Enhancement of optical forces using slow light in a photonic crystal waveguide

The paradigm of slow light in photonic crystal waveguides has already led to startling advances in nonlinear interactions and optical switching. Importantly, as slow light implies a highly reduced group velocity, this also leads to an original route for the enhancement of optical forces by appropriate tuning of the waveguide properties. Here, we demonstrate the use of slow light to enhance the guiding of sub-micron dielectric particles on a photonic crystal waveguide. Studies are based on a range of particle sizes and we observe a four-fold enhancement in guiding velocity simply by changing the wavelength of the exciting laser within the slow light region. The particle velocity is therefore seen to be dependent upon the group velocity of light in the waveguide in agreement with force simulations. Finally, the enhancement of the lateral trap stiffness transverse to the waveguide axis further confirms the benefit of slow light for particle manipulation.