NEAR FIELD CHARACTERISTICS OF OPTICAL LEAKY WAVES RADIATED FROM OPTICAL CONE WAVEGUIDE PROBES

摘要

Optical tapered cone waveguides are useful optical sensor devices for measurement of near fields of nano meter space,using leaky waves radiated from very small tapered top regions of the optical sharp cone fibers. Also,optical tapered waveguide couplers are important devices for coupling between optical fibers and semiconductor lasers or integrated optical circuits.Electromagnetic field in the optical tapered fibers have been discussed approximately by use of the coupling equation with coupling coefficients derived by equivalent refractive index distributions.Rigorous analysis of the optical field in the tapered waveguides has been shown using conformal mapping method by the author. However,these analyses can be only applied to the slowly varying tapered waveguide and may have large errors for sharp tapered cases. In this paper,optical tapered waveguides of cone shape with linearly varying radius are investigated rigorously as exact boundary value problems for interior core and exterior clad regions,where interior core radius varies linearly along the optical wave propagation axis. Coupling and near field properties are discussed using mode expansion and coupling methods for discontinuities between free space,circular fiber and cone waveguide to analyze the near field distribution for nano space measurement.