I really enjoy writing the yearly review because it is always encouraging to see how much Optical Engineering has improved over the previous year. It’s not that I am surprised that there is an improvement, because the associate editors and staff are gifted, hardworking, and diligent. It’s just that the magnitude of the change and what they have accomplished year after year are impressive.

A fiber loop mirror containing a section of high-birefringence suspended-core fiber is used for torsion sensing. The suspended-core fiber section has a triangular-shaped core with an in-circle diameter of approximately 1.8 μm. Due to its small dimensions and geometric structure, it presents high birefringence and intermodal interference simultaneously. A torsion sensitivity of 59.0  pm/deg is obtained in a very large linear range of 900 deg with a resolution of 1.2 deg.

For optimal management of agricultural fields by remote sensing, discrimination of the crop canopy from weeds and other objects is essential. In a digital photograph, a rice canopy was discriminated from a variety of weed and tree canopies and other objects by overlapping binary image layers of red-green-blue and other color components indicating the pixels with target canopy-specific (intensity) values based on the ranges of means ±(3×) standard deviations. By overlapping and merging the binary image layers, the target canopy specificity improved to 0.0015 from 0.027 for the yellow 1× standard deviation binary image layer, which was the best among all combinations of color components and means ±(3×) standard deviations. The most target rice canopy-likely pixels were further identified by limiting the pixels at different luminosity values. The discriminatory power was also visually demonstrated in this manner.

Water-soluble NdF ₃ , NdF₃ :Li⁺ , and NdF ₃ :Ba ²⁺ nanoparticles coated with polyvinylpyrrolidone were synthesized by a simple hydrothermal method. The products were characterized by x-ray diffraction, field-emission scanning electron microscopy, and photoluminescence spectra at room temperature. Codoping with Li⁺ ions does not change the emission intensity of water-soluble NdF ₃ nanoparticles, whereas codoping with Ba²⁺ ions improves the near-infrared emissions.

Almost every adult today holds some concept of a laser weapon and many children have at least one toy laser among their possessions. Fascination with these ideas reaches as far back as Archimedes' legendary defense of Syracuse with solar reflectors in 212 BC. Other examples include the Martian invaders of Earth who used "heat rays" with chilling efficiency in H. G. Well's 1898 War of the Worlds and the now-classic Star Wars movie series. While most fictional depictions of laser weapons (and some news stories) are without sound basis, these devices do offer the potential for a whole new class of weapons and capabilities that complement (but do not replace) existing kinetic energy weapons and electronic warfare.

A review of the extensive program of the pioneering research and development of high-power lasers and laser radar undertaken in the USSR during the years 1964 to 1978 under the scientific supervision of N.G. Basov is presented. In the course of this program, many high-energy lasers with unique properties were created, new big research and design teams were formed, and the laser production and testing facilities were extended and developed. The program was fulfilled at many leading research institutions and design bureaus of the USSR Academy of Sciences and defense industry.

Abstract. Recent progress in high-quality transparent ceramic window materials (MgAl₂O₄ spinel and β -SiC) and high-power solid-state laser materials (Yb³⁺ : Y₂O₃, Yb³⁺ : Lu₂O₃, and Ho³⁺ : Lu₂O₃ is reported. Spinel ceramic demonstrates a record low-absorption loss of 6 ppm/cm at 1.06 μm. The capability of fabricating various shapes and sizes of spinel ceramics is also demonstrated. We also report optical transparency from a β -SiC ceramic fabricated by field assisted sintering technology (FAST). We report lasing in hot-pressed Yb³⁺ : Y₂O₃ and Yb³⁺ : Lu₂O₃ ceramic made from coprecipitated powder. The highest ever reported output power and efficiency from 10% doped Yb³⁺ : Lu₂O₃ ceramic is also presented. Lasing oscillation from hot pressed composite of five-layered Yb³⁺ : Y₂O₃ ceramic is also demonstrated for the first time.

This paper is a summary of the history, theory, and development efforts of summator, an all-in-one device that coherently combines multiple high-power laser beams, lowers the beam divergence, and shifts the wavelength based on stimulated Raman scattering principle in USSR from early 1960s to late 1970s. This was a part of the Terra-3 program, which was an umbrella program of highly classified high-energy laser weapons development efforts. Some parts of the Terra-3 program, specifically the terminal missile defense portion, were declassified recently, including the information on summator development efforts.

Beam-control systems for high-average-power lasers began in the late 1960s and early 1970s. Early systems propagated the beams across laboratories using heavy-water-cooled copper optics and open-beam trains with commercial fans to provide fresh air. They have evolved in the intervening 40-plus years to include highly sophisticated gimbaled-control systems with extremely high-reflectance uncooled optics and adaptive optics to compensate for less-than-ideal laser beams and for atmospheric distortions. An overview of that evolution is presented.

Short historic review of the first experimental research efforts (1969 to 1972) in the fields of high power electroionization gas lasers is presented. Experiments with high-pressure gases (up to 100 atm), demonstrating no principal limitations on volume and density of gas laser media, exited with electroionization method, are discussed. The discussed physics of electric current pumping of high-pressure ionized gas lead to development of mega watt CO₂ lasers, multi-kW CO lasers and proposals for development of gig watt lasers. Future applications of such lasers in GW lasing design for cleaning space from cosmic man-made debris are mentioned. Literature based on original publications in these fields is presented.

Both the U.S. and Russia/USSR have made great strides toward developing high-energy laser weapons for their future national defense systems since the early 1960s. Many billions of dollars and rubles were invested in the effort. Many hundreds of gifted scientists and engineers devoted their careers to working on the problems. They achieved major technological advances and made impressive and successful demonstrations. After more than half a century, however, neither side has yet adapted the first laser weapon for a military use. Why? This paper discusses the history of key technological advancements and successes, as well as some of the difficulties encountered. It also discusses fundamental technological advantages and limitations of high-energy laser weapons, and also the unique social, cultural, and political environments that have contributed to the history. The high-energy laser technical community is in the process of finding ways to adapt to the new warfare environment by taking advantage of the lessons learned in the past while incorporating the new technologies and ideas evolved in recent years.

