KEYWORDS: 3D modeling, Data modeling, Depth maps, 3D acquisition, RGB color model, Neural networks, Data acquisition, Holographic displays, Computer generated holography, 3D image processing
We propose an advanced layering method of integrated dept-position map for real-world object. The depth map of far field object has not contain depth information and impossible to layering the far field objects. Therefore, the position map was rendered from generated high-quality 3D model used deep neural network, it is accurately layering for far field object. However, it has field loss of 3D model depending on the color density, when layering at near field. Therefore, by combining the depth map with the position map, the proposed integrated depth-position map was obtained for accurately layering in far and near field objects.
KEYWORDS: Cameras, Image acquisition, 3D modeling, 3D acquisition, 3D displays, Integral imaging, Image processing, Deep learning, 3D image processing, Digital cameras
In this report, we proposed an advanced integral imaging 3D display system using a simplified high-resolution light field image acquisition method. A simplified light field image acquisition method consists of a minimized number of cameras (three cameras placed along the vertical axis) to acquire the high-resolution perspectives of a full-parallax light field image. Since the number of cameras is minimized, the number of perspectives (3×N) and the specifications of the 3D integral imaging display unit (N×N elemental lenses) cannot be matched. It is possible to utilize the additional intermediate-view elemental image generation method in the vertical axis; however, the generation of the vertical viewpoints as many as the number of elemental lenses is a quite complex process and requires huge computation/long processing time. Therefore, in this case, we use a pre-trained deep learning model, in order to generate the intermediate information between the vertical viewpoints. Here, the corrected perspectives are inputted into a custom-trained deep learning model, and a deep learning model analyzes and renders the remaining intermediate viewpoints along the vertical axis, 3×N → N×N. The elemental image array is generated from the newly generated N×N perspectives via the pixel rearrangement method; finally, the full-parallax and natural-view 3D visualization of the real-world object is displayed on the integral imaging 3D display unit.
The waveguide-type full-color 3D-AR display system based on the integral imaging technique using the holographic mirror array is proposed. In the experiment, the AR feature has been successfully verified that the real-world scene and reconstructed virtual full-color 3D image were observed simultaneously.
A holographic stereogram printing system is a valuable method to output the natural-view holographic three-dimensional images. Here, the 3D information of the object such as parallax and depth information, are encoded into the elemental holograms, i.e. hogels, and recorded onto the holographic material via the laser illumination of the holographic printing process. However, according to the low resolution of the hogels, the quality of the printed image is reduced. Therefore, in this paper, we propose the real object-based fully automatic high-resolution light field image acquisition system using the one-directional moving camera array and smart motor-driven stage. The proposed high-resolution light field image acquisition system includes interconnected multiple cameras with one-dimensional configuration, the multi-functional smart motor and controller, and the computer-based integration between the cameras and smart motor. After the user inputs the main parameters such as the number of perspectives and distance/rotation between each neighboring perspectives, the multiple cameras capture the high-resolution perspectives of the real object automatically, by shifting and rotating on the smart motor-driven stage, and the captured images are utilized for the hogel generation of the holographic stereogram printing system. Finally, the natural-view holographic three-dimensional visualization of the real-object is outputted on the holographic material through the holographic stereogram printing system. The proposed method verified through the optical experiment, and the experimental results confirmed that the proposed onedimensional moving camera array-based light field image system can be an effective way to acquire the light field images for holographic stereogram printing.
In this paper, a fast and efficient multiple wavefront recording planes method with parallel processing is proposed for enhancing the image quality and generation speed of point cloud-based holograms. The proposed method gives an optimized fixed active area to generate depth-related multiple WRPs to improve the calculation speed and enhance the color uniformity of full-color hologram. In other to parallel processing the ray tracing intermediate plane is created. This method is more effective when the number of depths is smaller, such as the RGB-D image.
