Optical attenuator is a passive device used to reduce the power level of an optical signal. It is generally used in single-mode long-haul applications to prevent optical overload at the receiver. Optical attenuator is widely used in CWDM&DWDM, CATV systems, data center networks, test equipment and other high power applications. CVOA comprises a dual fiber collimator and a reflection component separated by a linear moveable ND filter. They are used to permit dynamic control of optical power levels in a fiber and can be applied to adjust power level of signal in the optical communication at the output of light sources, E/O converters and for the linear or dynamic range of power meter.