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A study on improved light extraction efficiency (LEE) of LEDs with photonic crystals formed by holographic lithography (HL) was present. The propagation and extraction of light in LEDs were simulated using FDTD method for LED structures with top HL PC and embedded HL PC respectively. By optimizing the design parameters of the HL PC, the best value of 88.3% enhancement of LEE were obtained. Result also revealed that the scattering and diffraction of photonic lattices play a more important role in the increased light extraction of HL PC LEDs than photonic band gap effects.

Warpage is a crucial factor to accuracy of sintering part in selective laser sintering (SLS) process. In this paper, The influence of process parameters on warpage when sintering polystyrene(PS) materials in SLS are investigated. The laser power, scanning speed, hatch spacing, layer thickness as well as temperature of powder are considered as the main process parameters. The results showed that warpage increases with the increase of hatch space. Contary to it, warpage decreases with the increase of laser power. Warpage decreases with the increase of layer thickness between 0.16~0.18mm and changes little with increase of the thickness. Warpage increases along with the increase of scanning speed but decreases when the speed is over about 2000mm/s. When the temperature changes between 82°C-86°C, warpage decreases little with the increase of temperature. But further increase of temperature leads to warpage decreasing sharply when the temperature changes between 86°C-90°C.

A novel digital image synthesis and multiple-image encryption technique based on parameter multiplexing and phase-shifting interferometry by discrete Fresnel transform is proposed. Both the image synthesis and the multiple-image encryption can be realized with the same system arrangement and similar principles, while the former is achieved by using different sets of parameters (wavelength and distance) and the same set of random phase masks, and the latter with different sets of random phase masks. The feasibility of this method and its robustness against occlusion and additional noise attacks are verified by computer simulations. The encryption capacity of the system is analyzed in term of the correlation coefficient. This technique is simple with a lensless setup, highly secure, and particularly suitable for the image transmission via Internet.

A wavefront reconstruction method by two-step generalized phase-shifting interferometry (GPSI) with blind phase shift extraction algorithm is verified by both the computer simulations and optical experiments. This method can retrieve complex object wave field by using two interferograms, the recorded object and reference wave intensities, and an unknown phase shift without additional processing. The simulations with irregular wavefronts have shown the effectiveness and high accuracy of this method for blind phase-shift extraction and wavefront reconstruction over a wide range of phase-shifts, while the optical experiments for both the direct and indirect objects have yielded satisfactory results with a higher resolution of reconstructed image than those reported recently.

We have proposed a full-phase image encryption method based on double random-phase encoding in Fresnel domain and pixel random permutation (PRP) technique with the use of two-step phase-shifting interferometry (PSI) we reported recently, and verified the effectiveness of this method and its robustness against occlusion and noise attacks by a series of numerical simulations. Comparing with other similar methods, this approach can decrease the number of the interferograms to be delivered from at least three needed in ordinary PSI to only two, give much better performance of image reconstruction than amplitude-based encryption, and provide much higher security level. This method is usable for both the gray-level images and binary images, and usually the latter will lead to better results.

We have investigated the effect of phase shift selection and phase shift errors on wave-front reconstruction errors in three-step generalized phase-shifting interferometry (GPSI) systematically. A general formula of the mean square wave reconstruction error for different phase shift selection and different phase shift errors is derived, and its specific expressions for the equal, linear, and random phase shift errors are deduced. The results reveal that there is a wide range for phase shift selection in GPSI, and the equal phase step algorithm is superior to the one of unequal step where the three kinds of phase shift errors are concerned. Specifically, the phase step leads to the minimum wave reconstruction error in the cases of equal and linear phase shift errors, while the phase step 1.91 rad yields the smallest wave reconstruction error for random phase shift errors. These results have been verified by a large number of computer simulations with over 100,000 samples.

A novel digital image watermarking system based on an iterative phase retrieval algorithm and sine–cosine modulation in the discrete-cosine-transform (DCT) domain is proposed. The original hidden image is first encrypted into two phase masks. Then the cosine and sine functions of one of the phase masks are introduced as a watermark to be embedded into an enlarged host image in the DCT domain. By extracting the watermark of the enlarged superposed image and decryption we can retrieve the hidden image. The feasibility of this method and its robustness against some attacks, such as occlusion, noise attacks, quantization have been verified by computer simulations. This approach can avoid the cross-talk noise due to direct information superposition and enhance the imperceptibility of hidden data.

