Chang-Hyeon Ji

Electromagnetic Two-Dimensional Scanner Using Radial Magnetic Field

In this paper, we present the design, fabrication, and measurement results of a two-dimensional electromagnetic scanning micromirror actuated by radial magnetic field. The scanner is realized by combining a gimbaled single-crystal-silicon micromirror with a single turn electroplated metal coil, with a concentric permanent magnet assembly composed of two concentric permanent magnets and an iron yoke. The proposed scanner utilizes the radial magnetic field rather than using a lateral magnetic field oriented 45deg to the horizontal and vertical scan axes to achieve a biaxial magnetic actuation. The single turn coil fabricated with electroplated copper achieves a nominal resistance of 1.2 Omega. A two-dimensional scanner with mirror size of 1.5 mm in diameter was fabricated. Maximum optical scan angle of 8.8deg in horizontal direction and 8.3deg in vertical direction were achieved. Forced actuation of the gimbal at 60 Hz and resonant actuation of the micromirror at 19.1-19.7 kHz provide slow vertical scan and fast horizontal scan, respectively. The proposed scanner can be used in raster scanning laser display systems and other scanner applications.

Electrostatic MEMS variable optical attenuator with rotating folded micromirror

The design and fabrication of an electrostatic MEMS variable optical attenuator (VOA) is described. The VOA is a reflection type with a folded micromirror actuated by a comb-drive actuator. The VOA is fabricated by a simple single-mask process. One photolithography and subsequent deep silicon reactive ion etching define all the microstructures of the VOA. The folded micromirror structure can reduce the overall size of the device by enabling the parallel alignment of an input fiber and an output fiber. Lensed fibers are used to maximize the coupling efficiency and the ease of assembly. The electrooptic characteristics and dynamic characteristics of fabricated VOA are measured. The initial insertion loss is 0.5 dB at 1550 nm and the maximum attenuation is 45 dB, respectively. The polarization dependent loss is measured to be 0.2 dB at 20-dB attenuation. The response time for maximum attenuation is less than 5 ms.

Electromagnetic 2/spl times/2 MEMS optical switch

This paper presents the design, fabrication, and measurement results of a 2/spl times/2 microelectromechanical systems optical switch. The switch comprises an electromagnet and lensed fibers assembled with a micromachined movable vertical micromirror. The optical switch utilizes the out-of-plane motion of the vertical micromirror actuated by electromagnetic force compared to the comb-driven linear actuation achieved by the electrostatic force. At a wavelength of 1550 nm, the insertion loss of 0.2-0.8 dB and the polarization-dependent loss of 0.02-0.2 dB are measured. The switching time is 1 ms. A novel method of realizing a latchable optical switch using an electromagnetic actuator is also provided and verified. The latch mechanism is based on the latchability of the electropermanent magnet instead of the mechanical one using conventional arch-shaped leaf springs.

Electromagnetic variable optical attenuator

Electromagnetically actuated micromirror is a promising candidate for optical switching applications. In this research, we have designed, fabricated and tested a microelectromechanical systems (MEMS) variable optical attenuator (VOA) composed of an electromagnetic micromirror and integrated fibers. The effects of fiber arrangement and the deployment of lensed fibers on the attenuator performance are analyzed based on experimental results.

Electromagnetic micromirror array with single-crystal silicon mirror plate and aluminum spring

We have designed and fabricated an addressable 4 /spl times/ 4 array of micromirrors capable of providing up to 90/spl deg/ of angular deflection. Each micromirror comprises a single-crystalline silicon mirror plate supported by aluminum springs, which provides an extremely flat reflective surface and a compliant spring material that enables the integration of the device into a limited area without mitigating its performance (i.e., total angular deflection). The device is fabricated using a combination of surface and bulk micromachining processes, such as electroplating, bulk wet etching and XeF/sub 2/ etch processes. Selective actuation is accomplished by the use of an electrostatic clamping force on each mirror plate. A mirror rotation angle of more than 80/spl deg/ can be obtained by applying an external magnetic field, and this angle can be further increased by the use of an electrostatic force. The designed structure can be used in microphotonic applications.

Design and Fabrication of Electromagnetic Micromirror with Bulk Silicon Mirror Plate and Aluminum Spring.

We have designed and fabricated an electromagnetic micromirror with a flat mirror plate capable of large angular deflection. Single-crystal silicon is used as a mirror plate to obtain an optically flat reflective surface. By a combination of surface and bulk micromachining processes, the single-crystal silicon mirror plate is connected to the substrate via an aluminum spring, which occupies a relatively small area without compromising the compliance. The proposed fabrication process can be applied to the fabrication of devices in which a flat moving part is supported by a compliant spring structure. Nickel electroplated onto the mirror plate enables a mirror rotation angle of up to 84.8° by applying an external magnetic field vertical to the substrate. This designed structure can be used individually or as an array in microphotonic applications.

Design and fabrication of electromagnetic micromirror with bulk silicon mirror plate and aluminum spring

We have designed and fabricated a magnetically actuated micromirror device. The fabricated device can be used in optical switching applications that require large angular deflection of the reflected beams. The fabrication process is a combination of surface and bulk micromachining, which can be characterized by the capability to form large flat bulk silicon structure and flexible metal spring. The fabrication process can be utilized in the fabrication of devices which require large flat structure and reduced energy in actuation.

Performance of a raster scanning laser display system using diamond shaped frame supported micromirror

We describe the design, fabrication, and experimental results of a raster scanning laser display system using micromachined electrostatic scanning micromirror. The micromirror is comprised of a diaphragm mirror plate supported by an array of diamond shaped support frame, and movable comb electrodes. A prototype raster scanning laser display system using the fabricated micromirror, having optical scan angle of 16.9deg at resonance frequency of 19.55 kHz, as the horizontal scanner was developed and tested. To compensate for the nonlinear characteristics of the scanner, a simple image correction method was developed, and the projected image was analyzed and compared with the simulation results

Diamond shaped frame supported electrostatic scanning micromirror

The paper presents the design, fabrication and measurement of an electrostatic scanning micromirror having a diaphragm mirror plate supported by an array of diamond shaped frame structures. Instead of supporting the diaphragm mirror of a different material with a stiff rim structure at the circumference, the diaphragm mirror plate and the frame structure are fabricated monolithically in the same layer of single-crystal-silicon (Nee, J.T. et al., Proc. IEEE Int. Conf. MEMS, p.704-9, 2000). The scanning micromirror with a 10 /spl mu/m-thick diaphragm mirror plate, having a planar dimension of 1.5/spl times/1.5 mm/sup 2/, supported by an array of 110 /spl mu/m-thick rhombic stiffening frames, was fabricated and tested. A mechanical deflection angle of 8.5/spl deg/ at the resonance frequency of 19.55 kHz and 44% reduction of dynamic deformation (Conant, R.A. et al., Proc. IEEE/LEOS Int. Conf. Optical MEMS, p.49-50, 2000), in comparison to the conventional rectangular parallelepiped micromirror, were obtained.

Electrostatic MEMS variable optical attenuator with folded micromirror

A reflection type VOA with folded micromirror was designed and fabricated. The proposed mirror structure can reduce the size of device by parallel alignment of the two fibers. Lensed fibers are used for high coupling efficiency and ease of assembly. The initial insertion loss is about 0.6 dB and the maximum attenuation is about 30 dB. The switching time of the fabricated VOA is about 1 ms.