There are generally three types of fiber grinding methods: PC, APC, and UPC, and each grinding method has different meanings for fiber propagation. In this issue, we will take a closer look at the specific functions of these three grinding methods and how to choose them in use.
Installing a connector on a fiber endface, return loss is unavoidable due to reflections from the light source. Severe light loss can damage the laser light source and interrupt the transmitted signal.
In order to allow the end faces of the two fibers to be in better contact, the ferrule end faces of the fiber patch cords are usually ground into different structures. As shown in the figure, there are three common fiber endface grinding methods: PC, UPC, and APC.
The microsphere surface is ground and polished, the ferrule surface is ground into a slight spherical surface, and the fiber core is located at the highest point of bending, which can effectively reduce the air gap between the fiber components and make the two fiber end faces reach physical contact.
The UPC connector end face is not completely flat and has a slight arc for a more precise mating. The UPC is based on the PC to optimize the end polishing and surface finish, and the end face looks more dome-shaped.
Fiber endfaces are typically ground into an 8° bevel, with an 8° angle bevel that makes the fiber endface tighter and reflects light through its bevel angle to the cladding rather than directly back to the light source, providing better connection performance.
It 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.
Pin is the input optical power, and Pout is the output power.
(1) In general, the typical insertion loss of PC, UPC and APC connectors should be less than 0.3dB.
(2) Compared to APC connectors, it is generally easier to achieve low insertion loss due to the smaller air gap.
(3) Insertion loss can also be caused by dust particles between connector end faces.
It refers to the number of decibels of the backward reflected optical power relative to the incident optical power at the connection of the optical signal through the optical fiber jumper.
Pin is the input optical power; Pr is the backward reflected optical power.
(1) The end face of the APC connector is beveled and polished, so the return loss of the APC connector is usually better than that of the UPC connector.
(2) In general, the return loss of the optical fiber jumper using the PC grinding method is -40dB.
(3) The UPC return loss is higher than that of PC, generally at -55dB.
(4) The APC industry standard return loss is -60dB.
(5) When using the UPC connector, some of the reflected light will be emitted back to the light source, and the beveled end face of the APC connector will make a part of the reflected light reflect to the cladding at a certain angle, so as to reduce more reflected light to return to the light source.
PC is the most common grinding method of fiber optic connector on fiber patch cord, which is widely used in telecom operator equipment.
It is commonly 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.
It is generally used in optical RF applications in the high wavelength range such as CATV, and is also used in optical passive applications such as PON network structures or passive optical LANs.
Tips: Because the end face of the APC is ground into an 8 degree angle, the APC cannot be connected to the UPC, which will lead to the degradation of connector performance. However, the fiber end faces of PC and UPC are flat, and the difference lies in the quality of grinding, so the mixing of PC and UPC will not cause permanent physical damage to the connector.
There are many types of grinding discs, and different materials and different pore sizes will affect the grinding effect. Generally speaking, the grinding disc made of tungsten steel is more suitable for the grinding of optical fibers, and the aperture should be appropriate. If the disc is too large, it will make the grinding surface too wide, and if it is too small, it will make the grinding surface too narrow and may even break the fiber.
Grinding time and strength are important and need to be adjusted according to the actual situation. In general, the rotation speed of the grinding disc is equal to the linear speed of the optical fiber. During the grinding process, the grinding surface should be checked at any time to determine whether the grinding meets the requirements.
First, the fiber needs to be placed in deionized water to clean the surface of dirt. Secondly, the fiber needs to be cut and the ends cut straight to facilitate subsequent grinding work. Finally, the end face of the fiber needs to be sanded to eliminate burrs and imperfections on the surface, so as to ensure the grinding effect.