Enhancement and manipulation of optical interaction between coupled nano-waveguides in hollow-core fibers

Optomechanical forces between evanescently coupled nano-waveguides serve as useful mechanisms to configure versatile functionalities of macro- and nano-devices. Strategies for boosting the optomechanical interaction strength are particularly compelling for the field of nanotechnologies. Here we show that the optical coupling strength between nano-waveguides can be enhanced by orders of magnitude when they are confined in hollow-core fibers. The presence of hollow core greatly increases the overlap integral between the nano-waveguides through excitation of the core modes. The excited higher-order core modes are able to mediate a long-range optomechanical interaction between the waveguides even though they are separated by tens of optical wavelength. It is found that the optical forces between the nanofibers can be switched from attractive to repulsive ones purely by tuning the gap between the nanofibers due to the optomechanical back-action effect induced by the higher-order core modes. The enhanced optomechanical coupling can be exploited to manipulate the collective eigenfrequencies of the coupled nano-waveguides via the optical spring effect. Our observation may find applications on the design of waveguide couplers embedded in the hollow core, or to realize miniaturized acoustic sensors.