Light Manipulation Devices Based On High Index Nanostructures

Metasurfaces are of great potential to control the spatial optical filed with high transmissivity,flexible design and low cost,and can modify the amplitude,phase and polarization of light within a thickness comparable to the wavelength.Dielectric and metal metasurfaces have been widely used in wavefront reshaping,special beam forming,imaging,display and other fields.In this thesis,we demonstrate novel mode converters and optical tweezers based on dielectric metasurfaces.In recent years,the data traffic in transmission systems is increasing exponentially.Mode division multiplexing(MDM)system is a promising candidate to improve the capacity.In this thesis,a cyclic mode permutation device is proposed based on multiplane light converter(MPLC)using metasurfaces for the first time,and it can be used in a long-distance MDM system to achieve a significant reduction of the intermodal dispersion.Compared with the traditional method of using multiplexer/ demultiplexer and single-mode jumper,this method can overcome the disadvantages of high system complexity,high power consumption,and low integration,which can help commercialize the cyclic mode permutation devices.The proposed 3-mode cyclic mode permutation device consists of 5 metasurface-based phase planes with 16 phase levels.The crosstalks between different modes are less than –20 d B,and the insertion loss is about 0.7 d B.The metasurface-based MPLC is also proposed for the first time as the mode multiplexer.Different from traditional mode multiplexers,the proposed one has high transmissivity and high resolution,and it can be fabricated more friendly with low cost.The 10-mode multiplexer consists of 7 phase planes with 16 phase levels and can exhibit a low insertion of 1.4 d B,with the mode crosstalks smaller than 15 d B.On the other hand,it is well known that optical tweezers are excellent tools for transporting particles in a non-contact manner,which can be applied in biomedical detection,chemical analysis,and optical sensing.This thesis demonstrates an optical tweezer formed by symmetric blazed gratings based on metasurfaces,which can transform the incident Gaussian beam into a Bessel-liked beam,and the transmissivity can be higher than 90% at normal incidence.The optical force is obtained by calculating the electromagnetic field distribution,and the influences of the properties of particle(size,position,and shape)and the period of the blazed grating are investigated.In the proposed optical tweezer,the generated optical force for a spherical particle with a diameter of 2.5 μm and a refractive index of 1.44 can be as large as tens of p N/W at a distance of 14 μm upon the grating,and the incident angle can vary from-50° to 50°.