Binary-phase Computer-generated Holograms Research Articles

The Wavefront Power Spectral Density Measurement of Aspheric Lens with Long Focal-Length Using a Computer-Generated Hologram

To ensure the performance of the optical system, the machining accuracy of lens with long focal lengths is required to ensure the image quality. A new method for lens transmission wavefront power spectral density (PSD) in mid-frequency domain measurement using binary phase computer-generated hologram (CGH) is presented. This technique is widely applicable and is particularly useful for measuring large-size lenses with long focal lengths. A comparison experiment of the CGH measurement with results from a Fizeau sphere interferometry method is carried out to verify the accuracy and convenience of the measurement. Furthermore, measurement uncertainty due to CGH fabrication process is analysed. Analysis of the CGH test showed the overall accuracy of less than 1 nm RMS for a sphere lens with over 30 m focal length and Φ410 mm clear aperture. CGH can provide reference spheres with high precision, in the meantime greatly shorten air space, thus reducing the effect of vibration and air turbulence, therefore is of great importance for lens transmission wavefront PSD measurement. The realization of high precision, high efficiency and nondestructive testing of long focal-lens wavefront PSD ensure the ultra-precision and certainty level of machining, hence improving the comprehensive performance of the optical system.

Numerical optimization of writing computer-generated holograms in threshold media

Recent developments in binary photo-magnetic materials showed efficient and ultra-fast rewriting of holograms where the intensity threshold allows for a dense, sub-diffraction limit packing of hologram points. This paper describes the numerical optimization of the process of writing and reconstructing of 2-D images in a binary-phase computer-generated holograms stored in the said threshold-like medium. Global optimization of the free parameters of the writing process is shown, including the intensity threshold level, propagation distance, hologram spot size and the shape of the boundary regions of the written spots. We present the optimal set of parameters for the best possible writing quality. Full Text: PDF ReferencesA. Stupakiewicz, K. Szerenos, D. Afanasiev et al., "Ultrafast nonthermal photo-magnetic recording in a transparent medium", Nature 542, 71 (2017). CrossRef J. Starobrat, A. Frej, J. Bolek, R. Trybus, A. Stupakiewicz, and M. Makowski, "Photo-magnetic recording of randomized holographic diffraction patterns in a transparent medium", Opt. Lett. 45, 5177 (2020). CrossRef V. Ostroverkhov, et al., "Micro-Holographic Storage and Threshold Holographic Recording Materials", Jap. J. App. Phys. 48.3S1, 03A035 (2009). CrossRef K. Matsushima, T. Shimobaba, "Band-Limited Angular Spectrum Method for Numerical Simulation of Free-Space Propagation in Far and Near Fields", Opt. Express 17, 19662 (2009). CrossRef F. Wyrowski, O. Bryngdahl, "Iterative Fourier-transform algorithm applied to computer holography", JOSA A 5.7, 1058 (1988). CrossRef I. Ducin, T. Shimobaba, M. Makowski, K. Kakarenko, A. Kowalczyk, Jaroslaw Suszek, M. Bieda, A. Kolodziejczyk, M. Sypek, "Holographic projection of images with step-less zoom and noise suppression by pixel separation", Opt. Comm. 340, 131 (2015). CrossRef M. Makowski, "Minimized speckle noise in lens-less holographic projection by pixel separation", Opt. Express 21, 29205 (2013). CrossRef

Modal wavefront sensor employing stratified computer-generated holographic elements

We describe a modal wavefront sensor that uses a stratified computer-generated holographic element (SCGHE). Each computer-generated hologram (CGH) in the SCGHE is coded with a single particular Zernike aberration mode, and arranged in parallel to one another with a slight separation. Four kinds of CGH, including continuous amplitude CGH, continuous phase CGH, binary amplitude CGH, and binary phase CGH are numerically analyzed. And the wavefront sensing principle is characterized firstly with a single CGH, and then with the SCGHE. The results show that wavefront sensor with the first three CGHs are feasible to detect specified Zernike aberration modes. Furthermore, some comparisons are provided to suggest an optimal choice in the actual implementation of sensor design.

Hybrid wavefront sensor for the fast detection of wavefront disturbances

Strongly aberrated wavefronts lead to inaccuracies and nonlinearities in holography-based modal wavefront sensing (HMWS). In this contribution, a low-resolution Shack-Hartmann sensor (LRSHS) is incorporated into HMWS via a compact holographic design to extend the dynamic range of HMWS. A static binary-phase computer-generated hologram is employed to generate the desired patterns for Shack-Hartmann sensing and HMWS. The low-order aberration modes dominating the wavefront error are first sensed with the LRSHS and corrected by the wavefront modulator. The system then switches to HMWS to obtain better sensor sensitivity and accuracy. Simulated as well as experimental results are shown for validating the proposed method.

