Whenever we install a connector on the end of fiber, loss will be incurred. Some of this light loss is reflected directly back down the fiber towards the light source which can damage the laser light sources and disrupt the transmitted signal. To reduce back reflection, we can polish connector ferrules to different finishes. Typically, there are two ferrule polish types widely used in fiber optic connectors—UPC and APC (the following image shows a SC APC fiber patch cord). What do UPC and APC stand for? What are the differences between them? And which one is the better solution to your network? The following part will solve these questions one by one.
UPC or ultra physical contact is an extended PC (physical contact) polish which results in a better surface finish (as shown in the image below). The rounded finish created during the polishing process allows fibers to touch on a high point near the fiber core where light travels. Offering -55dB return loss, UPC connector relies on machine polishing to deliver low optical return loss characteristics, making it acceptable in Ethernet network equipment such as serial services, media converters and fiber switches. (Tips: when using UPC connectors, make sure your laser’s specifications can handle the return loss that your UPC connector will generate.)
APC, also named as angled physical contact (shown in the picture), is another style of ferrule polish. Its ferrule is polished with an 8-degree angle that end-face brings the fibers tighter and reflects light at an angle into the cladding instead of reflecting it directly to the light source, which causes its optical return loss to be -60dB or higher, making it a better-performance connector. APC connector handles multi-play systems which are mostly employed in radio frequency (RF) applications, like CATV or distribution antenna systems. It is also available in optical passive applications, such as PON networks architectures or passive optical LANs.
- Color Codes
A simple way to distinguish UPC and APC is the color codes of the surface. In general, UPC connector is easily identifiable by their blue color on the connector boot, while the APC connector is green.
- Endface Geometry
A UPC polish results in a dome-shaped endface that aids in optimizing the connections between two jacketed fibers, while the endface on an APC connector is polished at an eight-degree angle, which reduces the amount of light reflected between the two connected fibers.
- Return Loss
The more significant performance characteristic between APC and UPC connectors is their return loss (or the amount of light reflected back to the original source). Return loss is a measurement of the light reflected back to the source at an optical interface. The higher the return loss, the better the performance. Generally, UPC connector is required -55dB or higher, while the APC is -65dB or higher.
- Insertion Loss
Insertion loss is different from return loss, which refers to the measurement for the amount of optical power loss through a mated pair. The connector insertion loss can be used with the cable length loss to determine the allowable loss budget for an installed link. Insertion loss of APC and UPC should be less than -0.3dB, and the lower the insertion loss, the better the performance. Achieving low insertion is typically easier with UPC connector due to less air gap than APC connector. However, manufacturing techniques have improved significantly to create more precise angles on APC connector and bring insertion loss down closer to that of UPC connector.
Choosing the right connector for a network depends on many aspects, such as the network design, the performance of the connector itself, and installation budget, etc. Through the information we have discussed above, there is no doubt that APC has better performance than UPC. But, UPC connector will cost less than APC connector. Besides, when applications are sensitive to return loss than others, for example, FTTX (fiber to the x), passive optical network (PON), and wavelength division multiplexing (WDM), APC connector will be more preferable than UPC connector. But if you have limited cost budget and not ask for higher-quality system, UPC connector can be chose.
When choosing fiber patch cable jumpers, it is essential to take UPC and APC into consideration. Both of them can reduce back reflection and damage to the laser source. And after reading this passage, hope you can choose the appropriate one for you network application.