Fibre Optics Workshop

Principle of operation

Before a glass fibre can be used in real applications outside laboratories, it has to be fixed to a connector. The entire process of stripping, cleaving, cementing and polishing the entrance window of the fixed fibre is termed as preparation of the fibre. Stripping means the removal of the protective plastic cladding of the fibre. This is done with so-called Miller pliers. Cleaving means the defined breaking of the fibre in such a way that the face of it is perpendicular and of optical quality after the process. This can be achieved by slightly scratching the fibre by means of a ceramic or diamond blade when it is bent and exposed to a defined force in direction of the fibre axis. For this process, a variety of tools are available. In a next step, the fibre is supplied with a connector. For a particular fibre, the right connector must be chosen. The ready cut fibre is dipped in one component of a two compound glue and inserted into the ferrule of the connector which already is filled with the second compound of the glue. After a while the fibre is fixed to the connector. By means of a fibre inspection microscope the connector is inspected if the fibre is fixed centrically to the mechanical axis of the connector and the face of the fibre has the desired optical quality. To increase the quality, the face of the fixed fibre is polished. In this workshop, a polishing machine is used where the connector is plugged into the polishing arm of the machine. From time to time the connector is removed, cleaned from grinding material and inspected with the fibre microscope until the desired quality is achieved. Another important technique is the splicing of fibres, which means the direct connecting of two separate optical fibres. there are two technologies which are commonly in use. In both cases, the two fibre ends must be prepared as described and aligned to each other. If one considers that the entire fibre has an outer diameter of 125 µm and the core diameter (this is the actual „tunnel“ where the light is guided through) a diameter of 5 µm, the splicing is a challenging but well established technology. Splicing can be done either by the arc diffusion process or by using a cement by which the hardening process is initiated by UV light. The arc diffusion splicing is a kind of welding where both fibre ends are exposed to an electrical arc. Before the arc is started the position of both fibres with respect to each other are monitored either visually or by a microprocessor unit. For splicing in the field, the second method is used as well. Both fibre ends are placed into the groove of a high precision preformed elastomer where they are aligned to each other due to the structure of the soft elastomer. The groove will now be filled with a UV curing optical cement and a small glass substrate is placed on the top of the arrangement. The UV lamp is switched on and the curing of the cement starts immediately. Since the cement does not interact with the elastomer, the ready spliced fibre is cemented to the substrate which is removed and supplied with a protective cover. Within this workshop, the arc fusion will be applied.
Once a student finishes the training within this work-shop he will become a specialist in this new exiting technology.