高温超导窄带广义切比雪夫函数滤波器

提出了一种用于高温超导滤波器制作的新结构——窄带广义切比雪夫函数高、低通滤波器级联方式．该方式利用高温超导低插损特性，可以有效地降低极陡峭广义切比雪夫函数低通、高通滤波器的带边频滚降．依靠高、低通滤波器级联方式构建新形式的窄带极陡峭低插损高温超导滤波器．并与已有高温超导滤波器进行了比较分析．     

一种以白宝石为衬底的高选择性高温超导滤波器

研制了一种高选择性的24阶切比雪夫(Chebyshev)型高温超导带通滤波器,其中心频率为1748MHz、带宽为75MHz,适用于GSM移动通讯基站系统.此滤波器是在直径为3英寸、厚度为0.43毫米的铝酸镧双面超导薄膜上制作的.滤波器的计算机仿真是用Sonnet软件完成的.在滤波器设计中,提出了一种结构新颖的谐振器.在77K时,它具有很高的品质因子,约为30000.测试结果表明,该滤波器具有很好的选择性,带边陡度为17dB/MHz,带外抑制优于-90dB.     

Tunable all-optical microwave notch filter with a negative tap based on a semiconductor optical amplifier and a dispersive medium

A tunable all-optical microwave notch filter with a negative tap based on a semiconductor optical amplifier and a dispersive medium is demonstrated. A negative tap is realized through the cross gain modulation in the semiconductor optical amplifier. The free spectrum range of the notch filter can be tuned by tuning the wavelength of one of the two laser sources. The influence of the amplitude mismatch of the two lasers on the performance of the filter is analyzed. The present notch filter is easy to implement and cost-effective.     

A tunable single-passband microwave photonic filter with positive and negative taps using a fiber Mach-Zehnder interferometer and phase modulation

In this paper, a tunable single-passband microwave photonic filter with positive and negative taps based on phase modulation and a fiber Mach-Zehnder interferometer (FMZI)) is presented, theoretically analyzed and experimentally demonstrated. The FMZI as the slicing filter results in a single-bandpass characteristic for the presented filter, and by using phase modulation, a number of negative taps are generated, thus making the baseband resonance suppressed, which is desirable for microwave photonic filter's application. The wavelength spacing of the FMZI can be tuned by employing an optical variable delay line, making the present filter continuously tunable. A tunable single-passband microwave photonic filter without baseband resonance is achieved in the experiment. The present filter shows an extinction ratio of up to ∼20 dB and good tuning linearity.     

Photonic generation of a microwave signal by employing a microfiber ring resonator

A novel approach to generate microwave signals is presented by employing a microfiber ring resonator. The microfiber ring resonator is assembled with a microfiber fabricated by heating and drawing standard single-mode fiber. By cascading microfiber ring resonator acted as a comb filter with a tunable bandpass filter, a wavelength-tunable dual-wavelength single longitudinal-mode laser is achieved. A microwave signal at 15.57 GHz with the linewidth of less than 21 kHz is demonstrated by beating the two wavelengths at a photodetector.     

Reconfigurable microwave photonic transversal filter using a variable gain tilt filter

A novel and simple technique to realize reconfigurable microwave photonic transversal filter is presented. In the proposed method, a multi-wavelength source and a dispersive medium are applied to achieve multiple taps; and an electro-optic ceramic material-based variable gain tilt filter (VGTF) is utilized to control the tap weights of the filter. The VGTF is computer-controlled via a universal serial bus interface, which enables real-time reconfiguration of the filter. Filter responses with different passband bandwidth and different sidelobe suppression can be achieved. Compared with previous approaches, the given method features in less optical components involved and faster response speed. A three-tap reconfigurable filter with sub-millisecond response speed is experimentally demonstrated.     

