High-efficiency reflective diffraction gratings in fused silica as (de)multiplexers at 1.55microm for dense wavelength division multiplexing application

We describe high-efficiency, high-dispersion reflection gratings fabricated in bulk fused silica illuminated by incident lights in the C + L bands as (de)multiplexers for dense wavelength division multiplexing (DWDM) application. Based on the phenomenon of total internal reflection, gratings with optimized profile parameters exhibit diffraction efficiencies of more than 90% under TM- and TE-polarized incident lights for 101-nm spectral bandwidths (1520-1620 nm) and can reach an efficiency of greater than 97% for both polarizations at a wavelength of 1550 nm. Without loss of metal absorption, without coating of dielectric film layers, and independent of tooth shape, this new kind of grating should be of great interest for DWDM application.     

薄膜体声波滤波器AlN压电薄膜的ICP刻蚀研究

随着5G通信技术的发展,通信频段不断提高,以氮化铝(AlN)为压电薄膜材料的薄膜体声波滤波器作为目前唯一可集成的射频前段滤波器成为研究热点之一。本文开展AlN材料刻蚀工艺的实验研究,实验中采用光刻胶作为刻蚀掩膜,Cl₂/BCl₃作为刻蚀工艺气体,通过一系列工艺影响参数调整及相应刻蚀结果分析,获得了ICP源功率、RF偏压功率、腔体压强和BCl₃气体流量对AlN材料和光刻胶掩膜刻蚀速率、刻蚀形貌的影响规律。通过综合优化工艺参数,最终得到了侧壁平坦、表面光滑的空气隙型薄膜体声波滤波器三明治结构。     

分布反馈量子级联激光器的光栅制备

利用全息曝光方法制备了分布反馈量子级联激光器的光栅掩模,选择和发展了恰当的用于InGaAs/InP材料的光栅腐蚀优化工艺,得到腐蚀规律,讨论了腐蚀机制。在量子级联激光器的InGaAs/InP层上制备光栅得到分布反馈量子级联激光器,其单模特性较好,信噪比大于30dB。     

Diffraction gratings of photosensitive ZrO2 gel films fabricated with the two-ultraviolet-beam interference method

Photosensitive ZrO(2) gel films were patterned with a two-beam interference method by use of a 325-nm-wavelength He-Cd laser for the first time to our knowledge. The ZrO(2) gel films were prepared from Zr(O-n-C(4)H(9))(4) chemically modified with benzoylacetone. We fabricated uniform gratings with a 0.5-mum period on Si or SiO(2) substrates by etching the gel films in ethyl alcohol after UV irradiation. A maximum diffraction efficiency of 28% was attained with the grating fabricated on Si substrate under a Littrow mounting condition by use of a 633-nm-wavelength He-Ne laser. Blazed gratings could also be fabricated.     

High-efficiency transmission gratings buried in a fused-SiO2 glass plate

Binary gratings were fabricated with high first-order diffraction efficiency by conventional electron-beam drawing and subsequent inductive coupled-plasma dry etching upon the surfaces of SiO2 glass plates. The gratings were covered with a thin SiO2 film by plasma-enhanced chemical-vapor deposition without the grooves' being filled in. The buried gratings exhibited first-order diffraction efficiencies of 84% for transverse-electric and 87% for transverse-magnetic polarized light at a wavelength of 1.55 microm when the period and the depth were 1.5 and 2.8 microm, respectively.     