The U.S. Department of Defense (DoD) has made large investments weaponizing laser technology for air defense. Despite billions of dollars spent, there has not been a successful transition of a high-energy laser (HEL) weapon from the lab to the field. Is the dream of a low-cost-per-shot, deep-magazine, speed-of-light HEL weapon an impossible dream or a set of technologies that are ready to emerge on the modern battlefield? Because of the rapid revolution taking place in modern warfare that is making conventional defensive weapons very expensive relative to the offensive weapons systems, the pull for less expensive air defense may necessitate a HEL weapon system. Also, due to the recent technological developments in solid-state lasers (SSL), especially fiber lasers, used throughout manufacturing for cutting and welding, a HEL weapon finally may be able to meet all the requirements of ease of use, sustainability, and reliability. Due to changes in warfare and SSL technology advances, the era of HEL weapons isn't over; it may be just starting if DoD takes an evolutionary approach to fielding a HEL weapon. The U.S. Navy, with its large ships and their available electric power, should lead the way.

The tactical high energy laser (THEL) program, conducted from 1996 to 2005, successfully demonstrated the capability of a high-energy laser to counter rockets, artillery, and mortars. The program was a US/Israeli cooperative research and development effort that was designated by the Secretary of Defense as an advanced concept technology demonstration with Presidential interest. The THEL system was designed and built under an SMDC/ARSTART prime contract awarded to TRW (now, Northrop Grumman Corporation), jointly managed by the Israel Ministry of Defence Directorate of Defence Research & Development. We summarize the effort and highlight some of the "firsts" of the THEL program.

In this review we present an analysis of optically pumped alkali laser research and development from the first proposal in 1958 by Schawlow and Townes to the current state. In spite of the long history, real interest in alkali vapor lasers has appeared in the past decade, after the demonstration of really efficient lasing in Rb and Cs vapors in 2003 and the first successful power scaling experiments. This interest was stimulated by the possibility of using efficient diode lasers for optical pumping of the alkali lasers and by the fact that these lasers can produce a high quality and high power output beam from a single aperture. We present a review of the most important achievements in high power alkali laser research and development, discuss some problems existing in this field, and provide future perspectives in diode pumped alkali laser development.

Scintillation and anisoplanatism significantly degrade a laser transmitter system or an imaging system when the optical field is required to propagate through deep turbulence. Here turbulence is defined as deep turbulence when the Rytov number is very much greater than 1 and the isoplanatic patch size is much smaller than λ/D, the diffraction limit. In this region a point beacon is of little use for imaging applications and a finite-sized beacon limits performance for both transmission and imaging because almost any finite-sized beacon is many isoplanatic patch sizes across and exhibits a significant level of beacon anisoplanatism. As a consequence, conventional adaptive optics techniques are of little value. To address this situation, five approaches are considered. These approaches include beacon deconvolution, Zernike tomography, gradient descent tomography (GDT), irradiance redistribution branch cut multiconjugate adaptive optics compensation, and minimum energy loss eigenfield propagation. GDT appears to have the most promise as it does not require a conventional wavefront sensor.

Diode-pumped solid-state laser technology is reviewed with an emphasis on laser materials and concepts important to high power systems with excellent beam quality. A first principal approach to power scaling is taken in order to summarize and compare the wide variety of laser architectures. Successful approaches are highlighted and directions for future work are discussed.

Ever since the first free-electron laser (FEL) was both conceived and demonstrated in the 1970s at Stanford, it has attracted much attention as a promising foundation for a high average power light source. Since its light is produced from free electrons, an FEL can be designed to lase at virtually any wavelength. Furthermore, since its light is generated from a relativistic beam that is continually replenished, its gain medium cannot be damaged by any conventional means. Accordingly, as there have been several ambitious attempts to design and construct high average power FELs over the past several decades, we chronicle some of these efforts. Additionally, we provide an overview of FEL technology and theory, discuss some of the obstacles that remain in the construction of a high-power FEL, and provide a road map toward a megawatt-class device.

Phase-shifting fringe projection is an effective method for three-dimensional shape measurements. Conventional fringe projection systems utilize a digital projector that images fringes into the measurement plane. The performance of such systems is limited to the visible spectral range (VIS), as most projectors experience technical limitations in ultraviolet (UV) or infrared (IR) spectral ranges. However, for certain applications these spectral ranges are of special interest. A novel fringe projector was developed on the basis of a single-tailored free-form mirror. The free-form mirror generates a sinusoidal fringe pattern by redistribution of light. Phase shifting can be realized by a slight rotation of the free-form mirror. In this system, the fringe pattern is generated by illuminating the free-form surface and not by the classical imaging technique. As the system is based on a single mirror, it is wavelength-independent in a wide spectral range and therefore applicable in UV and IR spectral ranges. Additionally it does not feature any chromatic aberrations. We present the design and an experimental setup of this novel fringe projection system. Fringe projection is realized in different wavelength ranges (VIS and UV) and the advantage of fringe projection in the UV spectral range can be shown for certain materials.

Here, we present a new double-side patterned sapphire substrate methodology that improves the efficiency of gallium nitride-light emitting diodes (GaN-LEDs). The light extraction efficiency of GaN-based LEDs was analyzed through the use of a ray-tracing simulation. The extraction efficiency was simulated using patterned sapphire substrate LEDs with a variety of shapes, depths, sizes, and spacing. Through the optimal patterning of the various factors, high extraction efficiency was realized and subsequently improved upon. The thermal LED characteristics were analyzed through the use of the COMSOL general heat transfer module. The LEDs patterned on the sapphire substrate were fabricated using nano imprint lithography. We found that the output power of the double-side patterned LED was 52% greater than that of a flat LED. The thermal resistance of the double side patterned LED was 9.5  K/W less than that found for the flat LED.

This study concerns the illumination system in a radial imaging capsule endoscope (RICE). Uniformly illuminating the object is difficult because the intensity of the light from the light emitting diodes (LEDs) varies with angular displacement. When light is emitted from the surface of the LED, it first encounters the cone mirror, from which it is reflected, before directly passing through the lenses and complementary metal oxide semiconductor (CMOS) sensor. The light that is strongly reflected from the transparent view window (TVW) propagates again to the cone mirror, to be reflected and to pass through the lenses and CMOS sensor. The above two phenomena cause overblooming on the image plane. Overblooming causes nonuniform illumination on the image plane and consequently reduced image quality. In this work, optical design software was utilized to construct a photometric model for the optimal design of the LED illumination system. Based on the original RICE model, this paper proposes an optimal design to improve the uniformity of the illumination. The illumination uniformity in the RICE is increased from its original value of 0.128 to 0.69, greatly improving light uniformity.