A novel asymmetric public key cryptographic algorithm is proposed by modifying the conventional RSA public key protocol, which can be optically implemented by using the phase-shifting digital holography. The proposed method involves a two-key encryption scheme so that it provides stronger security than the one-key encryption method. Optically, two unknown randomly generated numbers are changed to digital holograms which are used as public keys for asymmetric cryptography. The generated public keys and cipher texts by using them are Fourier transformed digital holograms with 256 gray level quantized intensities which are recorded on CCDs. The original plain text can be decrypted only with correct pairs of public-private keys and the holographic encryption-decryption keys in the proposed algorithm. The proposed optical schematic has an advantage of producing an enhanced asymmetric public key cryptosystem compared to the conventional RSA cryptosystem. The results of computer simulations verify that the proposed method shows the feasibility of application to an asymmetric public key cryptosystem with high security strength.
In this paper, we propose the well-enhancing method for the resolution of the reconstructed image of the mobile threedimensional integral imaging display system. A mobile 3D integral imaging display system is a valuable way to acquire the 3D information of real objects and display the realistic 3D visualizations of them on the mobile display. Here, the 3D color and depth information are acquired by the 3D scanner, and the elemental image array (EIA) is generated from the acquired 3D information virtually. However, the resolution of the EIA is quite low due to the low-resolution of the acquired depth information, and it affects the final reconstructed image resolution. In order to enhance the resolution of reconstructed images, the EIA resolution should be improved by increasing the number of elemental images, because the resolution of the reconstructed image depends on the number of elemental images. For the comfortable observation, the interpolation process should be iterated at least twice or three times. However, if the interpolation process is iterated more than twice, the reconstructed image is damaged, and the quality is degraded considerably. In order to improve the resolution of reconstructed images well, while maintaining the image quality, we applied the additional convolutional super-resolution algorithm instead of the interpolation process. Finally, the 3D visualizations with a higher resolution and fine-quality are displayed on the mobile display.
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.
We propose an optical design of cipher block chaining (CBC) encryption mode using digital holography, which is implemented by the two-step quadrature phase-shifting digital holographic encryption technique using orthogonal polarization. A block of plain text is encrypted with the encryption key by applying the two-step phase-shifting digital holographic method; then, it is changed into cipher text blocks which are digital holograms. Optically, these digital holograms with the encrypted information are Fourier transform holograms and are recorded onto charge-coupled devices with 256 quantization gray levels. This means that the proposed optical CBC encryption is a scheme that has an analog-type of pseudorandom pattern information in the cipher text, while the conventional electronic CBC encryption is a kind of bitwise block message encryption processed by digital bits. Also, the proposed method enables the cryptosystem to have higher security strength and faster processing than the conventional electronic method because of the large two-dimensional (2-D) array key space and parallel processing. The results of computer simulations verify that the proposed optical CBC encryption design is very effective in CBC mode due to fast and secure optical encryption of 2-D data and shows the feasibility for the CBC encryption mode.
We propose an optical design of cipher block chaining (CBC) encryption by using digital holographic technique,
which has higher security than the conventional electronic method because of the analog-type randomized cipher text
with 2-D array. In this paper, an optical design of CBC encryption mode is implemented by 2-step quadrature phase-shifting
digital holographic encryption technique using orthogonal polarization. A block of plain text is encrypted with
the encryption key by applying 2-step phase-shifting digital holography, and it is changed into cipher text blocks which
are digital holograms. These ciphered digital holograms with the encrypted information are Fourier transform holograms
and are recorded on CCDs with 256 gray levels quantized intensities. The decryption is computed by these encrypted
digital holograms of cipher texts, the same encryption key and the previous cipher text. Results of computer simulations
are presented to verify that the proposed method shows the feasibility in the high secure CBC encryption system.