Antireflective hydrophobic si subwavelength structures using thermally dewetted Ni/SiO2 nanomask patterns

We report the disordered silicon (Si) subwavelength structures (SWSs), which are fabricated with the use of inductively coupled plasma (ICP) etching in SiCl4 gas using nickel/silicon dioxide (Ni/SiO2) nanopattens as the etch mask, on Si substrates by varying the etching parameters for broadband antireflective and self-cleaning surfaces. For the fabricated Si SWSs, the antireflection characteristics are experimentally investigated and a theoretical analysis is made based on the rigorous coupled-wave analysis method. The desirable dot-like Ni nanoparticles on SiO2/Si substrates are formed by the thermal dewetting process of Ni films at 900 degrees C. The truncated cone shaped Si SWS with a high average height of 790 +/- 23 nm, which is fabricated by ICP etching with 5 sccm SiCl4 at 50 W RF power with additional 200 W ICP power under 10 mTorr process pressure, exhibits a low average reflectance of approximately 5% over a wide wavelength range of 450-1050 nm. The water contact angle of 110 degrees is obtained, indicating a hydrophobic surface. The calculated reflectance results are also reasonably consistent with the experimental data.     

Highly efficient transmission gratings in fused silica for chirped-pulse amplification systems

We report on highly efficient transmission gratings in fused silica with a grating period of 800 nm generated by electron-beam lithography. At a wavelength of 1060 nm, 95% diffraction efficiency is achieved under Littrow conditions. The damage threshold, extremely enhanced compared with conventional gold-coated diffraction gratings, makes these gratings the key elements in high average power (>100 W) femtosecond fiber chirped-pulse amplification systems.     

Wavelength demultiplexing with layered multiple Bragg gratings in LiNbO3:Fe crystal

Dense wavelength division multiplexing (DWDM) is an important technology for expanding the capacity of optical network. The optical component based on the superimposed Bragg gratings shows that it can be used as one of advantageous multichannel components because of its excellent angle and wavelength selectivities. An optimized method for recording multiple Bragg gratings for wavelength demultiplexing in optical telecommunication band is proposed to achieve gratings with equal diffraction efficiency. A structure of three layers with twenty four gratings is demonstrated in a LiNbO(3):Fe crystal by employing the optimized recording method. Then an initial wavelength demultiplexing experiment based on the formed gratings is carried out in optical telecommunication C-band. The results obtained by measuring and analyzing the transmitted spectra of the fabricated gratings show that the diffraction efficiencies of the gratings are uniform. It is suggested that this kind of multiple gratings can be used for increasing the number of the demultiplexed wavelengths in recording medium with unit volume for WDM.     

熔石英元件抛光加工亚表面缺陷的检测

亚表面缺陷的准确检测是进行亚表面损伤研究的前提和基础,对保证光学元件加工质量至关重要.基于HF酸化学蚀刻法对熔石英元件抛光加工产生的亚表面水解层、缺陷层深度和亚表面损伤形貌进行了定量检测,并利用X射线荧光光谱法研究了熔石英抛光试件杂质元素的种类和元素含量沿深度分布规律,提出了熔石英元件抛光加工亚表面损伤深度的判定方法.研究表明:由于水解层和亚表面缺陷层的存在,熔石英抛光试件的蚀刻速率随着时间的增加呈现递减的趋势,且在蚀刻的初始阶段蚀刻速率下降尤为明显;当蚀刻深度超过某一特定值后,全部或部分覆盖在水解层以下的缺陷层将会被完全蚀刻去除,蚀刻速率基本保持不变;另外,熔石英抛光试件存在多种形式的表面及亚表面缺陷,在不同蚀刻深度,亚表面损伤形貌、划痕的宽度和深度也存在一定的差异.     

单晶铌酸锂薄膜光波导的制备研究

为了优化单晶铌酸锂薄膜光波导的性能,研究了基于单晶铌酸锂薄膜材料的光波导刻蚀工艺。虽然Ar⁺物理刻蚀能够达到最高95 nm/min的刻蚀速率,但难以获得光滑的波导侧壁,且以Cr作为掩膜的刻蚀选择比为1∶1,这意味着较差的选择性使其难以实现铌酸锂的深刻蚀。而采用反应离子刻蚀(RIE)得到的刻蚀速率较低,但是以Cr作为掩膜的刻蚀选择比能够达到6∶1以上,同时能够获得光滑、陡直的侧壁形貌。最终在450 nm厚度的单晶铌酸锂薄膜上,采用RIE制备了宽度为4μm、高度为370 nm的脊型光波导,并以端面耦合的方法进行测试,得到该波导的传输损耗约为5.2 dB/cm。     

