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Frequency split is the frequency difference between the driving mode and sensing mode of a vibratory gyroscope, which significantly influences the performance of cylindrical vibratory gyroscopes. In order to reducing frequency split, a method of trimming by drilling micro-holes through laser has been introduced in this paper. Firstly, the processing method of the trimming hole is determined by the finite element simulation, and then the feasibility of the method is verified by the experiment. In the experiment, the frequency split of gyroscope is reduced from 2.090Hz to 0.119Hz.

A high coupling efficiency is required to guarantee high-output power for lasers. However, positioning errors in optical devices can lead to different degrees of attenuation for the coupling efficiency. This paper, investigates the effects of positioning errors on the coupling efficiency of optical devices. Specifically, the combining, focusing, and coupling processes of a three-wire single emitter laser array are studied through experiments and are supported by simulations. The results show that a 50 μ m position error in the Y-axis of the fiber will reduce the coupling efficiency by 44 %, and a rotation error of 0.5° in the X-axis of the reflector will reduce the coupling efficiency by 100 %. Moreover, the sensitivity of the coupling efficiency to each error is revealed.

The manufacturing cost of coaxial optical communication lasers mainly occurs during the packaging process, and the key technology of the packaging process is the coupling alignment of photonic devices. Therefore, a high-precision and high-efficiency alignment algorithm is of great importance to reduce the cost and improve the quality of coaxial optical communication lasers. The traditional alignment algorithm that is currently used has the following shortcomings: (1) it cannot achieve multidegree-of-freedom alignment at the same time; (2) it easily falls into a local extreme point. Particle swarm optimization (PSO) can achieve simultaneous alignment of multiple degrees of freedom, and it does not easily fall into a local optimum. According to the optical principle, the coupling efficiency function of a coaxial optical communication laser can be obtained. Then, PSO can be used to find the maximum value of the function. The simulation results showed that the PSO algorithm could locate 99% of the maximum optical power. Coupling search can be used for coaxial optical communication laser devices using PSO on packaged devices. The experimental results also proved that the PSO algorithm has high reliability and can realize multidegree of freedom simultaneous search.

The grating structure and its performance for coupling between fiber and silicon-based waveguide are studied and analyzed. The coupling mechanism is illustrated through the grating Bragg diffraction condition, and the effect of physical parameters and alignment parameters of the grating coupler on the coupling efficiency is analyzed by FDTD (Finite-difference time-domain). The optimum design values of the period, duty cycle, etching depth and alignment parameters of the grating coupler are obtained, and at the same time, the deviation analysis on the optimal size is carried out. We present high-efficiency grating couplers fabricated both in EBL (Electron Beam Lithography) and Deep Silicon Etching through process optimization on device dimension, which can be useful for grating coupler fabrication.

Arrayed Waveguide Grating (AWG) for Coarse wavelength division multiplexing (CWDM) system is a key component of above 100Gb/s high-speed optical transmission module in telecommunication and interconnects for data center. Based on the theory of light transmission, the relationships between structure parameters and optical performance of AWG chip are analyzed. Four-channel AWG MUX/DEMUX chips for CWDM system at O-band are designed and simulated according to the relationships. The simulation results show that the insertion loss of the MUX is below 0.8 dB with non-uniformity of 0.07 dB. The bandwidths at 1 dB and 3 dB are more than 10 nm and 17 nm, respectively. For DEMUX, multi-mode interference (MMI) couplers are introduced at the start of output waveguides to produce flat-top spectral response with 1 dB bandwidth of 12 nm. The lowest insertion loss and adjacent crosstalk are 2.78 dB and below −20 dB, respectively.

In this study, we propose an effective method for the fabrication of annulus micro-/nanostructures by a femtosecond laser doughnut beam. Compared with the traditional Bessel annulus beam shaping system, this method greatly compresses the light propagation path. It is theoretically and experimentally demonstrated that the obtained axial section of the peak envelope in the processing area is two waists of the isosceles triangle. By moving the relative position of the sample, annulus microstructures with different diameters on copper sheet could be fabricated. In addition, laser induced periodic surface structures with controllable direction are fabricated by this optical system.

