Optical cable insertion loss and return loss ratio

Although nothing has changed in its cable assembly production process, the measured insertion loss (IL) and return loss (RL) values of its products are not as good as before. Is there a problem with the measuring equipment? Well, it's possible, but very unlikely.

Obviously things have changed. If not a measurement device, it must be a product or measurement setup. Over time, the production process can become a familiar, possibly boring routine. Operators can become meticulous about cleaning, apply polishing films for longer than appropriate, or even take shortcuts. Ultimately, this is costly and reduces production.

Let's say you've eliminated that possibility by thoroughly cleaning the program and resetting it to strict production guidelines. But the problem still exists. At this stage, a "gold standard" product is useful - carefully keep a "known" example of the best product you have produced before, with very good IL and RL values documented. Using your current rigorous procedures, re-measure this gold standard product. It should still look good.

Optical cable test

I wrote that IL and RL testing cannot be done on a product alone. (Read more on this topic here.) Remember that we are measuring fiber optic connector loss and that the device under test (DUT) needs to be connected to a test cable (also known as a jumper cable, reference cable, or test leads). It is important to note that the quality and condition of the test cable is directly related to the IL and RL measurements of the product under test.

Assess the quality and condition of test cables

First, make sure the test fiber optic connector is clean. Next, double-check to make sure they're in good shape. Remember that neither fiber optic connectors nor splice sleeves last forever. They degrade with use, not just scratches and dents. Sliding surfaces are worn. As the mate becomes loose, the alignment will be affected.

How many matings can be done before replacing the test connector? There is an exact number that can be used. However, due to the type and quality of the connectors and the skill of the operator, it is difficult to give an exact answer.

Assuming replacing all test cables and couplers will restore your gold standard product to its previous good measurements. This is useful information. Take a minute to determine approximately how many times these particular test cables were mated. What date did you arrive? Now you know how much coupling is too much!

Identify usage limitations and establish replacement schedules

I recommend that you set your usage limit to half of the above number. Weigh ongoing replacement costs against the time required to replace test cables. How does this compare to the cost if you let the product go to the failure stage?

Mechanisms for frequently monitoring gold standard equipment may be helpful in determining usage limits for test cables. (Don't do this too often, or your gold-standard fiber optic cable will degrade.) This type of monitoring will help you create a reasonable replacement schedule.

Here's a helpful tip: If you use a Viavi MAP/PCT system, it can track meter patch cord usage and warn you when fiber optic cables exceed user-defined limits. If you use another test instrument, I suggest you check to see if it can track usage and provide such warnings.

Implement strong process control

Test cables do have a limited lifespan. And the longevity will vary. For example, improper mating or cleaning could potentially damage the endface of the test cable, rendering it unusable.

Implementing strong process control will greatly extend the life of the test cable and determine when the test cable needs to be replaced. As mentioned above, I recommend:

(1) Always check the end face of the test cable between the fits

(2) Observe good cleaning habits

(3) Use "well-known" fiber optic cables for troubleshooting

If you notice degraded IL/RL results for your fiber optic cable assemblies, it is recommended that you first establish tight production controls. Next, follow the guided steps in this article to assess the condition of your test cables, track usage, and create a reasonable replacement schedule.