The difference of End Grinding Angle
PC is Physical Contact. PC is a microsphere grinding and polishing, the surface of the ferrule is ground into a slight spherical surface, and the fiber core is located at the highest point of bending. This can effectively reduce the air gap between the fiber components and bring the two fiber end faces into physical contact.
UPC (Ultra Physical Contact). The end face of the UPC connector is not completely flat, there is a slight arc to achieve more accurate mating. UPC is based on PC to optimize the end surface polishing and surface finish, and the end surface looks more domed.
APC (Angled Physical Contact) is called beveled physical contact, and the end face of the fiber is usually ground into an 8 ° bevel. The 8 ° angle bevel makes the fiber end face tighter, and reflects light through its bevel angle to the cladding instead of returning directly to the light source, providing better connection performance.
The APC connector is usually green, and the UPC / PC connector is blue.
Return loss and insertion loss
Different grinding methods determine the quality of fiber transmission, which is mainly reflected in return loss and insertion loss. Insertion loss (Insertion Loss) refers to the signal loss generated by the connector or cable. In general, the typical insertion loss of PC, UPC and APC connectors should be less than 0.3dB. Compared with APC connectors, UPC / PC connectors are usually easier to achieve low insertion loss due to the smaller air gap. Insertion loss can also be caused by dust particles between the end faces of the connector.
Return loss (Return Loss), also known as reflection loss, is a parameter representing the signal reflection performance. Usually expressed in negative dB value, the higher the value of the parameter, the better. The end faces of APC connectors are beveled, so the return loss of APC connectors is usually better than UPC connectors. In general, the return loss of a fiber optic patch cable using a PC grinding method is -40dB. UPC return loss is higher relative to PC, generally at -55dB (or even higher). APC industry standard return loss is -65dB. When using the UPC connector, part of the reflected light is emitted back to the light source, and the beveled end face of the APC connector will cause a part of the reflected light to be reflected to the cladding at an angle, thereby reducing more reflected light to return to the light source. This is the main factor that causes the return loss to differ.
The Application of Connector
PC is the most common grinding method for optical fiber connectors on optical fiber jumpers, and is widely used in telecommunication operator equipment. UPC is usually used in Ethernet network equipment (such as ODF fiber distribution frames, media converters and fiber switches, etc.), digital, cable television and telephone systems. APC is generally used in optical radio frequency applications such as CATV, and also in optical passive applications, such as PON network structures or passive optical local area networks.
The connector connection needs to have the same end structure. For example, the end surface of APC is ground to an 8 degree angle. APC cannot be combined with UPC, which will cause the performance of the connector to decrease. However, the end faces of PC and UPC fibers are flat, the difference is in the quality of the grinding, so the mixed connection of PC and UPC will not cause permanent physical damage to the connector.
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In order to make the end faces of the two optical fibers better connect, the ferrule end face of the fiber jumper is usually ground into different structures. Common grinding methods are: PC, APC, UPC. PC / APC / UPC represents the front surface structure of ceramic ferrule.