In recent years, the resolution of video technology has been improved. As a result, the required data capacity is increasing as year by year. Therefore, storage that be able to store a huge amount of data is required. It is desirable for the storage to be able to store images for a long time, and holographic data storage is expected as long lifetime, high-density, large-capacity data storage. However, holographic data storage has not been commercially used yet because the size of holographic recording system is large, and it is difficult to increase the recording density further by the inter-pixel crosstalk noise and inter-page crosstalk noise. To achieve higher density, crosstalk separation is required. In this study, interpixel-crosstalk separation using a volume holographic optical element (VHOE) is investigated.
Volume holograms exhibit unique optical characteristics based on selective diffraction dependent on the state of incident light. For example, they are applicable to holographic data storage for ultra-high-definition video, holographic optical elements utilizing selective diffraction, super-resolution imaging, and optical combiners for AR head mount display. Since optical combiner is realized by using a partially reflective mirror, the larger the area to be displayed, the larger volume the mirror occupies. By using a holographic optical element, the volume occupied by the optical combiner can be decreased. However, thin holographic optical element exhibits strong wavelength dependence, so that multiple holographic optical elements are used for full color display. On the other hand, optical expansion system is important to decrease the volume of display system. In this study, a cylindrical wave volume holographic optical element was investigated to use as an optical combiner.
KEYWORDS: Holograms, Digital holography, 3D image reconstruction, Optical microscopy, Holography, Super resolution, Volume holography, Phase shifting, Holographic optical elements
Optical microscopes can observe living organisms under natural conditions. However, they have diffraction limit to use visible light, so it cannot also observe nano-level living organisms. We improved a super-resolution digital holographic microscopy to solve this problem. To fabricate this microscope, we used a spherical wave Volume Holographic Optical Element (VHOE). VHOE exhibits a function that light waves from two-point sources with a distance shorter than the wavelength are diffracted as plane waves with different wave vectors. This element was made of a two-chemistry photopolymer with a thickness of 10 mm. In our previous study, the diffractive waves from two points with an interval of 100 nm and a wavelength of 405 nm were individually observed by using the VHOE. That means that the resolution less than wavelength was achieved. In experiment, a test target was illuminated by a diode laser with a wavelength of 405 nm. The transmitted wave was diffracted, and the diffracted wave was combined with a reference wave by the VHOE. The interference pattern between the diffracted wave and the reference wave was captured by using an image sensor. Then, four-step phase shifting method was used by using a PZT mirror for phase imaging. The phase pattern is reconstructed by 2D Fourier transform because the wave vector is corresponding to the position.
In see-through head-mount displays such as AR display, lightweight characteristics are required for long-term use. In addition, large field of view and large eye-box are important as characteristics of head-mount displays. However, it is difficult to realize these characteristics simultaneously. To realize the characteristics, it is proposed that a cylindrical volume holographic optical element (CVHOE) is used as a waveguide for AR displays. In CVHOE, a cylindrical wave is diffracted as a plane wave. By using the CVHOE, multiple cylindrical waves can be transformed into multiple plane waves with different wave vectors. When pixels of a image is regarded as point sources, the point sources can be transformed into cylindrical waves. Therefore, point sources that consist of an image can be transformed into plane waves by using a cylindrical lens and CVHOE. By looking the CVHOE, the original point sources are imaged on a retina. Then, large eye-box can be achieved because of plane waves. Furthermore, large field of view can be enlarged by adjusting the diffraction angle of CVHOE. In this system, there is a characteristic that a CVHOE for a full-color display can be prepared by using a monochromatic light source. However, many times exposure are required in high-definition display. In this study, numerical simulation was performed to decrease the number of exposures. The method is based on perturbation theory in Maxwell’s equations. The diffraction properties of CVHOE were evaluated by the numerical simulation.
