Singlemode vs Multimode Fiber Optic Cable

Singlemode Fiber Optic Cable

Singlemode fiber optic cable, as the name suggests, allows only one mode of light transmission. It features a very small core diameter, typically ranging from 8 to 10 microns. This narrow core enables light to travel in a single, direct path, reducing signal dispersion and attenuation over long distances.

Singlemode fiber has a core that is physically sized to carry a single wavelength of light, nearly eliminating the modal dispersion and scattering effect. This was done by reducing the core diameter and tuning the cladding to not exceed the cut-off wavelength. You heard that correctly: The size of the core literally defines what modes the fiber optic cable can carry! The benefits are greatly increased speeds and distances. Of course there is always a tradeoff, and this comes at the need for more advanced and powerful lasers to transmit the data. This all seems rather counterintuitive doesn’t it? One would think a bigger pipe would allow for more data and therefore more speed. Well, with fiber optic cable the reverse is true. A bigger pipe just allows for more garbage to flow down it, and this results in crowding out the actual light you want.

Advantages of Singlemode Fiber:

• Higher bandwidth and longer distance capability
• Lower attenuation and signal dispersion
• Ideal for long-haul communications and telecommunications

Disadvantages of Singlemode Fiber:

• More expensive than multimode fiber
• Requires higher precision in manufacturing and installation practices.
• More expensive optics (transceivers)especially in higher speeds

Multimode Fiber Optic Cable

Multimode fiber optic cable allows multiple modes of light transmission simultaneously. It has a larger core diameter, typically 50 or 62.5 microns, which enables it to carry multiple light rays (modes) at once.

Multimode fiber optic has a core that exceeds the cut-off wavelength of the light pulse, resulting in modal dispersion. Think of modal dispersion as signal degradation caused by light bouncing off the walls as it travels through the fiber cable. This bouncing effect scatters the light and results in more modes of light going down the cable than you would like…hence “multi-mode”. This is NOT a feature, and is not technically desirable. As improvements were made to MMF core and cladding, the OM type increased. For example, OM3 is better than OM2 due to better reduction of modal dispersion giving higher OM types of multimode fiber longer reach with better bandwidth. That said, only so much can be achieved by optimizing the core and cladding. You have to make a bigger (actually, smaller) change.

Advantages of Multimode Fiber:

• Lower cost compared to singlemode fiber
• Easier to install and maintain
• Lower cost optics (transceivers)
• Well-suited for shorter distances (e.g., within buildings, campuses)
• Better bend radius with Bend Insensitive multimode fiber.

Disadvantages of Multimode Fiber:

• Lower bandwidth and distance capability compared to singlemode
• Higher signal dispersion and attenuation over longer distances
• Maximum speed of an OM4 multimode cable is 100G depending on distance, and only up to a distance of 400 to 550 meters. For OM3 fiber the maximum distance is 300 meters.

Physical Construction Differences

We now know that multi-mode fiber optic cable has a larger core. Singlemode fiber has a smaller core. What exactly does this look like? Well, a picture is needed. Just for reference, if you want to see the core of a multimode fiber cable (assuming you could remove the cladding) you would see a core that is as thin as fine human hair. Singlemode fiber cores are so small you need a microscope!

The above image shows a cross section of the actual core and cladding of fiber optic cable, sans all the additional stuff like color coatings, buffering, and cable jackets. This is the beating heart of fiber optic cable. The core and cladding are fused together, and no matter what kind of fiber cable you are talking about the diameter will be 125 microns (µm). Multi-mode fiber has a larger 50 micron core and operates at 850nm (nanometer) light wavelength. Singlemode fiber has a teeny 9 micron core and operates at 1310nm or 1550nm light wavelengths.

Just for reference, how does the 125 micron core/cladding look in relation to the rest of the cable? Let’s take a tight buffered fiber patch cord as an example: 

 It should be noted that in the above picture the overall diameter of that assembly is only 2mm! Compare this with the average Category copper cable like Cat6A which is typically 7.0mm and above, and you start to appreciate just how fiber optic cable is a huge benefit to installation. The advantages do not stop with physical size, they also come in speed and distance!

