Metasurface Spiral Focusing Generators with Tunable Orbital Angular Momentum Based on Slab Silicon Nitride Waveguide and Vanadium Dioxide (VO2)

Abstract

The metasurface spiral focusing (MSF) generator has gained attention in high-speed optical communications due to its spatial orthogonality. However, previous MSF generators only can generate a single orbital angular momentum (OAM) mode for one polarized light. Here, a MSF generator with tunable OAM is proposed and it has the ability to transform linearly polarized light (LPL), circularly polarized light or Gaussian beams into vortex beams which can carry tunable OAM at near-infrared wavelength by controlling the phase transition of vanadium dioxide (VO2). Utilizing this MSF generator, the beams can be focused on several wavelength-sized rings with efficiency as high as 76%, 32% when VO2 are in the insulating phase and in the metallic phase, respectively. Moreover, we reveal the relationship between the reflective focal length and transmissive focal length, and the latter is 2.3 times of the former. We further demonstrate the impact of Gaussian beams with different waist sizes on MSF generators: the increase in waist size produces the enhancement in spiral focusing efficiency and the decrease in size of focal ring. The MSF generator we proposed will be applicable to a variety of integrated compact optical systems, such as optical communication systems and optical trapping systems.

Recent Advances in Generation and Detection of Orbital Angular Momentum Optical Beams—A Review

“…To implement such an operating principle, not only functional methods are important, but also the features of the chosen PIC platform. The most common integrated photonics platforms which are used for in-plane OAM applications are based on Siliconon-Insulator (SOI) [161][162][163][164] and Silicon Nitride (SiN x ) [165][166][167]. Because of the low cost, the high material strength of Si and CMOS compatibility, PICs based on the Si platform are particularly well suited as a medium for integrating with other components.…”

Terahertz reconfigurable dielectric metasurface hybridized with vanadium dioxide for two-dimensional multichannel multiplexing

“…Therefore, generating the OAM beam [11][12][13][14][15], achieving OAM multiplexing [13,[16][17][18][19][20][21][22][23], and further realizing twodimensional or multi-dimensional multiplexing combined with OAM and other four physical domains by metasurface [24][25][26][27][28], have shown promising prospects in high-speed and huge-capacity communication systems, especially in terahertz communications. However, existing VO 2 reconfigurable metasurfaces are mainly concentrated on achieving active manipulation of the transmission coefficient [29], reflection coefficient [30], planar-chiral response [31], and Mie resonant [32], or realizing dynamic polarization converter [33,34], metalens [35], absorber [36,37], beam splitter [38,39], OAM generator [40], and meta-holography [41]. The VO 2 metasurface used for OAM multiplexing [42] is rarely reported to the present.…”