Optimum index profile of the perfluorinated polymer-based GIpolymer optical fiber and its dispersion properties

The significant advantages in bandwidth and low material dispersion of perfluorinated (PF) polymer-based graded-index polymer optical fiber (GI POF) are theoretically and experimentally reported for the first time. It is confirmed that the low attenuation and low material dispersion of the PF polymer enables 1 Gb/s km and 10 Gb/s km transmission at 0.85-μm and 1.3-μm wavelengths, respectively. The PF polymer-based CI POF has very low material dispersion (0.0055 ns/nm·km at 0.85 μm), compared with those of the conventional PMMA-based POF and of multimode silica fiber (0.0084 ns/nm km at 0.85 μm). Since the PF polymer-based GI POF has low attenuation from the visible to near infrared region, not only the 0.65-μm wavelength which is in the low attenuation window of the PMMA-based GI POF, but other wavelengths such as 0.85-μm or 1.3-μm etc. can be adopted for the transmission wavelength. It is clarified in this paper that the wavelength dependence of the optimum index profile shape of the PF polymer-based GI POF is very small, compared to the optimum index profile shape of the silica-based multimode fiber. As a result, the PF polymer-based GI POF has greater tolerance in index profile variation for higher speed transmission than multimode silica fiber. The impulse response function of the PF polymer-based GI POF was accurately analyzed from the measured refractive index profile using a Wentzel, Kramers, Brillouin (WKB) numerical computation method. By considering all dispersion factors involving the profile dispersion, predicted bandwidth characteristic of the PF polymer-based GI POF agreed well with that experimentally measured     

CMP后的晶圆的测量和评估方法研究

综述了CMP后的晶圆测量方法,比较指出：光学干涉法适宜于测量较厚的薄膜,而椭圆偏振法精度较高,但成本高昂,适宜于测量薄的薄膜。CMP后需要检测晶圆的表面状况,列举了常用的扫描电子显微镜、原子力显微镜和光散射探测仪。扫描电子显微镜常用于特征线宽的测量,其精度可达4nm;原子力显微镜是根据范德华力的原理制造,其探测精度高达0．1nm：但二者最大的缺陷就是操作复杂,成像十分费时。散射探测仪根据光的散射理论制造。可以快捷地全表面成二维图像,是值得推荐的一种测量手段。最后,指出今后的测量技术对半导体工艺的影响。     

Cascade self-induced holography: a new grating fabricationtechnology for DFB/DBR lasers and WDM laser arrays

A method of fabricating submicron gratings for optoelectronic devices from a glass mask was proposed and demonstrated. The glass mask has gratings on both sides with a period of at least four times the final feature size. By introducing an offset to the grating periods on the mask, one can achieve multiple-period gratings with a very fine period spacing for advanced wavelength-division multiplexing (WDM) devices. In this paper, we demonstrated 0.5-μm second-order gratings for 1.55-μm DFB lasers and gratings with a 6-Å period difference for a four-channel WDM laser array using only optical sources. The Moire pattern caused by the spatial frequency beating was also observed and discussed. The Moire pattern could serve as an effective tool to measuring wavelength channel spacing between devices with an unprecedented (0.1 Å) resolution     

InGaAsP-InP ridge-waveguide DBR lasers with first-order surfacegratings fabricated using CAIBE

The design and operation of InGaAsP-InP ridge-waveguide (RW) distributed Bragg reflector (DBR) multiple quantum-well lasers with first-order surface gratings are presented. The RW DBR lasers are fabricated using only a single growth step without growth on a corrugated surface. Uncoated devices with grating etch depths of 0.6 and 0.5-μm exhibit pulsed threshold currents of 32 and 43 mA with slope efficiencies of 0.34 and 0.24 W/A, respectively. The device with a grating etch depth of 0.5-μm operates on a single longitudinal mode with about 40 dB side-mode suppression. All these results are from devices with Bragg condition wavelengths which are red-shifted from the peak spontaneous emission wavelength by over 400 Å     

Line-profile and critical-dimension monitoring using a normal incidence optical CD metrology

