A fixed optical attenuator is the simplest solution. In DWDM systems, VOAs help equalize per-channel power and compensate amplifier gain tilt across the C/L bands. Thorlabs' Single Mode Fixed Fiber Optic Attenuators allow one to attenuate an optical signal easily by plugging an FC/PC- or FC/APC-terminated fiber directly into the back end of the attenuator connector. Corning's fixed optical attenuators reduce the optical power within a given optical path. An optical attenuator is a passive device that is used to reduce the power level of an optical signal. The attenuator circuit will allow a known source of power to be reduced by a predetermined factor, which is usually expressed as decibels. Key requirements include minimal effect on the beam profile, low wavelength and polarization dependence, and sufficient power handling capability.
[pdf] Fiber optical adjustable attenuator is a product which is dedicated manually to adjust the attenuation of fiber optical path. Tensile Load The temperature measurement environment is 23℃. MVOA features low insertion oss, good resolution, high stability and good reliability.
[pdf] 
