Roadmap on computational methods in optical imaging and holography [invited].

Unlabelled: Computational methods have been established as cornerstones in optical imaging and holography in recent years. Every year, the dependence of optical imaging and holography on computational methods is increasing significantly to the extent that optical methods and components are being completely and efficiently replaced with computational methods at low cost. This roadmap reviews the current scenario in four major areas namely incoherent digital holography, quantitative phase imaging, imaging through scattering layers, and super-resolution imaging.

Incoherent digital holography with two polarization-sensitive phase-only spatial light modulators and reduced number of exposures.

I propose methods for reducing the number of exposures in incoherent digital holography with two polarization-sensitive phase-only spatial light modulators (IDH with TPP-SLMs). In IDH with TPP-SLMs, no polarization filters are required, and not only three-dimensional (3D), but polarization information is also obtained. However, seven exposures are required to conduct filter-free polarimetric incoherent holography.

Polarization-filterless polarization-sensitive polarization-multiplexed phase-shifting incoherent digital holography (PIDH).

I propose a holography technique that detects both three-dimensional (3D) and polarization information on incoherent light without any polarization filters. Two polarization-sensitive phase-only spatial light modulators are used to generate self-interference holograms with different polarization directions. 3D images for different polarization directions are retrieved from the recorded polarization-multiplexed holograms, exploiting the developed phase-shifting interferometry and numerical refocusing.

Multidimension-multiplexed full-phase-encoding holography.

I propose a multidimension-multiplexed imaging method with which multiple physical quantities of light are simultaneously obtained as interference fringe images. The varieties of light are distinguished by exploiting the proposed phase-encoding technique. Neither measurements of point spread functions in advance, nor iterative calculations to derive multidimensional information, nor a laser light source is required.

Single-path single-shot phase-shifting digital holographic microscopy without a laser light source.

We propose single-path single-shot phase-shifting digital holographic microscopy (SSP-DHM) in which the quantitative phase information of an object wave is acquired without a laser light source. Multiple phase-shifted holograms are simultaneously obtained using a linear polarizer, a liquid crystal on a silicon spatial light modulator (LCoS-SLM), and a polarization-imaging camera. Complex amplitude imaging of a USAF1951 test target and phase imaging of transparent HeLa cells are performed to show its quantitative phase-imaging ability.

Real-valued diffraction calculations for computational holography [Invited].

Computational holography, encompassing computer-generated holograms and digital holography, utilizes diffraction calculations based on complex-valued operations and complex Fourier transforms. However, for some holographic applications, only real-valued holograms or real-valued diffracted results are required. This study proposes a real-valued diffraction calculation that does not require any complex-valued operation.

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.

Incoherent color digital holography with computational coherent superposition for fluorescence imaging [Invited].

We present color fluorescence imaging using an incoherent digital holographic technique in which holographic multiplexing of multiple wavelengths is exploited. Self-interference incoherent digital holography with a single-path in-line configuration and the computational coherent superposition scheme are adopted to obtain color holographic three-dimensional information of self-luminous objects with a monochrome image sensor and no mechanical scanning. We perform not only simultaneous color three-dimensional sensing of multiple self-luminous objects but also color fluorescence imaging of stained biological samples.

Two-step phase-shifting interferometry for self-interference digital holography.

We propose a phase-shifting interferometry technique using only two in-line phase-shifted self-interference holograms. There is no requirement for additional recording or estimation in the measurement. The proposed technique adopts a mathematical model for self-interference digital holography.

Multiwavelength three-dimensional microscopy with spatially incoherent light, based on computational coherent superposition.

In this Letter, we propose spatially incoherent multiwavelength three-dimensional (3D) microscopy that exploits holographic multiplexing and is based on computational coherent superposition (CCS). The proposed microscopy generates spatially incoherent wavelength-multiplexed self-interference holograms with a multiband-pass filter and spatially and temporally incoherent light diffracted from specimens. Selective extractions of 3D spatial information at multiple wavelengths from the holograms are realized using the CCS scheme.

Multiwavelength-multiplexed phase-shifting incoherent color digital holography.

We propose multiwavelength-multiplexed phase-shifting incoherent color digital holography. In this technique, a monochrome image sensor records wavelength-multiplexed, phase-shifted, and incoherent holograms, and a phase-shifting interferometry technique selectively extracts object waves at multiple wavelengths from the several recorded holograms. Spatially incoherent light that contains multiple wavelengths illuminates objects, and multiwavelength-incoherent object waves are simultaneously obtained without using any wavelength filters.

Multiwavelength-selective phase-shifting digital holography without mechanical scanning.

We propose multiwavelength in-line phase-shifting digital holography with a monochrome image sensor, single reference arm, and no mechanical scanning. We use phase-shifting interferometry selectively extracting wavelength information as a method to obtain multiwavelength object waves separately from wavelength-multiplexed phase-shifted holograms. By exploiting a liquid crystal on silicon spatial light modulator with a wide phase-modulation range as an electrically driven phase shifter in this interferometry, we remove mechanically moving parts during phase shifting.

Color single-pixel digital holography with a phase-encoded reference wave.