Volume holograms exhibit the characteristic of multiple optical functions in a common area by multiple exposure in preparation. From the characteristic, it is expected to be applied to large capacity recording medium and diffractive optical elements with unique functions. In this study, volume holograms are investigated to apply to diffractive optical elements for high-definition imaging of nanostructure. The assumed volume holographic diffractive optical element exhibits a function that light waves from two-point sources with a distance shorter than the wavelength are diffracted as plane waves with different wave vectors. When a volume hologram is prepared by exposing the interference fringes consist of a point source light and a plane wave, a plane wave is diffracted by illuminating a point source light onto the volume hologram. However, the wave vector of the diffracted plane wave is changed and the diffraction efficiency is decreased by shifting the position of the point source light. By wave vector filtering, the diffracted plane wave from a point source at shifted position becomes not to be detected. A volume hologram can be prepared that the point source at the shifted position is diffracted as a plane wave with a different wave vector by multiple exposure. Then, two-point sources can be resolved. The distance between two-point sources is called shift-selectivity. For preparing the volume holographic optical element, a photopolymer with a thickness of 10 mm was used to obtain short shift selectivity. The photopolymer was exposed by using a semiconductor lase with a wavelength of 405 nm. In this condition, a shift selectivity of 100 nm was achieved.
We have developed a holographic three-dimensional (3D) display with a wider viewing zone than conventional planar holograms by using a non-planar optical element generating a diverging spherical wave with a wide spreadangle. The convex parabolic mirror and non-planar holographic optical elements were used as such non-planar optical elements. If the computer-generated holograms are designed properly considering the reflection on the non-planar optical elements, a 3D object can be reconstructed inside them as a virtual image. Viewers can observe 3D objects from the periphery of the 3D object, and optical experiments successfully demonstrated our proposed methods.
The resolution of images is increasing year by year. High-definition images have a large amount of data so that high calculation cost is required for image processing. For example, when original data is restored from non-clear high-definition two dimensional coded images, it is necessary to improve the image quality. A volume holographic optical element works as a multiple lens for each pixel in an image so that spreading pixel patterns can be individually focused. Then, each pixel becomes clear and original data can be easily restored. However, it is difficult to analytically express the function of volume holographic optical elements. In our previous study, reconstructed images from a volume hologram, in which some data pages were recorded in multiple, were expressed by analytic function. The analytic function was called pixel amplitude function. In this study, the pixel amplitude function is used for an input image to a volume holographic optical element. Then, output image is analytically expressed.
In this study, we prepared a cylindrical wave diffractive optical element that diffracts color images using volume hologram technology to improve the performance and cost of HMDs.
In this study, we propose a method for reducing inter-pixel crosstalk noise using holographic optical elements, and confirm the reduction effect on 4×4 page data. Some experimental results are presented. undefined In this study, we propose a method for reducing inter-pixel crosstalk noise using holographic optical elements, and confirm the reduction effect on 4×4 page data. Some experimental results are presented.
This Conference Presentation, Improving method of noise robustness in holographic data storage using pixel amplitude function, was recorded at Photonics West held in San Francisco, California, United States
We propose a holographic augmented reality (AR) display by using a cylindrical holographic optical element (HOE). The cylindrical HOE is used as a wavelength-selective reflective screen. A three-dimensional (3D) object is not reconstructed on the cylindrical HOE directly, but behind it as a virtual image. Thus, it becomes possible to superimpose the 3D reconstructed image with a real-existent 3D object without physical contact: augmented reality can be achieved. Moreover, in our method, the shape of the HOE is not planar but cylindrical. Thanks to its shape, the viewing zone of our method becomes much wider than that of planar hologram, where the viewing zone is fundamentally limited to only the forward region of the planar hologram. In our method, information of the 3D object to be reconstructed is coded into a conventional planar hologram such as a spatial light modulator (SLM). Then, the wavefront modulated by the planar hologram enters the cylindrical HOE. Because the cylindrical HOE reflects the incident wavefront with a very wide diverging angle, viewers can observe the 3D object from a very wide horizontal range. For this purpose, our method utilizes the reflection on the cylindrical surface. Thus, holograms for modulating the wavefronts have to be designed considering the reflection on the cylindrical HOE properly. In our method, wavefront propagation via the cylindrical HOE is calculated based on the geometric optics. To verify our method, we performed optical experiments, and our holographic AR display was successfully demonstrated.
Recently, technology for high resolution device has improved. Accordingly, it is predicted that the demand is increasing. The device such as high-resolution display with amount of data requires large capacity data storage to store the data. Therefore, we considered that holographic data storage that is expected as large capacity can be used as storage device of UHD. However, many errors generate by noises in high density holographic data storage. It is supposed errors can be corrected by clarifying the cause of noises.
