Commonly we send electrical signals down copper cables in our telephone systems, ADSL systems, but signals are quickly degraded, which reduces the amount of data that can be passed according to the length of the copper line. If you are an ADSL broadband customer then the further you are down the line from the exchange, the slower your broadband speed, hence the reason that ADSL broadband is marketed with an "Up To" speed. Resistance in the copper and outside interference combine to reduce the capabilities of copper cables.
The capacity of a single glass fibre is enormous when compared to a copper cable and ways of increasing that capacity are always being developed, such as using different wavelengths of light to set up multiple channels of information simultaneously. Also, fibre optic cables can be used to send data signals much longer distances before some kind of optical repeater can be used to extend the distance even further. With the right kind of transmission equipment it has been possible to pass data at speeds measure in multiple Terabits over distances measured in the hundreds of kilometres.
For a long time fibre optic cables have been used within telecommunications and data communications networks, but not over what is known as the "Last Mile", mainly due to the cost of replacing all the old copper telecommunications cables. Some ISPs have been installing fibre optic cables that go directly into the home via the local street cabinet, thus potentially providing connections with speeds measured in the hundreds of kilobits per second. Presently in the UK, British Telecom are offering FTTH with speeds in the 100s of kilobits range as a download speed, promising 1 Gibabit per second in the near future. Even upload speeds are in the range of 20-30Mbps compared to under 1Mbps for a lot of standard ADSL connections.
FTTH requires power at the street cabinet with battery backup in case of any outages. However, some ISPs are testing and even implementing PON (Passive Optical Networks) which work on the theory of reflection and mirrors and have no power requirements from the exchange via an OLT (Optical Line Termination) unit to a remote POC (Passive Optical Coupler). At or near to the subscriber premises is an ONU (Optical Network Unit) that receives the optical signals. Multiple subscribers used different wavelengths of light in the reverse direction to the ISP which is inter-modulated at the POC to form a single beam of light back to the OLT.
At this present time FTTH is not available to everyone, mainly within inner cities and areas of dense population, but ISPs will rollout fibre networks and eventually most subscribers should be able to benefit from SuperFast broadband. In the meantime, certainly in the UK, ISPs are rolling out FTTC to ensure that high speed fibre optic communications are possible as far as the street cabinet. Short copper runs to the subscriber from the street cabinet will ensure reliable broadband at high speed.