This PDF file contains the editorial “Naming a New Society” for OE Vol. 38 Issue 01

This PDF file contains the editorial “Guest Editorial: Special Section on Optical Security” for OE Vol. 38 Issue 01

we investigate the robustness to noise of the double-phase encryption method and compare it with the exclusive-OR (XOR) encryption. we consider both additive and multiplicative noise and determine the theoretical mean square error of the decrypted image for the two methods. The theoretical results are verified by computer simulations. Theoretical and computer simulations indicate that the double-phase encryption method produces a lower mean square error than the XOR encryption method.

We propose a new optical stream cipher for security applications. The stream cipher's security is enhanced using hybrid cellular automata to replace uniform cellular automata as the keystream generators. The encoded ciphertext is obtained by randomly encoding both the initial states of cellular automata and their evolution rules. This results in an increase in complexity to crack the keystream generator and, thus, enhances the security of stream ciphers. The hardware implementation can be also correspondingly reduced. An optical solid-integrated scheme is suggested to implement the proposed stream cipher for high-speed encryption and decryption.

A security verification method using a transform phase mask as an optical mark bonded to a document or some other object is proposed. This mask consists of separated and shifted fragments of a reference phase mask. Both masks are entered into an optical correlator as input and reference images. We consider the model of autocorrelation peaks produced and of feature vectors formed in a classical joint transform correlator. We propose to use a reversible photoanisotropic material in the frequency domain of a joint transform correlator. We show that such a material can be used in optical security devices. The joint transform correlator experimental setup containing the photoanisotropic material is designed and the optimum exposures of material to produce autocorrelation peaks are found.

A new optical stream cipher system based on a threshold generator used as a random key bit stream generator is presented. To implement the threshold generator optically, we use conventional twisted nematic type spatial light modulators (sLMs). This proposed system is based on the shadow casting technique for the AND operation between taps and register stages. It is also based on the proposed polarization multiplication by rotation and shift (PMRS) method for modulo-2 addition. The proposed PMRS method uses the property of light polarization on a liquid crystal device (LCD) and can be implemented optically using one LCD and some mirrors. One of the major advantages of the proposed system is that the programmable tapping points can be realized easily by updating the pixel value represented on LCD. We present some simulation results that verify this proposed method.

Financial transactions using credit cards have gained popularity but the growing number of counterfeits and frauds may defeat the purpose of the cards. The search for a superior method to curb the criminal acts has become urgent especially in the brilliant information age. Currently, neural-network-based pattern recognition techniques are employed for security verification. However, it has been a time consuming experience, as some techniques require a long period of training time. Here, a faster and more efficient method is proposed to perform security verification that verifies the fingerprint images using the joint transform correlator as a feature extractor for nearest neighbor classifier. The uniqueness comparison scheme is proposed to improve the accuracy of the system verification. The performance of the system under noise corruption, variable contrast, and rotation of the input image is verified with a computer simulation.

We propose a new optical image encryption technique based on exclusive-OR (XOR) operations for a security system that controls the entrance of authorized persons. The basic idea is that we convert a gray-level image to eight bit planes for image encryption. We use the XOR operation that is commonly used such as the well-known encryption method. The input image is encrypted by performing optical xOr operations with the key bit stream that are generated by digital encryption algorithms. The gray level input image is converted to eight bit planes, which are represented on a liquid crystal device (LCD). The key data represented on different LCDs is reproduced to eight bit planes by a lenslet array. The optical XOR operations between the key data and the bit planes are performed by the polarization encoding method. The results of XOR operations, which are detected by a CCD camera, are converted to an encrypted gray-level image and the image is used as an input to the binary phase extraction joint transform correlator (BPEJTC) for comparison with reference images. We present some simulation results that verify the proposed method.

A new optical security application of an old color photographic technique (Lippmann photography, invented in 1891) is presented. Today, this type of photography can be applied as a unique security device on security documents, such as, e.g., identification cards, passports, credit cards, and other documents where a high degree of security is needed. A Lippmann photograph is very similar to the holograms currently used in this field; however, a unique recording of each document can be made to achieve a degree of security higher than that with mass- produced holograms. The recording of Lippmann photographs requires a special type of photosensitive medium in contact with a reflecting layer. Panchromatic photopolymer materials can be used and, after being recorded and processed, laminated to security documents. A special type of recording equipment is required. Lippmann photographs are virtually impossible to copy and, certainly, cannot be copied by conventional photography or color copying machines.