A new, economical, lenslet-array-based imaging sensor design is proposed, simulated, and analyzed. In this investigation a bare lenslet array model is first developed in Code V®. The results show that, as expected, intolerable optical cross-talk is present in this simple system. This problem has been addressed in previous systems via the inclusion of a physical image separation layer. The alternative system proposed here to alleviate crosstalk involves the introduction of both polarizers and spectral filters. As a consequence this simple system design also provides spectro-polarimetric resolution. Simulations were developed in order to analyze the system performance of two designs. The simulation results were analyzed in terms of a measure of signal-to-noise ratio (SNR) and in terms of an en-squared energy that includes all subimages. The results show that a design employing only a few spectral filters suppresses crosstalk for objects of small angular extent but does not suppress crosstalk to a tolerable level for 2π steradian illumination, as evidenced by SNR less than one. However, the inclusion of more spectral filters results in a spectro-polarimetric thin imager design that suppresses crosstalk and provides finer spectral resolution without the inclusion of a signal separation layer.

A sensory substitution device is developed in which nonretinal stimulus is used to generate input to the brain of blind people to substitute for damage or loss of retinal input. Although the final realization of this technology (direct stimulation of the corneal nerve endings) was not addressed, a device consisting of a contact lens delivering point mechanical or electrical stimulating of the corneal nerves and a camera mounted on a spectacles frame which wirelessly transmit processed image to the contact lens, translating the visual information into tactile sensation is expected to be constructed. In order to improve the spatial resolution of the constructed image, the camera will also time multiplex, compress and encode the captured image before transmitting it to the stimulating contact lens. Preliminary devices performing tactile stimulation of the fingers and of the tongue by applying point electrical stimulations, were constructed and tested. Subjects were taught to “see” using the mechanical and the electrical tactile sensory.

Laser detection and ranging (ladar) range images have attracted considerable attention in the field of automatic target recognition. Generally, it is difficult to collect a mass of range images for ladar in real applications. However, with small samples, the Hughes effect may occur when the number of features is larger than the size of the training samples. A random subspace ensemble of support vector machine (RSE-SVM) is applied to solve the problem. Three experiments were performed: (1) the performance comparison among affine moment invariants (AMIs), Zernike moment invariants (ZMIs) and their combined moment invariants (CMIs) based on different size training sets using single SVM; (2) the impact analysis of the different number of features about the RSE-SVM and semi-random subspace ensemble of support vector machine; (3) the performance comparison between the RSE-SVM and the CMIs with SVM ensembles. The experiment’s results demonstrate that the RSE-SVM is able to relieve the Hughes effect and perform better than ZMIs with single SVM and CMIs with SVM ensembles.

Compound eye lens (CEL) is expected to be applied in high-speed object tracking and depth perception. However, it is difficult to fabricate CEL due to the complex shape and structure. We study its mathematic and optical model. Based on the established model, a grid machining method is proposed for the fabrication of a CEL mold. To avoid the shape distortion caused by tool un-alignment, the off-centering machining configuration is proposed, which is also proved to improve the form accuracy. CEL is machined finally by molding technologies using the fabricated mold to avoid the tool interference. Experiments have been implemented to verify the design and fabrication method. The shape accuracy evaluation and optical testing are conducted to prove that the proposed method can be applied well for the machining of CEL.

The colors of thin and thick layers of graphene and graphene oxide films on either SiO₂ or Si ₃N₄ grown silicon substrates were generated by a theoretical calculation procedure. The effects of the thicknesses of the material and the dielectric layers on the visibility of the graphene-based materials were investigated. The theoretical investigation was supplemented by measurements of the thicknesses of the material layers using either an atomic force microscope or a profilometer, depending on the thickness range. By combining the color calculation procedure with the measured thickness profiles, optical images of graphene-based materials on dielectric substrates can be reconstructed. The reconstructed image corresponds well to the real microscope image, which suggests that the image reconstruction procedure is a convenient way to investigate colors and determine the thickness of graphene-based materials.

An objective-type dark-field imaging spectroscope is used for imaging the orientation of single nonspherical nanoparticles. This simple and effective technique is able to simultaneously provide the spectral and spatial information of single nanoparticles. The orientation information of the nanoparticles is determined by investigating their polarization dependent longitudinal and transverse plasmon resonant wavelengths. The determination of the nanoparticles’ orientation could be used as a complementary tool to fluorescent labeling in biological applications.

An asymmetric planar terahertz (THz) metamaterial (MM) is designed to be composed of two different single split-ring resonators (SRR) and its character is simulated in the THz region. Gallium arsenide (GaAs) is inserted between the gap of two separated single SRR, and through modulation of its conductivity (σ GaAs ) we achieved the switching of three different resonance modes and researched the influence of σ GaAs on transmission of MM. The resonant structure of MM can be switched from the two fundamental LC-modes to the new LC-mode and dipole resonance mode through the coupling LC-mode with the increasing σ GaAs . Such dynamical control of MM resonances provides an efficient way to manipulate electromagnetic wave to push mode-switching of resonance and could be implemented in terahertz devices to achieve additional functionalities.

Both in-phase and out-phase radially polarized femtosecond-pulse (RPFP) beams have been generated with one phase-only liquid crystal spatial light modulator, which effectively modulates the phase retardation distributions of a pulse beam wavefront by two reflections. The intensity distributions and polarizing properties of both in-phase and out-phase RPFP beams are detected, and the temporal properties of in-phase RPFP beams are investigated in detail. Experimental results indicate that we effectively produce an RPFP beam. And the temporal duration of the output in-phase RPFP beam is 183 fs about 14 fs shorter than the input Gaussian femtosecond-pulse beam. The temporal durations of arbitrary polarized components of an in-phase RPFP beam vary less than 3.5%.

We present a high compact structure laser diode (LD) side-pumped all-solid-state Q-switched master oscillator power amplifier (MOPA) laser system with high beam quality. Bidirectional voltage-supplied Q-switched and MOPA technologies were introduced in the design. An in-center wavelength of 1064 nm with pulse width adjustability from 5 to 18 ns was obtained at the repetition rate of 500 Hz. Through multistage Nd∶YAG amplifiers at the pulse width of 6 ns, the oscillator was scaled up to 145 W and the corresponding peak power reached 48.3 MW with single pulse energy fluctuation less than 0.45% in 1 h operation.

In ultraviolet pulse laser, damage performance of fused silica optics is directly dependent on the absorptive impurities and scratches in subsurface, which are induced by mechanical polishing. In the research about influence of subsurface defects on damage performance, a series of fused silica surfaces with various impurity concentrations and scratch structures were created by hydrofluoric (HF) acid solution etching. Time of Flight secondary ion mass spectrometry and scanning probe microprobe revealed that with increasing etching depth, impurity concentrations in subsurface layers are decreased, the scratch structures become smoother and the diameter:depth ratio is increased. Damage performance test with 355-nm pulse laser showed that when 600 nm subsurface thickness is removed by HF acid etching, laser-induced damage threshold of fused silica is raised by 40 percent and damage density is decreased by over one order of magnitude. Laser weak absorption was tested to explain the cause of impurity elements impacting damage performance, field enhancement caused by change of scratch structures was calculated by finite difference time domain simulation, and the calculated results are in accord with the damage test results.

