Optical Fiber vs. Copper Wires for Data Communication
Optical transmission or fiber optic communications involves transmitting data in the form of pulses of light through extremely thin strands of glass. Optical fibers are extremely thin, with a thickness that can be compared with that of a human hair. They transmit light from one end to another. During the optical transmission, the light is contained in the fiber itself through complete internal reflection. This is done by enveloping the core fiber with a cladding with a lower refractive index, which acts as a perfect mirror. The core of the fiber and the cladding are covered by a protective outer coating. The optical fiber that is formed in this manner is then bundled together with a number of other fibers in a sheath, in order to form a much larger optical fiber cable.
Optical fibers are very strong, flexible and lightweight. There are of two different types, which are classified according to their propagation mode. This is specified by the diameter of the fiber core in comparison with the wavelength of the light transmitted through the cable. Optical fibers that have a core diameter of at least 50 micrometers (μm) accept light in the near-infrared band at different angles. This is then propagated through the fiber in multiple transverse modes. That is why such fibers are called as multi-mode fibers.
Single-mode fibers or mono-mode fibers usually have a core diameter of between 8-10 μm and transmit light of wavelengths of the range 1300-1550 nm. Single-mode fibers are made from top quality, low attenuation silica glass that sends through signals of longer wavelengths. They are capable of delivering a superior performance with respect to the signal bandwidth and operating range. They work very well in telecommunications systems over a range of 100 km with 2.4 Gbit/s SDH links.
Multi-mode fibers have a limited range depending on the absorption of light, wherein the light is not reflected completely and is passed into the cladding. It is also based on dispersion. Dispersion means that light rays at various angles have different path lengths, so each light ray takes its own time to reach the receiver. Regardless, networks that make use of multi-mode fibers functioning at 850 nm are able to achieve rates of 1 to 2 Gbit/s, and can do so over hundreds of meters, which is fine enough for most industrial applications. There are many applications that do not operate in this range. So, plastic optical fibers (POF) are used in systems that operate over just tens of meters or so at 850 nm. They function well even when the visible light is at 650 nm.
Apart from the cable itself, there are other components involved in the fiber optic communication system such as the receiver and transmitter circuits that allow for the critical conversion between optical and electrical signals. The transmitter modules activate the LEDs and other light sources by making use of the inbound data along with the encoding, such as the Manchester coding. This ensures that the clocking information is retrieved in time by the receiver. LEDs are used at 850 nm when it comes to GaAs technology and at 1300 nm with respect to GaAsP devices.
Keep in mind the vertical cavity surface-emitting laser (VCSEL) devices operate over the same wavelengths and provide much better performance compared to LEDs in terms of speed and power, and cost pretty much the same. VCSELs are much better in the sense that they make use of lasers which produce coherent light. This helps lower the effect of dispersion. Also, they can be coupled more effectively into single-mode fibers.
Fiber optic receivers utilize a photodiode which is coupled into a Transimpedance amplifier. This converts the incoming optical signal into an electrical signal. This is the corrected to account for the distortion and attenuation that the signals go through during transmission. The transimpedance amplifier output is processed further with a limiting decoder and amplifier or by clock recovery circuits, so that the original data is fully restored.
Single-mode fiber optic receivers and transmitters cost more than multi-mode fiber optic transmitters and receivers as they have more expensive components. This is so because the connectors need to have a much higher level of precision in order to couple the light through the much smaller fiber core.
When you don’t need a particularly high range or speed for your applications, it makes more sense to use the less expensive multi-mode option. Keep in mind that multi-mode fiber costs much more than single-mode fibers; but since they operate over short distances this is not something to worry about.
Optical Fiber vs. Copper Wires
Fiber optic technology allows for a far more efficient communication at high data rates of gigabits and more over high distances of more than 100 kilometers. Single-mode optical fibers are able to achieve these speeds without requiring repeaters. They are even capable of achieving speeds in the range of 10 terabits or more by making use of wavelength-division multiplexing, which involves the parallel transmission of data at different wavelengths through light carriers and optical amplification. Repeaters can help regenerate the optical signals and extend the range of the transmission range.
Data transmission over copper wire cables, which is the traditional method used in most old fashioned communication systems has a much lower bandwidth and range than what you get with optical fiber. Twisted copper wires, which are used for most telephone lines have ADSL data rates of not more than 10 Mbit/s over a distance of 1 km. Coaxial cables which are used with cable TV can operate over a distance of 200-300 meters at speeds of 250 Mbit/s.
If your application is based on a combination of range and bandwidth which exceeds the capacity of a copper wire cabling, then you should certainly choose fiber optics as they have a higher range x bandwidth than copper wires by a factor of 2X to 3X. But if your applications require low bandwidth and with data transmission over a short range, then using copper wires is not a bad choice.
In many applications, which communications technology you choose is pre-decided by a system specification which makes use of an equipment for interfacing with a much wider network. So, if you have a large data center which makes of storage devices with a large capacity, then you will certainly need to make use of fiber optics.