A femtosecond laser raster-type in situ repetitive direct writing technique was used for the fabrication of anti-reflective microhole structures in Germanium (Ge) in the visible near-infrared range (300–1800 nm). This technique builds a layer of microstructured arrays on the surface of Ge, enabling Ge to exhibit excellent anti-reflective properties. The large-area micro-nanostructures of Ge were fabricated using femtosecond laser raster-type in situ repetitive direct writing. Ge microstructures are characterized by their structural regularity, high processing efficiency, high reproducibility, and excellent anti-reflective properties. Experimental test results showed that the average reflectance of the Ge microporous structure surface in the range of 300–1800 nm was 2.25% (the average reflectance of flat Ge was 41.5%), and the lowest reflectance was ~1.6%. This microstructure fabrication drastically reduced the optical loss of Ge, thus enhancing the photothermal utilization of Ge. The many nanoburrs and voids in the Ge microporous structure provided excellent hydrophobicity, with a hydrophobicity angle of up to 133 ± 2° (the hydrophobicity angle of flat Ge was 70 ± 2°). The high hydrophobicity angle allows for strong and effective self-cleaning performance. The femtosecond laser raster-type in situ repeatable direct writing technology has many desirable properties, including simplicity, high accuracy, flexibility, and repeatability, that make it one of the preferred choices for advanced manufacturing. The Ge micro-nanostructured arrays with excellent optical anti-reflective properties and hydrophobicity have become an attractive alternative to the current photo-thermal absorbers. It is expected to be used in many applications such as solar panels, photovoltaic sensors, and other optoelectronic devices.

Optical spectroscopy plays an essential role across scientific research and industry for non-contact materials analysis1-3, increasingly through in-situ or portable platforms4-6. However, when considering low-light-level applications, conventional spectrometer designs necessitate a compromise between their resolution and sensitivity7,8, especially as device and detector dimensions are scaled down. Here, we report on a miniaturizable spectrometer platform where light throughput onto the detector is instead enhanced as the resolution is increased. This planar, CMOS-compatible platform is based around metasurface encoders designed to exhibit photonic bound states in the continuum9, where operational range can be altered or extended simply through adjusting geometric parameters. This system can enhance photon collection efficiency by up to two orders of magnitude versus conventional designs; we demonstrate this sensitivity advantage through ultra-low-intensity fluorescent and astrophotonic spectroscopy. This work represents a step forward for the practical utility of spectrometers, affording a route to integrated, chip-based devices that maintain high resolution and SNR without requiring prohibitively long integration times.

Femtosecond laser processing technology is an advanced sub-micro-processing technique that enables the non-contact processing of various materials. This technology can be used to apply sub-micro structures for purposes such as hydrophilicity enhancement, optical transmittance improvement, and photonics detection. However, when it comes to processing micro/nanostructures on highly brittle materials using femtosecond lasers, there are challenges such as low processing efficiency, generation of debris, and microcracking. In this paper, we propose a method called the out-of-focus femtosecond laser direct writing technique combined with wet etching. This method offers simplicity, speed, and flexibility in preparing dense, large-area sub-microstructured surfaces on the brittle material sapphire. Our detailed investigation focuses on the impact of laser processing parameters (direct writing period, distance of focusing, direct writing speed, etc.) on the sub-microstructures of Al2O3 surfaces. The results demonstrate that this method successfully creates embedded sub-microstructures on the sapphire surface. The microholes, with a diameter of approximately 2.0 μm, contain sub-micro structures with a minimum width of 250 ± 20 nm. Additionally, we conducted experiments to assess the optical transmittance of sapphire nanostructures in the range of 350–1200 nm, which exhibited an average transmittance of approximately 77.0%. The water contact angle (CA) test yielded a result of 52 ± 2°, indicating an enhancement in the hydrophilicity of the sapphire nanostructures with only a slight reduction in optical transmittance. Our efficient fabrication of sub-microstructures on the sapphire surface of highly brittle materials offers a promising method for the production and application of brittle materials in the field of micro-optics.

