AN147

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OP740: Mechanical Shock Testing for Insertion Loss andReturn Loss of Optical Connectors and Components

Overview
Shock monitoring allows us to evaluate the performance and connectivity of a mated pair of optical connectors through shock
events. Many solutions require an optical power meter with an analog output (optical-to-electrical converter) and a sampling
device, such as an oscilloscope, to digitally capture and analyze the transient signal. Such solutions require calibration practices
to ensure the sampling device and analog signal accurately represent the optical signal levels. The OP740 and supporting
software combines this functionality into an all-in-one solution with no need for an external capturing device or excessive focus
on calibration.

Instrument Selection
When selecting equipment for shock (or general stress) testing, it is important to make sure that the equipment used canproduce reliable and accurate results with an adequate level of sensitivity.
The optical source should have sufficient output power so that it operates within the range of the optical power meter (OPM).
Ideally, the source is adjustable to maximize the dynamic range of the OPM when in range hold mode. An adjustable light source
eliminates the need for costly attenuators in the setup.
The OPM must have a fast sampling speed that is at least twice as fast as the discontinuity being monitored. The military
standard MIL-STD-1678-2A monitors for 50µs dropouts, so it requires at least a 25µs sampling period. The OP740 samples at8µs, which is more than sufficient. The 30dB of dynamic range that the OP740 has in range hold mode satisfies most of eventhe strictest requirements. This wide dynamic range allows for the discontinuity to be accurately captured without intermittent“ranging” hiccups.
The system should also be able to retain data of sufficient duration to capture the event in its entirety. When performing
shock and vibration testing, it is beneficial to be able to retain pre-event information as well as post-event information to fully
understand the effects of the shock event. After a shock event, it may take an extended amount of time for the optical signal
to reach a steady-state level and without sufficient data storage this information could be lost. The supporting software for theOP740 has an almost unlimited buffer size that is based on the hard drive space of the computer.

Key Parameters for Instrument Selection

1Optical Source

Optical Power Meter

1. Highly stable to eliminate false “triggers”
2. Sufficient power and adjustable
a. Needs to operate within the range of the opticalpower meterb. Ability to adjust source to maximize dynamic range(Eliminates need for costly attenuators)

1. Fast sampling speed. Must be twice as fast as opticaldropout
a. 50µs dropout requires sampling of at least 25µs.
(MIL-STD-1678-2A)
b. OP740 captures as fast as 8µs
2. Wide dynamic range
a. Drops require up to 10dB of dynamic range
b. OP740 in range hold mode allows up to 30dB ofdynamic range

OptoTest Corp.

SANTEC
4750
CalleCORPORATION
Quetzal5823
Ohkusa-Nenjozaka,
Komaki,
Camarillo,
CA 93012
Aichi 485-0802,
UnitedStates Japan+81-568-79-3536

Doc: AN-147 Rev. A 2/1/21

Advancing the World of Fiber Optics®
www.optotest.com
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SANTEC USA CORPORATION
1.805.987.170 0USA Toll Free+1-800-726-8321
sales@optotest.com
suppor t@optotes t.com
SANTEC EUROPE LIMITED
Tel. +44-20-3176-1550

OP740: Mechanical Shock Testing For Insertion Loss and Return LossThe Photonics Pioneerof Optical Connectors And Components.
AN-147

Test Setup

Return LegCoupler

PC to PC mating

Figure 1: Test setup utilizing a light source, a 1x2 coupler, and the OP740.

For this test setup we use a light source, a 1x2 coupler, and the OP740. To setup a shock test to monitor insertion loss (IL) andreturn loss (RL) of a component, route a light source into one of the two input legs of the coupler. The second input leg of thecoupler is connected to a channel on the OP740. The output leg of the coupler is connected to the device under test (DUT), in thiscase a mated pair, and the output of the DUT is connected to a channel on the OP740. For this test, the throughput or change
in transmittance is monitored on channel one and the RL is monitored on channel two. Angled connectors are used to minimize
back reflections.

Reference Process
To reference the system, the mated pair is disconnected and the RL is referenced on channel two (fig. 2). This reference power
will be associated with an open flat glass to air, Fresnel reflection, or ~-14.7dB. The IL is referenced by connecting the mated pairand referencing channel one (fig. 3). The baseline for the transmittance of this measurement is 0dB.

Figure 2: Mated pair is disconnected and the RL is referenced on channel two.

