Search

Unmanned aerial vehicles (UAVs)-based sensor network is an effective mechanism for recognising and tracking of manoeuvring targets as well as expanding the monitoring coverage in the battlefield. However, there exists redundancy among the spectrum data collected by a UAV monitor within a data collection period, which may waste storage space and reduce the speed of data uploaded to the control centre. The authors assume that each UAV is equipped with an edge computing server and propose a delta compression method, which can save cache space and transfer time. First, they present a cost model and evaluation model for delta compression of the COPY/ADD class. Then an optimisation problem is formulated aiming to obtain the optimal delta encoding. Additionally, a maximal total length of copied fragments (MTLC) algorithm is proposed to find more mutually separated L-grams common fragments between the data collected at two adjacent moments. Theoretical analysis proves that the MTLC algorithm can generate a good delta encoding with the maximum total length and then the minimum total number of the COPYs. Moreover, numerical results show that MTLC has better performance in constructing a good delta encoding than the simple greedy and hash suffix array delta algorithms.

In this paper, we study the diffraction properties of tunable cascaded VHGs by using the two-dimensional coupled wave theory and two-dimensional Runge-Kutta methods. The intensity distributions of the diffracted and transmitted beams are given, the total diffraction efficiency is calculated for multiple cascaded finite-sized VHGs. It is shown that the diffraction characteristics depend on the grating parameters such as the number of the cascaded VHGs and the sizes of each VHG, and the effects of the buffer gaps between two cascaded VHGs is also discussed. It demonstrates the possibility of shaping beam and improving the beam quality by controlling the grating parameters and the layers number of the VHGs. The analysis of this paper also will be valuable for novel applications of finite-sized VHGs.

Highly (111) preferred oriented PbZr 0.53 Ti 0.47 O 3 /Pb(Mg 1/3 Nb 2/3 ) 0.62 Ti 0.38 O 3 /PbZr 0.53 Ti 0.47 O 3 (PZT/PMNT/PZT) trilayered ferroelectric thin films were prepared on (111)Pt/Ti/SiO 2 /Si substrates. At room temperature, the films have a dielectric constant of 2175 that decreases to 1870 and a dielectric loss of 0.05 that increases to 0.06 with increasing frequency between 10 2 and 10 5 Hz. Also, they exhibit well saturated polarization-versus-electric field hysteresis loops with a large remnant polarization of 13.4 μC/cm 2 and a low coercive field of 30 kV/cm. The leakage current density in the trilayered films is 4.1 × 10 −10 A/cm 2 , which increases to 4.0 × 10 −7 A/cm 2 with increasing electric field between 1 and 140 kV/cm. Such properties of (111) preferred oriented PZT/PMNT/PZT trilayered films lead naturally to possibilities for ferroelectric capacitors and memories.

In this invited talk, we will review optical cryptography with biometrics for multi-depth objects using optical scanning holography (OSH). We also focus on the discussion of key distribution.

We propose an optical cryptosystem for encrypting images of multi-depth objects based on the combination of optical heterodyne technique and fingerprint keys. Optical heterodyning requires two optical beams to be mixed. For encryption, each optical beam is modulated by an optical mask containing either the fingerprint of the person who is sending, or receiving the image. The pair of optical masks are taken as the encryption keys. Subsequently, the two beams are used to scan over a multi-depth 3-D object to obtain an encrypted hologram. During the decryption process, each sectional image of the 3-D object is recovered by convolving its encrypted hologram (through numerical computation) with the encrypted hologram of a pinhole image that is positioned at the same depth as the sectional image. Our proposed method has three major advantages. First, the lost-key situation can be avoided with the use of fingerprints as the encryption keys. Second, the method can be applied to encrypt 3-D images for subsequent decrypted sectional images. Third, since optical heterodyning scanning is employed to encrypt a 3-D object, the optical system is incoherent, resulting in negligible amount of speckle noise upon decryption. To the best of our knowledge, this is the first time optical cryptography of 3-D object images has been demonstrated in an incoherent optical system with biometric keys.

In this research, a novel optical multiple-image encryption method based on angular-multiplexing holography, quick response (QR) code, and spiral phase keys is proposed. With this method, images are transformed into QR codes and subsequently encrypted into a series of encrypted holograms using an angular-multiplexing technique. The encrypted holograms can only be decrypted when the hologram is illuminated with a duplicate of the reference beam and correct fingerprint and spiral phase plate (SPP) keys. The multiplexing performance and key sensitivity of fingerprint and SPP order were both analyzed, showing the high strength of the security of our proposed method.

