Ryohei Hokari

A Varifocal Convex Micromirror Driven by a Bending Moment

A varifocal micromirror is designed and fabricated using silicon micromachining technology. A spherical convex surface of mirror is generated by applying a bending moment to the circumference of micromirror. This method is different from the conventional technique in which a distributed force is exerted on the central area of mirror. On the basis of the theory of materials strength, the deformation of a plate is purely spherical if only a bending moment is applied to the circumference. Spherical surface is well approximated to be a parabola if deflection is small. In order to generate only a bending moment, a force is applied to the plate in the region outside the fulcrum, by which the plate is supported freely in rotation. The proposed mirror was fabricated from a silicon on insulator wafer and a glass plate, which were connected by anodic bonding. The deviation in surface profile of mirror from a parabola was measured with an optical interferometer to be less than 4.7 nm rms in the mirror region inside the 400-mum-diameter fulcrum at the voltage lower than 215 V. The focal length of the fabricated mirror was varied from approximate infinity to 24 mm.

Comparison of electromagnetically induced transparency between silver, gold, and aluminum metamaterials at visible wavelengths

Electromagnetically induced transparency (EIT)-like effects in silver, gold, and aluminum metamaterials consisting of dipole resonators and quadrupole resonators were demonstrated at visible wavelengths. Optical characteristics of the metamaterials could be controlled by the gap distance between the two resonators. EIT-like effects were observed at wavelengths between 603 and 789 nm, 654 and 834 nm, and 462 and 693 nm for the silver, gold, and aluminum EIT metamaterials, respectively. At wavelengths longer than around 650 nm, the silver metamaterials had better EIT-like features. At wavelengths shorter than around 650 nm, on the other hand, the aluminum metamaterials showed promising EIT-like results.

MEMS for Plasmon Control of Optical Metamaterials

Metamaterials have attracted a great deal of attention as artificial electromagnetic materials having unique optical characteristics, and various innovative optical applications have been expected. Micro electromechanical systems (MEMS)-based reconfigurable metamaterials are candidate technologies for active optical control. In this paper, we focus on MEMS-based reconfigurable metamaterials operated in the optical region between visible and near-infrared wavelengths. A brief overview of static optical metamaterials and active optical metamaterials driven by MEMS actuators is presented. Moreover, points to be considered for a micromachining process of optical metamaterials are discussed with results of calculations.

Spherical silicon micro-mirrors bent by anodic bonding

We propose a method to generate spherical micro-mirror by anodic bonding. A flat silicon plate is bent with fulcrum to form a spherical shape by anodic bonding. Convex spherical surface is generated inside the fulcrum by the bending moment generated in circumference of micro-mirror. Due to the bent surface of silicon plate, a smooth spherical surface is obtained. The focal length is in the range form 0.4mm to 1.6mm for the fulcrum diameters from 100µm to 400µm. The fabricated micro-mirror is also used as mold for the replication of micro polymer lens. The surface profile of micro-mirror is transferred to the polymer replica with a high accuracy.

Spherical silicon micromirrors bent by anodic bonding

We propose a method to generate spherical micro-mirror by anodic bonding. A flat silicon plate is bent with fulcrum to form a spherical shape by anodic bonding. Convex spherical surface is generated inside the fulcrum by the bending moment generated in circumference of micro-mirror. Due to the bent surface of silicon plate, a smooth spherical surface is obtained. The focal length is in the range form 0.4mm to 1.6mm for the fulcrum diameters from 100µm to 400µm. The fabricated micro-mirror is also used as mold for the replication of micro polymer lens. The surface profile of micro-mirror is transferred to the polymer replica with a high accuracy.

A varifocal micromirror with pure parabolic surface using bending moment drive

We propose a method to generate a pure parabolic surface of varifocal micromirror by applying a bending moment to the circumference of the micromirror. Pure paraboloid can focus light without aberration a one of the ideal mirror surfaces. In the conventional method, varifocal mirror generates an approximate spherical surface or a paraboloid-like surface by applying a distributed load to the central part of the mirror with parallel plate electrodes. In this study, the micromirror is deformed only by applying a bending moment to the circumference of the mirror in order to generate an ideal paraboloid. The proposed mirror was fabricated from SOI wafer. The deviation of the varifocal mirror from the ideal paraboloid was measured to be smaller than 5 nm for the 400 mum diameter mirror with the focal lengths from the infinity to 24 mm at the voltages from 0 to 215 V.