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With the acceleration of urbanization, the amount of solid waste in rural areas continues to increase, bringing serious pollution problems to the environment. Therefore, the resource utilization of rural solid waste has become one of the important tasks of current environmental protection work. This article analyzes the current situation of rural solid waste resource utilization and proposes a path to achieve it, including government guidance, technological innovation, and social participation. At the same time, this article also discusses the difficulties and strategies for achieving the resource utilization of rural solid waste, providing a reference for the realization of rural solid waste resource utilization.

A solar absorber based on the Si3N4–W–Ti–SiO2 structure is presented. The absorption rate of the absorber is over 90% in the bandwidth of 500 nm to 2995 nm with an average absorption rate of 98.3%.

In this paper, a band-stop filter based on a surface plasmon polariton metal–insulator–metal is designed and studied. The relationship between wavelength and filter transmittance is simulated using the finite difference time domain method and coupled mode theory. Compared with a single-diamond resonator, the minimum transmittances of the double-diamond resonator and double-rectangular resonator at a fixed wavelength are increased by 11.33% and 14.25%, respectively, achieving an enhancement effect. The research results also show that the sensitivity of the filter can reach 860 nm/RIU. The structure has good application prospects in optical integration, optical communication, and optical information processing.

An all-fiber target-type flow velocity sensor was proposed and experimentally demonstrated based on the Michelson interferometer (MI). Commercially available single mode fiber (SMF) was used as the basic material and assisted with the arc discharge technology the sensing structure can be fabricated with high efficiency and quality. The designed sensor structure contains a peanut-shape structure that acts as a coupler/splitter, a SMF that acts as a cantilever beam, and a spherical tip that acts as a target, which all can be realized by arc discharge technology. The simulation verifies the effectiveness and high sensitivity of the peanut-shape structure for flow velocity measurement, and the key parameters were optimized. A comprehensive experiment was carried out on the flow velocity experiment. The experimental results show that the sensor has high sensitivity of −1.30 nm/(cm/s), precision of 1.4% and detection limit (DL) of 0.015 cm/s in the range of 0–11 cm/s. In addition, the temperature sensitivity is 58.5 pm/°C and the flow velocity-temperature cross-sensitivity is less than 0.05 (cm/s)/°C. Such a high-sensitivity, low cross-sensitivity and low-cost sensor, is very promising for the applications on high-precision liquid and abysmal sea flow velocity measurement.

We experimentally demonstrated a high sensitive gas pressure sensor, which also has more concise processing steps and lower cost. The sensor was fabricated by splicing the single-mode fiber (SMF) and a short section of hollow-core fiber (HCF) which was filled with a Polydimethylsiloxane (PDMS) film to form an enclosed air microcavity with the length of 55 μm. The thin PDMS film also plays a role in reflecting the beam. The thermo-optical effect and the thickness of PDMS film can affect the cavity that is sensitive to external pressure. When the thickness of the PDMS membrane is 3 μm, the measured gas pressure sensitivity reaches to 52.143 nm/Mpa, the linearity is 99.86%, and the cross-sensitivity of the gas pressure over temperature is lower than 2.51 × 10−3 Mpa/°C. Moreover, the compact structure, high sensitivity, high mechanical strength, and convenient fabrication make it suitable for measuring gas pressure in harsh conditions.

A novel fiber-optic sensor is demonstrated based on half-tapered single-mode-multimode-single-mode fiber structure, which consists of the multimode interferometer (MMI) and Mach–Zehnder interferometer (MZI). The comprehensive experiments in terms of temperature and refractive index (RI) are performed and the immunity to varied RI is observed in MMI. Further, to enhance precision of measurement, the fringe-visibility difference (FVD) based demodulation method is proposed to quantify and eliminate the influences from the fluctuations of light source power and ambient temperature. The corrected sensitivities present high linearity (>0.99) and the detecting resolution reaches 0.072 °C and 2.89 × 10−5 RIU, respectively. With FVD, our sensor can complete simultaneous measurement of RI and temperature without the crosstalk from light source power and ambient temperature.

An in-line Mach-Zehnder interferometer based on a multimode-fiber-assisted tapered open-cavity (TOC) is proposed. Light field distributions of the TOC were investigated using beam propagation method with different offsets and diameters of the taper waist. Bias and uniform taper (BT and UT)-based structures were fabricated and compared using one- and two-step arc-discharge methods, and comprehensive tests were then conducted considering axial-strain. The experimental results show that the UT structure has more than −45 pm/µɛ linear wavelength shift with the applied axial-strain. Owing to its compact size and low cost, the proposed sensor is promising for axial-strain-related high-precision engineering applications.

