Can I use a multimode fiber with a 50-µm core with the Model 18XX-FC receivers?
These receivers will work fine with a 50-µm core fiber. For the Model 1801-FC, the photodetector diameter is 0.9 mm, and the distance from the end of the fiber to the surface of the photodiode is about 3.5 mm, so there should be no problem collecting the light from a 50-µm core fiber. For the Model 1811-FC, the responsivity of the photodiode will decrease by about 10% as compared with a single-mode fiber because not all of the light will be captured by the photodiode. It is not recommended to use a multimode fiber with a core diameter greater than 50 µm.