Emblems using holograms or other diffractive devices have long been used to mark cards and other objects as a means of authentication. The effectiveness of such emblems as security devices is ultimately determined by the inspection system. Due to the expense and highly variable performance of the human inspector, automated machine reading devices are an attractive alternative for performing the verification task. An additional advantage of the machine reader is that information regarding the card or its holder can be stored covertly. A security verification system is presented consisting of a holographic security emblem in which information is covertly stored and an automated reader based on a joint transform correlator (JTC). A holographic encoding method is used to produce an emblem that stores the required phase and/or amplitude information in the form of a complex, 3-D diffraction pattern that can be interpreted only through the use of a second "key" hologram. The reader incorporates the use of the nonlinear material, bacteriorhodopsin, as a means of miniaturizing the system, reducing system cost, and improving system performance. Experimental results are presented that demonstrate the feasibility of the approach for security applications.

A laser-diode-based joint transform correlator (JTC) is reported here for the identification and discrimination of fingerprints. The system employs compact and inexpensive laser diodes as the light sources and a bacteriorhodopsin (BR) film in the Fourier plane, which can record the joint power spectrum without the need for expensive spatial light modulators or CCD cameras. The BR film also introduces nonlinearities in the Fourier plane which can improve JTC performance. In addition, real-time, all-optical programmable spatial filtering is demonstrated to improve the discrimination of the system. We present computer modeling and experimental results of this optical correlator, which shows excellent potential for the identification and discrimination of fingerprints.

Steven C. Verrall Abstract. The binary joint transform correlator is a good discriminator

Sinusoidal gratings of locally varying profile depth are incorporated into diffractive optically variable image devices (DOVIDs) for document security. The variation in profile depth is tailored to specific visual effects that can be readily authenticated. While the diffractive characteristics of these gratings depend very sensitively on the depth, the security of these DOVIDs is inherent to the diffractive structures insofar as the exact reconstruction of the original profile is required for the realization of the original visual effects. Sinusoidal gratings of locally varying profile depth are very resistant against copying by standard holographic techniques since these techniques are shown to lead to a loss of fidelity in profile form or depth.

A real-time, VanderLugt-type optical correlator using a single SLM is developed. A field programmable gate array is used to capture and process images obtained from a CCD camera at a rate of 60 video fields/s. During both enrollment and verification, a finger slides over a glass prism and is input to the system via the frustration of the total internal reflection process. An autoenrollment procedure captures the optimal image during each slide. An optimal composite filter is implemented. The correlation detection process comprises real-time tracking of the correlation peak while the finger is sliding and a decision process based on projective decision boundaries. Real-life tests yielded a false rejection rate of 1% and a false acceptance rate of 0.2%.

We present the derivation of an optimal trade-off filter developed for the correlation of fingerprints. The filter is comprised of multiple versions of the system user's fingerprint (i.e., it is a composite filter). Also, the characteristics of the filter can be adjusted so that its performance in a correlator is similar to that of a matched filter, an inverse filter, or some compromise between the two. These attributes make this filter structure attractive for the task of fingerprint verification. The composite nature of the filter offers distortion tolerance by encompassing several different versions of the fingerprint image, while the tailored characteristics of the filter enables us to produce a filter that is a trade-off between this distortion tolerance and its discrimination capability. The filter was developed using a "standard" database, with the objective of separating the two classes of input to the system: "legitimate users'' and "attackers." Specifically, the filter is optimized to minimize the probability of error (i.e., misclassification of user). Both the design and the implementation of the optimal fingerprint filter are covered.

Two techniques are presented to improve the performance of a binary joint transform correlator system for fingerprint recognition. Use of a Fourier plane binarization threshold that alternates between even and odd rows is shown to reduce noise in the output plane and to improve discrimination between matched and unmatched prints. Periodically correlating with a known standard input and normalizing the output peak intensity prevents correlator performance drift from degrading fingerprint recognition performance. Experimental system performance is assessed statistically in terms of the false pass rate seen when operating with a constant false alarm rate. By applying both techniques, a false pass improvement by a factor of almost 100 is experimentally demonstrated at a false alarm rate of 0.1%.

We have measured the permeation rates of helium and water through thin-foil UV-blocking filters used in the ASTRO-E/X-Ray Spectrometer (XRS) instrument. In the XRS program, there is a concern that outgassed contaminants such as water could permeate through the outermost filter, which will be at room temperature, and freeze on the inner filters, which will be at cryogenic temperatures. The filters tested consisted of ~ 1000 A Al on ~ 1000 A of either Lexan or polyimide. Results discussed include the permeation rate as a function of pressure difference across a filter, the ratio of helium to water permeation rate, and the effect of the aluminum layer thickness on permeation.

In currently selling video tape recorders (VTRs), two or more heads fixed at a revolving drum are used to record or reproduce video signals. To obtain uniform quality, the video heads should have similar characteristics such as geometrical shape and electromagnetic performance. This research is designed to develop a visual inspection system that can measure four geometrical parameters. To obtain reliable results, a digital signal processing-based image board and target-based imageprocessing algorithms were used. A series of experiments were performed on 1000 video heads. From observation of the experimental results, except for the cases of noise on the head and cracklike defects, we were able to obtain high inspection reliability, with an error bound within ±5 ?m.

