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Single Mode vs Multimode fiber

Singlemode vs Multimode fiber




If you are a network engineer then you must have an encounter with fiber cables which gets connected to various Cisco Devices. These optical fibers or Fiber cables are generally used to connect backbone network with switches. Like for instance,  Access switches are connected to core switch via  optical fiber cable. There are basically two types of Optical Fibers which are commonly used for interconnecting different Network Devices :

  1. Single Mode

  2. Multi mode

So, in this post I will talk about both the singlemode as well as  multimode fiber in the simplest way possible. I will not go in depth of Fiber optics but I will give you the required information which should suffice practically for a network engineer.

Fiber cable consist of mainly four parts:



  1. Core : This is the main component of the optical Fiber in which Lights travels. This is generally made up of pure glass.

  2. Cladding : Core is surrounded by cladding to trap the light which is travelling in the core to prevent diffraction of light while light travels through the core.This is also made up of Glass. But there is a difference between the refractive index of the glass used in cladding and a pure glass that is being used in the core.

  3. Buffer : Core and cladding is covered by buffer to prevent Core and cladding from Moisture and physical damage. So basically this layer secures the optical fiber from external threats.

  4. Outer Jacket : All above are covered with Outer Jacket for further protection from damage.



Multi Mode and Single mode fiber basically differs in Core Diameter present inside a fiber cable.

Here is the Video which I have created regarding multimode and single mode fiber :


Multi Mode Fiber :


First I want to tell you regarding Multi Mode fiber as it is most commonly uses in network setups. (Those orange and Blue color fiber patch cords from which many of you are already familiar with) . Their core diameter is large as compare to Single mode fiber. It is 50 Micron in diameter. Due to this we can send multiple light rays in single Core. This doesn't mean these are better than single mode fiber because in Multi mode fiber the distance limit is around ~500 Meter.





In this fiber, high power LED or  Low power Laser is used to produce light source which can be visible with naked eyes. They are cheaper to made as they have larger Core Diameter and less precise machines are used to produce these Multi mode optical fiber. In normal scenarios 500 M is more than enough to connect Access Switches to Core switches if we have small Campus or if they are physically placed separately on different floors.

They are available in different specifications based on Core diameter and light source frequency (or Bandwidth) which can be used with them. If you have an access to fiber cable , you can see on that cable some thing like 50/125 OM3 is printed.



This means 50/125 where 50 is Core diameter in micron and 125 is Cladding diameter. OM3  is the frequency of light which this Fiber cable can handle. OM3 basically handles 2000 Mhz of frequency of light. Here is the table which describe all the multimode fiber types in more details :




Fiber Types and Reach

Fiber Type


Bandwidth*Length

Product (MHz*km or GHz*m)

10GBASE-SR Distance (meters)


40GBASE-SR4 and 100GBASE-SR10 Distance (meters)


OM1


160-200


33


N/A


OM2


400-500


82


N/A


OM3


2000


300


100


OM4


4700


400


150




These multimode fiber cables are majorly available in two different colors : Orange & Blue

Orange : These are not laser optimized

Blue/Aqua : These are laser optimized and they come for OM3 specification and above.









My recommendation is to use OM3 Blue/Aqua Multimode fiber as they are fully compatible with 10 Gbps links.

Aaahhh....!! Lots of explanation right ? But trust me this is only a brief description otherwise Fiber optics is a wonderful field in itself to talk about :) . May be we can do that sometime in future for tech enthusiasts who are curious to know about it. But for now lets move further to Single Mode Fiber.


Single Mode Fiber : 


As compare to Multimode fiber, Single Mode fiber Core Diameter is very very small. It is only 9 Micron as compare to 50 Micron of Multimode fiber. This diameter is even less than the diameter of human single hair strand. Amazing no...Due to this we can only send single light ray in this cable. But this single light ray distance travel  limit is much higher as compare to multi mode fiber. It can be around 50 Km as compare to Multimode that is only ~500 M.




In single mode fiber,  high power laser is used to create single light ray source. Laser is used because they are most precise to enter into 9 micron core. This laser light source is not visible to naked human eyes.

We can use Single mode fiber cables as a backbone if we have very large campus or in which multi mode fiber distance is the limit. In overseas fiber cable or the fiber cables which are laid by ISP from city to city are single mode fibers. They are 2-3 times more costlier than multimode fibers. Since high power lasers are used as a light source in single mode fibers, the overall hardware setup cost is more than the hardware setup cost for multimode fibers.

Like multimode fibers ,  they are also available in different specifications. Most commonly used specification in campus is 9/125. Where 9 is the diameter of the core in micron and 125 micron is the diameter of the cladding.



Single mode fiber cable color is YELLOW. 





Here we have reached to an end of this post. Hope I  was successful in explaining the difference between single mode and multimode fiber excluding the deep technical details. Hope you enjoyed this post. Please share this post if you like this post.

Signing Off for now....Will post soon... Till then Keep networking!! :) :)

Comments

  1. Just a small note, the Core is called a ferule in the fiber world.
    Today where the tools to make fiber installations is more common, the singlemode tools and multimode tools are same today, som today the cost of making singlemode is only like x1,3. Because of that we always use singlemode even for short distances, because if you have a full singlemode installation you are able to patch from distribution field to distribution field many times, cause it is not the distance there define if it works or not, it is the lost of signal there is the issue, and you can make many more patch with singlemode compared to multimode.

    ReplyDelete
  2. Thanks Michael for providing this information.

    ReplyDelete
  3. Sukhjinder SinghJuly 29, 2017 at 8:12 PM

    Dear Samarth Singh
    how can i connect the two networks (separately running on multi mode FO) through a single mode FO cable? these two networks are located at 60 km distance, i have single mode FO link between these two networks. Should I use converters (Multimode to single mode)?

    ReplyDelete
  4. Yes you need a converter..

    ReplyDelete

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