We propose and demonstrate a multicolor single-pixel digital holography technique. The intensity and phase images of an object are simultaneously obtained from the time-sequence intensity data captured using a single-pixel photodetector. Moreover, phase-structured light and phase-shifting interferometry are implemented using only a spatial light modulator without any mechanical movements.

High-speed image-reconstruction algorithm for a spatially multiplexed image and application to digital holography.

We propose a high-speed image-reconstruction algorithm for a spatially multiplexed image that is obtained by spatial frequency-division multiplexing. The algorithm utilizes smoothing and does not require any Fourier transform (FT) or iterative procedure to extract the desired information selectively from a single image. Numerical and experimental results show its validity and color holographic imaging ability.

Digital holography and its multidimensional imaging applications: a review.

In this review, we introduce digital holographic techniques and recent progress in multidimensional sensing by using digital holography. Digital holography is an interferometric imaging technique that does not require an imaging lens and can be used to perform simultaneous imaging of multidimensional information, such as three-dimensional structure, dynamics, quantitative phase, multiple wavelengths and polarization state of light. The technique can also obtain a holographic image of nonlinear light and a three-dimensional image of incoherent light with a single-shot exposure.

Multiwavelength digital holography with wavelength-multiplexed holograms and arbitrary symmetric phase shifts.

We propose multiwavelength in-line digital holography with wavelength-multiplexed phase-shifted holograms and arbitrary symmetric phase shifts. We use phase-shifting interferometry selectively extracting wavelength information to reconstruct multiwavelength object waves separately from wavelength-multiplexed monochromatic images. The proposed technique obtains systems of equations for real and imaginary parts of multiwavelength object waves from the holograms by introducing arbitrary symmetric phase shifts.

Multiwavelength off-axis digital holography with an angle of more than 40 degrees and no beam combiner to generate interference light.

We propose single-shot multiwavelength digital holography with an extremely large incident angle and show the digital recording of multiple object waves at multiple wavelengths with an angle of more than 40 degrees and no beam combiner to generate interference light. Both the avoidance of the crosstalk between the object waves at different wavelengths and the space-bandwidth extension are simultaneously achieved with a single-shot exposure of a monochromatic image sensor and a reference beam even when the wavelength difference between the object waves is small. An extremely large angle can be set by utilizing the signal theory.

Dual-wavelength phase-shifting digital holography selectively extracting wavelength information from wavelength-multiplexed holograms.

Dual-wavelength phase-shifting digital holography that selectively extracts wavelength information from five wavelength-multiplexed holograms is presented. Specific phase shifts for respective wavelengths are introduced to remove the crosstalk components and extract only the object wave at the desired wavelength from the holograms. Object waves in multiple wavelengths are selectively extracted by utilizing 2π ambiguity and the subtraction procedures based on phase-shifting interferometry.

Digital holography based on multiwavelength spatial-bandwidth-extended capturing-technique using a reference arm (Multi-SPECTRA).

Single-shot digital holography based on multiwavelength spatial-bandwidth-extended capturing-technique using a reference arm (Multi-SPECTRA) is proposed. Both amplitude and quantitative phase distributions of waves containing multiple wavelengths are simultaneously recorded with a single reference arm in a single monochromatic image. Then, multiple wavelength information is separately extracted in the spatial frequency domain.

Phase-shift binary digital holography.

We propose phase-shift digital holography (DH) with a one-bit image sensor. In this method, the propagating complex field from an object is binarized by a one-bit sensor using a phase-shifter. The complex field on the hologram plane is then calculated with the one-bit image data.

Single-shot dual-wavelength phase unwrapping in parallel phase-shifting digital holography.

We propose a single-shot phase-unwrapping method using two wavelengths in parallel phase-shifting digital holography (PPSDH). The proposed method enables one to solve the phase ambiguity problem in PPSDH. We conducted an experiment of the proposed method using two lasers whose wavelengths are 473 and 532 nm.

Space-bandwidth extension in parallel phase-shifting digital holography using a four-channel polarization-imaging camera.

We propose a method for extending the space bandwidth (SBW) available for recording an object wave in parallel phase-shifting digital holography using a four-channel polarization-imaging camera. A linear spatial carrier of the reference wave is introduced to an optical setup of parallel four-step phase-shifting interferometry using a commercially available polarization-imaging camera that has four polarization-detection channels. Then a hologram required for parallel two-step phase shifting, which is a technique capable of recording the widest SBW in parallel phase shifting, can be obtained.

Multiwavelength parallel phase-shifting digital holography using angular multiplexing.

We propose a single-shot digital holography for recording multiwavelength and complex amplitude information by using a single monochromatic image sensor. The zeroth-order wave and conjugate image in each wavelength are removed from a recorded single hologram by applying parallel phase-shifting interferometry. Angular multiplexing is utilized to record the complex amplitude of an object wave in each wavelength separately, and no color filter is required.

Image reconstruction algorithm for recovering high-frequency information in parallel phase-shifting digital holography [Invited].

We propose an image reconstruction algorithm for recovering high-frequency information in parallel phase-shifting digital holography. The proposed algorithm applies three kinds of interpolations and generates three different kinds of object waves. A Fourier transform is applied to each object wave, and the spatial-frequency domain is divided into 3×3 segments for each Fourier-transformed object wave.