Single-Mode vs. Multimode Fiber Optic Cable: What’s the Difference?

Setting up the network infrastructure is a game of choice. You have a plethora of options when it comes to selecting the different materials in a network. You can either choose

1. copper wire cables for durability and cost-effective solutions
2. fiber optic cables for long-distance transmission and greater bandwidth.

There is further bifurcation available in fiber optic types:

1. Single Mode Fiber Optic Cable
2. Multimode Fiber Optic Cable
   

One point of difference lies in appearance, but there exist more. Choosing a suitable cable is vital as it has implications on the bandwidth, budget, and information travel distance. Hence it is essential to understanding the differences between both.

What are Single-mode and Multimode Fiber Optic?

By functionality, both operate by reflecting light many times inside a glass core. Yet, the main difference between both of them lies in their construction. By definition, a single-mode fiber optic cable works by transmitting a single beam of focussed light over a large distance. In comparison, the multimode fiber optic cable can send many light sources at the same time within the same glass core.

Hence, multimode has the better bandwidth. This, yet, doesn't mean that multimode fiber optic is superior to single-mode fiber optic. Both have individual applications and are placed in a network infrastructure. So, you can't interchange them.
Let's delve deeper to understand their differences better.

Here is Difference Between Single Mode & Multimode Fiber Optic Cable

Difference #1 Structural Difference

In a single glance, both single-mode and multimode fiber optics have no visual giveaway. Cutting open either cable will reveal a glass core covered in a protective cladding. The cladding allows bending to an extent. Yet, on comparing both cables, you may notice that the multimode core is slightly thicker. Usually, single-mode fiber optic cables only need to transfer one light signal and have a core diameter of 9µm. In comparison, multimode cables need to send many light signals and have a core diameter of 62.3µm (OM1) or 50µm (OM2/OM3/OM4/OM5).
For clear identification purposes, single-mode & multimode have different color protective sheaths. For example, single-mode fiber optic cables have orange-colored PVC jackets.

Multimode fiber optic cables have aqua-colored protective PVC coating.

Difference #2 Operation Mode

You may have learned about two properties of light in your science classes:

1. Reflection - A phenomenon where the light propagates at the same angle (angle of reflection) that it hits the surface (angle of incidence).
2. Refraction - A phenomenon where the light deviates in an angle related to the angle of incidence.

Multimode fiber optic operates as per the reflection property of the light. At the same time, a single-mode fiber optic cable transmits the light signal in a nearly straight path.
Due to the constant reflection, the relative distance traveled by the multimode signals is less than the single-mode fiber signal. The signal loss from fiber bending is low in multimode fibers. This is because the light signals adjust their path (to an extent) to bend radius. Owing to the thick core, multimode fiber optics can bend more without worrying about breakage. Hence, single-mode fiber optic cable is used more for long-distance communications. Multimode is more suited for inter-department or medium-sized businesses.

Difference #3 Modal Dispersion

Modal dispersion is a phenomenon where the propagation velocity of the different light signals changes inside. This is due to the different reflection angles. The different speeds cause individual light signals to reach at different times. This phenomenon causes the signal to distort at the receiving end. This phenomenon frequently occurs in multimode fiber optics. Hence, you need to repeat the signal after a specific length. The safe distance for a multimode fiber optic cable depends on the network bands. The signals need to be repeated every 200m while operating for 100BASE-FX. For 40GB BASE SR4, OM3 multimode can experience modal dispersion at length > 100mtrs.

(Image Source: Physics Stack Exchange)

Difference #4 Light Source

The light traveling inside a single-mode optic fiber should be in an almost straight path. So, the light source is either lasers or laser diodes sending refined polarized light of 1550nm wavelength. In multimode optical fibers, we know that the core diameter is larger than the single-mode optical fiber. So low-cost light sources such as LEDs operating in 850nm to 1300nm wavelength work best.

Difference #5 Overall Costs

Pricewise, a single-mode fiber optic cable is inexpensive compared to a multimode fiber optic of the same length. Yet, owing to the bigger core of multimode, the transceiver at both ends costs less for multimode operation. By purchasing pre-terminated multimode fiber optic cables, you can reduce the cable cost substantially.

Difference #6 Future Proofing

There are many different data bandwidth standards. You have separate multimode fiber optic cables that provide different bandwidth to distance ratios. For example, single-mode fiber optic cables can transmit information up to 10km in a 10GBASE SE-SR network. Yet, it is ineffective for higher bandwidth. You can use multimode fiber optic cables for data bandwidths as high as 100GBase SR10 networks, but distortion affects the cable length. For example, OM1 and OM2 are adequate for a 1GB ethernet 1000BASE-LX network. For network bandwidth up to 100GBase SR10, you need OM3, OM4, or OM5 multimode fiber optic cable.
Hence when it comes to future-proofing, multimode cables are more versatile. Yet, you should be clear about your network requirements for future-proofing scaling. As the data rate increases, you either compromise on the length or consider going for the expensive OM(x) (x=3,4,or5) cables.

Wrapping Up

As you may have deduced, there are many points of difference between a single mode fiber optic cable & a multimode fiber optic cable. Both provide a durable and data transmission at high bandwidth. Yet knowing their advantages and limitations allows you to make the correct choice. While setting up a network, a system architect can help you plan out suitable network infrastructure. An infrastructure that satisfies your current requirements and is scalable for the future.