Abstract
In this work, we theoretically study the cavity modes with transverse orbital angular momentum in metamaterial ring based on transformation optics. The metamaterial ring is designed to transform the straight trajectory of light into the circulating one by enlarging the azimuthal angle, effectively presenting the modes with transverse orbital angular momentum. The simulation results confirm the theoretical predictions, which state that the transverse orbital angular momentum of the mode not only depends on the frequency of the incident light, but also depends on the transformation scale of the azimuthal angle. Because energy dissipation inevitably reduces the field amplitude of the modes, the confined electromagnetic energy and the quality factor of the modes inside the ring are also studied in order to evaluate the stability of those cavity modes. The results show that the metamaterial ring can effectively confine light with a high quality factor and maintain steady modes with the orbital angular momentum, even if the dimension of the ring is much smaller than the wavelength of the incident light. This technique for exploiting the modes with optical transverse orbital angular momentum may provides a unique platform for applications related to micromanipulation.
Highlights
Optical angular momentum, which can be separated into spin and orbital parts of light, plays a key role in many fundamental and applied researches [1, 2]
The research indicated that a beam with a helical wave front, characterized by a phase of exp(ilθ), has a momentum component along the azimuthal direction resulting in an orbital angular momentum (OAM) of per photon along the beam axis
We have presented a detailed study on the cavity modes with the transverse optical OAM in a metamaterial ring based on transformation optics
Summary
Optical angular momentum, which can be separated into spin and orbital parts of light, plays a key role in many fundamental and applied researches [1, 2]. Pure transverse OAM of light is especially beneficial in manipulating particles into orbital motion in a two-dimensional plane This is different from the case of the traditional longitudinal OAM, wherein an additional force is required to balance the radiation force along the propagation direction of the light, owing to the existence of the linear momentum component. Because the persistent propagation of the light in the ring is significantly limited by energy dissipation, the confined electromagnetic energy and the quality factor (Q factor) of the modes inside metamaterial ring are studied in order to evaluate the stability of the modes with OAM In this way, the modes with pure transverse OAM in a metamaterial ring could applied to find immediate and interesting applications in small particle manipulation
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