There are two types of optical attenuators:
Fixed Optical Attenuator
A fixed optical attenuator can reduce the optical power on an optical path by a fixed value. The common attenuation specifications of fixed optical attenuators are 2 dB, 3 dB, 5 dB, 7 dB, 10 dB, and 15 dB.

Mechanical Variable Optical Attenuator
A mechanical variable optical attenuator (M***) can adjust the optical power on an optical path within a permitted range. The attenuation adjustment range of an M*** is 2 dB to 30 dB.