The Groove Profile Formation of Holographic Gratings

Models for predicting the groove profile of metal coated holographic gratings, fabricated in positive photoresist, are studied. Development is assumed to be an etching process, where the etching is directed perpendicularly to the resist-developer interface. Two methods for metal coating are considered; vacuum evaporation and sputtering, and models that describe the profile formation for these cases are presented. It is noted that even a thin coating has a considerable effect on the profile. The theoretical groove profiles are found to be in good agreement with experimental profiles, obtained from SEM photographs of fabricated gratings.     

Binary gratings for CO(2) laser-beam diagnostics

Properties of binary gratings for beam diagnostics of high-power CO(2) lasers are investigated. The layout uses a modal theory that includes absorption of metallic surfaces by an impedance boundary condition. Radiation-resistant gratings were fabricated in copper with photolithography combined with galvanic technology. In this way gratings have been realized in which the first-order diffraction efficiencies are polarization independent. Use of a second grating to reduce elliptical beam distortion is demonstrated. Finally it is shown that Rayleigh anomalies for binary diagnostic gratings are accompanied by high absorption.     

Fabrication and characterization of microstructures with optical quality surfaces in fused silica glass using femtosecond laser pulses and chemical etching

We present a study of the sidewall surface quality inside microchannels fabricated in fused silica glass by femtosecond laser pulses and chemical etching. Multiple combinations of laser exposure and etching solution parameters were examined. Results of scanning electron microscopy, atomic force microscopy, and optical reflection analyses of the surfaces are presented. The results obtained demonstrate the feasibility of optical quality surface fabrication, which in turn demonstrates the feasibility of fabricating complex integrated devices containing microfluidic channels and optical waveguides in the glass substrates.     

Fabrication and characterization of large-core Yb/Al-codoped fused silica waveguides using dry etching

A deep inductively coupled plasma etching process was developed as a part of a continuous effort to develop an all-silica on-chip platform for high-power optical devices. Combined F and Cl based etching chemistry was found most suitable since silica matrix and Al doping are generally etched using different chemistries. First large-core (∼20 × 20 μm) Yb/Al-codoped fused silica waveguides on pure silica substrate were successfully fabricated, featuring ∼1 dB/cm optical propagation loss.     

Broadband and wide-angle antireflection subwavelength structures of Si by inductively coupled plasma etching using dewetted nanopatterns of Au thin films as masks

We report the broadband and wide-angle antireflection subwavelength structures (SWSs) on silicon (Si) substrate by inductively coupled plasma (ICP) etching using gold (Au) nanopatterns as etch masks. The reflectance depends strongly on the etched profile of Si SWSs which is influenced by both thermal dewetting and etching conditions. The size, shape, and array geometry of nano-sized patterns, which are produced via the thermal dewetting of Au thin films, are optimized under proper heat treatment. The etched depth and shape of Si nano tips are controlled additionally by ICP power, thus achieving the efficient antireflection characteristics. The optimized Si SWS with the tapered structure and sharp tips at high ICP power leads to a significantly low reflectance value of < 1% at wavelengths of 350-1100 nm. Furthermore, it exhibits a wide-angle antireflection property of < 7.5% at incident angles of 8-70° over a wide wavelength range of 300-1100 nm.     

