Investigation of the parameters of planar optical waveguides fabricated by ion exchange in glass

An experimental investigation was made of the dependence of the effective refractive indices of the TM and TE modes on the depth of waveguides fabricated in glass by ion exchange in an AgNO₃ melt. It is shown that approximation of the refractive index profile by the function n(x)=n₀–Δn[(x/d)+b(x/d)²] (d and b are the profile parameters) gives a high degree of accuracy and permits waveguides with the required parameters to be fabricated. The results of direct measurements of the profile n(x) are presented. A method is proposed for determining the effective thickness of diffused waveguides having an arbitrary profile n(x). This method is based on measurements of the effective refractive indices of only the TM or only the TE modes. It is shown that as a result of the anisotropy of diffused waveguides, the proposed method of determining the effective thickness from the difference n*_TE – n*_TM may be used for few-mode waveguides.