Fiber optic connector is a passive optical device to achieve active connection between optical fibers, which has the function of active connection between optical fibers and active devices, optical fibers and other passive devices, optical fibers and systems and instruments. Currently, fiber optic communication technology is developing in the direction of high bandwidth and high data rate, which requires lower insertion loss and higher return loss of fiber optic connectors in terms of performance.
Fiber optic connector manufacturing process is a key process is the grinding of the fiber end face, as the fiber is a hard and brittle glass materials, processing material removal mechanism is generally brittle fracture, if not to take appropriate measures, the processing process will inevitably produce a large number of micro-cracks or pits, resulting in its high surface roughness, which is easy to cause scattering and absorption of optical signals, to improve the optical fiber connector performance is extremely unfavorable.
Data show that the ceramics, glass and other brittle materials for grinding, grinding processing, as long as the depth of cut of the abrasive grain is less than a critical value related to the performance of the workpiece material, brittle materials will be removed in a plastic flow, so that the surface roughness of the processing surface to the nanometer level.
Optical fiber is an amorphous quartz glass composed of SiO2 with a purity of 99.999% or more, which has high hardness and low fracture toughness and exhibits a highly brittle nature, which leads to brittle cracking during the precision machining of optical fiber.
The fiber optic connector grinding machine uses a planetary orbital running mechanism, which makes every point of the fiber end face and the grinding sandpaper produce uniform wear. In order to make physical contact between the two fiber ends when the connector is docked, the ceramic core end requires a pre-ground spherical surface. The grinding pad is made of very elastic rubber, and the diamond abrasive is attached to the rubber pad so that the spherical end of the insert is still guaranteed when grinding the fiber ends. The rough surface of the fiber obtained by grinding with an average size of 9 μm diamond sandpaper has an opaque surface with more pits and flakes, indicating that the fiber material is removed in a brittle fracture mode; the surface obtained by grinding with an average size of 3 μm diamond sandpaper has cracks and intermittent grinding stripes, but the grinding surface also shows plastic deformation, and the material is removed in a semi-brittle and semi-ductile mode The surface of the fiber with an average grit size of 1 μm diamond sandpaper showed no micro-cracks and scratches, indicating that the micro-grained abrasive caused plastic flow on the surface of the fiber, and the bump on the surface was flattened by extrusion, and the fiber was in ductile grinding mode. There are three material removal modes when grinding optical fibers with diamond sandpaper with an average particle size of 1~9 μm: brittle fracture mode, semi-brittle semi-ductile mode and ductile mode. To obtain excellent surface quality on the fiber end face, the brittle fracture grinding mode should be avoided during grinding, and the ductile grinding mode, which causes plastic flow of the fiber material, should be used. It has been demonstrated that brittle materials such as glass can achieve brittle-delayed transformation when the energy required for crack expansion is greater than that required for plastic deformation under appropriate processing conditions, and the material is removed in a ductile mode, resulting in a smooth surface with very low roughness. The condition for achieving the brittle ductile transition when grinding glass materials, i.e., the cutting depth of a single abrasive grain should be less than the critical cutting depth of brittle materials. The data shows that the critical depth of cut for optical fiber is about 0.023 μm. In the grinding process, when the depth of cut of the abrasive grain is lower than the critical depth of cut for brittle delay transition, a high quality optical fiber end face can be ground in ductile mode. When the average particle size of diamond abrasive is 3 μm, the depth of cut of abrasive grains is similar to the critical depth of cut, however, there are actually some abrasive grains larger than 3 μm, so that the depth of cut of these grains is larger than the critical depth of cut, and the material removal is half brittle and half ductile; when the average particle size of diamond abrasive is less than l μm, the depth of cut of most of the abrasive grains is smaller than the critical depth of cut, and the fiber surface The material is removed in ductile mode with plastic flow. The relationship between diamond particle size and fiber end-face roughness was obtained from the following data.
The purpose of precision grinding of optical fiber is to improve the return loss value of the fiber optic connector and reduce its insertion loss value, the insertion loss and return loss of the connector corresponds to the roughness of the fiber surface, the lower the surface roughness value, the lower the insertion loss value of the fiber optic connector, the higher the return loss value. The insertion loss and return loss of the connector correspond to the roughness of the fiber surface, the lower the value of surface roughness, the smaller the insertion loss value of the fiber connector, the higher the return loss value. According to the relevant information, the relationship between abrasive particle size and return loss and insertion loss is obtained as follows.
In conclusion, when diamond abrasive paper is used to grind optical fibers: (1) with an average particle size of 1~9 μm diamond abrasive paper, there are three material removal modes for optical fiber grinding processing, such as brittle fracture, semi-brittle semi-ductile, and ductile, etc. The grinding mode is mainly controlled by the abrasive particle size. When the abrasive particle size is larger than 3 μm, the fiber produces brittle damage to fracture mode; when the abrasive particle size is smaller than 3 μm, the fiber surface produces plastic flow and removes in ductile mode. (2) The surface roughness of the fiber is related to the removal mode of the material during grinding. In the ductile removal mode, the surface roughness changes gently with abrasive size, while in the brittle fracture removal mode, the surface roughness decreases rapidly with decreasing abrasive size. (3) The surface roughness of the fiber can reach 5.18 nm when the fiber endface is processed by ductile mode grinding, and no scratches can be seen on its surface, which can make the optical properties of the fiber connector such as insertion loss and return loss meet the requirements of high-speed and broadband fiber optic communication.