Plastic fiber (POF) is a large core diameter step fiber with a diameter of 1mm.Because of their large size, plastic fibers can be easily coupled to a variety of light sources and connectors without great accuracy.As a result, the connectors commonly used in plastic fibers cost only 10-20% of the connectors used in glass fibers, and plastic fibers require only a blade to complete the cutting process!Plastic fiber is made of a strong material, so it is easy to install without worrying about damaging the fiber.Plastic fiber has been "lurking in the background" among all kinds of fiber;It is a special optical fiber used for lighting and low speed and short range data connections.Now, there is much increased interest in plastic fiber optics, for example, which R&D says has high performance, is easy to install, and costs are low.

From an optical standpoint, the performance of traditional plastic fiber is much lower than that of glass fiber.At the wavelength of 650nm, the loss of the plastic fiber is 0.15-0.2dB per meter, because the plastic fiber has a large Na value and step refractive index distribution, and its frequency band width is also limited.However, plastic fiber optics can still be used to run short links, such as inside an instrument or between desks in a room, over distances of up to 50 metres.

With the development of plastic fiber technology, there have been plastic fiber with lower NA value, which can provide higher frequency band width, and gradient index - plastic fiber (GI-POF), which not only have higher bandwidth, but also lower cost.The current design of graded index plastic fiber provides a bandwidth of 2 GHz over a transmission range of 100 meters, but there are manufacturing problems that hinder its use.Recent developments in new types of lasers (vertical-cavity surface-emitting lasers) hold the promise of very low cost, high power and high speed emitters.

Since plastic fibers do offer so many advantages, step refractive index PMMA fibers are widely used in short range and low speed data transmission applications.However, the traditional step index PMMA fiber does not have its inherent limiting factors.Because of its strong optical absorption properties near visible and near-infrared wavelengths, PMMA fibers are limited to light with a single transmission wavelength of 650nm.But even at this wavelength, the step refractive index PMMA still has a large attenuation, so its actual link length is shortened to 50 meters or less.

Latest advances in plastic fibers: graded index PMMA fibers

Gradual index refraction distributions have long been used in glass fibers to improve their band width and eliminate other limitations.The technology is also introduced into plastic fiber optics.By distributing the refractive index of the fiber core step by step, the plastic fiber obtains many higher frequency band widths.

How to fabricate graded index PMMA fiber

In the process of producing graded index plastic fibers, a mixture of MMA monomers and dopants with increased refractive index is used, placed in a PMMA tube and heated.The MMA permeates the inner wall, creating an expanded "gel" phase in which the polymer is formed.Some of the larger dopant molecules are precipitated out of the colloidal phase, and as the polymerization expands inwards, the dopants gradually become more and more concentrated in the center of the preforming.When the preforming process is completely polymerized, the doped fiber core with graded refractive index is formed, and the outer coated PMMA conduit is used as the cladding.

This kind of graded index PMMA fiber can provide a relatively wide band width.However, like traditional step index PMMA fibers, such fibers are limited to visible wavelengths.