Polish Types in fiber optic connectors

In my previous article, we have seen different types of fiber optics connectors.

What if we can provide a more secure and reduce signal lose in at the tip(polish) of the connector? Isn’t it worth to implement that also when considering the importance of your data? Let us have a look into that concepts also as this is also part of fiber optic connectors.

When a connector is installed on the fiber end, the loss will be incurred. Some light loss would be reflected back directly down the fiber towards the light source that generated it. These back reflections or Optical Return Loss (ORL) will damage the laser light sources and also disrupt the transmitted signal. Fiber connectors with different polishing types(indicates the tip of the connectors) have different back reflections (see the picture below). Those are mainly referred to as below,

·      Flat Connector(FLAT)

·      Physical contact Connector(PC)

·      Ultra-Physical contact Connector(UPC)

·      Angled Physical contact Connector(APC)

  

Flat Fiber Connector(FLAT)

The original fiber connector is a flat-surface connection or a flat fiber connector. The primary issue of it is that a small air gap between the two ferrules is naturally left when mated. This is partly because the relatively large end-face of the connector allows for numerous slight but significant imperfections to gather on the surface. The flat fiber connector is not suitable for single-mode fiber cables with a 9µm core size, thus it is essential to evolve into Physical Contact (PC) connectors.

PC Fiber Connector(PC)

The Physical Contact is polished with a slight spherical design to reduce the overall size of the end-face, which helps to decrease the air gap issue faced by Flat Fiber connectors. It results in lower Optical Return Loss (ORL) with less light being sent back towards the power source.

Ultra-Physical contact Connector(UPC)

The Ultra Physical Contact polish type has more extensive polishing than the PC type, this creates a better contact/signal than the PC type. However, this polish type is not as robust as the PC polish type. Repeated connections and disconnections will cause degradation of the surface and ultimately reduce performance.

Usually, the UPC single-mode fiber connector is blue, but the UPC multimode fiber connector is beige(Note: 10G UPC multimode fiber connector is aqua).

PC and UPC connectors do have a low insertion loss, but the back reflection (ORL) depends on the surface finish of the fiber. The finer the fiber grain structure, the lower the back reflection. When PC and UPC connectors are continually mated and unmated, the back reflection will begin to degrade. So there is a need for a connector with low back reflection and it could sustain repeated mating/un-matings without ORL degradation.

Angled Physical contact Connector(APC)

The end faces of Angled Physical Contact connectors are still curved but are angled at an industry-standard eight degrees, which allows for even tighter connections and smaller end-face radii. Combined with that, any light that is redirected back towards the source is actually reflected out into the fiber cladding, again by the virtue of the 8°angled end-face. APC connector back reflection does not degrade with repeated mating/unmating. APC fiber connector can only be used with single-mode fiber and it is green.

So which one to choose?

It is clear that all of the connector end-face options mentioned above? And it is hard to claim that one connector beats the others when your specification needs to consider cost and simplicity, not just optical performance. Your particular need decides which one to choose. For those applications calling for high precision optical fiber signaling, APC should be the first consideration, but less sensitive digital systems will perform equally well using UPC.

Have a comment or points to be reviewed? Let us grow together. Feel free to comment.