We demonstrated a fiber in-line Mach-Zehnder interferometer (MZI) coated with platinum (Pt) for the simultaneous measurement of strain and temperature. The sensor was fabricated by splicing a section of multimode fiber (MMF) between two single mode fibers (SMFs) and the Pt coating was prepared by iron sputtering technology. Fine interference fringes of over 20 dB with a compact size of 20 mm were achieved. The experimental results of the two different resonant dips showed strain sensitivities of &minus, 2.06 pm/&mu, &epsilon, and &minus, 2.21 pm/&mu, as well as temperature sensitivities of 55.2 pm/&deg, C and 53.4 pm/&deg, C, respectively. Furthermore, it was found that the Pt coating can improve the strain sensitivity significantly, resulting in an increase of about 54.5%. In addition, the sensor has advantages of easy fabrication, low cost, and high sensitivity, showing great potential for the dual-parameter sensing of strain and temperature.

We have proposed a high sensitive photonic crystal fiber (PCF) strain sensor based on the Mach-Zehnder interferometer (MZI). The sensing head is formed by all-fiber in-line single mode-multimode-photonic-crystal-single mode fiber (SMPS) structure, using only the splicing method. Such a strain sensor exhibited a high sensitivity of −2.21 pm/με within a large measurement range of up to 5000 με and a large fringe visibility of up to 24 dB. Moreover, it was found that the strain sensitivity was weekly dependent of the length of PCF or MMF. In addition, the sensor exhibited the advantages of simplicity of fabrication, high sensitivity and larger fringe visibility.

To improve the jet performance of a bi-piezoelectric jet dispenser, mathematical and simulation models were established according to the operating principle. In order to improve the accuracy and reliability of the simulation calculation, a viscosity model of the fluid was fitted to a fifth-order function with shear rate based on rheological test data, and the needle displacement model was fitted to a nine-order function with time based on real-time displacement test data. The results show that jet performance is related to the diameter of the nozzle outlet and the cone angle of the nozzle, and the impacts of the flow channel structure were confirmed. The approach of numerical simulation is confirmed by the testing results of droplet volume. It will provide a reliable simulation platform for mechanical collision-based jet dispensing and a theoretical basis for micro jet valve design and improvement.

The alignment coupling between optical waveguide chips and optical fiber arrays is the basis of the alignment coupling of planar optical waveguide devices, and the precise position detection with angle and spacing adjustments is one of the key steps of alignment coupling. A methodology for position detection, and angle and spacing adjustment was proposed for optical waveguide chips and optical fiber arrays based on machine vision. The experimental results show angle detection precision levels higher than 0.05°, line detection precision levels higher than 0.1 μm, and detection time less than 2 s. Therefore, the system developed herein meets the precise requirements necessary for position detection, and angle and spacing adjustments for optical waveguide chips and optical fiber arrays.

In order to make the whole fiber core modified, an improved point-by-point inscription method (called a transversal-scanning inscription method) is proposed to fabricate long period fiber gratings (LPFGs) by using femtosecond laser. LPFGs with an attenuation depth of 16 dB are achieved within the wavelength range of 1580–1680 nm. We have compared the bending properties of LPFGs fabricated by the line-by-line scanning inscription method and the transversal-scanning inscription method at the orthogonal directions. It is found that increasing scanning area using the transversal-scanning method can enhance the bend sensitivity obviously. The resulting curvature sensitivities are −4.82 nm/m −1 and −1.63 nm/m −1 at the 0° and 90° bend orientations respectively, within the curvature range from 1.75 m −1 to 3 m −1 in the experiment. The LPFG-I fabricated by the line-by-line scanning inscription method experiences red-shift, while the LPFG-II fabricated by the transversal-scanning inscription method experiences blue-shift.

A fiberized refractive index (RI) Mach–Zehnder interferometer (MZI) based on a micro V-shaped slot in fiber core is fabricated in a standard single mode optical fiber by femtosecond laser machining and chemical etching. The interference fringe of the MZI would shift with the variation of the ambient RI. The experimental results show that the RI sensitivity for the sensor is about −104 nm/RIU (refractive index unit) within the RI range between 1.332 and 1.352. Its robust structure and high sensitivity will have attractive potential application in chemical, biological and environmental monitoring.

