Search

We experimentally implemented and proved the concept of multiplexing and demultiplexing in digital images using virtual phase conjugation, which was proposed in our previous study. In the experiment, we concluded that two digital images multiplexed in a single signal beam are recorded in a holographic medium, and these images are independently and successfully reproduced. In this method, the digital images are multiplexed by superimposing them on a complex amplitude, and not using volume hologram’s multiplexing. Thus, the exposure amount in the holographic medium is constant regardless of the number of multiplexing of digital images, and the method has great potential for achieving high recording density.

The intrinsic markers of nanoscale morphological alteration in fixed tissue biopsy referred to as disorder strength and local correlation length, which can be easily and time-efficiently obtained from quantitative phase images, are introduced. After presenting how to extract these markers from quantitative phase images obtained by highly sensitive quantitative phase imaging system, spatial light interference microscopy (SLIM), we demonstrate the effectiveness of these markers for diagnosis of benign and malignant breast tissues.

For increasing the data density of holographic data storage (HDS), combining more than two multiplexing techniques is effective. This is also true in self-referential holographic data storage (SR-HDS) that enables holographic recording purely with a single beam. In this paper, a focus-shift multiplexing technique is applied to $$xy$$ -shift multiplexed SR-HDS, the feasibility of which has been shown in our previous work. The focus-shift multiplexing technique enables the multiplexing of datapages by slightly changing the focal length of the objective lens. However, the required focus-shift distance for multiplexing and the implementation method of the focus-shift have not been clarified. First, the focus-shift selectivity is investigated by the numerical simulations. In the case where the focus-shift multiplexing technique is applied to $$xy$$ -shift multiplexed SR-HDS, the inter-page crosstalk properties are clarified to decide the recording layout that can achieve a low-crosstalk readout. Second, the technique of displaying an additional phase pattern onto the spatial light modulator (SLM) is introduced, which is a focus-shift method without any special optical components, such as varifocal lenses. Finally, we investigate the relationship between the accuracy of the focus-shift and the parameters of SLM.

We propose a new intrinsic cancer marker in fixed tissue biopsy slides, which is based on the local spatial autocorrelation length obtained from quantitative phase images. The spatial autocorrelation length in a small region of the tissue phase image is sensitive to the nanoscale cellular morphological alterations and can hence inform on carcinogenesis. Therefore, this metric can potentially be used as an intrinsic cancer marker in histopathology. Typically, these correlation length maps are calculated by computing 2D Fourier transforms over image sub-regions – requiring long computational times. In this paper, we propose a more time efficient method of computing the correlation map and demonstrate its value for diagnosis of benign and malignant breast tissues. Our methodology is based on highly sensitive quantitative phase imaging data obtained by spatial light interference microscopy (SLIM).

The standard method for cancer diagnosis is the microscopic investigation of tissue biopsies. Because the tissues do not significantly absorb and scatter light, traditionally, the observation is performed using bright-field microscopy after staining. Although this approach has been widely adopted all over the world for 100 years, it generally takes a long preparation time and sometimes the early carcinogenesis is missed due to a variation in a quality of a staining. Quantitative phase imaging (QPI) can access objective information on thickness and refractive index changes from an unstained tissue slice, which cannot be observed by conventional microscopes. This can be an attractive advantage in the field of a medical diagnosis, especially since QPI can access the tissue architecture information with nanoscale sensitivity. In this paper, we used quantitative phase imaging to measure the tissue disorder strength, which is known as one of the effective markers of early carcinogenesis. We retrieved the disorder parameter from the local refractive index fluctuation map obtained by spatial light interference microscopy (SLIM). We show that SLIM imaging combined with the disorder analysis is a valuable approach for screening of benign and malignant breast tissue biopsies.

Quantitative phase imaging (QPI) can access quantitative information on thickness and/or refractive index changes of weakly absorbing and scattering objects, which normally require staining prior to observation. The quantitative phase image itself yields significant information for a medical diagnosis, particularly in cancer biopsies. Previously, several parameters such as a local standard deviation of refractive index have been utilized as a marker of diseases. We focus on the local spatial autocorrelation length, which is calculated at each point in the field of view. The local spatial autocorrelation length is defined as the standard deviation of the local spatial autocorrelation function and reveals the local and directional disorder information of tissues. However, generally, a direct calculation of the local spatial autocorrelation length take an immense amount of time. In this paper, we propose a high-throughput calculation procedure of a local spatial autocorrelation length, by exploiting frequency-domain calculations. After deriving a simple equation to calculate the local spatial autocorrelation length map in a short time, we perform label-free screening of benign and malignant breast tissue biopsies using this parameter as a marker.