As lithographic technology drives the minimum integrated circuit feature size toward 0.1 /spl mu/m and below, process tolerances for critical-dimension profile excursion are becoming increasingly demanding. In response, optical critical dimension metrology (OCD), an optical-wavelength light-diffraction technique, is emerging as a fast, accurate, and nondestructive sub-100-nm linewidth and profile monitor. As such, a detailed understanding of the correlation between OCD and existing metrology tools is required. Correlation between CD measurements using OCD and CD-scanning electron microscopy (SEM) techniques is investigated by measuring two types of important structures, e.g., photoresist gratings on a polysilicon gate film stack and shallow trench isolation. Intragrating CD variation is shown to account for scatter in the correlation plot. A qualitative line-profile correlation between cross-section SEM (X-SEM) and OCD is presented for photoresist gratings in a focus exposure matrix. Finally, a summary of the capability of OCD as a monitor for various processing stages is presented.     

硅薄膜太阳电池高效陷光结构的研究

利用严格耦合波分析方法和模式传输线理论,对硅薄膜太阳电池结合DBR（Distributed Bragg Reflector,分布布拉格反射器）和衍射光栅的叠层底部背反射器结构进行了优化设计。结果表明,光栅周期、光栅厚度和光栅宽度分别为0.5λg、0.18λg、0.48λg（λg为硅的带隙波长）以及对应的DBR中心波长为0.85μm时,太阳电池对光子的总吸收最强,且总吸收的提高主要来自于对长波光子的吸收增强,提高了薄膜太阳能电池对长波光子的陷光能力。     

Fourier gratings as submillimeter beam splitters

Over the past years, a number of groups have developed phase gratings as local oscillator beam multiplexers for array receivers in the submillimeter wavelength domain. The most popular type of grating is the Dammann (1977) grating, a simple and versatile binary phase grating. We introduce a new type of grating, the Fourier grating, which, in contrast to the binary structure of Dammann gratings, uses a smooth grating structure. Due to the lack of sharp edges these gratings can be manufactured with high precision as reflection gratings even for two-dimensional (2-D) dispersion. Fourier gratings are designed using a simple optimization procedure that only involves a small number of parameters. Their diffraction efficiency is very high. We have produced a number of gratings and tested them at a frequency of 490 GHz, verifying the theoretical results     

Precise Grating Profile Evaluation for DFB Lasers Using an Optical Metrology

A precise grating profile evaluation method for distributed-feedback (DFB) laser diodes was achieved using a simple optical metrology. Spectroscopic scatterometry, an optical-wavelength light-diffraction technique, is emerging as a fast, accurate, and nondestructive means of monitoring profiles. A photoresist grating pattern on an InP substrate and an etched InP grating with periods of 0.2 and 0.24 mum were successfully evaluated by using unpolarized simple optical metrology. A precise grating profile evaluation technique with an accuracy of nanometers enabled us to obtain an accurate coupling coefficient (kappaL) for DFB laser diodes. DFB laser diodes with well-controlled kappaL are very promising for practical use in cost-effective optical networks.     

一种提高折叠光栅光谱仪信噪比的新方法

折叠光栅光谱仪由于折叠光栅制作、安装过程中的工艺问题,子光栅衍射图像易发生倾斜、变形。为了保证在对光栅衍射图像进行处理时不降低分辨率,每块子图像仅抽取单行像素校准,最终拼接成光谱,这导致光谱信噪比较低。为克服这一缺点,提出了一种软件提高折叠光栅光谱仪信噪比(SNR)的方法。通过对原始光谱图像进行校正、一维中值滤波和像素平均三个处理步骤,在不影响波长分辨率的情况下,使光谱信噪比提高约6倍。这种处理方法充分利用了光栅衍射图像的信息,对提高折叠光栅光谱系统探测微弱信号的能力具有实用价值。     

Phi-scatterometry for integrated linewidth and process control in DRAM manufacturing

A cost-effective scatterometry method is presented that is suited for integrated pattern and process control and is valuable as a supplement to conventional scanning electron microscopes. The phi-scatterometry procedure is carried out directly on periodic functional patterns instead of using additional test structures. Time-consuming simulations of diffraction effects are not required. The measurement results are evaluated by neural networks performing classifications of pattern and process parameters. Thereby, fast fault detection and immediate process control are achieved. The measurements were performed on a 300-mm wafer with systematically varied focus and exposure as well as on production lots, both with DRAM patterns featuring trenches in two dimensions. A phi-scatterometry prototype was built which is suited for flexible mobile metrology in 300-mm production environments.     

