Generation and optical display of a binary-sampled phase-only hologram

Past research has demonstrated that a phase-only hologram can be obtained by down-sampling the intensity image of the object scene prior to the generation of the hologram. In this Letter, we extend the method to the generation of binary phase-only holograms. A hologram derived with our proposed method is referred to as a binary-sampled phase-only hologram(BSPOH). Being different from the parent scheme, we have adopted an offaxis configuration in the generation of the BSPOH to avoid the quantization noise, the zeroth-order light, and the conjugate lights. An experimental evaluation reveals that the reconstructed image of the BSPOH is of good quality, and only contains slight amount of noise.     

Interferometric phase-only optical encryption system that uses a reference wave

An improved image decryption system is proposed that is based on phase-encoded images and the principle of interference and uses a reference wave. A novel technique for generating intensity patterns from the decrypted phase information consists simply of interfering a reference wave with the wave passing through the encrypted image and a phase-only decrypting key. Optical experiments have confirmed the proposed technique as a simple and robust architecture for optical encryption.     

An interference-based optical authentication scheme using two phase-only masks with different diffraction distances

A new method to eliminate the security risk of the well-known interference-based optical cryptosystem is proposed. In this method, which is suitable for security authentication application, two phase-only masks are separately placed at different distances from the output plane, where a certification image (public image) can be obtained. To further increase the security and flexibility of this authentication system, we employ one more validation image (secret image), which can be observed at another output plane, for confirming the identity of the user. Only if the two correct masks are properly settled at their positions one could obtain two significant images. Besides, even if the legal users exchange their masks (keys), the authentication process will fail and the authentication results will not reveal any information. Numerical simulations are performed to demonstrate the validity and security of the proposed method.     

Compact optical correlator based on one phase-only spatial light modulator

An optical correlator that utilizes one phase-only spatial light modulator (SLM) combined with a mirror is proposed and demonstrated. This system is compressed by displaying the input and filter pattern on different parts of the same SLM. The background noise is separated from the correlation signal by superimposing a high-frequency carrier with the filter pattern except in the zero-frequency regions, which will improve the signal-to-noise ratio in pattern recognition. Our architecture is compact and the cost is relatively low by utilizing only one SLM.     

Multiple optical line traps using a single phase-only rectangular ridge

An optical line trap has the ability to simultaneously trap and align microparticles in line formation due to its intensity profile. In this paper, we demonstrate a straightforward means to generate multiple optical line traps by simply placing a phase-only rectangular ridge in the path of a laser beam. By carefully positioning the rectangular ridge, we were able to control the separation between the optical trapping lines, which were then used to create multiple line formations of trapped particles. The simplicity of the proposed technique lends itself to the realization of a highly efficient optical line trap converter for easy modification of existing optical microscopes.     

Communicating with optical hyperchaos: information encryption and decryption in delayed nonlinear feedback systems

Recent theoretical studies and experimental demonstrations have shown the possibility of using chaos for the encryption of message signals in communication systems. Chaos is generated by systems with delayed nonlinear feedback, which feature hyperchaotic (i.e., of high dimensionality) dynamics. The different ways for the injection of the information in the emitter and the process of the synchronization of the receiver are considered. The analysis of all the possibilities can be used to choose the correct topology of communication systems and, more generally, to explain the behavior of any chaotic systems ruled by nonlinear difference-differential equations.     

Vertical input optical ring resonator with differential operation for optical sensor

A novel waveguide ring resonator optical sensor with two resonant wavelength channels is proposed for a refractive index measurement of a test sample placed on the sensor substrate and its performance characteristics are investigated analytically and numerically. The waveguide device consists of a ring resonator, a split-ring-shaped loop waveguide, and a vertical input/output grating coupler, in which the loop waveguide acts as an additional resonator and provides another output wavelength channel of the sensor. The differential detection between the two wavelength channels enables the highly sensitive detection with temperature compensation. A numerical simulation based on a finite difference time domain (FDTD) method shows that a precise index change detection with a resolution of 10⁻⁶ can be achieved using of the proposed device.     

A new distribution scheme of decryption keys used in optical verification system with multiple-wavelength information

A new distribution scheme of decryption keys used in optical verification systems is proposed. The encryption procedure is digitally implemented with the use of an iteration algorithm in computer. Three target images corresponding to three wavelengths are encoded into three sets of phase-only masks （POMs） by a special distributing method. These three sets of POMs are assigned to three authorized users as the personal identification. A lensless optical system is used as the verification system. In the verification procedure, every two of the three authorized users can pass the verification procedure cooperatively, but only one user cannot do. Numerical simulation shows that the proposed distribution scheme of decryption keys not only can improve the security level of verification system, but also can bring convenience and flexibility for authorized users.     

All optical phase-only filtering correlation with binarized inputs by a ferroelectric liquid-crystal spatial light modulator

All optical phase-only filtering correlator is constructed with an optically addressed ferroelectric liquid-crystal spatial light modulator (FSLM) for a binarized input object and a twisted-nematic liquid-crystal spatial-light modulator for a computer-generated phase-only filter. In order to improve the discrimination capability of a phase-only filtering correlator, a binarized amplitude with maximum contrast in a FSLM is used for an object input. The contrast of binarized intensities can be maximized by adjusting the rotation angles of a FSLM and polarizers. The threshold level of binarized input objects can be controlled by changing the power of a laser incident on a FLSM. Experimental results with a high discrimination capability are presented to support the numerical correlation performance.     