To improve heat-transfer performance, a novel integral three-dimensional fin-structure on the plat surface was presented to increase the evaporation efficiency. The three-dimensional fin-structure is composed of a spiral micro-groove and multi radial micro-grooves. Both ploughing-extrusion (P-E) and stamping were used to form the integral-fins with a connection between radial and circumferential directions. Based on the SEM results, the relationships among P-E speed vP-E, rotational speed np and feed fp, and among interference length Li, stamping feed angle θc and stamping depth ac were analyzed. The effects of processing parameters on the groove morphology and the matching relationship between parameters were also discussed. The integral finned surface with micro-grooves and cracks can be obtained under such processing conditions: P-E depth ap=0.3 mm, ac=0.3 mm, the interval of helical groove dp=1.24 mm, θc=2° and np=50 r/min.

In this study, an effective approach is presented for the fabrication of line-patterned superwetting surface on sapphire by using a femtosecond laser. The fabricated surface shows a powerful capillary action by which water could be rapidly sucked into the as-prepared surface structures and spread even on the vertical surface against gravitation. In addition, the effects of the period and the dimensions of the microgrooves on surface wettability are investigated. It is demonstrated that the wettability can be significantly enhanced in the case when the sizable line-patterned nanostructures exist. This work could provide a facile and promising strategy for enhancing the performance of heat dissipation in the electronic devices substrate.

Resonant effect is found in femtosecond laser ablating Pr–Nd glass. When processed with resonant wavelength of 807 nm, resonant ablation efficiency (RAE) with a single pulse can be improved by 45.22%. Furthermore, RAE closely relates to laser intensity. For resonant ablation, RAE is increased significantly when laser intensity 0.556×1014??W/cm2 at which tunnel ionization dominates. Besides, it is also found that the ablation depth increases along with the wavelength rise when multiphoton ionization dominates, while the change rule is inversed when tunnel ionization dominates.

The temperature sensing performance of long period fiber gratings (LPFGs) written by femtosecond laser pulses coated with platinum nanoparticles (PtNPs) is proposed and demonstrated. It is found that the PtNPs increase the wavelength sensitivity of the LPFG significantly compared with the bare LPFG. The temperature sensitivities of the bare LPFG for three dips, corresponding to 1438, 1485, and 1585 nm, are 74.04, 77.23, and 86.26 pm/°C, respectively, when the temperature changes from 10°C to 500°C, whereas the corresponding sensitivities of PtNP coated LPFGs are up to 90.58, 93.51, and 103.43 pm/°C, respectively. Moreover, the PtNP coated LPFG has shown better wavelength repeatability. A small wavelength hysteresis of ∼0.5 nm is observed when the temperature is less than 300°C.

Marine oil spills have induced severe water pollution and threatened sea ecosystems, which also result in a loss of energy resources. To deal with this problem, much work has been done for using superhydrophobic or superhydrophilic mesh for oil–water separation. Nevertheless, there are still great challenges in the rapid fabrication of extremely durable mesh with superwetting properties, particularly considering the highly efficient oil–water separation. In this study, we present a simple, efficient method to fabricate superhydrophilic and underwater superoleophobic stainless steel mesh surfaces with one-step femtosecond laser induced periodic nanoripple structures. The as-prepared mesh shows high separation efficiency, which is higher than 99% for various oil–water mixtures. More importantly, the wettability and the separation efficiency of the fabricated mesh show no obvious change after the abrasion tests and corrosion tests, indicating that the as-prepared samples possess robust stability. This study provides an efficient route for constructing durable and highly efficient separation mesh, which can be applied in the cleanup of large-scale oil spills in the near future.

The eigenfrequency of a resonator plays a significant role in the operation of a cylindrical shell vibrating gyroscope, and trimming is aimed at eliminating the frequency split that is the difference of eigenfrequency between two work modes. In this paper, the effects on eigenfrequency under resonator-top trimming methods that trim the top of the resonator wall are investigated by simulation and experiments. Simulation results show that the eigenfrequency of the trimmed mode increases in the holes-trimming method, whereas it decreases in the grooves-trimming method. At the same time, the untrimmed modes decrease in both holes-trimming and grooves-trimming methods. Moreover, grooves-trimming is more efficient than holes-trimming, which indicates that grooves-trimming can be a primary trimming method, and holes-trimming can be a precision trimming method. The rigidity condition after grooves-trimming is also studied to explain the variation of eigenfrequency. A femtosecond laser is employed in the resonator trimming experiment by the precise ablation of the material. Experimental results are in agreement with the simulation results.

