Optimisation and scaling effect of dual-waveguide optical trapping in the SOI platform

Optical trapping has potential applications in biological manipulation, particle trapping, Raman spectroscopy, and quantum optomechanics. Among the various optical trapping schemes, on-chip dual-waveguide traps combine benefits of stable trapping and mass production. However, no systematic research has been conducted to optimise on-chip dual-waveguide traps so that the trapping capability is maximised. Here, a numerical simulation of an on-chip silicon on insulator (SOI) dual-waveguide optical trap based on Lumerical FDTD Solutions is carried out to optimise the on-chip dual-waveguide trap. It was found that the waveguide thickness is a crucial parameter when designing a dual-waveguide trap, and its optical trapping capability largely depends on the distance between the two waveguides. We show that the optimal waveguide thickness to achieve the maximum trapping capability generally increases with the gap distance, accompanied by a periodic feature due to the interference and the resonant effects within the gap. This optimal waveguide thickness and gap distance are analysed to have clear scaling effects over the input optical wavelength, which paves the way for the design and optimisation of dual-waveguide traps for various applications.