Submicron dry-etching behavior of β-FeSi2 thin films towards fabrication of photonic crystals

We have investigated dry-etching properties of polycrystalline β-FeSi₂ films formed by ion-beam sputter-deposition (IBSD) and the films epitaxially grown on Si by metal organic chemical vapor deposition (MOCVD) in order to realize fabrication of photonic crystals with several hundreds nanometers in dimension. Using reactive ion etching with magnetic neutral loop discharge (NLD) plasma, we succeeded in realizing a comparatively higher etching rate than that obtained by inductively coupled plasma (ICP). Both reactive ion etching and impact ion etching modes may contribute to etching of β-FeSi₂. We have fabricated a two-dimensional photonic crystal of β-FeSi₂ on Si substrates and confirmed its predicted photonic properties in a reflectance spectrum of polarized light.     

石墨的微加工工艺研究

石墨具有固态超滑和耐酸、耐碱和耐有机溶剂腐蚀等特性, 使其有望成为微机电系统 (MEMS) 基础材料的一种选择。如能通过微纳米加工工艺对石墨进行微加工并在石墨上大批量、稳定、可控地制备各种掩模图案和石墨微结构, 一定程度上可以推动石墨成为MEMS基础材料。故本文通过工艺设计和参数摸索, 利用薄膜沉积、光刻、刻蚀等常用的微纳米加工工艺对石墨进行微加工研究, 并对加工后的石墨进行表征。结果表明, 利用薄膜沉积技术在石墨表面沉积的薄膜可以满足后续光刻和刻蚀等工艺的要求。同时, 采用光刻技术能在石墨表面大批量、稳定、可控地加工出不同形状, 不同尺寸的光刻胶掩模图案。此外, 利用刻蚀技术可以在石墨上大批量、稳定、可控地加工出形状较规则, 排列整齐且垂直度较高的石墨微结构。     

Antireflective subwavelength structures on microlens arrays-comparison of various manufacturing techniques

Antireflective subwavelength structures (ARS) resembling nanostructures found on the cornea of night-active insects reduce the reflection of light by providing a gradual change in the refractive index at the interface. These artificial ARS have mainly been fabricated by a combination of conventional lithography and reactive ion etching, which constrains their application to planar substrates. We report on the fabrication of ARS using three different techniques including bottom-up and top-down methods as well as their combination on microlens arrays (MLAs) made of fused silica. The optical performance of the resulting ARS on the MLAs is as good as ARS fabricated on planar substrates with increased transmission of up to 96% at certain wavelengths.     

Hot-wire chemical vapor deposition of silicon nanoparticles on fused silica

Silicon nanoparticles on fused silica have potential as recombination centers in infrared detectors due quantum confinement effects that result in a size dependent band gap. Growth on fused silica was realized by etching in HF, annealing under vacuum at 700-750 °C, and cooling to ambient temperature before ramping to the growth temperature of 600 °C. Silicon particles could not be grown in a thermal chemical vapor deposition (CVD) process with adequate size uniformity and density. Seeding fused silica with Si adatoms in a hot-wire chemical vapor deposition (HWCVD) process at a disilane pressure of 1.1 × 10^− 5 Pa followed by thermal CVD at a disilane pressure of 1.3 × 10^− 2 Pa, or direct HWCVD at a disilane pressure of 2.1 × 10^− 5 Pa led to acceptable size uniformity and density. Dangling bonds at the surface of the as-grown nanoparticle were passivated using atomic H formed by cracking H₂ over the HWCVD filament.     

Bragg gratings written in Sn-Er-Ge-codoped silica fiber: investigation of photosensitivity, thermal stability, and sensing potential

Bragg gratings were fabricated in an Sn-Er-Ge-codoped silica fiber with a phase mask and ultraviolet radiation from a 248-nm KrF excimer laser. The photosensitivity of the fiber was examined by studying the initial growth rate of the gratings written into it. The thermal stability of the gratings was investigated and modeled in terms of both the refractive-index modulation and the effective refractive index of the fiber core. It was shown that the temperature-induced irreversible shift in the Bragg wavelength could not be predicted by the isothermal decay of the refractive-index modulation. Finally, the potential of the gratings written into the fiber is discussed in terms of their use in high-temperature-sensing applications.