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Fiber Optic Connection Back Reflection

In addition to transmission loss, we also have to consider the back-reflection that occurs at the fiber optic connector interface. Back reflection always happen when there is a change of refractive index.

The amount of light that is reflected back can cause undesirable system and network effects, thus it must be minimized. With today’s 10Gbit/s, 40Gbit/s and even 100Gbit/s high date rates, video over fiber links with lots of connections, connection back-reflection has become very critical.

In those undesirable effects, increased noise if one of them. This noise is analogous to multipath interference noise of radio waves in the atmosphere. Both noise sources are generated by reflection propagating back and interfering.

There is also a secondary effect of increased noise caused by the back-reflection also being reflected and then traveling down the fiber in the original direction but with a time delay as compared with the original signal.

The time-proven method to reduce back-reflection on fiber optic connectors is to ensure that the fibers are in physical contact (PC) (touching). One way is to grind a radius on the ferrule, and another is to make a angle on the ferrule.

So four types of fiber connector physical contact shape are introduced in the industry. They are called PC (physical contact, <-30dB back reflection), SPC (super physical contact, <-40dB back reflection), UPC (ultra physical contact, <-50dB back reflection) and APC (angled physical contact, <-60dB back reflection).

You can find SC/PC, SC/SPC, SC/UPC and SC/APC connectors. But not all four types are available on all fiber connectors.

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