Research Of Multifocal Lens Based On U-shape Nano-antenna Arrays

Conventional optical components rely on gradual phase shifts accumulated duringlight propagation to shape light beams. However, metasurfaces shape light beams byabrupt phase shifts over the scale of wavelength along the optical path. Metasurfaces areoptically thin metal gratings with subwavelength periodicity and consist of series ofplasmonic antennas. Despite having negligible thickness, metasurfaces have flexiblecontrol of the wavefront with phase shifts over2π. Generally, the property ofmetasurfaces changes along with the changes of plasmonic antennas. Metasurfaceconsists of U-shape nanoslits is constructed by carving U-shape slits on a single thinmetallic sheet. Compared with other kinds of metasurfaces, the structure of metasurfaceconsists of U-shape nanoslits is simpler and the thickness is only dozens of nanometers.In this work, several basic optical components based on U-shape metasurface aredesigned including beam splitter, refractive index sensor, optical lens, polarizationdetector and multifocal lens.Firstly, a generalized Snell’s law on basis of metasurface with abrupt phase shifts isderived. Anomalous refraction phenomena are observed to verify the generalized Snell’slaw. Then some beam splitters based on U-shape metasurface with different phasegradient for certain part are designed and simulated.Secondly, we derived the theoretical relationship between the anomalous refractionangle and the refractive index of background from the generalized Snell’s law. Themodulated relationship between anomalous refraction angle and the refraction index ofbackground is shown in this work and it indicates that refractive index sensor based onU-shape metasurface is possible.Thirdly, we designed optical lens based on U-shape metasurface according thephase modulation curve of conventional cylindrical lens. The focusing performance ofthe lens based on U-shape metasurface agrees well with the design.Furthermore, we explored the influence of different polarization to these opticalcomponents based on U-shape metasurface. Contrary phenomenon is found when theincident wave changes from LCP (light-handed circular polarization) to RCP (right-handed circular polarization). In other words, polarization detector based onU-shape metasurface is realized.Finally, as the most important work, the design and modulation of multifocal lensesbased on U-shape metasurface are done. One straightforward method to achievemultifocal lens is the lens array. Yet, the interference between the adjacent focal pointscannot be neglected, especially when the focal points are very close to each other. Anovel method based on optical holography to design multifocal lens is presented. Thenseveral multifocal lenses are designed by using the lens array and the phase computationmethod based on optical holography. These mulitifocal lenses include lenses with samefocal length and different focal length. In addition, we compared the performancesbetween multifocal lenses designed by two methods. What’s more, we proposed amethod to design mulitifocal lens with controllable focused intensity according theholography method. Multifocal lenses with controllable focused intensity are designedand verified by modulation.