Optic Fiber Community
Connecting Fiber and connecting the Fiber Optic Community
2017 Communities of practice for all those who touch the Fiber Optic Highways and networks in any manner.
Here, we share best practices.
Worst nightmares on the field.
Lessons learned. Problems solved.
We can pose questions. State facts. Share views.
This is our professional space for collaboration and group wisdom.
Cheers to 2017!
With the rapid deployment of FTTx solutions, the need for Bend insensitive fibre is rising. Sharp corners and bends make it impossible for standard 652D fibre to be used because any 90 degree bend can cut off the light. The G.657 fibre is special in the sense that during a bending the most of the stray light goes back into the fibre core making it possible for it to be deployed in tight spaces with small bend radius.
The variants in the bend insensitive fibre are the following:
G.657.A.1/2/3 are backward compatible with G.652.D and support Multiplexed transmission in the 1310-1625nm wavelength region and are available with bend radii of 10mm, 7.5mm and 5mm respectively.
G.657.B.1/2/3 are not designed to be backward compatible and have a specified attenuation at 1310 nm, 1550 nm and 1625 nm, but not at intermediate wavelengths. They are available in 7.5mm and 5mm radii versions.
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Very often we come across installations where OFC cabling is completed but not properly tagged. This creates problems after splicing with either wrong cables in the right rack/panel or the right cable in the wrong rack/panel. How do we get over this problem –
Here are a few tips:
a. Using Labels:
Adopt a simple cable tagging code from which you can figure out the origin of the cable say three 6F Single mode cables laid between the Main Control Room(MCR) and Remote Panel/s -1, 2, 3(RP1, 2, 3).
At the MCR, just tag the cable RP1_SM_6F, RP2_SM_6F & RP3_SM-6F
At the Remote Panel/s just tag the cable MCR_SM_6F_1, MCR_SM_6F_2 & MCR_SM_6F_3 respectively at the three remote panels
b. Using colours:
In the above example assign colours to each of the Remote Panels say Red, Yellow, Blue for RP1, RP2 & RP3. Tape the cable ends Red, Yellow & Blue using colour insulation/duct tape.
Just deciding on any of the above tagging methods based on the number of cables to ensure easy identification will save lots of time & effort in resolving communication issues without having to reroute cables and redo splicing.
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There are a number of devices particularly in Plant automation and SCADA that communicate on serial protocols like RS-485/RS-422/RS-232 etc. Typically extending these serial communication signals on shielded cables has distance limitations apart from susceptibility to electromagnetic interference(EMI). To get over this limitation, we can incorporate Serial to Fibre optic converters that accept RS485/422/232 signals and convert them to optical signals for transmission over 2 Kms in the case of Multimode and 20 Kms in the case of Singlemode. The converters are transparent to the software protocols such as MODBUS-RTU, MODBUS-ASCI etc. Here is a picture of a typical serial to optical converter:
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There are multiple ways of extending fibre optic links that fall under the topology daisy chain, ring and star. Let’s just look at each of them briefly taking a simple 3-point network having location #A, B & C:
1.Daisy Chain: # Location A – # Location B – # Location C . The optical signals hop from A to B to C. If there is a cable cut between A & B the whole link goes down. If there is a cable cut between B & C then C is cut off from the network.
2. Ring: # Location A – # Location B – # Location C – # Location A . The optical signals hop from A to B to C and then return back to A. If there is a cable cut between A & B , then the communication happens through the path A -C-B. If there is a cable cut between B & C, the communication happens through the path A-B & A-C. So you can see that this is a better option than the daisy chain because for a single break in the link, the communication is not interrupted. However, this requires extra cable ( for the return path) and also managed switches/devices to detect break and switch communication to the available alternative path. Most preferred for critical communication and increasingly being adopted in CCTV surveillance networks communicating on optical fibre backbone.
3. Star: Location #A – Location # B ; Location # A – Location #C. Pretty straightforward..we now have two independent links from Location #A. If there is a cable cut between A & B, then only that link goes down, communication between A & C is not affected and vice versa.