We propose a new optical one-time password(OTP) authentication method by using digital holography, which enhances security strength in the cryptosystem compared to the conventional electronic OTP method. In this paper, a challenge-response optical OTP authentication based on two-factor authentication is presented by 2-step quadrature phase-shifting digital holography using orthogonal polarization, and two-way authentication is also performed using the challenge-response handshake in both directions. The ID (identification), PW (password) and OTP information are encrypted with a shared key by applying phase-shifting digital holography, and these encrypted information are verified each other by the shared key. Because the encrypted digital holograms which are transmitted to the other party are expressed as random distribution, it guards against a replay attack and results in higher security level. Optically, encrypted digital hologram in our method is Fourier transform hologram and is recorded on CCD with 256 gray-level quantized intensities. The proposed method has an advantage that it does not need a time-synchronized OTP and can be applied to various security services. Computer experiments show that the proposed method is suitable for high secure OTP authentication.
In this paper, the design and produce of the wedge-shaped waveguide head-mounted display (HMD) based on reflection holographic optical element (RHOE) are described. A variety of factors were considered when designing, such as loss of efficiency, volume, wide field of view (FOV), and eye box. The thickness of the designed wedge-shaped waveguide can be reduced to two times in comparison with the system that uses the conventional reflective optics in the waveguide. The measured optical efficiency of the monocular HMD using HOE is 34%, with 15° FOV and a large eye box. The results confirm that the designed and fabricated waveguide can be employed in future commercial HMD.
In this paper, we present the development of full color holographic optical element for light-emitting diodes display application using a photopolymer. The reflection HOE was evaluated by measuring the diffraction efficiencies of holographic volume gratings recorded individually at 633 nm, 532 nm, and 473nm wavelengths. The spectral characterization of the holographic optical element, recorded using a combined single beam, and recorded using sequential beam, was carried out. Practical methods for fabrication of high efficiency holographic optical element by single layer photopolymer were developed. As the reconstruction light source of the hologram, light-emitting diodes of 632nm, 523nm and 465nm in wavelength was used. The results represent a strong confirmation that the special recording method using photopolymer can be employed in future commercial holographic applications.
KEYWORDS: Digital holography, Binary data, Symmetric-key encryption, Phase shifts, Image encryption, Holograms, Holography, 3D image reconstruction, Computer security, Signal to noise ratio
We propose a new optical symmetric cryptographic system with simultaneous encryption and transmission of binary
data and secret key by using dual phase-shifting digital holography. Dual phase-shifting digital holography contains two
inner and outer interferometers which are used for encrypting data and a secret key at the same time. The technique using
dual phase-shifting digital holographic interferometry is efficient because this scheme has an advantage of interference
fringe data acquiring time. Binary information data is encrypted by the secret key by applying phase-shifting digital
holographic method, and this secret key is also encrypted by phase-shifting digital holographic method and transmitted.
Encrypted digital hologram in our method is Fourier transform hologram and is recorded on CCD with 256 gray-level
quantized intensities. These encrypted digital holograms are able to be stored by computer and be transmitted over a
communication network. With this encrypted digital hologram, the original binary data are decrypted by the same secret
key. Simulation results show that the proposed method can be used for a cipher and security system.
In this paper, we demonstrate the application of the spiral phase filter for image enhancement in phase shifting digital
holographic microscopy system. The method is based on Fourier plane filtering of the microscopic image with a spiral
phase filter which is located at a computer controlled Spatial Light Modulator (SLM) in the optical imaging pathway of
phase shift digital holographic microscopy system. Spiral phase filter is designed by radial isotropic Hilbert transform.
The spiral phase filter as a spatial filter in Fourier plane of an imaging setup has been proposed as an isotropic edge
detection method providing strong contrast enhancement of microscopic amplitude and phase objects. Since all threedimensional
information is captured by phase shifting digital holographic microscopy, the reconstructed phase object or
cell is reconstructed clearly observed in three-dimension.
We propose a novel optical cryptography of gray-level information image using QPSK digital modulation method and
digital holographic technique. A gray-level information image is digitized into 8-bits binary information data by ASCII
encoding method and these binary information data are expressed by four pair of quadrature phase values in a block
having 2×2 pixels by QPSK digital modulation. After encoding and modulation, the size of data to be encrypted expands
two times more than the original size of gray-level image. The modified information with corresponded phase values is
displayed on a phase-type spatial light modulator and is encrypted with a security key by using optical digital holography.
