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 $eHE_{01}$, $oEH_{01}$, and $e,oHE_{21}$ modes in a fiber waveguide with an elliptic core. The group delays of modes of the same configuration ($eHE_{01}$, $oEH_{01}$, and $e,oHE_{21}$ became almost equal for $V\ge V_c+0.1$ (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 ($\lambda_c$, $\lambda_e$) on the dispersion curves made it possible to check the approximate method for the calculation of the critical parameters $\bar V_c$ in the model of an equivalent circular waveguide and also to check the shift formulas governing the cutoffs of the $eHE_{01}$ and $oEH_{01}$ 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.