To endow catalyst supports with excellent co-catalytic activity is an effective way to strengthen methanol-tolerance of Pt-based catalysts towards oxygen reduction reaction (ORR). In this study, nitrogen-doped molybdenum selenide/biomass-derived carbon (N-MoSe2/BC) composite as a Pt-support/co-catalyst is prepared via a synchronous synthesis method to enhance methanol tolerance. The porous structure of N-MoSe2/BC with N-doping can improve the exposure of coordinated Mo–Sex sites along MoSe2 edges and provide the oxygen diffusion channels to promote ORR activity. Pt-N-MoSe2/BC (Pt, 5 wt.%) shows high activity (14.83 mA cm−2) and selectivity (4e− pathway) towards ORR, promising durability (11.9% decline) and excellent tolerance against methanol-crossover effects, which are superior to those of commercial Pt/C (10 wt.%). With the introduction of pyridinic N, graphitic N and Mo−Nx in MoSe2/BC, more active sites on Pt (111) facets are activated to enhance charge transfer efficiency and ORR activity. Both N-species in BC and exposed edge sites in N-MoSe2 contribute to high methanol-tolerance and co-catalytic activity towards ORR. Therefore, the remarkable ORR activity is originated from the synergistic effects among well-distributed Pt, N-species, and active edge sites of MoSe2. Design of porous (N)-MoSe2/BC provides a promising direction for preparation of co-catalyst/support with strong methanol tolerance and ORR activity.

To improve the sluggish kinetics of oxygen reduction reaction (ORR) is critically important for the development of fuel cells. It is generally recognized that catalysts with multi-transfer channels and varied active sites can energetically facilitate the ORR-relevant species transfer to improve the oxygen reduction rate. In this study, N-doped carbon nanotubes-crossed MoS2/carbon (N-MoS2/CNTs/C) catalysts are synthesized at temperatures of 600–900 °C using an in-situ reduction self-assembly method. In both acid (0.5 M H2SO4) and alkaline (0.1 M KOH) media, N-MoS2/CNTs/C (800 °C) catalyst exhibits a promising ORR activity and favors a four-electron reduction pathway. The highly-maintained tubular CNTs in N-MoS2/CNTs/C (800 °C) can supply the multidimensional pathways for transferring the ORR-relevant species. N atoms doping can not only increase the structural defects of MoS2 lattice (Mo–Nx) to expose more Mo–Sx sites, but also induce various N functional groups into the carbon matrix (CNTs and porous carbon), which are favorable to improve the activation, adsorption and reduction of oxygen. Therefore, the distinct structures endow the N-MoS2/CNTs/C catalysts with high activity towards ORR. Furthermore, the N-MoS2/CNTs/C (800 °C) also exhibits a promising ORR activity in neutral medium (microbial fuel cells (MFCs)). MFCs with the N-MoS2/CNTs/C (800 °C) cathode exhibits the maximum power density of 987.4 mW m−2, which is much higher than that of commercial Pt/C (601.96 mW m−2). These results indicate that N-MoS2/CNTs/C catalysts can be considered as a promising alternative to Pt/C for ORR.

In this paper, an all-fiber novel fabricated Mach-Zehnder interferometer (MZI) based on refractive index (RI) sensor is presented and simulated. This RI sensor is composed of a single-mode fiber (SMF) with a core diameter of 9 μm and a multimode fiber (MMF) with a core diameter of 105 μm. The microgroove can be etched by femtosecond laser or ground by grinding machine technology. It greatly reduces the limitations of structure fabrication. The RI response of this sensor is obtained by beam propagation method. In the range of 1.33-1.334 RIU, the RI sensitivity is -10373 nm/RIU and the linearity is 99.98% by wavelength demodulation. The intensity demodulation shows a nonlinear trend, and the sensitivity increases with the increase of RI . The maximum RI sensitivity is -9614 dB/RIU, and the fitting is 98.69%. The structure has the advantages of simple manufacture, high sensitivity and good linearity. It is very suitable for the practical applications of RI sensing with high sensitivity.

A novel simple plasmon filter based on metal–insulator–metal plasma waveguide is proposed. The relationship between the wavelength and the transmission of the filter is investigated by using the finite difference time domain (FDTD) method. Based on the mutual enhanced filtering effect of resonators, a filter combining double square ring and rectangle is designed. Compared with the square ring resonator structure, the minimum transmission is increased by 10.04% and 47.7%, and the filtering reaches 94.4% and 99.9% at 528 nm and 815 nm, respectively. This waveguide filter may become a potential application for the design of devices in highly integrated optical circuits.