In order to analyze the noises and correct the errors, light propagation analysis is required. Although several light propagation analysis methods are established, these are not suitable for analyzing holographic data storage. One of the reasons why not suitable is that heavy computation loads can be time-consuming in conventional methods because the thickness of volume holograms are much thicker than the wavelength of propagating light.
In this study, we propose light propagation analysis method based on analytic function. In addition, we investigate method that can calculate light propagation in holographic data storage using the method.
In holographic data storage, the information is recorded as electric susceptibility distribution of recording medium.
This study introduces a parameter related light intensity and sensitive of medium and the Maxwell’s wave equation is expanded by Born-expansion using the parameter. Then, solutions of the wave equation can be solved analytically. Therefore, behavior of light wave in volume hologram can be expressed. We analyze the noises and investigate methods correcting errors by using this method.
KEYWORDS: Data storage, Holography, Image sensors, Signal detection, Digital holography, Detection theory, Holographic data storage systems, Volume holography, Data archive systems, Image quality
Data amount circulated in the world is increasing year by year. Most of data are not desirable to erase even though the access frequency is not so high. To store the data, a data storage with long lifetime is required. TV program archives are the one of them and the data amount are increased with increasing the pixel number of display devices. Therefore, holographic data storage with large data capacity and long lifetime is expected for UHD TV. In holographic data storage, coded images called data pages are recorded on a recording medium by volume holography. However, the image quality is reduced by low-pass spatial frequency filtering, optical system error, and characteristics of recording medium. When the properties of optical system including recording medium are precisely known, the change of data page pattern can be expressed by an analytical function. In reconstruction, a deteriorated data page pattern from a volume hologram is captured by an image sensor. Then, an image sensor pixel detects signals from multiple data page pixels because a pixel pattern is spread. The weight coefficients from all data page pixels to an image sensor pixel can be calculated by using the analytical function. When the weight coefficients are calculated at all image sensor pixels, simultaneous equations are obtained. Original data page patterns can be reconstructed by solving the simultaneous equations. In this paper, the expression method of a deteriorated data page pattern with an analytical function is discussed.
Circularly polarized optical vortices are known to possess spin and angular momenta dependent on the degree of circular polarization and topological charge. And it is expected to rotate when circularly polarized optical vortices are irradiated on nanoscale materials possessing electric susceptibility. This phenomenon can be understood from the time average of optical Lorentz force and when applying the electromagnetic field of arbitrary optical vortex, the direction of rotational force is not dependent on the frequency of incident light that has been confirmed by previous studies. Therefore, the rotational force can be induced by white light with common rotation axis. And it means that can convert sunlight into circularly polarized optical vortices, which has the merit of being an increase in light intensity and renewable energy. In addition, if it is possible to exert rotational motion on the object only by light irradiation, it is possible to rotate a nanoscale gear without requiring an electric circuit. In this study, in order to generate a white light optical vortex with circular polarization, a computer generated hologram (CGH) with structural birefringence was fabricated by electron beam lithography. The CGH exhibits a beam splitting property, in which arbitrary polarized light is split to a transparent light and two diffracted beams with mutually opposite handedness. By extracting a diffracted beam, a circularly polarized white light optical vortex beam was obtained. And the interaction between the generated optical vortex and a matter is investigated.
Holographic data storage is a data storage with large data amount recorded by volume holography. Holography is well known as a method to record three-dimensional scenes. The principle is roughly established and major characteristics are well understood. In the case of three-dimensional scenes, some noises are acceptable because they are compensated by our brain. However, in the case of holographic data storage, the recording images are minute two-dimensional coded patterns so that the images are not robust for noises. Therefore, rigorous expressions of recording signal is required. In this study, the recording signal wave is expressed by Taylor expansion for small argument and asymptotic expansion for large argument. Then, the filling factor of pixels in a spatial light modulator (SLM), the size and the position shift of a rectangular aperture at a Fourier plane are considered. When the signal wave is ideally reconstructed, the signal wave at an image plane is captured by using an image sensor. Then, the signal wave is integrated by the area of pixels in the image sensor. In this study, the integral is analytically calculated whereas it is numerically calculated in general because the signal wave is expressed by analytic functions. Therefore, interpixel crosstalk is easily evaluated. In our previous study, high-density recording method of binary data pages is proposed by using four-step phase mask. The high-density recording characteristics are evaluated by analytic functions. When parameters such as the filling factor of pixels in a SLM and an image sensor and the size and the position shift of a rectangular aperture can be known, the analytic functions are obtained. Then, the analytic functions are expected for error corrections.
