Ridge waveguide laser in Nd:LiNbO3 by Zn-diffusion and femtosecond-laser structuring

Ridge waveguide lasers have been fabricated on Nd³⁺ doped LiNbO₃ crystals. The fs-laser writing technique was used to define ridge structures on a gradient-index planar waveguide fabricated by Zn-diffusion. This planar waveguide was formed in a z-cut LiNbO₃ substrate homogeneously doped with a 0.23% of Nd³⁺ ions. To obtain lateral light confinement, the surface was then micromachined using a multiplexed femtosecond laser writing beam, forming the ridge structures. By butting two mirrors at the channel waveguide end-facets, forming a waveguide laser cavity, TM-polarized laser action at 1085 nm was achieved by end-fire TM-pumping at 815 nm. The waveguide laser shows a threshold of 31 mW, with a 7% of slope efficiency.     

Fabrication of ridge waveguide on the ion-implanted TGG crystal by femtosecond laser ablation

The ridge waveguide on the TGG crystal has been fabricated through the combination of the ion implantation and the femtosecond laser ablation. Firstly, optical planar waveguide was formed on the top surface of TGG crystal by ion implantation. To investigate the damage induced by the 6.0?MeV Si ion implantation at a dose of 2.0 × 10¹⁵ ions/cm², the vacancy distribution was obtained by the SRIM simulation programme. Subsequently, the ridge waveguide with a width of 20?µm was produced by femtosecond laser ablation. The optical guiding properties of the ridge TGG waveguide were measured at the near-infrared wavelength (976?nm) by the end-face coupling technique. The work demonstrated that the manufactured waveguide structure possesses the ability to confine the light into guided mode, making it potentially valuable in integrated devices.     

Impact of microstructures by femtosecond laser direct writing on the LED efficiency

We report on fabricating microstructures on the surfaces of LED chips by femtosecond laser direct writing. The changed trend of LED light extraction efficiency with the variation of the laser power and pulse was studied. It is found that there is an optimal surface treating condition (laser power and pulse number) in fabricating the microstructures on the surface of the LEDs to make the LED luminous flux maximum. In our experiment, the luminous efficiency of LED is close to the optimum enhancement value when the LED was surface structured with a laser power of 0.48 μW, three laser pulses at one point and the point spacing of 5 μm. In this condition, it can be improved by 23.53%.     

脉冲激光沉积金刚石基c轴取向LiNbO3压电薄膜

采用等化学计量比的LiNbO3多晶陶瓷为靶材,利用脉冲激光沉积技术在以非晶SiO2为缓冲层的金刚石/Si衬底上制备c轴取向LiNbO3薄膜。研究了靶材与衬底之间的距离对LiNbO3薄膜的结晶质量和c轴取向性的影响,发现在靶材与衬底之间的距离为4.0cm时获得了具有优异结晶质量的完全c轴取向LiNbO3压电薄膜。采用扫描电子显微镜和原子力显微镜对最佳条件下制备的薄膜进行了分析,结果表明制得的薄膜呈与衬底垂直的柱状结构,且薄膜表面光滑,晶粒均匀致密,表面平均粗糙度约为9.5 nm。     

Process parameter dependencies of continuous and pulsed laser modes on surface polishing of additive manufactured aluminium AlSi10Mg parts

Laser powder bed fusion is a well-established 3D printing technique for metal alloys, but exhibits a poor surface quality. Laser polishing provides the possibility of a fast contact-free and fully-automatable surface treatment. This paper deals with the experimental investigation of laser polishing of laser powder bed fusion parts made of aluminium AlSi10Mg. Laser polishing is done with a 4 kW solid state disc laser in combination with a multi-axis system and a one dimensional scanner optic. The laser is operated at continuous and pulsed operation mode. The parameter study reveals a high dependency of the achievable roughness on the laser beam intensity, the track and pulse overlap, the energy density and the number of polishing passes and polishing directions. Pulsed laser polishing mode with up to four passes from different directions revealed the lowest surface roughness of 0.14 μm Ra. With respect to the initial average surface roughness of Ra = 8.03 μm a reduction of the surface roughness of greater than 98 % could be achieved. Polishing with continuous laser radiation at one polishing pass resulted in Ra = 0.23 μm at an area rate of 20 cm²/min. Laser polishing using four passes achieved a further improvement up to Ra = 0.14 μm.     