Fiber Optic Speed and Distance Comparison Chart

Fiber optic cable, regardless of whether it is single or multi-mode, confers huge advantages in bandwidth and distance over copper Ethernet cable. The differences between singlemode and multi-mode fiber can be just as pronounced. What it all comes down to is bandwidth over distance. As your speed needs increase, the permitted distances get shorter. If you need 1G (1Gb/s) then you can go really far with fiber. With copper Cat6A cable you hit a hard limit of 100m (328 feet) from powered device to powered device, whether it be 1G or 10G. Let’s compare a few examples and then toss in Cat6A just for kicks.

Note that distances for fiber optic cable can vary depending on the type of transmitter (light source). Light sources come in three primary types:

• LEDs (light emitting diode). This is bargain basement technology and not typically used with fiber any longer.
• VCSELs (Vertical Cavity Surface Emitting Lasers). This is a mass produced and lower powered laser. This is the type of laser typically used with multi-mode fiber that is “laser optimized” (OM3, OM4, OM5) and required to run at 10Gb/s and above or up to the maximum 1,800 feet with 1Gb/s.
• Fabry-Perot (FP) or Distributed Feedback (DFB) type lasers. These are the more pricey and powerful lasers typically seen used with singlemode fiber. These are the type of lasers associated with transmission of 10Gb/s at nearly 25 miles!

It's important to note that these distances can vary depending on the specific equipment used, the quality of the fiber, and the transmission technology employed. For singlemode fiber in particular, the distances can be significantly longer in some cases, especially at lower data rates. The distances provided for singlemode fiber are conservative estimates based on common standards, but in practice, singlemode fiber can often support much longer distances, particularly for 1 Gb/s and 10 Gb/s transmissions.

Also, for OM4 multimode fiber, some sources indicate that with certain technologies (like extended reach multimode transceivers), it's possible to achieve longer distances than those listed above, particularly for 40 Gb/s and 100 Gb/s transmissions. However, the distances provided here represent the typical standardized distances for these fiber types and data rates.

What does a Fiber Optic system cost?

Lets now talk about some of the key factors that affect the overall cost of a fiber optic system. Some of these are similar in cost between Singlemode and Multimode fiber but others there can be a big difference in cost.

Transceivers

This is the most significant factor in the cost difference. Singlemode transceivers are typically 1.5 to 5 times more expensive than multimode transceivers, depending on data rates. The precision required for injecting light into the smaller singlemode core drives up transceiver costs.

Installation and termination

Multimode fiber is easier to install and terminate in the field. Singlemode connections require greater care and skill, often needing pre-termination at the factory. This makes multimode more cost-effective for environments with frequent changes.

Power consumption

Multimode transceivers generally consume less power than singlemode transceivers. In large data centers with thousands of links, this can lead to substantial savings in power and cooling costs.

Cable cost

The actual fiber optic cable cost is a minor factor compared to transceiver costs.

Multimode cable is typically more expensive than singlemode cable, but this difference is overshadowed by other factors.

Connectors

Multimode connectors are generally less expensive than singlemode connectors due to less stringent alignment requirements. 

Manufacturing precision

Singlemode fiber requires higher precision in manufacturing due to its smaller core size, contributing to higher overall costs.

Testing equipment

Equipment for testing and troubleshooting singlemode fiber tends to be more expensive than that for multimode fiber.

Bandwidth and distance requirements

For shorter distances and lower bandwidth needs, multimode is often more cost-effective. As distance and bandwidth requirements increase, singlemode becomes more economical despite higher initial costs.

In summary, while the fiber itself is a minor cost factor, the associated equipment and installation costs make multimode fiber more economical for shorter-distance applications, particularly in enterprise and data center environments. However, for longer distances and higher bandwidths, singlemode fiber becomes more cost-effective despite its higher initial investment.

