What are SC/APC, LC/UPC?
You may have heard of SC UPC, LC UPC, SC APC, LC APC, FC APC, FC UPC? What do they mean? The LC, SC, and FC indicate the different structures of fiber connector types, whereas the UPC and APC indicate different polishing shapes of fiber connector end faces. Previously, in accordance with the classification criteria of different structures of fiber connector types, we have introduced LC, SC, FC, ST, MTP, and MPO fiber connector types. Today, this post will introduce APC, UPC, and PC fiber connector types, which are classified based on the different angle polished fiber end face shapes. Next, the post will introduce the polish style, structure, difference, application, and usage attention of these connectors.
LC/UPC, SC/UPC, LC/APC, SC/APC, FC/APC, FC/UPC Connector
APC, UPC, PC Fiber Connector Types Introduction
Before introducing APC, UPC and PC connectors, it should be aware that In order to maximum couple the fiber light output from the transmitting fiber to the receiving fiber, the two end faces of the optical fibers must be accurately connected. The accurate connection is mainly determined by the quality of the fiber physical connection, which matters the insertion loss and return loss of fiber. The insertion loss and return loss are exactly measuring the optical fibers’ performance. Therefore, the physical connections of fiber, also referred to as different polished fiber end face shapes, are essential to the performance of optical fibers. The shapes of optical fiber end faces have mainly experienced three types of PC, APC, and UPC connectors.
What is an APC Connector?
APC connector is the most widely used fiber connector type today. “APC” stands for Angled Physical Connect. The angle of the ferrule end face is the 8-degree angle, which is very helpful for the tight connection of fiber end faces.
Because of the sloping end face, the APC fiber connector allows the light to reflect to the fiber cladding instead of backward reflecting to the light source, thus significantly reducing the return loss of fiber. The return loss of the fiber optic APC connector is typically -60dB, which is the smallest among the three types of UPC, APC and PC fiber connectors.
APC Connector Structure
What is a PC Connector?
PC connector stands for physical contact fiber connector, which allows the end faces of two fibers to be in direct contact with each other. The fiber-end surface is polished similar to a convex spherical surface. However, it looks flat since the radius of curvature is large. The optical fiber core is located at the highest bending point, which effectively reduces the air gap within fiber components thus enabling physical contact of two fiber end faces.
The fiber optic PC connector is the oldest one among the three connectors. The almost flat end face structure isn't adequate to reduce the return loss. Since the PC connector has a relatively high return loss of -40dB at least, it had gone out of use and was replaced by optimized UPC and APC connectors.
PC Connector Structure
What is a UPC Connector?
UPC connector is an upgraded version of PC. "UPC" stands for Ultra Physical Contact. UPC fiber connector evolved from the outdated PC connector, still using a convex spherical surface, but looking more like a dome shape since the radius of curvature is smaller than the PC connector. The pronounced curve enables a more accurate contact of two fiber-end surfaces. Furthermore, it uses an optimized publishing technology, resulting in a better fiber surface finish. Therefore, the UPC polish connector has a lower return loss of -50dB than the PC connector.
UPC Connector Structure
Comparison: APC vs UPC vs PC
APC vs UPC vs PC
UPC vs PC
End Face Structure - The basic difference between UPC vs PC is the structure of the end face of fiber connectors. The PC connector features an almost flat surface, whereas UPC looks like a more dome-shaped convex spherical surface.
Polish Technology - UPC utilizes optimized extended polishing technology, getting a better fiber surface finish than PC.
Return Loss - The different structure and polish technology results in the different performance of the return loss. The minimum return loss of the UPC connector is --50dB while the PC connector is -40dB.
APC vs UPC
End Face Structure - Similar to UPC and PC, the basic difference between APC vs UPC is also their end face structure. The end face of the UPC connector is shaped as a flat-convex spherical without angle. Instead of flat, the end face APC connector is sloping, and the APC connector angle is 8-degree. The 8-degree sloping surface allows a more accurate contact of two end face surfaces on two fibers, also efficiently reduces the back reflection by reflecting the light to the fiber cladding.
Fiber APC vs UPC Light Back Reflection
Return Loss - APC connector has the best return loss performance of -60dB. The return loss of the UPC connector is -40dB, which is higher than the PC but lower than APC.
Color - According to industry standards, the typical APC connector color is green while UPC connector is blue. You can easily distinguish APC from UPC by their color. For example, as the following figure shows, the connectors LC UPC to LC UPC connector duplex OS2 single mode fiber are blue, and connectors of LC APC to LC APC connector duplex OS2 single mode fiber are green.
Single mode fiber with LC UPC vs LC APC connector
How to Choose Between APC and UPC
If your application is sensitive to return loss, such as FTTx and WDM system applications, the APC connector is more suggested. Considering UPC connector cost lower than APC connector, it could be the best choice for the less sensitive applications as it offers almost equivalent performance to APC. So it can be seen that UPC connectors are widely used in today's fiber networks.
Is PC, UPC, APC Compatible with Each Other?
Since both PC and UPC connectors have a flat surface, they are compatible with each other and can be mixed when used. However, it should be noted that APC and UPC connectors are NOT compatible, and can not be plugged into each other. Otherwise, the fiber surface will get permanent damage. If you want to connect APC to UPC, the fiber cable connected with APC and UPC connector at both ends is helpful, as shown in the following.
UPC to APC OS2 Single Mode Fiber
QSFPTEK offers custom fiber cables with LC, SC, ST, FC, and MPO connectors, optional of UPC or APC polishing style. Welcome to consult via email@example.com.