Antireflective properties of AZO subwavelength gratings patterned by holographic lithography

We fabricate the aluminum-doped zinc oxide (AZO) subwavelength gratings (SWG) on Si and glass substrates by holographic lithography and sequent CH₄/H₂/Ar reactive ion etching process. The etch selectivity of AZO over photoresist mask as well as the nano-scale shape is optimized for better antireflection performance. To analyze the antireflective properties of AZO SWG surface, the optical reflectivity is measured and then calculated together with a rigorous coupled-wave analysis. The reflectance spectrum can be considerably changed by incorporating the SWG into AZO film. As the SWG height of AZO on Si substrate increases, the magnitude of interference oscillations in the reflectance spectrum tends to be reduced with the larger difference between its maxima. The use of optimized SWG can significantly reduce the surface reflection of AZO film at the desired wavelengths. The measured reflectance data of AZO SWG are reasonably consistent with the simulation results. No considerable change in transmission characteristics is observed for AZO SWG structures.     

Effect of etching parameters on antireflection properties of Si subwavelength grating structures for solar cell applications

We fabricate the aluminum-doped zinc oxide (AZO) subwavelength gratings (SWG) on Si and glass substrates by holographic lithography and sequent CH₄/H₂/Ar reactive ion etching process. The etch selectivity of AZO over photoresist mask as well as the nano-scale shape is optimized for better antireflection performance. To analyze the antireflective properties of AZO SWG surface, the optical reflectivity is measured and then calculated together with a rigorous coupled-wave analysis. The reflectance spectrum can be considerably changed by incorporating the SWG into AZO film. As the SWG height of AZO on Si substrate increases, the magnitude of interference oscillations in the reflectance spectrum tends to be reduced with the larger difference between its maxima. The use of optimized SWG can significantly reduce the surface reflection of AZO film at the desired wavelengths. The measured reflectance data of AZO SWG are reasonably consistent with the simulation results. No considerable change in transmission characteristics is observed for AZO SWG structures.     

Third-order nonlinear optical properties in [(C4H9)4N]2[Cu(C3S5)2]-doped PMMA thin film using Z-scan technique in picosecond pulse

An organometallic complex, [(C₄H₉)₄N]₂[Cu(C₃S₅)₂], abbreviated as BuCu, was synthesized. Then the BuCu-doped polymethylmethacrylate (PMMA) thin film with a doping concentration 1% by weight (1 wt.%) was fabricated using a spin-coating method and its third-order nonlinear optical properties were characterized using the Z-scan technique with 20 ps pulse duration at 532 and 1064 nm, respectively. The Z-scan curves have revealed that the material exhibits a self-defocusing effect at both wavelengths. Saturable absorption at 532 nm and two-photon absorption at 1064 nm were also found, respectively. Additionally, the calculated results of the material in film were compared with that of acetone solution, which indicated that the values in film were larger than that of acetone solution for about two orders in magnitude. The origins were analyzed of the difference between the two wavelengths. Our results suggest that considerable nonlinear optical properties were confirmed in BuCu-doped PMMA film. The material can easily be doped into PMMA film and forms a waveguide mode. So this material should be considered to be manufactured into devices and applied in all-optical switching, laser locking-mode, optical limiting fields etc.     

双色俘精酸酐薄膜的双波长图像光存储

采用两种光致变色俘精酸酐体系化合物[1,2,4-三甲基-5-苯基-3-吡咯甲叉(异丙叉)俘精酸酐和对-N,N-二甲基苯基-2-甲基-3-恶唑甲叉(异丙叉)俘精酸酐]制备了单层双色聚甲基丙烯酸甲酯(PMMA)复合薄膜感光记录材料。采用双波长(650nm和488nm)图像存储和读出光路,实现了用两种波长在双色复合薄膜的同一位置同时记录两幅图像。当分别用各自对应的波长读出时,两幅图像各自获得了高衬比度,且二者之间的串扰很小,证明了在双色光致变色俘精酸酐材料上进行双波长复用图像光存储的可行性。     

Flexible subwavelength gratings fabricated by reversal soft UV nanoimprint

We present a replication process, named reversal soft ultraviolet (UV) nanoimprint, to fabricate a high- aspect-ratio flexible subwavelength grating (SWG) on a polyurethane acrylate (PUA). This nanopatterning technique consists of casting, reversal UV imprint, and dry release. The UV curing process of PUA to avoid pattern collapse is investigated. Revalpha film acts as the supporting and sacrificial layer during the whole process due to its special surface energy property. The free-standing PUA structures with a period of 200 nm and a depth of 350 nm can be automatically released from the Revalpha film by heating. The PUA resist is well suited to replicate fine patterns of the mold with high aspect ratio and large area precisely and uniformly for low surface energy and low viscosity. The measured transmittance is compared with the calculation results based on rigorous coupled-wave analysis in the wavelength region ranging from 500 to 800 nm. The experimental results agree well with the theoretical calculations.     