Technological Convergence

Given the stark differences between how far and fast you can go with various types of networking cable, a typical installation is going to be using a mix of technologies. This mix also includes copper Category cable too, as there is one big thing that copper Ethernet cable can do that fiber optic cannot do: Power over Ethernet (PoE).

Quite frankly the number of different types of installations is equal to the number of actual installations out there. No two are precisely the same due to a huge number of factors.

Singlemode fiber optic cable has been typically associated with long haul runs from service providers to business and residential areas. This would make sense, as this type of fiber can run for miles between transmission nodes. Multi-mode fiber is typically seen in businesses where the run requirements don’t exceed 1,000 feet or so. This is often referred to as a “campus” installation. Going deeper inside that campus structure, copper Ethernet technology is still used for various reasons and will be for some time to come. For our purposes, “campus” = anything from a residence to a large business or perhaps even a real college campus.

Singlemode fiber is replacing multi-mode fiber, however. The price differences between the actual cable are not large and the equipment costs are coming down. This lessens the worry of how far a fiber optic cable can run inside any one campus or large business. Prior to that, careful planning was required. Given higher bandwidths are associated with singlemode fiber up to those longer distances and the choice is starting to become clear. Singlemode fiber won out.

So now we have brought some clarity to the difference between single and multi-mode fiber and how this technology is of benefit. Choices are a good thing, and understanding the differences between those choices is key!

Common Questions and Answers

What are the differences between singlemode and multimode fiber?

A: Single-mode fiber uses solid lasers as the light source, while multi-mode fiber uses light-emitting diodes or VCSEL's as the light source. Single-mode fiber optic transmission has the characteristics of wideband and long transmission distance, but because it requires laser sources, the cost is higher, while multi-mode fiber is characterized by low transmission speed and short distance, but its cost is relatively lower. Single-mode fiber core diameter and dispersion is small, 8 -10 microns allowing only one mode of transmission, while multi-mode fiber core diameter 50 micron dispersion is large, allowing many modes of transmission.

What is the difference between singlemode and multimode optical transceiver modules?

A: multimode optical transceiver module works at 850nm, singlemode optical transceiver module works at 1310nm, 1550nm. The devices used in singlemode optical modules are twice as many as those used in multimode optical modules, so the overall cost of singlemode optical module is much higher than that of multimode optical transceiver modules. The transmission distance of singlemode optical transceiver module can reach 150 to 200km, and the transmission distance of multimode optical transceiver module can reach 5km.

Where are singlemode/multimode fiber and singlemode/multimode optical transceiver modules used?

A: Singlemode fiber enables the fiber to be launched directly to the data center, ISP location which is generally used for long distance data transmission, while in multimode fiber the optical signal is propagated through multiple paths. Therefore, multimode fiber is commonly used in short distance data transmission. Single-mode optical modules are often used in metro networks over long distances and at relatively high transmission rates.

Can singlemode/multimode fiber be mixed with singlemode/multimode optical module?

A: No! they can’t be mixed, we have to match the fiber and optical module to the type of fiber used. Multimode with Multimode and Singlemode with Singlemode.

Which one is right for you?

Both singlemode and multimode fiber optic cables have their place in modern networking infrastructure. Singlemode fiber excels in long-distance, high-bandwidth applications, while multimode fiber is ideal for shorter-distance, cost-sensitive installations. Understanding the differences between these two types of fiber optic cables is crucial for making informed decisions about your network infrastructure.

When planning your fiber optic network, it's essential to consider your current and future needs carefully. While multimode fiber may seem more cost-effective initially, singlemode fiber could provide better long-term value if you anticipate future bandwidth increases or network expansions. Always consult with networking professionals to ensure you choose the right type of fiber optic cable for your specific requirements.

By selecting the appropriate fiber optic cable type, you can build a robust, efficient, and future-proof network that meets your organization's needs both now and in the years to come.

HAPPY NETWORKING!

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