Will plastic fibers challenge glass for networking?

PLASTIC OPTICAL FIBERS (POF) have been around as long, if not longer, than glass fibers. We are all familiar with them, as they are used for consumer items such as signs, lamps and Christmas trees because they are inexpensive. But it might surprise you to know that the largest applications of optical fiber for communications use is POF.

By the end of 2006, approximately 30 million devices will be connected to POF in automobiles, using the MOST network. MOST was created as a network to connect many of the ever-growing number of electronic devices in cars. Using POF to connect the dashboard controllers, radio, CD/DVD player, cell phone, video screens, navigation system, etc., saved substantial weight over using copper cabling and provided much more bandwidth. While MOST is now used mainly in expensive cars (e.g., Mercedes, BMW, Jaguar, etc.), the cost of the network is dropping rapidly, becoming inexpensive enough that it is expected to be used in mid-priced cars soon.

POF is used in MOST and other automotive applications because it is fast, lightweight and inexpensive. The fiber itself is not the cost issue, as high-performance single-mode glass fiber is now cheaper than kite string or monofilament fishing line, but POF is very rugged, it can be installed in wiring harnesses, and it is quickly terminated with a crimp tool and razor blade. Furthermore, it uses inexpensive transceivers with red LEDs and silicon detectors. A POF transceiver is supposedly less than $5 in quantity and headed for half that price in the near future.

The other big application for POF is consumer electronics. Check the back of your digital cable box, DVD or CD player and you will find a optical port for POF, using Firewire or Toslink standards. POF allows these devices to connect with an inexpensive digital link. POF cables for connecting entertainment devices are available at all electronics stores at prices comparable to copper cables.

If POF is so popular in cars and consumer electronics, why is it not more widely used in commercial communications applications? The issue has been distance. Automotive networks and home electronics rarely use more than 5 meters of cable (about 16 feet), while local area networks (LAN) or closed circuit television links may go hundreds of meters. The TIA standards call for 100 meters for horizontal links and 300 meters for backbones, for example. POF has been limited in distance capability by both attenuation and bandwidth.

Multimode glass fiber is made from ultra-pure glass and uses a graded-index core to enhance bandwidth. Until recently, plastic fiber was made from a type of plastic that had 50 to 100 times more attenuation than glass, and it had a step-index core that limited bandwidth severely. Now graded-index POF is on the market made from new types of plastic that have much lower attenuation (only about three to 10 times that of glass fiber) and a graded index core for higher bandwidth (equal to 62.5/125 fiber.) This GI-POF can even be made similar in size to glass fiber, allowing it to use the same electronics.

GI-POF is now capable of being used for LANs and other applications where multimode fiber is now popular with the advantage of easier installation. This new POF can even use the same or similar transceivers as glass fibers. GI-POF has not reached the volumes of use needed to make it cheaper than multimode glass fiber, but it could if usage increases significantly. Its big advantage is still ease of termination.

One potential application for POF is home networking. As homes need networks for multiple PC connections to the Internet and for media PCs feeding programming to several digital TVs, homes will need cabling to support these devices. Wireless may not be feasible, as it is limited in bandwidth and distance. Copper wiring (unshielded twisted pair or coaxial) is an option for home networks, but unlike offices, homes are not made to allow easily removing obsolete cables and upgrading with higher performance versions. Optical fiber has always had the advantage of allowing higher bandwidth for future network speed upgrades.

Rumor has it that companies are even looking at the MOST network standard for home entertainment. MOST easily accommodates all types of electronic devices and even allocates network bandwidth according to device needs, setting aside adequate bandwidth for CDs, DVDs and TVs while still allowing control signals to use the same network without delays. MOST has one big advantage: a central controller runs the network, simplifying the design of a home entertainment command center, just what home networking needs.      EC

HAYES is a VDV writer and trainer and the president of The Fiber Optic Association. Find him at www.jimhayes.com.