A novel dual-wavelength fiber Bragg grating and its application in fiber ring laser

A novel method for fabricating dual-wavelength fiber Bragg gratings (FBGs) by using one phase mask is developed. The method is based on a double-exposure technique. Our technique lends itself to writing gratings with controllable reflectivity and separation of two Bragg wavelengths. A grating with two equal transmission peaks of 20.25 dB is obtained by this method and the separation of the two Bragg wavelengths is about 0.8 nm. With the grating, we demonstrate a dual-wavelength erbium-doped fiber ring laser whose interval of the two peaks is 0.8 nm. The laser's peak powers can get 3.1 mW above and have a good stability.     

偶氮染料掺杂高分子薄膜的光谱和光存储性质研究

利用旋涂法,制备了以二乙基胺基〖Ｎ（ＣＨ２ＣＨ３）２〗作为推电子基因、以具有强电负性的羧基（ＣＯＯＨ）作为拉电子基团的推－拉型偶氮染料掺杂的高分子（ＰＭＭＡ）薄膜。在室温下测试了该偶氮染料在溶液和薄膜态的吸收光谱、薄膜态的反射光谱和透过光,发现该薄膜在４００～５５０ｎｍ波长范围内具有强的吸收。在５１４．５ｎｍ光盘静脉测试仪上测试了膜片的静脉光存储性能,结果表明,用低功率Ａｒ＾＋激光（５１４．５ｎ     

Study on the thermo-optic properties of DR1/PMMA composite

This paper reports that the thermo-optic coefficient (\dd n / \dd T) as well as thermal expansion coefficients (\beta) of DR1/PMMA polymer film are measured for both TE (transversal electric) and TM (transversal magnetic) polarizations by using an attenuated total reflection configuration at the wavelengths of 832nm. The thermo-optic coefficients of DR1/PMMA are negative and as high as the order of 10^-4/℃. The influences of dopant concentration, poling process and photobleaching process on the thermo-optic properties of DR1/PMMA are also investigated.     

Optical limiting response by embedding copper phthalocyanine into polymer host

The multilayer film of PMMA containing mononuclear octakis(mercaptopropylisobutyl-POSS) substituted phthalocyaninato-copper (CuPc) was obtained by spin-coating on quartz substrate. The nonlinear absorption and optical limiting (OL) performance of CuPc have been described using the open-aperture Z-scan technique. The measurements were performed using collimated 4 ns pulses generated from a frequency-doubled Nd:YAG laser at 532 nm wavelength. The results indicate that CuPc/PMMA composite exhibits a much larger nonlinear absorption coefficient, a lower saturable fluence and a lower absorption cross-section ratio for optical limiting when compared to the same CuPc molecules in solution. No evidence of film fatigue or degradation was observed in the CuPc/PMMA film after numerous scans at varying laser intensity. This material is a good candidate for optical limiting applications.     

MOCVD多功能在线监测探头的设计与实现

根据MOCVD在线监测设备的发展需要,设计了一种多功能在线监测探头,能够同时实现带反射率修正的三种红外辐射测温以及两个波长的反射率曲线监测,即:940nm/1 550nm双波长比色测温、940nm单色辐射测温、1 550nm单色辐射测温、940nm反射率曲线以及1 550nm反射率曲线监测.对探头的比色测温性能进行测试分析,并利用该探头对Si(111)衬底在我国自主研发的MOCVD系统中生长InGaN/GaN MQW结构蓝光LED外延片进行在线监测.结果分析表明:比色测温900℃~1 100℃范围内精度高于1℃;在700℃~1 100℃范围内重复性误差均在0.7℃内;距离容差性为2mm;三种红外测温最低量程均为435℃;并能有效避免探测孔有效面积变化的影响;由940nm反射率曲线得:n-GaN层的膜厚监测相对误差为3.6%.该设计能够同时实现MOCVD在线测温及膜厚测量,可为MOCVD在线监测设备开发提供参考.     

