How to check noise in Optical Fiber Cable ?

Noise sources in a fiber optic link include noise from the RF amplifiers in the transmitter, the laser diode, the photodiode and RF amplifiers in the receiver.The two main noise contributors are fluctuations in light intensity, which comes from the laser diode, and interferometric noise, which arises because of multiple light reflections in the optical fiber.

by using of floting scope  and VNA SCOPE ANALYSER

You can check noice easily Through Optical Meter