Optical Loopback Testing Tutorial

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Testing loopbacks using OptoTest equipment

Loopback Testing 

Slideshow Tutorial Transcript

  1. Loopback Testing Testing Loopbacks Using OptoTest Equipment
  2. Background:  A loopback is an optical component that routes fiber optic lines from port(s) of a connector to other ports of that connector.  These can have additional attenuation induced.  Used for BER testing.  Routes transmit ports back to receive ports.  With additional attenuation it can simulate a worst-case link loss for stress testing transceivers. Used for OTDR testing of links.  Terminates a long transmit link to a long receive link and allows the technician to diagnose both links without needing to connect OTDR to opposite side of receive link
  3. Structure Duplex LC MTP® Loopback (4ch) One link loops from one port to the other Multiple ports routed to other ports of the same connector. In this example fibers 1 to 4 are routed back to fibers 9 to 12
  4. Transceiver testing MTP Duplex LC To test a transceiver, connect a loopback directly to the transceiver. With this, one can test bit error rate.
    1. IL system (light source and power meter)  RL if necessary.  Channel count at least equivalent to number of links of the loopback.  Duplex LC has one link (simplex system fine).  MTP loopback (8 ports populated) has 4 links. For highest accuracy MTP requires large area detector.
    2. Typically link loss is tested.  Measured for the entire link and both connections of the loop back.
    3. For MTP a fanout is needed as well as a return MTP ideally.  Use a fanout with the channels populated according to loopback. Launch cord with MTP connectors fanned into MTP connector
    4. Return Loss – RL measurement is typically a combination of input and output connectors due to short internal fibers Testing Loopbacks Equipment needed
  5. Testing Loopbacks (LC) Reference Setup Measurement Setup LoopbackThis measures total IL of the Link: fiber loss and connector loss for both connections on the loopback.  To reference, use a single reference cord connected to the OPM and reference IL and RL.  To measure, connect the reference connector to the input connector of the loopback and connect a receive cord from the output port of the loopback to the OPM.
  6. Cable setup • Equipment cord • Connects from the source to the launch cord Testing Loopbacks (MTP) 4 Fiber fanout (Only Ch1 to Ch4)
  7. Cable Setup (Cont.) • Launch/Return cord Testing Loopbacks (MTP)
  8. Equipment setup Testing Loopbacks (MTP) Type A Adapter Key-up/Key-down
  9. Referencing Testing Loopbacks (MTP) Type A Adapter Key-up/Key-down
  10. Measurement Testing Loopbacks (MTP) Type A Adapter Key-up/Key-down Type A Adapter Key-up/Key-down
  11. Measurement Results Insertion loss.  This will be a combination of both connectors and whatever loss inside the loopback. Return Loss.  Depending on length of fiber inside the loop back, this could be a combination of both interfaces.

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