FIBER-OPTIC AND OTHER WAVEGUIDES: Dispersion characteristics of the first higher modes in single-mode waveguides with elliptic cores
A spectral polarization method was used to determine the cutoff wavelengths and the spectral dependences of the relative group delays of eHE01, oEH01, and e,oHE21 modes in a fiber waveguide with an elliptic core. The group delays of modes of the same configuration (eHE01, oEH01, and e,oHE21 became almost equal for V≥ Vc +0.1 (where V is the normalized frequency) and a strong hopping between them resulted in depolarization of the radiation represented by these modes in a distance amounting to a few decimeters. The high precision of the measurements of some important wavelengths (λc, λe) on the dispersion curves made it possible to check the approximate method for the calculation of the critical parameters Vc in the model of an equivalent circular waveguide and also to check the shift formulas governing the cutoffs of the eHE01 and oEH01 modes. A good agreement between the calculated and measured values was obtained. This spectral polarization method was suitable for the investigation of the dispersion characteristics of single-mode fiber waveguides of any type, and its precision and information capacity are sufficient for checking approximate methods for the calculation of the dispersion characteristics of the first higher modes.