Far-off-resonant ring trap near the ends of optical fibers

We propose that micrometer-sized atom traps can be created using the optical dipole force between the ends of two single-mode optical fibers carrying counterpropagating light beams of two different wavelengths from both fibers. The traps have a simple design that is feasible to implement with commercially available products. They can be used as a flexible “atom tweezer” to manipulate atoms in free space without the need for traditional focused laser beams. A particularly interesting feature is the formation of a static ring-shaped trap for properly chosen beam parameters. Furthermore, this ring can be split into two longitudinally adjacent rings. Microscopic ring traps such as this could have important applications in atom interferometry and fundamental investigations of Bose-Einstein condensates.

Figure 1

(Color online) General experimental setup of fiber ring trap. (a) A single ring trap appears at the midpoint between the two fiber ends. (b) Increasing the separation causes the ring trap to split into two identical rings.

Figure 2

(Color online) Optical potentials plotted along a line perpendicular to the fiber axes. The red-detuned light (shown in red) provides an attractive potential, while the blue-detuned light (in blue) is repulsive. The sum (black) gives a ring-shaped potential with an off-axis minimum.

Figure 3

Dipole force derived from Eq. (4). The equilibrium at $z=0$ is stable (i.e., a trap exists) for values of $d<1.15z_{01}$. For values greater than this critical value, such as $d=1.23z_{01}$, the equilibrium at $z=0$ becomes unstable but two additional stable equilibria exist. That is, the trap splits into two.

Figure 4

Contour plot of potential as a function of $z$ and $x$ resulting in a ring trap for $d=\left(\mathrm{a}\right)$ 100 and (b) $160\mu \mathrm{m}$. Each contour is $20\mu \mathrm{K}$.

Figure 5

Longitudinal (a) and transverse (b) plots of the potential of the ring trap for various $d$. In each case, the profile is taken through the actual location of the trap minimum.

Figure 6

Distance of the trap minimum from the center $(z=0)$ as a function of $d$ for the ring trap.

Figure 7

Contour plot of the potential in the $x\text{−}z$ plane with one fiber displaced by $1\mu \mathrm{m}$. Each contour is $20\mu \mathrm{K}$.