Faculty Profiles - NOMURA Takanori

Published Papers - NOMURA Takanori

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Multiplexed recording based on the reference wave correlation for computer-generated holographic data storage

Yusuke Saita, Aoto Matsumoto, Naru Yoneda, Takanori Nomura （Part： Last author )

OPTICAL REVIEW ( OPTICAL SOC JAPAN ) 27 ( 4 ) 391 - 398 2020.08 [Refereed]

Holographic data storage (HDS) based on a computer-generated hologram (CGH) technique has been proposed as a promising approach to realize an in-line and simple HDS system. This work focuses on multiplexed recording for CGH-based HDS, and the approach based on the reference wave correlation is introduced to the HDS. For the proposed method, the processes for a CGH design are modified to generate reference waves with different phase distributions for each recording. Since holograms are recorded to the same region in a medium with independent reference waves, recorded data-pages are selectively reconstructed by the corresponding reference wave illuminations. The experimental demonstration confirms the feasibility of the proposed method, and the theoretical characteristic for the number of recordable multiplexed holograms is estimated by the numerical simulation.

Motionless optical scanning holography

Naru Yoneda, Yusuke Saita, Takanori Nomura （Part： Last author )

OPTICS LETTERS ( OPTICAL SOC AMER ) 45 ( 12 ) 2020.06 [Refereed]

Optical scanning holography (OSH) is an attractive technique since 3D information can be obtained with a single pixel detector. However, OSH requires an interferometer, scanning architecture, and a frequency shifter to scan a time-varying Fresnel zone plate (FZP), which makes the optical setup complicated. To reduce the complexity, the polarization sensitivity of a spatial light modulator (SLM) is applied. The proposed method implements a time-varying FZP with an in-line optical setup by using only an SLM. Observing results for a USAF pattern and a fluorescent bead reveals the feasibility of the new motionless holographic 3D imaging technique. (C) 2020 Optical Society of America

Computer-generated-hologram-based holographic data storage using common-path off-axis digital holography

Naru Yoneda, Yusuke Saita, Takanori Nomura （Part： Last author )

OPTICS LETTERS ( OPTICAL SOC AMER ) 45 ( 10 ) 2796 - 2799 2020.05 [Refereed]

A reconstruction method for multilevel complex encoded data-pages is proposed to increase the recording density of computer-generated-hologram-based holographic data storage by using off-axis digital holography. Although the detection process is based on off-axis digital holography, the proposed method keeps the optical setup a simple and common-path configuration owing to the computer-generated holography. Five-level complex encoded data-pages can be experimentally reconstructed. (C) 2020 Optical Society of America

Deep ghost phase imaging

Koshi Komuro, Takanori Nomura, George Barbastathis

Applied Optics ( OSA - The Optical Society ) 59 ( 11 ) 3376 - 3382 2020.04

Deep-learning-based single-pixel phase imaging is proposed. The method, termed deep ghost phase imaging (DGPI), succeeds the advantages of computational ghost imaging, i.e., has the phase imaging quality with high signal-to-noise ratio derived from the Fellgett's multiplex advantage and the point-like detection of diffracted light from objects. A deep convolutional neural network is learned to output a desired phase distribution from an input of a defocused intensity distribution reconstructed by the single-pixel imaging theory. Compared to the conventional interferometric and transport-of-intensity approaches to single-pixel phase imaging, the DGPI requires neither additional intensity measurements nor explicit approximations. The effects of defocus distance and light level are investigated by numerical simulation and an optical experiment confirms the feasibility of the DGPI.

Transport-of-intensity phase imaging with polarization directed flat lenses

Shunsuke Kakei, Koshi Komuro, Takanori Nomura

Applied Optics ( OSA - The Optical Society ) 59 ( 7 ) 2011 - 2015 2020.03

A phase imaging technique based on the transport of intensity equation with polarization directed flat lenses is demonstrated. Transport-of-intensity phase imaging enables one to obtain a phase distribution from throughfocus intensity distributions by solving the transport of intensity equation. In general, the through-focus intensity distributions are obtained by mechanical scanning of an image sensor or target object. Therefore, a precise alignment of an optical system is required. To solve this issue, the introduction of polarization directed flat lenses is presented. In the proposed method, two intensity distributions at different depth positions on the optical axis are obtained without mechanical scanning by changing polarization states of incident light. The feasibility of the proposed method is confirmed by an optical experiment.

