Grinding is the most important part of the connector assembly process. Grinding is mainly to adjust the 3D parameters of the ferrule end face and the end face treatment. 3D parameters will affect the docking performance of the connector, such as whether the docking is accurate, whether the contact is tight, etc.; thus, it will have a certain impact on the optical characteristics, mainly affecting its insertion loss and return loss. The quality of the end face will also affect the optical characteristics and service life of the connector. Grinding is one of the factors that affect the insertion loss of the connector; but for the return loss of the connector, grinding plays a decisive role.
The common sense that you need to know about grinding first, grinder: center pressure grinder, pressure applied from the center of the grinding disc. The biggest advantage is that the pressure can be adjusted, that is, the pressure can be adjusted to adjust the 3D parameters, and the 3D parameters can be adjusted by changing the hardness of the polishing pad. There are more options for the adjustment of 3D parameters, so the type of polishing pad can be reduced. need.
The shortcomings are: 1. It is difficult to install the plate, and the consistency of the ferrule assembly is relatively high, otherwise it will have an undesirable effect on the grinding. For example: Failure to tighten will result in insufficient grinding; crooked ferrule installation will cause apex offset, and severe cases will affect the tip deviation of several nearby ferrules or even the entire disk. When grinding, the ferrule mounting plate needs to be strictly symmetrical, not more on one side and less on the other.
2. The grinding procedure is difficult to control, and the grinding procedure is limited by the number of ferrules. It is possible to obtain better results by grinding the whole plate.
3. It is difficult to rework. If a part of the reworked ferrule is added to a new plate, the effect is often unsatisfactory, or the entire (disassembled) rework is performed. The repair process should start from the previous steps. Since the ferrule has been disassembled and installed, the length of the ferrule will inevitably be inconsistent. Therefore, the length of the ferrule can only be grind to be the same in the first few processes to get a good repair effect, but it will be damaged. Produce undesirable results.
Four-corner pressure grinder: Apply pressure from the four corners of the grinder.
Its advantages are: 1. The grinding process is relatively stable, and the design of the grinding disc is controlled by IPC (independent polishing). Theoretically, it can grind the number from one to its maximum hole position. Because each hole position is independent, it does not affect the ferrule of the surrounding hole position. In fact, when the quantity is small, the grinding time should be relatively reduced.
2. It is easy to install the plate, which can avoid the inconsistency of the length of the ferrule due to the installation. The phenomenon of crooked installation can also be easily checked out.
3. It is easy to repair, and the repair can generally be repaired from the next few steps (mainly for the end face with less serious defects, black spots, scratches, etc.). The disadvantage is: the pressure is not adjustable, and it depends entirely on the hardness of the polishing pad and the polishing time. Length to adjust the 3D parameters of the ferrule. In general, the four-corner pressure grinder is more stable than the center pressure grinder, and the operation is simpler.
Grinding pad: 1. The height and hardness of the rubber pad have an important influence on the 3D parameters of the ferrule end face. Seiko Gikken’s polishing pad model: PR5X-500 (height)-80 (Shore hardness) refers to a thickness of 5mm and a hardness of 80. Commonly used ones have a height of 5mm and a hardness of 60, 70, 80, 90 and so on. There is also a height of 4.8mm and a hardness of 80.
2. Glass mat: mainly used for grinding the ferrule with an angle of 8 degrees, that is, the APC type ferrule. Grinding sheet, sand material on the grinding sheet: SIC, diamond, SiO2, etc. The following are the different types of sand materials of Seiko Technical Institute’s abrasive pads, GA5D-30u abrasive pads: SIC material, brittle and sharp, with a Mohs hardness of about 8, and a life of 2 times. GR5D-9u Grinding Sheet: Diamond material, Mohs hardness is generally 10, life is 20 times. DR5D-5u polishing pad: diamond material, Mohs hardness is generally 10, life is 20 times. DI5D-1.5u Grinding Sheet: Diamond material, Mohs hardness is generally 10, life is 20 times. NTT FOS-01 polishing sheet: SiO2 material, Mohs hardness is generally 7, and the life span is 2 times. The size of the sand particles on the grinding sheet: 30um, 9um, 5um, 3um, 1.5um, 1um, 0.5um, 0.2um, etc.
Grinding fluid: PL-50: Seiko Gikken’s grinding fluid reduces the cutting force of grinding and increases the service life of the grinding sheet. It is mainly used with diamond abrasive pads.
