The light source is a laser. It has a typical core diameter of 50-100 microns. Duplex fiber is a two fiber cable suitable for data transmission. Typically, one fiber is used to transmit and the other is used to receive. It can be a singlemode or multimode fiber.
Simplex fiber is composed of a single fiber cable.
It can be a singlemode or multimode fiber. It is an older fiber 802.3 standard for connecting only hubs up to 1 KM apart. The intent for creating a model like this is so manufacturers can standardize on common platforms thereby making products from various manufacturers compatible with each other. This Model outlines seven areas, or layers, for the network. This is the level where the user applications software lies.