Tissue refractive index provides important information about morphology at the nanoscale. Since the malignant transformation involves both intra- and inter-cellular changes in the refractive index map, the tissue disorder measurement can be used to extract important diagnosis information. Quantitative phase imaging (QPI) provides a practical means of extracting this information as it maps the optical path-length difference (OPD) across a tissue sample with sub-wavelength sensitivity. In this work, we employ QPI to compare the tissue disorder strength between benign and malignant breast tissue histology samples. Our results show that disease progression is marked by a significant increase in the disorder strength. Since our imaging system can be added as an upgrading module to an existing microscope, we anticipate that it can be integrated easily in the pathology work flow.

A double phase conjugate mirror (DPCM), created by two mutually incoherent beams entering photorefractive nonlinear materials, can generate a phase conjugate beam whose reflectivity may be greater than 100%. Even though the conditions of the incident beams are changed, the DPCM can be dynamically reconfigured by using a Sn2P2S6 crystal with a high response speed. These features of the DPCM are advantageous, particularly in an optical inter-satellite communication system. In particular, use of the phase conjugate beam from the DPCM offers wavefront compensation and amplification in satellite communication. In addition, the dynamically reconfigurable DPCM using a Sn2P2S6 crystal relaxes the acquisition accuracy of the signal beam in the system. In this study, the temporal and spatial operating characteristics of the DPCM using a Sn2P2S6 crystal were first clarified. Next, an inter-satellite system based on the DPCM was proposed, and it was demonstrated that our system significantly improves the tolerance of the acquisition accuracy and tracking time.

Spatial resolutions of diffracted beams by photorefractive polymers are investigated in detail for applying the polymers to diffractive optical elements. The coupled wave equations for the four-wave mixing in photorefractive polymers and their solutions by applying the two-beam coupling approximation are derived taking the orientational enhancement effect into consideration. Characteristics of the diffraction efficiency of the polymers for the applied electric field, the incident angles of beams, the incident radiation intensity and the polarization are clarified. Furthermore, resolutions of diffracted images with the polymers are discussed by a numerical analysis from the viewpoint of the Bragg diffraction in a spatial frequency domain. An experiment with the TPD (tetra-phenyl-diphenyldiamine) acrylate based photorefractive polymers and the USAF test target is also performed to measure the spatial resolution of two-dimensional images diffracted by the polymer and to verify the calculated results. It is r...

We present various optical basic properties of a 1.5% doped Sb:Sn2P2S6 crystal experimentally and demonstrate a double phase conjugate mirror (DPCM). We measured the reflection, absorption and scattering of this crystal. The large coupling strength Γ L = 8.2 was obtained by the experiment of two-wave mixing. In addition, we succeeded in the formation of the DPCM and achieved the high diffraction efficiency of 42%. This crystal was suitable for DPCM applications of high speed response.

We propose a two-channel holographic diversity interferometer (2ch-HDI) system for single-shot and highly accurate measurements of complex amplitude fields with a simple optical setup. In this method, two phase-shifted interference patterns are generated, without requiring a phase-shifting device, by entering a circularly polarized reference beam into a polarizing beam splitter, and the resulting patterns are captured simultaneously using two image sensors. However, differences in the intensity distributions of the two image sensors may lead to serious measurement errors. Thus, we also develop a two-channel algorithm optimized for the 2ch-HDI to compensate for these differences. Simulation results show that this algorithm can compensate for such differences in the intensity distributions in the two image sensors. Experimental results confirm that the combination of the 2ch-HDI and the calculation algorithm significantly enhances measurement accuracy.

To improve the measurement speed of optical tomography based on the virtual phase conjugation, a virtual measurement position control technique is proposed. Tomographic images were observed with high depth-resolution and high acquisition rate in the numerical simulations.

