Kenta Nakazawa

Resonant Varifocal Micromirror with Piezoresistive Focus Sensor

This paper reports a microelectromechanical systems (MEMS) resonant varifocal mirror integrated with piezoresistive focus sensor. The varifocal mirror is driven electrostatically at a resonant frequency of a mirror plate to obtain the wide scanning range of a focal length. A piezoresistor is used to monitor the focal length of the varifocal mirror. The device is made of a silicon-on-insulator (SOI) wafer and a glass wafer. A mirror plate and a counter electrode are fabricated by a top silicon layer of the SOI wafer and on the glass wafer, respectively. The piezoresistor is fabricated by ion implantation on a supporting beam of the mirror plate. The stress variation of the beam, which is detected by the piezoresistor, correspond the focal length of the varifocal mirror. The focus length varies from −41 to 35 mm at the resonant frequency of 9.5 kHz. The focal length of the varifocal mirror is monitored by the piezoresistor in real time.

λ/8 Precision parabolic resonant varifocal mirror

An λ/8 precision parabolic resonant varifocal mirror is described. The varifocal mirror is electrostatically driven and made of single crystalline silicon. The varifocal mirrors having two types of circumferential structure were fabricated. One is clamped edge, the other is close to simply supported edge. The mirror surface profiles were measured at maximum oscillation amplitude. The deviation from parabola is smaller than λ/8 in the case of the mirror with simply supported circumference at the wavelength longer than 500 nm.

Confocal laser displacement sensor using MEMS varifocal mirror

A confocal laser displacement sensor using a micro-machined varifocal mirror is reported. The focal length modulation is a key function for the sensor. The measurement speed and range depend on the mechanism. In this study, we propose to use the micro-machined varifocal mirror for the mechanism of the focal length modulation in the confocal displacement sensor. The electrostatically actuated varifocal mirror made by silicon was used. The working distance of the displacement sensor is designed to be 31 mm. The measurement range at 7 kHz is 310 μm. The linearity in the full scale range is from −1.5% to 0.85%.

Fabrication of varifocal scanner integrated with piezoresistive focal length and angle sensor

We present the varifocal scanner combined with the piezoresistors to monitor the rotation angle and focal length. The angle sensor measures with the accuracy of ±0.021 degree in the range of ±1.2 degree.

Varifocal mirror integrated with scanner using wafer bonding technology

The integration of a varifocal mirror with a scanner using wafer bonding technology is presented. The wafer bonding technology enables us to enlarge the design possibility. A 2 mm diameter varifocal mirror is bonded on the scanner. The optical scanning angle is 7° at 3.59 kHz. The focal length changes from infinity to 139 mm.

Large-amplitude resonant varifocal mirror with an acoustic cavity

We report a large-amplitude resonant varifocal mirror with an acoustic cavity under atmospheric pressure. The amplitude of resonant varifocal mirror with acoustic cavity was measured by changing the cavity length. The amplitude of varifocal mirror was changed periodically depending on the cavity length. The period is in excellent agreement with the half of calculated wavelength of the acoustic wave. The maximum amplitude was about 4 times larger than the minimum amplitude. For designing of the acoustic cavity length, a theoretical approach on the basis of interaction between mechanical vibration and acoustic wave in the cavity is also described and compared to experimental results.

Piezoresistive displacement sensor integrated in resonant varifocal mirror

An electrostatically actuated resonant varifocal mirror with a piezoresistive displacement sensor is reported. The focal length of the varifocal mirror is monitored by the sensor. The device is fabricated from a silicon-on-insulator wafer and a glass wafer. The p-type silicon region which is formed in n-type top silicon layer by boron ion implantation is used as the piezoresistive displacement sensor. The mirror surface profile and sensor signal are measured.