The main factor of interference loss of optical connector is that the fiber core deviates from the design position. The dislocation of the fiber core in MPO connector is caused by the following factors: 1) the dislocation of the fiber hole in the sleeve from the design position; 2) The gap between optical fiber and optical fiber hole; 3) Dislocation of fiber core from fiber center; 4) The gap between the guide needle and the guide pinhole.
In order to reduce the interference loss, Sumitomo has studied the possibility of reducing the core misalignment and its standard deviation. It is determined that not only the mode needs to be improved to reduce the dislocation of the optical fiber hole, but also the gap between the guide pin and the guide hole and between the optical fiber and the optical fiber hole needs to be reduced. The results show that the deviation of the optical fiber hole from the design ideal position is less than 0.7 μ m. The gap between the guide pinhole and the fiber hole is less than 0.3 μ m。 It is also determined that the tilt tolerance of the fiber hole should be less than 0.2 degrees.
In the past, the most commonly used method of manufacturing sleeve is transfer forming, which is easier to get precise size. However, this method has low production efficiency and is not suitable for mass production. Sumitomo uses the injection molding method, and uses PPS (polyphenylene sulfide) as the base resin, which has low coefficient of thermal expansion, low water absorption and high mechanical strength. The suitable fillers were mixed into the resin to improve its properties.
The injection molding method is adopted, which not only reduces the hardening time in the forming process, but also reduces the overflow of the die by cleaning the die after forming, thus reducing the forming cycle to one third of the transfer molding method. The production efficiency of manufacturing sleeve is greatly improved.
In order to precisely align the optical fiber hole, a number of core pins fixed on a sliding frame for alignment, which form the guide hole and the optical fiber hole, are inserted into a cavity with a V-groove, and the V-groove is used for precise positioning. Although this structure is traditionally used in the transfer molding of epoxy resin to reduce the dislocation of the optical fiber hole of the sleeve and the gap between the guide hole and the optical fiber hole, the accuracy of the V-groove is improved, and the diameter tolerance is carefully selected to be less than 0.1 μ M core needle. In addition, the flow part and the inlet part of the mold are also improved, so that the mold can be formed better without the influence of high viscosity resin produced by adding a large amount of filler.
In order to obtain accurate size and dimensional stability in multiple forming, it is necessary to maintain excellent reproduction ability and reduce the residual stress in the forming parts. For the injection molding of MT sleeve, the forming conditions are particularly important, because very small diameter needle and high viscosity resin are used in the forming process. The best forming conditions are determined by experiments, including forming temperature, resin temperature, injection speed, injection pressure and cooling conditions. The experiment shows that low injection rate and low injection pressure show good results.