Fiber Optic Microscope versus Fiber Optic Video Inspection Probe
If you are new to fiber optics, when you hear the word microscope, you most likely think of the one that was used in science class to look at cells of animals. Well in the fiber optic world, microscopes are a vital tool that should be in all technicians’ tool bags.
An optical microscope is a hand held tool used to look at the end face of a fiber optic connector. What do you look at the end of a connector for you ask? Looking at the end of a connector is vital to making sure that there is nothing wrong with the connector. By looking at the end of a connector you can see if there is any contamination such as dirt or oils, a scratch or even a broken (shattered) ferrule on the connector. Although you look at the whole end face, the primary spot that is looked at is the core of the fiber. The core of the fiber is the vital part, because this is where the light, or your data, will travel. When you are trouble shooting a fiber, visual inspection of the end face of the connector(s) is one of the first steps that should be done - before you pull out your test equipment to shoot with a power meter and light source, or even an optical time domain reflectometer (OTDR).
The very first microscopes that came out were pretty much glorified magnifying glasses. These were the 100X magnification microscopes. They were primarily helpful with multimode fiber connectors due to the core size of multimode fiber being much larger than single mode fiber. The next one to come out was the 200X microscope. These higher powered scopes were needed to better look at the end face and also to view the core of single mode connectors because the size of the core is only 9 microns. They were also used to look at the ends of the multimode connectors more in depth. There are scopes that only use coaxial illumination and ones that illuminate two ways, these being oblique or coaxial illumination. What came out next was the 400x power scope. The 400x scope is the single mode version of what the 200x scope was for multimode. The higher power scope allows you to view the end of a single mode connector in a higher detailed view, which allows you to more closely look at the vital central core of the fiber.
After microscopes came video scopes. These come in the form of either a hand held probe or bench top scope, and they transfer the image onto some type of monitor. Bench top scopes are typically used in factory (cable assembly houses) or lab (research and development) type settings. A bench top inspection scope is a microscope that is positioned at a work area and that connects to a monitor. It will look at the connector and the image is transported over a connecting wire on to a bigger screen so it is easier to view. There will be better resolution and this makes it easier to focus and see the ferrule end face. These are not easily carried into the field, allowing for a different product known as video inspection probes. These are hand held devices that follow the same concept as the bench top scope, but they are smaller and portable, making them perfect for field use. The video inspection probes can work with several different monitors which makes them flexible for a variety of applications. Some probes come with a small hand held monitor that connects to the probe and allows you to see the end faces. Probes can also be hooked up to different OTDR’s, so while testing your fiber you can also look at the end face of connectors.
One thing that has always been a problem with microscopes and even video inspection probes when they were first introduced is the fact that you have multiple view points on what is passing and what is failing. This would leave a lot up to human judgment and we all know that one person’s idea of passing may be completely different from another’s. Introduce analysis software that is programmed with industry accepted standards and rules that can look at the end face of the connector and tell you whether or not a connector is passing, or good. Then there is failing which means that the connector may still work but based on the standards it will not be allowed to be used in its current state. This software has a whole system of algorithms built in to it to allow the end face of the connector to be compared to the industry standard or expected parameters in order for a connector to be considered good or bad.
We had a customer that we would make patch cords for and we would test them and send them out to them with everything passing to the standards of testing that are accepted by the industry. The customer would get them in and perform incoming checks on all the patch cords to make sure they were up to their standard. Well after they checked them all, they called us and said that they had rejected 60% of the shipment and needed to send them back. This was a very high amount and we took action and scheduled a visit with the customer. Come to find out, the customer was not using any analysis software so their decision to reject the patch cables was all based on human judgment. We informed them that we use the software that takes the human judgment out of it and instead uses the complex algorithms in the software to help with the decision to pass or fail a connector. Once they learned this, the customer invested in the software and after that we had a zero rejection rate from that customer. By visiting with the customer to evaluate their process and get on the same page for testing purposes, it made it so that the standards being used were the same.
This software has gotten even better throughout the cycle to improve the process of scoping. Scopes now have features that make it easy for a tech to auto focus and auto center the fiber on the monitor or viewing screen. This improves the process of scoping because instead of having to spend time trying to focus and get the end face lined up in the middle of the screen so you can have the software do the pass fail analysis, it now will do this for you and you will know if your connector will pass or fail in a matter of seconds.
Another improvement that has been made takes advantage of the ability of Wi-Fi. There is now a wireless probe that communicates without a cord to get in the way. So now, as long as you are in a location that has a strong Wi-Fi signal, you can use the wireless probe and it will sync to either a tablet or your cell phone or even your OTDR so you can view your connector end faces.
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