記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AIP Publishing  

Optical image stabilization (OIS) systems maintain the three-dimensional focal position of a lens through mechanical actuation systems. This paper examines an optical lens for OIS that utilizes ultrasound vibration to alter the focal position, not only in the depth direction but also in the radial direction. The lens has a simple structure with no mechanical moving parts and consists of an ultrasound transducer divided into four pieces, a glass disk, and a transparent viscoelastic gel film that functions as a lens. The acoustic radiation force generated by the resonant flexural vibration of the glass disk can alter the surface profile of the gel film, allowing for a variable-focus function. The concave and convex lenses can be interchanged using two resonant vibration modes: the standing-wave mode, in which the vibration loop appears at the center, and the traveling-wave mode, in which the vibration node appears at the center. The positions of ultrasound vibrations on the lens can be controlled in a two-dimensional plane by adjusting the driving amplitudes of each channel, thereby achieving focus control in the radial direction. The focusing characteristics of the lens are evaluated through ray-tracing simulation.

DOI： 10.1063/5.0218754

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Optica Publishing Group  

Conventional camera modules require mechanical moving parts to move their lenses and to adjust their focal points. This paper examines optically tunable lenses with a focal length and lens aperture that can be controlled using ultrasound vibration and a transparent gel. The lens uses the acoustic radiation force, which induces changes in the lens profile; varifocal convex and concave lenses can be fabricated by adjusting the input signals. The optical characteristics of the lenses were evaluated using ray tracing simulations. The aperture can be controlled with the driving frequency, with higher frequencies leading to a wider range of focal length changes with a lower input voltage.

DOI： 10.1364/ao.528980

記述言語：日本語  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AIP Publishing  

Modulation of the refractive index in a medium by external stimuli enables fast and reversible control of light propagation. This technology for controlling light has led to new discoveries in a wide range of research fields from physics to life sciences and has played a major role in the development of photonics devices. In this article, we focus on ultrasound as an external stimulus and have devised a method to control the refractive index of a medium using ultrasound. Our research group has previously discovered that a giant refractive-index gradient (Δn on the order of 10−2) was induced when water was irradiated with high-frequency (100 MHz range), high-intensity (on the order of MPa) ultrasound. Here, we report ray-tracing simulations in a medium with a refractive-index gradient induced by ultrasonic radiation. A numerical model of the refractive-index gradient was developed based on the experimental data, and ray-tracing simulations were performed using the Euler–Lagrange equation. The ray-tracing simulation results were close numerically to the profiles of the laser beam observed in the experiment when the laser beam was incident on the refractive-index-gradient medium.

DOI： 10.1063/5.0207446

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Optica Publishing Group  

Compound lens systems with mechanical actuators are used to focus objects at near to far distances. The focal length of ultrasound varifocal liquid crystal (LC) lenses can be controlled by modulating the refractive index spatial distribution of the medium through the acoustic radiation force, resulting in thin and fast-response varifocal lenses. The frequency characteristics of such a lens are evaluated in this paper, and several axisymmetric resonant vibration modes over 20 kHz are observed. The effective lens aperture decreased with the wavelength of the resonant flexural vibration generated on the lens, meaning that this parameter can be controlled with the driving frequency.

DOI： 10.1364/ao.515888

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AIP Publishing  

Spatiotemporal modulation of refractive index in an optical path medium allows for control of light propagation. This refractive index change (Δn) can be achieved by external stimulation such as temperature or density change, but there is a limit to the extent to which Δn can be controlled by external stimulation acting on a single medium. Here, we demonstrate a technique to form a giant refractive index gradient (Δn = 0.06) in a small region of water (< 10 mm) using a high-frequency, high-intensity (in the 100-megahertz-range, on the order of megapascals) ultrasonic wave. Ultrasonic radiation in water can statically modulate the refractive index in water from the initial value (n = 1.33) toward that of air.

DOI： 10.1063/5.0174915

記述言語：日本語  

記述言語：日本語  

担当区分：筆頭著者   記述言語：英語  

記述言語：日本語  

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP Publishing  

Abstract

This paper proposed a board-mounted ultrasonic variable-focus liquid crystal (LC) lens. The lens controls the focus using the acoustic radiation force generated by the resonant flexural vibration mode. The LC lens was fixed to an aluminum substrate with a hole whose aperture corresponded to the inner diameter of the transducer. The part of the LC lens attached to the substrates functioned as a fixed condition, and the flexural vibration mode was successfully generated. The fixed lens exhibited a gradual focal change with current, confirming that fixing the condition affected the rate of focal change.

DOI： 10.35848/1347-4065/acb71c

その他リンク： https://iopscience.iop.org/article/10.35848/1347-4065/acb71c/pdf

記述言語：日本語  

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP Publishing  

Abstract

Ultrasound multilayered variable-focus liquid crystal (LC) lenses have better optical performance compared to conventional ultrasound LC lenses. This paper investigates the effect of the distance between two LC layers on the optical characteristics of the lens. The LC molecular orientation in the lens was altered by the acoustic radiation force generated by the lens’ resonance flexural vibration mode, causing a change in the focal length. The focal length change was increased dramatically, and the electrical consumption was reduced in lenses with thinner interlayers.