The security key is expressed with random binary phase. Digital hologram in this method is Fourier transform hologram
and is recorded on CCD camera with 256 gray-level quantized intensities. These encrypted digital holograms are able to
be stored by computer and be transmitted over a communication network. With this encrypted digital hologram, the
phase values are reconstructed with the same security key by holographic technique and are decrypted into the original
gray-level information image by decoding. Simulation results show that the proposed method can be used for a cipher
and security system.
KEYWORDS: Digital holography, Phase shifts, Holograms, Digital imaging, Integral imaging, CCD cameras, 3D image reconstruction, 3D image processing, 3D displays, Charge-coupled devices
We propose a method generating elemental images for the auto-stereoscopic three-dimensional display technique,
integral imaging, using phase-shifting digital holography. Phase shifting digital holography is a way recording the digital
hologram by changing phase of the reference beam and extracting the complex field of the object beam. Since all 3D
information is captured by the phase-shifting digital holography, the elemental images for any specifications of the lens
array can be generated from single phase-shifting digital holography. We expanded the viewing angle of the generated
elemental image by using the synthetic aperture phase-shifting digital hologram. The principle of the proposed method is
verified experimentally.
We propose a digital holographic interference analysis method based on 2-step phase-shifting technique for measuring
optical surface. The technique using 2-step phase-shifting digital interferometry is more efficient than multi-step phase-shifting
techniques because 2-step method has an advantage of the reduced number of interferograms. In this
measurement system, 2-step phase-shifting digital interferograms are acquired by moving the reference flat mirror
surface which is attached to PZT with phase step of 0 or π/2 in the reference beam path and are recorded on CCD device.
The optical interferometry is designed on the basis of polarization characteristics of polarizing beam splitter. Therefore
the noise from outside turbulence can be decreased. The proposed 2-step algorithm uses the relative phase difference of
the neighbor pixels. Experiment has been carried out on the optical mirror. The measurement of the optical mirror
surface topography shows that the result using 2-step algorithm is similar to that of other multi-step algorithms. Thus, the
proposed method is expected to be used in nondestructive testing of optical components.
A fully optical encryption system based on the single-phase encryption method is presented. A two-dimensional array of
real-valued data is phase encoded and scrambled with a random phase key for encryption. The encrypted data is stored
holographically in a DuPont photopolymer, and is reconstructed by conjugate readout. The original data can be retrieved
using a same phase key for decryption and an interferometer for phase-to-intensity conversion. The influence of a limited
bandwidth on the bit-error-rate in the decrypted data is evaluated. With binary data, error-free decryption can be possible
even when a large fraction of encrypted data is lost.
An improved image encryption/decryption approach is proposed. In the encryption system, a binary amplitude image is
encoded in the Fourier domain. Then, the encoded image is scrambled with a random binary phase image to produce the
encrypted image. Both the encoding and encryption processes are done electronically. The encrypted image is stored in
an encrypted phase mask of which the transmittance is proportional to the phase components of that image. In the
decryption process, the encrypted phase mask is optically descrambled with another phase mask which has the
transmittance identical to phase components of the random image used in the encryption process. The descrambled field
is inversely Fourier transformed by a Fourier lens in order to reproduce the original image. The simplicity and the
misalignment free characteristics are the most significant advantages of our method. The Fourier encoding process using
an optimization algorithm with iteration technique is discussed in detail. The effect of noise on the quality of the
decrypted image is investigated. The innovation of the system is demonstrated through simulations. The most critical
issue of our technique is that the encryption process requires an optimization search which consumes some computation
time so that the system is expected to be applied for unreal-time applications.
