光纤光栅温度调谐特性分析与实验

提出了均匀调制光纤光栅的热调谐数学模型,确定了储热与布拉格波长之间的数学关系,分析光纤光栅热敏度,计算出热调谐的响应时间。设计和建立了一套光纤光栅温度调谐实验装置,利用光谱分析仪测试出光纤光栅反射波长漂移量受温度变化的关系曲线。测试了0～100℃的温度变化过程中光纤光栅反射波中心波长调谐量,测得光纤光栅反射中心波长λB为1546.8～1548.8nm,每摄氏度光纤光栅反射光波的中心波长平均漂移量为0.0210nm/℃。讨论了波长调谐量与温度的变化方向的关系和调谐响应速度等问题。实验结果表明光纤光栅反射波长漂移量与温度具有比较好的线性关系,且与温度的变化方向无关。     

Rb5Nd(MoO4)4 a self-tunable birefringent laser crystal

In this paper we report an experimental demonstration of broadband wavelength self-tuning in Rb₅Nd(MoO₄)₄ laser crystal (RNM) together with the theoretical treatment which explains the system behaviour based on its birefringent properties. The self-frequency tuning in RNM was obtained by inserting an a-cut plate inside the laser resonator close to the Brewster's angle. At a given position of the crystal plate, when the wavelength of the oscillating mode corresponds to an integral number of full-wave retardation in the plate, the laser operates in the p polarization of the Brewster surface with no losses. The experimental self-frequency tuning of the laser emission along the free spectral range of the RNM crystal (1062.94–1067.84 nm) was obtained by rotating the birefringent gain plate in its own plane. To investigate the tuning characteristics of the spectral filter, we have used the Jones-vector formalism. The calculated wavelength-selective tuning matches the experimental observations.     

Simulation of the initial tuning of a Mach-Zehnder interferometer

A phase difference equation is obtained describing the interference pattern of the initial tuning of a Mach-Zehnder interferometer on the basis of simulating the mutual orientation of wave fronts. The effect of parameters on this tuning is analyzed. A procedure is suggested for computing interferograms for any initial tuning. __________ Translated from Izmeritel’naya Tekhnika, No. 9, pp. 30–33, September, 2006.     

Bandgap Tuning by Using a Lattice Distortion Induced by Two Symmetries That Coexist in a Quantum Dot

Among the interests in the application of quantum dots (QDs), the bandgap tuning is of key importance in controlling their material properties. The bandgap of a QD can be adjusted by adopting a variety of different physicochemical methods. Herein, a novel way of the bandgap tuning is developed in an Ag2S‐based QD system by suitably quenching the transformation from monoclinic Ag2S to cubic Ag and by subsequently inducing a lattice‐distorted region of ≈1‐nm‐scale in a QD. The two distinct crystalline phases of Ag2S and Ag coexisting with the lattice‐distorted region are experimentally demonstrated by visually showing this remarkable coexistence in a QD. A new approach is presented to the bandgap tuning (2.51 to 1.64 eV) and enhancing optical properties by suitably tailoring the degree of the lattice‐distorted region in a QD. This conceptual method could pave a new way to utilizing quantum effects in various QD applications.     

A Two-stage Tuning Method of Servo Parameters for Feed Drives in Machine Tools

Based on the evaluation of dynamic performance for feed drives in machine tools, this paper presents a two-stage tuning method of servo parameters. In the first stage, the evaluation of dynamic performance, parameter tuning and optimization on a mechatronic integrated system simulation platform of feed drives are performed. As a result, a servo parameter combination is acquired. In the second stage, the servo parameter combination from the first stage is set and tuned further in a real machine tool whose dynamic performance is measured and evaluated using the cross grid encoder developed by Heidenhain GmbH. A case study shows that this method simplifies the test process effectively and results in a good dynamic performance in a real machine tool.     

压电陶瓷驱动三自由度精密定位系统的弹性动力学与输入调理特性研究

对压电陶瓷驱动三自由度精密定位系统的动力学性能进行了研究。首先建立了系统的弹性动力学模型，采用变截面框架单元描述柔性铰链，给出了其单元刚度矩阵和质量矩阵。通过实验获得了系统的低阶模态参数，并和分析结果进行了比较，验证了所建动力学分析模型的正确性。提出了基于动力学特性分析的驱动输入调理概念。分别采用正弦曲线和五次多项式作为调理函数对系统驱动的动态性能进行了研究。研究结果表明：对驱动输入进行必要的调理是十分必要的，所采用的两种调理方法均有效改善了系统的驱动特性，但由于采用五次多项式作为调理函数完全避免了驱动开始和结束时的加速度冲击，因而可获得更好的驱动效果。     