A new kind of two-dimensional (2D) photonic crystals conforming to the 6-fold hybrid triangular configuration formed by holographic lithography is proposed. The relations between their photonic band gap (PBG) properties and their specific holographic designs for both the inverse and the normal structures are systematically investigated. Computations have shown that a series of complete band gaps of large sizes exist over a wide range of system parameters for inverse structures; especially, when the dielectric constant ? = 13.6, the optimized relative PBG can reach 24.1%, among the highest in all 2D structures. Furthermore, complete PBGs can also be obtained in normal structures of this kind even with a much lower dielectric constant contrast such as 5.3?:?1. The evolutions of band gap maps of these structures and their dependence on the structure parameters are demonstrated. The transverse electric and magnetic light propagations are simulated to prove the existence of complete band gaps in normal structures of low dielectric constant and their potential use as waveguides.

A new kind of two-dimensional 3-fold photonic crystal (PhC) conforming to the hybrid triangular configuration formed by holographic lithography (HL) is proposed, and the relation between its photonic band gap properties and its specific holographic design is systematically investigated. This structure can be conveniently produced using a multiple-beam dual-exposure technique. In addition to its high complete relative band gap, namely a 22.1% gap/mid-gap ratio for the dielectric constant contrast 13.6:1 in optimized design, it has very large tolerance on the system parameters and fabrication conditions and requires a quite low dielectric constant contrast to open complete band gaps. This study reveals that the band gaps of PhCs made by HL may be widened by introducing irregularity in the columns and lowering the symmetry of the structure. Light propagation in this structure is also simulated. The results show that a transverse electric (TE) or transverse magnetic (TM) band gap can be obtained in this structure even with a very low dielectric constant contrast (e.g. 2.56:1), and this fact makes it very suitable for low-index waveguides.

An iterative algorithm to extract the arbitrary unknown phase shift in two-frame phase-shifting interferometry and then reconstruct the complex object wave is proposed. In combination with the least square principle and some calculation formulae we developed, this algorithm allows us to find the value of unknown phase shift by using only two interferograms without additional knowledge or measurement. Computer simulations have shown that this algorithm works well for both the smooth and diffusing objects to a very high accuracy over a wide range of the phase shift from 0.4 to 2.5 rad.

In previous image watermarking methods an encoded host image and a watermark image are usually directly added, consequently the two images have cross-talk in the decryption step. To eliminate this effect, we propose a novel method based on digital holography, in which all the image pixels of the two sets of holograms resulted from two hidden images are rearranged and integrated into one set of composite holograms with a random scattering matrix (RSM). In decryption the use of this matrix can ensure the exact retrieval of each hologram, and then the perfect reconstruction of each image without cross-talk noise can be achieved. The feasibility of this method and its robustness against occlusion and additional noise are verified by computer simulations with phase-shifting interferometry and double random-phase encoding technique. This approach is suitable for both two- and three-dimensional images, and the additional RSM as a key provides a much higher level of security.

The shape and size of the dielectric columns or particles (“atoms”) of photonic crystals (PhCs) formed by holographic lithography are determined by the isointensity surfaces of the interference field; consequently the PhCs’ photonic band gap (PBG) properties are closely related to their fabrication design. Here we have proposed a new structure of two-dimensional (2-D) hexagonal lattice with irregular columns, which can yield a 2-D complete relative band gap of 24.0% in case of the dielectric columns of e = 13.6 in air, about 27% increase compared with that of the same lattice with regular triangular columns. This band gap size is among the largest for all the possible 2-D PhCs reported until now. The relationship between band gap properties of resultant structure and the specific fabrication conditions such as structure design and the choice of optimum intensity threshold and filling ratio are systematically discussed. The optical design for making this structure by two exposures is explained. This work may demonstrate the unique feature and advantages of photonic crystals made by holographic method and provide a guideline for their design and experimental fabrication.

Three-dimensional periodical microstructures can be fabricated by the interference of four noncoplanar beams. Generally the basis vector choice for a certain lattice is not unique and the same lattice structure can be formed with different recording geometries. It shows that, for certain special cases, the lattice constant can be tuned by proper single-exposure holographic design without distortion of the lattice element and then one can shift the photonic band gap to a different frequency range. In addition, a simple optical setup for fabricating body-centred cubic lattice with a large band gap is proposed.

A theoretical investigation of the possible three-dimensional photonic crystal structures that can be created by holographic interference using the symmetric umbrella configuration of four plane waves is made. The irreducible Brillouin zones and the photonic band gap (PBG) properties of the possible resulting crystal lattices when the apex angle is varied from 10° to nearly 180° are investigated. Our calculations indicate that a complete PBG can exist in the resulting structure in a very wide range of the apex angle, from 33° to 135° except a narrow region at 49° to 55°. The study has also shown that a larger band gap may be obtained in a structure that slightly deviates from the standard cubic lattice and that the optimum exposure threshold or optimum filling ratio of the dielectric material is roughly a step-like function of apex angle. These results may give a general outlook on this method and relax some requirements in experiments.