We propose an optical encryption/decryption technique based on 2-step phase-shifting digital holography for a cipher
system. The technique using 2-step phase-shifting digital holography is more efficient than 4-step phase-shifting digital
holography because the 2-step method has less data than 4-step method to restore or transmit the encrypted data. In our
system, 2-step phase-shifting digital holograms are acquired by moving the PZT mirror with phase step of 0 or &pgr;/2 in the
reference beam path and are recorded on CCD camera. The information data and the key are expressed with random
binary amplitude and random phase. Digital hologram in this method is Fourier transform hologram and digitized with
256 gray-level. DC-term removal is essential to reconstruct and decrypt the original binary data information. The
simulation shows that the proposed method gives good results for cipher system. The quantization error is also analyzed.
We present a novel information or key encryption and transmission technique based on phase-shifting digital holography for a security system. Phase-shifting digital holography is used for recording phase and amplitude information on CCD device. 4-step phase-shifting is implemented by moving the PZT mirror with equidistant phase steps of π/2. The information and the key are converted to random phase patterns. Digital hologram in this method is Fourier transform hologram and quantized with 256 gray-level. The basic idea is that we reuse a 256 gray-level digital hologram to encrypt the information or the key with 4-step phase-shifting digital holography. The encrypted binary data/image in the form of digital hologram can be transmitted through communication network, and is reconstructed and decrypted digitally. The simulation shows that the proposed method gives good results for a successive encryption/transmission.
KEYWORDS: Holography, Diffraction, 3D image reconstruction, Holograms, Digital imaging, Sol-gels, Data storage, Digital holography, Holographic materials, Optical properties
Monomer diffusion in an organic-inorganic nanocomposite films during the holographic recording was investigated. The photopolymer films with low shrinkage were prepared by dispersing an aromatic methacrylic monomer and a photo-initiator in organic-inorganic hybrid sol-gel matrices. The shrinkage of the photopolymer film and the diffusion of monomers during the holographic recording could be controlled by optimizing the content of an organically modified silica precursor (ORMOSIL) in the sol-gel matrices. The photopolymer film showed high diffraction efficiency (>90%) under an optimized condition. Photo-sensitivity, angular selectivity and application potential for holographic data storage and optical application will be discussed.
The effect of monomer functionality on the diffraction efficiency of the photopolymer containing multi- and monofunctional monomers was investigated. A mixture of tri-, di-, and mono functional monomers were dispersed in a solution of polysulfone dissolved in organic solvent containing a photo initiator. The monomer contents were varied by changing the ratio between them. The average functionality (Fav = Σ φiFi) was determined, where φi is the mol fraction of the monomer with functionality Fi. The holographic recording was performed and diffraction efficiency (η) of each film was determined by using a 532 nm laser. In the photopolymer film having an optimized composition, η was increased within 20 sec and reached a maximum of >90% with an exposure power of 5 mW laser. The rise of η (response time), maximum η, and stability of η value over prolonged recording were dependent on the monomer structure and composition and the average functionality. The result could be ascribed to the reactivity and functionality of monomers under interference light, to generate refractive index contrast.
In this paper, we propose a method to fabricate the grating for a laser diode shaper. During the grating recording, a beam that has polarization mode orthogonal to those of two recording beams is added. The intensity of the additional beam is controlled by a spatial light modulator to provide the spatial variation of intensity modulation, which leads to the difference of the saturation diffraction efficiency. As the results of the experiment, the laser beam shaped by the obtained grating has Gaussian desired profile intensity and is not aberration along the propagation.
In this paper, we present a scheme of recording apodized grating using an additional laser beam polarized orthogonally to two recording beams. The additional beam has a function to control beam intensity modulation of the recording beams and, therefore, changes the saturated modulation amplitude of the grating. An investigation of the diffraction efficiency depending on the intensity modulation is implemented in DuPont’s HRF-150-38 photopolymer. As results of the experiment, holographic apodized gratings with uniform, inverse Gaussian, and triangular profiles are fabricated successfully in this material.
