A compact, high-speed variable-focus liquid lens using acoustic radiation force is proposed. The lens consists of an annular piezoelectric ultrasound transducer and an aluminum cell (height: 3 mm; diameter: 6 mm) filled with degassed water and silicone oil. The profile of the oil-water interface can be rapidly varied by applying acoustic radiation force from the transducer, allowing the liquid lens to be operated as a variable-focus lens. A theoretical model based on a spring-mass-dashpot model is proposed for the vibration of the lens. The sound pressure distribution in the lens was calculated by finite element analysis and it suggests that an acoustic standing wave is generated in the lens. The fastest response time of 6.7 ms was obtained with silicone oil with a kinematic viscosity of 100 cSt.

We propose a fiber Bragg grating (FBG) sensor array system using a high-speed swept light source. The light source is an external cavity semiconductor laser using an optical fiber coupling with a Littrow-mounted grating spectroscope, where the fiber end is vibrated in the cantilever bending mode using a piezoelectric transducer. The incident angle to the grating is scanned at an ultrasonic frequency, and the output wavelength is swept according to the vibration displacement amplitude. The maximum sweep rate of 172 kHz was achieved for the sweep range of 70 nm. In this paper, the light source is used for high-speed and high sensitivity FBG sensor interrogation. First, to test the operation of the proposed FBG sensor, the center wavelength variation due to temperature shift is measured in water. Second, we experimentally demonstrate the measurements of dynamic strain oscillating at 10 and 28 kHz. The observation of high frequency vibrations is achieved with a sufficient sampling rate.

A variable-focus lens that employs acoustic radiation force and a viscoelastic material and that has no mechanical moving parts is investigated. The lens has a simple and thin structure that consists of an annular ultrasonic transducer and silicone gel. An axially symmetric acoustic standing wave can be generated in the gel by exciting a vibration mode in the radial direction on the transducer. The lens profile can be altered by varying the acoustic radiation force of the transducer. The focal length can be controlled by varying the transducer input voltage so that the lens functions as a variable-focus lens.

A liquid lens was fabricated with a focal point that can be varied in the axial and radial directions. We have been developing a variable-focus liquid lens that employs acoustic radiation force and does not contain any mechanical moving parts. Our liquid lens is more compact and has a faster response than conventional mechanical lenses. Rapid scanning of its focus at 1 kHz has been realized by excitation with an amplitude-modulation (AM) signal. The liquid lens consists of a cylindrical acrylic cell (inner diameter: 10 mm; thickness: 3 mm), two immiscible liquids with different refractive indices (water and silicone oil), and an annular piezoelectric lead zirconate titanate transducer with four electrodes. The oil-water interface functions as a lens surface and it can be deformed by the acoustic radiation force generated by the transducer; this enables the lens to act as a variable-focus lens. The variation of the oil-water interface was observed by optical coherence tomography. The laser beam path through the lens was calculated by ray-tracing simulations. The oil-water interface could be deformed and its focal point could be varied in three dimensions by controlling the input voltages of the PZT electrodes. The displacement angle in the radial direction was approximately 3° when two of the electrodes were excited by an input voltage of 45 V at a frequency of 1.9 MHz. The dynamic performance of the lens was investigated using a high-speed cam- era. Excitation by AM signals with a phase difference caused the hemispherical water droplet to oscillate, enabling the focus to be scanned in the axial and radial directions.

In this paper, we present a high-frequency optical scanner based on a vibrating optical fiber where the lateral displacement and rotation of the optical fiber end and the acoustooptic effect due to the stress induced in the fiber core by the vibration provide a large deflection angle of the light beam. First, the configuration used to excite high-frequency bending vibrations on the optical fiber using a piezoelectric element is described, and the relationship between the resonant frequency and the fiber length is reviewed, on the basis of the simple beam theory. Then, the principle of deflecting the light beam with the vibration and a ball lens is presented. Second, the deflection angle is estimated through the geometrical optics for the bending optical fiber, while the acoustooptic effect is simulated using the stress distribution along the optical fiber. The acoustooptic effect is observed by the stroboscope method under a microscope. The possible maximum vibration displacement was increased as the atmospheric pressure was reduced, and two-dimensional (2D) scanning was demonstrated with the fiber vibration at 42 kHz and the 0.5-mm-diameter ball lens displacement at 460 Hz.