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The material dispersion of a tapered fiber is described by Sellmeier’s equation. The dependence of refractiveindex on wavelength and doping concentration is discussed. A He-Ne laser with the output wavelength of632.8 nm is used in the experiment. When the cutoff frequency of the fiber is less than the laser frequency,the guiding modes of a single-mode fiber (at 1550 nm) are investigated. The results show that the originalsingle-mode fiber becomes a multi-mode waveguide. The propagation and mode coupling of the light inthe taper region are analyzed. By controlling the taper end size of the fiber, the unique tapered fiber canconvert a multi-mode beam into a single-mode one.
The dependence of refractiveindex on wavelength and doping concentration is discussed. A He-Ne laser with the output wavelength of632.8 nm is used in the experiment. When the cutoff frequency of the The results show that the originalsingle-mode fiber becomes a multi-mode waveguide. The propagation and mode coupling of the light inthe By controlling the taper end size of the fiber, the unique tapered fiber canconvert a multi-mode beam into a single-mode one.