My IDEA and DESIGN about Micromirror

Micro-Electro-Mechanical Systems, or MEMS, are integrated micro devices or systems combining electrical and mechanical components. They are fabricated using integrated circuit (IC) batch processing techniques and can range in size from micrometers to millimeters. These systems can sense, control and actuate on the micro scale, and function individually or in arrays to generate effects on the macro scale. This design presents an overview of MEMS technology with emphasis on optical applications. Applications of MEMS devices vary in many fields from automotive transducers, biomedical technologies, communication systems, robotics, aerospace, micro-optics, industrial sensors and actuators.
The applications of MEMS in optics include display systems, optical switching, optical communication, optical data storage, optical processing and interconnection, and adaptive optics.

This design focuses on the state-of-the-art of technologies for the design, fabrication and applications of MEMS micro-mirrors. I will discuss the major design issues, considerations, calculations and restrictions of micro mirrors. The materials employed for the reflective surfaces are described along with their properties. The materials used for the static and dynamic MEMS micro structures as well as the different configurations are also presented and summarized. The two most widely used techniques for actuation, namely, Electrostatic and Magnetic are presented along with the formulas, tables and curves used to design the movable structures. The different options of fabrication processes are presented and discussed. Finally, the applications of micro mirrors are described.

Micro mirrors are the centerpieces of MEMS optical switches. They are tiny mirrors fabricated in silicon using MEMS technology. The switching function is performed by changing the position of a micro mirror to deflect an incoming light beam into the appropriate outgoing optical fiber. The three important properties of micro mirrors are reflectivity, light transmission, and surface roughness. Coating its surface with metal can increase the reflectivity of a micro mirror.

MIRRORS are an important component in an optical system. Mirrors are found in almost every system that makes use of light sources and lenses. Their ability to reflect light and change its direction of propagation has been used for several centuries. Mirrors in the macroscopic world are very well understood and present no major challenges in their design and calculation. However, when the size of the mirror is in the order of a few microns, several issues and challenges come into place. The advances of MEMS technology in the last decade have made possible to design and fabricate micro mirrors that are actually used in real industrial and commercial applications. MEMS micro-mirrors are used today in fiber optic communications as switching devices, in digital displays and projectors, in laser scanners, printers and barcode readers, and in bioengineering for laser surgery.

The area in which MEMS has seen one of its biggest commercial breakthroughs lately is micro machined mirrors for optical switching in both fiber optic communications and data storage applications. Optical switches are to optical communications what transistors are to electronic signaling. What makes Si single-crystal attractive in this case is the optical quality of the Si surface. The quality of the mirror surface is primordial to obtain very low insertion loss even after multiple reflections. Wet bulk micromachining has an advantage here over deep reactive ion etching (DRIE),as the latter leaves lossier Si mirror surfaces due to the inevitable ripples.

MEMS optical switch. The optical signals passing through the optical fibers at the input port are switched independently by the gimbal–mounted MEMS mirrors with two-axis tilt control and then focused onto the optical fibers at the output ports. In the switch, any connection between input and output fibers can be accomplished by controlling the tilt angle of each mirror. As a result, the switch can handle several channels of optical signals directly without costly optical-electrical or electrical-optical conversion.

The MEMS micro-mirrors can be used in the making of optical sensors and display both of which involves the controlling and directing of the light band. Today, information is being transferred to people from electronic devices through display technologies like the Cathode Ray Tubes (CRTs) and Liquid Crystal Display (LCD). In the future, MEMS-based Micro-Mirror array is a likely candidate to replace them as the dominant form of display technologies. This is due to the low-cost and high performance of the micro-mirrors. Furthermore, due to the similar processes and facilities used in the fabrication of the MEMS micro-mirrors, it is relatively easy to incorporate them with their controlling IC chip onto a single silicon substrate.

I have used the angle of the rigid mirror in order to control the location of a reflected beam
of light. This allows the mirror to act as an optical switch for optical fiber networks. The mirror is made of a material with sufficient stiffness to prevent bending. The mirror is attached to a thin beam that is anchored in place at the opposite end. The beam is free to twist and acts as a torsion spring. the mirror is attached to two beams, one on each side rather than a single beam. Thermo pneumatic, thermo elastic, electrostatic, magnetic, or piezoelectric forces may be used to make the mirror move. Here the use of electrostatic force is imagined.A pair of electrodes reside below the mirror. When a potential difference is applied between either of the electrodes and the mirror, a torque is exerted causing the desired rotation.

When electrostatic forces are used to actuate the system, the range of operation is limited by the pull-in instability. The device is actuated by applying a potential difference between the mirror and one of the ground electrodes. This causes a torque on the system, which is countered by the effect of a torsion spring. For this system, the pull-in instability occurs once rotation through a critical angle has taken place. That is, the range of angular motion is limited by the pull-in instability.

Micro-mirror arrays are currently being developed by a number of companies for optical switching. To bring these products to the market quickly, a rapid development cycle is needed, leaving little time for multiple fabrication runs. CAD tools for MEMS can reduce the number of fabrication iterations run by allowing prototyping to occur within the virtual environment. Here, many models can be tested quickly and the design can be optimized prior to initial fabrication.

Modeling of micro-mirrors requires unique simulation capabilities beyond those required for traditional MEMS devices. In many cases, the device alone has unique features which require that CAD tools offer additional capabilities beyond typical electro-mechanical analysis. Second, the entire array must be studied, both from a fabrication and optical perspective. The output of a MEMS software CAD tool is input into an optical ray-tracing program to provide optical system performance of the total MEMS micro-mirror and provide non-sequential ray-tracing of a micro-mirror array.