We observed efficient transient optical grating effect from the TiO 2 –Nb 2 O 5 –TeO 2 glasses excited by femtosecond laser pulses. The glass samples were prepared via melt-quenching technique. The optical nonlinearities were calibrated by forward degenerate four wave mixing (DFWM) experiment with 50 fs laser pulse at 800 nm. The magnitude of the third order nonlinear susceptibility χ (3) was about 7–9 × 10 − 13 esu, and its temporal response is up to the resolution limit of the laser 50 fs pulse-width. It has been found that χ (3) is critically dependent on the stoichiometry of between TiO 2 and TeO 2 . The results of Raman experiment have indicated that TiO 2 dopant induces transformation from the [TeO 4 ] unit into [TeO 3 ] via [TeO 3+1 ], and it results in reinforcement in the rigidity of the glass network so that the χ (3) was suppressed.

The anisotropic Bragg diffraction of the volume holographic gratings in photorefractive crystals are investigated based on the model of anisotropic coupled-wave theory. The effect of the initial intensity ratio and the recording angles of the two recording waves on the anisotropic Bragg diffraction properties is discussed. It is shown that both the ratio of the initial intensity and the incident angles of the recording waves are selective action for the anisotropic Bragg diffraction efficiency of the volume holographic gratings, while these two recording conditions are not selective action for the isotropic Bragg diffraction. Furthermore, the Bragg phase matching condition of anisotropic diffraction is analyzed when the recording angles change.

We propose a new method called modified optical scanning cryptography using Fresnel telescope imaging technique for encryption and decryption of remote objects. An image or object can be optically encrypted on the fly by Fresnel telescope scanning system together with an encryption key. For image decryption, the encrypted signals are received and processed with an optical coherent heterodyne detection system. The proposed method has strong performance through use of secure Fresnel telescope scanning with orthogonal polarized beams and efficient all-optical information processing. The validity of the proposed method is demonstrated by numerical simulations and experimental results.

A lossy hologram compression method is investigated to compress three-dimensional (3-D) images holographically recorded with optical scanning holography. Without loss of major reconstruction details, results have shown that the lossy compression method is able to achieve high compression ratio of up to 100.

We propose a holographic display method to reconstruct two on-axis holograms free of the zeroth-order light and the twin image using two amplitude-modulation spatial light modulators (SLMs).

Based on the two-dimensional coupled-wave theory, the wavefront conversion between cylindrical and plane waves by local volume holograms recorded at 632.8 nm and reconstructed at 800 nm is investigated. The proposed model can realize the 90° holographic readout at a different readout wavelength. The analytical integral solutions for the amplitudes of the space harmonics of the field inside the transmission geometry are presented. The values of the off-Bragg parameter at the reconstructed process and the diffracted beam's amplitude distribution are analysed. In addition, the dependences of diffraction efficiency on the focal length of the recording cylindrical wave and on the geometrical dimensions of the grating are discussed. Furthermore, the focusing properties of this photorefractive holographic cylindrical lens are analysed.

For cement plants, great attention is being given to the emission of the pollutant gases, especially NO. Because of the increasingly stringent emission constraints at cement plants, it is becoming more important to predict emissions accurately and then decrease the release quantity. The precalciner is an important apparatus in the cement production process, in that it can reduce not only the heat loading of the rotary kiln but also the NO emission, because of its relative low operating temperature. In this paper, the NO release was simulated based on the full-scale modeling for the precalciner and the model results were compared with measurements to validate the simulation models. The optimum cases of air staging and fuel staging were analyzed by executing a simulation technique on the restructuring precalciner with no effect on the operation process, and the conclusion is that the fuel staging case is the optimum method economically.

The formation dynamics of crossed-beam photorefractive gratings formed by the in Fe doped LiNbO3 crystal is studied based on jointly solving the material equations and the two-dimensional coupled-wave theory. The numerical calculations of the temporal and the spatial evolutions of the space-charge field and the light modulation depth are given, and the influence of the recording conditions, including the recording wavelength, the two-dimensional sizes of the holographic grating are presented, and the time evolution of diffraction efficiency during holographic recording is also presented.