Three-dimensional (3D) plasmonic metamaterials have become a trend in the application of nanophotonic devices. In this paper, a convenient and inexpensive method for the design of 3D multilayer plasmonic metamaterials is constructed using a one-step self-shielded reactive-ion-etching process (OSRP) and a thermal evaporation system, which provides an efficient and low-cost method for the preparation of surface-enhanced Raman spectroscopy (SERS) substrates. The near-field enhancement of the 3D plasmonic metamaterials provides highly efficient electromagnetic resonance, and highly sensitive and uniform SERS sensing capabilities. The SERS detection results of rhodamine B (Rh. B) and rhodamine 6G (R6G) on this substrate show that the detection limit could reach 10–13 mol/L, and the signal could give expression to excellent uniform stability. The results show that high sensitivity and high robustness SERS substrates can be prepared with high efficiency and low cost.

Because of its incomparable advantages in light field phase control, multifunctional composite, micro-nano integration, and other aspects, metalens has great application potential in many fields. However, the design of metalens requires professional knowledge and rich experience, which makes it difficult for non-professionals to master it quickly, thus hinders the large-scale preparation of hyperlens. By means of MATLAB and finite difference time domain (FDTD) hybrid programming, the design process of dielectric metalens independent of preset physical model is studied, and the automatic design of dielectric metalens is realized. By inputting the required metalens parameters on the software interface written by MATLAB and calling FDTD design simulation program in the background to build the nanostructure, the relationship among the size of the structure, phase, and transmittance can be calculated. According to the required phase distribution, the superlens is constructed and its performance is evaluated by numerical simulation. The design process and software can greatly facilitate the design of metalens by non-specialists.

Electromagnetic metamaterial perfect absorbers have unique subwavelength structures, which can generate effective electromagnetic resonance with the incident electromagnetic wave, and achieve nearly 100% perfect absorption over a specific frequency range. Electromagnetic metamaterial perfect absorbers, especially the terahertz band perfect absorbers, have been widely concerned by researchers at home and abroad, and have made some progress. In this paper, the research progress of the terahertz band-based electromagnetic metamaterial perfect absorber is reviewed, the basic structural characteristics, performance, and theoretical model of the metamaterial absorber are described, and the future development trend and application prospect of them are briefly discussed.

This paper proposes a novel model for an high-efficiency tunable broadband near-infrared absorber. The proposed absorber consists of an Al bottom mirror, SiO2-VO2 hybrid spacing layer, and certain MoS2 top nanostructures. Owing to the thermal tunability of the refractive index of VO2 materials, the near field coupling resonance in the multilayer metamaterials can be tuned by regulating the temperature, and henceforth, the efficiency of the absorber and the absorption band are also tunable. MoS2 has an excellent thermal-stability in the near-infrared range, which can nullify the influence of the temperature regulation of VO2. The results from our study demonstrated that the absorber achieved an average absorbance of 86.5% at 75 °C for a broadband range of 800–2350 nm. At 25 °C, the absorber attained an average absorbance of 96.6% for the wavelength range of 800–1160 nm, and a narrow-band absorption peak around 1489 nm. The absorber we have studied, which was based on tunable metasurfaces, displays tremendous potential for the applications such as camouflage coatings, solar energy, information sensing, and atmospheric environment monitoring.

