How to know that the fiber which is laid down in organisation is a single mode or multimode ?

Answer 1

Singlemode is an optical fiber with a small core (2-9 microns) that supports one mode. The core/cladding size (e.g. 8.3/125) is stamped on the cable jacket, which is traditionally yellow. Singlemode is commonly used for high speed, long distance links.

Multimode is an optical fiber with a core (25-200 microns) that supports several modes. The core/cladding size, commonly 62.5/125 or 50/125, is stamped on the cable jacket which is traditionally orange.