Optical fiber lengths of sufficiently good quality to produce low light loss in connectors can be made by abrasive polishing of the cut fiber end with successive finer grits. In practice, the abrasive medium is kept wet to provide lubricity and to assist the floating away of loose material. Successive polishing and inspection steps are employed until observation, usually with a microscope, shows that all scratches have disappeared. This method is time consuming and requires considerable operator skill. In addition, such a method is not easily adaptable to automatic machines. There is need, therefore, for a rapid method to generate an optically smooth end surface on an optical fiber which will minimize light losses when two such ends are brought into contact or preferably near-contact as in the case of a light conducting fiber optic connector.
It is desirable to have a procedure producing an end surface on a cut fiber which will contribute less than 1.0 db loss in the light transmitted through a connection between two similarly treated and accurately juxtaposed fibers. It is also highly desirable that such ends be produced either by unskilled labor or in automated equipment.
In an effort to resolve the problems presented by the grinding and polishing process, it has been proposed to utilize a fiber end coating material such as thermoplastic urethane which is cast onto the end of a fiber to produce a button-like cap. This button elastically deforms under pressure to provide good optical contact when used with a compression type connector. This method is described in U.S. Pat. No. 4,221,461. Unfortunately this procedure still does not solve all the problems since it involves on-the-spot application of a liquid substance to the fiber end and subsequent evaporation of a solvent before a cap is developed. In addition, since the final shape of the cap is not flat, compression is needed to maintain good optical qualities, necessitating a more complicated connector.