The Positive Impact of Using Optical Fibers on Cell Towers

While fiber optic technology has been utilized for many years in the communications industry, consumers generally identify with the role that it plays in wired communications such as Cable TV, Fiber-To-The-Home, and the related networking equipment.  However, what most overlook or do not realize is the significant impact that deploying optical fibers has also had on something consumers use every day – mobile devices.  In order to achieve the high speed data levels that we have become accustomed to when using mobile devices, cell towers and their supporting networks had to be retrofitted with optical fiber cables.

 

The transition from copper to fiber first started when 3G mobile technology was first introduced, but when 4G LTE technology was deployed, the service providers’ equipment in almost every cell tower had to be upgraded.  The primary reason for this was to support the need for the higher frequencies and faster speeds that the existing 1 5/8 ” coax cables on most cell towers could not handle. Since the primary feed line to most cell towers had been upgraded already, connecting the cell systems in the towers with fiber was the next step.

 

So what positive changes occurred when transitioning to optical fiber in the cell tower?

 

First, engineers could now design systems with fiber that run solely off of DC power.  The result was that a very small (less than a ½” in diameter) 16-pair optical fiber cable and two small multi-strand DC cables could replace as many as 12 to 18, 1 5/8” coax cables which are sometimes called “hard lines”.  As you can see, this is a significant improvement.

 

Secondly, after the hard lines are taken off and replaced with optical fiber cables, both the weight and wind drag are drastically reduced on the cell tower.  The amount of weight and wind drag that is reduced when swapping coax for a fiber-based system is almost unbelievable.  Thousands of pounds of materials are removed and space on the tower is dramatically increased.  In addition to amount of material, a lot of time is saved in comparison to having to add 12 to 18 more hard lines to each system.

 

By upgrading to incorporate optical fiber cables into the infrastructure, today’s cell towers have realized significant improvements not only in mobile network performance, but also from an architectural standpoint.

Why is important to clean optical fibers?

by www.fiber-mart.com

A high percentage of fiber optic transmission problems are the result of contaminated connectors and couplers. Dirt not only impacts the speed and performance of a network, but also damages equipment.

 

As a manufacturer of fiber optic cables Datcom is keenly aware of the implications of improper cleaning of end faces and recommends the following points to ensure that your fiber networks are always up and running. 

 

Dust caps are for protection only and do not mean that the fiber inside is clean. 

Inspection of ferrules with a scope is a must and if possible used with an analysis software. Even the most experienced technician cannot visually determine the cleanliness of a fiber. 

 

Do not use alcohol when cleaning fiber. It is hygroscopic which means it attracts water molecules from the air. 

Use a wet to dry cleaning process to avoid electrostatic attraction. 

Use an optical grade cleaning fluid for the static to dissipate. 

 

Use optical grade lint free wipes that have high absorbency and strength. 

Use cleaning sticks that are made from multiple fibers and can spread and contact the entire surface of the end face when port cleaning. 

 

Proper installation practices, coupled with advanced inspection procedures and professional cleaning products will not only save a technician repeated onsite visits and time. But also eliminate customer complaints along with loss of confidence and money. 

HOW ARE OPTICAL FIBERS MADE?

by www.fiber-mart.com

Now that we know how fiber-optic systems work and why they are useful -- how do they make them? Optical fibers are made of extremely pure optical glass. We think of a glass window as transparent, but the thicker the glass gets, the less transparent it becomes due to impurities in the glass. However, the glass in an optical fiber has far fewer impurities than window-pane glass. One company's description of the quality of glass is as follows: If you were on top of an ocean that is miles of solid core optical fiber glass, you could see the bottom clearly.

 

Making optical fibers requires the following steps:

 

Making a preform glass cylinder

Drawing the fibers from the preform

Testing the fibers

 

Making the Preform Blank 

The glass for the preform is made by a process called modified chemical vapor deposition (MCVD).

 

In MCVD, oxygen is bubbled through solutions of silicon chloride (SiCl4), germanium chloride (GeCl4) and/or other chemicals. The precise mixture governs the various physical and optical properties (index of refraction, coefficient of expansion, melting point, etc.). The gas vapors are then conducted to the inside of a synthetic silica or quartz tube (cladding) in a special lathe. As the lathe turns, a torch is moved up and down the outside of the tube. The extreme heat from the torch causes two things to happen:

 

The silicon and germanium react with oxygen, forming silicon dioxide (SiO2) and germanium dioxide (GeO2).

The silicon dioxide and germanium dioxide deposit on the inside of the tube and fuse together to form glass.

 

The lathe turns continuously to make an even coating and consistent blank. The purity of the glass is maintained by using corrosion-resistant plastic in the gas delivery system (valve blocks, pipes, seals) and by precisely controlling the flow and composition of the mixture. The process of making the preform blank is highly automated and takes several hours. After the preform blank cools, it is tested for quality control.

 

Drawing Fibers from the Preform Blank 

Once the preform blank has been tested, it gets loaded into a fiber drawing tower.

 

The blank gets lowered into a graphite furnace (3,452 to 3,992 degrees Fahrenheit or 1,900 to 2,200 degrees Celsius) and the tip gets melted until a molten glob falls down by gravity. As it drops, it cools and forms a thread.

 

The operator threads the strand through a series of coating cups (buffer coatings) and ultraviolet light curing ovens onto a tractor-controlled spool. The tractor mechanism slowly pulls the fiber from the heated preform blank and is precisely controlled by using a laser micrometer to measure the diameter of the fiber and feed the information back to the tractor mechanism. Fibers are pulled from the blank at a rate of 33 to 66 ft/s (10 to 20 m/s) and the finished product is wound onto the spool. It is not uncommon for spools to contain more than 1.4 miles (2.2 km) of optical fiber.

 

Testing the Finished Optical Fiber 

The finished optical fiber is tested for the following:

 

Tensile strength - Must withstand 100,000 lb/in2 or more

Refractive index profile - Determine numerical aperture as well as screen for optical defects

Fiber geometry - Core diameter, cladding dimensions and coating diameter are uniform

Attenuation - Determine the extent that light signals of various wavelengths degrade over distance

Information carrying capacity (bandwidth) - Number of signals that can be carried at one time (multi-mode fibers)

Chromatic dispersion - Spread of various wavelengths of light through the core (important for bandwidth)

Operating temperature/humidity range

Temperature dependence of attenuation

Ability to conduct light underwater - Important for undersea cables

 

Once t­he fibers have passed the quality control, they are sold to telephone companies, cable companies and network providers. Many companies are currently replacing their old copper-wire-based systems with new fiber-optic-based systems to improve speed, capacity and clarity.