Optical sensors measure temperature, distances, gas concentrations, and many others. In general, we can group optical sensors into three categories: single element sensors, 2D sensor arrays, and fiber based sensors. The single element sensor detects the optical properties of device or material. The sensor can be a passive or active element. The passive element can be used to measure brightness or temperature. Active elements send out a signal and detect the reflected signal in most cases. Reflective sensor, encoders, and light barriers all fall into this category. The 2D sensor arrays include CCD or CMOS cameras that can be applied in imaging-related devices. Fiber based optical sensors detect the optical properties of silica fiber to measure a physical parameter at a remote location, such as optical fiber with a Bragg grating within the fiber.

Traditional optical sensors only include the optoelectronicchip in a simple housing. However, nowadays, customers prefer to use smart optical sensors where an optoelectronic interface circuit chip (OEIC) is integrated within the sensor housing. The OEIC processes the information and generates a standard electrical signal output. For most of the applications this will be a TTL level digital signal. Applications of the smart optical sensor technology include finger sensors and optical keyboards for industrial applications.