Figure 3: IL is referenced by connecting the mated pair and referencing channel one.

Once the system is referenced, the software is put into capture mode where the software is reading constantly from theinstrument. The software in capture mode retains all data to the hard drive and is stored for post testing analysis. Once in2capturemode,a shock (or other stress) is induced on the mated pair. After the shock, capture modeis stopped
in the software
SANTECCORPORATIONSANTECUSA CORPORATION
5823
Komaki,andthenOhkusa-Nenjozaka,
the data is analyzed.
USA Toll Free +1-800-726-8321
Aichi 485-0802, JapanSANTEC EUROPE LIMITED
www.santec.com+81-568-79-3536
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OP740: Mechanical Shock Testing For Insertion Loss and Return Loss
The Photonics Pioneerof Optical Connectors And Components.
AN-147

Analyzing Results
When analyzing a shock signal, we look for three main parameters of an “event”: depth, width, and residual loss (fig. 4).
The depth represents the maximum signal increase or decrease during the event. This value is usually with respect to thebaseline. In this case, because we referenced to 0dB for throughput, then the depth is the maximum deviation from 0dB. In mostcases, these tests are only concerned with a reduction in signal power. On the right, the depth of the event is about 0.225dB.
The width of the event is typically the time that the signal
dropped beneath the specification’s threshold. In this case, thethreshold was -0.05dB. The width of this dropout was foundto be about 2.6ms
The residual loss is the power deviation from the power level
before the drop to after the drop when the signal reaches
steady state. The residual loss is usually measured withrespect to the reference level. The discontinuity on the rightis referenced to 0dB, so the residual loss is the steady state
deviation from 0dB after the event. The event here has aresidual loss of about -0.032dB. Note that the residual “loss”
can also be a gain as seen in the next example.

Figure 4: Graph of a typical shock event showing the depth, width,
and residual loss of the optical signal.

Positive Residual Loss

Discontinuity Event

In this example (Fig. 5), the residual loss is a positive value.

Residual Loss

The mated pair experiences a shock and then over a period,
after the shock, the signal experiences an increase in power.
This means that the two connectors after the shock are
better aligned than they were prior to the shock. Anotherexplanation for the increase in power after the shock isthat the connection may have had contamination thatwas impeding throughput, and then the shock moved thiscontamination in the connection where it may not impede
throughput.

SANTEC CORPORATION
5823 Ohkusa-Nenjozaka, Komaki,
Aichi 485-0802, Japan3+81-568-79-3536

Figure 5: Graph of shock event with a positive residual loss showing
a gain in power after the event.

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SANTEC EUROPE LIMITED
Doc: AN-147 Rev. A 3/5/21
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OP740: Mechanical Shock Testing For Insertion Loss and Return Loss
The Photonics Pioneer
of Optical Connectors And Components.
AN-147Return Loss Monitoring
Shock Event (Insertion Loss)

Shock Event (Return Loss)

Figure 6: Corresponding insertion loss and return loss graphs for a shock event.

In the above shock test (Fig. 6), both insertion loss and return loss were monitored using the OP740. In this test, the insertion
loss drops by about 9dB, and at the same time as the IL drop, there were also spikes in the return loss monitored. There
were two brief return loss spikes up to about -22dB. These spikes in return loss could be the result of a slight separation in theferrules leading to an air gap in the connection. After the shock event the two connectors returned to a fully mated state again
and the insertion loss and return loss values returned to acceptable levels.

Conclusion
Monitoring insertion loss and return loss during stress testing, such as shock and vibration tests, requires an optical power
meter that is fast and responsive to capture the dynamic signal during these tests. The OP740, coupled with the supporting
software, allows for an endless buffer of high-speed optical power measurement data. This virtually endless buffer ensures noloss of data or missed events during the testing process. The OP740 is uniquely suited for testing against shock and vibration
standards such as the military standard MIL-STD-1678-2A and other similar standards.

SANTEC CORPORATION
5823 Ohkusa-Nenjozaka, Komaki,
Aichi 485-0802, Japan

4+81-568-79-3536

SANTEC USA CORPORATION
USA Toll Free +1-800-726-8321

www.santec.com
www.optotest.com
The Photonics Pioneer

SANTEC EUROPE LIMITED
Doc: AN-147 Rev. A 3/5/21
Tel. +44-20-3176-1550