Bandgap Tuning with Thermal Residual Stresses Induced in a Quantum Dot

Lattice distortion induced by residual stresses can alter electronic and mechanical properties of materials significantly. Herein, a novel way of the bandgap tuning in a quantum dot (QD) by lattice distortion is presented using 4‐nm‐sized CdS QDs grown on a TiO₂ particle as an application example. The bandgap tuning (from 2.74 eV to 2.49 eV) of a CdS QD is achieved by suitably adjusting the degree of lattice distortion in a QD via the tensile residual stresses which arise from the difference in thermal expansion coefficients between CdS and TiO₂. The idea of bandgap tuning is then applied to QD‐sensitized solar cells, achieving ≈60% increase in the power conversion efficiency by controlling the degree of thermal residual stress. Since the present methodology is not limited to a specific QD system, it will potentially pave a way to unexplored quantum effects in various QD‐based applications.     

Tunable lasing from a cholesteric liquid crystal film embedded with a liquid crystal nanopore network

Continuous tuning of lasing wavelength is achieved in cholesteric liquid crystal lasers by embedding a network of nanopores with an average size of 10 nm filled with liquid crystals inside a polymerized matrix with helical order. The device possesses both high transparency and a fast response time because the tuning is driven by local reorientation of the liquid crystal molecules in the nanopores.     

Fuzzy supervisory predictive PID control of a plastics extruder barrel

Abstract

The paper describes the design of single‐loop fuzzy supervisory predictive PID controllers for a plastics extruder barrel. A fuzzy supervisory shell is proposed to improve the set‐point tracking performance of the proposed PID method by appropriate adjustment of the weighting term for the control effort. Experimental results show that the proposed method is capable of giving a good result on the barrel.     

Wideband tunable Q-switched fiber laser using graphene as a saturable absorber

An ultra-wide wavelength tuning range, which covers three different band regions consisting of the S-, C-, and L-bands, is proposed and demonstrated for a graphene-based Q-switched erbium-doped fiber laser using a tunable bandpass filter as the wavelength tuning and filtering mechanism. A 3?m length of erbium-doped fiber is used as the gain medium in a ring laser cavity configuration, with absorption coefficients of between 11 and 13 dB?m^?1 at 980?nm and about 18?dB?m^?1 at 1550?nm. The tuning range of the Q-switching pulses covers a wide wavelength range of 58?nm, which spans from 1512.5?nm to 1570.5?nm. In addition, the lasing and Q-switching thresholds are considerably low, with respective values of ～11.0?mW and ～18.4?mW. A repetition rate of 55.3?kHz is obtained at the maximum pump power of 100.4?mW, together with pulse width and pulse energy of 1.6?μs and 25.8?nJ, respectively.     

Nanoarchitectonics on Bi2MoO6 by alkali etching for enhanced photocatalytic performance

As a layered photocatalyst, the photogenerated carriers separation efficiency of bismuth molybdate (Bi₂MoO₆) can be improved by introduction of oxygen vacancy. The alkali etching method provides a facile structural tuning way for modifying the bismuth-based semiconductors. Defect state bismuth molybdate (Bi₂MoO₆) photocatalyst was synthesized by alkali etching. The structure of Bi₂MoO₆ was tuned by adjusting the concentration of alkali solution. The phase structure, morphology, surface chemistry, and optical property of Bi₂MoO₆ were characterized by kinds of characterization methods such as X-ray diffraction, scanning electron microscope, X-ray photoelectron spectroscopy, UV–vis diffuse reflectance absorption spectroscopy. The phase of Bi₂MoO₆ can be transformed to Bi₂O₃ accompanied with the change of morphology due to the etching of molybdenum atom and oxygen atom from the Bi₂MoO₆ body structure by sodium hydroxide solution. Meanwhile, the concentration of oxygen vacancy increased obviously as indicated by the XPS results. Therefore, the separation efficiency of photogenerated carriers was enhanced because of the promotion of oxygen vacancy. Alkali etching Bi₂MoO₆ by 0.075 M sodium hydroxide solution exhibited an excellent photocatalytic performance owing to the suitable vacancy concentration. Superoxide free radicals instead of hydroxyl radicals took the important role in the photodegradation process.     

Measurement of the range rate of airborne objects in a frequency tuning regime

A new method is proposed for measuring the range rate of an airborne object in a frequency tuning regime. Mathematical modelling is used to study the effect of different factors on characteristics of the method. Limits for its application are determined. __________ Translated from Izmeritel’naya Tekhnika, No. 2. pp. 43–47, February, 2008.