DOI： 10.35848/1882-0786/aca0da

その他リンク： https://iopscience.iop.org/article/10.35848/1882-0786/aca0da/pdf

記述言語：英語  

担当区分：筆頭著者   記述言語：日本語  

記述言語：英語   出版者・発行元：Acoustical Society of America (ASA)  

Piezoelectric thin film transducers that can receive and transmit high-frequency and high-intensity ultrasound are powerful tools for future medical and industrial applications. Our group has developed acousto-optic devices where the refractive index can be controlled at high speed and high precision using ultrasound, but there are few reports on the interaction between high-frequency (tens to hundreds MHz) and high-intensity (MPa) ultrasound and visible light in liquids. In this study, we evaluated the acousto-optic interaction using polarized CW laser (532 nm) and a piezoelectric KNbO3 thin film transducer formed by hydrothermal method. The transducer was driven continuously at the fundamental or higher resonance frequencies (32, 96, 160, or 210 MHz) in a water cell, and the projection light of a laser beam penetrating perpendicularly to the sound axis was observed. The length of the projection light was elongated in the sound axis on the screen as the driving frequency increased. These results implies that the relationship between the wavelength of ultrasound and the laser beam width is the critical parameter for the acousto-optic phenomenon; the profile of the projection light is dependent on a ratio of the wavelength of ultrasound and the beam width of the laser beam.

DOI： 10.1121/10.0016207

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Institute of Electrical and Electronics Engineers (IEEE)  

DOI： 10.1109/tuffc.2022.3194861

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Springer Science and Business Media LLC  

Abstract

A method to estimate orientation direction of liquid crystal molecules three-dimensionally under ultrasound excitation was proposed and the relationship between the ultrasound vibration and the molecular orientation was discussed. Our group have reported a technique to control orientation direction of liquid crystal molecules using ultrasound vibration which could be applied to an optical variable-focus liquid crystal lens. The lens consisted of a liquid crystal layer sandwiched by two glass circular discs and a piezoelectric ring. Ultrasound vibration induces change in the refractive index of the lens, enabling the variable-focus function. The three-dimensional orientation direction of the liquid crystal molecules in the lens was predicted from the transmitted light distributions under the crossed Nicol conditions. The liquid crystal molecules were inclined from vertical alignment by the ultrasound vibration, and larger ultrasound vibration gave larger inclination of the molecules. There was a strong correlation between the distributions of ultrasound vibration and the liquid crystal molecular orientation; the molecular orientation was changed remarkably between the antinodal and nodal parts of the ultrasound flexural vibration on the glass plate and the molecules aligned towards the antinode.

DOI： 10.1038/s41598-020-62481-2

その他リンク： https://www.nature.com/articles/s41598-020-62481-2

記述言語：英語  

記述言語：日本語  

記述言語：日本語  

記述言語：日本語  

記述言語：英語   出版者・発行元：Acoustical Society of America (ASA)  

Nematic liquid crystals are widely used in optical devices such as liquid crystal displays and controlled by electric fields through the liquid crystal layer. The authors have proposed a technique to control the orientation of liquid crystal molecules using ultrasound vibration without indium tin oxide electrodes. An ultrasound liquid crystal cell was fabricated; it consists of a liquid crystal layer sandwiched by two glass plates having two ultrasound PZT transducers. When exciting the transducers at the resonance frequencies, the flexural vibration modes were generated on the cell and the acoustic radiation force acted to the liquid crystal molecules so that the orientation direction can be changed. The relationship between the molecular orientation and the vibration distribution of the cell was investigated from the transmitted light distribution of the liquid crystal cell under the crossed Nicol condition. In addition, the orientation of liquid crystal molecules was evaluated as ultrasonic wave velocity in the GHz range by the Brillouin scattering method. The ultrasonic wave velocity in the long axis direction of the liquid crystal molecules was higher than that in the short axis direction, which indicates the uniaxial anisotropy of the liquid crystal molecules.

DOI： 10.1121/1.5068570

記述言語：英語   出版者・発行元：Acoustical Society of America (ASA)  

Nematic liquid crystal is widely used in optical devices such as liquid crystal displays and controlled by electric fields through the liquid crystal layer. Our group has proposed a control technique of liquid crystal molecular orientation using ultrasound vibration without indium tin oxide electrodes [1]. In this study, using ultrasound and nematic liquid crystal, we realized a variable focus liquid crystal lens. The liquid crystal lens has no transparent electrodes and consists of a simple structure; a nematic liquid crystal layer with a thickness of 50 μm is formed between two circular grass plates. An annular PZT ultrasonic transducer was bonded on the glass plate. By exciting the transducer at the resonance frequencies (28 kHz), the flexural vibration modes were generated. The acoustic radiation force from the vibration changed the molecular orientation of the liquid crystals, which induced the distribution of the execution refractive indices. The liquid crystal layer then worked as a lens. The focal points could be controlled by the radiation force and moved in the radial direction. [1] S. Taniguchi, D. Koyama, Y. Shimizu, A. Emoto, K. Nakamura, and M. Matsukawa, Appl. Phys. Lett. 108(2016), 101103.

DOI： 10.1121/1.5014415

記述言語：日本語  

記述言語：日本語  

記述言語：英語  

記述言語：英語  

記述言語：英語  

記述言語：英語  

記述言語：英語  

記述言語：日本語  

記述言語：日本語  

記述言語：日本語  

記述言語：日本語  

記述言語：日本語  

記述言語：英語   会議種別：口頭（一般）  

記述言語：日本語  

記述言語：日本語  

記述言語：日本語  

記述言語：英語   会議種別：ポスター発表  

記述言語：英語   会議種別：口頭（一般）  

記述言語：英語   会議種別：口頭（一般）  

記述言語：英語   会議種別：ポスター発表  

記述言語：日本語  

記述言語：日本語  

記述言語：日本語  

記述言語：日本語  

記述言語：英語  

記述言語：英語  

記述言語：英語  

記述言語：英語  

記述言語：日本語  

記述言語：日本語  

記述言語：日本語  

記述言語：英語  

記述言語：英語  

記述言語：英語  

記述言語：英語  

記述言語：英語  

記述言語：英語  

記述言語：日本語  

記述言語：日本語  

記述言語：日本語  

記述言語：英語  

記述言語：日本語  

記述言語：英語