聚合物材料PMMA/DR1光漂白过程中折射率的变化

用双光束扫描法研究了在488nm的Ar^ 激光照射下，聚合物材料RMMA／DR1的光漂白过程，为精确测量光漂白模型中的参数提供了一种简单实验方法。这对于今后用光漂白的方法制备光波导器件具有重要意义。     

同时辐射六种可见波长的CW-氦氖激光器的稳频及其输出的650nmCW氦氖受激Raman辐射

在中国计量科学研究院研制的612激光管上,利用反射率为99.95%宽带激光反射镜,得到同时辐射六种波长的连续振荡,其波长为:611.8,629.8,632.8,635.1,640.1和650um,测量了它们的物理参数,验证了650nm为氦氖Raman激光.对六种波长在简易装置上进行了稳频,各条激光谱线的频率稳定性优于10~(-10),利用锁模技术,各条激光谱线的频率稳定性可达10~(-12).     

Vacuum ultraviolet smoothing of nanometer-scale asperities of Poly(methyl methacrylate) surface

Smoothing of the nanometer-scale asperities of a poly(methyl methacrylate) (PMMA) film using vacuum ultraviolet (VUV) with the wavelength λ = 123.6 nm was studied. The exposure time and the residual air pressure in an working chamber were varied during the process of VUV treatment. A nanostructured surface of PMMA film is used as a sample to be exposed. The nanostructured surface of the PMMA film was obtained by treating the initially smooth spin-coated film in oxygen radio-frequency plasma. The degree of VUV exposure is estimated using changes in the morphology and roughness of the nanostructured surface, which were determined by atomic-force microscopy (AFM). Recognition of morphological surface features on the AFM-images and determination of main geometrical characteristics of these features are performed by using virtual feature-oriented scanning method. It is discovered by morphology and Fourier spectra that the nanostructured surface of the PMMA film is partially ordered. The developed VUV smoothing procedure can be used to treat the electron-beam, UV, and X-ray sensitive PMMA resists, PMMA elements of microelectromechanical systems, biomedical PMMA implants, as well as to certify nanotechnological equipment incorporating UV radiation sources.     

Light emitting CdS quantum dots in PMMA: Synthesis and optical studies

Freshly prepared CdS-quantum dots (QDs) in DMF (clear pale solution) when loaded in polymethylmethacrylate (PMMA) lead to excellent optical properties. The tuning of the absorption and emission wavelengths via experimentally control parameters is considered novel and significant. The absorption band for CdS was observed at about 370 nm in polymeric matrix. The blue, green and orange light emissions from such composite solution were tuned and stabilized by simply varying the concentration of CdS, cadmium and sulphur in the final product. Photoluminescence (PL) measurement with 2% CdS loading showed band-edge emissions from the composite with only about 20-25 nm Stokes shift in emission wavelength. Observation of such optical properties indicated that the composite has narrow particle size distribution and particle diameter may well be below 10 nm. X-ray diffraction (XRD) patterns of the film with higher loading of CdS showed broad pattern for hexagonal CdS. Thermo-gravimetric analysis (TGA) of CdS/PMMA composite film revealed that it has better thermal stability than PMMA alone. Transmission electron microscopy (TEM) showed agglomerated tiny dots in nano-meter regime.     

Thermal stability of Mo/Si multilayer soft-X-ray mirrors fabricated by electron-beam evaporation

Mo/Si multilayers are fabricated by electron-beam evaporation in UHV at different temperatures (30° C, 150° C, 200° C) during deposition. After completion their thermal stability is tested by baking them at temperatures (T _bak) between 200° C and 800° C in steps of 50° C or 100° C. After each baking step the multilayers are characterized by small angle Cu_K-X-ray diffraction. Additionally, the normal incidence soft-X-ray reflectivity for wavelengths between 11 nm and 19 nm is determined after baking at 500° C. Furthermore, the layer structure of the multilayers is investigated by means of Rutherford Backscattering Spectroscopy (RBS) and sputter/Auger Electron Spectroscopy (AES) technique. While the reflectivity turns out to be highest for a deposition temperature of 150° C, the thermal stability of the multilayer increases with deposition temperature. The multilayer deposited at 200° C stands even a 20 min 500° C baking without considerable changes in the reflectivity behaviour.     

