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Improving the spot brightness and uniformity of arrangement of the array laser is conducive to ensuring the beam quality of the fiber laser. Based on the light tracing principle, the optical model performance of two common fiber lasers was first analyzed. Then, a novel rotationally polarized optical model with high power and spot uniformity was designed and optimized on the basis of the aforementioned analysis. The results of the evaluation metrics of the multi-indicator optical model show that the spot uniformity of our proposed model improved by 24.03%, the power improved by 0.55%, and the maximum light distance was shortened from 120 mm to 82.58 mm. Further, the results of the coupling tolerance analysis of the optical elements show that the total coupling efficiency was 89.04%. The coupling power and tolerance relationships did not produce degradation compared with the traditional model. Extensive comparative results show that the designed rotationally polarized optical path model can effectively improve the optical coupling efficiency and spot uniformity of arrayed semiconductor lasers. [ABSTRACT FROM AUTHOR]

Infrared antireflection of a zinc sulfide (ZnS) surface is important to improve performance of infrared detector systems. In this paper, double-pulse femtosecond laser micro-machining is proposed to fabricate a subwavelength quasi-periodic array (SQA) on ZnS substrate for infrared antireflection. The SQA consisting of approximately 30 million holes within a 2 × 2 cm2 area is uniformly formed in a short time. The double-pulse beam can effectively suppress the surface plasma shielding effect, resulting in obtaining a larger array depth. Further, the SQA depth is tunable by changing pulse energy and pulse delay, and can be used to readily regulate the infrared transmittance spectra as well as hydrophobicity. Additionally, the optical field intensity distributions of the SQA simulated by the rigorous coupled-wave analysis method indicate the modulation effect by the array depth. Finally, the infrared imaging quality captured through an infrared window embedded SQA is evaluated by a self-built infrared detection system. [ABSTRACT FROM AUTHOR]

In this study, the mechanical and optical properties of silica-based planar lightwave circuit (PLC) optical splitters under uniaxial tensile loading are studied by building an in situ experimental test platform. The tensile test results revealed that the adhesively-bonded fiber array-PLC chip joints are weak areas of the PLC optical splitter. Combined with the real-time monitoring of the optical performance index insertion loss (IL) during the tensile test, it was found that the changing trend of ΔIL-time curves is related to the deformation, damage, and debonding process of the weak area. Based on the experimental results and phenomena, the correspondence between ΔIL at 1.55 μm wavelength and the damage degree of PLC optical splitters is established, that is, ΔIL in (−5 dB; 0 dB], (−15 dB; −5 dB], and (−∞, −15 dB] belong to light damage, moderate damage, and severe damage, respectively. This research can provide a useful reference for damage characteristics analysis and reliability design of PLC optical splitters. [ABSTRACT FROM AUTHOR]

As a special kind of Bragg grating, phase-shifted fiber Bragg grating (PS-FBG) has attracted extensive attention because of its extremely narrow transmission window and excellent sensing performance. The main purpose of this manuscript is to discuss the PS-FBG with special sensing characteristics and explore the influence of different inscription technologies on the sensing characteristics of PS-FBG by comparing the existing inscription methods. The sensing characteristics, advantages and disadvantages of PS-FBG with different structures are analyzed. [ABSTRACT FROM AUTHOR]

Silica optical film specifications are determined by their processing capability and their fabrication stability. Here, a statistical process control (SPC) approach usually used in planar lightwave circuits (PLC) is adopted to analyze the stability of the silica optical film fabrication process. Apart from the raw materials, certain key external factors have to be taken into consideration during the PLC process, such as temperature, relative humidity, process variation and machine aging. The fabrication process can be adjusted according to SPC-based results in real-time, so as to produce high quality silica optical film. By using this method, it is possible to assess the effectiveness of older production lines and extend their production capacity at minimal cost. [ABSTRACT FROM AUTHOR]