Shape analysis of a three-dimensional (3-D) scene is an important issue and could be widely used for various applications: city planning, robot navigation, virtual tourism, etc. We introduce an approach for understanding the primitive shape of the scene to reveal the semantic scene shape structure and represent the scene using shape elements. The scene objects are labeled and recognized using the geometric and semantic features for each cluster, which is based on the knowledge of scene. Furthermore, the object in scene with a different primitive shape could also be classified and fitted using the Gaussian map of the segmented scene. We demonstrate the presented approach on several complex scenes from laser scanning. According to the experimental result, the proposed method can accurately represent the geometric structure of the 3-D scene.

Nanosecond laser ablation of polyvinylpyrrolidone (PVP) protected silver nanoparticle (20 nm diameter) film is studied using a frequency doubled Nd:YAG nanosecond laser (532 nm wavelength, 6 ns full width half maximum pulse width). In the sintered silver nanoparticle film, absorbed light energy conducts well through the sintered porous structure, resulting in ablation craters of a porous dome shape or crown shape depending on the irradiation fluence due to the sudden vaporization of the PVP. In the unsintered silver nanoparticle film, the ablation crater with a clean edge profile is formed and many coalesced nanoparticles of 50 to 100 nm in size are observed inside the ablation crater. These results and an order of magnitude analysis indicate that the absorbed thermal energy is confined within the nanoparticles, causing melting of nanoparticles and their coalescence to larger agglomerates, which are removed following melting and subsequent partial vaporization.

The nonlinear Schrödinger equation and Drude equation are simultaneously solved taking into account diffraction, group velocity dispersion, self-focusing, multiphoton ionization and plasma creation, and plasma absorption inside a transparent material, i.e., silica. Contact and noncontact geometries, where the focusing lens is, respectively, in contact with the sample or at a specified distance from it, are studied. It is observed that for noncontact geometry, maximum electron density in the vicinity of the focal point inside silica is lower than that in contact geometry. Furthermore, it is observed that locations for initiation of pulse splitting for two geometries are different. The effect of the variations of the peak power of the incident pulse, its beam waist, the focal length of the focusing lens, and the air gap length on the maximum electron density is also investigated in noncontact geometry. Calculation reveals that for higher peak powers and larger beam waists, maximum electron density increases and occurs at closer distance relative to linear focus point inside glass. Simulations are performed in time domain by operator-split technique and alternating-direction implicit algorithm to reduce execution time of the program.

Eigen frequency is a very important parameter in a fiber optic gyroscope (FOG). To establish an accurate measurement of eigen frequency, we propose a new measurement method based on employing the square-wave, over-bias modulation with double eigen frequency. We investigate the proposed method both experimentally and theoretically. Experimental results show the measurement accuracy of eigen frequency is better than ±5  Hz, which satisfies the eigen frequency measurement of most FOGs. A theoretical model of the method gives a good explanation of the experimental results. The method is simple, low-cost, and easy to implement. In addition, it can greatly improve the accuracy of the eigen frequency measurement without needing additional hardware for existing gyro systems.

We present a fiber-optic sensor based on a fiber Bragg grating (FBG) whose core has an offset to that of the lead-in fiber from splicing for simultaneous refractive index (RI) and temperature measurement. Due to the core offset, the core mode in the lead-in fiber is coupled to both the core mode and the cladding modes of the sensing fiber with the FBG. Then the two oppositely propagating code modes, the cladding modes, and the core modes are coupled by the FBG at particular wavelengths determined by the effective indices of the modes and the FBG structure, resulting in two peaks in the FBG reflection spectrum. The peak wavelength corresponding to the core-cladding mode coupling is sensitive to both RI and temperature, while the peak wavelength corresponding to the core-core mode coupling is only sensitive to temperature. Utilizing the difference of two reflection peaks of these coupling modes, both RI and temperature can be detected simultaneously. We fabricate and characterize a sensor. The preliminary experimental results show that it can detect the refractive index in a range of 1.33 to 1.4421, with a temperature sensitivity of 10  pm/°C .

This paper discusses the concept and hardware development of an all fiber-based, solid state, coherent array directional sensor that can locate and track bright objects against a darker background. This sensor is not an imager. It relies on the inherent structure of the global fiber distribution. Methods for characterizing and calibrating hardware embodiments are also presented.

We present a numerical model of intensity-based interrogation systems for optical fiber Bragg grating (FBG) sensors. The numerical model is based on previous analytical modeling, which could only be utilized for perfect Gaussian profiles. However, FBG interrogation systems can make use of non-Gaussian shaped filters or sources. The numerical modeling enables the different variations to be compared using identical component performance, showing the relative strengths and weakness of the systems in terms of useful parameters, including sensitivity and dynamic range. The two different detection methods for intensity-based FBG sensors can also be compared side by side using the same FBG. Since the model is numerical, it enables real spectral data to be used for the various components (FBG, light source, filters). This has the added advantage of increasing the accuracy and usefulness of the model over previous analytical work.

Here, we report the guidelines to be followed to optimize the design of a new angular velocity sensor based on an indium phosphide (InP) ring resonator. Optical properties of InP ring resonators have been investigated together with some significant physical effects for improving the sensor sensitivity. Three-dimensional algorithms have been utilized for the theoretical estimation of the waveguide loss. An optimized waveguide with propagation loss <0.3  dB/cm and a ring resonator with a quality factor of 1.5×10⁶ have been designed. Performance of angular velocity sensors based on InP low-loss ring resonators has been estimated and discussed. Resolution of 10  deg/h and bias drift in the range of 0.1 to 0.3  deg/h have been evaluated for a fully integrated optical gyro including an InGaAsP/InP optical cavity having a footprint less than 24  cm² .

We examine the properties of the defect modes arising in the zero-effective phase (zero-φ ) gap when a dielectric defect layer is introduced in a one-dimensional photonic crystal containing single negative materials. We show that the defect modes inside the zero-φ gap can be as sensitive to the incidence angle as those inside the Bragg gap. In addition, adjusting the properties of the dielectric defect layer can control the frequencies and the number of defect modes. We present a brief design of a polarization-independent spatial filter based on those defects. The proposed spatial filter can work at dual carrier frequencies with low-pass and wide-pass characteristics. Our results can help improve the performance of microwave devices independent of the source wave polarization.