We used 1030-nm femtosecond-laser pulses focused above/at/below the interface of two fused-silica glass substrates in optical and partial-optical contact to successfully weld them at a moderately high repetition rate of 600 kHz. Variation in the laser focal position for these two gap-distance regimes (optical and partial-optical contact) yields different bonding strengths (BSs) and machining mechanisms. The maximum bonding strength (58.2 MPa) can be achieved for a gap distance $$ {\le}\lambda /4 $$ for optical-contact welding when laser focused below the interface, and the corresponding height of the welding seam was 23 μm. In addition, our results demonstrated that the “filamentation welding technique” is critical to the femtosecond-laser direct welding of glasses. Furthermore, line welding is significantly easier to realize when the femtosecond laser focuses at the interface in partial-optical-contact welding applications due to the combined effects of filamentation welding and ablation.

We demonstrate an efficient method for fabricating high-quality cylindrical microlens arrays (CMLAs) on the surface of fused silica, fully based on spatially shaping of a femtosecond laser beam from Gaussian to Bessel distribution. As the envelope of shaped spatial intensity distribution matches the profile of cylindrical microlens perfectly, a CMLA with more than 50 uniform microlenses is fabricated by simple line scanning. The radius and height of these microlens units can be finely controlled by adjusting the power of laser pulses. Excellent optical imaging and high-speed fabrication performances are also demonstrated by our fabricated CLMA.

In this paper, it demonstrated one-step femtosecond laser welding and internal machining of three fused silica substrates in the optical- and non-optical-contact regimes by focusing 1030-nm laser pulses at the middle of the second substrate. Focusing laser pulses within the second glass in optical-contact and non-optical-contact samples induces permanent internal structural modification, leading to the three glass substrates bonding together simultaneously. The bonding mechanism is based on the internal modification of glass, and this mechanism is different from that of ordinary glass welding at the interface. Welding-spot size is affected by not only the gap distance (ablation effect) and heat transmission, but also by gravity through examining the sizes of the welding spots on the four contact welding surfaces. The maximum bonding strength of the lower interface (56.2 MPa) in the optical-contact regime is more than double that (27.6 MPa) in the non-optical-contact regime.

The observation of the bright pulses and dark square pulses in a graphene-oxide saturable absorber (GOSA) passively mode-locked ytterbium-doped fiber laser has been investigated experimentally. Bright pulses are achieved at a pump power of $\sim$ 200 mW. However, the dark-square-pulse generation starts at a much higher pump power of $\sim$ 450 mW. At the maximum pump power of 600 mW, the dark-square-pulse bunches and harmonic mode locking (HML) can be also obtained by tuning the polarization controller (PC) to different orientations. It is the first demonstration of the bunches and HML of dark square pulses in a GOSA passively mode-locked ytterbium-doped fiber laser with large normal dispersion cavity.

We give a systematic experimental study of multipulse bunches in a graphene oxide saturable absorber (GOSA) passively mode-locked all-normal dispersion ytterbium-doped fiber laser (YDFL). Some special phenomena such as harmonic multipulse bunches, harmonic mode-locking, and chaotic multipulse states are also obtained. Our experiment reveals that the inserted 2.5-nm narrow bandwidth filter plays an important role in the formation of multipulse in all-normal dispersion fiber lasers. Because of the effective gain bandwidth depends on both the 2.5-nm narrow bandwidth filter and the artificial fiber birefringence filter, the multipulse operation states are sensitive to the polarization. It is the first demonstration of multipulse evolution in a GOSA passively mode-locked all-normal dispersion YDFL.

In this paper, a kind of bi-layered asymmetrical split ring metamaterial was proposed as a circular polarization converter. Simulations and experiments at the microwave regime showed that the proposed structures can achieve the conversions from right-handed circularly polarized electromagnetic waves to left-handed ones and the reversed conversions in the opposite propagating direction. The linear to circular polarization transmission coefficients and the surface currents were investigated to understand the mechanism of the circular polarization conversions. Moreover, we optimized the proposed metamaterials by increasing the distance between the two metal layers. The proposed circular polarization converters have applications in microwave wave plates and metamaterial antennas.

