Full-Dimensional Geometric-Phase Spatial Light Metamodulation.

Full-dimensional spatial light modulation requires simultaneous, arbitrary, and independent manipulation of the spatial phase, amplitude, and polarization. This is crucial for leveraging the complete physical dimension resources of light. However, full-dimensional metamodulation can be challenging due to the need for multiple independent control factors. To address this challenge, here we propose parallel-tasking metasurfaces to enable full-dimensional spatial light metamodulation based fully on the geometric-phase concept. Indeed, the meta-atoms are divided into several subphases, each of which serves as an independent control factor to manipulate light phase, amplitude, and polarization through geometric phase, interference, and orthogonal polarization superposition, respectively. Therefore, the macroscopic group of meta-atoms leads to metasurfaces that can achieve broadband full-dimensional spatial light metamodulation, as demonstrated by various types of structured light generation. This approach paves the way to future wide applications of light manipulation enabled by full-dimensional spatial light metamodulation.

Exopolysaccharide riclin and anthocyanin-based composite colorimetric indicator film for food freshness monitoring.

Food freshness monitoring is vital to ensure food safety. Recently, packaging materials incorporating pH-sensitive films have been employed to monitor the freshness of food products in real time. The film-forming matrix of the pH-sensitive film is essential to maintain the desired physicochemical functions of the packaging. Conventional film-forming matrices, such as polyvinyl alcohol (PVA), have drawbacks of low water resistance, poor mechanical properties, and weak antioxidant ability. In this study, we successfully synthesise PVA/riclin (P/R) biodegradable polymer films to overcome these limitations. The films feature riclin, an agrobacterium-derived exopolysaccharide. The uniformly dispersed riclin conferred outstanding antioxidant activity to the PVA film and significantly improved its tensile strength and barrier properties by forming hydrogen bonds. Purple sweet potato anthocyanin (PSPA) was used as a pH indicator. The intelligent film with added PSPA provided robust surveillance of volatile ammonia and changed its color within 30 s in the pH range of 2-12. This multifunctional colorimetric film also engendered discernible color changes when the quality of shrimp deteriorated, demonstrating its great potential as an intelligent packaging material to monitor food freshness.

Multi-tasking geometric phase element array based self-referenced vortex interferometer for three-dimensional topography.

Interferometry is a basic physical method to record and reconstruct the three-dimensional (3D) topography of a complex object. However, mainstream interferometers using two beams can be unstable in a volatile environment. Here, we present a self-referenced optical vortex interferometer employing multi-tasking geometric phase elements. Compared with conventional devices, the multitasking elements can enable vortex filters while deflecting the interference beams to achieve high mode purity in broadband. We use the proposed system to reconstruct the 3D topography of a sample while determining its surface elevations and depressions accurately and conveniently in one static interference pattern.

Prototype system for underwater wireless optical communications employing orbital angular momentum multiplexing.

The orbital angular momentum (OAM) multiplexing technology is an essential method to boost underwater wireless optical communication (UWOC) capacity. However, state-of-art UWOC systems are often demonstrated in the laboratory using bulky and high power-consumption instruments, which can be impractical in a realistic environment. In this work, we propose, design and demonstrate a compact and energy-efficient OAM multiplexing UWOC prototype with complete packaging. Indeed, we improve the signal generation, modulation, receiving and processing components by employing the integrated programmable chips. We also employ two geometric phase Q-plate chips as an OAM multiplexer and de-multiplexer, respectively. Owing to the improvement of these components and the optical design, we package the complete UWOC system in two 65cm×35cm×40cm boxes with the power consumption of 20W. Our experiment demonstrates such a completely packaged prototype can support two 625Mbit/s channels (OAM+3, OAM-3) multiplexing in a 6-meter underwater environment with fidelity.

Fundamental challenges induced by phase modulation inaccuracy and optimization guidelines of geometric phase metasurfaces with broken rotation symmetry.

Geometric phase metasurfaces feature complete phase manipulation of light at the nanoscale. While a majority of prior works assume the structure rotation in a fixed lattice of unit cells as equivalent to the element rotation required by the geometric phase principle, we argue that this assumption is fundamentally challenged for many current schematics which induce phase modulation inaccuracy. Here we take the dielectric nanobar type geometric phase metasurfaces as an example and perform an in-depth analysis about the physical origins of the phase modulation inaccuracy: imperfect structure rotation, resonance, tilted incidence and aperiodic arrays. We clarify the trade-off in phase modulation accuracy, efficiency, broadband property and wide angle acceptance. Furthermore, we present several examples of geometric phase metasurface devices to evaluate the performance degradation under different applications. Finally, based on the research, we provide a set of practical design and optimization guidelines to outperform the present devices of geometric phase metasurface.

Feedback-enabled adaptive underwater twisted light transmission link utilizing the reflection at the air-water interface.

Line-of-sight link is widely used in common free-space optical (FSO) laser communications between two fixed locations. While in practical underwater wireless optical communications (UWOC), the environment is relatively complicated. In some scenarios there exist irremovable obstacles, which block the line-of-sight optical link. Fortunately, the air-water interface can function as a natural mirror to enable non-line-of-sight optical link using the total internal reflection. Very recently, twisted light beams carrying orbital angular momentum (OAM) have attracted researchers' great attention to improve the transmission capacity in UWOC. Here, we propose and experimentally demonstrate a non-line-of-sight underwater twisted light transmission link utilizing the total internal reflection at the air-water interface. To overcome the beam fluctuation and drift caused by the change of interface states, we develop a proof-of-concept adaptive feedback system to provide a stable output. Moreover, we study the degrading effects of the slight wind effect, the salinity (turbidity) effect, and the vertical thermal gradient-induced turbulence effect. The results show that the water wave caused by the slight wind causes the most beam drift, the thermal gradient causes the most distortions, and the salinity causes the most power loss.