A Variable Optical Attenuator (VOA) is a controllable device used to reduce the optical power traveling through a fiber or free-space optical path. Attenuators emulate signal loss, balance power levels, and protect sensitive devices during testing. These EVOAs provide attenuation of up to at least 25 dB, which can be. The NSAI series of NanoSpeed™ fiber optic attenuators uniquely feature large attenuation of 50dB, low optical loss, fast response, and high optical power handling. The. OZ Optics offers a complete line of low cost, compact PC board mountable motor driven variable attenuators with low backreflection.