Complete Single Mode Condition for Silica-Titania Rib Waveguides on Glass Substrates

A single mode condition (SMC) for silica-titania rib waveguides on glass is the subject of this work. There are two mechanisms leading to the single mode propagation of a lightwave in rib waveguides. Considering waveguides whose rib width is greater than a thickness of a parent-slab waveguide, the one that would be created by extending the rib in the horizontal direction, the first mechanism is related to the leaking of HE01 and EH01 modes to slab waveguides on either side of the rib. The second mechanism is related to cut-off of those modes. Presented condition is expressed by two criterion functions. The first function, corresponding with the first mechanism, was introduced in our previous work describing the SMC for shallow rib waveguides. The second one, allowing to predict when the first order modes are cut-off is presented in this work. As a result, the complete SMC is formulated. It allows to predict a range of morphological parameters in which propagation is single mode, not only in shallow but also in deep rib waveguides. Moreover, considering the leaking of the HE01 mode, it is shown that the prediction is accurate by using coefficients of criterion functions obtained by the linear interpolation.