Design and modeling of microwave photonic devices

Different types of finite element methods (FEMs) for microwave and optical waveguides are reviewed and are utilized for modeling of a traveling-wave (TW) optical modulator, as one of the typical microwave photonic devices. Using the quasi-TEM and the full-wave vector FEM solvers for microwave waveguides and the scalar FEM solver for optical waveguides, the behaviour of a TW Z-cut Ti:LiNbO3 Mach–Zehnder optical modulator with a ridge structure is investigated.     

Design and optimization of a microwave photonic filter exploiting differential mode group delay of a multi-mode fiber

Optical Review - A reconfigurable and application-specific tunable microwave photonic filter having finite impulse response is proposed. The filter exploits the differential mode group delays of...     

Waveguide circuits in three-dimensional photonic crystals

Waveguide circuits in three-dimensional photonic crystals with complete photonic band gaps are simulated with finite difference time domain (FDTD) simulations, and compared with measurements on microwave scale photonic crystals. The transmission through waveguide bends critically depends on the photonic crystal architecture in the bend region. We have found experimentally and theoretically, a new waveguide bend configuration consisting of overlapping rods in the bend region, that performs better than the simple waveguide bend of terminated rods, especially in the higher frequency portion of the band. Efficient beam splitters with this junction geometry are also simulated.     

Experimental evidence of photonic crystal waveguides with wide bandwidth in two-dimensional Al_2O_3 rods array

A cross-shaped photonic crystal waveguide formed by a square lattice Al_2O_3 rods array is numerically and experimentally investigated. The band gap of the TE mode for the photonic crystals and transmission characteristics of waveguides are calculated by the plane wave expansion method and the finite element method.We perform the experiments in the microwave regime to validate the numerical results. The measured reflection and transmission characteristics of the photonic crystals show a large band gap between 8.62 and 11.554 GHz(relative bandwidth is 29.34%). The electromagnetic waves are transmitted stably in the waveguides, and the transmission characteristics maintain a high level in the band gap.     

二维光子晶体T型波导分支器数值模拟研究

采用平面波展开法和时域有限差分法,对GaAs二维正方晶格光子晶体的色散特性和带隙结构进行了数值模拟研究,并对GaAs二维光子晶体线缺陷构成的T型波导分支器的微波传输特性进行了模拟和优化。数值模拟结果表明,光子晶体填充比对带隙结构有显著地影响。通过在拐角处插入额外的电介质棒对GaAs二维正方光子晶体T型波导分支器进行优化,数值模拟的结果表明,优化的GaAs二维正方光子晶体T型波导分支器在一阶带隙范围内透射系数将提高到0.96以上。     

基于椭圆偏振光注入垂直腔表面发射激光器的正交偏振模式单周期振荡产生两路光子微波

提出了基于椭圆偏振光注入下垂直腔表面发射激光器(VCSEL)输出的正交偏振模式单周期(P1)振荡来同时获取两路光子微波的实现方案, 并进行了相关仿真研究. 结果表明: 在合适的参数条件下, 一个自由运行的VCSEL(定义为主VCSEL, M-VCSEL)可输出椭圆偏振光, 其X偏振分量和Y 偏振分量具有相同的激射频率; 将M-VCSEL输出的椭圆偏振光注入到另外一个VCSEL(定义为副VCSEL, S-VCSEL), 在给定主副VCSEL间频率失谐的条件下, 通过选择合适的注入强度可使S-VCSEL 中两个偏振分量均呈现单周期(P1)振荡, 从而可获得两正交的光子微波信号; 随着注入强度的增加, 光子微波的频率以及功率均呈现增加的趋势; 结合微波频率、功率以及输出光谱中第一边带和第二边带的幅度差在由注入强度和频率失谐所构成参数空间下的分布图, 可确定获取高品质微波信号的优化注入参数范围.     

Metallic graded photonic crystals for graded index lens

We have designed a flat graded index lens made from a metallic graded 2D photonic crystal. The gradient of index has been obtained by varying the filling factor of a flat slab of photonic crystal in the direction perpendicular to that of the propagation of the electromagnetic field. This gradient has been designed in such a way that the flat slab focuses a plane wave. With applications in the microwave range in view, we considered a photonic crystal which consists of copper strips.     

Graded photonic crystals for graded index lens

A graded index lens made from graded 2D photonic crystal has been designed by the means of the Finite Difference Time Domain (FDTD) method. The gradient of index has been obtained by varying the filling factor of a flat slab of photonic crystal in the direction perpendicular to that of the propagation of the electromagnetic field. This gradient has been designed in such a way that the flat slab focuses a plane wave. As only a few layers are necessary, graded photonic crystals show their ability to efficiently control the propagation of light and may apply to various photonic devices, from the microwave range to the optical domain.     

Microwave photonic filter’s application on the microwave signal generation based on an active mode-locked fiber laser

A novel scheme which utilizes the microwave photonic filter technique for the optical generation of a microwave signal based on an active mode-locked fiber laser is proposed. A microwave signal generator using a microwave photonic filter based on a 2: 1 optical coupler with a fiber loop which can effectively suppress a low-order frequency component of the microwave signal is demonstrated and a ～10-GHz microwave signal is achieved based on an active mode-locked fiber laser with the original pulse repetition rate of ～5 GHz.     

