In your fiber cabling systems, you will find essential components such as fiber connectors and optic cables. These may have different end-face polish and color codes. Understanding the differences between APC vs UPC vs PC polished fiber connectors is crucial. This article aims to provide you with the necessary details to become more familiar with their distinctions. Take the time to read and comprehend the information presented here.
What is PC Fiber Connector?
The PC fiber connector is polished in the physical contact style and is commonly used on OM1 and OM2 multimode fiber. It was developed to overcome the air gap issue caused by small imperfections in the original flat fiber connector. The PC connector features a slightly cylindrical cone head to eliminate the air gap, resulting in a higher typical return loss of about -40dB in single-mode applications, compared to the original flat polish style with a return loss of approximately -14dB or 4%. Over time, the PC polish style has become outdated, and the evolution of the UPC polish style has taken its place.
What is UPC Fiber Connector?
UPC stands for Ultra Physical Contact, an enhancement of the PC fiber connector with a superior surface finish achieved through extended polishing. The return loss in UPC connectors is better than in PC connectors, reaching nearly -50dB or higher. However, UPC connectors are not as robust, and repeated connections and disconnections may lead to surface degradation and a decline in performance over time.
What is APC Fiber Connector?
APC (Angled Physical Contact) fiber connectors were developed to reduce back reflection. The ferrule endface is polished at an 8° angle, minimizing back reflection by allowing reflected light to leak into the cladding. APC connectors should only be mated with other angled-polished connectors to avoid high insertion loss. The optical return loss of APC connectors is -60dB or higher, making them superior in reducing reflections compared to other connector types.
APC vs UPC vs PC: What Are Their Differences?
Based on the definitions of APC, UPC, and PC fiber connectors, the primary distinctions are in their fiber end face design, return loss characteristics, and overall performance.
Physical Appearance
The primary noticeable difference lies in the ferrule end face. UPC and PC connectors have a 0° polished end face radius, while APC connectors have an 8° polished angle.
Another visible distinction is the connector color code. APC connectors are typically green, while PC and UPC connectors are beige for multimode or blue for single mode. These color codes are also used for fiber optic adapters, attenuators, and jumper assemblies, making it easy to identify the polish style by the connector body color.
Performance
- Insert Loss (IL)
Initially, the insertion loss in APC, UPC, and PC end faces was a concern due to air gap issues at the vertex offset, particularly in angled physical contact connectors. However, advancements in connector design and manufacturing have substantially reduced the insertion loss in APC connectors, now comparable to the low insertion loss in UPC connectors. As a result, in current applications, the insertion loss of these connectors can be disregarded. - Return Loss (RL)
Return loss, which measures the amount of light reflected at an optical contact, is the most significant distinction between APC, UPC, and PC connectors. APC connectors, with their end face polished at an 8° angle, exhibit the lowest return loss, typically around -60 dB or better, as per industry standards. In comparison, UPC connectors have a return loss of around -50 dB, while PC connectors have around -40 dB return loss.
Application
APC connectors are preferred for specific applications that are more sensitive to return loss. These include RF video signal transmission systems, FTTx applications, passive optical networks, and other WDM systems that use high wavelengths over single-mode fiber. These systems are susceptible to back reflection, and reflected light can negatively affect the signal.
For applications that are not as sensitive to return loss, UPC or PC connectors are preferred. UPC connectors are commonly used in digital TV, telephone, and data systems, while PC connectors find application in telecom transmission.
FAQ about APC vs UPC vs PC Fiber Connector
Q: Is APC better than UPC?
A: Angled Physical Contact (APC) has better return loss performance, but it is only necessary in specific applications. The choice depends on your specific needs.
Q: How to Choose Between APC and UPC?
A: If your application is sensitive to return loss, such as FTTx and WDM system applications, the APC connector is recommended. However, if cost is a factor and your application is less sensitive to return loss, the UPC connector can be the best choice as it offers almost equivalent performance to APC at a lower price. As a result, UPC connectors are widely used in today’s fiber networks.
Q: Is PC, UPC, APC Compatible with Each Other?
A: PC and UPC connectors, both having flat surfaces, are compatible and can be mixed when used. However, APC and UPC connectors are NOT compatible and should not be plugged into each other, as it can cause permanent damage to the fiber surface. If you need to connect APC to UPC, a fiber cable with APC and UPC connectors at both ends can be used as a solution.
Q: What are the Guidelines for Connecting Fiber Optic Connectors with APC and UPC End Faces?
Here are the fundamental guidelines for connecting fiber optic connectors with different end faces:
- UPC to UPC is a good combination.
- UPC to APC is not recommended.
- APC to UPC is not recommended.
- APC to APC is a good combination.
However, it is essential to avoid aligning APC to APC incorrectly as it can lead to negative consequences.
Q: Do SFP modules support APC, UPC, and PC fiber?
A: No, they do not. Most SFP modules support both UPC and PC connectors, but they do not support APC type connectors. Using APC connectors with SFP modules can risk physically harming the connectors and cause transmission failure. If you must use APC connectors, remember to add a UPC to APC patch cable for compatibility.
Q: What is the most common polish type for SFP transceivers?
A: In most cases, optical transceivers have UPC polished end faces, like most SFP transceivers. Remember, DON’T attempt to connect an APC fiber cable with the SFP transceiver.
Conclusion
Selecting the best polish type for fiber connectors depends on the specific application, considering factors like cost and operability. For applications requiring high precision optical fiber signaling, APC is recommended. For less sensitive digital systems, PC or UPC connectors are suitable. The key rule is to match the connector type with the application’s needs.