In this paper, to enhance practicality, a novel tapered thin-core fiber (t-TCF) based modal interferometer is proposed and demonstrated experimentally. The light field distribution of t-TCF structure is investigated by a beam propagation method, and the quantitative relationship is gained between light intensity loss and waist diameter. Under ~30 μm waist diameter, multiple t-TCF based sensor heads are fabricated by arc-discharged splicing and taper techniques, and comprehensive tests are performed with respects to axial strain and temperature. The experimental results show that, with near-zero wavelength shift, obvious intensity strain response is exhibited and negative-proportional to the reduced length of TCF. Thus, the maximum sensitivity reaches 0.119 dB/με when the TCF length is equal to 15 mm, and a sub-micro-strain detection resolution (about 0.084 με) is obtained. Besides, owing to the flat red-shifted temperature response, the calculated cross-sensitivity of our sensor is compressed within 0.32 με/°C, which is promising for high precision strain related engineering applications.

In this paper, a novel in-line modal interferometer for refractive index (RI) sensing is proposed and experimentally fabricated by cascading single-taper and multimode-double- cladding-multimode (MDM) fiber structure. Owing to evanescent field in taper area, the ultra-sensitive and linear intensity-responses to the varied surrounding RI are gained in both single- and double-pass structures. Moreover, the crosstalk from temperature can be effectively discriminated and compensated by means of the RI-free nature of MDM. The experimental results show that the RI sensitivities in single- and double-pass structures, respectively, reach 516.02 and 965.46 dB/RIU (RIU: refractive index unit), both with the slight wavelength shift (~0.2 nm). The temperature responses with respect to wavelength and intensity are 68.9 pm&deg, C&minus, 1/0.103 dB&deg, 1 (single-pass structure) and 103 pm&deg, 1/0.082 dB&middot, &deg, 1 (double-pass structure). So the calculated cross-sensitivity of intensity is constrained within 8.49 &times, 10&minus, 5 RIU/&deg, C. In addition, our sensor presents high measurement-stability (~0.99) and low repeatability error (&lt, 4.8&permil, ). On account of the ~620 &mu, m size of taper, this compact sensor is cost-efficient, easy to fabricate, and very promising for the applications of biochemistry and biomedicine.

Recently, metasurface has attracted lots of attentions because of its great capability in phase engineering for the transmitted cross-polarization light, and many functional optical elements have been designed and investigated. Commonly, the co-polarization and cross-polarization lights will coexist in the transmitted fields. Here, we propose a planar metalens composed of L-shaped nanoholes, which can focus an incident plane wave to two different focal spots in longitudinal direction for the co-polarized and cross-polarized transmitted lights respectively. In our design, the focal length of the transmitted cross-polarized lights can be tuned easily according to Fermat principle. Meanwhile, the focal length of the co-polarized transmitted lights can also be modulated by the ring number of the designed metalens. Because of the polarization-independent characteristic of the L-shaped nanoantenna, the designed planar metalens can also be suitable for both linear and circular polarized incident lights.

In-fiber modal interferometers have been widely used in the applications of biochemical sensing, mine safety and health monitoring of buildings. The temperature feature of sensors is one of the most important characteristics, but the studies are rarely reported under the condition of subzero temperature. In this paper, through core-mismatch fiber splicing method, three in-fiber Mach-Zehnder interferometers (MZIs) are fabricated based on single-mode fiber (SMF), erbium-doped fiber (EDF, with core diameter of 3.6 μm) and multimode fiber (MMF, with core diameter of 50 μm), respectively. Their interference patterns are investigated through beam propagation method and Fast Fourier Transform analysis. The comprehensive tests of temperature are then performed in the range from -40 to 0°C. The experimental results show that, in subzero temperature, the transmission spectrums of MZI sensors based on single mode fiber (SMF) and MMF are worsened in terms of fringe visibility and intensity. And the sensitivity of MMF-based structure is 68.8 pm/°C with a 12.3-dB deduction of fringe visibility. Comparatively, the EDF-based MZI presents ideal sensitivity due to negative gain-temperature feature. By calculation, the 124.7 pm/°C sensitivity is gained with the linearity of 0.9892. Moreover, 10-dB enhancement in intensity and over-20-dB fringe visibility are demonstrated, which indicates that the EDF-based sensor is potential and promising for the applications of cryogenic sensing.

