Fiber optic attenuators are used to reduce the power level of an optical signal, either in free space or in an optical fiber. These are devices that decrease the optical power in a fiber by a fixed or adjustable amount. It can be divided into two categories: fixed and variable. These are widely used in fiber optic telecommunication systems. The basic principle of operation of a common attenuator is controlled by the offset of the input and output fibers, or an air gap between the input and output fibers. Other techniques are used in the operation of advanced fiber optic attenuators; it uses temperature, twisting, tension, or current acting of some type of optical material. Optical attenuator selection depends on a multitude of factors, including wavelength, attenuation levels, and temperature stability.