Quantitative phase imaging based on motionless optical scanning holography.

Optical scanning holography (OSH) can be applied to 3D fluorescent imaging. However, the optical setup for OSH is complicated due to the requirement of a phase shifter, a 2D mechanical scanner, and an interferometer. Although motionless optical scanning holography (MOSH) can overcome the problem, quantitative phase imaging (QPI) has not yet been realized because MOSH can only obtain incoherent holograms. If QPI in MOSH is realized, MOSH can be applied to various applications. In this Letter, MOSH-based QPI (MOSH-QPI) is proposed. In addition, a simple description of a coherent mode of OSH is presented. In the proof-of-principle experiment, the spatially divided phase-shifting technique is applied to reduce the number of measurements. The feasibility of MOSH-QPI is confirmed by measuring a phase distribution of a microlens array. MOSH-QPI is also applied to measure practical samples, and its results are compared with the experimental results of the conventional one using a Mach-Zehnder interferometer.

Common-path off-axis single-pixel holographic imaging.

Common-path off-axis single-pixel holographic imaging (COSHI) is proposed to obtain complex amplitude information using an in-line interferometer and a single-pixel (point-like) detector. COSHI is more robust to disturbances such as vibration than the conventional single-pixel digital holography technique because of its common-path configuration. In addition, the number of measurements can be reduced due to COSHI's reconstruction process based on the Fourier fringe analysis. In COSHI, an off-axis digital hologram can be obtained using the structured patterns composed of Hadamard basis patterns and stationary tilted phase distribution. Interestingly, COSHI's space bandwidth is larger than of the conventional off-axis digital holography because COSHI does not reconstruct the self-correlation term of an object. The proposed method is theoretically confirmed and numerical and experimental results show its feasibility.

Single-shot compressive hyperspectral imaging with dispersed and undispersed light using a generally available grating.

Commercially available hyperspectral cameras are useful for remote sensing, but in most cases snapshot imaging is difficult due to the need for scanning. The coded aperture snapshot spectral imager (CASSI) has been proposed to simultaneously acquire a target scene's spatial and spectral dimensional data, employing a refractive prism as a disperser. This paper proposes a CASSI-based technique using a generally available diffraction grating of a Ronchi ruling and blazed grating and its improvement using the undispersed zeroth-order light. The feasibility and performance of the proposed technique are experimentally validated, and the grating parameters are identified.

Roadmap on digital holography [Invited].

This Roadmap article on digital holography provides an overview of a vast array of research activities in the field of digital holography. The paper consists of a series of 25 sections from the prominent experts in digital holography presenting various aspects of the field on sensing, 3D imaging and displays, virtual and augmented reality, microscopy, cell identification, tomography, label-free live cell imaging, and other applications. Each section represents the vision of its author to describe the significant progress, potential impact, important developments, and challenging issues in the field of digital holography.

Roadmap on Recent Progress in FINCH Technology.

Fresnel incoherent correlation holography (FINCH) was a milestone in incoherent holography. In this roadmap, two pathways, namely the development of FINCH and applications of FINCH explored by many prominent research groups, are discussed. The current state-of-the-art FINCH technology, challenges, and future perspectives of FINCH technology as recognized by a diverse group of researchers contributing to different facets of research in FINCH have been presented.

Fast and accurate phase-unwrapping algorithm based on the transport of intensity equation: comment.

In [Appl. Opt.56, 7079 (2017)APOPAI0003-693510.1364/AO.56.007079], an attractive phase unwrapping algorithm based on the transport of intensity equation is proposed. Although the effectiveness is experimentally evaluated, the derivation of the angular spectrum based expression is ambiguous. In this paper, the ambiguity is clarified with the Helmholtz equation.

Single-shot higher-order transport-of-intensity quantitative phase imaging using deep learning.

Single-shot higher-order transport-of-intensity quantitative phase imaging (SHOT-QPI) is proposed to realize simple, in-line, scanless, and single-shot QPI. However, the light-use efficiency of SHOT-QPI is low because of the use of an amplitude-type computer-generated hologram (CGH). Although a phase-type CGH overcomes the problem, the accuracy of the measured phase is degraded owing to distortion of the defocused intensity distributions, which is caused by a quantization error of the CGH. Alternative SHOT-QPI with the help of deep learning, termed Deep-SHOT, is proposed to solve a nonlinear problem between the distorted intensities and the phase. In Deep-SHOT, a neural network learns the relationship between a series of distorted intensity distributions and the ground truth phase distribution. Because the distortion of intensity distributions is intrinsic to an optical system, the neural network is optimized for the system, and the proposed method improves the accuracy of the measured phase. The results of a proof-of-principle experiment indicate that the use of multiple defocused intensities also improves accuracy, even the nonlinear problem.

Common-path angular-multiplexing holographic data storage based on computer-generated holography.

An unconventional angular-multiplexed recording technique is proposed for holographic data storage based on a computer-generated hologram (CGH) technique. While general angular-multiplexed recording techniques require a Mach-Zehnder interferometer to record data pages as volume holograms, the proposed method records ones with a common-path configuration with the help of a CGH technique, which prevents the optical setup from being bulky. In the proposed method, the CGH reconstructs signal and reference beams simultaneously, and these beams interfere in a recording medium. By changing the diffraction angle of the reference beam from the CGH, angular multiplexing is accomplished with a common-path optical setup without additional optical elements. Multiplexed recording of four data pages is demonstrated in a proof-of-principle experiment, which indicates the feasibility of the proposed method.

Pupil-modulation ghost phase imaging.

