Optical fiber vs electrical cable communications
An optical fiber is a flexible and transparent fiber made of extruded glass (silica) or plastic, slightly thicker than a human hair. It is able to transmit light between the two ends. Light can only be coupled to a fiber at its entry points.
The main advantages of optical fiber communication over electrical cable transmission is its high bandwidth capability (almost 10Gps) over long distances due to the extremely low loss at same specific wavelengths (e.g. 1.3 um and 1.55 um). Morover optical fibers are also immune to electromagnetic interference whilst copper wires act as an antenna collecting EM radiation and turning it into current (EM interference).
Here is a brief summary of the multiple advantages of optical fibre communications over electrical cable transmissions.
Fiber optics are:
The fiber is nonconducting, and is
therefore safe in all electromagnetic
environments. This means it can safely
be used around electrical transmission
lines, as well as in high RF and
A broken or damaged, optical fiber can be detected extremely quickly by monitoring the actual power transmission. With a suitable crowbar circuit, the laser transmission can be shut off within 1-2 microseconds. At a 1 kW laser power level, even a worst-case fiber break releases at most a few mJ of laser power, with no high temperature arc. By contrast, a break in a 1 kV electrical power cable will almost certainly result in an arc discharge and unless great care is taken in the circuit design to detect arcs and minimize energy storage, the arc can persist for milliseconds and deliver joules of energy.
Both high voltages and high power lasers are potential hazards to users or (particulary) service personnel; both hazards can be readily mitigated in most cases by suitable safety interlocks. We do note, however, that high voltage, high current sources can kill if even a small fraction of the power escapes; laser sources can cause eye damage and in extreme circumstances burn skin, but cannot be lethal.
For many combinations of power and distance, optical fiber is much lighter than any practical electrical cable.
At voltages below ~1,000 V,
electrical conductors are much heavier
than optical fiber for similar power
delivery capacity. Conductor weight
tends to scale as 1/voltage^2 (because
power loss varies as V^2/R), so even at
400 volts, copper weighs over twice as
much as fiber.
Aluminum conductors are roughly half as heavy as copper for equivalent resistance but still heavier than our best estimate for optical fibers, even with no insulation. However, aluminum is much lower strength than copper and more difficult to make into fine, highly flexible cables.
No RF interference, emissions , or inadvertent antenna
An optical fiber has no RFI/EMI issue, because it is not a conductor. Copper wire, on the other hand, can leak signals and can be impacted by RFI.
It can act as an antenna, interfering with data being sent along the cable. In extreme cases, copper wire can pick up energy from nearby high power transmitters, not only interfering with data transmission but potentially overheating the wire.
Higher data bandwidth
Multimode optical fiber can readily
transmit high bandwidth data over long
distances; a typical bandwidth-distance
product for multimode fiber is 500
MHz/km, so a 500 m tether can transmit 1
GHz (several Gbits/second, with
Signal losses over 500 m are negligible; the bandwidth is limited by dispersion of signals.
Lightweight copper cable, by contrast, has very high losses at high frequencies. Twisted pair optimized for high data rates (Cat 6) can transmit 500 MHz over only 100 meters (bandwidth-distance product of 50 MHz/km); lightweight unshielded cable optimized for power transmission will have even lower bandwidth-distance product.
Both fiber and copper are reasonable in terms of durability
The ultra-pure silica glass used in
optical fiber has a higher tensile
strength than copper. The jacketing
material further strengthens and
protects the fiber. The toughness of
fiber optic cables is well understood.
The durability of very fine copper wire without thick insulation is not as well understood.
Electrical power transmission over copper or aluminum wire is, and will likely remain, cheaper than laser power transmission over fiber. The dominant cost of the laser system is the laser itself, which is not present in the electrical system.