The principle and the characteristics of the bias-scanning based tunable localized surface plasmon resonance (LSPR) sensors for environmental refractive index have been theoretically and numerically investigated in detail. The sensors exhibit linear negative-shifts in the scattering-bias spectral position when the refractive index of the surrounding medium increases. By bias-scanning, a single-wavelength measurement for sensing the environmental refractive index can be realized effectively. In addition, we demonstrate that the sensing performance of the designed sensor can be adjusted by nano-scale manipulations of metal nanoparticles' sizes and shapes. The proposed devices may pave the way for the development of electrochemical sensors that can convert spectrum scanning into bias scanning.

An in-fiber hybrid modal interferometer (HMI) is theoretically and experimentally demonstrated in a section of bias-tapered multimode fiber only fabricated by arc-discharge technique, which consists of multimode interferometer (MMI) and Mach-Zehnder interferometer (MZI). The MZI has the sensitivity as high as −31.08 nm/RIU, but the MMI presents the immunity of both wavelength and intensity to ambient refractive index (RI). In strain test, MMI has a 9.8-dB intensity deduction and MZI shows high wavelength sensitivity (−6.31 pm/ $\mu \varepsilon$ ). Thus, our HMI shows a strong multi-parameter discriminative proficiency and simultaneous measurement of RI, strain and temperature is achieved by the means of joint wavelength and intensity demodulation-based inversion-matrix method. Such a compact and low-cost sensor, without the crosstalk from the temperature and the light source, is very promising for the applications of biochemical sensing and structural health monitoring.

Self-organized periodic surface structures on ZnO have been observed after multiple linearly polarized femtosecond laser pulse irradiation. The observed self-organized structures are attributed to the second harmonics in the sample surface excited by the incident laser. The grating orientation could be adjusted by the laser polarization direction. We also find that fluences play an important role in the formation of self-organized nanostructures.

Laser-induced periodic surface structures with different spatial characteristics have been observed after multiple linearly polarized femtosecond laser pulse (120 fs, 800 nm, 1 Hz to 1 kHz pulse repetition frequency) irradiation on alloys. With the increasing number of pulses, nanoripples, classical ripples and modulation ripples with a period close to half of classical ripples have all been induced. The generation of second-harmonic has been supposed to be the main mechanism in the formation of modulation ripples.

We presented a microfabrication process for optical volume vortex grating inside glass by femtosecond laser pulses. The self-trapped filament of femtosecond laser pulses can induce hundreds μm-long region refractive-index changes in glass. We realized the restructured optical vortex beams using a collimated He–Ne laser beam. The maximum first-order diffraction efficiency was about 19.6%. The volume vortex grating structure fabricated in glass is polarization dependent.

Modulation grating has been achieved by two interfered femtosecond laser pulses on the surface of the silica glass. The modulation grating formed at the middle of each bulge of the common grating and was attributed to the higher-order modulation arising from second-harmonic generation (SHG) of the femtosecond laser pulse incident to the surface of silica glass. The periods and depths of the fundamental grating and the modulation grating have been observed by using an atomic force microscopy (AFM). Experimental results show that the average depth of the modulation grating is nearly a half of the depth of the fundamental grating.

A series of symmetrical nanoantennas with a symmetrical axis orientation angle of 45° or 135°, which are suitable for both X/Y linear and circular polarizations incidences simultaneously, have been designed and investigated in detail. We have deduced the transmitted matrix of the metasurface structure by rigorous mathematical theory, and found that the essential reason for the polarization-independence characteristics is that there are the same transmitted amplitudes and phases under the incidences of X/Y linear and circular polarization lights due to metasurface structure with the symmetrical axis's orientation angles of 45° or 135°. Based on the V-shaped, C-shaped, U-shaped and elliptical slit nanoantennas, we have verified the proposed theory fully by numerical simulations. The independence of the incident polarizations is very important for the practical applications and developments of the metasurfaces.

In recent years, with the developments of the laser technology, femtosecond laser technology is becoming more and more consummate as a novel technology. Femtosecond laser pulse is also becoming into a powerful tool for microfabrication and micro-machining of various multi-functional structures in dielectric materials through multi-photon absorption because of its high-quality and damage-free processing. Up to now, many highquality material processing techniques have been achieved by using femtosecond laser pulses with the methods of directly writing [1-10] and holographic fabrication [11-22], such as waveguide [1], special diffractive optical elements (DOE) [4-10], micro-gratings [11-15], and photonic crystals [16-20]. Because multiphoton nonlinear effects play a major role in this process, the resulting change in refractive index or cavity formation can be highly localized only in the focal volume where the fluence is above a certain material dependent threshold, which makes it possible to micro-fabricate devices inside the bulk of transparent materials. These structures were usually fabricated with a focused beam and written dot by dot by translation of the sample with respect to the focal point.

