Geometric Phase Optical Elements Via Patterned Liquid Crystals

The ultrathin,compactness,and high-efficiency properties make the geometric optical elements very attractive for new applications in polarization beam splitters,helicity multiplexed holograms,imaging,optical communications,quantum science,and nonlinear optics.Recent achivements are focused on the arbitrary optical field manipulation,especially on the generation of structured beams.Liquid crystals(LCs)are broadband applicable electro-optical materials with excellent performance,which can modulate the amplitude,polarization,and phase of the incident light.LC optical elements have prospects in many fields such as optical communication,imaging and sensing.This thesis aims to bring readers some new insights,and demonstrate the designs,fabrications,as well as analysis the functionalities of the ultrathin,dynamically tunable LC optical components based on geometric phase.All these designed geometric LC elements provide a new strategy not only for the high-performance optical elements,but also for the generation,modulation,and detection of high-quality structured beams.It also broaden the applications of geometric LC elements in more research fields of science and technology.The major research results are summarized as follows:1.A dual-frequency liquid crystal polarization grating is fabricated on the basic of geometric concept,and can be demonstrated as a fast-response optical switch.Its periodically and spatially variant director distributions are accomplished by photo-aligning technique.The switching process is realized on single first order by alternating the frequency of certain applied electric field.Through optimizing the cell parameters,the switching On/Off time reaches submillisecond scale via merely alternating the frequency of applied electric field.Moreover,this optical switch still remains the characteristic of high efficiency of polarization gratings.A high diffraction efficiency up to 95%is obtained for a single first order with circular incident polarization.The switching On and Off time reaches 350μs and 550μs,respectively,both of which are in the submillisecond scale.This work supplies a new design for fast-response and high-efficiency optical switch with the merits of easy fabrication and low power consumption.2.A dual-frequency liquid crystal lens integrated with Pancharatnam-Berry(PB)phase was fabricated via a dynamic photo-patterning technique.By introducing the geometric phase,the response time of the lens has been improved,as well as the increasing of the diffractive efficiency.The proposed lens exhibited distinctive polarization-dependent characteristics and ultra-high efficiency rates of 95%.Via merely alternating the frequency of the applied electric field,the switching time between unfocused and focused states were measured in submillisecond.Further,by introducing a blazed PB phase,we propose polarization forked vortex lens(PFVL)which can separate the generated(de-)focused vortices spatially.It exhibits distinctive helicity-dependency and ultra-high diffraction efficiency up to 95%.The topological charges of generated optical vortices are detected via astigmatic transformation.These works supply a new strategy for fast-response,high-efficiency and helicity-dependent elements with merits of easy fabrication and low power consumption.It provides a feasible method for beam generation,focusing and coupling in orbital angular momentum(OAM)mode multiplexing,augmented reality(AR)display,precision instrument manufacturing,particles manipulation and optical communication.3.The propagation dynamics of Bessel beam has been analyzed.An axicon iterm is integrated in a q plate optical axis distribution.Owing to the extrodinary thermal and photochemical stability properties of liquid crystal polymer(LCP),the functionalized LCP film is fabricated by photo-alignment technique,after being polymerizing under the UV light.The holographic pattern is introduced into the LCP system,thus,the functional film could simultaneously modulate the amplitude and phase of the wavefront.The obtained LCP film can directly generated Bessel vortex beam(i.e.higher-order Bessel beam)via modulating the wavefront of the incident Gaussian beam.Different modes of Bessel vortex could be generated in this way.A theoretical diffraction efficiency achieves 100%for a high-order Bessel beam.The topological charges and non-diffracting properties of the Bessel vortex beams are experimentally verified,which compared with the vortex beam generated by q plate.Due to the good stability and flexibility of the LCP film,the LCP can be spin-coated multiple times to match the designed thickness.In addition to the visible band we reported,these functional films can be adopted in a wide range of waveband,not only the ultraviolet spectrum,but also in the infrared and terahertz band.