Description of the optical connectors SC / APC and SC / UPC used in GPON devices

Description of the optical connectors SC / APC and SC / UPC used in GPON devices. What are the main differences between SC / APC and SC / UPC fiber optic connectors used in GPON devices?

In this article, we will look at the main differences between the SC / APC and SC / UPC fiber-optic connectors used in GPON devices.

SC (Subscriber Connector) designates the type of fiber optic connector. This type of connector is widely used for both singlemode and multimode fiber. The SC connector belongs to the class of common use connectors and is widely used in various-scale networks.

To connect to the SC connector, fiber-optic patch cords are used (with connectors of the same type or connectors of different types), which are intended for switching between the ports of the active equipment.

APC and UPC designates the type of polishing (grinding) of a fiber optic connector.

First, let us explain what polishing / grinding of connectors is needed for. Polishing is designed to ensure that there is no air gap between the connecting surfaces (ends) of the fibers when they are connected to the connector. Those. polishing should ensure the physical contact of the fibers in order to reduce the back reflection of the signal (reflectivity).

Currently, there are 4 types of polishing of the connecting surface: PC , SPC , UPC and APC .

Modern telecommunications equipment typically uses optical connectors with UPC polishing and less commonly APC. APC polished connectors are widely used in cable television networks.

Please note: optical connectors (connectors) with APC polish are incompatible with other types of connectors, so green is used to designate them.

Next, we consider in detail each type of polishing (grinding) of fiber-optic connectors.

PC (Physical Contact) polishing initially envisaged only a flat version of the connector, but operating experience showed that a completely flat end of the connector cannot exclude the formation of air gaps between the ends of the optical fibers. Therefore, the ends of the connectors acquired rounding (spherical surface). The ST, SC, FC connectors and some other less common ones now also have such rounding. All the modern connectors made using adhesive technology fall into this class. They are suitable for most data transmission systems, in which we are talking about short distances and not too demanding applications. First of all, these are small networks.

Since manual polishing of the PC as a whole didn’t give the best results (typical insertion loss for single-mode fiber is 0.2 dB, reflectivity is within –30 dB), manufacturers continued to search for new grinding methods; So there were types of grinding SPC and APC.

Polishing SPC (Super Physical Contact) differs from regular PC polishing only in higher quality. The end of the fiber is polished in the usual way, just instead of hand polishing it is used machine.
So, if you buy one-sided fiber-optic jumpers (pigtails) that will terminate the cable by welding, then most likely, these pigtails have a SPC polished connector. Fiber optic pigtails are designed to terminate fiber optic cables. A pigtail is a piece of optical fiber in a protective sheath terminated on one side with a specific type of connector. They are better than hand-grounded and hand-polished connectors, and have a reflectivity of –40 dB.

The APC (Angled Physical Contact) connector differs from the PC connector in that the end of its fiber is polished at an angle of 8 ° (8 degrees), which makes it possible to achieve a significant improvement in the results. With APC polishing, angular (oblique) physical contact is used.

Due to this angle, almost all of the reflected (unwanted) signal leaves the fiber. Optical connectors that use APC polish today provide the best results; reflectivity can be both –60 dB and –65 dB. Since less than one ten-thousandth of a signal is reflected, the APC connectors are usually used to implement the most demanding applications, for example, when transmitting video, in the main provider communication lines, etc. It is almost impossible to make independently (manually) patch cords that meet the requirements for polishing APC, therefore they have a factory assembly.

The latest option was the UPC (Ultra Physical Contact) polishing, which does not use plain polishing, but ordinary straight polishing, but using certain machine technologies, including taking into account the tip radius. This connector polishing option allows you to achieve reflectivity at –50 dB, which is slightly worse than APC polished connectors, but better than other polishing options (this is important for single-mode connectors).

PC, SPC and UPC polishing types are compatible with each other. But from this group of optical connector with polished UPC gives the best performance. As a rule, this type of polishing is used in high-speed active optical equipment. This type of connector is often found in the purchase of optical patch cords or pigtails.
UPC polishing often uses blue connectors.

The following is a summary table of the dependence of the insertion loss (insertion loss) and the reverse reflection of the signal on the type of polishing / grinding the fiber-optic connector:

Attention! APC and UPC polishing types are not compatible . If you connect an APC polished connector (and vice versa) to the UPC polished connector, both of them will have a polished surface damaged.

For more information about connectors used in fiber-optic systems, you can find on the website: http://citforum.ru/nets/hard/connector/