Fiber optics are hair thin strands. These strands are made out of pure glass/plastic fiber, they consist out of 2 layers; the core and the cadding. Information is sent through these strands via light as a medium.
The core's density is less than the cadding, causing the light to change direction depending on the angle of the light when going from the core to the cadding. This technique is called Total internal reflection.
This is then coated by a buffer to protect it from moister and physical damage.
The bigger the core, the bigger the amount of rays you can let in.
Simply put.... you can transfer data via light which means that data can travel at the speed of light. So if your Internet is connected through fiber, I should go over a Gigabit speed.
Small form-factor pluggable transceiver(SFP)
Transferring data over light is all good and well but what do you do when it actually gets to its destination? That is what GBIT (Gigabit interface converter) is for; it is essentially a transceiver that can support a wide range of physical media, with fiber included in that range.
GBIT has been made obsolete by a smaller version known as mini-GBIC or 'Small form-factor pluggable transceiver(SFP)'
Technically speaking light-up is when you put light through fiber, which should be all the time. But in the network industry jargon light-up means the first time you start up a fiber connection in an area. So if you somehow light-up the entire Maharashtra, that means the entire Maharashtra will have a active fiber network.