Since the Internet started changing people’s lives engineers have been constantly trying to find a way to provide the highest performance possible to their customers. In addition they have been focusing on providing the best possible service to their businesses. One of the main and most important developments in the Internet Era has been the optical network technology. This technology provided a huge leap forward for every Internet user and has been the main foundation of today’s high performance demanding businesses and Internet users.
This technology is based on the optical fiber which is the main part of optical networking. The optical fiber is defined as a single, hair thin, filament drawn from molten silica glass. These optical fibers have substituted the copper wires to produce high performance and high capacity transmission. They are optimized and pure so that light transmitted by optical devices like transceivers, can pass through them carrying the network traffic across a network architecture. The transceivers are the ones converting this light in electrical input and vice-versa, so various switches, routers, firewalls etc. can understand the traffic.
The main ingredient of the optical fibers is a chemical called silicon dioxide (SiO 2). In addition there are other chemical compounds found such as germanium tetrachloride (GeCl 4) and phosphorus oxychloride (POC1 3), however these are mainly used to produce the outer layer of the fiber, also known as the cladding. In the early days of this technology researchers were trying to connect the purity of the glass used to the attenuation of the signal and because in recent years this has been proved, the main focus today is developing optical fibers made from silica glass with the highest possible purity. One of the most important part of the composition of the glass is the fluoride content. It has been confirmed that glass with high fluoride content is improving the overall performance due to its purity along the whole fiber. This makes it suitable for deployment in multi-mode solutions because of the fact that multi-mode fibers transmit hundreds of discrete light wave signals concurrently.
In optic network architectures light travels across many individual optical fibers which are bound together around a high-strength plastic carrier for support. This is also called the core of the cable. In addition the core is then covered with a couple protective layers to protect it from outside stress. The protective layers are mainly made of Aluminum, Kevlar, and polyethylene which is the main ingredient of the cladding. The cladding plays a very important part of the network. This is mainly because light will constantly bounce off of it while traveling across the optical fiber. The amount of energy lost from the bouncing is called attenuation. The attenuation is measured in terms of loss (in decibels, a unit of energy) per distance of fiber. A high quality optical fiber should not lose more than 0.3 decibels per kilometer. This attenuation causes the light to lose power eventually therefore the signal must be repeated and strengthened with the help of laser repeaters. In today’s high performance networks these laser repeaters are deployed at every 30 kilometers in average. However, the good news is that recent studies showed that the newly developed ultra-pure glass will eventually provide the optical fiber to reach the 100 kilometer mark without the need of a laser repeater.
As with every electronical device found today, the manufacturing process is one of the most interesting parts of the whole picture. When it comes to optical fibers there are two methods in manufacturing them and each of those methods has its own purpose. To produce a multi-mode fiber where multiple light waves will pass through it and bounce off the cladding, reducing in shorter reach, the so called crucible method is used. This is the easier and simpler method out of the two because simply put the silica glass is melted and shaped to produce a fatter optical fiber.
The second method is called a vapor deposition process. Researchers developed three different vapor deposition techniques:
Outer Vapor Phase Deposition
Vapor Phase Axial Deposition
Modified Chemical Vapor Deposition (MCVD)
The most common technique used at present is the MCVD technique. With this technique a solid cylinder of core is produced and cladding material is put on top of it. After that process the core is heated and drawn into a thinner, single-mode fiber for long-distance communication. The step by step process shown below is far more interesting:
By depositing layers of specially formulated silicon dioxide on the inside surface of a hollow substrate rod, a cylindrical shape is formed. The deposition happens by applying pure oxygen, in gas form, to the rod. Together with the vaporized gas a couple of important chemicals are added including silicon tetrachloride (SiCl 4), germanium tetrachloride (GeCl 4) and phosphorous oxychloride (POC1 3). With the help of underneath flames the surface of the rod is kept constantly hot and when the oxygen contacts the rod a high purity silicon dioxide is formed inside the rod itself. This high purity silicon dioxide is the basis of the fiber optic core.
The second process of this technique starts by measuring the thickness of the formed silicon dioxide inside the rod. When the expected thickness is reached the rod will be put under a couple heating procedures to remove excess bubbles and moisture trapped inside. After this second step the formed silicon dioxide is usually 10 to 25 mm in diameter.
The solid shape of silicon dioxide is then transferred to an automatic fiber drawing system. This system can be up to two stories high and has the ability to produce continuous fibers of up to 300km.
In the above system the fiber first passes through a furnace where will be heated up to 2000 degrees Celsius. As the fiber is being pulled through the system the material in the original substrate rod forms the outer layer called the cladding.
As the fiber is pulled and drawn out, special sensors monitor its diameter and at the same time a separate device applies a protective coating on top. The process ends when the optical fiber reaches the desired thickness and is then sent to quality control.
It is safe to say that this process is the foundation to producing ultra-pure optical fibers. Today researchers try to find another solution which will offer even lower attenuation. They focus their hope on experimental fibers which are high in zirconium fluoride (ZrF 4) in content. These fibers have been tested and their attenuation results are astonishing, providing performance loss of only 0.005 to 0.008 decibels per kilometer. When these fibers enter in production and reach the networking market, they will provide a huge window to the future and honestly, we can’t wait for that to happen!