Focusing waveguide mirror with a tapered edge

We propose a focusing waveguide mirror with a shallow tapered edge in a slab waveguide and demonstrate it by planar processes and wet etching. A light beam 2 mm wide is focused to 6.5 μm full width at half-maximum at a wavelength of 0.6328 μm. A reflectivity of higher than 90% at the tapered edge is obtained. The inclination ratio of the tapered mirror edge is 1:90. Fairly good correspondence between measured and calculated focused spot sizes is obtained.     

玻璃基掩埋式光波导堆栈的制作与表征

在硅酸盐光学玻璃基片上制作了光波导堆栈, 这种光波导堆栈通过Ag⁺/Na⁺熔盐离子交换和电场辅助离子扩散技术顺次制作了两层掩埋式光波导. 对光波导堆栈的横截面显微结构进行了观察, 并对堆栈中两层波导的损耗特性进行了测试. 所获得的光波导堆栈中的上、下两层波导芯部分别位于玻璃表面以下14和35 μm处; 上层光波导芯部尺寸约为12 μm×7 μm; 下层光波导芯部尺寸约为9 μm×8 μm. 通光测试显示两层波导在1.55 μm工作波长下均为单模光波导, 且两者之间没有相互耦合. 损耗测试分析结果显示: 堆栈中两层光波导的传输损耗均约为0.12 dB/cm,与单模光纤之间的耦合损耗分别为0.78和0.73 dB. 分析表明, 这种光波导堆栈在玻璃基集成光芯片的高密度集成方面具有很好的应用前景.     

Laser generation in microdisc resonators with InAs/GaAs quantum dots transferred on a silicon substrate

Microdisc resonators based on InAs/GaAs quantum dots separated from a GaAs substrate by selective etching and fixed to a silicon substrate by epoxy glue are studied using luminescence spectroscopy. A disc resonator 6 μm in diameter exhibits quasi-single-mode laser generation at a temperature of 78 K with a threshold power of 320 μW and λ/Δλ ～ 27000.     

粉末微注射成形ZrO_2微结构表面质量控制

采用粉末微注射成形技术制得了二氧化锆陶瓷微结构件,注射成形最小微结构尺寸为Φ300μm×250μm.分析了微注射成形工艺参数、模具抽真空及硅模具对微结构表面质量的影响.实验结果表明在模具温度和注射压力较低时,相同工艺参数下随着微型腔尺寸的减小微结构顶端的表面平整度逐渐下降,提高模具温度和注射压力以及注射前对模具进行抽真空可以改善微结构表面平整度.另外,注射前的模具抽真空有助于减少微结构的表面气孔.亚微米陶瓷超细粉的使用明显改善了烧结后微结构的表面质量,其表面粗糙度值由烧结前的0.33μm降低为约0.28μm.     

Fast fabrication of silicon based microstructures using 355 nm UV laser

Abstract

In this study, a 355 nm UV Nd:YAG laser is used to process silicon wafers. In order to obtain microstructures with high aspect ratio, a dual prism optical system is set up to control the cutting linewidth of the UV laser beam. During the laser beam propagation through the prisms, the two prisms are rotated with the same angular velocity, which results in the focal spot of the laser beam moving in a circular path on the silicon substrates. When the laser beam moves relative to the holder (workstation), a laser cutting process can be carried out. With this laser system, the cutting linewidth is controllable ranging from 10 μm to 1 mm by adjusting the initial phase difference in the two prisms. The experimental results show that arbitrary shaped silicon based microstructures with high aspect ratio can be fabricated by this 355 nm UV laser system, and the aspect ratio over 10 can be obtained.     

Laser ablation of silicon using a Bessel-like beam generated by a subwavelength annular aperture structure

Using a femtosecond laser incident to an oxide-metal-oxide film engraved with a subwavelength annular aperture (SAA) structure, we generated a Bessel-like beam to ablate silicon. Experimental results show that the silicon can be ablated with a 0.05 J/cm(2) input ablation threshold at 120 fs pulse duration. We obtained a surface hole possessing a diameter less than 1 μm. Optical performance, including depth-of-focus and focal spot of the SAA structure, were simulated using finite-different time-domain calculations. We found that a far-field laser beam propagating through a SAA structure possesses a submicrometer focal spot and high focus intensity. Our method can be easily adopted for surface machining in microfabrication applications.     

