PC vs UPC vs APC Connector: Choose the Right Fiber Connector Type
PC, UPC and APC are the three ways to grind the inner collar of a fiber optic connector (as shown in the figure below). The collar of a fiber optic connector is the housing of the exposed end of the fiber and is used to connect to the transmitting or receiving end of another fiber. When the connector is installed at the end of an optical fiber, light is reflected back to the fiber towards the light source, thus affecting the transmission of the signal. In order to improve the transmission efficiency of the fiber, engineers introduced the technique of collar polishing. The following article describes the three main types of connector polishing and the differences and how to choose the correct connector type.
PC Fiber Connector
PC fiber connectors are connectors that are polished with physical contact, and it is the most common polishing type on OM1 and OM2 multimode fibers. Its butt end face is physical contact, i.e. the end face has a convex arch structure and its connector cross section is flat, which is actually micro spherical grinding and polishing, and is most widely used in telecom operators’ equipment. In the PC fiber connector design, there is a slightly cylindrical, tapered head that is used to eliminate the air gap, resulting in a typical return loss of about -40 dB in single-mode fiber applications, which is higher than the return loss of the original flat polished style (-14 dB). However, this polishing style for PC connectors has become obsolete and continues to evolve into UPC connectors.
UPC Fiber Connector
UPC, or Ultra Physical Contact, evolved from PC connectors with a better surface finish.UPC connectors rely on machine polishing and have a higher return loss than PC connectors, approaching -50dB or higher. The circular finish it produces during polishing allows the fiber to contact high points near the fiber core where light propagates. In addition, when using UPC connectors, make sure that the laser specifications can handle the return loss produced by the UPC connector. It is important to note that repeated connections and disconnections can cause degradation of the quality and performance of the UPC connector end face.
APC Fiber Connector
APC refers to angular physical contact. Unlike UPC connectors, the end face of APC connectors is precisely ground at an 8 degree angle to the fiber cladding, which allows most of the return loss to be reflected back into the cladding without interfering with the transmitted signal and damaging the laser source.
APC fiber optic connectors are commonly used in broadcast and early CATV application networks with fiber optic connectors with inclined end faces to improve the quality of the TV signal, mainly because the TV signal is analog light modulation, when the coupling surface of the connector is vertical, the reflected light returns along the original path.
PC vs UPC vs APC Connectors: What’s the Difference?
The following article will introduce you the differences between PC, UPC and APC fiber optic connectors from three aspects: appearance, performance and application.
In terms of appearance, the main difference between PC, UPC and APC connectors is the end face. Although the end face of the UPC connector is slightly curved, PC and UPC fiber optic connectors are no angle polishing method, while the end face of the APC fiber optic connectors are 8 degrees and do a micro spherical polishing.
Another more obvious difference is the color, you can distinguish the connector type by the color of the connector. In general, PC/UPC connectors are blue and APC connectors are green.
Previously, it was difficult to achieve low insertion loss with APC connectors due to certain gaps in the connector design. However, as technology has improved, the performance of APC connectors has improved and the difference in insertion loss between APC and UPC fiber connectors has been reduced.
As far as return loss is concerned, the different polished end surfaces create a difference in their light reflection. As a result, the return loss values vary. According to industry standards, the return loss of PC, UPC and APC fiber connectors is approximately -40dB, -50dB and -60dB or higher, respectively. The higher the return loss, the lower the reflection, the better the connector performance. It is clear that APC fiber optic connectors have higher performance.
APC fiber optic connectors are more suitable for applications in areas with high return loss requirements, such as for RF video signal transmission, especially FTTx applications as well as passive optical networks and other applications using high bandwidth WDM systems.
PC connectors are ideal for telecom operator networks, while UPC connectors are widely used in digital TV, telephone and data systems.
PC, UPC and APC are all ways to grind fiber optic connectors, and cost and operability factors should be considered when selecting fiber optic connectors for certain specific applications. For example, for those applications that require high precision fiber optic signal transmission, APC connectors with high return loss should be selected; while for applications where the fiber optic signal is less sensitive, PC or UPC fiber optic connectors can be selected.