Testing Fiber Optic Media Lab Last Update 2014.07.25 1.1.0 Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 1.

Testing Fiber Optic Media The basic test of a fiber optic cable based link is loss or attenuation This loss can be measured automatically by using a calculated loss limit or manually by just observing the power measured at the end of the cable Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 2

Testing Fiber Optic Media The automatic method requires an OLTS with this capability built-in such as the Fluke DTX CableAnalyzer and SmartRemote set The manual method requires an OLTS with a power source and a power meter The Fluke DTX CableAnalyzer and SimpliFiber set does this Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 3

Loss Limit Let’s first look at how the acceptable loss is calculated Many fiber optic cable testers such as the Fluke DTX will calculate the maximum loss that could occur for the link to still work For example in this test report the Loss Limit is 1.67 Why is that Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 4

Loss Limit In this case as the test report shows the length of the cable is 156 feet The standard loss for 62.5 multimode fiber optic cable is 3.5 dB per kilometer which is.0010167 dB of loss per foot 156 feet times.0010167 dBs per foot comes to.17 dB of loss due to attenuation in the cable Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 6

Loss Limit It is assumed in this case by the DTX that there will be two connectors in the path since the test method selected was Method B Method B assumes two connectors The standard maximum loss for a 62.5 multimode fiber optic cable connector is.75 dB, which as we will see is a very high value Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 7

Loss Limit For two connectors this is 1.50 dBs.17 plus.75 plus.75 is 1.67 So the computed limit of loss that can be tolerated for this link to pass is 1.67 If the measured loss is found to be higher than this, we need to find out why and fix it Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 8

Loss Limit Now if we actually calculated this Loss Limit using these standard values for each part of the link under test in this example the Loss Limit would be 4.67 dBs broken down this way DTX Main – 1 Meter Patch Cable – 150 Roll of 62.5 Fiber Optic Cable – 1 Meter Patch Cable – DTX Remote The link looks like this Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 9

Loss Limit Connector.75 MainOutputPatchFiber.0035 Connector.75 Connector.75 Roll of FiberFiber.17 Connector.75 Connector.75 RemoteInputPatchFiber.0035 Connector.75 Total Loss4.67 Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 10

Loss Limit If we put a basic light source at the other end of the link instead of the SmartRemote, and then measure the received power for this link we find it is 19.18 This means the real loss is.82 Why would there be such a large difference between the expected loss of 4.67 and the actual loss of.82 Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 11

Loss Limit It seems the standard loss figures for connectors are way too high Corning for example states that the loss one should expect from a connector such as this is.1 as seen here Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 12

Loss Limit Connector.1 MainOutputPatchFiber.0035 Connector.1 Connector.1 Roll of Fiber150 Feet62.5Fiber.17 Connector.1 Connector.1 RemoteInputPatchFiber.0035 Connector.1 Total Loss.77 Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 16

Loss Limit Now this is much closer to the value we measured of.82 The difference between the realistic Loss Limit calculated using the published specifications for these components and the loss actually found in the link is.05 Regardless of what caused the difference it is so small a value it can be ignored as insignificant Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 17

Loss Limit This is likely due to measurement error, more loss somewhere than the specifications state, dirt on end faces, or gaps between one or more of the connection ends Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 18

So What The next question you should be asking yourself is - is this amount of received power good, bad, or what Further, just how sloppy can I really be in the installation Just how much loss can I measure without it causing a problem Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 19

So What To answer this we must look at the specifications of the receiving port at the far end of the link How much power must it receive at a minimum to receive data Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 20

Power Budget The power budget is the difference between the Launch or Transmit Power which is the energy level of the light as it leaves the transmitter and the Receive Sensitivity or Power of the receiving device which is the minimum energy required for the fiber receiver to detect an incoming signal Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 21

Power Budget The Power Budget then is simply the result of subtracting the Receive Sensitivity from the Launch Power For example for a Cisco SFP being used on each end of a link such as this –GLC-SX-MM SFP –WS-G5484 –For 1000BASE-SX –Using 850 nm Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 22

So What Why do we care The Power Budget is just a term used to describe the total amount of light energy available for a certain link The Power Budget serves as a useful estimation to determine if sufficient optical power will remain on the receiver side of an optical link Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 24

So What Why might sufficient optical power not be received at the far end of a link The Power Budget then also tells us how much loss we can tolerate in the link’s components such as the fiber attenuation, connector induced loss, dirt on end faces, and so on Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 25

So What So in this case for a link of unknown length with an unknown number of splices and connectors and an unknown amount of dirt we have 14 dBs in our pocket to spend on this sort of stuff In our example above for a link made up of DTX Main – 1 Meter Patch Cable – 150 Roll of 62.5 Fiber Optic Cable – 1 Meter Patch Cable – DTX Remote Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 26

So What We measured the real loss as.82 We then have some 13 dBs to spend on adding more splices, connectors, dirt, a longer cable to extend the link, and so on For a typical installation we are unlikely to add anything to this link as why would we have calculated the expected loss at.77 in the first place if we expected to add devices later Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 27