Distilled water: For the final polishing, general tap water cannot be used, because the general tap water contains impurities that will have undesirable effects on the end face of the optical fiber.
Alcohol + distilled water: The effect is the same as that of distilled water. It can reduce bad imagination such as black spots and aprons, and improve the yield rate. But it will reduce its own service life and have a greater impact on the height of the optical fiber.
Interferometer: DORC ZX-1, NORLAND AC3000/CC600, etc., mainly to test the 3D parameters of the end face of the ferrule. The principle is to use the Newton ring interference principle to detect the 3D condition of the ferrule end face. It is mainly used for detection to judge the 3D parameters of the ferrule after grinding. It needs to be corrected every fixed time, and the judgment criterion of the correction is based on the vertex offset AO at 0. , 90. , 180. , 270. The difference between the maximum and minimum values in the four directions is judged (△≦4um). The calibration instrument generally has no effect on the radius of curvature of the ferrule end face and the height of the fiber. Therefore, if the radius of curvature and the height of the fiber are generally only the test error caused by the repeatability of the instrument itself, the vertex offset will also be in the calibration process. Come a certain error. It should also be noted that the end face and cylindrical surface of the ferrule need to be wiped clean before testing to avoid testing errors.
Ferrule: The material is generally alumina/zirconia, (PSZ) Mohs hardness is generally about 7.5. The material of the ceramic ferrule generally has low strength and large particle size, and it is easy to break when it touches a hard surface. Zirconia: small hardness, small particles, easy to grind and polish (this kind of material is commonly used for ferrules). In addition, the ferrule mentioned above may also be mixed with iron to increase the wear resistance of the ferrule. Ferrules of steel and rubber are less used.
The classification of the ferrule: according to the diameter: Φ2.5mm, Φ1.25mm. Type: UPC (Ultra Physical Contact, super plane physical contact), APC (Angle Physical Contact, angled physical contact-usually 8 degrees). Ferrule end face: SC type ferrule end face diameter is 1.92mm. The diameter of the LC end face is 0.9mm and 0.6mm (IEC standard). The end face diameter of MU is 0.53mm (NTT standard) and 0.6mm (IEC standard). The diameter of the APC (tapered) end face is 1.0mm, and the chamfer is 30 the same as the PC type. , But the chamfer becomes longer and longer. The diameter of the end face of the APC (step) is 1.4mm. Knowing the size of the end face is of great help in adjusting the new ferrule grinding procedure. For example, the grinding program of the LC ferrule end face of 0.9mm and 0.6 is very different. The end face of 0.9mm has a better grinding effect. Because the end face of 0.6mm is small, the radius of curvature during grinding is too small. Only a harder grinding pad can be used for grinding. The consequence is that the 3D parameter is 0.9mm than the end face. The difference.
3D parameter analysis: 1. ROC radius of curvature R (PC: 7～25mm/APC: 5～12mm): the radius of the end surface arc should not be too large (the largest radius of curvature is infinite, which means it becomes a plane. It can seriously affect the return loss); it can’t be too small, too small, it is easy to appear because of poor concentricity, which will cause an air gap in the butt, which will affect the performance of the butt.
The specification of UPC in the factory is 10～25mm, and IEC adopts this standard. GR-326-CORE uses 7～25mm. The choice of APC is 5-12mm. 2. Apex Offset (AO≤50um): the distance of the highest point from the central axis of the fiber. When two joints with large apex offsets are butted, the direct contact must be the highest point, and the optical fiber center is not directly contacted, which causes an air gap, which is prone to interference and other phenomena, which affects the docking characteristics. (Vertex offset) calculation formula: Apex Offset=R*△, where R is the radius of curvature and △ is the offset angle (Note: because △ is very small, sin△≈△, sin is omitted in the above formula). Generally △ is set to ≦0.2. 3. Fiber Undercut Protrusion fiber height: the amount of fiber protruding or retracting the ferrule. In GR-326-CORE, the fiber height when the fiber height is 7～10mm in the radius of curvature is -125～+50nm . The area with a radius of curvature of 10-25mm is: -0.02R3+1.3R2-31R+325～+50nm.
