Blog posts of '2019' 'January'

So you’re sitting there and wondering to yourself, Singlemode, Multimode. What’s the difference? Well wonder no more the answer you’re looking for is just below, but first let’s briefly discuss fiber optics in general.

Fiber optics is essentially sending signals in the form of light, down very thin strands of glass or plastic. The light is sent down the center of the fiber known as the core. The core is encased in an optical material called “cladding”. The cladding ensures the light remains trapped within the core by making use of an optical technique known as “Total Internal Reflection“. Both the core and the cladding are generally made of ultra-pure glass. The cable is then covered and protected by and outer plastic cover called a “jacket”. Jackets come in various types and colors as well but this is a topic for future article.

Singlemode Fiber Optic Cable 

Singlemode cables feature a core with a very small diameter that only allows one mode of light through (thus the term Singlemode). As a result of this the number of reflections resulting from the light traveling down the core are dramatically reduced. This in turn lowers the attenuation and allows the signal to travel both faster and further. If it helps, think of it in terms of a lot of water flowing through a very thin hose pipe, it will be far more compressed, travel faster and further through small the hose than through a large one.

Singlemode fiber cable is usually identifiable by a standard yellow jacket and available in a typical 9/125 ratio, this means the core has a diameter of 9µm (microns) and the cladding has diameter of 125µm.

Multimode Fiber Optic Cable 

Multimode fiber optic cables sport a larger diameter core that allows multiple modes of light to propagate, simple right? Well not quite, as you would expect due to the larger core diameter more data is able to be transmitted. However, far more light refraction and attenuation takes place. This means that they are generally used over far shorter distances thaningle-mode cables due to signal degradation. They are most commonly found in short distance data applications such as LANs (Local Area Networks).

Multimode fiber is typically available in both 50/125 and 62.5/125 ratios. That is a core to cladding ratio of 50µm to 125µm and 62.5µm to 125µm.

While this is a somewhat simplistic break down of the differences, hopefully you have found it useful in understanding the basic differences between Single-mode cables and Multimode cables and can use this to help you decide which type of cable will best suit your fiber optic cable needs.

These days fiber optic cables are used everywhere to connect our modern world and are able to send information across countries and vast oceans, but how do they work? Before we get too stuck in to the more technical stuff, why not check out the video below for a nice, simple summary of how it all comes together. 

How They Work 

Fiber optics are fairly simple to understand on a basic level. Essentially information in the form of light is sent from one place to another, this is generally done through fiber optic cable. The beauty of this comes from something known as Total Internal Reflection (TIR), what this means is that the light is able to be sent through a flexible fiber optic cable by simply ‘bouncing from one surface to another’ until it reaches it’s destination.

Reflection vs Refraction 

Any time light strikes a surface it can either be reflected from it (reflection) or pass through it (refraction). The key to transmission of light via fiber optics is to ensure that light hits the surface greater than the critical angle to ensure complete reflection and not refraction. This requires quite a bit of mathematics, but to simplify it one should ensure that the angle of the surface the light hits is not too great so as to ensure reflection takes place and not refraction.
 

Understanding the Structure of Fiber Optic Cable 

Fiber optic cable typically contains a core made of ultra-pure glass which is then surrounded by an outside layer of glass known as cladding. The cladding is designed manufactured in such a way as to decrease it’s index of refraction by using small bits of boron or germanium. The core and cladding are manufactured as a very long, thin piece of glass that is made by heating what is know as a preform with the center being the pure glass core and the outside is the cladding. It is then stretched to an length of unusually around 18.2 m (60 ft).

Sending Data by Light 

Data is sent and received in our modern society in what is known as binary numbers, essentially 1’s and 0’s. Think of it as a light switch with 2 settings, either On (1) or Off (0). If you turn the light on and off at the switch with a specific pattern it can be used to form somewhat complex messages. Such as the example one below:

Data is sent similarly through fiber optic cable in the form of laser light pulses using what is known as Pulse Code Modulation or PCM. Unfortunately this is a lengthy topic which maybe discussed in a future article.

In Summary 

Fiber optics allows us to send information across the globe at the speed of light (186,000 miles per second ) via specifically designed fiber optic cables by making clever use of light reflection and refraction.