So What What we can spend these 13 dBs on is for junk on the end faces of the various connectors in the link In this case 6 connectors or end faces For each one of these we could tolerate an average of 1.11 dBs of crud covering the core Just how dirty does a end face need to be to produce 1.11 dBs of loss Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 28

So What Dirt and other crud is commonly mentioned as causing loss but no one ever provides sample loss numbers for the various types of crud that could block the signal Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 29

So What Cisco says in one document that a 1micrometer dust particle on a singlemode core can block up to 1% of the light based on 0.05 dB of loss Fluke in a BICSI presentation says the EPA says that typical dust particles in the office are from 2 to 10 microns in size Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 30

So What 62.5 fiber is going to be able to still connect with a lot of dust particles if the loss for each one on singlemode fiber is.05 dB as 62.5 end faces are going to have a lot more surface area available to handle these particles Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 31

So What If we just use the singlemode loss factor per dust particle of.05 dB we have at least room for 134 of these pesky little dust particles spread among six connectors before the link fails In short keep the connections clean and tight, but do not obsess over it Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 32

The Test Let’s now perform a test to see how this is done We will do two types of tests –Automatic test using the DTX CableAnalyzer and SmartRemote –Manual test using the DTX CableAnalyzer and SimpliFiber light source Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 33

Select the Link Type Regardless of whether the automatic or manual test is used the type of link being tested must be setup in the CableAnalyzer Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 34

Select the Link Type In this case to do this select Setup Select Fiber Loss –In Tab 1 Select Fiber Loss Press enter to select the Test Limit –Select TIA568C Backbone MM Select the Fiber Type –Select Multimode 62.5 MBW=200 Select the Remote End Source –Select SmartRemote Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 35

Select the Link Type –In Tab 2 Select Test Method Method B –Select Number of Adaptors 2 –As we will be plugging into the link for the actual test –Thus there will be 6 adaptors in total –Two are accounted for at each end by setting the Test Method to Method B –The other 2 - one at each end of the link under test - are accounted for here Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 36

Set the Reference What color boot goes to which input or output depends on how the patch cables are made In this lab we are using a green patch cable at the CableAnalyzer end and a blue patch cable at the SmartRemote end The boots of these are both color coded so that red goes to red and black goes to black Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 41

Set the Reference Regardless of the color of anything it does matter where the mandrels are They are always at the output port of each unit Therefore, in this lab connect the two units to each other in this manner Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 42

Set the Reference With the cables connected as shown, on the CableAnalyzer select Special Functions Select Set Reference Press Enter Verify the connections Press Test Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 44

Automatic Test To perform the automatic test Move the switch to AutoTest In Room 227 connect the cables as shown next DO NOT disconnect the output port cables from the OLTS Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 51

Manual Test Let’s see next how to do the manual test where a known amount of power is sent into a link, and then at the far end of the link the power received is measured If as discussed above this received level is high enough for the fiber modules to send and receive data then the link as installed can be considered to have passed Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 62

Manual Test For this test we will use a 150 foot roll of 62.5 fiber optic cable We will need to calculate the actual expected loss before running the test so that we can compare it to the test results It will be up to us to then decide if the link passed or failed For this calculation we can just pull the figures from above down here Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 63

Loss Limit Connector.1 MainOutputPatchFiber.0035 Connector.1 Connector.1 Roll of Fiber150 Feet62.5Fiber.17 Connector.1 Connector.1 RemoteInputPatchFiber.0035 Connector.1 Total Loss.77 Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 64

Set the Reference What color boot goes to which input or output depends on how the patch cables are made In this lab we are using a blue patch cable only to set the reference and then both the green and blue cables for the test Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 67

Set the Reference Regardless of the color of anything it does matter where the mandrel goes It is always at the output port of each unit Therefore, in this lab connect the two units to each other in this manner since the only power source is the remote end SimpliFiber unit Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 68

Set the Reference With the cables connected as shown on the CableAnalyzer select Special Functions Select Set Reference Press Enter Verify the connections Press Test Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 77

Manual Test The AutoTest function of the CableAnalyzer can be used just as it was for the automatic test or the Power Meter function of the CableAnalyzer can be used This is what we will do in this case Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 84

Manual Test Select Monitor Select Power Meter Select Test Select 850 nm Press Test The result is a real time display of the power level received by the CableAnalyzer The received power is -18.78 dB Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 85

Manual Test Now compare this received power level of -18.78 to the expected power level which is -20.00 minus.77 or 19.23 So in this case we have.45 dB of unexpected and unexplained loss Do we need to worry about this.45 dB Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 86

Manual Test To determine this we first need to see what level of power the device at the end of the link needs to receive in order to send and receive data over this link As we saw above in this example that value is -17 So we have enough room as there is a difference of 1.82 Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 87

Fiber Optic Cable Testing In this lab we have seen how to perform both an automatic and a manual test of multimode cable such as would be used for a backbone link Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 91

Testing Fiber Optic Media Lab Last Update 2014.07.25 1.1.0 Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 1.

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Testing Fiber Optic Media Lab Last Update 2014.07.25 1.1.0 Copyright 2013 - 2014 Kenneth M. Chipps Ph.D. www.chipps.com 1.

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