Analytical solutions for optical forces between two dielectric planar waveguides immersed in dielectric fluid media

TL;DR

This paper derives simple analytical solutions for optical forces between dielectric waveguides in fluid media, extending previous models to include non-vacuum backgrounds and validating results with dispersion relation methods.

Contribution

It introduces a straightforward set of equations for optical forces in dielectric fluids using Minkowski stress tensor and validates them with dispersion methods, broadening analysis capabilities.

Findings

TM modes are more sensitive to fluid index changes than TE modes.

Repolar forces of antisymmetric TM1 mode increase with higher refractive index.

Symmetric TM0 mode's attractive force weakens as fluid refractive index rises.

Abstract

We investigate optical (transverse gradient) forces between two high-index dielectric planar waveguides immersed in low-index dielectric fluid media. Complimentary to previous studies, we extend optical forces calculations, in order to take into account a non-vacuum (and non-air) background medium, by using the Minkowski stress tensor formulation; we derived a very simple set of equations in terms of the effective refractive indexes of the waveguide eigenmodes. We also used a normalized version of the dispersion relation method to calculate the optical forces, in order to validate our results for different dielectric fluid media. Excellent agreement between the two methods was obtained for all analyzed cases. We show that, due to slot-waveguide effect, the TM modes are more sensitive to changes in the fluid refractive index than the TE ones. Furthermore, the repulsive optical force of the antisymmetric TM1 mode becomes stronger for higher refractive indexes, whereas the attractive force of the symmetric TM0 mode becomes weaker. The methodology and results presented in this work provide a rigorous analysis of nano-optomechanical devices actuated by optical forces in a broader range of materials and applications.