Single mode fiber, short as SMF, is a fiber cable that only allows one mode of light to transmit. Typically, this fiber includes a small light-carrying core of about 9µm diameter. These feature a small modal disp.
Most fiber-optic attenuators exhibit a relatively high return loss (at least several dozens of decibels), i.e., there is not much light which is reflected back into the input fiber. For some sensitive applications, e.g.