Laser beam scanners are important optical elements with a large variety of applications in the measurement techniques, optical communications, laser imaging ladar, etc. Agile beam steering of optical radiation using phased arrays offers significant advantages, such as weight, stability and power requirements over conventional beam steering systems. There are several kinds of optical phased array technology to be developed, such as Lithium tantalite phase shifters, lithium niobate electro-optic prism deflectors, and liquid crystal and ferroelectric liquid crystal phase modulations. However, one of the major drawbacks of these approaches is low light efficiencies because of the side lobes in far-field pattern of the steering beam. In this paper, a new low side lobe optical beam steering technique using phase correction technique is proposed. A stable and fast single-lobed far-field pattern in steering beam can be obtained from the optical phased array with a phase plate by optima design. It can result in a substantially increased light efficiency and beam quality. The quantitative calculation results of typical optical phased array are demonstrated. The low side lobe optical beam steering technology of optical phased array will benefit many practical applications such as laser ladar, laser communications and high resolution displays.

Volume gratings are of wide interest in many applications because of their properties of high diffraction efficiency, excellent wavelength selectivity and angular selectivity. Ultrashort pulsed laser has many promising applications in the fields such as optical communication, signal and imaging processing. Because of its abundant spectrum and wide bandwidth, the diffraction properties of volume gratings under illumination by ultrashort optical pulse will be different from that of a monochromatic continuous wave. A periodical structure is highly dispersive and such a dispersive property can be used to control the group velocity of light beams. So the spectral properties and dispersive properties of the periodically layered structures such as volume gratings when a linear chirped Gaussian pulse illuminated are very necessary. These properties can be applicable to addressable filter, switching, and controllable optical delay line. In this paper, a detailed study of linear chirped ultrashort pulsed beams diffracted by volume gratings in dispersive media is performed. The group delay characteristics of the diffraction spectrum of the transmitted and reflected volume gratings were studied based on the modified coupled wave theory. The analysis and observation of this paper will be valuable for the designing optical elements based on diffractive structure for the use with linear chirped ultra-short pulsed waves.

The diffraction properties of ultrashort pulsed by the volume gratings with arbitrary boundaries are studied based on the extended two-dimensional coupled wave theory for volume grating readout by ultrashort pulsed beam. The intensity distributions of the diffraction and transmitted pulsed beams in spectral and temporal domains are given. And the total diffraction efficiency is also presented. Our study presents a possibility of shaping a broad band UPB by controlling the boundary of the local volume hologram grating.

A new type of photorefractive volume holographic lenses for converting a plane wave to a lateral-spread spherical wave with different wavelength has been suggested, which are recorded at 632.8nm wavelength and reconstructed at 800nm wavelength. Using the coupled-wave theory, the wave-front conversion by photorefractive volume holographic lenses between spherical and plane waves is studied. The off-Bragg parameter values of the holographic lenses in the reconstruction process are analyzed. The dependence of diffraction efficiencies on the focal length of recording spherical wave and the geometric sizes of the photorefractive holographic lenses are discussed in detail. In addition the intensity distributions of the diffracted beam are analyzed also.

A new technique for ultrashort pulsed beams (UPBs) shaping that uses volume holographic gratings (VHGs) recorded in anisotropic crystals by modulating the polarization states of the input UPBs is proposed and analyzed. Our approach is based on the investigation that when a VHG recorded in anisotropic crystals is illuminated by a UPB, the spectral and temporal widths and the shapes of the diffracted and transmitted pulsed beams vary with the polarization state of the input UPB, based on the extended coupled wave theory of Kogelnik which combines with the dispersion effect of the crystal materials. By using this approach, the modulation ranges of the spectral and temporal widths of the output UPB can be controlled by the parameters of the grating. Moreover, the diffraction efficiency of the volume holographic grating is analyzed, which also varies with the polarization state of the input UPB. An example of using this approach is given that a linearly polarized Gaussian-shaped UPB with duration of 30fs is effectively shaped with a transmission volume holographic grating recorded in photorefractive LiNbO3 crystals.

Using the two-dimensional coupled-wave theory, the diffraction characteristics of volume holographic gratings (VHGs) with finite size planar are studied for the ultrashort pulsed beam (UPB) readout. Numerical simulations are show for the special case of the overlapping VHGs reconstructed by a Gaussian-shaped UPB in temporal domain. The effects of the material dispersion and the finite size of the grating on the intensity distributions of the diffracted and transmitted pulsed beams, and the total diffraction efficiency are given. Our study also shows the differences between the diffraction characteristics of the finite size planar VHG for the UPB readout and those for the CW readout. And, comparison of the diffraction characteristics between the finite size VHGs and the one dimensional VHGs under the UPB readout is given.

