AN-113 Bidirectional MultiFiber Insertion and Return Loss Testing Using OP725-OP940 and Two OP720s

AN-113 Bidirectional MultiFiber Insertion and Return Loss Testing Using OP725-OP940 and Two OP720s

Overview

With 100G Ethernet and beyond quickly becoming the standard for the fiber optics communication industry, many cable manufacturers want to be able to test multifiber cables with relative speed and ease. Using an OP725-OP940 and two 1xN OP720 switches with OPL-MAX, an operator can test bidirectional insertion loss and return loss on high-fiber-count cables.

The test setup should be as follows:

OP940-OP725-01
Figure 1: Test setup for measuring IL/RL bidirectionally for multiple channels

* DUT: device under test
* *HPR: high performance reference cable

The OP725-OP940 Bidirectional Insertion Loss and Return Loss Test System, connects to the inputs of each OP720. HPR cables are then connected to the output of the OP720 (up to 144 channels) which then connect to fanouts with the DUT residing between these fanouts; an MPO ribbon fiber DUT is used in this illustration.

OPL-MAX Test Sequence

Configuring OPL-MAX to run correctly with this configuration is similar to configuring a  multi-channel OP725-OP940. For a 12-fiber MPO cable, the sequence file should be as follows:

OPL-MAX
Figure 2: Sequence file for 12-fiber MPO cable

As with all sequence files, Column D will specify which fiber in the cable will be tested, Columns E and F will specify wavelength(s) and Columns G and H specify the power meter and channel used for testing. In the case of the bidirectional test with an OP725-OP940, these Columns G and H, as above, should read “OPMRL1” and “1-12”, respectively.

Since the distance from the front panel to the RL reference is not guaranteed to be the same for both directions, it is advised that Column N appears as shown above. The “1” in the first channel in the forward direction (coming from the A-B port) and a “-1” for the remaining channels in that direction will allow the RL Reference to be copied from the first channel to all forward direction channels. Likewise, a “2” and “-2” for the reverse direction (coming from the B-A port) channels will have the same effect, but allow for these channels to be referenced separately from the forward channels.

Columns S,T, and U are the only fundamental departure from a standard sequence file since it is not necessary to include on unidirectional sequence files. For all forward direction channels, columns should read “1” and for all reverse direction channels, this column should read “2”.

Referencing Instructions

Bidirectional Insertion Loss Reference

To properly reference insertion loss bidirectionally, connect the launch leads from the A-B/B-A source connectors to the input ports of the two switches.  Do not use the external power meter port for reference.  Connect the reference fanout from the A-B switch to the reference fanout on the B-A switch via a mating adapter and perform an insertion loss reference in the software.  This will perform two separate reference cycles—one for the A-B direction and one for the B-A direction.

Figure 3: Test setup for measuring bidirectional insertion loss
Figure 3: Test setup for measuring bidirectional insertion loss

Bidirectional Return Loss Reference

To reference return loss for a bidirectional test system, connect the system as above leaving end faces open between the two HPR cables to create the Fresnal reflection (if either fanout is terminated in an APC connector, an APC-to-PC stub will need to be utilized to produce an adequate reference reflection). Once the reflection is established, perform a return loss reference cycle in the software. During the reference cycle, the unit will reference both in the A-B direction and the B-A direction and retain these distances separately for their respective measurement cycles.

Figure 4: Test setup for measuring bidirectional return loss
Figure 4: Test setup for measuring bidirectional return loss

Measurement Instructions

Once the system has been referenced, place the device-under-test into the setup between the two fanouts (as illustrated on the left) and simply select the Test option. Following this, the software will test the cables in the forward direction and then the reverse direction.

Figure 5: Test setup after system has been referenced
Figure 5: Test setup after system has been referenced

Test Report

Figure 6: Sample test report.
Figure 6: Sample test report.