Dynamic data compression algorithms in speech coding

Abstract

The single transverse mode AlGaAs/GaAs laser array with pulsed peak power up to 100 mW has been fabricated successfully. The ridge waveguide laser structure was chosen since it needs only one step liquid phase epitaxy which greatly improves the yield. The ridge waveguide was formed by etching the top p‐type cladding layer through a 4 μm to 5 μm mask down to the neighborhood of the active layer to form a lateral refraction index difference. It is found that when the spacing between ridge is 5 μm, individual lasers are not coupled, and the far field pattern displays a diverged single lobe with a half width of 18° similar to that of a single laser. When an end broad area region is inserted, however, the laser array starts to couple and forms a narrow two‐lobe beam with a half width of 5°. The near‐field pattern can be used to analyze the coupling condition.     

激光微加工对陶瓷表面化学镀铜的影响研究

采用扫描电镜(SEM)、X射线光电子谱(XPS)、X射线衍射能谱仪(XRD)等手段比较激光微加工处理前后陶瓷表面形貌发生的变化,探讨了激光微处理在陶瓷表面无敏化活化化学镀铜工艺中的作用.结果表明,陶瓷基底经激光处理后,其表面成分并未发生改变,但其表面活性增强,从而促进了化学镀铜反应的进行.     

Surface Modification of Fluorine-Doped Tin Oxide Thin Films Using Femtosecond Direct Laser Interference Patterning: A Study of the Optoelectronic Performance

Transparent conductive oxides (TCOs) are used in solar cells not only to extract photogenerated carriers but also to allow sunlight to reach the photoactive material. Therefore, controlling the electrical and optical properties of such oxides is crucial for the optimization of the efficiency of solar cells. Herein, direct laser interference patterning (DLIP) method is used to control the surface morphology, optical and electrical properties of fluorine-doped tin oxide (FTO) by applying femtosecond laser pulses. The topography characterization reveals periodic line-like microstructures with a period of 3.0 μm and average heights between 20 and 185 nm, depending on the applied laser fluence levels. Laser-induced periodic surface structures are observed on the valleys of the texture aligned perpendicularly to the laser radiation polarization. A relative increase in the average total and diffuse optical transmittance up to 5% and 500%, respectively, is obtained in the 400–800 nm spectral range as a consequence of the generated micro- and nanostructures. Calculations of two figures of merit suggest that the texturing of FTO might enhance the efficiency of solar cells, in particular dye-sensitized (DSSCs). The findings of this study confirm that DLIP is a convenient technique for structuring electrodes for highly efficient optoelectronic devices.     

Fabrication of diamond microstructures for microelectromechanical systems (MEMS) by a surface micromachining process

Selective polycrystalline diamond thin film has been grown on a silicon dioxide/silicon substrate using high pressure microwave plasma-assisted chemical vapor deposition from a gas mixture of methane and hydrogen at a substrate temperature of 950°C. A simple process flow has been developed to fabricate diamond microstructures such as diamond beams and cantilever beams using surface micromachining and photolithography for the first time. Scanning electron and optical microscopy has been used to characterize the surface micromachined diamond microstructures.     

X-ray determination of strain and texture in sputtered molybdenum and titanium films on silicon

Molybdenum and titanium films prepared with a rotating r.f. diode system were examined by X-ray diffraction for strain and texture. Both films were deposited onto (111)-oriented silicon crystal substrates. Molybdenum films 1.13 μm thick sputtered with a target voltage of -2.7 kV, a zero substrate bias and an average temperature of 180°C were in compression on cooling to room temperature. Pole density plots for the (200), (211), (220), (222), (301) and (321) planes gave relatively sharp peaks. The (220) plane showed a strong peak parallel to the (111) plane on silicon. In contrast, a 1.25 μm titanium film was found to be in tension after sputtering at -2.7 kV, a substrate bias of -50 V and an average temperature of 180°C. Relatively broad pole density plots were found for the (002) and (110) planes. The (100) and (110) planes gave peaks parallel to (111) Si. Intrinsic strains from embedded argon were determined from χ scan X-ray data.     

