Media Converters for Fiber Optic Networks

Getting Fiber Optics & Wire to Talk to Each Other with Media Converters

Copper wires are by far the most common method of connecting networks together. Every computer you buy these days has a T10/100 connector for connecting a CAT-5 or CAT-6 network cable. It is a rare person who still uses an internal modem to connect their computer to the Internet, and most of us have local area networks in our offices, homes and businesses.

Cat-5 cableThat doesn't mean that they're the only means available though. Nor does it really mean that twisted copper wires are the most efficient way of transmitting data, especially over long distances. If they were, why are the major communications companies using fiber optics almost exclusively?

The only problem is, most computers and other electronic equipment don't come equipped with fiber optic connectivity. So, even if the average Joe wanted to switch over to fiber optics, it's a little bit difficult to accomplish. Since fiber optics and electronic signals over wire operate totally differently, you can't just change connectors or adapt one to the other. That's where media converters come in.

Digital Data Transmission

We usually refer to digital data signals as being a bunch of ones and zeros. It's called "binary" because binary is a numbering system using only ones and zeros. When we transmit this digital data over wires, it is in the form of an electrical signal, the "ones" being indicated by having voltage on the line, usually +5 VDC and the "zeroes" by having the line at ground potential 0 VDC.

Since the switching back and forth between the two is happening extremely fast, a clock signal, going back and forth between one and zero at a constant, predictable rate is used to keep everything working on the same time. This "clock rate" is what we refer to when we talk about a computer's speed, or the speed of a digital transmission. In other words, the USB on your computer, which operates at 400 MBit/s is actually sending 400 million ones or zeroes per second. Or, 400 million times per second, the receiving device (your computer, an external hard drive, a printer, etc.) checks the voltage on the incoming wire, to see if it there is voltage, indicating a "one" or no voltage, indicating a "zero."

That's fast, but not as fast as the information moving around in your computer's microprocessor. The microprocessor is the computer chip which is like the brain of your computer. Typically, they operate at multiples of the "buss speed" (the speed that information is moved around inside your computer). So, a 2.8 GHz computer is actually reading two billion eight hundred million ones or zeros per second.

How Fiber Optics Works for Data Transmission

As we've just discussed, copper wires move all this digital data as electrical voltage; but, fiber optic lines, which are plastic, can't transmit electricity. In fact, they are a great insulator against electricity. So, if fiber optics can't transmit data with electricity, what do they use?

Simple, they use light.

In general, fiber optics is using clear fibers to transmit light. For data transmissions, the light is provided by a special LED (light emitting diode). While incandescent and fluorescent bulbs take a moment to illuminate fully or to darken fully, LEDs can illuminate and darken instantaneously. This allows them to switch between ones and zeros very quickly, allowing a very high transmission rate.

Fiber Optic CableWhere digital signals sent across wires count on the presence or absence of electricity to indicate ones and zeroes, fiber optics accomplish the same thing by the presence or absence of light. So, if the light is on, that's a one; if the light is off, that's a zero. Just the same as with data transmitted across electrical lines, a clock signal is used, to insure that the equipment at both ends of the line select the same moment of time to "read" the data.

As the light goes down the fiber, it travels in straight lines. That's great, as long as the fiber optic line is straight, but that rarely happens for more than a few feet. So, the beam of light ends up hitting the sides of the fiber, bouncing off it and going farther down the "line" until it gets to the other end.

Advantages of Fiber Optic Data Transmission

There are a number of advantages in using fiber optics for data transmission, as compared to using copper wires, even twisted pairs of copper wires:

     •    Less attenuation - Light propagates (travels) through the fiber with less signal loss than electricity through wires. This is especially advantageous over long distances.

     •    Higher modulation - Data rates with light can be made to be faster than with electric lines. In experiments, data rates of as much as 111 GBit/s have been achieved, although 40 or 40 GBit/s is typical in use.

     •    Multiple signals - Each fiber can carry multiple signals at the same time, by using different frequencies (colors) of light. In commercial applications, as many as 80 separate channels are sent through the same fiber.

     •    Space saving - Since each fiber can carry multiple signals, one fiber optic "cable" can take the place of several CAT-5 cables in building cable ducts.

     •    Ethernet Media ConverterNo electrical noise - Since fiber optics has no electricity flowing through it, there is zero possibility of electrical noise from nearby electrical wires, radio frequency waves, or electrical equipment (motors are notorious for this).

     •    No crosstalk - Crosstalk (data from an adjacent line, like hearing someone else's conversation on the phone) doesn't exist, because there is no magnetic field produced by electricity running through a wire.

     •    No electrical conductivity - Which makes fiber optic cables ideal for high voltage environments, such as power generation facilities.

Getting the Two Together - Media Converters

Adapting data signals from wire to fiber optics and vice-versa requires a device that can read the data coming in from one device and converting that data to the other format. Let's say that you have several computers in a remote equipment building, which you're having trouble connecting to the network. Due to the location of the building, you are forced to run the network cable over the same power poles that are providing power to that building. No matter what you do, there's too much electrical noise, destroying the quality of the signal between your network and that remote location.

Digital Video Media ConverterThis is a perfect application for a fiber optic connection. By using media converters at both the remote building and at your main facility, you can string fiber optic cable out to that remote building, instead of copper wire. Media converters at both ends receive the electronic data transmission from the network and convert it to an optical data signal for transmission over the fiber optic line. At the other end, the signal is converted back to a standard electronic signal for transmission to the computers over CAT-5 cable.

There are two basic formats of Media Converters on the market, both of which function essentially the same, but are designed for transmitting different types of data:

     •    Ethernet 10/100 - For conversion between fiber optics and 10/100 Ethernet (standard wired network connection).

     •    DVI - For transmission of DVI (Digital Visual Interface) signals over fiber optic cables. Used when a remote video monitor is needed.

While the 10/100 media converters are typically sold as individual units, the DVI media converters come as a pair, to be used at both the computer and monitor ends. If you think about the monitors used in an airport to display flight information, you can see where this type of connection would be useful. Digital data sent over fiber optic lines can go as far as 5,000 feet, without amplification.