An Optica Sponsored Webinar: The Harsh Realities of Testing Ruggedized Fiber Assemblies

OptoTest Webinar October2021 1Ruggedized fiber optic cable assemblies are gaining prevalence in the communication industry. They are used in a wide breadth of applications, from connecting high speed 5G communication hubs together to facilitating high speed communications on modern fighter aircraft. The plethora of variations among these assemblies and their basic physical structure present unique challenges in measuring them for insertion loss and return loss.

This webinar will focus on different methods and test setups for qualifying optical connections of ruggedized and harsh environment assemblies while maintaining a high level of accuracy in the measurements. The webinar will review the different methods and the benefits and drawbacks of each method.


Presented by:
Chris Heisler, CTO, OptoTest
Chris Heisler graduated from CalPoly San Luis Obispo with a Bachelor of Science in Electrical Engineering with a focus on Communications and Fiber Optics.  He continued with his Master’s Degree at CalPoly in Digital Signal Processing and Photonics.  Chris has been working in the fiber optics industry for 14 years, and currently holds the position of CTO at OptoTest Corporation, where he has helped to refine the return loss measurement process and push development of test equipment that satisfies customer’s needs.  Chris is also a regular contributor to the TIA TR42 Fiber Optic Engineering Committees.

Questions & Answers

When we use an interface cord, instead of to connect directly to the meter, How do we know that loss are in the correct side of the DUT? Can your equipment do it properly?

The reference process will zero out any loss caused by the interface cable. Similar to how the reference zeros out the loss from a reference cable.

Is it possible to measure return loss for lens connectors?

Yes, but it is a bit more difficult than standard mated connectors.  Refer to the webinar regarding “Return Loss testing on Complex Cable Assemblies“.

Is there any standard summarizing the different setups for IL/RL measurement?

FOTP-171 and IEC 61300-3-4 specify different test methods for insertion loss testing.

How does it affect launch conditions to come back into a switch? (example : Laser Source (overfilled or 100%) -> Modcon 85/85 -> Switch -> Reference -> DUT -> Power Meter) Am I sure to keep the launch conditions of 85/85 all the way to the Power Meter?

Any change in medium can affect your launch condition, especially a switch.  To maintain a launch condition all the way to your DUT, you’d want to add the modal conditioners after the switch, and use reference quality cables, inspected and cleaned, up to your DUT.

Is it possible to measure a higher RL than -14dB on lens connectors with OptoTest ? Somehow I have tried to scan 2 connected lensed connectors and the scan stops at the connection saying it found air. Does it mean that 2 lensed connectors can't have better RL than air ?

Yes, it is.  However, if your lens is not AR coated or the assembly isn’t angled in a manner to reduce light reflected towards the source, then you may still measure return loss in the 14dB range.  If you scan the lensed connector and it finds a large reflection, it could be due to an open glass to air interface or it could be due to there just being a large reflection.  The OP960/OP940 system will scan for a large reflection typically <25dB and consider that large enough to reference to.  The return loss of the mating though is dependent on the construction of the lens assembly.  Many lensed assemblies measure in the mid-50s for single-mode assemblies or better than 40dB for multimode assemblies.

Would you explain some example of “how to perform simulation of testing dust contaminated one” for DUT with Bucket Cable? It would be difficult to make a simulating test of the contaminated DUT with Bucket cable. (Not to damage any to Bucket cable).

Simulating or inducing insertion loss or return loss on fiber optic connector matings is difficult.  There is no clear correlation between contaminants and return loss and insertion loss.  One can’t easily add contamination to create insertion loss or return loss on a mating.

Are there pros and cons between IL in dBm vs. in dB?

IL is typically given in dB.  Absolute power is given in dBm (sometimes mW in our applications).  Two measured absolute power differences is IL, given in dB.

If my DUT is 50µm, then bucket cable should be 62.5 or 100µm?

It could be either 62.5µm or 100µm, but 62.5µm is easier to obtain.

If you are using a golden cable to measure insertion loss, how do you measure the return loss?

The golden cable is just used when referencing.  This golden cable is a low-loss cable of the same polarity structure as the DUT.  Return loss is referenced without the golden cable connected and the position at the end of the reference cord is found for the return loss measurement.  To measure insertion loss and return loss, replace the golden cable with the DUT, and insertion loss is measured through the DUT, while return loss is measured at the interface between the DUT and the reference cord.

What would be the core diameter of the "bucket cable" for the measurement of a 62.5µm DUT?

100/140 graded-index fiber.

Related to RL measurement, do you see an issue using a mode conditioner before an expanded beam DUT?

Using a mode conditioner shouldn’t be an issue when testing an expanded beam DUT.

Is bucket cable and receive cable same?

Bucket cable refers to a larger core receive cable so that the receive cable connection is little to no loss.

Are these probe type testing common being used and are they commercially available?

They are available, but you need to find a good supplier for them because they are somewhat specialized.

What test standards do you reference?

FOTP-171 and IEC 61300-3-4 specify cable setups for insertion loss measurements.  They do not explicitly mention a “bucket cable” but the bucket cable connection can be considered part of a pigtailed optical power meter.   AS5675 is an aerospace standard and gives guidance on ruggedized assembly testing and does specifically mention the usage of a bucket cable.

Are golden cables only solution to connectors that do not mate?

Golden cables can be used for assemblies that can mate to an OPM, but they introduce a new level of complexity.  Golden cables can also be handy when a polarity change is necessary between the referencing process and the measurement process.  For example, if testing a type C DUT when using a multichannel source and multichannel OPM, a type C golden cable can be used for the reference to guarantee that the proper source channels are referenced to the OPM channels.

Why don't you plug the launch cord directly to the meter? Why is there an interface cord?

Harsh environment connectors, such as 38999 are not capable of plugging directly into a detector or sphere with accuracy, due to the distance between fibers in these types of connectors.


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