Application Note: Switching Midstream
Everyone has had the experience of reaching for an object at the bottom of a pool of water only to find that it is not at the location where your eye says it should be. This well-known phenomenon is the result of light refraction at the water’s surface. At the micro-level this same phenomenon can be used to alter the course of a light beam in an optical circuit. A small mass of liquid moved in or out of the path of the beam can redirect it by refraction or reflection into a different path.
This concept is particularly attractive in connection with optical fibers where once a beam enters a fiber it is trapped by internal reflections. To make optical circuits of any complexity, it is necessary to have a 'switch' that can redirect light from one fiber to another. A successful switch must be robust, fast acting, easy to make, and consume little energy. Needless to say, there is a considerable amount of research currently underway to develop an effective optical switch (see, for example, Scientific American January 2001).
One concept that has been proposed is based on thermo-capillarity. A small drop of liquid is placed in a micro channel that intersects a fiber-optic light beam. When the drop is moved along the channel to where the beam must pass through it, the beam is reflected into a different fiber. The drop is moved by differentially heating its two sides. This causes changes in the surface tension in the menisci on either side of the drop such that the drop is pulled toward the cooler end of the channel. The accompanying figure shows a FLOW-3D simulation of a drop of water in a 14mm-wide channel that is being heated at the bottom.
A light beam may switch when it is mid-stream of the liquid drop, but there is no need for you to switch software mid-stream for your optical-switch or other MEMS research. FLOW-3D has a comprehensive kit of physical modeling tools that will satisfy nearly all your MEMS needs.