In the present work, Al–Pb alloy was irradiated by high current pulsed electron beam. X-ray diffractometer, electronic probe microanalysis, scanning electron microscopy and Knoop hardness indentation were used to characterize the microstructure and mechanical property of Al–Pb alloy. The results show that the microstructure and mechanical property can be greatly improved. The tribological properties of high current pulsed electron beam irradiated Al–Pb alloy were investigated under dry sliding conditions using a pin-on-disc type wear testing machine. The overlapped zone beneath the melted zone exhibits good resistance to wear. Optical observation and scanning electron microscopy analysis reveal that the low wear rate and lowest level in coefficient of friction at high load level for irradiated Al–Pb alloy are due to a lubricious tribolayer covering almost the entire worn surface. The wear mode varies from oxidative wear at low load to film spalling at high load and, finally, adhesive wear.

A ternary photopolymer system consisting of a new photoinitiator, an oligomer and a binder has been developed. Experiments show that one-, two- and three-dimensional periodic microstructures can be successfully holographically fabricated by single-photon photopolymerization with this material and a low-power (tens of mW) continuous-wave laser at 532 nm. The preparation of this material is explained and its absorption spectra are tested. The optical setup and the experimental results including the diffraction patterns verifying the formation of periodic structures are given. Compared to other methods with the use of high-power lasers, this approach is much more accessible to most laboratories and researchers and therefore may promote the use of holographic fabrication techniques for photonic crystals.

The tribological properties of Al–Si–Pb alloys irradiated by high current electron beam (HCPEB) were investigated under dry sliding conditions using a pin-on-disc type wear testing machine. The HCPEB parameters used to treat the samples are: electron energy: 21–25 keV; energy density: 1.5–2.5 J/cm 2 ; pulse duration: 1.5 μs; number of pulses: 15. The results show that the microstructure and mechanical properties can be greatly improved. These factors contribute to great increase in wear resistance of HCPEB irradiated Al–Si–Pb alloys at 2.0 J/cm 2 and 2.5 J/cm 2 . Optical observation and X-ray photoelectron spectroscopy (XPS) analysis reveal that the low wear rate and lowest level in coefficient of friction at high load levels for Al–Si–Pb alloys HCPEB irradiated with more than 1.5 J/cm 2 are due to a film of lubricant covering almost the entire worn surface. This film is a mixture of different constituents containing Al, Fe, Si, O and Pb, in which Pb exists in the form of Pb 4 SiO 6 . With the applied load increased, the dominant wear modes exhibit successively the oxidative wear, film spalling, and adhesive wear.

A novel method of virtual shearing interferometry (VSI) is proposed. In this method, the shearogram is obtained by interference of a real object wave-front and a virtual object wave-front. The former is optically recorded and then digitally reconstructed; and the latter is introduced digitally by repositioning or reforming the former. The obvious advantages of VSI over conventional shearing interferometry (SI) are its versatility, accuracy, and simplicity. Only one real field is necessary to produce shearogram; there is no need of any real shearing device or even the phase unwrapping computation; and the digital shear can take any possible form according to different purposes. Both the optical experiments and computer simulations with lateral shearing, 180° rotational shearing and double lateral shearing for evaluation of lens aberrations in the general case including spherical aberration, coma, astigmatism, defocus, and tilts based on phase-shifting interferometry are given to verify the effectiveness of this method.

A novel digital method of double-image encryption and watermarking by constructing a complex field with one non-negative image as its amplitude and another as its phase and then encrypting this complex field by means of digital optics, such as phase-shifting interferometry with double-random phase encoding, is proposed. Since no direct addition of the information of two hidden images is employed in the encryption process, each image can be perfectly retrieved without cross-talk caused by the existence of the other. The feasibility of this method and its robustness against occlusion and additional noise from watermarked images with different weighting factors are verified by computer simulations. The signal-to-noise ratio and mean square error of the retrieved images are calculated for different distortions. This technique can considerably improve the efficiency of data transmission, and it is particularly suitable for the image transmission via the Internet.

