When a connector is installed on the end face of an optical fiber, return loss is inevitable. If the optical return loss is inevitable, it will damage the laser light source and interrupt the transmission signal. Therefore, different grinding methods of the connector ferrule can to a certain extent avoid sever return loss. Fiber optical connectors can also be classified as APC, UPC and PC based on the different polishing shapes of their end faces. The main content of this article is to introduce how to distinguish APC/UPC/PC connectors.
What is PC connector?
PC (Physical Contact) connector is a physical contact, micro-spherical grinding and polishing. It enables the end faces of two optical fibers to come into direct contact. The fiber end faces are ground into a slight spherical shape, with the optical fibers located at the highest point of the curvature. This effectively reduce the air gap between the optical fiber components and enables the two fiber end faces to achieve physical contact.
What is UPC connector?
UPC (Ultra Physical Contact) connector is ultra physical interface. Its connection surface is neither as flat as that of PC nor as slanted as that of APC. It has a slight curvature to achieve more precise alignment. UPC is an optimized version of PC with improved end face polishing and surface finish, and the end face appears more dome-shaped.
What is an APC connector?
APC (Angled Physical Contact) is angled physical contact. The end face is ground to an 8° angle, forming a bevel. It is very helpful for the tight connection of the optical fiber end face and can also allow the light to be reflected to the cladding through the APC bevel angle instead of directly returning to the light source, providing better connection performance.
Comparison of optical fiber transmission quality of APC, UPC and PC connectors
Different grinding methods determine the transmission quality of optical fibers, mainly reflected in return loss and insertion loss. Generally, the insertion loss of the connections of APC, UPC and PC should be less than 0.3 dB. Compared with APC connectors, due to the smaller air gap, UPC/PC connectors are more likely to achieve the insertion loss.
Return loss is a parameter of signal transmission performance. It is usually expressed in negative dB value, and the higher the value, the better. The end faces of APC connectors are polished like shoe soles, so the return loss of APC connectors is better than of UPC connectors. The return loss of UPC connectors is slightly stronger than that of PC connectors.
What are the application scenarios of APC, UPC and PC?
PC was the earliest grinding method for optical fiber connectors on fiber optic jumpers. Currently, with the advancement of equipment, it has gradually been phased out.
UPC is usually used in Ethernet network devices (such as ODF optical fiber distribution frames, media converters and optical fiber switches, etc.) for digital, cable television and telephone systems, etc.
APC, due to its advantages of low insertion loss and high return loss, is naturally applied in high-speed rate and long-distance transmission environments.
Can APC, UPC, and PC be used interchangeably?
Since both the PC and UPC connectors have flat surfaces, the difference lies in the quality of the grinding. Therefore, they are compatible with each other. PC and UPC can be used together and mixed.
Because the end face of the APC connector is inclined, while the port of the UPC connector tends to be flat, when used together, the fiber surface will suffer permanent damage, which will lead to a decline in the performance of the connectors.
Conclusion
APC, UPC and PC are all types of fiber optic connector grinding methods. When choosing a fiber optic connector for certain specific applications, one should consider factors such as cost and operability. For example, for applications that require high-precision fiber signal transmission, an APC connector with higher return loss should be selected. For applications that are less sensitive to optical signals, an UPC or APC fiber optic connector can be chosen.
