1. What is FC/APC?

“FC” means “fiber channel”, and “APC” stands for “angled physical contact”.

Below is a FC/APC connector product from Thorlabs.

These connectors allow the surfaces of two connected fibers to be in direct contact with each other and because the fiber end is polished at an angle to prevent reflected light from traveling back up the fiber. These FC/APC connectors have an 8° pre-angled ceramic ferrule, which when properly polished, results in a typical return loss of 60 dB.

Fig.1. FC/APC Fiber Connectors: Single Mode (from Thorlabs).

2. What is insertion loss

Insertion loss is the loss of signal power resulting from the insertion of a device in a transmission line or optical fiber and is usually expressed in decibels (dB).

If the power transmitted to the load before insertion is $P_T$ and the power received by the load after insertion is $P_R$, then the insertion loss in dB is given by,

IL(dB) = 10{\log _{10}}(P_T/P_R)

3. Fiber cleanser and fiber microscope

Fig.2. Fiber cleanser.

Fig.3. Fiber microscope.