Locally oxidized silicon surface-plasmon Schottky detector for telecom regime

We experimentally demonstrate an on-chip nanoscale silicon surface-plasmon Schottky photodetector based on internal photoemission process and operating at telecom wavelengths. The device is fabricated using a self-aligned approach of local-oxidation of silicon (LOCOS) on silicon on insulator substrate, which provides compatibility with standard complementary metal-oxide semiconductor technology and enables the realization of the photodetector and low-loss bus photonic waveguide at the same fabrication step. Additionally, LOCOS technique allows avoiding lateral misalignment between the silicon surface and the metal layer to form a nanoscale Schottky contact. The fabricated devices showed enhanced detection capability for shorter wavelengths that is attributed to increased probability of the internal photoemission process. We found the responsivity of the nanodetector to be 0.25 and 13.3 mA/W for incident optical wavelengths of 1.55 and 1.31 μm, respectively. The presented device can be integrated with other nanophotonic and nanoplasmonic structures for the realization of monolithic opto-electronic circuitry on-chip.     

Structural investigation of silicon films chemically vapour deposited onto amorphous SiO2 substrates

The influence of substrate temperature and the silane-to-nitrogen ratio on the structure of silicon films 0.5–0.6 μm thick deposited onto amorphous SiO₂ substrates was investigated by X-ray diffraction. The investigations were carried out for silicon films deposited at various temperatures in the range 500–750 °C and with various silane-to-nitrogen ratios in the range 3.04 × 10^-4-2.84 × 10^-3 by volume. The silicon films deposited at 500 °C were amorphous while the films deposited at 550 °C were randomly oriented polycrystalline. The films deposited in the temperature range 600–700 °C were polycrystalline with a preferred orientation that changed from 〈110〉 through 〈100〉 to 〈111〉. The structure of the films deposited at 750 °C was randomly oriented polycrystalline. Investigations of the influence of the silane-to-nitrogen ratio on the silicon film structure revealed that the structure of films deposited at a substrate temperature of 500 °C was independent of the silane-to-nitrogen ratio. The structure of the films deposited at 600 °C depended on the silane-to-nitrogen ratio and changed from polycrystalline with a 〈110〉 preferred orientation to randomly oriented polycrystalline when the ratio was increased. The structure of films deposited at 700 °C also depended on the silane-to-nitrogen ratio and changed from randomly oriented polycrystalline to polycrystalline with double preferred orientation (〈100〉 and 〈111〉) when the ratio was increased.     

The microstructure of aluminium thin films on amorphous SiO2

The microstructure of aluminium thin films deposited onto amorphous SiO₂ by tungsten filament evaporation was studied by transmission and scanning electron microscopy and grazing-incidence X-ray diffraction. The early stages of film growth were characterized by an island or connected-network structure and a random grain orientation. The thickness at which complete coverage occurred ranged from 15 nm at 295 K to 100 nm at 625 K, and above this thickness a 〈111〉 fibre texture became apparent.The grain size distribution of films 1 μm thick was log-normal and the average grain size ranged from 500 nm for deposition at 295 K to 4 μm for deposition at 675 K. “Growth hillocks” were observed on the surface of films deposited at 295 K but were absent when higher substrate temperatures were used. Annealing caused grain growth and the formation of “annealing hillocks” which were of different structure from the growth hillocks.Examination of a small number of electron-beam-deposited aluminium films showed these to have similar microstructures to the filament-evaporated films, whereas sputter-deposited films were characterized by a smaller grain size and random orientation.     

Great enhancement of infrared light absorption of silicon surface-structured by femtosecond laser pulses in N2 ambient

The enhanced light absorption of surface-microstructured silicon, prepared by cumulative irradiating with femtosecond laser pulses in ambient gas of N₂, was presented in this letter. The blunt conical spikes formed on silicon surface after irradiation are of elliptic conical shape due to the linearly polarized laser irradiation. Greatly enhanced light absorption of such surface-structured silicon was observed in the whole measured wavelength range from 0.3 to 16.7 μm. The light absorptance is up to 95% over the wavelength range of 0.3∼1.1 μm and as high as 75% or more in wavelength range of 8.8∼13.3 μm, though it is down to about 30% in the wavelength range of 2∼7 μm.