The Research On Design,Fabrication And Applications Of Diffractive Moiré-Lens Based On Liquid Crystal Polymer

Diffractive Moiré-lenses are flat optical elements that can adjust focal lengths by mutual rotation of the two cascade devices.They adjust focal lengths with no need to replace the devices and additional lateral or longitudinal displacement distance,which is easy to be integrated.Moiré-lenses have a large adjustable focus range,and have broad application prospects in fields of adaptive optics,zoom systems,and integrated optics.As far as the authors know,its physical fabrication has only realized through the array-structure design of metasurface and related processes or femtosecond laser direct writing.However,the fabrication and application of diffractive Moiré-lenses are greatly limited due to its complex design processes,strict fabrication requirements and high cost.In this thesis,we proposed to combine the above two concepts for the first time.We have designed and realized physical fabrication of the diffractive Moiré-lens with the low-cost liquid crystal polymer with mature manufacturing technology as the material,and carried out some related application.The main research results are as follows:The phase diagram of diffractive Moiré-lens simulation with complete concentric circle pattern is complicated based on its transmission function and the principle of phase grading.When the rotation angle changes from negative to positive,the negative to positive focal length of Moiré-lens can be realized smoothly.In addition,the simulation of Moiré-lens with a certain offset value instead of zero as the focal length symmetry center is realized,which satisfies more practical application requirements.The fabrication method of liquid crystal photoalignment has the advantages of non-contact,good realization of complex phase design and wide substrate applicability.Therefore,we fabricated the diffractive Moiré-lens based on liquid crystal polymer by photoalignment successfully in demonstration,using azo dye solution as the alignment layer.The pattern area is 5 mm×5 mm,and the pre-designed phase pattern has been well presented.The transmittance is over 90%when the incident light is in visible range.The focal length of cascaded Moiré-lens is verified well changed by simple mutual rotation.The Moiré-lens has the range of refractive power between±0.85 m^-1within the efficient tuning range±π/2,which also has high 75%diffraction efficiency.The cascaded Moiré-lens based on liquid crystal has met the demand of application within a longer wavelength range.As to the practical application of cascaded Moiréelements,we designed an optical edge detection system with dynamic resolution based on liquid crystal polymer Moiré-lens,and carried out experiments.The great 2D edge detection performance is confirmed when the incident light is 450 nm,532 nm and 635 nm,which proves the applicability of the samples for the whole visible light range.The minimum edge width is 13.2μm,and can be adjusted within 100μm when the rotation angle changes from0 toπ/2,which has great potential to be used in compact optical systems.