The 3D shift multiplexing method for high-density self-referential holographic data storage is proposed. As the fundamental evaluations of the proposed method, we focus on the multiplexing properties along the z-axis. Concretely, we demonstrate the z-shift multiplexing of 25 datapages after clarifying the shift selectivity along the z-axis.

Two methods are proposed to improve the readout quality of signals in self-referential holographic data storage (SR-HDS), in which no reference beam is required to record and read digital data holographically: the off-the-focus (OtF) method and the oversampling additional pattern (OsAP) method. The focal point is located outside of the recording medium in the OtF method, and the signal pattern is recorded with an additional pattern that possesses a higher spatial frequency than the signal pattern in the OsAP method. Experimental results show that both methods are effective for drastically improving the signal-to-noise ratio (SNR). In addition, through numerical simulation, it can be observed that the readout quality is improved by the achievement of homogeneous hologram distribution.

In 2004, the officially announced Japanese standard for the evaluation of car–front safety performance in terms of pedestrian child head protection required a 3.5 kg headform impactor as a test tool simulating a child pedestrian head. Currently, ACEA–TNO have jointly developed a 3.5 kg headform impactor in Europe. The primary aim of the present study is to investigate the availability of the 3.5 kg ACEA–TNO headform impactor in terms of the Japanese standard. Meanwhile, JAMA–JARI have together developed a 3.5 kg headform impactor in Japan. The secondary aim of our study is to present the physical characteristics and measured head injury criteria (HIC) of the JAMA–JARI and ACEA–TNO headform impactors obtained here as a point of reference for the formulation of the Global Technical Regulation (GTR) standards now under way. The technical specifications regarding mass, outer diameter, moment of inertia, location of centre of gravity, seismic mass location of accelerometers, natural frequency, and bio...

A pedestrian legform impactor is a tool for the evaluation of car front bumper aggressiveness when simulating a pedestrian leg hit by a car. The Transport Research Laboratory (TRL) developed a legform impactor in compliance with the European Enhanced Vehicle-safety Committee (EEVC)/ WG17 specifications. The Commission of the European Communities (EC) proposed a dynamic certification test for a legform impactor, however, the test results using the TRL legform impactors manufactured to date have indicated an extremely wide scatter, especially in the maximum lower leg acceleration. Thus, the objectives of the present research are to clarify the factor possibly causing this scatter in the lower leg acceleration of the TRL legform impactor in the setup of the dynamic certification test, and to propose a way to adjust lower leg acceleration so as to comply with the corridor proposed by the EC. The repeatability and reproducibility of the legform impactor products and different impact points of the ram in the setup for the dynamic certification test were thus investigated. High repeatability and reproducibility of the legform impactor products were observed. No difference was observed in the effect of different ram points of impact against a stationary legform impactor on the maximum lower leg acceleration. On the other hand, the lower leg acceleration was found to be greatly affected by humidity in the test apparatus. Therefore, the effect of humidity on the dynamic certification test setup was also investigated. The results indicated that the maximum lower leg acceleration increased drastically with higher humidity. Next, the relation between humidity and acceleration measured by a ram impacting a piece of confor™ foam was investigated using a simplified test rig, since such foam sheathes the metal part of the legform impactor in a dynamic certification test setup. A strong relation between the humidity and acceleration was found. Thus concluded that humidity is a key factor affecting lower leg acceleration, and that adjusting it will be one of the many ways the lower leg acceleration can be made to comply with the proposed EC corridor in the dynamic certification test.

The feasibility and the properties of shift-multiplexed self-referential holographic data storage (SR-HDS) were investigated. Although SR-HDS has attractive features as typified by referenceless holographic recording, its multiplexing properties, which are consummately important for holographic data storage, have not been clarified until now. The results of numerical and experimental evaluations of medium shift dependence in SR-HDS clarified that the shift selectivity is almost the same as in collinear holography. Furthermore, 25 datapages were successfully shift-multiplexed with the shift pitch of 8.3 μm by the numerical simulation.