This paper presents a fast calculation method for spherical computer-generated hologram by using a spherical harmonic transform. A three-dimensional (3D) object defined in the 3D Cartesian coordinate system is numerically Fourier transformed with fast Fourier transforms (FFTs). Fourier components on the spherical surface of the radius 1/λ are extracted. The wavefronts on the spherical surface can be calculated from the single spherical Fourier components. This paper reveals the analytical diffraction integral between the spherical Fourier components and the wavefront on the spherical surface. This diffraction integral is expressed in the form of convolution integral on the sphere and can be calculated very fast based on the spherical harmonic transform. By the numerical simulation, the validity and the effectiveness of our proposal has been verified.
We discovered that a helical surface relief can be created in azo-polymer film merely by the irradiation of circularly-polarized
light without any orbital angular momentum. The chirality of the surface relief was also determined by the
handedness of the circular polarized light.
Holographic memory is expected for cold storage because of the features of huge data capacity, high data transfer rate, and long life time. In holographic memory, a signal beam is modulated by a spatial light modulator according to data pages. The recording density is dependent on information amount per pixel in a data page. However, a binary spatial light modulator is used to realize high data transfer rate in general. In our previous study, an optical conversion method from binary data to multilevel data has been proposed. In this paper, the principle of the method is experimentally verified.
In the proposed method, a data page consists of symbols with 2x2 pixels and a four-step phase mask is used. Then, the complex amplitudes of four pixels in a symbol become positive real, positive imaginary, negative real, and negative imaginary values, respectively. A square pixel pattern is spread by spatial frequency filtering with a square aperture in a Fourier plane. When the aperture size is too small, the complex amplitude of four pixels in a symbol is superposed and a symbol is regarded as a pixel with a complex number.
In this work, a data page pattern with a four-step phase pattern was generated by using a computer-generated circular polarization hologram (CGCPH). The CGCPH was prepared by electron beam lithography. The page data pattern is Fourier transformed by a lens and spatially filtered by a variable rectangular aperture. The complex amplitude of the spatial filtered data page pattern was measured by digital holography and the principle was experimentally verified.
KEYWORDS: Thermography, 3D image processing, Cameras, Diagnostics, Image sensors, 3D acquisition, 3D image reconstruction, 3D scanning, Visible radiation, Microlens array
This paper proposes a method to obtain three-dimensional thermal radiation distribution. In the method, multiple oblique projection thermal images are obtained by moving a target object and three-dimensional thermal radiation distribution is reconstructed based on projection-slice theorem. In experiment, incandescent light bulbs or a plant is used as a sample object. The three-dimensional position measured is coincided with actual position and the principle is experimentally verified.
In this study, a light-driven deformable mirror is fabricated by electron beam lithography. The mirror is consisted of a deformation layer and a micromirror array. The deformation layer is made of an azobenzene polymer and the micromirro array is deposited on the deformation layer. The deformation of azobenzene polymer is induced by illuminating a continuum wave beam or femto-second pulse laser beam. Then, the micromirror is displaced. The displacement modulation is experimentally confirmed by interference measurement.
This paper proposes a method to increase the recording density of binary data pages in holographic memory. The recording density is increased by decreasing the rectangular aperture size on a Fourier plane. To extract the original data page from the low quality image, a four-step phase mask is designed. The principle of the proposed method is numerically verified.
This paper introduces a method to reconstruct a polarization hologram recorded by dual-channel polarization holography. In this method, simultaneously reconstructed two images with p- and s-polarization components are captured by an image sensor with p- and s-polarized plane waves. The principle is explained and numerically verified.