We present a new simulation code able to simulate the entire propagation of a laser pulse, from the amplifiers up to the focusing stage. This algorithm has some new features. It computes the threedimensional optical propagation equation using no approximation other than the picosecond one. Its stability has been carefully studied, and it can be applied to any geometry. This is a great improvement in that up to now, only the cylindrical geometry was accessible with accuracy. We also present a method, using the fast Fourier transform, for evaluating with a high accuracy the Fresnel distribution of a focused laser pulse. The advantages provided by this algorithm are its rapidity and its close relation to physical understanding of the focusing phenomena.

A multiwavelength method to improve the accuracy of a differential absorption lidar (DIAL) for measuring SO2 in the lower atmosphere is presented. A dual-DIAL method consisting of a combination of two DIAL pairs (three or four measurement wavelengths) is proposed, and the measurement error is estimated from the lidar equation. By the selection of appropriate measurement wavelengths, the effects of ozone and aerosols can be suppressed. In principle, the accuracy can be improved to below 1 ppb for 300-m range resolution.

An effective technique for the fabrication of refractive microlens arrays in silica wafers relies on the transfer by reactive ion etching (RIE) of melted photoresist microlenses. Anisotropic RIE allows the modification of the transferred profile by changing the relative etch rate of silica and photoresist, accomplished through continuous adjustment of the etching-gas composition. Material etch rates may spontaneously vary during the transfer process although operative parameters are held unchanged. An accurate survey of the etching process has been carried out to observe the principal responses of etch-parameter variations and to elaborate a procedure to adapt microlens shaping to the most severe requirements.

A new method for developing optical code division multiplexed access (CDMA) address code sequences is presented. The method is based on the genetic algorithm, which has already shown success in developing two-dimensional correlation functions for pattern recognition. The algorithm is very flexible in its optimization criteria and is thus adequate for various optical CDMA applications, including coherent and noncoherent systems. Preliminary computer experimental results are presented that indicate very good discrimination ratios and very fast convergence of the search process. Important implications include synchronization-independent CDMA system design, reduction in optical beat noise, optical power budget improvement, and enhanced security.

A flexible numerical method for analyzing diffraction of realtime holograms written in bacteriorhodopsin films is described. The method calculates the propagation of writing and reading beams in bac- teriorhodopsin films using the finite-differential beam propagation method. The changes of the films in refractive index and absorption are deduced from rate equations for B-state and M-state molecules. We apply this method to a real-time holographic lens and calculate the spot profile on the focal plane and the diffraction efficiencies for various parameter values. We also measured diffraction efficiencies experimentally and compared the values with numerical results.

Angular-reflectance measurements were performed on several retroreflectors: metal-backed solid cube-corner arrays, metal- backed microspheres, and bare microspheres. Their peak values were 140% msr-1, 30% msr-1, and 2.0% msr-1, respectively. An instrument for measurement of angular reflectance is described. Methods for characterization of retroreflectors are developed for the purpose of predicting radiance and image contrast. Issues related to the minimum and maximum range of detection are discussed. Angular reflectance characteristics of cube-corners and microspheres are measured and discussed.

A compact microscope system for direct strain measurement is presented. it involves the grating diffraction method coupled with microscopy and image-processing technique. A Leitz optical transmitting microscope with white light source was rebuilt to incorporate a loading and recording system. Gratings with median density from 40 to 200 lines/mm are used. with the help of a Bertrand lens, the Fourier spectrum of the grating is formed on the CCD sensor plane with high image quality. Software that can precisely, quickly, and automatically determine the diffraction spot centroids has been developed. The local strain is measured with high resolution. Various ways of improving the sensitivity are suggested.

We calculate the chromatic dispersion of rectangular geometry waveguides and focus on the conditions for obtaining zero chromatic dispersion at a wavelength of 1.55 ?m. We consider single-mode waveguides fabricated from six distinct compositions of silica-based materials whose dispersive characteristics are modeled by use of a Sell- meier relation. Our analysis takes account of the two transverse dimensions of the guiding channel and provides for a determination of the dispersion coefficient ?" as a function of the values of both dimensions. The results allow us to compute a spectrum of values of the two transverse widths for which the total dispersion is zero. By definition of an effective mode field diameter for a channel waveguide we are able to discuss the end-to-end coupling of such a waveguide to a commercial single-mode fiber.

Most image compression methods used today are based on block transform coding. The use of block transforms has many benefits, but two major drawbacks. Most block transform coders suffer from blocking artifacts: the borders between adjacent blocks become visible when the compression ratio is high.