Sapphire, with extremely high hardness, high-temperature stability and wear resistance, often corroded in molten KOH at 300 °C after processing. The fabrication of microstructures on sapphire substrate performed by femtosecond laser irradiation combined with KOH solution chemical etching at room temperature is presented. It is found that this method reduces the harsh requirements of sapphire corrosion. After femtosecond irradiation, the sapphire has a high corrosion speed at room temperature. Through the analysis of Raman spectrum and XRD spectrum, a novel insight of femtosecond laser interaction with sapphire (α-Al2O3) is proposed. Results indicated that grooves on sapphire surface were formed by the lasers ablation removal, and the groove surface was modified in a certain depth. The modified area of the groove surface was changed from α-Al2O3 to γ-Al2O3. In addition, the impacts of three experimental parameters, laser power, scanning velocities and etching time, on the width and depth of microstructures are investigated, respectively. The modified area dimension is about 2 μm within limits power and speed. This work could fabricate high-quality arbitrary microstructures and enhance the performance of sapphire processing.

The convex grid-patterned microstructures were fabricated on a silicon substrate by using femtosecond laser assisted with chemical etching in this study. Along the femtosecond laser scanning traces, the isosceles trapezoidal microstructures were generated. According to Raman spectra and elemental distribution, the formation of the convex microstructures is investigated. Also, the effect of experimental parameters including laser power, scanning speed, etching duration and etching temperature on the microstructures’ three-dimensional size is discussed in detail. In addition, the hydrophobic property of a surface with large-area convex grid-patterned microstructures was explored.

Laser offset welding of 5052 aluminum to press-hardened steel using a brass interlayer was carried out. The cross-sectioned macrostructure and tensile strength were governed by varying the thickness of the brass interlayer. The maximum tensile strength reached 56.4 MPa when the thickness of brass interlayer was 0.05 mm. Subsequently, the interface microstructure, the nanoindentation characterization, and the fracture behavior were evaluated experimentally by means of scanning electron microscopy (SEM), energy-dispersive X-ray spectrometer (EDS), and micro-X-ray diffraction (micro-XRD), respectively. It was found that the intermetallic compound (IMC) layer at the interface consisted of an Fe2Al5 layer and an FeAl layer, and the estimated nanohardness of Fe2Al5, FeAl, and Fe3Al were 16.11 GPa, 9.48 GPa, and 4.13 GPa, respectively. The fracture of the joint with the 0.05 mm brass interlayer was a mixture of cleavage fracture and intergranular fracture, while that of the joint with the 0.1 mm brass interlayer exhibited the characterization of a major dendrite arm, leaving a metallurgical connected zone consisting of the Al2Cu and the &alpha, Al phase.

The side wall profile roughness of the silicon waveguide prepared by electron beam lithography and reactive ion etching is extracted by using the boundary tracing method. The maximum, minimum, and average roughness values are extracted from the side wall boundary, and the changes of the side wall boundary of waveguide after electron beam exposure and reactive ion etching were compared. The roughness variation of the waveguide side wall is similar with the same length. And roughness from the bottom of the waveguide etched region is measured directly by laser confocal microscope and roughness correlation statistics are also obtained.

In this study, we present a facile method to enhance the transmittance of soda lime glasses through hydrothermal processing. By adjusting the treated parameters, we obtain two types of glass with enhanced transmission: one frosted glass and one clear glass. Our results show that after surface modification with ammonium hydroxide solution, the transmittance of the frosted glass reach more than 95%. Scanning electron microscopy studies reveal that the treated surface is covered with irregular micro-craters. On the other hand, the treated clear glass is covered with extensive nanoflakes structure. We achieve a maximum of 5.4% transmittance enhancement for the clear glass over a wide wavelength range, to 96.7% for normal incidence.

Lightwave transmission model for optical waveguide chip and input/output fiber array on coupling interface has been established on the basis of Fresnel Reflection Principle. Mechanism and rules for the influence on the devices’ optical performance from the features of adhesive and the geometric parameters of the interface has been analyzed and verified through experiments. Numerical calculation results have shown that with the variations in the refractive indexes of the adhesive, there is a periodical change in the return loss of the devices, namely the optical performance of the devices is related to the refractive index of the adhesive, while the experimental results have shown that the refractive-index-matching adhesive can effectively decrease the insertion loss and increase the return loss of the devices. And the insertion loss before and after adding the adhesive falls by 1.0 dB and the return loss rises by 10 dB averagely.