Complex amplitude mapping based on adaptive autofocusing algorithm

Komuro, Koshi, Oe, Kazusa, Tamada, Yosuke, Nomura, Takanori （Part： Last author )

OPTICAL REVIEW ( OPTICAL SOC JAPAN ) 26 ( 3 ) 342 - 348 2019.06 [Refereed]

Since a complex amplitude distribution can be obtained in only a single two-dimensional plane using conventional imaging techniques, it is hard to obtain in-focus complex amplitude of three-dimensional structure (not a thin object) or multiple objects in different depth positions. The disadvantage often turns an obstacle to practical applications such as cell observation, particle measurement, and industrial inspection. To overcome the problem, adaptive autofocusing algorithm (AAA) is proposed. AAA consists of a complex amplitude measurement, numerical propagation, and local sharpness evaluation. In the proposed method, object positions can be determined for each pixel in the complex amplitude distribution using adaptively chosen area size of local sharpness evaluation. The proposed method gives a complex amplitude distribution which focuses on all objects or structure over an entire field of view. An optical experiment is carried out using the transport of intensity equation as a complex amplitude measurement. Performance of the proposed method is confirmed using living leaves of the moss Physcomitrella patens. Experimental results show that the object positions can be determined pixelwise and a focused complex amplitude distribution can be obtained by the proposed method.

Binary computer-generated-hologram-based holographic data storage

Naru Yoneda, Yusuke Saita, Takanori Nomura （Part： Last author )

APPLIED OPTICS ( OPTICAL SOC AMER ) 58 ( 12 ) 3083 - 3090 2019.04 [Refereed]

Conventional computer-generated-hologram-based holographic data storage (CGH-HDS) needs to use a multilevel modulatable spatial light modulator (SLM). A binary SLM usually has a higher refresh rate than a multilevel one, and it enables HDS to increase the data transfer rate. To increase the data transfer rate by using a binary SLM, the introduction of a binary CGH is proposed. In general, a binary CGH degrades the image quality of reconstructed intensity distribution and emphasizes high spatial frequency components of datapages. In the proposed method, reconstructed intensity distributions that satisfy image quality as datapages can be obtained with low-pass filtering with an aperture at a plane of a recording medium. The optimum size of an aperture is numerically evaluated. The proposed method is experimentally verified. Moreover, the proposed method can achieve single and multiplexed recording of three datapages by a spherical reference beam with a binary CGH. (C) 2019 Optical Society of America

Computational ghost imaging with designed low spatial frequency masks

Yuya Yamazaki, Takanori Nomura （Part： Last author,　Corresponding author )

APPLIED OPTICS ( OPTICAL SOC AMER ) 57 ( 31 ) 9375 - 9380 2018.11 [Refereed]

Minimally invasive imaging using weak illumination is required in the biomedical field. Computational ghost imaging (CGI) achieves imaging under illumination. However, CGI requires a large number of measurements to obtain an image. The number of measurements increases as illumination weakens. In this paper, decreasing the number of measurements of CGI with designed low spatial frequency masks is proposed. The proposed method allows us to image an object with a smaller number of measurements than with the conventional method. Numerical simulations and experiments confirm the feasibility of the proposed method. (C) 2018 Optical Society of America.

Transport-of-intensity holographic data storage based on a computer-generated hologram

Naru Yoneda, Yusuke Saita, Koshi Komuro, Teruyoshi Nobukawa, Takanori Nomura （Part： Corresponding author )

APPLIED OPTICS ( OPTICAL SOC AMER ) 57 ( 30 ) 8836 - 8840 2018.10 [Refereed]

To increase the recording density of computer-generated-hologram (CGH)-based holographic data storage, a phase data page reconstruction method by the transport of intensity equation (TIE) is proposed. The TIE generally requires a scanning image sensor because the phase retrieval process needs at least two defocused intensity distributions. Although the TIE is applied, the proposed method enables detection of the distributions simultaneously by utilizing an extra conjugate component reconstructed from the CGH. Experimental results show that the proposed method allows reconstructing of a phase data page without any additional elements, which keeps the optical setup simple and low cost. (C) 2018 Optical Society of America

Phase-unwrapping-free and iterative reconstruction methods for propagated refractive index tomography

Ikezaki, Aina, Nomura, Takanori （Part： Last author,　Corresponding author )

JAPANESE JOURNAL OF APPLIED PHYSICS ( IOP PUBLISHING LTD ) 57 ( 9 ) 2018.09 [Refereed]

