Optical implementation of iterative Fourier transform algorithm using spatial light modulator

We carried out real-time optical image subtraction and edge enhancement based on a speckle modulation technique by using ferroelectric liquid-crystal polarization switches and a ferroelectric liquid-crystal spatial light modulator. A ferroelectric liquid-crystal spatial light modulator is employed as a real-time and multiple-exposure optical device, and successful results are obtained from three-exposure images modulated by speckles. Thus, image subtraction and edge enhancement are realized in real time. The whole operation is performed within several milliseconds with modest operating conditions. Because the spatial light modulator has a high resolution of greater than 100 line pairs/mm and can store fine speckle patterns, the image qualities we obtained are quite satisfactory.

Image encryption based on extended fractional Fourier transform and digital holography technique

In this work we implemented a hybrid joint Fourier transform correlator (JTC optical/electronic) helpful in the pattern recognition when the scene is in movement. We have been use the standard architecture JTC, but in our case, the first step of the correlation process is carried out optically, using coherent illumination to obtain the joint power spectrum (JPS) of each frame display on a spatial light modulator, we used a liquid crystal display CRL XGA4 with 1024 x 768 pixels of resolution in gray scale. It display a video sequence where is include a mobile scene and the reference, then, the JPS of each frame will be obtain in real time with the quadratic sensor (camera CCD) that is located in the back focal plane of the lens. For the second step was use the tools of the Imaging Developer Kit TMS3206711 DSP (IDK) of Texas Instruments, in order to take advantage of the high speed arithmetic offers by the Digital Signal Proccessor (DSP) and the electronics versatility offers to take decisions. The IDK is a tool of hardware and software that allows capture, process and display images in real time. The DSP microprocessor makes a Fourier transform of the image captured by the CCD, in this way, we obtain the correlation of the scene in movement in quasi real time. Using an efficient computation of the digital Fourier transform of a 2N-point real sequence, the hybrid correlator achieve 15 correlations per second, if the final result is display on the monitor the rate fall to 13 frames per second, the correlation peak was use to determine in real time the target position in the mobile scene.

This paper presents a method for measuring the complex mode of a vibrating structure using two separate dual reference stepped strobe phase (0, 90 degrees) holograms and a new spatial phase shifting technique during reconstruction. Spatial phase shifting is accomplished by scanning a pencil of a laser conjugate reconstruction beam in four equal steps across the hologram; four shifted phase real images are obtained for each of the two holograms and each set of four images is processed to get the unwrapped phase distribution. The vibration amplitude and phase are then obtained using these two phase distributions. The new spatial phase shifting technique greatly simplifies data acquisition and optical readout since only a single reconstruction beam is used to reconstruct both wavefronts for each hologram. The theory and experimental results are presented.

A programmable opto-electronic analogic CNN computer (POAC) provides an efficient frame for diverse image processing applications, as it combines the enormous inherent computational capabilities of our new, massively parallel, but flexibly programmable optical CNN implementation with the capabilities of a visual CNN-UM chip. Our optical CNN implementation is based on an original, semi-incoherent optical correlator architecture, which is superior to other optical implementations in several respects. It makes real time reprogramming of a new type of joint Fourier transform correlator (t/sub 2/-JTC) possible while preserving the inherent speed of VanderLugt type of systems. Furthermore the POAC architecture overcomes the main limitations of both the microelectronic (VLSI) and other optical implementations. In this paper it will be shown that this device is particularly useful in image-processing algorithms, which cannot be fulfilled real time by any other existing optical or digital system due to the high number of pattern matching tasks required.

A real-time recursive back projection (BP) imaging algorithm is presented in this paper. Real time imaging is an intense demand but a challenging task in impulse surface penetrating radar (ImpSPR)'s application. Based on 'delay-sum' operation in time domain, BP imaging algorithm can precisely focus the scattering intensity and obtain high quality subsurface profile. But it's heavy computation burden restricts it's application in ImpSPR's real-time processing. By minutely analyzing it's procedure, a recursive model of BP imaging algorithm is established and real-time BP imaging algorithm is educed subsequently. The computation complexity of both non real time BP imaging algorithm and real time BP imaging algorithm are analyzed. Through processing the experimental data obtained by a ImpSPR system- RadarEye, the imaging algorithm validates its capability at the aspect of ImpSPR's real time processing.

The real-time processing of synthetic aperture radar (SAR) data has a high requirement for the processor, which is a difficult problem in SAR real-time processing. With the rapid development of optoelectronic devices, traditional electrical SAR data processing can be converted into optoelectronic processing to improve the processing speed. In this paper, a new type of optical device is proposed to improve the processing speed of SAR data. With the help of a spatial light modulator (SLM), the initial SAR signal and matched filter function are loaded on the input plane and spectrum plane of the 4f system, respectively. Using an optical lens with the function of the Fourier transform, the Fourier transform and inverse Fourier transform of the SAR signal are carried out to realize the fast imaging of SAR. In theory, the processing speed of SAR data is the speed of light. Compared with traditional methods such as the range-Doppler (RD) algorithm, it is no longer necessary to carry out a one-dimensional Fourier transform but to carry out matching filtering for the azimuth and range of the spectrum plane of 4f system at the same time. In this way, it is not necessary to introduce a cylindrical lens, only a spherical lens is needed to realize the Fourier transform imaging of SAR. Finally, a two-dimensional SAR processing optical system is built to obtain the SAR image in real time.