新型AgInSbTe相变薄膜的光学及记录性能

利用直流磁控溅射法制备了一种新型AgInSbTe相变薄膜。示差扫描量热(DSC)实验测定的结晶峰温度为193．92℃。X射线衍射(XRD)表明未经热处理的沉积态薄膜是非晶态,而经过200℃热处理,X射线衍射图出现衍射峰,薄膜从非晶态转变到晶态。同时,研究了晶态和非晶态相变薄膜的吸收率、透射率和反射率随波长的变化。测定了650nm激光作用下的相变薄膜的记录性能,分析了记录功率、记录脉宽对薄膜反射率衬比度的影响,在同一记录脉宽条件下,记录功率越大,反射率衬比度也越大;在同一记录功率条件下,随记录脉宽的增加,反射率衬比度也增大。结果表明,新型AgInSbTe相变薄膜在激光作用下具有较高的反射率衬比度,可获得良好的记录性能。     

金属Al背电极二维AZO光栅的制备和陷光特性

研究了背电极金属Al膜上二维ZnO:Al光栅的制备及其反射光谱特性.在厚度为300 nm的Al膜上溅射80 nm ZnO:Al薄膜,旋涂AZ5206光刻胶,用波长为325 nm的激光进行光刻制作光栅掩模.采用溶脱-剥离法在Al衬底上制备周期(624~1250 nm)和槽深(100~300 nm)可独立调控的ZnO:Al二维光栅.表面形貌采用原子力显微镜和扫描电镜观察,反射光谱用带积分球的分光光度计测试,双向反射分布函数用散射仪测量.结果表明,300 nm Al膜上织构二维ZnO:Al光栅背电极结构,当光栅槽深为228 nm,周期从624 nm增加到986 nm时,背电极总反射率、漫反射率以及雾度均随光栅周期增大而显著增加,而当周期从986 nm增加到1250 nm时,总反射率、漫反射率以及雾度略有增加.双向反射分布函数测试结果进一步证实了上述实验结果,即随着周期增大,漫反射峰值越大,衍射峰个数也增多.提示背反电极上槽深为228 nm、周期为986 nm的二维ZnO:Al光栅具有较好的散射效果,其中漫反射占总反射的百分比为45%.     

Development of high-throughput, high-damage-threshold beam separator for 13 nm high-order harmonics

We demonstrate a high-throughput, high-damage-threshold beam separator for wavelengths shorter than 30 nm, which uses a 10 nm thick niobium nitrogen film prepared on a Si substrate, set at the Brewster angle relative to the pump wavelength. The film was deposited by rf reactive magnetron sputtering on a Si substrate. The beam separator has an attenuation ratio of 0.01 and a damage-threshold intensity of at least 0.8 TW/cm2 for a 26 fs pump pulse. The measured reflectivity of the beam separator exceeded 70% in a wavelength range of 13-18 nm. This broadband beam separator may be used to eliminate energetic laser pulses from longitudinally pumped x ray lasers as well as from high-order harmonics.     

Focusing subwavelength grating coupler for mid-infrared suspended membrane waveguide

A mid-infrared (mid-IR)-focusing subwavelength grating (SWG) coupler and suspended membrane waveguide (SMW) on a silicon-on-insulator wafer are studied. For a transverse-electric mode uniform SWG, finite-difference time-domain simulation predicts 44.2% coupling efficiency with 1 dB bandwidth of about 220 nm and backreflection of 0.78% at 2.75 μm. Then the uniform SWG is curved to a focusing SWG using a phase-matching formula. The SMWs are analyzed by the finite element method and fabricated. An Er3+-Pr3+ co-doped mid-IR fiber laser is used for device characterization. The fabricated mid-IR SWG coupler has 24.7% coupling efficiency.     

Fabrication of Dual-Wavelength Fiber Bragg Grating with a Longitudinal Stretch

A method of fabricating dual-wavelength fiber Bragg grating with a uniform phase mask is demonstrated. Theoretical analysis and numerical simulation using Matrix method are given. The moving exposing technique is adopted. Good control over the grating’s reflectivity and the separation of the two Bragg wavelengths is enabled by adjusting the stretch, the length of the grating, and the exposure. A grating with two equal transmission peaks of 19.5 dB is obtained by using this method, and the separation of the two Bragg wavelengths is 0.78 nm. Translated from Chinese Journal of Quantum Electronics, 2005, 22(1) (in Chinese)