Spectral control and temporal properties of resonant optical propulsion of dielectric microspheres in evanescent fiber couplers

Abstract

Resonant light pressure effects provide new degrees of freedom for optical manipulation of microparticles. In particular, they can be used for optical sorting of photonic atoms with extraordinary uniform resonant properties. These atoms can be used as building blocks of structures and devices with engineered photonic dispersions. To study the spectral shape of the force peaks, we developed a method to precisely control the wavelength detuning between the tunable laser emission line and central position of the whispering gallery mode (WGM) peaks in tapered fiber-to-microsphere water-immersed couplers. Our method is achieved by integrating optical tweezers to individually manipulate microspheres and based on preliminary spectral characterization of WGM peak positions followed by setting a precise amount of laser wavelength detuning for optical propulsion experiments. We demonstrated dramatic enhancement of the optical forces exerted on 20 μm polystyrene spheres under resonant conditions. Spectral properties of the resonant force enhancement were studies with controlled laser line detuning. In addition, we observed the dynamics of radial trapping and longitudinal propelling process and analyzed their temporal properties. Our studies also demonstrated a stable radial trapping of microspheres near the surface of tapered fiber for high speed resonant optical propulsion along the fiber.