Modal and material dispersion

Optimization of Modal and Material Dispersions in High-Bandwidth Graded-Index Polymer Optical... 

The optimum refractive-index distribution of the high bandwidth graded-index polymer optical fiber (GI POP) was clarified by consideration of both modal and material dispersions. The ultimate bandwidth achieved by the POP is investigated by a quantitative estimation of the material dispersion as well as the modal dispersion. 

Refractive-Index Profile. The refractive-index profile was approximated by the conventional power law. The output pulse width from the GI POF was calculated by the Wentzel-Kramers-Brillouin (WKB) method (10) in which both modal and material dispersions were taken into account as shown in Equations (3), (4), and (5). Here, aintemodai cTintramodai, and CTtotai signify the root mean square pulse width due to the modal dispersion, intramodal (material) dispersion, and both dispersions, respectively. 

B) Both modal and material dispersions at 780-nm wavelength are considered. 

C) Both modal and material dispersions at 650-nm wavelength are considered. Reproduced with permission from reference 14. Copyright 1996 The Society of Polymer Science, Japan. 

Nihei, E. Ishigure, T Koike, Y. Optimization of Modal and Material Dispersions in High-Bandwidth Graded-lndex Polymer Optical Fibers, in Photonic and Optoelectronic Polymers Jenekhe, S. A. Wyrme, K. T., Eds. ACS Symposium Series, American Chemical Society Washington DC, 1997 Vol. 672, pp 58-70. 

The crucial factor defining the refractive index profile in GI POFs is the coefficient g, and the optimum value for maximizing the bandwidth can be determined from the modal and material dispersions [79-81]. From analyses using the Wentzel-Kramers-Brillouin (WKB) method, the modal dispersion niate-rial dispersion total dispersion fftotai can be expressed as follows ... 

It is well known that the dispersion in the optical fibers is divided into three parts, modal dispersion, material dispersion, and waveguide dispersion. In the case of the SI POF, the modal dispersion is so large that the other two dispersions can be approximated to be almost zero. However, the quadratic refractive-index distribution in the GI POF can dramatically decrease the modal dispersion. We have succeeded in controlling the refractive-index profile of the GI POF to be almost a quadratic distribution by the interfacial-gel polymerization technique (2). Therefore, in order to analyze the ultimate bandwidth characteristics of the GI POF in this paper the optimum refractive index profile is investigated by taking into account not only the modal dispersion but also the material dispersion. 

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