This paper introduces a novel polarization structured light pattern projector was done by taking into account the
unique characteristic of the pixelated camera and a spatial light modulator (SLM) used. Height variations of reflective
samples are retrieved by using fringe contrast modulation on an uniaxial configuration. By placing a special retardance
pattern on the SLM, the pixelated camera will detect a phase shifted sinusoidal pattern where later its contrast change
will be used to retrieve the height information of the sample under study. The presented system takes into account the
defocus change obtained by the height variation of the sample by encoding the information on the fringe contrast of the
projected structured light pattern by the SLM. The final purpose of this work is to present a single shot 3D profilometry
system based in fringe contrast analysis. Experimental results of a moving glass slide are presented.
Holographic data storage based on polarization techniques is proposed. Angular and shift multiplexing techniques, as well as polarization multiplexing, are developed to increase storage capacity. Some experimental results are presented.
Optical information of linearly polarized light recorded on a photoinduced birefringent medium
was clearly expressed using an optical anisotropy matrix in the circular polarization basis.
The theoretical expression was related to the principle of retardagraphy,
that is, an optical recording technique for the retardance pattern of an optical anisotropic object.
Furthermore, the polarization holographic characteristics were explained by the principle.
As a demonstration of optical information recording,
a retardance pattern displayed on a parallel aligned
liquid crystal spatial light modulator was recorded on an azobenzene copolymer film,
and the retardance pattern was reconstructed by imaging polarimetry.
The transmission axis of a polarizer in the imaging polarimetric system
was adjusted using a homogeneous pattern.
Multi-valued phase patterns were multiply recorded by retardagraphy in order to improve recording density and data
transfer rate. In the experiment, the phase pattern consists of four values were recorded on a polarization-sensitive
medium by focusing the recording beam, and three patterns were multiply recorded by shifting the focal point. The
recorded patterns could be independently reconstructed.
An optical recording technique, called retardagraphy, can record a retardance pattern of a birefringent object on a polarization-sensitive medium made of azobenzene copolymer. In holography, a recording laser beam must be split into signal and reference parts. In contrast, it is not necessary for the retardagrapy to split the recording laser beam. This feature simplifies the optical system. The multi-valued phase pattern recorded on the polarization-sensitive medium can be reconstructed by measuring a retardation between two polarization components. The optical recording and reconstructing methods of binary and multi-valued phase patterns are demonstrated by retardagraphy.
A remarkable conversion efficiency from laser to protons is demonstrated by particle simulations in a laser-foil
interaction. The total laser-proton conversion efficiency becomes 16.7% in an optimized multi-hole target, though a
conventional plane foil target serves a low efficiency. When an intense short-pulse laser illuminates the thin foil target,
the foil electrons are accelerated around the target by the intense laser. The hot electrons generate a strong electric field,
which accelerates the foil protons, and the proton beam is generated. In our previous study, we found that multihole thin-foil
target was efficient for the energy conversion from laser to protons [Phys. Rev. E 78, 046401 (2008)], and the energy
conversion efficiency was 9.3%. In this paper the results clarify the role of the target hole thickness and depth in the
laser-proton energy conversion. The optimized multi-hole foil target provides a remarkable increase in the laser-proton
energy conversion efficiency.
Multiple recording characteristics of polarization hologram was investigated for high density optical data storage.
Polarization and angular multiplexing was performed. Some polarization holograms were independently
recorded on the same position of a polarization-sensitive medium. The recorded images could be independently
reconstructed.
An optical recording technique, called retardagraphy, has been proposed, in which, retardance distribution of a birefringent object can be recorded on a polarization-sensitive medium made of an azobenzene copolymer. The phase difference distribution between two orthogonal polarization components of the wavefront to be recorded can be directly recorded. The multi-valued phase pattern recorded can be reconstructed by measuring retardation between two polarization components by an imaging polarimetry technique. In this paper, the optical recording and reconstructing methods in retardagraphy are presented. Its application to optical mass data storage is discussed.