Potentialities are investigated for using acousto-optic cells based on a TeO₂ crystal to stabilize a microwave signal generated by an optoelectronic oscillator. Bulk acoustic waves at two radio frequencies (RF) near 60 MHz are launched in the two identical cells providing a required locking on of a microwave signal. Differences between RF signals are up to 400 kHz to follow quality factor of the optic resonator typically in the range of 5×10⁸ . Critical alignment of the two cells is performed thanks to an extraordinary polarized laser beam launched at a very low Bragg angle of light incidence. Moreover, the system is operating for any resonator to be inserted into the optoelectronic oscillator with a Q factor in the range of 2×10 ⁷ −10 ¹¹ .

Our group has developed a silicon-based guided-wave optical accelerometer, consisting of a proof mass centered on a diaphragm and a waveguide across the diaphragm. The sensor operates based on phase retardation induced by the elasto-optic effect. Designing the sensor is considerably complicated since it is strongly suggested that sensitivity is related to many parameters, such as waveguide position, diaphragm dimensions, and size and weight of proof mass. Hence, these relations should be clearly identified to establish a design guideline. In this study, sensitivity dependences on waveguide position and diaphragm thickness were experimentally examined. Regarding sensitivity dependence on waveguide position, phase sensitivity was highest for the waveguide at the diaphragm edge and was also relatively high for the waveguide at the edge of proof mass, whereas the sensitivity was quite low around the midposition between the edges of the diaphragm and proof mass. Regarding diaphragm thickness, phase sensitivity was found to be inversely proportional to the square of the diaphragm thickness.

We have theoretically and numerically investigated polarization-insensitive all-optical wavelength conversion for polarization multiplexing quadrature phase shift keying (QPSK) signals based on four-wave mixing (FWM) in a semiconductor optical amplifier (SOA) with a polarization diversity and digital coherent detection. The simulation results show that the different frequency spacing between pumps and the signal have serious effects on the conversion efficiency, that there is an optimal SOA injection current by considering a high conversion efficiency and a small pattern effect, and that the pattern effect on polarization multiplexing QPSK signals is much lower than non-return-to-zero signals.

We propose a novel photonic technique for unknown microwave frequency measurement by employing an optical group delay line. The 7-bit optical delay line composed of several magneto-optical switches and 1.6 km single-mode fiber is designed as a tunable dispersive medium in the measurement system. In our scheme, the measurable frequency range of 1 to 20 GHz with a measurement error less than ±40  MHz was demonstrated experimentally. Also, we studied the sensitivity of the whole measurement system, and the minimum detectable power reached −50  dBm .

Based on the exact solution of the Maxwell’s equations, the group velocity dispersion characteristics of micro/nano optical fibers near 2-μm wavelength have been studied numerically. The results show that the micro/nano optical fiber has large normal dispersion near 2-μm wavelength by carefully choosing the core size. For air-clad micro/nano optical fiber with core size 900 nm, the group velocity dispersion can be up to 3318.78  ps ² /km . By introducing a thin dielectric layer, the maximum dispersion can be adjusted by varying the thickness and refractive index of the dielectric layer.

Multispot diffusing configuration (MSDC) in optical wireless links provide uniform optical power needed for multiaccess and spatial dependence that can be used to allow space diversity techniques over the link. The spatial channels are furnished in MSDC through utilizing multibeam transmitter that produces spatially confined diffusing spots, and a multibranch receiver with small enough branch field-of-view (FOV) to restrict the number of diffusing spots within its FOV. Here, we study different encoding techniques that use space and time diversity to reduce the bit error rate. An improved technique, constellation rotation, is proposed for pulse amplitude modulated (PAM) to increase the Euclidian distance between signal points, and thus reduce bit error. Our study shows that when a cap is placed on the amount of power allocated per channel, the performance of the improved 4-PAM using three spatial channels and soft binary decision provide the optimal performance. When the power allocated per user is restricted, the best performance is obtained through soft binary decision and by using symbols identified by their level and spatial channel to carry 2 bits per signal level-channel.

A photonic analog-to-digital converter (ADC) utilizing the modal birefringence of the polarization maintaining fiber (PMF) is proposed. In the PMF, sampling pulses with different wavelengths have different phase shifted transfer functions, which could be used for quantizing and encoding in a photonic ADC. A proof-of-concept experiment is performed and a 2.5 GHz sinusoidal electrical analog signal is quantized by using 16 different wavelengths. The experimental result with an effective number of bits of 4.5 is achieved.

Factors that affect the transient effect on small duty-cycle pulse in a cascaded erbium-doped fiber amplifier (EDFA) system are studied in simulation and experiment. The considered factors consist of the numbers of cascaded EDFAs, the peak power and the extinction ratio of optical pulse, with results showing that the optical pulse will be severely distorted by the transient effect of EDFA. The distortion becomes more serious with the increase of the three parameters. To avoid or mitigate the transient effect, a method of adding another optical signal with a different wavelength to the objective pulse is employed in the experiment. The experimental results show that this method could effectively restrain the transient effect in a cascaded EDFA system.

A passive optical network (PON) based real-time Ethernet (PONRTE), which can take advantage of PON features such as broad bandwidth, high reliability, and easy maintenance to satisfy the determination and real-time requirements of high performance industrial applications, is proposed. The protocol model and network architecture having a compatible physical layer and MAC layer with Ethernet passive optical network are presented for the proposed PONRTE. A fixed periodic time slot allocation mechanism including a synchronic time division multiplexing transmission and an asynchronic data transmission is adopted to guarantee the determination and real-time of the communication. A simple and easy to implement time synchronization approach, where the starting time of the first transmission slot of an access node is synchronized by a relative time synchronization while the starting time of subsequent slots is determined by the fixed period and a dynamic time synchronization, is designed to support the fixed time slot allocation mechanism and avoid the collision in PONRTE. A 100  Mb/s PONRTE experimental testbed with 16 access nodes and a time allocation period of 240 μs is demonstrated. The results show that the experimental PONRTE can work stably and reliably with a frame loss ratio less than 10⁻⁷ .

A novel method is proposed for optical up-converted single-sideband (OSSB) signal generation in radio over fiber links, which can realize optical carrier reuse synchronously. The OSSB signal is generated in order to overcome the fiber dispersion problem by using two intensity modulators in combination with fiber gratings. With this up-conversion technique, a 25 GHz OSSB radio frequency signal is generated by mixing an intermediate frequency signal (5 GHz) and low frequency local oscillator signal (10 GHz). The signal is transmitted over 25 km standard single-mode fiber successfully. And the received signal error vector magnitude is 5.8% root mean square, with eye diagram widely open.

