Compatibility issues between SFP optical modules and PC/APC/UPC optical fiber jumpers

PC/APC/UPC refers to the different grinding methods of optical fiber connectors on fiber jumpers, and different grinding methods determine the quality of optical fiber transmission, which is mainly reflected in return loss and insertion loss. So what are the differences between these three grinding methods?

PC (Physical Contact) is the most common grinding method for fiber optic connectors on fiber optic patch cords and is widely used in telecom operator equipment. Although the end face of the optical fiber connector appears to be flat, in fact the end face is slightly bent and polished, and the highest bending point is the center of the fiber core. This can effectively reduce the air gap between the optical fiber components. In general, PC polished optical fibers are used The return loss of the jumper is -40dB.

UPC (Ultra Physical Contact) is evolved from PC. It optimizes the end surface polishing to obtain better surface finish. UPC is the same as PC, its highest bending point is at the center of the fiber core, but UPC return loss is higher than PC, generally -50dB (or even higher). It is usually used in Ethernet network equipment (such as ODF fiber optic distribution frames, media converters and fiber optic switches, etc.), and is also used in telephone systems.

APC (Angled Physical Contact) is the latest technology for optical fiber end face grinding. The end face adopts an 8-degree angle grinding method to make the end face grinding more precise and effectively reduce reflections. The return loss is about -60dB. APC is generally used in high wavelength range optical RF applications such as CATV.

Note: Return loss (reflection loss) refers to the reflection caused by impedance mismatch in the optical fiber link, which is the reflection of a pair of lines themselves. This percentage of reflected light is usually expressed in -dB, with higher values being better.

After the above detailed introduction to PC/APC/UPC, you will find that PC/APC/UPC have differences in end faces, return loss, applications, etc.

PC and UPC are both planar interface types. PC is the earliest grinding method and has poor return loss. UPC is based on the PC structure and has better return loss than PC. APC is an end-face tape. There is an 8-degree angle grinding method that can effectively reduce reflections. The return loss is better than PC and UPC, making it more suitable for use in high-bandwidth and long-distance links.

As we all know, the SFP optical module has two transmission channel ports, one of which is used to send signals and the other is used to receive signals. Normally, signal transmission needs to be achieved through optical fiber jumpers. The above mentioned three types of fiber jumpers with different grinding types: PC/APC/UPC. Can these three types of fiber jumpers be used with SFP optical modules? In fact, this is not the case. Since the connection port of the SFP optical module is flat, it can only be connected to the optical fiber jumper of PC and UPC. If it is connected to the optical fiber jumper of APC, it will cause invalid connection or network failure.

In principle, PC/APC/UPC fiber optic connectors with three different polishing methods cannot be interconnected, but since the fiber end face structures of PC and UPC are both flat (with slight bends) structures, they can They are compatible and interchangeable, but there will be polishing quality issues, but they will not cause any damage to the connector. Although SFP optical modules can be connected to PCs and UPC fiber optic jumpers, in order to ensure the integrity of the fiber link, it is recommended that your SFP optical module be used with UPC fiber optic jumpers.

The fiber end face structure of APC is completely different from that of PC and UPC, so APC cannot be interconnected and compatible with them. If the connection is forced, the connector will be damaged; if you want to connect APC to UPC/PC, you must connect the two through APC-UPC/APC-PC conversion fiber jumper, but considering the waste of resources and the difficulty of wiring, For other reasons, FS does not recommend that you do this, so it is best not to use APC fiber jumpers on SFP optical modules. Unless the instructions of the SFP optical module say that APC fiber jumpers are allowed, it is still recommended that you use UPC fiber jumpers.

All in all, PC and UPC fiber optic patch cords can be used on Ethernet equipment such as fiber optic switches and used with SFP optical modules; APC fiber optic patch cords are mainly used for FTTx, Passive Optical Network (PON) and Wavelength Division Multiplexing (WDM) , it is best not to use it with SFP optical modules. The specific choice depends on your network needs.