Fabricating holographic apodized gratings is often impeded by nonlinear property of materials, which makes the resultant profile out of expectation. In this paper, the new scheme to fabricate Gaussian apodized grating is proposed. Instead of fixed Gaussian recording beams, recording beam profiles that can compensate the nonlinear sensitivity of the material at low recording intensities are created by a gray level spatial light modulator (SLM). DuPont’s HRF-150-38 photopolymer is chosen because of its stability and ease to use. As the first result of the experiment, a Gaussian grating of 2.7±0.02mm standard deviation is recorded at 0.3mW/cm2 recording intensity after exposure of 300 seconds.
Organic-inorganic nanocomposite films were prepared by dispersing an aromatic methacrylic monomer and a photo-initiator in organic-inorganic hybrid sol-gel matrices. The film properties could be controlled by optimizing the content of an organically modified silica precursor (TSPEG) in the sol-gel matrices. The photopolymer film modified with the organic chain (TSPEG) showed high diffraction efficiency (>90%) under an optimized condition. High diffraction efficiency could be ascribed to the fast diffusion and efficient polymerization of monomers under interference light to generate refractive index modulation. The TSPEG modified photopolymer film could be successfully used for holographic memory. Angular selectivity of the film were 0.46 ~ 0.16 depending on the film thickness in the incident angles between 20° ~ 70°. A digital holographic image and a real object were recorded successfully in the photopolymer film.
We analyze the thermal properties of the DuPont HRF150-38 photopolymer for digital holographic card manufacture. In case of recording after heating, the diffraction efficiency of the hologram is more than 70% at 100°C but is decreased exponentially at temperatures over 100°C. It is observed in the recording before heating that the diffraction efficiency of the hologram fixed by a UV light is increased to approximately 10% at 100°C, but the hologram are erased at temperatures over 120°C.
Parallel stereoscopic camera has a linear relationship between vergence and focus control. We introduced the automatic control method for a stereoscopic camera system that uses the relationship between vergence and focus of a parallel stereoscopic camera. The automatic control method uses disparity compensation of the acquired image pair from the stereoscopic camera. For faster extraction of disparity information, the proposed binocular disparity estimation method by the one-dimensional cepstral filter algorithm would be investigated. The suggested system in this study substantially reduced the controlling time and error-ratio so as to make it possible to achieve natural and clear images.
Multi-phase and binary-phase computer-generated holograms were designed and demonstrated for full-color image generation. Optimize a phase profile of the hologram that achieves each color image, we employed a simulated annealing method. The design binary phase hologram had the diffraction efficiency of 33.23 percent and the reconstruction error of 0.367 X 10-2. And eight phase hologram had the diffraction efficiency of 67.92 percent and the reconstruction error of 0.273 X 10-2. The designed BPH was fabricated by micro photolithographic technique with a minimum pixel width of 5micrometers . And the it was reconstructed using by two Ar-ion lasers and a He-Ne laser. In addition, the color dispersion characteristic of the fabricate grating and scaling problem of the reconstructed image were discussed.
For analysis of an effective phase code multiplexing in a holographic memory system, the Hadamard matrix (HAM) and the pseudorandom phase code (PRC) are generated and used as a reference beam. In computer simulations, the size of the address beam is fixed to 32 X 32 pixels, and 0%, 5%, 10%, 15%, 20%, or 25% phase error rate in a pixel is purposely added to the real phase values in order to consider the nonlinear phase modulation characteristics of the practical spatial-light modulator. Crosstalks and signal-to-noise ratios (SNRs) are comparatively analyzed for these two phase codes by calculating the auto- and cross-correlation. The cross-correlation mean values of the PRC and the HAM are 0.067 and 0.139, respectively, which means that the SNR of the PRC is higher than the HAM.
The possibility of solid-state ring laser (SSRL) as a gyroscope was examined first in a frame of diode-laser pumped monolithic Nd:YAG ring resonator. Weak coupling between the counter-propagating waves results in antiphase sinusoidal self-modulation of the intensities. It is observed that the self-modulation frequencies depend on the external rotation rate.
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