Single Mode (Mono Mode)
Single mode fibre has a thinner core than multimode and uses a single beam of light for data transmission. The light pulses are generated by Light Emitting Diodes (LEDs).
Single mode is faster and can work over longer distances than multimode and as such it is suitable for use as backbones between buildings. Single mode has a 50% greater data carrying capacity than multi mode cable with an acceptable transmission range is up to 3km.
Even although fibre is manufactured to a high quality there can still be imperfections that could led to signal loss. To overcome this fibre cable is tested by a device called an optical loss meter and the measurement that shows whether the cable is fit to use is referred to as the optical link loss budget.
Click here to review the wikipedia resource on single mode optical fibre.
Next: Fibre Connectors