A new technique is proposed, in which a phase-shifting algorithm
utilizing the optical Doppler effect and a high-speed CMOS
camera are employed. In many phase-shifting algorithms,
the phase distribution of the object is calculated by
using a few reference phases with equal phase difference. In our proposed method, a reference mirror is moved continuously or randomly to make phase shift based on the Doppler effect. The phase distribution of the object is calculated by Fourier transforming the time-depending interference fringe data. If the reference phase shift is equally introduced to all the data points in the interference fringe image,
the phase distribution at the peak frequency component
in the Fourier spectrum gives the phase distribution of the object.
Since a few hundred or more images were required in this method, a CMOS camera with a high frame rate of 500fps was used.
Digital holography utilizing optical Doppler effect is proposed,
and the surface shapes of objects are measured
in an environment with a disturbance.
In this method, the time variation of interference fringes are recorded using a high speed CMOS camera.
The complex amplitude of the object beam included in the recorded images are extracted by time-domain Fourier analysis.
Light propagation is calculated using the complex amplitude,
and the surface shape of the concave mirror is obtained.
We also apply the Doppler phase-shift digital
holography to two-wavelength interferometry.
The phase distribution for the effective wavelength
with two different wavalenghes of
light sources is obtained.
The experimental results show our proposed method is very useful
in industrial sensing and experimental mechanics.
Photoinduced birefringence in the film made of our azobenzene copolymer was demonstrated using blue excitation
laser beams and observed by a red probe laser beam. The birefringence values was obtained by polarimeter. The
polarization state of the probe beam was changed by the photoinduced birefringent film when the polarization
state is not agreed with the polarization state of the excitation laser beam. Then, a polarization component
orthogonal to the polarization state of the incident probe beam was observed. Using the principle, an image
pattern was recorded in the film using one-beam.
Theoretical models for photoinduced birefringence and chiral structure formation in achiral azobenzene-containing materials were proposed considering phototriggered molecular reorientation via trans-cis-trans photoisomerization cycles of azobenzene. The photoisomerization cycles were expressed by two rate equations of the orientation distributions of trans- and cis-forms. Phototriggered molecular reorientation by illuminating linearly polarized light was verified theoretically. The photoinduced helical structure formation was simualted by elliptically polarized light. The molecular rotation angle was dependent on the sign of the ellipticity. The time evolution of the helical structure formation was consistent with the experimental result that reported by other papers.
A novel photoresponsive polymer containing bisazo chromophores have been synthesized for comparative study with
monoazo polymer. Since the bisazo structure has an extended Π-conjugation electronic system, it is expected to have
large intrinsic molecular birefringence that can realize large macroscopic photoinduced birefringence (ΔnPI) via
photoinduced molecular re-orientation process of bisazo molecules. As a result, it was found that the large value of ΔnPI
(0.17) could be obtained by using bisazo polymer at 514.5nm excitation with 1.0W/cm2.
Surface relief holograms are fabricated by means of irradiation of laser interference patterns. The diffraction efficiency
and the surface relief depth depend on the writing energy and the polarization of the writing laser beam. The formation
and erasure of photoinduced surface relief gratings (SRGs) on azobenzene-containing polymers are simulated using a
numerical model based on the moving-particle semi-implicit (MPS) method. Particle motions in SRG formation and
erasure are calculated and the SRG pitch and polarization dependences of the SRG growing and erasing rates are
investigated. These theoretical results coincide qualitatively with our experimental results.
In this paper, new azobenzene copolymers (PCDY and PPDY) with large photoinduced birefringence and good long-term stability of a recorded data have been introduced. The largest photoinduced value of 0.289 was obtained on the PCDY50 at 458 nm light irradiation. This value was brought about a result of molecular cooperative reorientation of cyanoazo and bisazobenzene moieties. It should be noted that the PCDY50 exhibited quite stable characteristics on the archival viewpoint. Furthermore, if we can optimize experimental conditions, more than 105 cycles of reversible data storage could be achieved. Making use of these superior characteristics of the PCDY50, an application for rewritable holographic memory and/or other optical addressable devices is anticipated.
The formation of holographic surface relief gratings (SRGs) on azobenzene containing polymers are simulated using the moving particle semi-implicit (MPS) method. The gradient force of optical electric field and the influence of surface tension were considered as the driving forces for mass transport. The particle motions of SRG formation are calculated by giving particles two beams interference with various polarization states. The model for time evolution of SRG formation coincided with experimental results qualitatively.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.