The photorefractive volume holographic cylindrical lens taking on the wavelength conversion and the wave-front conversion synchronously was designed. Based on coupled wave theory, the wave-front conversion by local photorefractive volume holograms between cylindrical and plane waves which recoded at 632.8 nm and reconstructed at 800 nm is studied. The off-Bragg parameter at arbitrary point of the hologram in the reconstruction process is analyzed. The dependences of diffraction efficiency on the focal length of recording cylindrical wave and on the geometric size of the gratings on the hologram are discussed in detail. The amplitude distribution of the diffracted beam at the output boundary is also analyzed. Furthermore, the effect of selectivity of different on-Bragg reference point for recording hologram on the diffraction efficiency of the grating is discussed.

In this paper, the theory model in which both the two-center material equations and two-dimensional two-wave coupled equations were solved jointly based on two-center holographic recording method is presented to analysis the dynamic formation of the crossed-beam photorefractive gratings in two doped LiNbO 3 crystals. The influence of the light intensity on the basic holographic properties of the crossed-beam photorefractive gratings in LiNbO 3 :Fe:Mn crystals is explored. The numerical simulation results are presented. The investigation yields quantitative predictions of the expected behavior of the dynamics of these gratings, which can be useful for the design of finite boundary photorefractive holographic optical elements.

With digital holographic interferometry, we have investigated the phase differences of a plane wave transmitting through a partly-poled RuO2:LiNbO3 crystal sample. The holograms recorded by a CCD array are reconstructed by both the Fresnel transform method and the angular spectrum backward propagation algorithm. Comparison of the reconstructed results shows a higher resolution can be achieved by the angular spectrum backward propagation algorithm.

A Bragg grating focusing device composed of electro-optically induced refractive index grating in periodically poled lithium niobate was designed for integrated optics systems. The device are induced and controlled by the application of an external electric field. The theoretical analysis of the proposed optical device is carried out using two-dimensional coupled wave theory. The focusing properties and the diffraction intensity are investigated at the focal plane. It is shown that the designed device has good performance of focusing when a plane wave incidents on it at a certain angle. This type of Bragg diffraction devices can be act as a focusing lens and will have many potential applications such as in integrated optics and opto-electronics.

In this paper, effect of polarization of light on photorefractive grating formulation with any light modulation in birefringent photorefractive material is studied in detail. The diffraction efficiency with various modulations and different polarization mode is calculated. Theoretical analytic results are presented. It is shown that both the ratio of the initial intensity and the incident angle of the writing waves are selective when the polarization of mode of the readout wave and that of diffracted wave are different. But these two recording conditions are not selective for the isotropic diffraction. On the other hand, it is also found that the length of the grating is selective for anisotropic diffraction.

Stratified volume holographic optical elements (SVHOE's) comprise a recently proposed class of novel diffraction structure, it's unique angular selectivity of the SVHOE's Bragg diffraction process have more promising applications. The previous study of SVHOE's are mainly based on isotropic materials, in this paper we study the diffraction properties of holographic gratings in anisotropic media separated by buffer layers using the method of Coupled wave theory. It is shown that the diffraction efficiency of such system also exist the uniform periodic angular sensitivity, in addition the dependence of the periodic SVHOE angular sensitivity on number of layers and total SVHOE thickness have been discussed.

On the basis of two-dimensional coupled-wave theory, diffraction properties of ultrashort pulsed beams (UPBs) generated from volume holographic gratings with arbitrary boundaries are studied. The resulting differential coupled equations are solved numerically by a two-dimensional Runge–Kutta method. The effects of the grating boundaries on the intensity distributions of the diffracted and transmitted pulsed beams in spectral and temporal domains are presented, and the effects on the Bragg selectivity bandwidth, the diffracted bandwidth and the total diffraction efficiency of the gratings are also given. Simulation results show that use of a characteristic grating will result in distorted profiles for the diffracted beam and that truncated grating shapes significantly improve the output beam quality. This study presents the possibility of shaping a broadband UPB by controlling the boundaries of local volume hologram gratings.