Tunability of the multiple-bandpass response of cascaded single-source and continuous-sample microwave photonic filters

We report a theoretical and experimental investigation on the structure and tuning capabilities of cascaded associations of microwave photonic filters composed of a single-source incoherent filter and a continuous-sample filter based on periodically-sliced broadband sources that undergo dispersion after being modulated. We derive the condition that guarantees both incoherent operation and cascading of the radio-frequency responses. This condition implies a lower bound for the ratio between resonance bandwidth (Δf) of the continuous-sample filter and the free spectral range (FSR) of the single-source filter, thus showing the possibility of cascading filters in two complementary regimes, Δf/FSR < 1 and >1. The tunability of the cascaded responses is also explored in a series of proof-of-concept experiments, where a static response of a single-tap, incoherent loop filter is reconfigured by use of a Solc filter. In particular, it is demonstrated a reconfigurable single and dual-bandpass cascaded response, which can be further modified by changes in dispersion, spectral period of the slicing filter, central wavelength or spectral width of the broadband source, and apodization of the resonance. The results are compared with the predictions of the Gaussian model for the degradation of resonances in continuous-sample filters due to second-order dispersion.     

Continuously tunable photonic microwave filter based on a spatial light modulator

An optical microwave filter architecture which can be continuously tuned is proposed and demonstrated. The architecture is based on a nematic liquid crystal spatial light modulator in parallel configuration and has the potential to control a large number of taps. Proof-of concept experimental results are provided.     

银化微孔滤膜制备及其SERS活性研究

将微孔滤膜浸入柠檬酸三钠和硝酸银混合液通过微波加热银化制得一种新型、高活性的SERS活性基底。以结晶紫为探针分子, 采用便携式拉曼光谱仪检测其SERS活性, 同时探讨浸泡时间与SERS活性的变化关系。实验结果显示, 在浸泡2~8小时区间, 基底的SERS活性随着浸泡时间的增加而增强。     

Microwave photonic filter with negative coefficients based on counter-phase modulation using a single electro-optic phase modulator

A simple photonic approach is proposed for the implementation of a reconfigurable multi-tap microwave filter with negative coefficients. In this scheme, a dual-optical-input intensity modulation module which can perform counter-phase modulation is constructed using a single electro-optic phase modulator. Two inter-complementary microwave signals are experimentally obtained for verification of the function of counter-phase modulation. A reconfigurable four-tap microwave filter with two negative coefficients is implemented by experiment.     

声光可调滤光片作原子吸收光谱法波长选择器的初步研究

本文以微波等离子体炬 (MPT)为原子化器 ,以声光可调滤光片为波长选择系统 ,用原子吸收光谱法测定了Na元素。实验中考察了观察高度、微波功率、MPT工作气流量对Na吸收信号强度的影响。在最优化操作参数下测定Na的检出限为 0 2 3μg·mL- 1 ,测定精密度为 2 6 %。     

基于高双折射光子晶体光纤与光纤环的超宽带可调谐微波光子滤波器

提出一种基于高双折射光子晶体光纤与光纤环的超宽带可调谐微波光子滤波器.以多波长光纤激光器作为光源,向高双折射光子晶体光纤内填充温敏液体,通过改变填充温敏液体的温度,高双折射光子晶体光纤可具有不同的双折射,得到不同波长间隔的激光,从而使微波光子滤波器具有不同的自由频谱范围.当温度的变化范围为20~80℃时,仿真测得微波光子滤波器自由频谱的变化范围为2.49~39.9GHz.引入光纤环构建级联型微波光子滤波器,滤波器的主旁瓣抑制比可提高到33.6dB,Q值可达到499,提高了滤波器的频率选择性.     

All-optical microwave notch filter with flat passband based on semiconductor optical amplifier

An all-optical filter structure for interference mitigation of microwave signals is proposed and demonstrated. The structure is based on a recirculating delay line loop (RDLL) and a fiber Bragg grating. The RDLL is comprised of a semiconductor optical amplifier (SOA) followed by a tunable narrowband optical filter and an optical variable delay line. Negative tap is generated using wavelength conversion based on the cross-gain modulation of amplified spontaneous emission spectrum of the SOA. A negative band-pass filter and a broadband all-pass filter are synthesized to achieve a narrow notch filter with flat passband which can excise interference with minimal impact on the wanted signal over a wide microwave range. Experimental results show the notch rejection ratio of 30 dB, good shape factor and tunability.     

