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Millimeter scale electrostatic mirror with sub-wavelength holes for terahertz wave scanninga)
a)Millimeter-Scale Scanning MEMS Mirror with Sub-Wavelength Micro-hole Arrays for Terahertz Wave Scanning, published as part of the IEEE Optical MEMS and Nanophotonics 2012, Banff, Canada, August 2012.
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Image of FIG. 1.
FIG. 1.

Millimeter scale MEMS mirror with subwavelength microhole arrays for THz wave scanning: (a) a schematic diagram of millimeter-scale scanning MEMS mirror with sub-wavelength microhole arrays and (b) an optical image of the fully integrated MEMS mirror and a SEM image of microhole arrays on the aluminum coated silicon mirror plate (inset). A silicon mirror plate with microhole arrays is vertically assembled with two axis torsional microactuators.

Image of FIG. 2.
FIG. 2.

THz reflectivity of aluminum coated Si mirror plates with microholes. (a) A numerical model for FDTD simulation. Rectangular and sub-wavelength microhole arrays of width ri and period rc were implemented on an aluminum coated silicon mirror plate. (b) Spectral THz reflectivity at a constant period of 100 μm. Dips in specular reflectivity are observed due to either extraordinary light transmission or coupling by surface plasmon resonance on the Al-Si interface. (c) THz reflectivity for different widths and periods of microholes. The microhole width below 10 μm at different periods shows high reflectivity over 99% without the dips in reflectivity.

Image of FIG. 3.
FIG. 3.

Microfabrication procedures and microassembly for THz scanning MEMS mirror, which consist of (a) aluminum coated silicon mirror plate with microhole arrays, (b) two axis torsional microactuators, and (c) microassembly for mounting MEMS mirror plate on the microactuator. Both the silicon mirror plate and the microactuator are precisely assembled with thermal epoxies while monitoring pre-defined align keys on an actuator and vertical positions with top and side view microscopic cameras.

Image of FIG. 4.
FIG. 4.

Dynamic responses and optical scanning patterns of THz scanning MEMS mirror with microhole arrays; resonant frequency of a torsional actuator was 5.1 kHz with mechanical Q-factor of 114. The resonant frequency shifts to 123.5 Hz and Q-factor was decreased to 66 after mounting 3 × 3 mm2 mirror plate. However, the Q-factor was increased to 105 when implementing microhole arrays on a mirror plate by minimizing the damping loss, while the resonant frequency was slightly increased due to the inertia of microholes. Two-dimensional optical scanning of the MEMS mirror was visualized using HeNe laser of 530 nm wavelength (inset).

Image of FIG. 5.
FIG. 5.

Experimental demonstration of THz wave scanning using a millimeter scale scanning MEMS mirror with microhole arrays; (a) experimental set-up for reflection type THz TDS system. (b) Time-domain waveform of the reflected THz wave were well remained. (c) Change in the amplitude of 1 THz waves while the MEMS mirror scans with a scanning frequency at 118 Hz. The scanning frequency of THz waves is doubled.


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Scitation: Millimeter scale electrostatic mirror with sub-wavelength holes for terahertz wave scanninga)