Theory of resonant absorption effect and its application to single-mode single-polarization fibers

A slight deviation from the resonant condition virtually stops the exchange of energy between two parallel fibers. When one fiber is birefringent, and the other isotropic and lossy, the energy of only one polarization mode swaps back and forth between two fibers and is eventually absorbed. The scalar wave equation is used to investigate the resonant effect. It is found that energy conservation is an intrinsic property of the solution of the scalar wave equation for any trial function, and that standard coupled mode equations obtained from Maxwell´s equations can be derived from the scalar wave equation in an exact way. The resonant effect discussed can provide very high extinction ratio at extremely low penalty of additional loss. For example, an extinction ratio of 1.2×10⁴ dB with a penalty of 0.2 dB can be expected after 1-km transmission for waveguide parameters common in fiber optics