A novel tunable cascaded IIR microwave photonic filter

A new tunable cascaded infinite impulse response (IIR) microwave photonic filter is presented, based on a novel configuration in which a semiconductor optical amplifier (SOA) is inserted between two active recirculating delay line (RDL) loops. Due to wavelength conversion with cross-gain modulation (XGM) in SOA, interferences between light beams traveling different paths are canceled, ensuring a stable transmission. By employing this configuration, a cascaded IIR microwave photonic filter is firstly achieved. The free spectral range (FSR) and the Q factor are both increased significantly by adopting “vernier effect” technique in the IIR filter. The structure is also tunable by adjusting the length of one RDL loop.     

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.     

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.     

A tunable and reconfigurable microwave photonic filter based on two cascaded modulators and a dispersive medium

A novel tunable and reconfigurable microwave photonic filter based on two cascaded modulators and a dispersive medium is proposed, theoretically discussed and experimentally demonstrated. A single-wavelength LD and a modulator (either a Mach-Zehnder modulator or a phase modulator which can avoid the dc bias drift problem) are used to obtain a multi-wavelength optical source. By adjusting the modulation frequency and the bias voltage on the modulators, the wavelength spacing and the relative amplitude of the optical tones change, thus making the filter tunable and reconfigurable. The experimental results show that the proposed filters have good tunability and reconfigurability and the mainlobe-to-sidelobe ratio of around 25 dB is achieved.     

基于等离子体缺陷层的一维可调谐微波光子晶体滤波特性

等离子体填充到一维介质-真空微波光子晶体的缺陷层构成一种可调谐单通道滤波器.据等离子体的强色散特性,其等效折射率与电磁波频率及等离子体频率等参数有关,因而可以通过改变等离子参数,使一维微波光子晶体缺陷层的谐振频率发生偏移,实现微波光子晶体的可调谐滤波特性.介质层和等离子体层分别采用了时域有限差分（FDTD）算法及分段线性电流密度卷积时域有限差分（PLJERC-FDTD）算法.数值模拟表明,通过改变等离子体频率可以实现滤波通道在光子禁带内较大带宽范围的移动. 关键词： 等离子体 微波光子晶体 可调谐滤波     

Tunable and reconfigurable photonic microwave filter based on stimulated Brillouin scattering

A high Q-factor photonic microwave filter showing tuning and reshaping capabilities and based on stimulated Brillouin scattering is demonstrated. The filter bandpass can be continuously tuned, changing the microwave oscillator used to generate the pump power, and the filter shape can be modified by modulating the microwave tone. A single bandpass over the microwave spectrum can be obtained by using single-sideband suppressed carrier modulation. Experimental results demonstrate the wide tuning range of the filter, its reshaping capability, and Q factor of 670.     

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.     

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.     

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.     

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.     

All-optical coherence-free microwave filter with switchable passbands based on phase and intensity hybrid modulation

A simple all-optical coherence-free microwave notch filter is proposed and experimentally demonstrated. The filter with switchable passbands is based on a single-wavelength optical source and phase-intensity hybrid modulation scheme. The DC bias voltage applied to the Mach-Zehnder intensity modulator can be adjusted to switch signs of the tap coefficients, which affect the baseband response. Both lowpass and bandpass filtering responses are observed in the experiment and agree well with the simulated results.     

Tunable and switchable multi-wavelength Erbium-doped photonic crystal fiber ring laser incorporating a length of highly nonlinear photonic crystal fiber

A tunable and switchable multi-wavelength Erbium-doped photonic crystal fiber ring laser incorporating a length of single-mode highly nonlinear photonic crystal fiber is proposed and demonstrated experimentally. Stable dual-wavelength and triple-wavelength operations at room temperature are achieved by employing the highly nonlinear photonic crystal fiber to induce four-wave mixing effect and a polarization controller to vary the polarization states of propagation lights in the laser cavity. The laser cavity is free from any wavelength selection components. The laser obtains maximal 30 dB signal-to-noise ratio and the peak power fluctuations of lasing lines are less than 1.39 dB.     