A three-dimensional (3D) shift multiplexing technique is applied to increase the number of multiplexed datapages in self-referential holographic data storage (SR-HDS), enabling holographic recording with purely one-beam geometry. In the 3D shift multiplexing technique, the recording medium is shifted not only along the x- and y-axes but also along the z-axis to multiplex the datapages. Because the shift directions in the 3D shift multiplexing technique are expanded compared with the conventional 2D technique, the number of multiplexed datapages is expected to be increased. We numerically clarify the appropriate 3D recording layout of holograms in which the effect of the inter-page crosstalk can be reduced after showing that datapages are multiplexed on shifting the recording medium along the z-axis. The results show 3D shift multiplexing can effectively realize high-density SR-HDS when appropriately designed layouts are used.

Since the optical inter-satellite communication has attractive advantages such as high-speed transmission with high confidence, almost no electronic magnetic interference, and low power consumption, it has been activity investigated. However, directivity control of the laser beams requires a bulky and complicated system in satellite mobile communications. A more flexible and high accurate system with small and simple mechanism has been desired. In this study, we propose a new method of optical inter-satellite communication with a dynamically reconfigurable optical directional device in which diffraction gratings are automatically rewritten and reorganized in response of incident conditions by moving satellites. For realizing such a device, we have developed Sn2P2S6 crystals which have a high sensitive photorefractivity and dynamic reconfigurable property. Furthermore, this crystal has hundreds times faster response than conventional photorefractive materials such as BaTiO3. These features are extremely advantageous to construct a high-speed and flexible communication system with a large tolerance to displacement of moving satellites. To investigate the possibility of the dynamically reconfigurable optical inter-satellite communication system, we experimentally evaluate the temporal and spatial characteristics of Sn2P2S6 crystals for the variation of the beam incident angle. Moreover, the diffraction beam from the crystal has phase conjugate wavefronts of the beam entering from the counter direction. We try to utilize this behavior to suppress the beam spread and to reduce the background light such as sunlight with a spatial filtering technique that has sensitivity in wavefront differences of the signal and background light.

We demonstrated that introducing multi-layered technique into collinear holographic memory can realize higher quality holographic recording/reading and expand the storage density by a factor of 2 through homogeneous utilization of the recording medium.

Our new analysis tool can be capable of calculations more than 30 times faster than the previous method and enables to estimate practical memory densities including not only recording and reconstruction process but also error correction process.

A double-referential method, in which the reference light necessary for phase detection can be generated as diffraction light of the optical hologram automatically, is newly proposed. 16-SQAM signals can be reconstructed through dual-stage holography.

A self-referential holographic recording geometry, in which signal beam works as reference beam for recording of itself, having many attractive advantages is newly proposed. The purely one-beam holographic operation is performed by simulation and experiment.

We develop a tunable optical wavelength filter with PR (photorefractive) materials applied the external field for achieving higher sensitivity and efficiency. In the past, the diffraction efficiency of the PR tunable filters with transmission gratings has been much lower than other conventional wavelength filters, such as the array wavelength gratings filter, the thin film filter, and the fiber Bragg gratings filter. By applying the external field to PR materials, we can obtain the refractive index modulation depth of 13 times larger than that without applied field, specifically in lithium niobate with the acceptor density of ~1022 [1/m3] and the voltage of 10 [kV/cm]. Our PR tunable filter provides reconfigurable wavelength routing of the signal beam since the various diffraction gratings can be immediately induced and multiplexed by changing incident conditions of two coherent writing beams viewpoint in comparing experimental results to numerical simulations, and can be rewritten dynamically through the PR effect. These advantages allow us to achieve more flexible optical net work based on the wavelength division multiplexing technique. In this work, we calculate the relationship between the diffraction efficiency and the magnitude of the applied external field by solving coupled wave equations in the case of lithium niobate, respectively.

We propose a new method for detection of phase-modulated signals that provides higher energy efficiency detection and simplified alignments of position and intensity between interference images. By using time-domain differential detection with 2x over sampling, phase-modulated signals can be exactly distinguished.

We propose a spatial cross modulation method using a random diffuser and a phase-only spatial light modulator (SLM), by which arbitrary complex-amplitude fields can be generated with higher spatial resolution and diffraction efficiency than off-axis and double-phase computer-generated holograms. Our method encodes the original complex object as a phase-only diffusion image by scattering the complex object using a random diffuser. In addition, all incoming light to the SLM is consumed for a single diffraction order, making a diffraction efficiency of more than 90% possible. This method can be applied for holographic data storage, three-dimensional displays, and other such applications.

