrypted signal is first Fourier transformed and multiplied by the encryption key used in encryption. The derived signal is then inverse Fourier transformed to generate the output signal. The proposed system offers a nonlinear encryption without the involvement of any complex mathematical operation on the encryption key otherwise required in similar encryption techniques and is invariant to noise. Computer simulation results are presented to show the effectiveness of the proposed scheme with binary, as well as gray images in both noise-free and noisy environment.

In this article we present the bandgap engineering and spectral properties of ZnO-CdS and ZnO-TiO₂ nanocomposites prepared by colloidal chemical synthesis. The optical bandgap (E_g) of the material is tunable between 2.62 and 4.12 eV. Emission peaks of ZnO-CdS change from 385 to 520 nm and those of ZnO-TiO₂ change from 340 to 385 nm almost in proportion to the changes in E_g. It is possible to obtain a desired luminescence color from UV to green by simply adjusting the composition. ZnO-CdS and ZnO-TiO₂ are potential nanocomposite materials for the tunable light emission.

Changes have been made to this article. See the full text for a description of the changes.

Changes have been made to this article. See the full text for a description of the changes.