Study On Optical Trapping Based On Triangular Wedge Surface Plasmon Waveguides

With the in depth study of bioscience, many new requirements are proposed for manipulating small bio-particles. Thus, conventional optical trapping encounters many challenges. And surface plasmon-based optical trapping becomes novel and efficient nanotools for optical manipulation. Waveguide structure can not only satisfy the requirements of the optical trapping force, but also there is enough space for the continuous manipulation of nanoparticles.In this paper,firstly we studied the electromagnetic field distribution of surface plasmon which is excited on the interface between metal and dielectric.Secondly, based on the Maxwell’s stress tensor we calculate the optical trapping force on nanoparticles. At last, both numerical simulation and analytical treatment are carried out to study the dependence of the optical trapping forces on the size of the apex angle of triangular wedge, the actual shape, height, the refraction index of surrounding medium etc. The calculation on realistic waveguide structures indicates that nanoparticles can be trapped nearby the apex angle of the triangular wedge in comsol. The resonant wavelength becomes 1480nm and the predicted giant optical forces are achievable which can be 5.78nN when the size of the apex angle of triangular wedge waveguides is 20°and the height is 600nm. As nanoparticles moving through the waveguides, optical forces will be fluctuating. The resonance condition and the optical trapping forces will be influenced when the refractive index of the surrounding medium changes. Optical trapping forces reach to 6.082nN at the resonance wavelength of 1430nm with the water surrounding, In the actual process the apex angle of triangular wedge will be round or trapezoidal and optical forces will be reduced. When the apex angle of triangular wedge waveguides is making to round, optical trapping forces will decrease while the radius of the round conner increase, the maximum of which is 937. 1pN. When the apex angle of triangular wedge waveguides is to be trapezoidal, the maximum of optical trapping forces is 369.2pN, and it will decrease while its upper bottom increase. It can be see that the method with round corner is superior to the method with trapezoidal corner.