The microstructures of the arc sprayed (AS) and zinc-rich (ZR) coatings were observed by scanning electron microscopy (SEM). Furthermore, the different anti-corrosion properties were investigated through electrochemical experiments including potentiodynamic polarization measurements and electrochemical impedance spectroscopy (EIS). The SEM observations revealed that the AS coating was more porous and coarser, while the ZR coating surface was composed of uniform spherical particles. The corrosion potential of AS coating was shifted to a more negative value than that of the ZR coating. From EIS results, it was proposed that the ZR coating exhibited much larger impedance values than the AS coating. General models are applied to simulate EIS data of the AS coating, while two transmission line models (modified de Levie's type) are used to account for ZR corrosion behaviour. The ZR coating performed better as a protective passive film during the long-term immersion test while the cracks that occurred in the cross section of ZR coating indicated that the adhesive strength of the AS coating was superior to that of the ZR coating.

After reviewing three different definitions of mode field diameter of single-mode fibers, coupled efficiency calculation methods associated with lateral offset, longitude separation and wavelength, the effects produced by them, and the influences of splicing defects were discussed in detail. The regularities of the effects were studied according to the first order derivation of couple efficiency formula, and a simplified formula for couple efficiency calculation was presented under the circumstance of slight misalignment, with respect to wavelength, λ, and in a good agreement with the theoretical model. The simplified formula provides a new but simple approach to evaluate wavelength dependent couple efficiency of single-mode fibers. Theoretical analyses and numerical calculations show that, when those defects exist, the wavelength produces additional effects on the couple loss that growth of wavelength causes an increase on the couple efficiency for the lateral offset or longitude separation whereas lessens the couple efficiency due to angular misalignment or mode fields mismatching, and that the wavelength degrades the couple efficiency distinctly when λ ≥ 2.5 μm whereas it distorts the couple slightly in range of λc≤λ≤2 μm.

A novel automatic alignment algorithm of integrated photonic devices based on improved particle swarm algorithm is proposed. The combination of dynamically changing inertia weight and selection mechanism is used in the standard particle swarm algorithm to overcome the premature phenomenon in alignment search process, which improves the global search ability and convergence speed compared to particle swarm algorithm. The method used in engineering can significantly improve the alignment and coupling efficiency of photonic devices.

In this work, a simulated corrosion electrolyte was employed in order to assess the effect of sealing treatment on the corrosion resistance of arc sprayed zinc coatings in atmospheric environment. The microstructures and corrosion behaviours of unsealed and sealed coatings had been studied using scanning electron microscopy and electrochemical testing. Scanning electron microscopy observations revealed that the unsealed coating consisted of an outer coarse layer and an inner impact layer. As for the sealed coating, the sealing agent not only covered the surface but also permeated into the original microdefects on the outer coarse layer of the as sprayed coating. The results of electrochemical testing and corrosion morphology observations indicated that the corrosion resistance of the sealed coating was enhanced a great extent due to the blocking and shielding effect of the sealing layer.

Constant elastic alloy is widely used material with high applied performance. In order to develop the application of constant elastic alloy, laser ablation of constant elastic alloy in different ablation mediums was investigated with different femtosecond lasers. Constant elastic alloy was ablated in solution with different ethanol contents and different thicknesses of the liquid layer above the target material and for comparison, in air. Also, the effects of laser energy and laser pulses of femtosecond laser on the morphology are studied. The effects of the position of the laser focus relative to the target surface were also discussed. The experimental results indicate that larger laser-induced area and smaller depth of craters tend to be obtained in solution than in air. The laser-induced area firstly increases and then decreases, and depths of craters decrease at first and increase later with the increase in ethanol content. Furthermore, the larger were energy of laser pulses, the larger were laser-induced area and deeper craters made in all different ablation solutions.

Sapphire has a potential as a new generation of electronics display. However, direct processing of sapphire surface by visible or near-IR laser light is challenging since sapphire is transparent to these wavelengths. In this study, we investigate the formation of femtosecond laser-induced periodic surface structures (LIPSSs) on sapphire coated with nanolayered gold film. We found a reduced threshold by about 25 % in generating uniform LIPSSs on sapphire due to the nanolayered gold film. Different thickness of nanolayered gold films are studied, and it is shown that the change in thickness does not significantly affect the threshold reduction. It is believed that the diffusion of hot electrons in the gold films increases interfacial carrier density and electron–phonon coupling that results in a reduced threshold and more uniform periodic surface structure generation.

