![]() ![]() Soft glass fibers are often fabricated with the double crucible method, where core and cladding are simultaneously drawn from the crucible. Fabrication Methods Not Involving a Preform For that purpose, ultraviolet nanosecond laser pulses are shot at the fiber through some phase mask just before the fiber is coated.Ĭoncerning the fabrication of fiber preforms, see the article on fiber preforms. It is also possible to write type-II fiber Bragg gratings into the fiber during the fabrication process. ![]() For example, one sometimes applies an overpressure to the preform in order to prevent the collapse of the tiny air holes and/or to control the thickness of the resulting tiny silica strands. for fluoride fibers, have a much smaller temperature range suitable for pulling, and the method is accordingly more delicate.Īdditional measures may be required for drawing photonic crystal fibers. Such spun fibers have become common for optical fiber communications with high data rates and are also used for certain fiber-optic sensors.įiber pulling works quite well for the usual silica fibers, since silica has a rather broad glass transition, i.e., a large range of temperatures in which the viscosity is in a suitable range. Particularly for fibers which need to have a small polarization mode dispersion, it is common to spin either the preform (around its axis) or the fiber itself during the pulling process. Some fibers need to be spun for achieving low PMD. Simpler machines for smaller production volumes may only use pulling speeds of the order of 1 m/s. Particularly telecom fibers are needed with long length, and it is desirable to obtain a high pulling speed of typically well over 10 m/s or even above 20 m/s. The fiber from a single preform can be many kilometers long. Industrial fiber drawing towers work with rather high speeds. Additional PVC or similar protective coatings can be made by extrusion after the drawing process. Typical coating materials used are acrylate, silicone and (for fibers with high temperature resistance) polyimide, but there are also carbon and metal coatings for special applications. for telecom fibers frequently consist of two or more different layers for optimum suppression of microbends. Multiple coating layers may be applied using a suitable sequence of coating cups (applicators) and curing facilities. For that purpose, the fiber can (after having be cooled down enough) be fed through a coating applicator, followed by a curing oven and/or a UV irradiator for curing the coating. A protective polymer coating is usually applied directly before winding up the fiber.īefore the fiber is wound up, one usually applies a thin polymer coating for mechanical and chemical protection. This also leads to a quite constant fiber core diameter, which is important for various reasons. ![]() During the pulling process, the fiber diameter is held constant by automatically adjusting the pulling speed (and possibly the furnace temperature) with an automatic feedback system (containing a diameter monitor just below the furnace). It is then wound up on a spool, using a spinning machine. When the preform is heated in a furnace (oven) at the top of the drawing tower, such that its bottom part becomes soft, a thin fiber can be pulled out of the bottom of the preform and cooled to become solid. Carefully controlled pulling is required for obtaining a constant fiber diameter. Along its axis, the preform contains a region with increased refractive index, which will form the fiber core. The preform is a glass rod with a diameter between about 1 cm and 10 cm and roughly 1 m to 2 m length. Most glass fibers are fabricated by pulling from a so-called preform in a fiber-drawing tower, an apparatus which is typically several meters high. Fiber Pulling from a Preform Figure 1: A fiber drawing tower. In the following, this article first discusses how a fiber can be made from a preform, then how preforms are fabricated, and finally methods not requiring a preform. based on extrusion, are common for plastic optical fibers and for some specialty glasses. Preform-based methods are most important at least in the context of glass fibers (which are mostly silica fibers), whereas direct methods, e.g. In a first step, these can be divided into methods involving a so-called fiber preform and methods of direct fiber production. There is a wide range of methods for the fabrication of optical fibers. ![]()
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