Free-radical copolymerizations of vinylbenzyl-terminated polystyrene (PS-VM; M 1 ) and methacryloyl-terminated poly(ethylene glycol methylether) (PEG-MC; M 2 ) were carried out in various solvents (benzene, 1,4-dioxane and N , N -dimethylformamide). The reactivity ratios obtained for the binary macromonomer systems were different from corresponding model system of styrene and methyl methacrylate ( r 1 =0.52 and r 2 =0.46) due to phase separation. PEG macromonomers could not interpenetrate sufficiently into propagating copolymer chains that had radical sites due to phase separation. On the other hand, the reactivity ratios ( r 1 =0.25 and r 2 =0.02) obtained for the binary copolymerizations of PS-VM and PEG-MC/tin tetrachloride macromonomers showed strong alternation. It was suggested that alternation results from the homopolymerization of 1:1 complexs formed between the donor and acceptor monomers.

It is well known that the square lattice of isolated single-atom dielectric rods in air does not give rise to complete bandgaps even when asymmetry is introduced to lift some degeneracy. However, in this paper, a new kind of two-dimensional square photonic crystal with isolated single-atom dielectric rods in air formed by holographic lithography is proposed, and the relation between their photonic bandgap properties and their specific holographic design are systematically analyzed. In addition to the large complete relative bandgap, namely 9.68% gap/midgap ratio for the dielectric constant contrast of 13.6:1, this structure has very large tolerance on the system parameters and fabrication conditions. This fact can greatly relax the experimental requirements. This work may demonstrate the unique feature and advantages of photonic crystals made by the holographic method and provide a guideline for their design and fabrication.

We have investigated the transmission properties of a photonic crystal waveguide (PCW) formed by holographic lithography for the first time with a two-dimensional (2D) triangular holographic photonic crystal (PhC) including a line defect with two 60 masculine bends. Calculations have shown that for this PCW high transmission (90%) through sharp corners can be obtained in a wide frequency range from 0.298 to 0.310 (omega alpha/2pi c) with the relative band gap of 4% when the dielectric contrast is 7.6:1. As far as we know, this result should be the widest frequency range with high transmission (90%) in the waveguide of similar 2D triangular PhCs ever reported. We have also found that the specific holographic designs of PhC have strong influence on the resonance between the two waveguide bends, and thus this fact can be used as an effective means to improve the transmission property of 2D holographic PCW. In addition to the simplicity and low cost of holographic fabrication of PhCs, these features may reveal the possibly better guiding ability of holographic PCW than the conventional waveguide and the promising potential of the former in the application of photonic integrated circuits.

An algorithm to extract the arbitrary unknown phase shift and then reconstruct the complex object wave in generalized phase-shifting interferometry (GPSI) without the iteration process and measurement of object wave intensity is proposed. This method can be used for GPSI of any frame number >or=2. Both computer simulations with smooth and diffusing object surfaces and optical experiments have verified the effectiveness of this method over a wide range of phase shifts with very satisfactory results.

A novel fast convergent algorithm to extract arbitrary unknown phase shifts in generalized phase-shifting interferometry (PSI) is proposed and verified by a series of computer simulations. In this algorithm an error function is introduced and then the unknown phase shifts are found by an iterative tangent approach. In combination with the statistical method, this algorithm can give the most exact results in the fewest iteration steps. It can be used for generalized PSI of arbitrary frames for both smooth and diffusing objects and can usually reach the exact phase shifts with only four or five iterations for three- or four-frame PSI.

Conventional phase-shifting interferometry (PSI) needs at least three interferograms. A novel algorithm of two-step PSI, with an arbitrary known phase step, by which a complex object field can be reconstructed with only two interferograms is proposed. This algorithm is then applied to an information security system based on double random-phase encoding in the Fresnel domain. The feasibility of this method and its robustness against occlusion and additional noise attacks are verified by computer simulations. This approach can considerably improve the efficiency of data transmission and is very suitable for Internet use.

In the recording process of phase-shifting interferometry, intensity fluctuation caused by light source instability may occur and then introduce amplitude and phase errors to the reconstructed object wavefront. A simple direct algorithm of digital data processing to correct these errors is proposed and satisfactorily verified by both computer simulations and optical experiments. This method can work without specific knowledge of the source intensity fluctuation, and it reduces both the amplitude and phase errors of the reconstructed wavefront by about two orders of magnitude in computer simulations.

Conventional double-random phase encoding is vulnerable to a chosen or known plaintext attack owing to the linearity of the system. We introduce a technique to break down this linearity with an undercover amplitude modulation in the encryption scheme. As an additional key, this operation can significantly enhance the security of the system. A series of computer simulations have shown the effectiveness of this method and its resistance against the known plaintext attack. The design and parameter choice of the amplitude modulator is also discussed.

