Research On The Three-dimensional Focusing Effect Of One-dimensional On-chip Superlen

In recent years,photonic integrated chips have achieved rapid development,and their applications have become more and more extensive.A variety of on-chip devices have also been deeply studied by researchers.How to achieve high-efficiency controlling of light in small area has been widespread concerned.On-chip metalens are expected to be a solution for onchip integration and multi-functionalization of optical systems due to their outstanding ability of controlling the phase,amplitude,and polarization of light at subwavelength scales.At this stage,the application of on-chip metalenses is mainly focused on realizing efficient on-chip optical information transmission and interconnection.Some reported works have discussed the FWHM of the focusing spot as well as the focusing efficiency.On this basis,we discuss the energy distribution of the focused spot of the one-dimensional on-chip metalens in threedimensional space in detail.Through the optimized design,the focusing efficiency is further improved and the focusing angle is reduced.The main contents and innovations of this paper are:In the first part we design and optimize a one-dimensional on-chip metalens based on the same dielectric nanoantenna element.We design a one-dimensional on-chip metalens consisting of a one-dimensional array of dielectric nanoantennas,which scatters the evanescent wave from the nano-waveguide into free space and focuses this scattered light into a 3D ring.The corresponding phase profile of the metalens is controlled by the relative locations of antennas in the array.Through antenna-waveguide distance optimization,the designed metalens only scatters 1.5% of propagation light into the free space and 55% of the scattered energy is focused into the 3D ring.When we use the antennas with an optimized shape,50.18% of the focused energy is focused in a circular arc of the ring,which subtends an angle of 48°.In the second part we design and optimize a one-dimensional on-chip metalens based on the different dielectric nanoantenna element.According to the far-field scattering of the different nanoantenna elements,we first select appropriate sizes of the nanoantenna element at different positions of the metalens.These antenna elements can efficiently scatter the evanescent wave to the focal point of the lens.We further analyzed the phase difference introduced by the difference in the structure parameters of the elements,then we offset the introduced phase difference through slightly adjustment of the antenna element position,and we finally get a one-dimensional on-chip metalens with a focusing efficiency of 50.42% and a focusing angle of 42°,which means we further reduce the focusing angle with almost constant focusing efficiency.