Precision measurement system using binary phase computer-generated holograms

We present a novel method of obtaining precision measurement using two binary phase diffractive optical elements, termed the hologram, and phase mask. By encoding multiple views into the hologram, each of which corresponds to a horizontal or vertical relative displacement of the phase mask, the system is able to provide a visual feedback of the measurement without the use of electronics. A probabilistic method for detection of the resultant images, matched to the statistical properties of holographic replay, shows promise for enabling a fully automated measurement system.

DCT영역에서 스크램블된 이진 위상 컴퓨터형성홀로그램을 이용한 디지털 영상 워터마킹 기술

본 논문에서는 DCT 영역에서 스크램블된 이진 위상 컴퓨터형성홀로그램을 이용한 디지털 영상 워터마킹 기술을 제안하였다. 워터마크 삽입과정은 워터마크로 사용되는 은닉영상 대신 은닉영상을 손실 없이 재생할 수 있는 이진 위상 컴퓨터홀로그램을 생성하고 이를 스크램블기법으로 암호화 하여 워터마크로 사용한다. 그리고 암호화된 워터마크에 가중치 함수를 곱하고 호스트영상의 DCT 영역에서 DC성분에 삽입한 후 IDCT를 수행한다. 워터마크의 추출은 워터마킹된 영상과 원래의 호스트영상의 DCT계수 차이를 구하고, 삽입시 적용한 가중치 함수를 나눈 후 디스크램블링 하여 복호화 한다 그리고 복호화된 워터마크를 역푸리에 변환하여 은닉영상을 재생한다 마지막으로 원래의 은닉영상과 복호화된 은닉영상과의 상관을 통해 워터마크의 존재여부를 결정한다. 제안된 워터마킹 기술은 이진 값으로 구성된 은닉영상의 홀로그램정보를 이용하고 스크램블링 암호화 기법을 활용하였음으로 기존의 어떠한 워터마킹 기술보다 압축, 잡음 및 절단과 같은 다양한 외부공격에 안전하고 견실한 특징을 가지고 있음을 컴퓨터시뮬레이션을 통해 그 장점들을 확인하였다. In this paper, we proposed a digital image watermarking technique using scrambled binary phase computer generated hologram in the discrete cosine transform(DCT) domain. For the embedding process of watermark. Using simulated annealing algorithm, we would generate a binary phase computer generated hologram(BPCGH) which can reconstruct hidden image perfectly instead of hidden image and encrypt it through the scramble operation. We multiply the encrypted watermark by the weight function and embed it into the DC coefficients in the DCT domain of host image and an inverse DCT is performed. For the extracting process of watermark, we compare the DC coefficients of watermarked image and original host image in the DCT domain and dividing it by the weight function and decrypt it using descramble operation. And we recover the hidden image by inverse Fourier transforming the decrypted watermark. Finally, we compute the correlation between the original hidden image and recovered hidden image to determine if a watermark exits in the host image. The proposed watermarking technique use the hologram information of hidden image which consist of binary values and scramble encryption technique so it is very secure and robust to the various external attacks such as compression, noises and cropping. We confirmed the advantages of the proposed watermarking technique through the computer simulations.

Simple distortion-invariant optical identification tag based on encrypted binary-phase computer-generated hologram for real-time vehicle identification and verification

A simple distortion-invariant optical identification (ID) tag is presented for real-time vehicle identification and verification. The pro- posed scheme is composed of image encryption, ID tag creation, image decryption, and optical correlation for verification. To create the ID tag, a binary-phase computer-generated hologram (BPCGH) of a symbol image representing a vehicle is created using a simulated annealing algorithm. The BPCGH is then encrypted using an XOR operation and enlargement transformed into polar coordinates. The resulting ID tag is then attached to the vehicle. As the BPCGH consists of only binary phase values, it is robust to external distortions. To identify and verify the vehicle, sev- eral reverse processes are required, such as capturing the ID tag with a camera, extracting the ID tag from the captured image, transformation of the ID tag into rectangular coordinates, decryption, an inverse Fourier transform, and correlation. Computer simulation and experimental results confirm that the proposed optical ID tag is secure and robust to such distortions as scaling, rotation, cropping (scratches), and random noise. The ID tag can also be easily implemented, as it consists of only bi- nary phase components. C 2010 Society of Photo-Optical Instrumentation Engineers.

