Non-reciprocal devices are essential in many field that require unidirectional wave transmission, such as communications, sensor technology and quantum computing. However, most existing devices are constrained by factors including power supply, external magnetic field, efficiency, and bandwidth. We demonstrated an all-passive, broadband and high efficient nonreciprocal metasurface based on vanadium dioxide (VO2). The electromagnetic thermal coupling simulation results show that when the incident light power density is 40-55 kW/cm2, the transmittance is 90% in one direction and nearly 20% in the other direction. Moreover, benefiting from the non-resonant structure of the metasurface, the device can be used at a broadband wavelength of 7-12 μm. Thus, the demonstrated device has the advantages of broadband and high efficiency, offering a simple but effective scheme of all-passive unidirectional devices.
With orbital angular momentum, tightly focused vortex beams can impose optical torque on particles through momentum transfer. In this paper, based on the Richards-Wolf vector diffraction theory, we examine the forces and moments exerted on Mie particles by a tightly focused beam, including the impact of the beam's intensity distribution and the topological charge (TC) number on particle trapping stability. Numerical calculations are conducted to assess the effects of corresponding parameters on the characteristics of the optical radiation force and the tight focusing properties. Our results show that the direction of the particle’s rotation is determined by the sign of the TC numbers and that there is a direct relationship between the magnitude of the induced torque and the TCs. Furthermore, the stability of particle control can be improved by OAM beams with small TCs. These results have potential applications in light capture, optical storage, and optical imaging.
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