4. The general specification of APC polishing angle is 8. ±0.3. Apexoffset≈R*sin(8)*δ where R is the radius of curvature of the end surface, and δ is the azimuth error angle of the positioning bolt. Ferrule end face area definition (refer to GR-326-CORE): area definition: D=250um, E=140um, F=50um. The area in D area is the ferrule docking area, and the area outside D does not need to be monitored because it does not affect the docking characteristics. Therefore, the D area is acceptable if it does not have serious defects, after all, it does not directly affect the optical characteristics. The E area does not need to be tested, because this area does not affect the docking performance, nor does it affect the light transmission performance. The F area is the key area, because the vertex offset is in this area. There is only an area of 50um. The condition of the fiber end face is the most stringent, and no defects are allowed. (This is for SM fiber, because the single-mode fiber core is only about 10mm. For MM fiber, such as 50/125 or 62.5/125, the F area should be at least 100um.) The F area defined in the factory is at least 120um . No defects are allowed under 400 times the end inspection instrument, this definition is much higher than the requirement of 326.
The law of grinding: 1. Add grinding pressure and use a softer grinding pad, and you will get a smaller radius of curvature of the spherical surface R. The greater the pressure applied to the grinding pad, the greater the deformation, and the smaller the radius of curvature of the deformation. , So that a smaller radius of curvature will be obtained during grinding. Similarly, when the pressure is constant, the softer the cushion, the greater the deformation, and the smaller the radius of curvature can also be obtained.
2. The high stability of the grinding machine and the use of a softer grinding pad can reduce the apex offset of the spherical surface. AO improves the stability of the grinding machine and can reduce the shaking amplitude of the ferrule, thereby reducing the apex offset. The more certain point here should be to reduce the offset angle of the vertex. The softer polishing pad can not only reduce the shaking amplitude of the ferrule, reduce the offset angle of the apex, but also reduce the radius of curvature and control the two factors of the top deflection, so as to achieve the purpose of reducing the top deflection. Therefore, the hardness of the polishing pad has a great influence on the vertex offset.
3. Reducing the speed of the grinder and using smaller abrasive particles can reduce the shrinkage/protrusion of the fiber. Lowering the speed of the grinder can reduce the height of the fiber. The reason is unknown. The above grinders can adjust the speed, but they have not been used before, and the actual effect is unknown. The smaller the abrasive grit, the smoother and flatter the end face of the optical fiber can be polished, thereby reducing the height of the optical fiber. In addition, as the number of uses of the polishing pad increases, the height of the optical fiber will drift negatively, that is, continue to shrink inward. The polishing pads include FOS-01 and ADS, etc. The height of the optical fiber limits the service life of the FOS-01 polishing pad more significantly. Taking LC as an example, FOS-01 has only two lifetimes, after which the fiber height will generally be below -50nm. The ADS can be used more than 10 times, and the amount of change in the height of the fiber is not large.
4. The impact of grinding time on 3D: If the grinding time is long, the ferrule will become shorter, and the pressure on the grinding pad will decrease accordingly; and the end face of the ferrule will also become larger (except for Step APC). Then the radius of curvature of the ferrule will become larger, and the top offset will also become larger. If the polishing time is short, it will cause insufficient polishing and adversely affect the end face of the optical fiber. Such as black blocks, scratches, aprons and other end-face defects. Therefore, it is necessary to select an appropriate amount in the grinding time. Try to reduce the time as much as possible while meeting the 3D value and the end face at the same time, in order to improve efficiency.
5. The impact of the polishing sheet on the polishing: uneven particle size: If the size of the sand on the polishing sheet is not uniform, that is, some sand particles are more protruding, this situation will easily cause scratches on the fiber end face. Inconsistent cutting speed: If there is a problem in the design of the grinding sheet, the residue after grinding cannot be removed and the gaps on the sand surface are filled. This situation is likely to cause uneven cutting speeds on the end face of the same disc, and scratches will also appear. The service life of the abrasive sheet is unstable: If there are the above quality problems, it will cause inconsistent use times of each piece of sandpaper, which will cause certain difficulties in the control of the abrasive program. Whether the thickness of the polishing sheet itself is uniform will also affect the final polishing effect.
6. Grinding angle error and positioning pin azimuth error have a great influence on the eccentricity value. Improving the azimuth accuracy of the positioning pin and the grinding fixture slot can reduce the eccentricity.
The above rules are important rules for grinding, especially the first 3 rules are particularly important. It is the law that must be mastered for grinding. Grinding program: For the grinder, the pressure is fixed, so the following grinding program does not involve pressure adjustment.
