Optimization of torque on an optically driven micromotor by manipulation of the index of refraction

Frank M. Wing III; Satish Mahajan; Walter Collett

doi:10.1117/12.580273

30 December 2004 Optimization of torque on an optically driven micromotor by manipulation of the index of refraction

Frank M. Wing III, Satish Mahajan, Walter Collett

Proceedings Volume 5641, MEMS/MOEMS Technologies and Applications II; (2004) https://doi.org/10.1117/12.580273
Event: Photonics Asia, 2004, Beijing, China

Abstract

Since the 1970’s, the focused laser beam has become a familiar tool to manipulate neutral, dielectric micro-objects. A number of authors, including Higurashi and Gauthier, have described the effects of radiation pressure from laser light on microrotors. Collett, et al. developed a wave, rather than a ray optic, approach in the calculation of such forces on a microrotor for the first time. This paper describes a modification to the design of a laser driven, radiation pressure microrotor, intended to improve the optically generated torque. Employing the wave approach, the electric and magnetic fields in the vicinity of the rotor are calculated using the finite difference time domain (FDTD) method, which takes into account the wave nature of the incident light. Forces are calculated from the application of Maxwell’s stress tensor over the surfaces of the rotor. Results indicate a significant increase in torque when the index of refraction of the microrotor is changed from a single value to an inhomogeneous profile. The optical fiber industry has successfully employed a variation in the index of refraction across the cross section of a fiber for the purpose of increasing the efficiency of light transmission. Therefore, it is hoped that various fabrication methods can be utilized for causing desired changes in the index of refraction of an optically driven microrotor. Various profiles of the index of refraction inside a microrotor are considered for optimization of torque. Simulation methodology and results of torque on a microrotor for various profiles of the index of refraction are presented. Guidelines for improvised fabrication of efficient microrotors may then be obtained from these profiles.

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Frank M. Wing III, Satish Mahajan, and Walter Collett "Optimization of torque on an optically driven micromotor by manipulation of the index of refraction", Proc. SPIE 5641, MEMS/MOEMS Technologies and Applications II, (30 December 2004); https://doi.org/10.1117/12.580273

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KEYWORDS

Refraction

Finite-difference time-domain method

Magnetism

Radiation effects

Optical fibers

Geometrical optics

Dielectrics

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