We study the performance of automatic bias control for three bias voltages in optical quadrature phase-shift keying modulator. The interaction between multiple bias controls for two Mach-Zehnder modulators’ (MZMs’) bias voltages and a Mach-Zehnder interferometer’s (MZI’s) bias voltage is analyzed theoretically. The condition for achieving global extremum of the monitored optical power with two MZMs’ bias voltages at the null transmission points is also studied by numerical simulations. The results show that the bias voltages of two MZMs can be controlled regardless of the MZI’s bias voltage and can avoid the risk of trapping in local extremum if the driver signal amplitude operates in the proper range.

We propose and experimentally demonstrate a novel loading scheme to improve the maximum system power budget for orthogonal frequency division multiplexing access-passive optical network (OFDMA-PON). For the downstream traffic, optical network units (ONUs) with asymmetric distribution fiber lengths are paired together, and information for the paired ONUs is loaded into the same OFDM signal by forward error correction loading combined with bit and power loading scheme. Power budgets of ONUs with long distribution fiber lengths can be improved at the cost of the power budget degradation of ONUs with short distribution fiber lengths, while maintaining the data rates for both ONUs. Besides, the total number of subcarriers used in downstream OFDM signal remains unchanged. A proof-of-concept experiment is performed to demonstrate the feasibility of the proposed scheme. A maximum of 80 km transmission and a 1∶128 split ratio is achieved by the scheme, which improves the maximum system power budget by ∼4  dB than traditional methods.

In this paper, a new scheme of all-optical binary half adder is proposed. This scheme realizes a kind of all-optical computation which is based on the effect of spatial property in photonic crystal. The line defect, which is obtained by reducing the radius of host rod, is used to produce the appropriate phase difference between the input signals. The two input signals and the reference signals interfered offer a desired logic function. Because of the device utilizing the linear material, this structure operation is independent of the input power. The proposed adder is demonstrated, numerically, by computing electromagnetic field distribution using finite difference time domain method.

The optical irradiance scintillation for an extended source and a dual-aperture system with variable aperture separation is analyzed with respect to the effect of turbulence. The scintillation index and the correlation between the dual-aperture signals emanating from an extended source are used to study the turbulence spectral model and the deviation from the common Kolmogorov atmospheric weak-turbulence model. Signal decorrelation as a function of aperture separation is presented. The relative errors introduced by using dual-aperture systems are also discussed.

Advancements in the geometric resolution of space images have improved the conditions for generations of large-scale topographic maps. Using WorldView-1, WorldView-2, and GeoEye-1, images can now be captured from space with a 0.5 m ground sampling distance (GSD). Geometric accuracy and information content are the most significant components of mapping from space images. Depending on the resolution, image quality, and shadows, the identification and classification of ground objects may prove challenging. In this research, the geometric accuracy and information content, of panchromatic WorldView-1 images, were analyzed by covering parts of Istanbul and Zonguldak in Turkey. Each of these locations has various topographic characteristics. For the orientation and investigation of the geometric accuracies of images, a number of ground control points (GCPs) were developed as independent checkpoints. Based on bias-corrected rational polynomial coefficients with one GCP, a standard deviation of independent checkpoints on the range of one GSD was obtained. The information content of images was analyzed by mapping all buildings, in both test areas, and comparing the results with reference 1/5000 scaled topographic maps. The results verified that the WorldView-1 images can be utilized for generating and updating 1/5000 scaled topographic maps of urban areas.

Most chemical gas detection algorithms for long-wave infrared hyperspectral images assume a gas with a perfectly known spectral signature. In practice, the chemical signature is either imperfectly measured and/or exhibits spectral variability due to temperature variations and Beers law. The performance of these detection algorithms degrades further as a result of unavoidable contamination of the background covariance by the plume signal. The objective of this work is to explore robust matched filters that take the uncertainty and/or variability of the target signatures into account and mitigate performance loss resulting from different factors. We introduce various techniques that control the selectivity of the matched filter and we evaluate their performance in standoff LWIR hyperspectral chemical gas detection applications.

An open-path tunable diode laser absorption spectroscopy (OP-TDLAS) detector was applied to detect the methane emission from a biogas plant in a dairy farm. Two OP-TDLAS scanning systems were built according to maximum likelihood with expectation minimization (MLEM) and smooth basis function minimization (SBFM) algorithms to reconstruct the two-dimensional (2-D) distribution maps. Six reconstruction maps with the resolution of 30×80 were obtained by the MLEM algorithm with “grid translation method” and three reconstruction maps were obtained by the SBFM algorithm with 2-D Gaussian model. The maximum mixing ratio in the first result was between 0.85 and 1.30 ppm, while it was between 1.14 and 1.30 ppm in the second result. The average mixing ratio in the first result was between 0.54 and 0.49 ppm, and between 0.56 and 0.65 ppm in the second result. The reconstruction results validated that the two algorithms could effectively reflect the methane mixing ratio distribution within the target area. However, with the more simple optical rays and less equipment requirements, the OP-TDLAS scanning system based on SBFM algorithm provides a useful monitoring tool of methane emissions in agricultural production.

Ship self defense against heat-seeking anti-ship missiles is of great concern to modern naval forces. One way of protecting ships against these threats is to use infrared (IR) offboard countermeasures. These decoys need precise placement to maximize their effectiveness, and simulation is an invaluable tool used in determining optimum deployment strategies. To perform useful simulations, high-fidelity models of missiles are required. We describe the development of an imaging IR anti-ship missile model for use in countermeasure effectiveness simulations. The missile model’s tracking algorithm is based on a target recognition system that uses a neural network to discriminate between ships and decoys. The neural network is trained on shape- and intensity-based features extracted from simulated imagery. The missile model is then used within ship-decoy-missile engagement simulations, to determine how susceptible it is to the well-known walk-off seduction countermeasure technique. Finally, ship survivability is improved by adjusting the decoy model to increase its effectiveness against the tracker.

