AN-116
Performing Insertion Loss and Return Loss Measurements
Using a Single-Channel OP940
Over view
OptoTest’s OP940 allows operators to test Insertion Loss and Return Loss of fiber optic cables accurately and efficiently. Once
Insertion Loss and Return Loss references are completed, the unit will automatically update test results on the screen in real-time.

Performing a Reference Measurement
Return Loss Reference
The OP940 references Return Loss by searching for the first large reflection in the reference cable. After such a reflection is found,measurements begin at a distance from the front panel to the unmated end of the cable. It is recommended that an unmated PC
connector be used for RL reference (for more information see our White Paper) and that the number of connections between thefront panel and the reference connector be minimized to reduce loss and reflectors to the OP940 front panel. The open PC connector
should yield approximately 14dB reflection.
NOTE: It is strongly recommended that the reference cable and DUT each be at least 3 meters in length. It is also strongly recommended
that a short SAVer cable should be used to prevent damage to the front panel connector. For more information on SAVer cables, pleasesee our Application Notes: AN-132 SAVer Cable Short Instructions, and AN-137 Preventing Damage to Optical Connectors.

Referencing and Measuring Return Loss
To take the reference for a return loss measurement, connect
the APC side of the reference cable to the front panel connector
on the source port; alternatively, connect the reference cableto the SAVer cable if one is being used.
Note: If the reference cable is APC-to-APC, other methods
must be employed to perform a proper reference due to thelack of a reflection associated with an APC connector. For
more information on these methods, please see Application
Note AN-114 Testing APC Cables.

1SANTEC CORPORATION
OptoTest
Corp.

5823 Calle
Ohkusa-Nenjozaka,
Komaki,
4750
QuetzalAichi
485-0802,
Japan
Camarillo, CA 93012
Doc:
AN-116 Rev. B 5 / 3 /17+81-568-79-3536

www.santec.com

SANTEC USA CORPORATION
1.8 05.987.170 0
USA Toll Free
+1-800-726-8321
sales@ optotest.com
engineering @ optotest.com
SANTEC EUROPE LIMITED
Tel. +44-20-3176-1550

AN-116
Performing Insertion Loss and Return Loss Measurements
Using a Single-Channel OP940
Select the desired mode screen, such as ILRL, and then select the RL Ref option.

On the proceeding screen, select the Start RL Ref option.
The instrument will begin scanning for the first large reflection
and will store that reference position. This process may takea few seconds.

If the reference is good, the OP940 will display the reference
distance and RL value, along with a yellow progress bar.
Typical RL values are -14dB for an open UPC connector.

If a large reflection is present at the front panel, the progress
bar will turn blue.

2SANTEC CORPORATION
OptoTest
Corp.

5823 Calle
Ohkusa-Nenjozaka,
Komaki,
4750
QuetzalAichi
485-0802,
JapanCamarillo, CA 93012
Doc:
AN-116 Rev. B 5 / 3 /17+81-568-79-3536

www.santec.com

SANTEC USA CORPORATION
1.8 05.987.170 0
USA Toll Free
+1-800-726-8321
sales@ optotest.com
engineering @ optotest.com
SANTEC EUROPE LIMITED
Tel. +44-20-3176-1550

AN-116
Performing Insertion Loss and Return Loss Measurements
Using a Single-Channel OP940
If the RL reference fails or is stopped, the progress bar willturn red.

After referencing return loss, the unit will begin to display
the return loss readings for both wavelengths in real-time. To
return to the measurement screen, press the Home Button.

Note: It is important that the Return Loss reference is performed where the device-under-test, or DUT will be connected. If a receive
cable is being used during measurement, it should not be included in the RL reference.

Insertion Loss Reference
To take the reference for an insertion loss measurement,
connect the reference cable from the source directly to thedetector port of the instrument.

Next, select the IL Ref option.

Source1310nm1550nm1mm InGaAs

OP940-SM

SAVer Cable

3HPRCable

SANTEC CORPORATION
OptoTest
Corp.

5823 Calle
Ohkusa-Nenjozaka,
Komaki,
4750
QuetzalAichi
485-0802,
Japan
Camarillo, CA 93012
Doc:
AN-116 Rev. B 5 / 3 /17+81-568-79-3536

www.santec.com

SANTEC USA CORPORATION
1.8 05.987.170 0
USA Toll Free
+1-800-726-8321
sales@ optotest.com
engineering @ optotest.com
SANTEC EUROPE LIMITED
Tel. +44-20-3176-1550

AN-116
Performing Insertion Loss and Return Loss Measurements
Using a Single-Channel OP940
On the proceeding screen, select the Start IL Ref option.
The instrument will select each of the sources, measure theirabsolute power, and store the reference accordingly. The
process may take a few seconds.

After referencing insertion loss, the unit will begin to display
the relative power in real time. After referencing insertion loss,
press the Home Button to return to the measurement screen.

Testing
The OP940 will begin continuously taking measurements forInsertion Loss and Return Loss, depending on which modethe unit is in. Connect the DUT to the unmated connector of
the reference cable and the other endface to the detector
port to begin taking real-time measurements for the DUT.

The unit will begin displaying live results.

Source1310nm1550nm1mm InGaAs

OP940-SM

From the measurement screen, press the Pass/Fail Button
to display live test results based on the user-configurable
settings.

SAVer Cable
HPRCable

DUT

4SANTEC CORPORATION
OptoTest
Corp.

5823 Calle
Ohkusa-Nenjozaka,
Komaki,
4750
QuetzalAichi
485-0802,
Japan
Camarillo, CA 93012
Doc:
AN-116 Rev. B 5 / 3 /17+81-568-79-3536

www.santec.com

SANTEC USA CORPORATION
1.8 05.987.170 0
USA Toll Free
+1-800-726-8321
sales@ optotest.com
engineering @ optotest.com
SANTEC EUROPE LIMITED
Tel. +44-20-3176-1550