회절격자의 변조방식에 따라 형성된 CGH의 재생 영상 분석

회절격자의 회절 효율은 회절격자의 내부에 형성되는 격자의 구조에 의해 영향을 받으며, 이러한 격자의 구조는 변조방식에 의해 결정된다. 컴퓨터 형성 홀로그램(CGH) 역시 기본적으로 회절격자의 원리와 같기 때문에 CGH의 내부에 기록된 패턴은 변조 방식에 따라 달라지며 이 때문에 재생 영상의 성능에 영향을 미치게 된다. 본 논문에서는 이러한 사실을 바탕으로 싸인파 변조 및 구형파 변조 방식에 따른 CGH를 제작하고 재생 영상의 특성을 분석하였다. 또한 각각의 변조방식에 대하여 진폭 및 위상형, 위상형 그리고 이진 위상형 CGH의 재생 능력을 분석하였다. The diffraction efficiencies of gratings are affected by the inner structure which is determined by modulation type. CGH (Computer generated Hologram) basically uses the principles of a diffraction grating. As like as the diffraction gratings the patterns recorded in the CGH are different according to modulation methods which result in the performances of the reconstructed images. In this paper, on this fact CGHs are recorded according to sinusoidal and rectangular modulation methods and the characteristics of reconstructed images are analyzed. Also the reconstruction performances of the amplitude and phase, phase-only and binary phase CGH are analyzed.

Optical information security system using an interference-based computer-generated hologram and <inline-formula><math altimg="none" display="inline" overflow="scroll"><mrow><msub><mi>BaTiO</mi><mn>3</mn></msub></mrow></math></inline-formula>

This paper proposes a novel simple image encryption and decryption technique based on the principle of interference and a binary-phase computer-generated hologram (BPCGH). To obtain a stable interference pattern, a technique involving a photorefractive material is also proposed. The proposed scheme is composed of digital encryption and optoelectronic decryption. For the encryption process, a BPCGH that reconstructs the original image perfectly is designed, using a simulated annealing algorithm, and the resulting hologram is regarded as the image to be encrypted digitally. In addition, a reference image with key information is created using a random two-phase generator. The hologram is then encrypted using the reference image and the interference rule. For the decryption process, the interference intensity is obtained by interfering the reference image and the encrypted image, binarized with software, and then transformed into phase information. Finally, the original image is recovered by an inverse Fourier transformation of the binary-phase information. During this process, since the intensity information generated by the interference of the two images is very sensitive to external vibrations, a stable interference pattern is achieved using a self-pumped phase-conjugate mirror made of the photorefractive material BaTiO 3 .

Two-dimensional, three-dimensional, and gray-scale images reconstructed from computer-generated holograms designed by use of a direct-search method

A direct-search method for the computer design of holograms is demonstrated. Two-dimensional, three-dimensional, and containing holograms with different levels of intensity (gray scales) were designed, fabricated, and optically reconstructed. The number of effective gray levels and the image-intensity noise and contrast are discussed. A modification of the state-variables cost function used in the direct-search algorithm that permits reliable control of gray scales is presented. Optical reconstructions of two-dimensional, three-dimensional, and gray-scale binary phase computer-generated holograms are presented.

64-channel correlator implementing a Kohonen-like neural network for handwritten-digit recognition

We present an optical implementation of an improved version of the Kohonen map neural network applied to the recognition of handwritten digits taken from a postal code database. Improvements result from the introduction of supervision during the learning stage, a technique that also simplifies the map layer labeling. The experimental implementation is based on a frequency-multiplexed raster computer-generated hologram used to realize the required N(4) interconnection. The setup is shown to be equivalent to a 64-channel correlator. Computer simulations are used to study various detection and classification procedures. The results of the optical experiments, obtained with binary phase computer-generated holograms, are presented and shown to be in excellent agreement with the simulations.

Polarization-selective computer-generated holograms

We demonstrate polarization-selective computer-generated holograms with independent phase profiles for the two orthogonal linear polarizations. The holograms are made of two surface-relief-etched birefringent substrates joined face to face. We describe their design and fabrication and present experimental results for dual binaryphase computer-generated holograms fabricated in lithium niobate. The first-order diffraction efficiency varied from 6% to 25%, with as much as 40:1 contrast between polarizations. Such elements can be used in compact optoelectronic systems or combined with electro-optic polarization rotators to make electrically controlled optical elements.

Efficient multiple-image holographic optical element

An efficient holographic optical element that combines the beammultiplexing properties of binary-phase computer-generated holograms with the efficiency of volume holograms formed in dichromated gelatin is described. Experimental results for an element that improves both the efficiency and the signal-to-noise ratio of a computer-generated hologram are presented. The possibility of using this element as an optical interconnect is discussed.