Optical-fiber sensors have two distinct roles in sensing. Firstly, they enable the registration of opto-mechanical and opto-chemical interactions under investigation. The second role is to serve as a channel of communication for remote sensing. This is particularly useful in subsurface or hazardous environments. Optical fibers can efficiently transmit light in wavelengths ranging from the higher range of Ultraviolet radiation to Near-Infrared wavelengths. Developments in optical waveguides and components in microelectronics and communications, such as those utilized in long-distance communication or short distance applications for vehicles and local area networks, have also led to advances in research and development for the sensing community. When combined with advances made in molecular probes for analytical chemistry and biology, optical waveguides have made significant contributions to sensing in both the physical and chemical domains.