When customers make inquiries, they often ask us to quote without telling us PC UPC APC, especially for new comers in fiber optic field. At this time, we need to communicate with customers about the specific details.
Generally speaking, PC patch cords can be understood as network-grade jumpers, and UPC/APC patch cord can be understood as carrier-grade jumpers. The difference lies in the workmanship of their connector heads and the loss of the jumper. The upc/apc jumper has fine workmanship and low loss.
Why does the fiber end face need to be polished?
When installing a connector on a fiber end face, return loss is inevitable due to reflection from the light source. Severe light loss will damage the laser light source and interrupt the transmission signal. In order to allow better contact between the end faces of the two optical fibers, the ferrule end faces of the optical fiber jumpers are usually ground into different structures.
What are the methods of optical fiber end face grinding?
Common fiber end face grinding methods mainly include PC, UPC, and APC, same as the cross-section of connector. Among them, PC and UPC have optical fiber microspherical end faces that are parallel to the end faces of the ceramic body, while APC optical fiber microspherical end faces are at an 8º bevel angle with the end faces of the ceramic body. There are three main aspects to measure the quality of optical fiber end-face grinding: radius of curvature, vertex offset and fiber height, here not specify in detail please refer to article if need: Three Indicators Of Fiber End-face Grinding Quality.
PC is physical contact. Microsphere grinding and polishing, the ferrule surface is ground into a slightly spherical surface, and the fiber core is located at the highest point of bending, which can effectively reduce the air gap between fiber components and bring the two fiber end faces into physical contact. PC is the most common grinding method for fiber optic connectors on fiber optic patch cords and is widely used in telecom operator equipment.
According to the difference in return loss, connectors are divided into PC, SPC, UPC and APC. Return loss refers to the proportion of light that is reflected by the end face of the connector. The smaller the return loss, the better. Of course, you can also say that the larger the return loss value, the better, regardless of the negative sign in front. SPC refers to super physical contact, and UPC refers to ultra physical contact. The return losses specified by PC, SPC and UPC industry standards are -35dB, -40dB and -50dB respectively. In principle, different connectors cannot be mixed, but the optical fiber end faces of PC, SPC and UPC are all flat, and the difference lies in the quality of grinding. Therefore, the mixed connection of PC, SPC and UPC will not cause permanent physical damage to the connectors.
UPC is ultra-physical contact end face. The end face of the UPC connector is not completely flat, but has a slight arc to achieve more precise docking. UPC is based on PC and has optimized end face polishing and surface finish, and the end face looks more dome-shaped.
UPC is usually used in Ethernet network equipment (such as ODF fiber optic distribution frames, media converters and fiber optic switches, etc.), digital, cable TV and telephone systems. APC is generally used in high wavelength range optical RF applications such as CATV, and also in optical passive applications such as PON network structures or passive optical LANs.
APC (Angled Physical Contact) is an inclined plane physical contact. The fiber end face is usually ground into an 8° bevel. The fiber end face is in closer contact and can reflect the light to the cladding through its bevel angle instead of directly returning to the light source, providing better connection performance. Its industry standard return loss is -60dB.
APC connectors can only be connected to APC connectors. Since the structure of APC is completely different from that of PC, if a adapter is used to connect the two connectors, the fiber end face of the connector will be damaged. How to connect APC to PC: through PC to APC conversion fiber jumper. You can provide a picture of the transfer jumper and attach a link to make the jump.
Since the end face of APC is ground to an 8-degree angle, APC cannot be connected to UPC, which will cause the performance of the connector to decrease. However, the optical fiber end faces of PC and UPC are both flat, and the difference lies in the quality of grinding. Therefore, the mixed connection of PC and UPC will not cause permanent physical damage to the connector.
In addition, when the optical fiber connector is ready, we can also identify the polishing method of the optical fiber from the color of the outer shell of the optical fiber connector:
| Connector Shell | Polish Method | Fiber Type |
| Green | APC | Single mode fiber |
| Blue | UPC | Single mode fiber |
| Beige | PC | Multi-mode fiber |
| Aqua | PC | Multi-mode fiber |
| Violet | PC | Multi-mode fiber |
| Green | PC | Multi-mode fiber |
What impact do different grinding methods have on the performance of the connector?
Different polishing methods determine the quality of optical fiber transmission, which is mainly reflected in insertion loss and return loss.
Insertion loss
Insertion Loss refers to the number of decibels of the output optical power relative to the input optical power after the optical signal passes through the optical fiber jumper.
IL(dB)=-101g Pout/Pin
Pin is the input optical power; Pout is the output power. Insertion loss is a positive value, and the smaller the value, the better.
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 generally easier to achieve low insertion loss due to the smaller air gap. Insertion loss can also be caused by dust particles between the connector end faces.
Return loss
Return Loss, also known as reflection loss, refers to the number of decibels of the retroreflected optical power relative to the incident optical power at the connection point where the optical signal passes through the fiber jumper.
RL(dB)=-101g Pout/Pin
Pin is the input optical power; Pr is the retroreflected optical power. Return loss is usually expressed as a negative dB value, with higher values being better.
The end face of the APC connector is bevel polished, so the return loss of the APC connector is usually better than that of the UPC connector. Under normal circumstances, the return loss of fiber optic jumpers using PC polishing method is -40dB. UPC return loss is higher than PC, generally at -55dB. The APC industry standard return loss is -60dB.
When using a UPC connector, part of the reflected light will be emitted back to the light source, while the beveled end face of the APC connector will cause part of the reflected light to be reflected to the cladding at a certain angle, thereby reducing more reflected light from returning to the light source. This is the main factor causing the difference in return loss.