Microwave photonic filter with multiple taps based on single semiconductor optical amplifier

A novel technique to implement a microwave photonic filter structure with multiple taps and arbitrary frequency response is presented. The proposed filter is based on Four-Wave Mixing (FWM) and Cross-Gain Modulation (XGM) in a semiconductor optical amplifier (SOA). Two-tap notch filter and three-tap bandpass filter with arbitrary bipolar tap generation, high rejection ratio, and widely tunability are successfully demonstrated in the experiment. Extensions to this concept by adding new probe light to provide more taps and improve the bandwidth to high frequency regime are also discussed.     

Fiber Grating Based Optical Recirculating Filter with an Optimized Response

A novel optical recirculating filter for RF applications is described, which exploits a specially designed fiber grating with a ramped spectral profile to enable optimization of the filter response. The design overcomes the limitations imposed by loss in conventional fiber recirculating filters. Additionally, a tunable free spectral range is demonstrated by using the device in a grating array. Both theoretical and experimental results are presented and discussed.     

基于DFB腔注入锁定效应的可调谐光电振荡器

提出一种基于分布反馈光注入锁定效应的可调谐光电振荡器,其环路主要由马赫曾德尔调制器、光电探测器、环形器、分布反馈激光器和射频放大器顺接而成,分布反馈激光器是系统关键器件,通过分布反馈激光器光注入锁定效应,分布反馈腔在光域实现了微波光子滤波器功能,无需传统光电振荡器必须的射频带通滤波器.同时,由于分布反馈激光器注入锁定提高了环路Q值,因此系统可采用短环路结构,从而降低了光纤因温度敏感对微波信号稳定性的影响并减小了整个系统的尺寸.另外,通过调节注入光波长和功率可改变该微波光子滤波器的中心频率,从而可实现系统的可调谐性.理论分析了该光电振荡器的原理和微波光子滤波器的调谐性,在此基础上开展了实验验证.结果表明该光电振荡器能够产生18.7～21.6 GHz的可调微波信号,在1 kHz频偏处的相位噪声为-90 dBc/Hz.     

Optical fiber dispersion properties management for optimized narrowband bandpass microwave photonics slicing filter applications

The analysis of the influence of dispersion properties of the dispersive line used in a microwave photonic slicing filter is presented. We establish a general relation between both chromatic dispersion value and slope, allowing the optimization of the frequency response of the filter. Experimental validations are presented in good agreement with theoretical and numerically simulated results. Narrow bandwidth bandpass filter (<100 MHz) is achieved at the central frequency of 6.48 GHz, corresponding to the limit value in reference to the used broadband light source and fiber dispersion.     

High-Q, tunable, photonic microwave single passband filter based on stimulated Brillouin scattering and fiber Bragg grating filtering

We experimentally demonstrate a single passband, photonic microwave bandpass filter scheme based on stimulated Brillouin scattering (SBS) in optical fiber. A single side band (SSB)-modulated probe and a single frequency, tunable pump beam that have been produced by the combination of conventional Mach-Zehnder modulators and fiber Bragg grating filters, are used for the generation of SBS phenomenon in a 1-km long highly nonlinear dispersion-shifted optical fiber. Using the proposed scheme a single microwave passband with a ∼26 MHz bandwidth is readily achieved over a radio frequency tuning range from 1.3 to 9.3 GHz. The maximum Q-factor is measured to be ∼360.     

高温超导滤波器应用在移动通信基站中的优势

由于高温超导滤波器应用到移动基站前端可以提高基站的性能,因此受到了广泛的重视。该文介绍了高温超导滤波器的发展状况,研究了高温超导薄膜材料的微波性能。与普通的金属滤波器相比,高温超导滤波器在移动通信基站的应用中显示出了它的优越性能:其具有接近于理想的频率响应特性;能很好地抑制带外信号的干扰;可以节约频率资源、增加基站覆盖面积和通话容量;还能够提高通话质量和降低功率辐射等。文中还进一步介绍了国内外高温超导滤波器在移动通信基站中的应用情况。     

Novel tunable microwave photonic notch filter using a 3 × 3 coupler based Sagnac loop

We propose a simple and stable structure to realize a tunable negative coefficients microwave photonic notch filter. A 3 × 3 coupler based Sagnac loop interferometer with an asymmetrically placed phase modulator is used to acquire the notches. Our system is simply implemented and with good stability. Theoretical analysis and experimental results are presented and show a good agreement. The structure is proved to be a robust filter with more than 35 dB rejection deep notches.