The Gradual Evolution To All-Optical Networks - Part 1
I An optical fibre has three structural components. The glass core transmits the light. It is the optical highway that the light travels. If the light is single mode, the core is 8.3 microns. A single mode fibre can be thought of as a single lane road. If the light is multi-mode, the core is 50 or 62.5 microns.
The 125 micron cladding is also glass. It is made ofglass that keeps the core glass from leaking light as long as the angle of incidence is not too big. The buffer consists of a hard and soft layer of plastic, often urethane acrylate. The soft layer surrounds the cladding and cushions it. The hard layer prevents abrasion. For a more complete explanation, click on https://learn.aflglobal.com/home/the-basic-structure-of-optical-fiber.
II Modes of Optical Strands
A single mode strand has one path. Think of it as a straight path down which the light travels. To keep the path straight the diameter is relatively small at 8.3 microns. Multimode glass allows the glass to travel many paths via bouncing off the core's walls. This requires a much higher diameter, which I noted earlier is usually 50 or 62.5 microns. But light pulses overlap in multimode glass. The result is dispersion which limits bandwdith. Hence multimode fibre is used only over short distances such as within data centres. Long haul networks are exclusively single mode. For more details, click on https://learn.aflglobal.com/enterprise/single-mode-vs-multimode.
III All Optical Networks
A optical switching network has several advantages. Generally, you can get higher transmission rates by eliminating the OEO conversions as well as lower latency. In principal optical switching should be much more scalable. One way to seeing this is to consider how optical amplification versus OEO amplification in subsea cables made them upgradable. TAT-8 had OEO amplifiers. Since the terrestrial could be upgraded to higher transmission rates, but OEO amplifiers could not, TAT-8 could not be upgraded and was maxed out in 18 months. Optical amplification has an upper limit with current technology of 40 Tbps. At such a high level it is not gating factor. Another advantage is less power consumption. OEO equipment consumes electricity. Using glass to modulate or demodulate light or switch paths is lower power consumption. Disadvantages is that it is difficult to monitor light performance without electronics to do it. Another weakness is that Moore's law has made transponders very cheap. Optical switches are more expensive.
It may be argued that current packet switching networks are more efficient than all optical networks because the former uses buffering so less optical long haul lanes are necessary. Conversely, a well provisioned all-optical network is non-blocking and should have no packet loss or congestion delays.
So far optical switching is only seen in data centers with Google adopting them widely to move traffic between server racks.
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