We investigate the formation of micro- and nano-structures induced by femtosecond laser pulses on the surface of amorphous alloys. Periodic ripples aligned perpendicular to the direction of laser polarization has been observed. Particularly aperiodic ripples with orientation parallel to the laser polarization are formed depend on the number of laser pulses. Nanoripples with orientation parallel to the laser polarization are formed over the entire laser-scanned regions. Measurement of X-ray diffraction shows that the amorphous structures still keep their original amorphous states.

With the developments of the laser technology, femtosecond laser technology is emerging as one of the useful microfabrication tools in recent years for both microfabrication and micromachining of various multi-functional structures in dielectric materials through multiphoton absorption because of its high-quality and damage-free processing. Many highquality material processing techniques have been achieved to date by using femtosecond laser pulses with the methods of holographic fabrication [1-8] and direct writing [9-16], such as micro-gratings [1-4], photonic crystals [5-8], waveguide [9] and diffractive optical elements (DOE) [10-16]. In this chapter, we have reported to fabricate several diffractive optical elements (DOEs) on the surface of the metal film or inside transparent silica glass by femtosecond laser pulses writing directly. Firstly, we introduce a method for holographic data storage with the aid of computer-generated hologram (CGH) on the metal film (Au) by femtosecond laser pulses writing directly. Both the simulated and the experimentally restructured object wave show high fidelity to the original object. Then, we introduce a novel method for generating the optical vortex (OV) by fabricating the computer generated hologram (CGH) of the OV inside glass using femtosecond laser directly writing. And the superpositions of the photon orbital angular momentum (OAM) have also been obtained by using a combined computer generated hologram (CCGH). We also give a concrete explanation to the superpositions of the photon OAM. Lastly, we have fabricated volume grating inside silica glass induced by a tightly focused femtosecond laser pulses for improving the first order of the diffractive efficiency. Experimental results show the first order diffractive efficiency (FODE) of the fabricated gratings is depending on the energy of the pulses and the scanning velocity of the laser pulses greatly, and the highest FODE reaches to 30% nearly. The diffraction pattern of the fabricated grating is also numerically simulated and analyzed by using a two dimensional FDTD method and Fresnel Diffraction. The numerical simulated results proved our prediction on the formation of the volume grating is correct which agree well with our experimental results.

A relative broadband circular polarization analyzer based on a single-turn Archimedean nano-pinholes array has been proposed and investigated systematically from visible spectrum to near infrared region. The spiral arrangement of circular nano-pinholes can implement spatially separated fields according to the relationship between the spiral direction of Archimedean structure and chirality of circularly polarized light (CPL). The enhanced-characteristics mechanisms of the single-turn spirally arranged Archimedean pinholes array have been deduced and investigated by the theoretical analysis and numerical simulation in detail. Different from the single operating wavelength of the spiral slit structure, this novel design also shows a relative wide range of the operating wavelengths in the focusing and defocusing effects. The new proposed circular polarization analyzer could find more extensive applications, such as analyzing the physiological properties of chiral molecules based on circular polarizations, full Stokes-parameter polarimetric imaging applications and so on.

When linearly polarized light illuminates a plasmonic lens, it is challenging to realize centrally symmetric focal spot in the near field since there is mismatch between the symmetries of the plasmonic structures and the polarization spatial distribution of the incident light. In this paper, we propose a plasmonic lens that can focus surface plasmon to a centrally symmetric field when illuminated by light with linear polarization. Remarkably, the intensity distribution of the focal field is insensitive to the polarization direction, which makes it more reliable in optical applications. Numerical simulations are used to check the performance of the proposed structure. Comparisons with two conventional plasmonic lenses are made to demonstrate its unique superiority in polarization-insensitive focusing.

The rotational motions of the optically trapped microscopic particles by the vortex femtosecond laser beam are investigated in this paper. Black particles can be trapped and rotated by a vortex femtosecond laser beam very effectively because the vortex beam carries orbital angular momentum due to the helical wave-front structure in assoication with the central phase singularity. Trapped black particles rotate in the vortex beam due to the absorption of the angular momentum transferred from the vortex beam. The rotating directions of the trapped particles can be modulated by reversing the topological charge of the optical vortex in the vortex femtosecond beam. And the rotating speeds of the trapped microscopic particles greatly depend on the topological charges of the vortex tweezer and the used pulse energies.

Two-dimensional periodic microstructures, including both microholes and micro-orbicular platforms, have been fabricated on the surface of silica glass by a single shot of three interfered femtosecond laser pulses. The three-dimensional structure of a fabricated hexagonal lattice can be revealed by atomic force microscopy. The formation of the microstructure and the dynamic process of the interaction between the femtosecond laser and the silica glass have been discussed.