The reflective optical multi-films with high damage thresholds are widely used in intense-light systems. Metasurfaces, which can manipulate light peculiarly, give a new approach to achieve highly reflective films by a single-layer configuration. In this study, reflective metasurfaces, composed of silicon nanoholes, are numerically investigated to achieve high damage thresholds. These nanoholes can confine the strongest electric field into the air zone, and, subsequently, the in-air electric field does not interact directly with silicon, attenuating the optothermal effect that causes damage. Firstly, the geometrical dependencies of silicon nanoholes’ reflectance and field distribution are investigated. Then, the excitation states of electric/magnetic dipoles in nanostructures are analyzed to explain the electromagnetic mechanism. Furthermore, the reflection dependences of the nanostructures on wavelength and incident angle are investigated. Finally, for a typical reflective meta-film, some optothermal simulations are conducted, in which a maximum laser density of 0.27 W/µm2 can be handled. The study provides an approach to improve the laser damage threshold of reflective nanofilms, which can be exploited in many intense-light applications.

Optical meta-surface element is a kind of two-dimensional ultra-thin device based on the regular arrangement of single-layer or multi-layer sub-wavelength nanostructure array. It can realize the sudden operation of optical amplitude, phase, polarization, the wavelength in a subwavelength scale. In this paper, we design a Huygens meta-surface based on low loss all-dielectric, which can approach the phase control of the outgoing beam after the parallel beam incident on the meta-surface. By the single-layer dielectric nanostructure array, so called Huygens surface, the abnormal transmission without reflection and low loss meta-atoms are realized. Five different beam deflectors were design by these meta-atoms. The different performance of five beam deflectors were discussed, and the effect of wavelength for different beam deflector was investigated next. The highest efficiency of beam deflector is around 85%. The largest deflection angle is 13.248˚ for one polymer grating. These silicon-based beam deflection meta-surfaces may be applied as blazed grating in the monochromator r, precision measurement, and laser shaping.

In this study, the high-efficiency phase control Si metasurfaces are investigated based on aperiodic nanoarrays unlike widely-used period structures, the aperiodicity of which providing additional freedom to improve metasurfaces’ performance. Firstly, the phase control mechanism of Huygens nanoblocks is demonstrated, particularly the internal electromagnetic resonances and the manipulation of effective electrical/magnetic polarizabilities. Then, a group of high-transmission Si nanoblocks with 2π phase control is sought by sweeping the geometrical parameters. Finally, several metasurfaces, such as grating and parabolic lens, are numerically realized by the nanostructures with high efficiency. The conversion efficiency of the grating reaches 80%, and the focusing conversion efficiency of the metalens is 99.3%. The results show that the high-efficiency phase control metasurfaces can be realized based on aperiodic nanoarrays, i.e., additional design freedom.

Recently, dynamic metasurfaces have attracted significant attention due to their ability to actively control electromagnetic waves upon external tunings. The realization of high performance dynamic metasurfaces-based devices remains a great challenge due to very limited modulation depths. Here based on the Huygens metasurfaces, the high efficient active control of transmitted wave was realized by the combination of dielectric resonators and a phase transition material (vanadium dioxide, VO2). At Huygens-mode wavelength, the metasurface demonstrated 82.5% transmission and -80% modulation depth. Besides, it exhibits angle-sensitivity and polarization-independence under normal incidence. The proposed metasurface provides a new way for optical switching, filtering, passive temperature control modulation, which would possess broad application prospects for integrated optical devices, near-infrared photodetection, and smart temperature control systems.

As a non-invasive detection technology, integrated sensors for surface-enhanced Raman spectroscopy (SERS) have been widely studied to realize inexpensive in situ measurements. Unfortunately, most existing SERS sensors are comprised of noble metals nano-structure, which introduce the disadvantages of high cost, poor adhesion, and high wear rates. In this study, integrated SERS substrates based on TiN plasmonic antennas and Si waveguides are investigated. The electromagnetic coupling between TiN plasmons and Si waveguides are demonstrated. In addition, we analyze Raman enhancement as a function of the geometric parameters of the antenna and find a maximum enhancement factor of 9.7 × 105. These SERS substrates provide not only strong enhancement but also low cost and mechanical stability due to the all-dielectric structure. The results show that the proposed configuration leads to inexpensive integrated SERS sensors that can be used for on-road drug detection, environmental protection, and other applications.