Self-alignment and instability of waveguides induced by optical forces

We introduce a fundamental property of waveguides induced by the forces of the guided light, namely, the ability to self-align or be in instability. A nanoscale waveguide broken by an offset and a gap may tend to self-align to form a continuous waveguide. Conversely, depending on the geometry and light polarization, the two parts of the waveguide may be deflected away from each other, thus, being in an unstable state. These effects are unique as they rely on the presence of both the guided mode and the scattered light. Strong self-alignment forces, in both the transverse and longitudinal directions, may be facilitated by near field interaction with polarization surface charges.

Figure 1

(Color online) A single mode slab waveguide broken by an offset and a gap.

Figure 2

(Color online) Transverse force as a function of $d$ for an offset $\Delta$ of 2% of $d$. The permittivity of the waveguides is ${\epsilon }_{\text{r}}={3.48}^2$, and the wavelength is $\lambda =1.55\mu \text{m}$. (a) TE incident mode. (b) TM incident mode.

Figure 3

(Color online) Transverse force $F_{x2}$ as a function of the offset $\Delta$ for different values of waveguide half-width $d$. The solid line corresponds to the analytic analysis and the square markers indicate FEM simulation results. (a) TE incident mode. (b) TM incident mode.

Figure 4

(Color online) Contours of $F_{x2}/F_0$ as a function of $g$ and $\Delta$ for $d=110\text{nm}$ and ${\epsilon }_{\text{r}}={3.48}^2$. (a) TE incident mode. (b) TM incident mode.