In fiber optic cabling, there are usually scenarios where two fiber optic jumpers or jumpers are connected to devices. The industry has introduced grinding and polishing technology to allow better contact between the end faces of the two fiber optic jumpers. The ferrule end face of the patch cord is ground into different structures.
PC, APC, and UPC are three different ferrule polishing methods, representing the structural differences of the front face of the ceramic ferrule. As shown below, the ferrule is the housing for the bare end of an optical fiber, designed to be connected to another fiber optic or into a transmitter or receiver. When a connector is installed at the end of a fiber, light can bounce along the fiber back to the source, disrupting the signal. To improve the efficiency of fiber optics, engineers began to upgrade the surface of critical connection points, which is how ferrule polishing technology was introduced. So how to distinguish?
Ferrule Polishing End Faces are Different
PC (Physical Contact) Refers to Physical Contact
Usually found on OM1 and OM2 multimode fiber. The butt end face is a convex arched structure, and the cross-section of the joint is flat. After microsphere grinding and polishing, it can effectively reduce the air gap in the fiber optic component and make the two fiber end faces reach physical contact.
It should be noted that the polishing method of PC fiber optic connectors is outdated and has continuously evolved into UPC connectors.
UPC (Ultra Physical Contact) is Ultra-physical Contact
The end face of the UPC connector is not completely flat, and there is a slight curvature to achieve more precise docking. Based on PC, UPC has optimized the end-face polishing and surface finish, and the end face looks more dome-shaped.
PC and UPC, fiber optic connectors, belong to the non-angle polishing method, and the end faces are arc-shaped. The difference is that UPC fiber optic connectors optimize the end face polishing and surface finish based on PC fiber optic connectors.
APC (Angled Physical Contact) is the Physical Contact of the Slope Angle.
The end face of the fiber is precisely ground into an 8° bevel, forming an 8° angle with the fiber cladding to reduce reflection. And the light has reflected the cladding through its bevel angle instead of directly returning to the light source, which will not interfere with the transmission signal and damage the laser source.
Loss is Different
Different polishing methods determine the quality of fiber optic transmission, mainly reflected in return loss and insertion loss.
It is the loss of signal through a connector connection. Generally speaking, the insertion loss of PC, UPC, and APC connectors is less than 0.3 dB. Compared with APC connectors, UPC/PC connectors usually easier to achieve low insertion loss due to the smaller air gap at the connection end face. Dust particles between the connector end can also cause insertion loss faces.
This is a parameter that indicates signal reflection performance. The different polished end faces cause differences in their light reflection. The UPC/PC fiber optic connector will reflect the reflected light directly back to the light source during use. In contrast, the APC connector will reflect the reflected light into the cladding at a certain angle, not directly to the light source. And the end face of the APC connector is beveled polished, so its return loss is usually better than that of the UPC connector.
Usually, the return loss of the fiber optic using the PC grinding method is -40 dB. UPC return loss is higher than PC’s, generally at -55dB (or even higher). The APC industry standard return loss is -65dB. The higher the return loss value and the lower the reflection, the better the performance of the fiber optic connector. So, regarding return loss, the performance of APC fiber optic connectors is better.
Fiber End Face
The PC and UPC connectors are polished without an angle, and the UPC end face is slightly curved. In contrast, APC connectors have 8° angled end faces.
The color of the fiber optic connector can distinguish its type. Generally speaking, PC/UPC fiber optic connectors are blue, while APC fiber optic connectors are green.
Different Application Scenarios
- PC is the most common polishing method for fiber optic connectors on fiber optics and is widely used in telecom operator equipment.
②UPC is usually used in Ethernet network equipment (such as ODF fiber distribution frame, media converter, fiber optic switch, etc.), digital, cable TV, and telephone systems.
③APC is generally used in optical radio frequency applications in high wavelength ranges, such as CATV, and passive optical applications, such as PON network structure or passive optical local area network.
The connector connection needs to have the same end-face structure. For example, the end face of APC is ground into an 8-degree angle, and APC cannot be combined with UPC, which will lead to a decrease in connector performance. However, the fiber end faces of PC and UPC are flat; the difference lies in the grinding quality. Therefore, the mixed connection of PC and UPC will not cause permanent physical damage to the connector.
In short, APC fiber optic connectors are preferred for scenarios requiring high-precision fiber optic signal transmission and high callback loss, while for scenarios that do not require high fiber optic return loss, UPC or PC fiber optic connectors can be selected.
It is inappropriate to say that PC, UPC, or APC are the best fiber optic connector types. Cost and operability should be considered when selecting the fiber optic connector for a specific application. However, one rule must be followed: choose APC for high-precision fiber optic signal transmission applications; PC or UPC is capable of less sensitive digital systems.
Have you learned how to tell the difference? Hope that HOLIGHT‘s sharing can be helpful to you!