Being able to measure a Fresnel reflection (14dB return loss) accurately is paramount to identifying the accuracy of the return loss measurement. This is covered in some depth on our white paper which can be found at: http://www.optotest.com/importance-verifying-reference-reflection-accurate-rl-measurements/ In short, without verifying the return loss of a reference cable (e.g. an open flat or some other known artifact), it is nearly impossible to know that the measurement does not have some offset due to insertion loss in the reference setup. This can lead to false positive test results where cables that are below the necessary thresholds are assessed passing values.
While we do not make devices that will apply the tensile stressors required for these tests, many of our units, such as our OP750 Multichannel Optical Sources and our OP1100 Discontinuity Test Sets, can be used to collect the necessary optical measurement data for these types of tests.
There is no limit. We will design a system that matches the customer’s needs. To date, we have built units of many different channel counts up to 144 channels.
Our standard units have stability of ±0.02dB per hour per °C and ±0.05dB per 12 hours per °C. If these specifications need to be tightened for a customer’s needs, we have the capability to improve the stability and to reduce the influence of the temperature on the measurement.
A 12 channel assembly takes approximately 30 seconds for dual wavelength ILRL tests and a 24 channel test takes approximately 60 seconds. For quad wavelength (FTTX) measurements, these times are approximately 60 seconds for 12 channels and 120 seconds for 24 channels.
This error message occurs when the unit discovers a large reflection at or around the front panel of the unit. The most common causes for large reflections at the front panel are contaminated or damaged endfaces and broken ceramic sleeves inside the front panel bulkhead. A broken ceramic sleeve on the bulkhead can cause a poor connection which can result in an air gap between the internal connector and the reference cable’s connector which would appear, to the unit, as an unmated connector at the front panel. The easiest way to avoid this sort of problem is to purchase an SAVer Cable, a six- to twelve-inch FC-APC to FC-APC cable which protects the front panel interface from damage and dirt.
I have a multimode OP930 and I am using a modal conditioner to comply with EF launch conditions. I am getting return loss reference values around -19 and -20dB through the modal conditioner. Is this correct? Does it affect my return loss measurements? Without the conditioner I get a normal 14dB reflection.
Since the return loss of a UPC connector is known to be around -14dB, but the RL is currently measuring at -19dB, the measurements should be adjusted by 5dB. A modal conditioner for EF compliant launch will typically add a certain amount of loss to the system as it strips out the higher order modes from the fiber, so this is nothing out of the ordinary. However the added loss in the system affects not only the value at reference, but also the readings for all DUTs. This can affect whether cables pass by increasing the measured return loss to make a cable seem as though it has passing values. Assume that all reference cycles have been completed but the 5dB of additional loss is not referenced out. Now imagine a cable is connected and the RL meter reads 56.1dB. At first glance, this cable has passing return loss and if its insertion loss also passes, it will move on to the next stage of the production line. However, if that additional 5dB of return loss is subtracted out, our meter will now report that the return loss is 51.1dB - a value which is failing in many production facilities. Please refer to AN126 - Measuring Accurate Return Loss through Optical Components, for methods of correcting for this added loss.
This error is usually the result of the drivers not being installed or initialized properly. The drivers should be available on the installation disk for your software. Once the drivers are installed, the unit must be initialized through the drivers. This is done by connecting the unit via USB and turning the unit on. If the unit had already been connected to the computer, it should just need to be turned off and then back on.
This error message occurs when the unit discovers a large reflection at or around the front panel of the unit. The most common causes for large reflections at the front panel are contaminated or damaged endfaces and broken ceramic sleeves inside the front panel bulkhead. A broken ceramic sleeve on the bulkhead can cause a poor connection which can result in an air gap between the internal connector and the reference cable’s connector which would appear, to the unit, as an unmated connector at the front panel.
The easiest way to avoid this sort of problem is to purchase an Endface Saver Cable, a six- to twelve-inch FC-APC to FC-APC cable which protects the frontpanel interface from damage and dirt.
The most common reason that a singlemode OP930 fails to properly reference return loss is because the customer attempts to reference to an angle-polished connector. All OP930 Insertion Loss and Return Loss Test Sets require an open flat connector to reference return loss. This provides our customers with the best possible return loss reference and, in turn, the most accurate return loss possible. If the reference cable is terminated in an APC connection on the end which will be used to reference return loss, OptoTest offers reference reflector cables which can be used to produce a large reflection at the end of the reference cable. Since many singlemode cables are terminated in an angle-polished connector, while most multimode cable are terminated in a flat-polished connector, this is a problem that can seem to begin suddenly for customers unfamiliar with singlemode cables.
Another possibility is that there is a large amount of attenuation in the reference setup. Attenuation, such as from an optical switch or a lossy cable/connector, can cause a reference reflection to measure around 18-20dB, which can be enough to cause the OP930 to miss the reflection and it will continue looking for the reflection.