We proposed a double-referential holography (DRH) that allows phase-detection without external additional beams. In the DRH, phantom beams, prepared in the same optical path as signal beams and preliminary multiplexed in a recording medium along with the signal, are used to produce interference fringes on an imager for converting a phase into an intensity distribution. The DRH enables stable and high-accuracy phase detection independent of the fluctuations and vibrations of the optical system owing to medium shift and temperature variation. Besides, the collinear arrangement of the signal and phantom beams leads to the compactness of the optical data storage system. We conducted an experiment using binary phase modulation signals for verifying the DRH operation. In addition, 38-level spatial quadrature amplitude modulation signals were successfully reproduced with the DRH by numerical simulation. Furthermore, we verified that the distributed phase-shifting method moderates the dynamic range consumption for the exposure of phantom beams.

A technique for the phase and amplitude detection of object beams with multivalued phase and amplitude modulation is proposed for holographic storage systems. Generally, the spatial distribution of the complex amplitude of the object beam can be precisely detected by phase-shifting interferometric measurements in which the phase of the reference wave for interferometry is temporally or spatially changed in the datapage retrieval process. On the other hand, our technique allows fast, accurate, and feasible phase and amplitude demodulations by preliminary embedding phase shift into the phase signal of the datapage during recording. This technique will significantly improve the data transfer rate and vibration tolerance of the holographic storage system because the complex amplitudes of the object beam carrying datapages can be detected by single-shot image capturing. The optical system for datapage replay will also be simplified because there is no need to use any phase-shifting device during data retrieval. The single-shot detection of the phase-modulated datapage is experimentally demonstrated.

Holographic recording methods require the use of a reference beam that is coherent with the signal beam carrying the information to be recorded. In this paper, we propose self-referential holography (SRH) for holographic recording without the use of a reference beam. SRH can realize purely one-beam holographic recording by considering the signal beam itself as the reference beam. The readout process in SRH is based on energy transfer by inter-pixel interference in holographic diffraction, which depends on the spatial phase difference between the recorded phase and the readout phase. The phase-modulated recorded signal is converted into an intensity-modulated beam that can be easily detected using a conventional image sensor. SRH can be used effectively for holographic data storage and phase-to-intensity conversion. (C) 2013 Optical Society of America

For the purpose of increasing the data density of holographic memories, we propose a novel signal modulation method named hybrid modulation method, which is a combination of multi level phase-modulated signals and intensity-modulated signals. As a first step, we show that the data density of holographic data storage is mainly determined by multiplexing numbers and by coding efficiency in input signals. In this study, we focus on increasing coding efficiency using the hybrid modulation method. From the results of recording and reading simulations based on the fast-Fourier transform beam propagation method, the hybrid modulation method achieves approximately 2 times higher data density than the conventional methods of two-level phase-only modulation and two-level intensity-only modulation.

This study proposes holographic diversity interferometry (HDI), a system that combines information from spatially dispersed plural image sensors to reconstruct complex amplitude distributions of light signals. HDI can be used to generate four holographic interference fringes having different phases, thus enabling optical phase detection in a single measurement. Unlike conventional phase-shifting digital holography, this system does not require piezoelectric elements and phase shift arrays. In order to confirm the effectiveness of HDI, we generated optical signals having multilevel phases and amplitudes by using two SLMs and performed an experiment for detection and demodulation with HDI. (C) 2011 Optical Society of America

Holographic data storage with phase-modulated signals has great advantages over conventional intensity-based memory. These include the efficient use of material dynamic range and light power in a spatial light modulator. On the other hand, phase-based holographic data storage has a disadvantage, which is the difficulty in distinguishing phase-modulated signals. We propose and demonstrate a new phase-modulated signal detection method with photorefractive two-wave mixing. This method has several advantages such as high energy efficiency, detection of multi valued phase-modulated signals, and alignment-free optics. In this study, we investigate the spatial resolution of the phase-modulated signal detection method and obtain a spatial resolution of 300–500 µm of incident pixels.

We propose a new method to detect multi-level phase signals by generating 4-pieces of digital hologram by single shot hologram reading without using the reference light of a resolution higher than the signal page data.