Large-area optical metasurface fabrication using nanostencil lithography

Dielectric metalens for miniaturized imaging systems: progress and challenges

Lightweight, miniaturized optical imaging systems are vastly anticipated in these fields of aerospace exploration, industrial vision, consumer electronics, and medical imaging. However, conventional optical techniques are intricate to downscale as refractive lenses mostly rely on phase accumulation. Metalens, composed of subwavelength nanostructures that locally control light waves, offers a disruptive path for small-scale imaging systems. Recent advances in the design and nanofabrication of dielectric metalenses have led to some high-performance practical optical systems. This review outlines the exciting developments in the aforementioned area whilst highlighting the challenges of using dielectric metalenses to replace conventional optics in miniature optical systems. After a brief introduction to the fundamental physics of dielectric metalenses, the progress and challenges in terms of the typical performances are introduced. The supplementary discussion on the common challenges hindering further development is also presented, including the limitations of the conventional design methods, difficulties in scaling up, and device integration. Furthermore, the potential approaches to address the existing challenges are also deliberated.

Review of Metasurfaces and Metadevices: Advantages of Different Materials and Fabrications

Flat optics, metasurfaces, metalenses, and related materials promise novel on-demand light modulation within ultrathin layers at wavelength scale, enabling a plethora of next-generation optical devices, also known as metadevices. Metadevices designed with different materials have been proposed and demonstrated for different applications, and the mass production of metadevices is necessary for metadevices to enter the consumer electronics market. However, metadevice manufacturing processes are mainly based on electron beam lithography, which exhibits low productivity and high costs for mass production. Therefore, processes compatible with standard complementary metal–oxide–semiconductor manufacturing techniques that feature high productivity, such as i-line stepper and nanoimprint lithography, have received considerable attention. This paper provides a review of current metasurfaces and metadevices with a focus on materials and manufacturing processes. We also provide an analysis of the relationship between the aspect ratio and efficiency of different materials.

Multifunctional metasails for self-stabilized beam-riding and optical communication

The photonic propulsion of lightsails can be used to accelerate spacecraft to relativistic velocities, providing a feasible route for the exploration of interstellar space in the human lifetime. Breakthrough Starshot is an initiative aiming to launch lightsail-driven spacecrafts accelerated to a relativistic velocity of 0.2c via radiation pressure of a high-power laser beam in order to probe the habitable zone of Alpha Centauri, located 4.2 light years away from the Earth, and transmit back the scientific data collected in the flyby mission to an Earth-based receiver. The success of such a mission requires the lightsail to provide maximal acceleration while featuring beam-riding stability under the illumination of an intense laser beam during the launch phase. Moreover, the large-area lightsail can be harnessed to improve the margin in the photon-starved downlink channel throughout the communication phase by maximizing the gain of the transmitter despite extending the acceleration period and reducing the stability margin due to the elimination of a portion of the propulsion segments. Owing to the potential of metasurfaces to serve as low-weight versatile multifunctional photonic components, metasurface-based lightsails or metasails are deemed to be ideal candidates to simultaneously address the requirements of photonic propulsion and optical communication in laser-driven deep-space probes. Here, we demonstrate the design of a multifunctional metasail for providing high acceleration and enabling the self-stabilized beam-riding of a spacecraft with a detached payload from the sail while maximizing the transmission gain in the downlink optical communication. The metasail consists of two interleaved sub-arrays of dielectric unit cells operating based on the Pancharatnam-Berry geometric phase, optimized to meet the propulsion and communication requirements, respectively. The beam-riding stability of the sail is analyzed through simulation of the motion trajectory during the acceleration phase, while taking into account the effect of the relativistic Doppler shift, and the downlink communication performance is enabled by providing the required conjugate phase by the metasail elements, resulting in beam collimation. The obtained results verify the multifunctionality of the platform and point toward the promise of metasails for extended mission applications.