A new publication from Opto-Electronic Advances, 10.29026/oea.2024.230171 discusses a miniature tunable airy beam optical meta-device.
The Airy beam has attracted extensive research interest due to its unique properties, such as non-diffraction, self-acceleration, and self-healing. Since its discovery, research has been systematically advancing with the increasing demand for tunable Airy beams, including optical manipulation and laser processing. Optical trapping is typically achieved by tightly focused Gaussian beams to generate optical gradient forces, which are utilized to confine particles within a few micrometers, primarily due to the relatively short Rayleigh length. In contrast, Airy beams, with precise control over their propagation trajectory, can optically manipulate particles in air or liquid along specified paths and possess the capability to traverse obstacles. These beams can also facilitate the processing of surfaces with the desired curvature to enhance the adaptability of laser manufacturing.
Methods for generating Airy beams generally involve complex and expensive optical devices, such as intricate optical lens systems and spatial light modulators (SLM). These technologies provide pathways to achieve tunable Airy beams. Complex optical lens systems can generate tunable Airy beams by adjusting the tilt angle of a cylindrical lens system. SLM achieves tunable Airy beams by executing pixel-level phase changes. Although these methods have advantages in earning a certain degree of control over Airy beams, each technique has its corresponding drawbacks. Complex optical setups inevitably encounter difficulties in achieving precise alignment. SLM faces issues such as low conversion efficiency, limited resolution, incident polarization, and power constraints. Due to the use of bulky components, these technologies also struggle to realize compact and integrated optical systems.
Currently, there exist several studies focusing on the generation of Airy beams utilizing metasurfaces. For instance, various Airy beams with diverse trajectories can be produced by combining cubic phases with different lens profiles. Additionally, integrating the cubic phase and gradient phase into a single metasurface enables precise control over the trajectory of Airy beams. Despite the various methods demonstrated in current research for manipulating the propagation trajectories or focal positions of Airy beams within confined spaces, the real-time adjustment of the generated Airy beams remains challenging.
The authors of this article propose a novel approach to generate tunable Airy beams utilizing a dual-layer, all-dielectric meta-device. The method involves integrating and rotating carefully designed phase profiles, including cubic and two off-axis Fresnel lens phase profiles. By dynamically manipulating the trajectories of Airy beams through the rotation of these two metasurfaces, as illustrated in Figure 1, the tunability of Airy beam generation is achieved. We conduct experimental investigations on a proof-of-concept meta-device to validate its viability and flexibility. These experimental findings align well with the theoretically predicted intensity profiles and propagation dynamics of the Airy beam.
This technique for adjusting the focal spots and propagation paths of Airy beams will be able to facilitate optical manipulation and laser manufacturing. The manipulation capabilities of the Airy beam's propagation trajectory and coverage range can be easily customized by adjusting the parameters of these phase profiles. This approach effectively enhances the modulation flexibility of Airy beams without increasing the device footprint. The real-time rotation of metasurfaces, achieved through piezoelectricity, further enhances the tunability and flexibility of these meta-devices. In comparison to conventional tilted cylindrical telescopic systems or SLMs, the demonstrated meta-device significantly reduces volumetric thickness and operational complexity. This can aid us in better leveraging the three distinctive characteristics of Airy beams: non-diffraction, self-acceleration, and self-healing. Moreover, it can be seamlessly adapted to other working bands without being constrained by polarization or other limitations. Leveraging the benefits of miniaturization and straightforward control, the proposed meta-device is compatible with various optical devices and holds great promise for diverse applications.
Keywords: metasurface / miniature device / tunable Airy beam / tunable meta-device