Most military targets of strategic importance are very small in size. Though some of them may get spatially resolved, most cannot be detected due to lack of adequate spectral resolution. Hyperspectral data, acquired over hundreds of narrow contiguous wavelength bands, are extremely suitable for most military target detection applications. Target detection, however, still remains complicated due to a host of other issues. These include, first, the heavy volume of hyperspectral data, which leads to computational complexities; second, most materials in nature exhibit spectral variability and remain unpredictable; and third, most target detection algorithms are based on spectral modeling and availability of a priori target spectra is an essential requirement, a condition difficult to meet in practice. Independent component analysis (ICA) is a new evolving technique that aims at finding components that are statistically independent or as independent as possible. It does not have any requirement of a priori availability of target spectra and is an attractive alternative. This paper, presents a study of military target detection using four spectral matching algorithms, namely, orthogonal subspace projection (OSP), constrained energy minimisation, spectral angle mapper and spectral correlation mapper, four anomaly detection algorithms, namely, OSP anomaly detector (OSPAD), Reed–Xiaoli anomaly detector (RXD), uniform target detector (UTD), a combination of RXD–UTD. The performances of these spectrally modeled algorithms are then also compared with ICA using receiver operating characteristic analysis. The superior performance of ICA indicates that it may be considered a viable alternative for military target detection.

We aim to study the short-wave infrared (SWIR), medium-wave infrared (MWIR), and long-wave infrared (LWIR) imaging ability based on optical readout bimaterial microcantilever focal plane array (FPA) uncooled infrared imaging system. First, the principle of the bimaterial microcantilever sensing and the fabrication of the microcantilever array are introduced. Second, the optical-thermal-mechanical sensing theories based on the FPA are given. Finally, an optical readout microcantilever FPA infrared imaging system is developed for SWIR, MWIR, and LWIR imaging experiments. The experimental results show that the system can acquire the clear images of the SWIR, MWIR, and LWIR targets.

Phase reconstructions from a two-dimensional shearing interferometer, based on two orthogonal phase gratings in a single plane, and a Hartmann sensor are compared. Design alternatives for both wavefront sensors are given, and simulated performance of both the two-dimensional x-ray shearing interferometer and Hartmann wavefront sensor are presented for two different phase profiles. The first comparison is an evaluation of metrology on deuterium-tritium (DT) ice layers in an inertial confinement fusion capsule, and the second comparison is a high frequency “asterisk” phase profile, which tests the ability of these wavefront sensors to detect spikes of ablator material seen in DT fuel capsule implosions. Both of these sensors can measure the two-dimensional wavefront gradient of an x-ray beam, as well as the x-ray absorption. These instruments measure the two-dimensional wavefront gradient in a single measurement, and the wavefront sensor is located in a single plane, making them much less sensitive to vibrations than most other wavefront sensing techniques.

Reconstruction of a high-resolution face image, from a low-resolution observation based on a set of high- and low-resolution training image pairs, is an important problem for optical engineering applications. In this paper, we study this facial superresolution problem and propose a novel locally nonlinear transformation based approach. Multiple locally nonlinear transformation are utilized to approximate the global nonlinear connections between low resolution (LR)/high resolution (HR) images. LR/HR images are initially divided into multiple pairs of patches with the corresponding position information. As facial images are highly structured, patches at the same position spanned a subspace. Since the curse of dimensionality is avoided in these subspaces (patches in the same position), the Euclidean distance can express the intrinsic “radial” between samples in the same subspace. Therefore, multiple radial basis functions are utilized to approximate the nonlinear mapping between LR/HR pairs at each position from training examples. The proposed locally nonlinear transformation (LNT)-based reconstruction is achieved by applying the learned nonlinear transformation to each position patch of an LR input. The final SR results are obtained by refining the LNT reconstruction by the projection onto a convex sets algorithm using the consistency constraint. Extensive experiments on benchmark databases and real world images validate the superiority of the proposed method.

We propose adaptive grids, an image-based approach for constructing navigation meshes, which are used for path planning. A cellular navigation mesh, called an adaptive grid, is constructed from a top-view range image of a three-dimensional urban model. A navigation graph can then be extracted from this adaptive grid for path planning. We compare our approach with two popular navigation mesh–generation approaches and obtain promising results in terms of path accuracy and memory cost.

In an automatic finger-vein recognition system, finger-vein image quality is significant for segmentation, enhancement, and matching processes. In this paper, we propose a finger-vein image quality evaluation method using support vector machines (SVMs). We extract three features including the gradient, image contrast, and information capacity from the input image. An SVM model is built on the training images with annotated quality labels (i.e., high/low) and then applied to unseen images for quality evaluation. To resolve the class-imbalance problem in the training data, we perform oversampling for the minority class with random-synthetic minority oversampling technique. Cross-validation is also employed to verify the reliability and stability of the learned model. Our experimental results show the effectiveness of our method in evaluating the quality of finger-vein images, and by discarding low-quality images detected by our method, the overall finger-vein recognition performance is considerably improved.

For the purpose of representing the feature of the gray image, illumination normal of pixels in a two-dimensional gray image plane is proposed, which can reflect the high-frequency information of the gray image. In order to get an accurate dense disparity map based on the adaptive support weight (ASW) approach in RGB vector space, a matching algorithm is proposed that combines the illumination normal similarity, gradient similarity, color similarity, and Euclidean distance similarity to compute the corresponding support weights and dissimilarity measurements. After testing by the Middlebury stereo benchmark, the result of the proposed algorithm shows more accurate disparity than many state-of-the-art stereo matching algorithms.

Sparse subspace learning has drawn more and more attention recently. We propose a novel sparse subspace learning algorithm called maximum margin sparse representation discriminative mapping (MSRDM), which adds the discriminative information into sparse neighborhood preservation. Based on combination of maximum margin discriminant criterion and sparse representation, MSRDM can preserve both local geometry structure and classification information. MSRDM can avoid the small sample size problem in face recognition naturally and the computation is efficient. To improve face recognition performance, we propose to integrate Gabor-like complex wavelet and natural image features by complex vectors as input features of MSRDM. Experimental results on ORL, UMIST, Yale, and PIE face databases demonstrate the effectiveness of the proposed face recognition method.

Person reidentification tackles the problem of building a correspondence between different images of the same person captured by distributed cameras. To date, attempts to solve this problem have focused on either feature representation or learning methods. Usually, the greater the number of the samples for each person, the better the reidentification performance is. However, in the real world, we may not be able to acquire enough samples to give acceptable performance. Here, we focus on the so-called “single-shot versus single-shot” problem: matching one image of a person to another. Because of the extremely small sample class size, there is limited scope to statistically weaken the empirical risk for hand-crafted feature representation. Therefore, we resort to metric learning methods, such as the ranking-specialized metric learning to rank (MLR) and the classification-based maximally collapsing metric learning (MCML). Taking advantage of the complementarity between them, we propose a novel “coupled metric learning” approach. This searches for the optimal linear projection for the original feature space using MCML before minimizing the ranking loss via MLR. Experiments on widely used benchmark datasets show encouraging results.

