Low-Loss POFs

Naritomi, M. Dec. 1996. CYTOP Amorphous Fluoropolymers for Low Loss POF Proc. POF-Asia-Pacific Forum, Tokyo. 

Because the high attenuation of PMMA is caused by overtones of the C-H vibrational absorption, the most effective method for obtaining a low-loss POF is to substitute all the hydrogen atoms with heavier atoms such as fluorine, which helps to avoid the water absorption problem mentioned above. The replacement of hydrogen with fluorine also improves the thermal stability, chemical resistance, and electrical properties of POFs. The size of the fluorine atom allows the formation of a uniform and continuous sheath around the carbon-carbon bonds and protects them from attack, thus imparting heightened chemical resistance and stability to the molecule. 

Since all commercially available POF have been of the step-index (SI) type, the modal dispersion limits the possible bit rate of POF links to less than 100 megabit per second (Mb/s). Because of this, it has been thought that POF cannot be utilized for high speed transmission medium. Recently, however, we proposed a large core, low loss, and high bandwidth graded-index polymer optical fiber (GI POF) (7,2) for the first time and we confirmed that 2.5 Gb/s signal transmission for 100 m distance was possible in the GI POF (2,5). 

With various improvements in the fabrication process enabling the avoidance of contaminants and the formation of Gl profiles, low-loss and high-bandwidth POFs have become leading candidates for short-distance networks (e.g.. 

In fact, the excellent low-loss characteristic of CYTOP-based GI POF (e.g., 10 dB/km) is far beyond the requirement of home networking. However, its real uniqueness is the low material dispersion derived from the low refractive index. In the past, there have been several reports on perdeuterated PMMA (PMMA-dg)... 

As far as GI-POFs are concerned, Ohtsuka and co-workers reported several GI-POFs with low losses. By using the interfacial-gel-polymerization technique, the GI-POF attenuation loss was reduced to nearly the same value as that of SI-POF. Single-mode POF was also reported by several researchers around 1992. ... 

The residual hydrogen atoms in such matmals still give rise to their characteristic absorption bands. Although the intensities of these bands will be reduced, their influence in the near IR may still be sufficiently strong to interfere with the low-loss windows. By fluorination of alkyl methacrylate polymers, the refractive indexes of the fluorinated polymers reduce significantly. As a result, it becomes difficult to choose an appropriate cladding material that has lower refractive index and that maintains sufficient numerical aperture for the POF — one of the most important features for a POF. Styrene derivatives, on the other hand, are expected to maintain appropriate refractive indexes even after the introduction of fluorine because their refractive indexes are high (about 1.590). 

Naritomi, M. (1996) CYTOP amorphous fluoropolymers for low loss PDF. Proceedings POF-Asia-Pacific... 

In order to achieve low-loss, high bandwidth and high transmission rate in POF, the fabrication methods for GI-POF have been considerably studied. (1-5) Major efforts were carried out to obtain the optimum refractive index profile with the minimizing modal dispersion of the input hght signal. In the production of GI-POF, many technological problems were experienced to have the index of refraction progressively increases toward the center of POF and to maintain this stable for the duration of its service life. MSI-POF with the multiple index of refraction steps is one approach to solve these problems with low production cost. (6,7)... 

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