Generally the photonic band gap (PBG) is a multi-variable function of several parameters related to the shape and size of the dielectric columns of photonic crystals (PhCs), and a time-consuming step-by-step scanning process for each parameter has to be used to find their best combination yielding maximum PBG. In this letter, the widely used Nelder-Mead simplex algorithm is introduced to optimize these parameters simultaneously to find a larger PBG for a new kind of two-dimensional (2D) hexagonal GaAs-Air PhC. This structure can be conveniently produced by the single-exposure holographic lithography, and the specific holographic design is also systematically investigated. This study reveals that the band gaps of PhCs made by holographic lithography may be widened by introducing irregularity of the columns and lowering the symmetry of the structure.

A novel kind of two-dimensional (2D) photonic crystals conforming to the 6-fold hybrid triangular configuration formed by holographic lithography is proposed. The relations between their photonic band gap properties and their specific holographic designs for the normal structures are systematically investigated. Computations show that this normal structure has complete band gaps over wide ranges of system parameters, and the minimum dielectric constant required to open a complete band gap with Δω/ω>1% is as low as 3.8, which is the lowest compared with the results of 2D periodic photonic crystals ever reported. The latter fact is also verified by light propagation simulation in waveguide. This work may make holographic photonic crystals promising for application in the range of optical devices and provide a guideline for their design and experimental fabrication.

A novel single-channel color-image watermarking with digital-optics means based on phase-shifting interferometry (PSI) and a neighboring pixel value subtraction algorithm in the discrete-cosine-transform (DCT) domain is proposed. The converted two-dimensional indexed image matrix from an original color image is encrypted to four interferograms by a PSI and double random-phase encoding technique. Then the interferograms are embedded in one chosen channel of an enlarged color host image in the DCT domain. The hidden color image can be retrieved by DCT, the improved neighboring pixel value subtraction algorithm, an inverse encryption process, and color image format conversion. The feasibility of this method and its robustness against some types of distortion and attacks from the superposed image with different weighting factors are verified and analyzed by computer simulations. This approach can avoid the cross-talk noise due to direct information superposition, enhance the imperceptibility of hidden data, and improve the efficiency of data transmission.

We present a study on negative refractions in the four lowest bands of two-dimensional (2D) square lattices formed by holographic lithography (HL) and compare these features with those of a lattice of the same kind but with regular dielectric columns. The plane wave calculations and FDTD simulations have shown that in some bands or for some interfaces the negative refraction can only happen in holographic structures, and generally the rightness of holographic structures and regular structures of the same kind may be different.

We propose a holographic design of five-beam symmetric umbrella configuration, where there are a central beam and four ambient beams symmetrically scattered around the central one with the same apex angle, for fabrication of three-dimensional photonic crystals with tetragonal or cubic symmetries, and systematically analyzed the band gap properties of resultant photonic crystals when the apex angle is continuously increased. Our calculations reveal that large complete photonic band gaps exist in a wide range of apex angle for a relatively low refractive index contrast. Specifically, the face-centered cubic structure with a relative band gap of 25.1% for epsilon = 11.9 can be obtained with this recording geometry conveniently where all the beams are incident from the same half-space. These results will provide us with more understanding of this important recording geometry and give guidelines to its use in experiments.

Theoretical analysis has shown that a two-dimensional (2D) lattice with circular columns connected by veins can produce a large complete bandgap when the radius of the columns and the width of the veins are properly chosen. We propose a holographic method to fabricate a similar 2D structure of irregular columns that can yield a 2D complete bandgap for a wide range of dielectric contrasts and a bandgap as large as 15.0% for e=11.4 and 15.8% for e=13.6. The specific problems of interference beam design, intensity threshold selection, and the effect of the shape and size of the unit cells on the final bandgap are discussed. This analysis demonstrates the unique features and advantages of the holographic method in bandgap engineering and gives a guideline for practical fabrication.

A novel information security system based on multiple-phase retrieval by an iterative Fresnel-transform algorithm and pixel random permutation (PRP) technique is proposed. In this method a series of phase masks cascaded in free space are employed and the phase distributions of all the masks are adjusted simultaneously in each iteration. It can achieve faster convergence and better quality of the recovered image compared with double-phase encoding and a similar approach in the spatial-frequency domain with the same number of phase masks and can provide a higher degree of freedom in key space with more geometric parameters as supplementary keys. Furthermore, the security level of this method is greatly improved by the introduction of the PRP technique. The feasibility of this method and its robustness against occlusion and additional noise attacks are verified by computer simulations. The performance of this technique for different numbers of phase masks and quantized phase levels is investigated systematically with the correlation coefficient and mean square error as convergence criterions.