Giant and tunable optical torque for micro-motors by increased force arm and resonantly enhanced force

Abstract

Micro-motors driven by light field have attracted much attentions for their potential applications. In order to drive the rotation of a micro-motor, structured optical beams with orbital angular momentum, spin angular momentum, anisotropic medium, and/or inhomogeneous intensity distribution should be used. Even though, it is still challenge to increase the optical torques (OT) in a flexible and controllable way in case of moderate incident power. In this paper, a new scheme achieving giant optical torque is proposed by increasing both the force arm and the force amplitude with the assistance of a ring resonator. In this case, the optical torque doesn’t act on the target directly by the incident beam, but is transmitted to it by rotating the ring resonator connected with it. Using the finite-difference in time-domain method, we calculate the optical torque and find that both the direction and the amplitude of the torque can be tuned flexibly by modifying the frequency, or the relative phases of the sources. More importantly, the optical torque obtained here by linearly polarized beams can be 3 orders larger than those obtained using the structured beams. This opt-mechanical-resonator based optical torque engineering system may find potential applications in optical driven micro-machines.

Strong Solar Radiation Forces from Anomalously Reflecting Metasurfaces for Solar Sail Attitude Control

“…The torque along the roll axis can then be found by crossing each position vector r , from the center point on the sail to a given sail element, with each corresponding differential element of force and adding up all of the contributions 28 . Since there is no y component of force, the torque along the roll axis comes out to be, …”

Gain-induced large optical torque in optical twist settings

“…Angular momentum carried by light can induce optical torque via scattering or absorption, [1][2][3][4][5][6][7][8][9][10] which was first demonstrated by Beth, [11] and provides applications in DNA unfolding, sequencing, and binding, [12][13][14][15] biological molecular motors, [16][17][18] nano-electromechanical systems, [3,[19][20][21][22][23] and so on. However, harvesting light for a large torque is difficult.…”