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.     

光注入半导体激光器产生可调谐高频微波

利用光注入半导体激光器产生的单周期振荡,实验获得了61—129 GHz范围内频率连续可调的微波光信号.同时利用半导体激光器速率方程,对光注入半导体激光器产生高频微波进行了数值模拟.模拟和实验结果均表明微波信号产生于注入光和激光器腔模之间的拍频现象,其频率随着注入光强度和波长失谐的增大而增大,模拟结果预测该方法可以产生频率大于40 GHz的高频微波. 关键词： 光通信 光生微波 拍频 半导体激光器     

A software tool to evaluate the frequency response of a microwave photonic filter in MATLAB based on a Graphical User Interface

The aim of this paper is to describe the development and application of a software tool in MATLAB based on a Graphical User Interface that allows evaluation of the frequency response of a microwave photonic filter. Microwave photonic filters have potential applications in optical communication systems. The main characteristic of this software tool is the friendly way to edit the parameters involved to determine the frequency response. In order to validate the results obtained by the use of this software tool, a series of experiments were carried out in our laboratory and the results were compared qualitatively showing a good agreement. The developed software has a potential application as a didactic tool in a course of microwave electro-optical systems.     

Tunable microwave signal generation based on an Opto-DMD processor and a photonic crystal fiber

Frequency-tunable microwave signal generation is proposed and experimentally demonstrated with a dual-wavelength single-longitudinal-mode （SLM） erbium-doped fiber ring laser based on a digital Opto-DMD processor and four-wave mixing （FWM） in a high-nonlinear photonic crystal fiber （PCF）. The high-nonlinear PCF is employed for the generation of the FWM to obtain stable and uniform dual-wavelength oscillation. Two different short passive sub-ring cavities in the main ring cavity serve as mode filters to make SLM lasing. The two lasing wavelengths are electronically selected by loading different gratings on the Opto-DMD processor controlled with a computer. The wavelength spacing can be smartly adjusted from 0.165 nm to 1.08 nm within a tuning accuracy of 0.055 nm. Two microwave signals at 17.23 GHz and 27.47 GHz are achieved. The stability of the microwave signal is discussed. The system has the ability to generate a 137.36-GHz photonic millimeter signal at room temperature.     

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.     

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.     

星间微波光子链路调制方式的优化

针对外调制星间微波光子链路输出信噪比优化问题,建立了基于双电极马赫 曾德尔调制器的强度调制直接探测星间微波光子链路模型,通过优化调制器调制方式来提高链路性能。用数值模拟方法得到了单边带、双边带和推挽式3种调制方式下链路输出信噪比,利用曲面投影法求得了最优调制方式时一定信噪比要求下发射端所需最小光放大器增益和对应的调制器直流偏置相位。结果表明:相同输入射频信号功率和发射光功率情况下,双边带调制输出信噪比比单边带调制高3 dB,低直流偏置相位推挽调制可以进一步优化输出信噪比。输入射频信号功率为-20 dBm,输出信噪比为17.3 dB时,所需最小光放大器增益为43.9 dB,对应的直流偏置相位为0.87。     

Performance limitation of chirped-fiber-Bragg-grating-based photonic microwave notch filter due to group delay and reflectivity ripples

We investigated the performance limitation of a frequency-tunable photonic microwave notch filter incorporating a chirped fiber Bragg grating (FBG) as a group delay line. In particular, we carried out theoretical and experimental studies to analyze the impact of the reflectivity ripple (RR) and group delay ripple (GDR) in the chirped FBG on the output notch performance. The results of experimental and theoretical analyses performed on a photonic microwave notch filter in which an S-bending-based linearly chirped FBG was incorporated, revealed that the notch depth and notch frequency were significantly affected by imperfections in the chirped FBG. The notch depth was found to be decreased by the RRs, whereas significant fluctuations in the notch frequency were caused by the GDRs. On the basis of the obtained results, we conclude that the RR and the GDR are the fundamental factors that degrade the performance of chirped FBG-based photonic microwave filters.