Arbitrary and reconfigurable optical vortex generation:a high-efficiency technique using director-varying liquid crystal fork gratings

A high-efficiency technique for optical vortex(OV) generation is proposed and demonstrated. The technique is based on liquid crystal fork gratings with space-variant azimuthal orientations, which are locally controlled via polarization-sensitive alignment layers. Thanks to the optical rewritability of the alignment agent and the dynamic image generation of the digital micro-mirror device, fork gratings can be instantly and arbitrarily reconfigured.Corresponding optical vortices carrying arbitrary azimuthal and radial indices are demonstrated with a conversion efficiency of 98.5%, exhibiting features of polarization control and electrical switching. The technique may pave a bright road toward OV generation, manipulation, and detection.

An all-optical modulator based on a stereo graphene–microfiber structure

An in-line,all-optical fiber modulator based on a stereo graphene–microfiber structure(GMF)utilizing the lab-on-rod technique was demonstrated in this study.Owing to its unique spring-like geometry,an ultra-long GMF interaction can be achieved,and a modulation depth of,7.5 dB(,2.5 dB)and a modulation efficiency of,0.2 dB mW^(-1)(,0.07 dB mW^(-1))were demonstrated for two polarization states.The modulation depth and modulation efficiency are more than one order of magnitude larger than those of other graphene–microfiber hybrid all-optical modulators,although at the cost of a higher insertion loss.By further optimizing the transferring and cleaning process,the upper limit of the modulation depth is mainly determined by the loss from the intrinsic absorption,which depends on the light–graphene interaction.Then,the modulator can quickly switch between the on-state and the off-state with a theoretically maximized modulation depth of tens of decibels.This modulator is compatible with the current fiber-optic communication systems and may be applied in the near future to meet the impending need for ultrafast optical signal processing.

Liquid crystal depolarizer based on photoalignment technology

We propose a depolarizer based on the principle of a collection of half-wave plates with randomly distributed optic axes. The design is demonstrated by means of dynamically photopatterning liquid crystal into randomly aligned homogeneous domains. We characterize the liquid crystal depolarizer for 1550 nm and C-band(1520–1610 nm). A degree of polarization of less than 5% is obtained for any linearly polarized light. This study provides a practical candidate for high-performance depolarizers.

Pancharatnam-Berry phase reversal via opposite-chirality-coexisted superstructures

Recently discovered reflective Pancharatnam-Berry phase(PB phase)from chiral anisotropic media(e.g.,cholesteric liquid crystal,CLC)has aroused great interest in the emerging frontier of planar optics.However,the single chirality of common CLCs results in the intrinsic limitation of the same spin-selective PB phase manipulation,which means the reversal of the input spin cannot realize the conjugated PB phase.In this work,an innovative scheme based on opposite-chirality-coexisted superstructures is proposed to simultaneously modulate orthogonal circular polarization and get PB phase reversal.Through refilling CLC into a washed-out polymer network with opposite chirality and delicate photo-patterned structures,reflective optical vortex(OV)with opposite topological charges and vector beams with conjugated spiral PB phases are efficiently generated depending on the incident polarization.Furthermore,OV holograms are encoded to reconstruct polarization-selective OV arrays,indicating the strong capability of such opposite-chirality-coexisted anisotropic media.This work provides a new compact platform for planar optics,and sheds light on the architectures and functionalities of chiral superstructures.