PC vs UPC vs APC Fiber Connectors – What’s the difference?

Written by Ben Hamlich, Director of Technical and Product Innovation at trueCABLE RCDD, FOI

Have you wondered what the difference is between Optical fiber connector Polishes and when using one will it be better than the other? Keep reading this article and I am sure we will answer your question. Often times, the focus on choosing a fiber optic connector is, “Do I need an LC, SC, ST, etc. connector?” These are the most common questions a person might focus on based on their fiber composition. But an often overlooked question is: “What fiber connector polish should I use, and why would it make a difference?”

First, we will mention the three most common types of polishing. There are three main types of fiber connector polishes used in fiber optic applications today.

Computer (physical contact)
UPC (ultra physical contact)
Armored personnel carrier (corner physical contact)

To keep it simple, PC, UPC, and APC specify the type of coating used on the face or end-ring of a fiber optic connector. The connector end face or ferrule is a wrap for the exposed end of the fiber core and cladding. When a fiber connects to another fiber connector, transmitter, or receiver, it is important (depending on the application) to choose the appropriate fiber connector polish.

We will return to the three types of polishing of fiber connectors in more detail in the following sections. If you prefer to watch a video on this topic, you can also watch the video below where we cover the same information.

Why does it matter whether I use PC, UPC, or APC?

One major difference is the amount of light that is returned or reflected as light travels between two coupled connections, called reflection.

Reflectance (also called back reflection or optical return loss) is the amount of light that is reflected back to the source it came from. Light travels through the fiber cable and when it comes to the mating connection, between these two surfaces, there is what is called an air gap. This air gap, although small, can represent a significant loss of optical signal upon mating contact.

However, this can vary depending on the type of coating used on the fiber connector. The greater the reflection loss, which is measured as a negative value, the better the fiber connection. This reflection loss improves as we move from PC to UPC and finally to APC.

Reflection loss values ​​for each type of conductor polishing:

Reflection loss values ​​for polishing PC, UPC and APC connectors

Let’s take a look at the three fiber connector polishers in more detail.

Computer physical connection connector:

PC, which stands for physical contact, is the primary contact or surface polish on a fiber connector. It is the most common type found in OM1 and OM2 multimode fibers. Computer fiber connectors are designed to overcome the air gap between two surfaces caused by small imperfections in the original flat fiber connector. Flat style fiber connectors are no longer used.

In computer fiber connector design, there is a slight cylindrical curve to the end face of the fiber in order to eliminate or improve the air gap. Typical return loss in single mode applications is about -30 dB, which is much lower (better) than the original flat polishing pattern reflection, which is typically -14 dB.

Physical connection style fiber connectors

UPC superior physical contact connector

When we move on from PC polishing connector, our next polishing type is UPC Polish. This Polish type has become the most common. the LC-UPCAnd SC-UPC Connectors are the most common in fiber installations today. Based on the features of the convex end face of PC but using an extended polishing method, a finer surface finish is created from the fiber, giving us the Ultra Physical Contact (UPC) conductor. This results in a lower back reflection (ORL) or reflection value compared to a standard PC connector, allowing for more reliable signals in digital TV, telephone and data systems. In today’s market, UPC is the most popular end-face coating, covering most of the needs of fiber optic applications.

Most often, the poor performance found in a UPC connector is not the result of the design but rather poor cutting and polishing techniques. UPC connectors have low insertion loss, but back reflection (ORL) will depend on the quality of the fiber segment. Although most fiber connectors or pigtails are pre-sanded from the factory, a fiber strip with a mechanical splice or fusion splice is very important to the performance of the connector in terms of return (reflection) loss. Another factor depends on how often the connector is repeatedly mated (disconnected and connected) from its connection point.

Superior physical connection connectors

APC physical contact connector at an angle

Finally, we have APC coating. This is the conductor Which usually has a green fiber connector to indicate APC. This connector coating has minimal back reflection and can sustain redundant connections without any significant return loss degradation of connector performance.

PC and UC connectors are commonly used in most fiber applications, and are sufficient for the majority of applications. However, in some cases, the application requires very low reflection loss, and this is where APC polishing joints shine. This is because adding a small 8 degree angle to the end face allows for a tighter connection with less air gap. Additionally, any light that is redirected back towards the source is more easily reflected back onto the fiber cladding, thanks to the 8° end face.

However, APC communications are not without limitations. The above mentioned PC and UPC polishing connectors are all combinable or interchangeable. However, the performance of the connector will depend on the lowest performing connector in the paired connection. In this case the computer connector. Can you mix APC and UPC fiber connectors? Are APC and UPC interchangeable? no! This is not true with APC polishers connected to a UPC or PC polishing joint. APC connectors must be mated with APC connectors, otherwise there will be large return loss and insertion loss, causing test links to fail and data loss.

APC connectors They can often be found in applications such as DAS, FTTH and CCTV. APC connectors are also commonly used in passive optical applications (both GPON and passive optical LANs) because many of these systems also use RF signals to deliver video. Future high-speed passive optical networks and other WDM applications that will use higher wavelengths over single-mode fiber will also likely require reduced return loss for APC connectors.

APC splices can only be found in single-mode fiber, so how can you tell the difference between single-mode UPC and single-mode APC? After all, the connector rings are very small and it is very difficult to recognize whether they are at an angle or not. This is where connector colors come into play.

If the connector body is blue, it is a single-mode UPC connector, and if the connector body is green, it is a single-mode APC connector. It’s that easy!

Angled physical contact fiber optic connectors

The most common fiber face polishes in today’s applications are UPC and APC. UPC is used in both multimode and singlemode, while APC is typically only used in singlemode, although there are some applications that have begun to use APC connectors in multimode applications.

In today’s high-speed networks, where high-quality fiber patch cords are essential to providing high-quality fiber alignment and durability, UPC polishing over PC polishing fiber connectors are the best choice.

Decide on a choice UPC or Armored personnel carrier It will depend on your needs. With applications requiring high-resolution fiber optic signals, APC should be the first consideration, but less sensitive digital systems will work equally well using Polish UPC connectors.

Happy communication!

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