  Manipulating mega biomolecules and micro-devices with light is highly
appealing. Opto driving torque can propel micro-rotors to translational motion
in viscous liquid, and then separate microsystems according to their
handedness. We study the torque of dielectric loss generated by circular
polarized lasers. The unwanted axial force which causes the handedness
independent translational motion is cancelled by the counter propagating
reflection beams. The propelling efficiency and the friction torque of water
are obtained by solving the Navier-Stokes equation. In the interesting range of
parameters, the numerical friction torque is found to be linear in the angular
velocity with a slope depending on the radius or rotor as $r^3$. The
time-dependent distribution of angular velocity is obtained as a solution of
the Fokker-Planck equation, with which the thermal fluctuation is accounted.
The results shed light on the micro-torque measurement and suggest a
controllable micro-carrier.