A pixellated grating array using photoelectrochemical etching on aGaAs waveguide

We have demonstrated and evaluated a grating array outcoupler fabricated by photoelectrochemical (PEC) etching, a manufacturable and practical approach for fabrication of grating-based III-V semiconductor waveguide devices. An array of submicron period gratings was etched into photolithographically delineated areas in a single PEC step. The fabricated devices are: 10-μm wide rib waveguides with 0.35-μm first-order outcoupling gratings; and 10-μm wide rib waveguides with 10 μm×10 μm pixellated areas of gratings. Device characterization demonstrates the effectiveness of outcoupling grating fabrication using PEC and that the pixellated grating outcoupler is an effective and simple means of generating an optical beam array     

飞秒激光在LiNbO3晶体上烧蚀衍射光栅

利用脉冲宽度为50 fs,中心波长为800 nm,重复频率为1000 Hz的乜秒激光脉冲在LiNbO3晶体上烧蚀表面衍射光栅,采用632.8 nm的He-Ne激光测量不同光栅的衍射效率.在激光脉冲能量和光栅常数相同的情况下,烧蚀速率由20 μm/s增大到200 μm/s时,所加工光栅的1级衍射效率从1.7%增大到2.3%;如果光栅常数和烧蚀速率不变,将激光脉冲能量由70 nJ增大到110 nJ,所加工光栅的1级衍射效率从1.9%减小到1.3%;随着光栅常数的增大,在LiNbO3晶体上烧蚀光栅的各级衍射效率也随之增加.对实验结果进行理论分析表明,可以通过提高烧蚀速率、降低激光脉冲能最和增大光栅常数来提高飞秒激光加工光栅的衍射效率.     

Generation of multiple-pitch gratings in WDM devices by using a single computer-generated phase mask

Use of a single computer-generated phase mask (CGPM) for monolithic fabrication of submicronmeter multiple-pitch gratings is proposed. The CGPM is a computer-generated Fourier hologram generating multiple diffracted beams with equal intensity from a single incident beam. The submicronmeter grating periods differing by as little as a few angstroms are estimated with basis of the multiple diffraction angles. As a result of preliminary experiment, an array of nine gratings has been achieved by using a CGPM with 2-/spl mu/m minimum feature size. Limit of the CGPM period due to increase in wavelength spacing of WDM devices is also discussed.     

Investigation of Bragg gratings on planar InGaAsP/InP waveguides atnormal and oblique incidence

The polarization-dependent mode coupling of Bragg gratings on planar InGaAsP/InP waveguides is investigated by transmittance and reflectance measurements at normal and oblique incidence in the 1.5-μm wavelength region. Strong coupling between TE (transverse electric) and TM (transverse magnetic) modes is observed at oblique incident, whereas the TE-TE coupling vanishes at an incidence angle of 45°. The behavior of the near field close to the Bragg wavelength and the effects of radiation into the substrate are analyzed. It is experimentally shown that small deformations of the phase fronts on the input side lead to strong interference effects on the output side     

Plane wave diffraction by dielectric gratings finite-differenceformulation

Plane-wave diffraction by dielectric gratings of arbitrary profile (groove shape and size) is analyzed using an analytical-numerical technique. The solution method is simple, general, and numerically efficient. It involves expansion in a Fourier series of the periodic permittivity function in the inhomogeneous grating region and application of the finite differences to solve numerically the inhomogeneous vector wave equation in the region. The obliquely incident radiation is of linear polarization with either of its fields parallel to the rulings. Numerical results are presented for several gratings to demonstrate the convergence, accuracy, and reliability of the method. These also show the effect of the grating profile on its diffraction characteristics     