Reconfigurable generation of high-repetition-rate optical pulse sequences based on time-domain phase-only filtering

We propose and demonstrate a fiber-based phase-only filtering technique for programmable optical pulse shaping, in which the filtering operation is implemented in the time domain by means of an electro-optical (EO) phase modulator. The technique has been applied for generating customized ultrahigh-repetition-rate optical pulse sequences (>40 GHz) from single input pulses by driving the EO phase modulator with a periodic electronic waveform (RF tone). The generated output pulses are replicas of the input pulse and both the repetition rate and the envelope profile of the generated sequences can be controlled and tuned electronically using this approach.     

Three-zone phase-only filter increasing the focal depth of optical storage systems with a solid immersion lens

The field distribution of a Weierstrass solid immersion lens (SIL) is presented, which shows that its focal depth is only in nanoscale. A novel filter design based on a three-zone binary phase pupil function is introduced for increasing the focal depth of a near-field Weierstrass SIL system and a procedure for designing a rotationally symmetric binary phase filter is presented. Numerical results show that an appropriate three-zone phase-only filter not only can evidently increase the focal depth of the SIL system, but also can effectively lower the spreading of the spot size with distance and suppress the side-lobe intensity. PACS 42.79.Ci; 42.40.Lx; 42.79.Vb; 42.25.-p     

Frequency encoded optical four-bit adder/subtractor with control input using semiconductor optical amplifiers

Optical adder/subtractor for two four-bit frequency encoded binary numbers are proposed and designed based on four wave mixing, add drop multiplexing and frequency conversion in semiconductor optical amplifier. The input bits and the control input are intensity-modulated signal of two specific frequencies suitable for optical communication in the C band of wavelength. The device can distinguish negative and positive results and controlled operation are most promising in this proposal. The use of semiconductor optical amplifiers along with frequency encoding makes the system very fast and useful for future optical communication and computation systems.     

Transverse superresolution with tunable phase-only pupil filters

A new set of tunable phase-only filters for realizing the transverse superresolution is introduced.The filters,whose significant features are their ability to tune and simplicity,consist of one half-wave plate between two quarter-wave plates,and the half-wave plate is made of two zones that can rotate with respect to each other.Through analyzing the transverse point spread function of such system,it can be concluded that by rotating any zone of the half-wave plate,the transverse resolution can be realized and can be tunable.     

Lensless Vanderlugt optical correlator using two phase-only spatial light modulators（Invited Paper）

A lensless Vanderlugt optical correlator using two phase-only spatial light modulators （SLMs） is proposed. The SLMs are used for displaying input and filter patterns respectively. The SLMs are also used as programmable lenses in order to realize the lensless construction. This lensless system is simple and its alignment adjustment is easy. The performance of the SLMs as programmable lenses is also described.     

Comment on "Interferometric phase-only optical encryption system that uses a reference wave"

We explain the vulnerability of the phase-only encryption procedure suggested by Seo and Kim [Opt. Lett. 28, 304 (2003)] and clarify issues regarding its robustness and degree of security compared with those of a previously reported phase-only encryption method.     

Discretized amplitudemodulated phase-only filter

The amplitude-modulated phase-only filter (AMPOF) effectively utilizes both amplitude and phase information to obtain a narrower and larger autocorrelation peak. To make it readily suitable for real-time target recognition applications, we consider discretizing both its amplitude and phase. Accordingly, both amplitude and phase of the AMPOF are ternerized to yield improved performance statistics of the correlator.     

A method of implementation of frequency encoded all optical encryption decryption using four wave mixing

All optical encryption decryption method using frequency encoding is proposed based on semiconductor optical amplifiers. The plain text and key are encoded in frequency encoding format i.e. the states of information ‘0’ and ‘1’ are represented by two different frequencies in the c-band. The ultra fast speed of operation of the devices used for the implementation of this system makes it very attractive for future all optical secure communication network. A simple method of conversion of frequency encoded data stream and intensity encoded data stream is also described, which enables us to use same technology of production and detection of intensity encoded data signals until new techniques based on frequency encoding comes out.     

Compensation of scintillation with a phase-only adaptive optic

To compensate for scintillation we allow the real, nonnegative field in an aperture to propagate a distance z toward a detector, where the field will be complex. There, we modify its phase to emulate that of a clear aperture. The modified field that is propagated to the detector is nearly diffraction limited. No light is lost, and the Strehl ratio is improved substantially. We show how to modify the phase, and we present a computer simulation.     

Encryption and decryption of images with chaotic map lattices

We propose a secure algorithm for direct encryption and decryption of digital images with chaotic map lattices. The basic idea is to convert, pixel by pixel, the image color to chaotic logistic maps one-way coupled by initial conditions. After small numbers of iterations and cycles, the image becomes indistinguishable due to inherent properties of chaotic systems. Since the maps are coupled, the image can be completely recovered by the decryption algorithm if map parameters, number of iterations, number of cycles, and the image size are exactly known.