Computational ghost imaging (CGI) allows us to reconstruct images under a low signal-to-noise-ratio condition. However, CGI cannot retrieve phase information; it is unsuitable for observation of transparent objects such as living cells. A phase imaging method with CGI architecture is proposed. The proposed method realizes phase imaging with a simple optical setup by introducing pupil modulation differential phase contrast (PMDPC) to CGI. In PMDPC, phase information can be obtained from intensity distributions, which have phase gradient information, and its optical setup is similar to that of CGI. Therefore, the two methods are highly compatible, and the introduction of PMDPC to CGI can be easily achieved. Numerical simulation and an optical experiment demonstrated the feasibility of the proposed method.

Single-shot higher-order transport-of-intensity quantitative phase imaging based on computer-generated holography.

The imaging quality of quantitative phase imaging (QPI) based on the transport of intensity equation (TIE) can be improved using a higher-order approximation for defocused intensity distributions. However, this requires mechanically scanning an image sensor or object along the optical axis, which in turn requires a precisely aligned optical setup. To overcome this problem, a computer-generated hologram (CGH) technique is introduced to TIE-based QPI. A CGH generating defocused point spread function is inserted in the Fourier plane of an object. The CGH acts as a lens and grating with various focal lengths and orientations, allowing multiple defocused intensity distributions to be simultaneously detected on an image sensor plane. The results of a numerical simulation and optical experiment demonstrated the feasibility of the proposed method.

Thiophene-based twisted bistricyclic aromatic ene with tricoordinate boron: a new n-type semiconductor.

The incorporation of tricoordinate boron into conjugated systems is of current interest in the field of organic electronics. In this study, a tricoordinate boron-embedded thiophene-based bistricyclic aromatic ene (BAE) was synthesized as a new boron-containing conjugated system. The combination of tricoordinate boron and fused thiophene rings imposed the twisted conformation in the BAE structure, resulting in the narrow energy absorption with the low-lying LUMO. Preliminary studies on the application of the highly electron-deficient boron-embedded BAE to organic field-effect transistors (OFETs) were also performed, revealing its moderately high electron mobility.

Deep-learning-based binary hologram.

Binary hologram generation based on deep learning is proposed. The proposed method can reduce the severe effect of quality degradation from binarizing gray-scaled holograms by optimizing the neural network to output binary amplitude holograms directly. In previous work on binary holograms, the calculation time for generating binary holograms was long. However, in the proposed method, once the neural network is trained enough, the neural network generates binary holograms much faster than previous work with comparable quality. The proposed method is more suitable for opportunities to generate several binary holograms under the same condition. The feasibility of the proposed method was confirmed experimentally.

Single-shot in-line Fresnel incoherent holography using a dual-focus checkerboard lens.

Fresnel incoherent correlation holography (FINCH) is a technology that can acquire three-dimensional information of incoherent objects such as fluorescence with an in-line optical system. However, it is difficult to apply FINCH to dynamic phenomena, since FINCH has to detect phase-shifted holograms sequentially to eliminate twin and zero-order images. In this paper, a method in which the phase-shifted holograms can be obtained simultaneously with an in-line setup by using an optimized simulated diffraction optical element (sDOE), realized by a phase-only spatial light modulator, is proposed. The optimized sDOE is an optical device with a dual-focus lens, 2D grating, and spatial phase shifter. Therefore, the sDOE is called a dual-focus checkerboard lens. The optical experiment confirms the feasibility of the proposed method.

Motionless optical scanning holography.

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.

Deep ghost phase imaging.

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.

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

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.

High temporal and spatial resolution single-shot digital holography with Fresnel domain filtering using witch's hat illumination.

High-resolution, single-shot on-axis digital holography is proposed. Generally, an on-axis configuration samples carrier fringes with higher spatial resolution compared to an off-axis configuration. However, the reconstructed image is obtained with unnecessary images of a conjugate image and a zero-order beam. The proposed method uses a phase-modulated illumination beam and image processing to eliminate these unnecessary images. Since time-division and parallel phase-shifting methods are not required, the proposed method has higher temporal and spatial resolutions. During image processing, the conjugate image is removed by filtering on the Fresnel domain while keeping most of the information of the object image intact. The usefulness of the proposed method is confirmed by a numerical simulation and an optical experiment.

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

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 through-focus 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.

Direct comparison of dithienosilole and dithienogermole as π-conjugated linkers in photosensitizers for dye-sensitized solar cells.

Dithienosilole (DTS) and dithienogermole (DTG) are useful building units of π-conjugated organic materials. In the present work, donor-π-acceptor (D-π-A) dyes with bis(dihexyloxyphenyl)aminophenyl, DTS or DTG, and pyridine or cyanoacrylic acid as the donor (D), the π-conjugated linker (π), and the acceptor (A) units, respectively, were prepared and their optical properties were investigated. The D-π-A dyes exhibited strong absorption in the visible region, indicating efficient intramolecular donor-acceptor interaction. The addition of trifluoroacetic acid to solutions of pyridine-containing dyes led to red-shifts of the absorption bands as a result of pyridinium salt formation. Similar red-shifts were observed for cyanoacrylic acid dyes, which were due to the enhanced formation of neutral dyes relative to the separated ion pairs. The D-π-A dyes, however, showed similar absorption spectra when attached to the TiO2 surface, indicating that the dye-TiO2 electronic interaction was rather weak. In contrast to the finding that these dyes exhibited similar optical properties regardless of the π-linker (i.e., DTS or DTG), dye-sensitized solar cells (DSSCs) based on DTG-containing dyes exhibited superior performance compared to those based on DTS-containing dyes. Electrochemical impedance spectroscopy measurements supported the higher performance of the DSSCs with DTG-containing dyes.

Binary computer-generated-hologram-based holographic data storage.

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.