High-throughput mapping of short-range spatial variations usingactive electrical metrology

Spatial variations of parameters in semiconductor manufacturing, such as critical dimension (CD) and overlay, have significant impact on the performance and yield of integrated circuits (IC). Among these spatial variations, the variations of parameters between transistors separated by a very short spatial distance such as 1 μm to 100 μm (intertransistor variations) can be particularly hazardous for those types of ICs that require exact transistor-transistor matching. To measure these intertransistor variations, both high-throughput and high-spatial-sampling-density beyond the scope of currently available metrology tools are needed. We have thus developed an active electrical metrology method of measuring intertransistor variations using on-chip, active, electrically addressable arrays of test structures to provide the high-throughput (5 μs/data point) and high-density (3 μm/grid spacing) needed. Test chips were designed and fabricated on a HP 0.35-μm process, and the testing configuration was set up to optimize throughput and precision. This method was verified with the measurements of on-chip calibration arrays. The spatial variations of both intertransistor CD (effective gate length) and overlay (between poly/diffusion) within the test chips were mapped with this method. For these circuits, the intertransistor CD variations were found to depend primarily on the layout, whereas the intertransistor overlay variations were found to be dominated by errors of the pattern generator used to fabricate the masks     

薄膜太阳电池二元光栅结构

提出了采用二元光栅结构提高太阳能薄膜衍射效率的技术方法。利用对透射率函数的傅里叶变换计算出垂直入射时二元光栅的衍射光场分布。研究了不同阶次二元光栅在可见和近红外波段的衍射零级光强和总衍射效率随波长变化的规律。以硅基太阳能薄膜为例,分别计算了普通相位光栅和二阶、三阶二元光栅随波长零级光强的变化规律和衍射效率。结果表明,与普通相位光栅结构相比,二元光栅结构能够在较宽波段提高光衍射效率。     

Crosstalk characteristics of a 1.3-μm/1.5-μm wavelengthdemultiplexing photodetector using laser-assisted MOMBE growth

This paper demonstrates a monolithic 1.3-μm/1.5-μm wavelength demultiplexing photodetector fabricated using Ar ion laser-assisted metal organic molecular beam epitaxy (MOMBE) growth. Reduction of crosstalk to -24 dB is accomplished in both 1.3-μm and 1.5-μm wavelength regions. The dependence of the crosstalk on the coupling efficiency between the fiber and device and the polarization dependence of the responsivity is also discussed     

Plasmonic Metasurfaces for Simultaneous Thermal Infrared Invisibility and Holographic Illusion

In 1860s, Gustav Kirchhoff proposed his famous law of thermal radiation, setting a fundamental contradiction between the infrared reflection and thermal radiation. Here, for the first time an ultrathin plasmonic metasurface is proposed to simultaneously produce ultralow specular reflection and infrared emission across a broad spectrum and wide incident angle range by combining the low emission nature of metal and the photonic spin–orbit interaction in spatially inhomogeneous structures. As a proof‐of‐concept, a phase gradient metasurface composed of sub‐wavelength metal gratings is designed and experimentally characterized in the infrared atmosphere window of 8–14 µm, demonstrating an ultralow specular reflectivity and infrared emissivity below 0.1. Furthermore, it is demonstrated that infrared illusion could be generated by the metasurface, enabling not only invisibility for thermal and laser detection, but also multifunctionalities for potential applications. This technology is also scalable across a wide range of electromagnetic spectrum and provides a feasible alternative for surface coating.     

Corrugation-pitch-modulated MQW-DFB laser with narrow spectrallinewidth (170 kHz)

A spectral linewidth of 170 kHz was achieved at a 1.5-μm wavelength in a 1200-μm long corrugation-pitch-modulated (CPM) distributed feedback (DFB) laser having multiple quantum wells (MQW). This is the narrowest linewidth ever reported for InGaAsP DFB lasers. The CPM structure is effective in maintaining the single longitudinal mode at a high output power by suppressing the spatial hole burning effect. The linewidth-power product is 400 kHz-mW, and the extrapolated residual spectral linewidth is 150 kHz