We propose a novel human detection approach that combines three types of center symmetric local binary patterns (CS-LBP) descriptors with a cascade of random forests (RFs). To detect human regions in a low-dimensional feature space, we first extract three types of CS-LBP features from the scanning window of a downsampled saliency texture map and two wavelet-transformed subimages. The extracted CS-LBP descriptors are applied to a three-level cascade of RFs, which combines a series of RF classifiers as a filter chain. The three-level cascade of RFs with CS-LBPs delivers rapid human detection with higher detection accuracy, as compared with combinations of other features and classifiers. The proposed algorithm is successfully applied to various human and nonhuman images from the INRIA dataset, and it performs better than other related algorithms.

Video fire detection is playing an increasingly important role in our life. But recent research is often based on a traditional RGB color model used to analyze the flame, which may be not the optimal color space for fire recognition. It is worse when we research smoke simply using gray images instead of color ones. We clarify the importance of color information for fire detection. We present a fire discriminant color (FDC) model for flame or smoke recognition based on color images. The FDC models aim to unify fire color image representation and fire recognition task into one framework. With the definition of between-class scatter matrices and within-class scatter matrices of Fisher linear discriminant, the proposed models seek to obtain one color-space-transform matrix and a discriminate projection basis vector by maximizing the ratio of these two scatter matrices. First, an iterative basic algorithm is designed to get one-component color space transformed from RGB. Then, a general algorithm is extended to generate three-component color space for further improvement. Moreover, we propose a method for video fire detection based on the models using the kNN classifier. To evaluate the recognition performance, we create a database including flame, smoke, and nonfire images for training and testing. The test experiments show that the proposed model achieves a flame verification rate receiver operating characteristic (ROC I) of 97.5% at a false alarm rate (FAR) of 1.06% and a smoke verification rate (ROC II) of 91.5% at a FAR of 1.2%, and lots of fire video experiments demonstrate that our method reaches a high accuracy for fire recognition.

The performance of mobile phones has rapidly improved, and they are emerging as a powerful platform. In many vision-based applications, human hands play a key role in natural interaction. However, relatively little attention has been paid to the interaction between human hands and the mobile phone. Thus, we propose a vision- and hand gesture-based interface in which the user holds a mobile phone in one hand but sees the other hand’s palm through a built-in camera. The virtual contents are faithfully rendered on the user’s palm through palm pose estimation, and reaction with hand and finger movements is achieved that is recognized by hand shape recognition. Since the proposed interface is based on hand gestures familiar to humans and does not require any additional sensors or markers, the user can freely interact with virtual contents anytime and anywhere without any training. We demonstrate that the proposed interface works at over 15 fps on a commercial mobile phone with a 1.2-GHz dual core processor and 1 GB RAM.

Features extracted at salient points are used to construct a region covariance descriptor (RCD) for target tracking. In the classical approach, the RCD is computed by using the features at each pixel location, which increases the computational cost in many cases. This approach is redundant because image statistics do not change significantly between neighboring image pixels. Furthermore, this redundancy may decrease tracking accuracy while tracking large targets because statistics of flat regions dominate region covariance matrix. In the proposed approach, salient points are extracted via the Shi and Tomasi’s minimum eigenvalue method over a Hessian matrix, and the RCD features extracted only at these salient points are used in target tracking. Experimental results indicate that the salient point RCD scheme provides comparable and even better tracking results compared to a classical RCD-based approach, scale-invariant feature transform, and speeded-up robust features-based trackers while providing a computationally more efficient structure.

Fireflies light up our warm summer evenings. There is more physics behind these little animals than any one of us could imagine. We analyze from a physical point of view one structure found on the firefly lantern, the one which best improves light extraction. Moreover, simulations will be done to show why this specific structure may be more effective than one designed by humans.

Resonances inside metallic nanoslots and along metal–substrate interfaces have been investigated theoretically, which shows the fact that the transmission characteristic of a double periodic metallic nanoslot array could be manipulated by adjusting the structural parameters. A transmission structure over a wide band of infrared and terahertz waves has been proposed, with 30 dB isolation between peaks inside the infrared band and high flexibility in tuning.

This study presents a steganographic optical image encryption system based on reversible data hiding and double random phase encoding (DRPE) techniques. Conventional optical image encryption systems can securely transmit valuable images using an encryption method for possible application in optical transmission systems. The steganographic optical image encryption system based on the DRPE technique has been investigated to hide secret data in encrypted images. However, the DRPE techniques vulnerable to attacks and many of the data hiding methods in the DRPE system can distort the decrypted images. The proposed system, based on reversible data hiding, uses a JBIG2 compression scheme to achieve lossless decrypted image quality and perform a prior encryption process. Thus, the DRPE technique enables a more secured optical encryption process. The proposed method extracts and compresses the bit planes of the original image using the lossless JBIG2 technique. The secret data are embedded in the remaining storage space. The RSA algorithm can cipher the compressed binary bits and secret data for advanced security. Experimental results show that the proposed system achieves a high data embedding capacity and lossless reconstruction of the original images.

Collision is a phenomenon in which two distinct inputs produce an identical output, so if an attacker finds the encryption keys in such a way that when it is applied to an encrypted image, it produces an arbitrary image instead of original one. We propose collision in an asymmetric cryptosystem based on a phase-truncated Fresnel transform. For encryption, instead of using conventional random-phase masks, structured phase masks with desired construction parameters are used. The decryption keys are generated using the amplitude and phase truncation. An attacker generates an arbitrary (collision) image from the encrypted image using a modified Gerchberg-Saxton phase retrieval algorithm. Two different users, authorized and unauthorized user (attacker), can claim the retrieved image as the original data. The authorized user uses the correct decryption keys and retrieves the original image, while an unauthorized user uses the generated keys and retrieves the collision image. In order to verify the authenticity of the retrieved data, a joint transform correlator is used. A sharp auto-correlation peak is obtained when an image retrieved by authorized user is matched with the encrypted image. However, cross-correlation is obtained when an encrypted image is matched with the collision image. Results of computer simulation support the idea of the proposed collision.

In this paper, we explore the effects of polarization, incidence angle, layer thickness, and permittivity profiles on reflection and transmission characteristics. Hill’s method used in this work is an efficient tool to obtain an analytical solution of the propagation equations and can be applied to all arbitrary profiles of permittivity and permeability. Using Hill’s method and an arbitrary profile of permittivity, numerical simulations for both polarizations transverse electric and transverse magnetic waves are performed to compute the reflection and transmission coefficients of spectrum analyzer, frequency selective surfaces (FSS), and electromagnetic bandgap (EBG) structures having optimized thickness.