APC vs UPC vs PC Fiber Connector, What is the Difference?

If you look at your fiber cabling systems, you may find essential gear like fiber connectors and fiber optic cables. They may have different end-face polish and color codes. Many people may need to become more familiar with the difference between APC vs UPC vs PC polished fiber connectors. Please read this article and take the time to understand the details of how they differ.

*Figure 1:* *Flat vs PC vs UPC vs APC Connector*

What is Flat Fiber Connector

The flat fiber connector is like the figure above; the most apparent feature is the FLAT end face. When two flat fiber connections are joined, they naturally create a little air gap between the two ferrules, which is their main problem. This is partially due to the connectors’ relatively broad end faces, which enable numerous minor but noticeable defects to accumulate on the surface. With a core size of only 8 to 9 µm, this is not very useful for single-mode fiber cables, necessitating the development of Physical Contact (PC) connectors.

What is PC Fiber Connector?

PC is an abbreviation for “physical contact”. PC fiber connector refers to the connector with physical contact polished. It was first created in the 1980s to overcome the shortcomings of the original flat fiber connector.

Unlike flat fiber connectors, physical contact connectors have a slight taper around the endpoint. The cylindrical taper created by polishing the fiber ends reduces the air gap between the fiber ends that often occurs with flat connectors. Correspondingly, this small air gap reduces optical return loss (ORL), reducing the amount of light returning to the power supply and improving overall signal quality.

Generally, the typical return loss in single mode applications is about -40 dB, higher than the original flat polished style (-14 dB or about 4%). They are commonly used in multimode and single mode applications. However, as times have changed, this polishing style has become obsolete and is gradually replaced by the UPC polishing style.

What is UPC Fiber Connector?

UPC stands for Ultra Physical Contact. In fact, it is an enhanced version of the PC fiber connector. Based on the convex face properties of the PC, the connector utilizes an extended polishing method to create a better surface finish on the fiber.

Compared to standard PC connectors, this extended polishing results in lower optical return loss (ORL). Because of superior insertion and return loss performance, They have been used in many networks like digital TV, telephone, and data systems.

What is APC Fiber Connector?

APC stands for Angled Physical Contact. The emergence of APC fiber optic connectors is to achieve the need for lower back reflection. By grinding the radius of the end face of the fiber ferrule to an angle of 8°, we can minimize the back reflection. While that may not seem like much, the angled edges change the pitch at which light bounces back. So light reflected from the APC end face is directed into the cladding surrounding the fiber optic cable, rather than returning more directly to the fiber core.

The insertion loss of the APC fiber connector is comparable to that of the UPC fiber connector. Still, it can achieve a better optical return loss (-60dB or lower), which is better than other connectors.

But remember, unlike flat, PC, and UPC fiber connectors, this slight angle on the APC connector creates a rotation problem. Therefore, it can only be mated with other bevel-polished connectors, not with regular PC and UPC connectors paired, which would otherwise cause very high insertion loss.

APC connectors are commonly used in passive optical networks (PON) deployed in RF video or fiber-to-the-home (FTTP) networks because these systems are sensitive to any back reflections from connectors within the network.

APC vs. UPC vs. PC: What Are Their Differences?

Learning from the definition of APC, UPC, and PC fiber connectors, the most obvious difference is the fiber end face, return loss, and overall performance. Let’s look at the critical differences in the following chart.

Name	Endface Angle	Insert Loss	Return Loss	Connector Color Code	Application	Connector	System Cost
APC	8° angle	0.3dB	-60 dB	Green	RF video, FTTX	LC, SC, ST, FC, E2000, MPO/MTP	Higher
UPC	0° angle	0.3dB	-50 dB	Multimode: Beige Single mode: Blue	Telecom, Datacom	LC, SC, ST, FC, E2000, MPO/MTP	Medium
PC	0° angle	0.3dB	-40 dB	Multimode: Beige Single mode: Blue	Telecom, Datacom	LC, SC, ST, FC, E2000	Lowest

Table 1: APC vs UPC vs PC Connector Comparison

Physical Appearance

The first apparent difference is the ferrule end face. UPC and PC ferrule end face radius are polished at a 0° angle, while the APC end face radius is polished at an 8° angle.
The second appearance difference is the connector color code. Generally, the APC connector was color coded as green, while the PC and UPC connectors were beige for multimode or blue single mode. These color codes also apply to fiber optic adapters, attenuators, and jumper assemblies. You may easily distinguish which type of polish style by the color of the fiber connector body.

*Figure 2: UPC vs APC Fiber Connector Color*

Performance

Insert Loss (IL)

First, let’s look at the effect of insertion loss on the APC, UPC, and PC end face. Insertion loss refers to the optical power lost by measuring a paired connector. In the past, the insertion loss of angled physical contact connectors was usually high because of the significant losses caused by the air gap at the vertex offset.

However, due to improvements in connector design and manufacturing processes, the insertion loss of APC connectors has significantly been reduced, eventually rivaling the low insertion loss of UPC connectors.

Therefore, in today’s practice, we can ignore the insertion loss of these connectors.

Return Loss (RL)

Return loss is the amount of light the source reflects at an optical contact. It is the most significant difference between APC, UPC, and PC connectors.

Note: RL= -10xLog(PR/P) where PR = power reflected at the connector interface

From the introduction earlier in this article, we know that APC connectors use an end face that is polished at an 8° angle, resulting in the lowest return loss. According to industry standards, its return loss value will typically be -60 dB or better, while the UPC connector typically is -50 dB, and the PC connector typically is -40 dB.

Application

For specific applications that are more sensitive to return loss, APC connectors are preferred. Because these particular systems are susceptible to back reflection from any connector in the network, reflected light can adversely affect the signal. These areas include RF video signal transmission systems, FTTx applications, passive optical networks, and other WDM systems that use high wavelengths over single-mode fiber.

Then, for those applications that are not sensitive to return loss, UPC or PC connectors are preferred. PC connectors are generally used in telecom transmission applications, while UPC connectors are popular in digital TV, telephone, and data systems.

FAQ

Q: What type of connection are optical transceivers?

A: In most cases, it is UPC, like most SFP transceivers with UPC polished end faces. Remember, DON’T try to connect an APC fiber cable with the SFP transceiver.

Q: Is APC better than UPC?

A: Angled Physical Contact has better performance on return loss. However, only somewhere need better return loss. Therefore, it depends on your specific need and decides which is better.

Q: Can UPC connect to APC?

A: For the fiber connector, the answer is NOT. Because they are incompatible, This can damage the optical transmission.

But for the fiber adapter, ignore it because the only difference between them is the color, which means you may connect two APC connectors through the UPC adapter.

Q: Can UPC connect to the PC?

A: Yes, you can. Because those two fiber connectors are compatible.

Do SFP modules support APC, UPC, and PC fiber?

No, it does not. Since UPC and PC connectors are interchangeable, most SFP modules support both but can not support APC type.

If you use APC with SFP, it will risk physically harming the connectors and cause failer transmission. Rember to add a UPC to APC patch cable if you must use it.

Final Words

Do you know the difference between APC vs UPC vs PC connectors?

Which type of fiber connectors are used in your network?

Are there any other topics missed on this post?

Leave your comments below.

Reference

https://www.ppc-online.com/blog/picking-the-right-fiber-connector-pc-upc-or-apc

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