Phase-unwrapping-free and iterative reconstruction methods for propagated refractive index ( RI) tomography, which introduces lightwave back-propagation to a filtered back-projection method, are proposed. The phase-unwrapping-free method utilizes phase retrieval using a transport-of-intensity equation that does not require phase unwrapping. This method overcomes phase unwrapping problems of high calculation cost and phase unwrapping error when measuring millimeter-thick and/or large-RI-changes specimens. In the iterative method, a simultaneous iterative reconstruction technique in X-ray computed tomography is applied to the propagated RI tomography. This method leads to the reduction of the radial artifacts and the elimination of the need for a high-pass filter regardless of the shape and size of specimens. Hence, the accuracy of a reconstructed RI map is improved. Numerical simulations and optical experiments are carried out to prove the feasibility of the proposed methods. (c) 2018 The Japan Society of Applied Physics

Refractive index tomography based on optical coherence tomography and tomographic reconstruction algorithm (vol 56, 09NB03, 2017)

Kitazawa, Takahiro, Nomura, Takanori （Part： Last author )

JAPANESE JOURNAL OF APPLIED PHYSICS ( IOP PUBLISHING LTD ) 57 ( 8 ) 2018.08 [Refereed]

Twin-image reduction method using a diffuser for phase imaging in-line digits holography

Oe, Kazusa, Nomura, Takanori （Part： Last author,　Corresponding author )

APPLIED OPTICS ( OPTICAL SOC AMER ) 57 ( 20 ) 5652 - 5656 2018.07 [Refereed]

Phase imaging by digital holography is widely used. An in-line optical setup is preferable for a practical use. A twin image, however, is a serious obstacle to achievement of high-quality phase imaging in in-line digital holography. For in-line digital holography, a time-division phase-shifting method or a wave-splitting phase-shifting method is used to eliminate the twin image. The former requires multiple exposures, and the latter requires specially designed optical elements. To solve these problems, a twin-image reduction method using a diffuser is proposed. In the proposed method, recording a digital hologram using a diffuser and signal processing enable reduction of the twin image on a reconstructed plane. A preliminary experimental result confirms the feasibility of the proposed method. (C) 2018 Optical Society of America

Transport-of-intensity computational ghost imaging

Komuro, Koshi, Yamazaki, Yuya, Nomura, Takanori （Part： Last author )

APPLIED OPTICS ( OPTICAL SOC AMER ) 57 ( 16 ) 4451 - 4456 2018.06 [Refereed]

Computational ghost imaging (CGI) allows us to obtain a sample image under a low signal-to-noise-ratio (SNR) condition. However, phase information cannot be obtained by CGI; therefore, observation of transparent objects such as living cells is difficult. Although interferometry has been applied to CGI for phase retrieval, its optical setup is cumbersome. In this paper, an alternative approach, which is based on a transport-of-intensity equation, is proposed. Compared with conventional interferometric methods, the optical setup of the proposed method is robust because it does not require additional optical elements. The proposed method achieves phase retrieval by slight modification of the standard CGI setup. Numerical and optical experiments with low SNR confirm the effectiveness of the proposed method. (C) 2018 Optical Society of America

Transport of intensity phase imaging for pure phase objects in computational ghost imaging

Koshi Komuro, Yuya Yamazaki, Takanori Nomura

Proceedings of SPIE - The International Society for Optical Engineering ( SPIE ) 10816 2018

Computational ghost imaging (CGI) is expected to be applied to noninvasive biomedical imaging because of its characteristic which allows us to obtain the object's image under a low signal to noise ratio (SNR) condition. However only an amplitude distribution can be obtained by the CGI. Therefore the imaging of the pure phase objects is difficult. Although the phase shifting digital holography has been used for reconstruction of the complex amplitude in the CGI, its experimental setup is cumbersome and sensitive to vibrations. Furthermore four holograms are required for the reconstruction of the complex amplitude because of the phase shifting algorithm, rendering the acquisition time of the phase image slow. Therefore the method is difficult to be applied to the biomedical imaging. An alternative non-interferometric method is proposed in this study. The proposed method uses the transport of intensity equation for the phase retrieval of the pure phase objects, termed transport-of-intensity CGI (TI-CGI). In the TI-CGI, the phase distribution is retrieved from a single defocused image obtained by a modulated optical setup of the CGI, achieving the fast and robust imaging compared with the conventional phase shifting method. Therefore the TI-CGI may be more suitable for the biomedical imaging than the phase shifting method. The TI-CGI is demonstrated by an optical experiment under the low SNR condition generated by the neutral density filters with 1% and 0.1% transmittance. The experimental results conform the effectiveness of the TI-CGI.

