| 摘要 |
In a process for producing a multi-mode optical fibre preform by internal coating of a tube (20) with successive layers having a refractive index which is increased from the first larger diameter layer to the central layer by varying the proportions of reactive gas (24) used to form the layers, the velocity (v) of gas (24) introduction into the tube is chosen to make the radial index profile uniform in the longitudinal direction. Preferably, the velocity (v) is kept the same for production of all the layers or is increased with each layer deposited. Also claimed is a preform for making a multimode optical fibre with a refractive index which decreases from its axial centre to its periphery, the preform length having a first portion (34), which is an entry cone, and a second portion (38) which has a constant index profile along its length. Further claimed is a method of making an optical fibre with a refractive index which is a maximum along its axis and which is lower at its periphery, the method involving the above process. |
