FACULTY OF ENGINEERING LAB SHEET OPTICAL COMMUNICATION SYSTEMS EOP4066 TRIMESTER 1 (2013/2014) OC1 FIBER LINK CHARACTERIZATION WITH OTDR *Note: On-the-spot evaluation may be carried out during or at the end of the experiment. Students are advised to read through this lab sheet before doing experiment. Your performance, teamwork effort, and learning attitude will count towards the marks. 1
OC1 Fiber Link Characterization with an OTDR Objectives: 1. To determine the fiber's length and overall attenuation, including splices and connectors losses. 2. To demonstrate ghost and determine the real length of the fiber cable. 3. To locate faults, such as breaks, and to measure optical return loss. Equipment: 1. JDSU MTS-6000 Compact Optical Modular Platform 2. Small single mode fiber optic cable reels has the following specification: Length: 2.2 km Att.1310nm: 0.34 db/km. Att.1550nm: 0.19 db/km. 3. 9/125/250 UM single mode simplex PC/B01020036005/SP1 (Launcher cable with FC connectors) 4. FC adapters. Theory: An optical time-domain reflectometer (OTDR) is an optoelectronic instrument used to characterize an optical fiber. An OTDR injects a series of optical pulses into the fiber under test. It also extracts, from the same end of the fiber, light that is scattered and reflected back from points in the fiber where the index of refraction changes. (This is equivalent to the way that an electronic time-domain reflectometer measures reflections caused by changes in the impedance of the cable under test.) The strength of the return pulses is measured and integrated as a function of time, and is plotted as a function of fiber length. An OTDR may be used for estimating the fiber's length and overall attenuation, including splice and matedconnector losses. It may also be used to locate faults, such as breaks, and to measure optical return loss. In addition to required specialized optics and electronics, OTDRs have significant computing ability and a graphical display, so they may provide significant test automation. However, proper instrument operation and interpretation of an OTDR trace still requires special technical training and experience. OTDRs are commonly used to characterize the loss and length of fibers as they go from initial manufacture, through to cabling, warehousing while wound on a drum, installation and then splicing. The last application of installation testing is more challenging, since this can be over extremely long distances, or multiple splices spaced at short distances, or fibers with different optical characteristics joined together. OTDR test results are often carefully stored in case of later fiber failure or warranty claims. Fiber failures can be very expensive, both in terms of the direct cost of repair, and consequential loss of service. OTDRs are also commonly used for fault finding on installed systems. In this case, reference to the installation OTDR trace is very useful, to determine where changes have occurred. Use of an OTDR for fault finding may require an experienced operator who is able to correctly judge the appropriate instrument settings to locate a problem accurately. This is particularly so in cases involving long distance, closely spaced splices or connectors. Ghosts: If you are testing short cables with highly reflective connectors, you will likely encounter "ghosts" like in Figure 1. These are caused by the reflected light from the far end connector reflecting back and forth in the fiber until it is attenuated to the noise level. Ghosts are very confusing, as they seem to be real reflective events like connectors, but will not show any loss. If you find a reflective event in the trace at a point where there is not supposed to be any connection, but the connection from the launch cable to the cable under test is highly reflective, look for ghosts at multiples of the length of the launch cable or the first cable you test. You can eliminate ghosts by reducing the reflections, using a trick we will share later. 2
Figure 1.OTDR "Ghost" On very short cables, multiple reflections can really confuse you! We once saw a cable that was tested with an OTDR and deemed bad because it was broken in the middle. In fact it was very short and the ghosted image made it look like a cable with a break in the middle. The tester had not looked at the distance scale or he would have noted the "break" was at 40 meters and the cable was only 40 meters long. The ghost at 80 meters looked like the end of the cable to him. Experimental Methodology: Use the highly integrated platform MTS-6000 with single module slot and an intuitive graphical user interface (GUI) shown on a large 8.4 inch transreflective colour display (with an optional touch screen) to improve viewing under any condition. Then, connect the equipments as it appears in Figure 2 below, and continue with the following experimental procedure. Figure 2. Using MTS-6000 OTDR to locate faults or breaks Experimental Procedure: A- Determination of the fiber's length and overall attenuation, including splices and connectors losses. (Please refer to Figure 2 for the connection of this experiment.) 1. Connect the launch cable by connecting the FC connector to the plug in module. 3
2. Use FC adapter to connect the FC connector to reel A of fiber optic cable which has a length of 2.2km. 3. Lift the protective cover over the power supply socket on the top of the 6000 Base unit (Top left hand corner as it appears in Figure 3) and plug in the main adapter. 4. Now press the On/Off key. The On indicator lights up. 5. The JDSU logo appears on the screen briefly, then an autotest is carried out, the software is installed (this just takes a few seconds), then the screen goes dark for about three seconds. Finally the opening screen appears. 6. Press the setup key appears in Figure 4. 7. On acquisition menu select Mode then click on Auto or in case you select one of the wavelengths (1310nm or 1550nm) make sure that the Pulse and Resolution are set to auto. 8. Press Start/Stop Key to start the laser. 9. The result of the measurements will appear in the result page within less than one minute and can be memorized in the table. Assignment: i. Connect reel B to reel A using another FC adapter. Compare the measurements between reel A and the cascaded reel A and reel B. (Cognitive Analysis, Level 4) [4 marks] B- Ghost Image and it effects on results. 1. In order to activate ghost detection, press Setup key again. 2. On Measurements menu select Detection, then select Ghost and click on Yes. 3. Ghost detection can be deactivated again by clicking on No. Assignments: i. Using cascaded reel A and reel B, perform an experiment to observe the effects of ghost on the results of the measurements. (Cognitive Synthesis, Level 5) [6 marks] ii. Sketch the measurement images and evaluate the effects of ghost on the results of the measurements. (Cognitive Evaluation, Level 6) [6 marks] C- Locating faults or breaks 1. The OTDR allow location of the fault or breaks by clicking on Fault locator in Mode menu, after selecting acquisition menu. Assignments: i. Using cascaded reel A, reel B, reel C and reel D, perform an experiment to find the location of the fault or breaks. (Cognitive Synthesis, Level 5) [8 marks] ii. Sketch the measurement images and deduce the location of the breaks, based on what you learnt from the previous experiments. (Cognitive Analysis, Level 4) [8 marks] Report Writing: 1. An individual report should be nicely typed and should include the following: Date of experiment Names and IDs of all members Objectives [3 marks] 4
Procedures, results, answers and discussions for all questions and assignments [32 marks] Conclusions [5 marks] 2. The lab report has to be submitted to the lab staff of Optical Laboratory after 2 weeks. Figure 3. MTS-6000 ports Figure 4. Controls of the interface module 5