Based on the number of points to be connected and the critical nature of the application, we need to make a technically and commercially feasible choice by picking one or a combo of all the three types.
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Have you come across a situation where you are stuck with singlemode cable and multimode converters and you have to establish fast ethernet communication ?
You can’t relay multimode cable or replace the multimode converters supplied with singlemode converters – What do you do ?
Well, you can install singlemode to multimode converters. These are active devices with two SFP slots that take a MM 100FX SFP on one and a SM 100FX SFP on the other. Hook up the LIU end with a SM patchcord to the singlemode SFP and the MM SFP to the MM media converter with a Multimode patchcord and power on the converters…Your link should be up and running !!
A smart way to get around cable and converter mismatches. Want to know more about our products and services ? Please visit http://www.yaminiengineers.com. We are all about passive and active fiber optic products.
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Pigtails are short pieces of 0.9mm buffered fibre connectorised at one end and the other end free to be spliced with the optical fibre cable. The No. of pigtails is generally equal to no of fibres in the cable unless some fibres in the cable are left unspliced. It is a good practice to splice all the fibres with pigtails and have all fibres ready for use.You will find the pigtails inside the LIU as you can see from the pictures in the attached file.
Adapters aka Mating sleeves aka couplers are mating points of the pigtail and patchcord. The pigtail is plugged into the adapter at the end inside the LIU and the patchcord is plugged into the end outside the LIU.
Patch cords are flexible fibre optic cable assemblies that facilitate connection between the LIU and the active equipment viz. Ethernet switches and media converters. Patch cords can be simplex or duplex. Simplex means one fibre and duplex means two fibres. Generally fibre optic communication is full duplex meaning a dedicated fibre for the transmit signal and a dedicated fibre for the the receive signal. Accordingly the patch cords are more often duplex than simplex particularly for data communications.
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Splice closures (aka Joint closures) are weatherproof enclosures used to splice 2 or more optical fibre cables. They come in either rectangular or cylindrical construction. The splice closures have 2 -4 cable entry ports to bring the the cables in, splice trays for joining the individual fibres of the cables to each other and properly routing the same. Upon splicing the cable entry ports are sealed with heat shrinkable sleeves. There is also a mechanical design which enables re-opening of the closure if required. The closures are made out of light weight plastic. Once properly sealed the closure is water proof and air tight. Hardware used in the closure is rust proof. The closure generally conforms to IP-68 and suitable for underground direct burial, aerial or duct burial applications.
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The LIU as you can see above is a meeting place for Fiber optic Cable, Fiber optic pigtails, Fiber optic adapters and Fiber optic patchcords. The Fiber optic cables are anchored rigidly in the LIU…
Source: LIU – Lightguide Interface Unit
The LIU as you can see above is a meeting place for Fiber optic Cable, Fiber optic pigtails, Fiber optic adapters and Fiber optic patchcords.
The Fiber optic cables are anchored rigidly in the LIU and the fibers spliced to pigtails and plugged into respective adapters. From the picture you will see 12 adapters which means 12 fibers are available for use. Now Fiber optic patchcords can be used to extend these fibers to the fiber optic port of the active device be it switch, media converter or any other product with inbuilt fiber optic ports.
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Let’s think of a MRI versus an X-ray.. A simple X-ray is all that is needed to find out if a bone is broken or not but an MRI is called for if one needs to go down to the tissue level to find out more serious problems..
Similarly , do we really need to do OTDR testing all the time for our fibre optic links ? The answer is No. A simple source and power meter test is more often than not enough to determine the attenuation on a fibre optic link and check if it is within the link budget specified for having a functional link.
Yes if we do have long haul fibre optic links running into a few tens of kilometers an OTDR trace will more accurately measure the attenuation to qualify the link not only in terms of optical link loss but also in terms of bends/kinks in the cable, inherent defects in the fibre (Macro & Micro bends).