A highly sensitive strain sensor based on a novel fiber in line Mach-Zehnder interferometer (MZI) was demonstrated experimentally. The MZI was realized by splicing a section of photonic crystal fiber (PCF) with the same length of thin core fiber (TCF) between two single mode fibers (SMFs). The fringe visibility of MZI can reach as high as 20 dB in air. In particular, the strain sensitivity of -1.95 pm/µe was achieved within a range from 0 to 4000 µe. Furthermore, the strain properties of different length of MZI was investigated. It was found that the sensitivity was weekly dependent on the length of MZI. The strain sensitivities corresponding to the MZI with 35 mm PCF, 40 mm PCF and 45 mm PCF at 1550 nm band were -1.78 pm/µe, -1.73 pm/µe and -1.63 pm/µe, respectively. Additionally, the sensor has advantages of simple fabrication, compact size and high sensitivity as well as good fringe visibility [ABSTRACT FROM AUTHOR]

The high-quality, high-efficiency micro-hole drilling of structural ceramics to improve the thermal conductivity of hot-end parts or achieve high-density electronic packaging is still a technical challenge for conventional processing techniques. Recently, the laser drilling method (LDM) has become the preferred processing tool for structural ceramics, and it plays an irreplaceable role in the industrialized processing of group holes on structural ceramic surfaces. A variety of LDMs such as long pulsed laser drilling, short pulsed laser drilling, ultrafast pulsed laser drilling, liquid-assisted laser drilling, combined pulse laser drilling have been developed to achieved high-quality and high-efficiency micro-hole drilling through controlling the laser–matter interaction. This article reviews the characteristics of different LDMs and systematically compares the morphology, diameter, circularity, taper angle, cross-section, heat affect zone, recast layer, cracks, roughness, micro–nano structure, photothermal effect and photochemical reaction of the drilling. Additionally, exactly what processing parameters and ambient environments are optimal for precise and efficient laser drilling and their recent advancements were analyzed. Finally, a summary and outlook of the LDM technology are also highlighted. [ABSTRACT FROM AUTHOR]

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 α-Al phase. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In order to improve the performance of silver nanowire (AgNW) flexible transparent conductive films (FTCFs), including the conductivity, uniformity, and reliability, the welding of high repetition rate femtosecond (fs) laser is applied in this work. Fs laser irradiation can produce local enhancement of electric field, which induce melting at the gap of the AgNWs and enhance electrical conductivity of nanowire networks. The overall resistivity of the laser-welded AgNW FTCFs reduced significantly and the transparency changed slightly. Meanwhile, PET substrates were not damaged during the laser welding procedure in particular parameters. The AgNW FTCFs can achieve a nonuniformity factor of the sheet resistance as 4.6% at an average sheet resistance of 16.1 Ω/sq and transmittance of 91%. The laser-welded AgNW FTCFs also exhibited excellent reliability against mechanical bending over 10,000 cycles. The welding process may open up a new approach for improvement of FTCFs photoelectric property and can be applied in the fabrication of silver nanostructures for flexible optoelectronic and integration of functional devices. [ABSTRACT FROM AUTHOR]

Laser welding–brazing of 5A06 aluminum to Ti6Al4V titanium in a butt configuration was carried out to discuss the influences of welding parameters on dissimilar joint properties. The effects of laser offset, welding speed, and laser power on the spreading length of the molten aluminum liquid, interface fracture zone width (IFZW), fracture roughness, intermetallic compounds (IMCs) thickness, and tensile strength were also investigated. The microstructure and fracture of the joint were also studied. The results show that the tensile strength of the joint is not only influenced by the thickness and type of IMCs, but also influenced by the spreading ability of the aluminum liquid, the fracture area broken at the Ti/fusing zone (FZ) interface, and the relative area of the brittle and ductile fracture in FZ. A dissimilar butt joint with an IMC thickness of 2.79 μm was obtained by adjusting the laser offset, welding speed, and laser power to 500 μm, 11 mm/s and 1130 W, respectively. The maximum tensile strength of the joint was up to 183 MPa, which is equivalent to 83% of the tensile strength of the 5A06 aluminum alloy. [ABSTRACT FROM AUTHOR]

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 −2.06 pm/με and −2.21 pm/με, as well as temperature sensitivities of 55.2 pm/°C and 53.4 pm/°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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 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., Competing Interests: The authors declare no conflict of interest.