Are you in the singlemode or multimode fiber camp?

Traditionally, in the past, most of us in the fiber optic industry have separated ourselves into two basic camps. The Singlemode camp, this group always consisted of the BIG BOYS!! I need my fiber to do everything and more, a consideration of distance, bandwidth and future proofing led their charge. Then there was the Multimode camp, the dabblers in fiber. Their philosophy was the need for fiber at short distance in building for networks, cameras, and specialty applications. Multimode fiber gave their camp greater distances than copper - UTP - cabling at a lesser expense than Singlemode electronics. Obviously, not everyone falls into the Singlemode or Multimode only category with many end users and installers using both types of fibers, but in this article, I will contend that the days of Multimode fiber may be numbered.

Multimode fiber

To use or not to use

That is the question - thank you, Shakespeare. I have always stated in my fiber classes that technically Multimode fiber really only exists for one reason and that reason has nothing to do with technology and everything to do with, you got it, good old money, or the expense of the network. I have always contended that Singlemode fiber optic cable is always the better answer for your cabling choice when considering performance, upgradability, distance, and bandwidth. The real reason that Multimode optical fiber exists is the price of the electronics, more specifically the price of the light source.

For decades, Multimode fiber used LED light sources to generate its signal. The only real advantage of an LED is the significant price savings compared to the LASERs used with Singlemode fiber. At one time, I can remember, yes, I am dating myself the price variance between a Multimode 100 Mbps converter being up to 10 times less expensive than the Singlemode equal. For this reason, Multimode fiber fits extremely well in the Local Area Network: LAN world where the limited distance provided by LEDs did not limit its use. The true fact of the matter is that Multimode fiber can provide 2 kilometer distances at 100 Mbps, more than enough for most networks. What a great time for Multimode fiber as it flourished in the network and camera world.

Things changed several years ago

Multimode fiber with the advent of 1 Gbps - 1000 Mbps Ethernet. A few things happened when this new network speed hit the market. Number one was that the traditional LEDs that we were so happy with outlived their usefulness. The operating threshold of an LED is about 620 Mbps, meaning the light source could not deliver the 1 Gig - 1000 Mbps need. An answer to this problem was to replace the traditional LED with a Vertical Cavity Surface Emitting LASER, or VCSEL, as we know it as today. This new light source was still fairly inexpensive but could handle, as of today, network speeds up to 10 Gbps. So problem solved, right? Not so fast... it was found that the standard FDDI used for all Multimode fibers was never tested for use with VCSEL light sources and upon further testing, it was found that 1 Gig speeds could not be achieved with this standard. Well, technically the speeds could be met, but only with the use of expensive Mode Conditioning Patch Cords.

Multimode fiber had a design flaw

This needed to be addressed, so a new standard of Multimode fiber came to be. This new Multimode, LOMMF - LASER Optimized Multimode Fiber corrected the issues with the older FDDI standard. LOMMF is currently categorized into 5 new standards, OM1 - 62.5/125, Orange outer jacket, OM2 - 50/125, Orange outer jacket, OM3 - 50/125, Aqua outer jacket, OM4 - 50/125, Aqua outer jacket in North America, Magenta outer jacket in Europe and the new OM5 - 50/125, Lime Green outer jacket. When considering your choice of Multimode standards, one thing in my opinion limits the use of OM1 and OM2, and that is neither of these fibers can support 10 Gbps Ethernet more than 40 meters. When recommending a Multimode fiber I strongly encourage the use of OM3 or higher for its usability in 10 Gbps applications, 300 meters for OM3, and 550 meters for OM4. Remember, the price of your network is not equipment or even the price of the fiber, it is labor costs during installation that raises the budget, so the cost difference between OM1 and OM2 compared to OM3 or OM4 is meaningless compared to the life span of OM3 and OM4.

As we all know, nothing stays stagnant and network speeds are always increasing. Time waits for no one. With the advent of 40 and 100 Gbps - 400 and 800 Gbps in the future Ethernet, Multimode fiber needed an answer, and that answer is not always simple. Knowing that currently, VCSELs have a peak speed of 10 Gbps, how then do we get the 40 and 100 Gbps needed with Multimode fiber? This is a twofold answer. Knowing the 10 Gbps VSCEL limit, 40 Gbps speeds require using multiple 10 Gbps lanes, meaning to get the 40 Gig needed we must use 4 OM3 or OM4, fibers 4 x 10 Gig = 40 Gig in each direction or 8 total fibers “lanes” for bidirectional 40 Gig transmissions, OM3 - 8 fibers = 100 meters, OM4 - 8 fibers = 150 meters and the same is true for 100 Gig except now we need 10 lanes in each direction or 20 total fibers OM3 - 20 fibers = 100 meters, OM4 - 20 fibers = 150 meters. Remember that OM5 I mentioned - well here is why it came to be. OM5 is the only Multimode that has the ability to do SWDM - Short Wavelength Division Multiplexing transmissions meaning we can use four multiplexed 10 Gig VCSELs over just two fibers one transmit, one receive. OM5 multiplexes 850, 880, 910, and 940nm to achieve the needed 40 Gig. Isn't it getting interesting?

Singlemode fiber

So now the real question

What about Single mode? We know that as a technology nothing is better than Single mode fiber, this is a given, but what about the huge price differences in equipment costs? As I stated earlier, the delta between Multimode and Single mode equipment was as high as 10 times more for the Single mode but this was the past. Over the last several decades we have seen a dramatic decrease in the price of Single mode LASERs and with that, a large cost savings in the related equipment. Currently, you can purchase a Singlemode 1 Gig SFP - Small Form Pluggable or transceiver for about $2 more than the Multimode version. Remember, the Multimode 1 Gig SFP can give us up to 2 kilometers of distance where the weakest Single mode SFP is 10 kilometers with larger distances up to 80 Km available. When looking at 40 Gig SFPs the price difference is on average $5 more for the Singlemode version but consider that Multimode shifts its distances down to 550 meters, but Singlemode keeps its 10 kilometer minimum.

So is an all Single mode installation something we should consider?

In my opinion, it isn't something we should just consider, it is something we should encourage. An important fact regarding fiber pricing is that Single mode fiber is always less expensive. Looking at bare unjacketed fiber prices, typically Corning SMF28 Ultra sells for $0.08 per meter, where OM3 is $0.20 per meter and OM4 is $0.30 per meter. If you calculate that expense alone, for every 100 meters of Single mode cable the fiber will cost you about $8.00, where OM3 is $20.00 and OM4 is $30.00 per 100 meters. This is a savings of at least $12.00 - $22.00 per fiber per 100 meters of length. How can Single mode fiber today be a more expensive installation? When we consider the equipment SFP price differences between Multimode and Single mode, remember $2 difference for 1 Gig and $5.00 difference for 10 Gig the Single mode wins every time. When considering 40 and 100 Gig applications OM3 and OM4 require 8 and 20 fiber minimums for multi lane transmission - the optical fiber price savings compared to Single mode is staggering.

One of the more important facts I have mentioned

In this article is the cost of installation and life span future proofing of your fiber. When installing Single mode fiber cable you can expect that would be the last optical fiber you would need to use. As stated before - I have always contended that Singlemode fiber is always the better answer for your cabling choice when considering performance, upgradability, distance, and bandwidth. So in conclusion, when asking, what is the best fiber to use in my application? There is really only one answer - SINGLEMODE - it provides the longest life span, longest distance, highest performance, and now I thought I would never say this it is the least expensive option. Long Live Singlemode!