Fiber Cable Then and Now

Our Work

Jul 10, 2017

Contributor: Joann Lawler

I was an outside plant junior engineer in New Jersey when a fiber optic trunk cable was installed from Washington, DC to New York City. One of our senior engineers was part of the project: bringing the cable across the Delaware River from Philadelphia to Camden then north to our district boundary. It was exciting to be even at the periphery of this major innovation, though the most notable challenge of his project was purely mechanical: the removal of a retired cable under the river to open a duct for the new cable. Friction had softened the outer waterproofing compound when the cable was installed and basically glued it to the duct. The first two winches broke trying to get it moving.

My manager believed fiber would only ever be used for long distance trunks. Two to three years later it was being used to feed carrier systems in the local exchange. A few years later the SONET standard was introduced, starting a steady increase in the fiber throughput.

Fiber cable manufacturers have continually researched chemical enhancements and manufacturing techniques to improve the distance a light signal can be carried. Some older cables may not be compatible with the latest electronics, which rely on these improvements. The International Telecommunications Union (ITU) has six major standards for fiber cable, which define attenuation, dispersion at the major transmission bands, and bending radius. Of those, the following are currently in use.1

Standard Cable Type Notes

ITU G.651

Multimode

Short range, under 1000 meters. Used for patch cords and short indoor runs. May become obsolete as laser costs decline for Singlemode.

ITU G.652

Singlemode non-dispersion-shifted (standard SMF).

The latest subcategory, G.652D cable, is suitable for Fiber to the Home.

ITU G.655

Singlemode nonzero dispersion-shifted (NZ-DSF)

Used for long-haul trunking with DWDM, including undersea cables.

ITU G.657

Singlemode bend-insensitive

Developed for fiber-to-the-home indoor fiber wiring.

1http://www.thefoa.org/tech/smf.htm ; http://www.ciscopress.com/articles/article.asp?p=170740&seqNum=7

From the 1980s to mid-2000s the important thing was the number of calls per pair of fibers. SONET systems were designed for voice calls and were adapted to carry data. As data became more important, competition among standards eventually led to the triumph of Ethernet.

SONET topped out at a speed of about 40 Gbps using time-division multiplexing, that is, interleaving the individual sources by picking a few bits from each in turn and transmitting them faster. The massive growth in data traffic—about 20 percent a year since the 1990s—made this inadequate. To get to the next level, transmission equipment manufacturers looked at simultaneously transmitting bitstreams on different wavelengths, “colors” of light, though they’re all invisible to people.

The early standard, now called Coarse Wave Division Multiplexing (CWDM), allowed 8 wavelengths on a single system. The current standard, Dense Wave Division Multiplexing (DWDM), now allows 96 wavelengths, although individual manufacturers’ equipment may provide fewer. These divide the available band into equal-width sections, with the transmission wavelength at the center and a buffer. The newest systems use a flexible grid, which assigns the bandwidth based on the desired speed. This, plus new modulation schemes, is pushing the highest speed from 100 Gbps to 200 and 400 Gbps.

Capacity Purpose

1­­­–2 Mbps

Average peak traffic on one customer’s Gigabit Passive Optical Network (GPON) distribution fiber.

1.25 Gbps 

Downstream capacity of the GPON system’s feeder fiber, with a 1:2 split at the Central Office. This split reduces the total power so that multichannel video can be carried on a third wavelength.

2.5 Gbps 

Downstream capacity of a GPON feeder fiber serving broadband only on two wavelengths, downstream and upstream.

10, 40 or 100   Gbps 

Capacity of one wavelength on a DWDM system. 200 Gbps is starting to become available. 400 Gbps and 1 Tbps are research goals.

9.6 Tbps 

Capacity of a DWDM system with 96 wavelengths at 100 Gbps each

160 Tbps 

Capacity of the Facebook/Microsoft transatlantic cable under construction in 2017.

If I look back at the beginning of my career, telephone trunking was limited to DS1—24 conversations, or 1.5 Mbps—over four copper wires. Fiber has massively increased the capacity. Today, one fiber or fiber pair can carry different amounts based on the customer’s need.

Fiber optic cable manufacturing documentaries are viewable on YouTube. Videos by The Fiber Optic Association are available as self-paced training for technicians and engineers.