This study proposes an ablation enhancement approach to fabricate microgrooves in PMMA by femtosecond laser irradiation assisted with a microtorch. The influences of pulse energy and scanning speed on the groove depth and removal area of groove are investigated. It is demonstrated that the improvement of groove depth has a close relationship with the scanning speed. When the scanning speed was less than 50 µm/s, the ablated groove depth is considerably improved with various pulse energies, up to 100 %. Moreover, the removal area of groove has significant enhancements of up to 250 % in various processing parameters. It is suggested that the ablation enhancement of microgrooves fabrication is related to the status of plasma plume and substrate heating. With the assistance of the microtorch, laser-induced plasma plume is confined and its density at center region is raised, which results in the increment of the central plasma’s temperature and more energy deposited on the PMMA surface, ultimately leading to the ablation enhancement. Meanwhile, the instantaneous substrate heating also plays a crucial role on enhanced microgrooves fabrication.

In order to take advantage of microhole fluidynamics, laser-induced periodic surface structures (LIPSS, ripples) orientation should offer the lowest angle γ as possible with respect to hole axis. Investigations have been performed to explore the morphology of LIPSS formed on the sidewalls of microholes by circularly polarized femtosecond laser trepanning. The period of LIPSS on average was smaller than laser wavelength. The energy density of laser beam generally affected the processing effect. Experiments showed that the angle of the LIPSS decreases with increasing single pulse energy. However, increasing trepanning speed led to a decreasing in LIPSS angle.

In this study, a remarkable spatial shaping approach is proposed to transform Gaussian femtosecond laser into quasi-Bessel optical field with compressed central lobe and amplified side lobes of the spatial intensity profile. Based on this technique, inward bulge trench (IBT) structures are fabricated with high efficiency on the surface of PMMA by a single illumination step, whose cross-sectional profile is opposite to the results fabricated by Gaussian beam. And plano-convex cylindrical microlens array, which is consistent in size and shape throughout a large sample area, is formed through simply piecing together the IBT structures during fabricating process. Furthermore, numerical simulations of optical field in radial direction and on-axial direction are exploited to rationalize the dependence of the patterned microstructures on the spatial intensity distribution of femtosecond laser.

This paper has proposed a methodology for position detection, and angle and spacing adjustment, for optical waveguide chips and optical fiber arrays, based on machine vision. The experimental results of automatic aligning are reported.

ZnAlLa-CO3 layered double hydroxides (LDHs) with different Zn/Al/La molar ratios were prepared by the constant pH coprecipitation method. The synthetic materials were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), Brunauer-Emmett-Teller method (BET) and particle analysis. The results showed that the hydrotalcite-like materials had a layered structure. The ZnAlLa-CO3-LDHs as stabilizers were mixed with PVC resin. The tests of thermal aging, mass loss test and Congo red for the PVC composites were carried out at 180±1 °C, respectively. The results showed that ZnAlLa-CO3- LDHs used as single thermal stabilizers could enhance both the long-term thermal stability and initial thermal stability of PVC, and 2.4 phr (parts per hundred PVC resin) ZnAlLa-CO3-LDHs with Zn/Al/La (molar ratio)=20/8/2 had a better stabilizing effect on PVC than others. Compared with single thermal stabilizers, the composite thermal stabilizers including 0.3 phr calcium stearate (CaSt2), 0.4 phr β-diketone and 2.4 phr ZnAlLa-CO3-LDHs significantly enhanced the thermal stability of PVC sample. And rare earth ion could optimize the conformation of PVC and refrain the initiation of the thermal stability and the thermal stable time was over 220 min. The main reason could be concluded to the special structure of rare earth ion, which had longer atom radius and more coordination numbers. So the rare earth ion (REδ+) could react with the labile chlorine atoms (Clr−) to form a stable coordinate complex.

This paper describes a new active optical alignment method that is developed for the alignment of optical fibers to planar waveguide in order to improve the precision and efficiency of that. A new coupling mode, which is a polynomial function, is rebuilt by simplifying effect factors of the light field coupling process, such as angular offsets and line offsets. The optimum curve which is calculated to fit those sampling points by taking advantage of the least square method assists to locate the maximum coupling point of the alignment. Simulation results show that the alignment of two single mode fields is improved into 0.1μm precision with only 6 sampling points by the new method instead of 0.4μm offset with average 21.4 sample points by hill-climbing method. Using this alignment method, a fiber-to-waveguide, high-efficient coupling that provides higher accurate alignment with less sampling points is achieved.