Calculation of the power of the field, peneting into the external environment of the weaknessing guide of a single-mode fiber

A regular circular weakly guiding double clad optical fiber is considered. For a single-mode regime of the waveguide, an expression for estimating the proportion of the mode field power penetrating into the outer continuous cladding is obtained using a standard approach and a Gaussian model. It is shown that a simpler and more transparent result is obtained in the Gaussian model, which can be used in practical applications, in particular, when designing this type of waveguides with a minimal proportion of power penetrating into the outer shell.