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Microactuators, microsensors, and signal processors have long been envisioned as the essential components of completely integrated microsystems.1 The schematic of a typical cell of a microintegrated optical system is shown in Fig. 4.1. It is composed of optical components, microactuators, microsensors, signal processors, and control electronics. The processor first receives a command from the outside world to achieve a certain goal, and then sends a command to the control electronics. Upon receiving this command, the microactuator may mechanically alter or displace the optical component to complete the task for the first cycle. At the same time, the microsensor examines if the requirements of the task have been fulfilled, and then the sensing signals are fed back to the signal processors to determine if the task is really completed or if another cycle is needed. Because of advances in both microelectronics and micro-electro-mechanical systems (MEMS) technologies, each cycle can be processed almost in real time. For example, an external command may arrive to select a specific wavelength as the data carrier in one optical channel in a communication network. The microactuator, controlled by electronics, then performs work on the optical component (e.g., actuates the MEMS-based tunable laser or filter) to choose a desired wavelength. The sensing signals from the microsensor are then fed back to the processor and used to determine if the goal has been reached.
This chapter only covers two basic components in the microintegrated system: microsensors and microactuators. It distinguishes itself from other textbooks by categorizing microactuators from the point of view of optical applications and only covering one group of microsensors, which are based on optical sensing techniques.
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