Large dynamic range wavefront sensing using Shack-Hartmann wavefront sensor based on pattern correlations

Yusuke Saita, Takanori Nomura

Proceedings of SPIE - The International Society for Optical Engineering ( SPIE ) 10815 2018

Wavefront sensing techniques are mainly needed in an adaptive optics system for high resolution imaging. One of them is a Shack-Hartmann method which is composed of very simple structure. Although the method is widely utilized, it also has the limitation for the measurable magnitude of wavefront aberrations. To overcome the problem, the improved Shack-Hartmann method for larger aberrated wavefronts has been proposed. In this paper, the principle of the proposed method and the numerical evaluation of the performance of the proposed method are presented.

Three-dimensional shift multiplexed recording in coaxial holographic data storage with virtual varifocal lens

Yusuke Saita, Masahiro Karaike, Takanori Nomura

Optics InfoBase Conference Papers ( OSA - The Optical Society ) 2018 2018

Holographic data storage (HDS) is one of attractive solutions for archiving huge number of data produced all over the world. A coaxial system in HDS has some advantages of simple setup, tolerance to vibrations, and so on. In a coaxial system, the two-dimensional (2D) shift multiplexing is achieved by lateral medium shifts corresponding to disk rotation. Also, the multi-layer recording with a kinoform varifocal lens has also been proposed, which is based on adding a defocus phase distribution to signal and reference patterns displayed on a spatial light modulator (SLM) [1]. In this paper, we propose the three-dimensional (3D) shift multiplexing combining these multiplexed schemes and the criteria to determine the appropriate recording condition. The proposed method confirms the feasibility of improving the recoring density in coaxial HDS.

Correlation-Based Multiplexing of Complex Amplitude Data Pages in a Holographic Storage System Using Digital Holographic Techniques (vol 9, 375, 2017)

Teruyoshi Nobukawa, Takanori Nomura （Part： Last author )

POLYMERS ( MDPI AG ) 9 ( 10 ) 2017.10 [Refereed]

Object plane detection and phase-amplitude imaging based on transport of intensity equation

Koshi Komuro, Takanori Nomura （Part： Last author )

OPTICAL REVIEW ( OPTICAL SOC JAPAN ) 24 ( 5 ) 626 - 633 2017.10 [Refereed]

By using transport of intensity equation (TIE), phase distribution of an object is retrieved from through-focus intensity images. This technique allows simple and robust phase imaging compared with an interferometric approach. However, it is hard to measure phase distribution when a dynamic object moves in the direction of an optical axis. To clear this problem, autofocusing TIE which is based on local statistics is proposed. The proposed technique achieves the detection of the object plane and the retrieval of a focused object phase distribution simultaneously. In this approach, an object plane is determined by the focusing techniques based on local statistics such as variance, gradient, and Laplacian of amplitude distribution, after phase distribution in an image sensor plane is retrieved by the TIE. The performance of these three statistics is evaluated in numerical and optical experiments, and a suitable focus value is determined for precise phase imaging.

Refractive index tomography based on optical coherence tomography and tomographic reconstruction algorithm

Takahiro Kitazawa, Takanori Nomura （Part： Last author )

JAPANESE JOURNAL OF APPLIED PHYSICS ( IOP PUBLISHING LTD ) 56 ( 9 ) 2017.09 [Refereed]

Refractive index (RI) tomography based on not quantitative phase imaging (QPI) but optical coherence tomography (OCT) is proposed. In conventional RI tomography, the phase unwrapping process deteriorates measurement accuracy owing to the unwrapping error. To eliminate the unwrapping process, the introduction of OCT is proposed, because OCT directly provides optical thickness. The proposed method can improve measurement accuracy owing to the removal of the phase unwrapping error. The feasibility of the method is confirmed by numerical simulations and optical experiments. These results show that the proposed method can reduce measurement errors even when an object shows phase changes much larger than a wavelength. (C) 2017 The Japan Society of Applied Physics

Orthogonal polarization encoding for reduction of interpixel cross talk in holographic data storage

Teruyoshi Nobukawa, Daisuke Barada, Takanori Nomura, Takashi Fukuda

OPTICS EXPRESS ( OPTICAL SOC AMER ) 25 ( 19 ) 22425 - 22439 2017.09 [Refereed]

Interpixel cross talk decreases the quality of a reconstructed signal in holographic data storage and imposes a limitation on its storage capacity. To reduce the interpixel cross talk, an orthogonal polarization encoding method is proposed. In the proposed method, the polarization state of each pixel is set to be orthogonal with that of surrounding pixels. This prevents the interference between nearest- neighboring pixels and significantly reduces the gross of the interpixel cross talk. The quality of the data page obtained with the proposed method is numerically and experimentally evaluated. Those results suggest that the proposed method can improve the quality of a reconstructed signal. (C) 2017 Optical Society of America

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