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A varifocal concave-convex lens using ultrasound and transparent viscoelastic gel is reported. The configuration of the lens is simple and thin, consisting of four pieces of a piezoelectric ultrasound transducer, a glass disk, and a transparent silicone gel film. It uses a combination of the ultrasound resonant flexural standing- and traveling-wave modes excited by in-phase and four-phase drives so that the lens can change its shape to both concave and convex by switching the resonance mode with the same structure. The acoustic radiation force (ARF) originated from the resonant flexural vibration modes changed the surface profile of the gel. Convex and concave deformation were generated at the center of the lens at the resonance frequencies of 38 and 60 kHz, respectively, indicating that a varifocal concave-convex lens could be fabricated by controlling the driving frequency, voltage amplitude, and phase differences among the ultrasound transducers. The deformational displacement on the lens surface and the change in the focal length increased with the input voltage amplitude. The optical microscopic images observed through the lens were enlarged 1.28× (reduced 0.92× ) in the convex (concave) mode with 20 [Formula: see text]. The response time for focusing and the temperature stability under operation were evaluated. By switching the resonance vibration modes of the lens through the input signals to multiple ultrasound transducers, the variable-focus function with both concave and convex lenses was achieved in the same configuration.

A variable focus optical lens using a thixotropic gel and ultrasonic vibration is discussed. The surface profile of the gel could be deformed via acoustic radiation force generated by ultrasound. A thixotropic gel in which the viscosity was changed by shear stress was employed as a transparent lens material. The thixotropic gel allowed the lens to maintain shape deformation in the absence of continuous ultrasound excitation. The lens had a simple structure with no mechanical moving parts and included an annular piezoelectric transducer, a glass disk, and the thixotropic gel film. The axisymmetric concentric flexural vibration mode was generated on the lens at 71 kHz, which resulted in static surface deformation of the gel via the acoustic radiation force. The preservation rate was investigated after switching off the ultrasonic excitation. There was a trade-off between the preservation rate of the lens deformation and the response time for focusing. The focal length could be controlled via the input voltage to the lens, and a variable-focus convex lens could be realized; the change in the focal length with 4.0 Vpp was 0.54 mm. The optical transmittance of the lens was measured and the transmittance ranged 70%–80% in the visible spectral region.

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.

Although ultrasonically controlled liquid crystal lens may play in important role in future optical systems, many optical properties in the liquid crystal layer are still unclear. Moreover, most of the previously conducted studies control the liquid crystal molecular orientation by an applied electric field using transparent electrodes. In this study, using multichannel piezoelectric transducer, standing wave and traveling wave actuation mechanism were applied to the liquid crystal lens and further reported about its optical characteristics using a Shack-Hartmann wavefront sensor. The surface data obtained from the sensor was analyzed and the optical aberrations measured. Traveling wave actuation showed small optical aberrations when compared to the standing wave.

The orientation angles of liquid crystal (LC) molecules were measured during ultrasound vibrations. Light transmitted through a fabricated LC lens was analyzed via the crossed Nicol condition and a crystal rotation method. The LC orientation angle was estimated with a theoretical model, and its distribution in the lens was determined. There was a strong correlation between the molecular angles and ultrasonic vibrational distributions, indicating that the angle was changed by the acoustic radiation force. The maximum tilt angle was 12° for a 50 V peak-to-peak input.

A method to improve the performance of an ultrasound liquid crystal lens is proposed. A double-layer-based lens model tailored based on the liquid crystal’s physical properties, e.g., its dielectric anisotropy and elastic constants, is presented as an alternative method to improve the lens’s optical performance while forming weak anchoring surfaces for nematic liquid crystals, thus promoting easier reorientation of the liquid crystal molecules. The lens configuration was simulated by finite-element analysis using Ansys software. The lens’s physical and optical characteristics were evaluated via comparison using two different liquid crystal materials: 5CB and RDP-85475. The birefringence distribution within the liquid crystal layer was investigated under ultrasound excitation, and the molecular angles of inclination were estimated. A higher birefringence distribution, greater molecular inclination, and a longer focal length were obtained for the double-layered liquid crystal lens using the 5CB material.

The effect of the liquid crystal (LC) layer thickness on the optical characteristics of an ultrasound LC lens was explored. Three LC lenses with differing LC layer thicknesses (100, 200, and 300 μm) were fabricated, and the optical focal lengths were measured by an optical microscope with a varying driving voltage. For the lens with a 200 μm thick LC layer, a larger change in the focal length was observed for a smaller driving voltage compared with that of the other two lenses, indicating that the LC layer thickness is appropriate for a variable-focus lens.

New technologies for adaptive optics are becoming increasingly important for miniature devices such as cell-phone cameras. In particular, motion-free autofocusing and optical image stabilization require sophisticated approaches for alternative lens architectures, materials, and processing to replace multiple solid elements. We discuss a new method, to the best of our knowledge, that provides image stabilization via an annular piezoelectric ceramic that uses ultrasound to drive a liquid crystal layer sandwiched between two circular glass substrates. The piezoelectric ceramic is divided into four quadrants that are independently driven with sinusoidal voltages at the resonant frequency of the lens. The technique is based on ultrasound vibrations with a suitable driving scheme. The lens configuration was modeled via finite-element analysis. Various combinations of the four-channel ultrasound transducer can be used to define the focal point of the liquid crystal lens. Clear optical images could be obtained with the lens. By using two-dimensional fast Fourier transforms, the focal point position was defined and shifted in the radial direction.

A new type of ultrasonically controlled concave liquid crystal lens based on traveling waves (TWs) with a divided electrode structure and an appropriate driving scheme is proposed in this Letter. The lens uses an annular piezoelectric ceramic divided into four parts for four-phase driving and consists of a liquid crystal layer in a sandwich structure between two circular glass substrates. The lens configuration was simulated by finite element analysis using the Ansys software. Here we discuss the use of TWs to expand the lens aperture and clarify the lens’ optical characteristics using a Shack–Hartmann wavefront sensor. The effective lens aperture using TWs was 4.4 mm, and the focal length was 3.8 m.