基于光注入半导体激光器单周期振荡的光子微波产生及全光线宽窄化

本文对基于光注入半导体激光器的单周期动力学态产生光子微波并利用光反馈压缩其线宽进行了实验研究. 研究结果表明: 通过适当调节注入参数, 能对该方法产生的光子微波频率在数十GHz范围内进行连续、大范围地调节; 通过引入光反馈并精细调节反馈强度, 光子微波的线宽能够从40—100 MHz的范围被压缩约两个数量级至300—900 kHz范围;反馈长度对光子微波的线宽几乎没有影响, 但当反馈长度精细变化时, 光子微波频率会出现一定范围内的周期性漂移.     

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.     

A tunable and reconfigurable microwave photonic filter based on a Raman fiber laser

A tunable and reconfigurable microwave photonic filter is demonstrated by employing a tunable Mach-Zehnder interferometer (MZI) and a wavelength-controllable Raman fiber laser. The free-spectral-range and spectral response of the microwave photonic filter are tuned and reconfigured by controlling the optical variable delay line in one arm of the MZI and the powers of the pump LDs. Experimental results are given to show the enhanced flexibility of the present microwave photonic filter.     

Subwavelength resolution in a two-dimensional photonic-crystal-based superlens

We experimentally and theoretically demonstrate single-beam negative refraction and superlensing in the valence band of a two-dimensional photonic crystal operating in the microwave regime. By measuring the refracted electromagnetic waves from a slab shaped photonic crystal, we find a refractive index of -1.94 that is very close to the theoretical value of -2.06. A scanning transmission measurement technique is used to measure the spatial power distribution of the focused electromagnetic waves that radiate from a point source. The full width at half maximum of the focused beam is measured to be 0.21 lambda, which is in good agreement with the finite difference time domain method simulations. We also report a subwavelength resolution for the image of two incoherent point sources, which are separated by a distance of lambda/3.     

FIR Photonic Microwave Filter Design Employing Simulated Annealing Algorithm

Photonic microwave filters are important parts of fiberoptic microwave/millimeter wave processing systems. In this paper, the synthesis problem of fiberoptic FIR microwave filters is addressed and a novel method for designing photonic microwave filter employing a simulated annealing (SA) algorithm is proposed. The design problem of photonic microwave filter can be reduced to be a multivariable function optimization problem, which can be solved by a simulated annealingbased algorithm. As an illustration of the application of SA to photonic microwave filter design, the synthesis of an optimizedFBGbased photonic microwave filter is discussed. Numerical results show that the global minimum finding capability of SA makes it be an efficient way to design the photonic microwave filter. Numerical results also demonstrate that the proposed method can be applied to design different filtering systems with different constraints.     

Experimental demonstration of self-collimation beaming and splitting in photonic crystals at microwave frequencies

I studied experimentally beam self-collimation and splitting in two-dimensional microwave photonic crystals. Using a microwave photonic crystal fabricated from alumina rods, I present an experimental proof of principle for an earlier theoretical proposal [A.F. Matthews, S.K. Morrison, Yu.S. Kivshar, Opt. Commun. 279 (2007) 313] of a photonic crystal beam splitter based on the self-collimation effect.     

On‐chip stimulated Brillouin Scattering for microwave signal processing and generation

Demonstration of continuously tunable delay, low‐noise lasers, dynamically controlled gratings, and optical phase shifting using the stimulated Brillouin scattering (SBS) process has lead to the emergence of SBS as a promising technology for microwave photonics. On‐chip realization of SBS enables photonic integration of microwave photonic signal processing and offers significantly enhanced performance and improved efficiency. On‐chip stimulated Brillouin scattering is reviewed in the context of slow‐light based tunable delay, low‐noise narrow linewidth lasers and filtering for integrated microwave photonics. A discussion on key material and device properties, necessary to enable on‐chip Brillouin scattering using both the single‐pass and resonator geometry, is presented along with an outlook for photonic integration of microwave signal processing and generation in other platforms.     

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.     

Design and Validation of Rugged Microwave Photonic Network for Phased-Array Radar

Abstract

Military radar has the requirement of 24 × 7 operation in harsh environments with a high level of safety and integrity built in for equipment and personnel working with it. This article presents an application of a microwave photonic network for phased-array military radar. The design challenge is to realize faithful reproduction of the input microwave signals over extreme temperature and frequency ranges. Environmental testing has been carried out to validate the performance of the proposed microwave photonic network over 2–4 GHz and a temperature range of –20°C to +55°C. The result shows that the photonic network can be successfully utilized for phased-array radar.     

Electromagnetic crystals in microstrip technology

Recently, new promising periodic structures called photonic crystals (PCs), or more appropriately electromagnetic crystal (ECs), for the microwave and millimetre wave range, have been considered for both microwave and photonic applications. Planar microstrip waveguides are very attractive in microwave engineering and several innovative designs have been proposed for them to expand the scope of application of the new PC concepts to the microwave domain. We review some of these microstrip EC structures looking at them as counterparts of their analogues in optical wavelengths. Moreover, very recent solutions that open new promising applications both in microwave and millimetre wave integrated circuits and antennas are presented.     

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.