Longitudinal Lorentz force on a subwavelength-diameter optical fiber

We analyze the longitudinal Lorentz forces that a propagating continuous-wave light exerts on a subwavelength-diameter optical fiber. Our theoretical results show that, during the propagating process, the guided light exerts no net time-averaged force on the fiber. Via numerical simulation, we find a significant overall pull force of 0.4 pN/mW acting on a 450-nm-diam fiber tip at a wavelength of 980 nm due to the scattering of the end face and a calculated force distribution reveals the feature of a near-field accumulation. Our results may be helpful to the configuration of optomechanical components or devices based on these fibers.

Figure 1

The solid line shows the instantaneous longitudinal force distribution as a function of $z$ for a typical SD silica fiber with a diameter of 450 nm and incident light with a wavelength of 980 nm. The dashed line shows the time-averaged longitudinal force.

Figure 2

(a) Schematic of the reflected and diffracted light at the end face of the SD fiber. (b) Calculated $z$-direction Poynting vector distribution in the $x$-$z$ ($y=0$) cross-sectional plane for a 450-nm-diam silica fiber with a refractive index of 1.45 at a wavelength of 980 nm (quasi-$x$-polarized). The white line represents the profile of the fiber.

Figure 3

(a) Computed instantaneous $E_x$ distribution on the $x$-$z$ ($y=0$) cross-sectional plane. The white line represents the profile of the fiber. (b) Time-averaged Lorentz force over the transverse cross-sectional plane $F_z$ as a function of $z$. (c) Integrated $F_z$ from the fiber end face to a position where $z<9.5$ $\mu$m.