Many advancements in the fields of holographic displays, image projection, and structured illumination rely on phase-only spatial light modulators (SLMs) to generate light fields with high dynamic range and little light loss. However, commonly used Liquid Crystal on Silicon (LCoS) SLMs are typically slow (<120Hz), while SLMs which can be modulated faster tend to have limited diffraction efficiency or binary bit depth. Recently, a new class of MEMS devices, Phase Light Modulators (PLMs), have shown promise for fast (>5 kHz) holographic illumination and display technologies. However, their bit depth is still limited to four-to-five bits, causing many light field modulation and optimization methods, such as Gerchberg-Saxton phase retrieval, to produce poor-quality results. In this contribution, we introduce an iterative modulation algorithm which combines a four-phase PLM level averaging method with Gerchberg-Saxton phase retrieval to enable complex field modulation while simultaneously improving the bit depth of the modulator, the PSNR of projected images, and contrast of projected images.

We propose a new optical secret key sharing method based on the modified Diffie-Hellman key exchange protocol required in cipher system. The proposed secret key sharing algorithm is optically implemented by 2-step quadrature phase-shifting digital holographic encryption technique using orthogonal polarization. An unknown user’s private key is encrypted into three ciphered digital holograms which are supposed to be opened to the public for secret key sharing. The encrypted digital holograms are Fourier transform holograms and are recorded on CCDs with 256 gray level quantized intensities in the optical setup. The decryption with three ciphered digital holograms reconstructs each user’s private key information, which is used to generate the same shared secret key to each other. The advantage of the proposed method is that the optical setup has a kind of double key encryption scheme and provides the discretion of the user’s private key. The proposed method is very efficient in applying to a secret key sharing cryptosystem with high security strength.

This paper discusses the advantages of spatial light modulators (SLM) for the application of digital holography and dynamic pattern generation. Implementation demands are discussed on the example of designing an optical system for diffractive element synthesis based on LCOS SLM that is applicable not only for fringe pattern fabric structures but as well to allow for more complex patterns including polarization grating formation in polarization-sensitive liquid-crystalline polymers. We report a new method for the synthesis of digital holograms made by using the interference of laser beams that are diffracted on two amplitude and phase SLM's. Combining the original image-matrix technology with an interferometric image formed by two LCOS SLM's allows for obtaining new visual effects for hologram or diffractive elements synthesis. The proposed method for computer-generated holograms (CGH) enables one to synthesize CGH's and to simulate digital image processing techniques for 3D image reconstruction. The extension of the proposed technique of modeling diffraction on amplitude-phase masks and the possibilities of its practical application such as computer modeling of diffraction on a SLM, which consists of rectangular cells, for wavefront reconstruction are considered. Conclusions regarding the possibilities of the representation of the arbitrary fields by using the discrete matrix of elementary diffractive aperture cells for an enhancement of the iteration algorithm of hologram synthesis and phase retrieval are obtained. The results obtained by numerical and experimental means are presented together with a discussion of the limitations and further possibilities of this method.

Recording of Complex Amplitude Data Pages in Holographic Data Storage with Digital Holographic Techniques

The paper presents a novel approach to detect and monitor nonradiative transitions in singlet oxygen molecules in water by means of holographic recording of thermal disturbances. The approach is realized experimentally using classical and digital holographic techniques. Advantages and disadvantages of each of the techniques are considered.

Crystallization inside micro channel is key technology to making new materials. In order to control the quality of crystal, solubility observation is required. Interferometry is technique to measure solubility using refractive index but it requires complex optical layout. In this paper new technique to measure refractive index inside micro channel using digital holographic technique are proposed. Calculated particle positions are shifted because of variation of refractive index. With this shift, the refractive index inside channel canbe calculated. With simple experiment, feasibility of the technique are confirmed.

We propose a data security system that combines the optical encryption and a digital holographic technique. The proposed system enables us to store, transmit, and decrypt the encrypted data digitally. The data is encrypted optically using the double random phase encryption and is recorded as a digital hologram. The optical key, that is, the Fourier phase mask is also recorded as a digital hologram. The encrypted data is decrypted digitally by using the hologram of the optical key. Figure 1 (a) shows the input images used in the experiments to be decrypted. The electrically reconstructed image is obtained with an input phase mask without the Fourier phase mask. The digitally reconstructed encrypted images are shown in Fig. 1 (b). The image is obtained by inverse Fourier transforming the digital hologram of the encrypted data. The original image cannot be recognized. The digitally reconstructed decrypted images using the hologram of the Fourier phase mask are shown in Fig. 1 (c). Here one can see the original images. The experimental results demonstrate the feasibility of the proposed method.

In this Letter we report on an alternative approach to get multiple images in microscopy, exploiting the capabilities of both a lithium niobate diffraction grating and digital holographic technique. We demonstrate that multi-imaging can be achieved in a lensless configuration by using a hexagonal diffraction grating but overcoming, thanks to digital holography (DH), the many constrains imposed by the grating parameters in multi-imaging with Talbot effect or Talbot array illuminators. In fact, DH permits the numerical reconstruction of the optical field diffracted by the grating, thus obtaining in-focus multiple images in a plane different from the fractional or entire Talbot ones.