The microrotor is an important part in the MEMS. There are many advantages of using light to drive micro-rotors

such as its merits of no mechanical contact

no wire needed and small friction. So it is important to find an effective way to design and evaluate the torque on microrotor. With the development of computer

using the wave optics model to calculate the complex rotors’ optical torques has come true. In this paper

a modularized Matlab program was built to analyze the force-field produced by the optical trapping. The finite-differential time-domain method (FDTD) is attempted to analyze the forces and torques on our designed micro-rotors. The electric and magnetic intensity distribution of the scattered light on the surface of the rotor are calculated. Maxwell’s stress tensor is then employed to calculate the force over the rotor surfaces

enabling the determination of the rotor torque about the axis of rotation. The result is also compared with the experiment.