非扫描式光纤法 珀解调仪分析与设计

利用相关解调原理研制了非扫描式光纤法 珀解调仪,进行了理论分析和系统优化。仪器以线阵电荷耦合器件(CCD)为光电探测器,结合现场可编程门阵列器件(FPGA)和上位机(ARM)处理,实现信号的实时处理。线性光不均匀性和杂散光所带来的背景噪声,导致不能准确检测出相关信号的极大值。为此,提出了一种能有效滤除背景噪声信号处理算法,提高了仪器对微弱信号的探测能力和稳定性,使其对光纤法 珀传感器腔长测量的相关系数达到0.999 9,测量波动仅为7 nm。实验结果表明,该仪器能实现对传感器腔长的实时测量,且测量精度高,稳定性和一致性好。     

高精度双波长光纤F-P传感系统正交特性研究

针对光纤Fabry-Perot(F-P)传感器在实际应用中,受外界环境干扰,造成输出精度较低,提出了一种采用波分复用器(DWDM)输出两路正交信号的双波长稳定系统。基于微分进化(DE)算法建立了光纤F-P传感系统的双波长稳定优化模型,设计了一高正交精度传感系统,构建了传感系统正交实验方案,研究了其正交输出特性和正交误差。结果表明,DE算法运行速度快,能在较短运行时间内得到全局最优解,可很好的用于光纤F-P传感系统结构优化,误差小于10-3;设计的传感系统具有较高的正交输出精度,当腔长变化为-1¹μm时,两路工作波长相位差接近π/2,传感系统正交误差均小于6%,具有良好的稳定性和抗干扰能力,能满足实际需求。     

Dual-wavelength erbium-doped fiber laser with asymmetric fiber Bragg grating Fabry-Perot cavity

A novel dual-wavelength fiber laser with asymmetric fiber Bragg grating（FBG） Fabry-Perot（FP） cavity is proposed and experimentally demonstrated. A couple of uniform FBGs are used as the cavity mirrors, and the third FBG is used as intracavity wavelength selector by changing its operation temperature. Experimental results show that by adjusting the operation temperature of the intracavity wavelength selector, a tunable dual-wavelength laser emission can be achieved. The results demonstrate the new concept of dual-wavelength lasing with asymmetric FBG FP resonator and its technical feasibility.     

Impact of signal filling factor for switching in reflective vertical cavity-based fast semiconductor saturable absorbers

A numerical model on reflective vertical cavity-based fast semiconductor (carrier recombination time in ps regime) saturable absorbers (VC-FSSA) is investigated for all-optical high-speed future applications, where the fluctuation of cavity optical length due to thermo-optic effects and cavity heating, and optically induced carrier density change are considered simultaneously with the increase of input signal intensity. The phase-shift due to thermal-optic effects and cavity heating is very important for high-speed device performances. At first, intensity and wavelength bi-stabilities are modelled with the different intensity time filling factor of RZ modulated pump signals and also, with the different input intensities, where the intensity tuning time is considered at few μs. Then the inverse saturation characteristics of reflectivity for the universal logic operations are shown for probe signal with the proper wavelength, which can control the negative effects of optically induced heating effects. These characteristics can be used for the high-speed thermally stable bi-stable optical switch and all-optical logic applications.     

Fabry–Perot Cavity Control for Tunable Raman Scattering

The Fabry–Perot (FP) resonator is an intuitive and versatile optical structure owing to its uniqueness in light-matter interactions, yielding resonance with a wide range of wavelengths as it couples with photonic materials encapsulated in a dielectric cavity. Leveraging the FP resonator for molecular detection, a simple geometry of the metal-dielectric-metal structure is demonstrated to allow tuning of the enhancement factors (EFs) of surface-enhanced Raman scattering (SERS). The optimum near-field EF from randomly dispersed gold nano-gaps and dynamic modulation of the far-field SERS EF by varying the optical resonance of the FP etalon are systematically investigated by performing computational and experimental analyses. The proposed strategy of combining plasmonic nanostructures with FP etalons clearly reveals wavelength matching of FP resonance to excitation and scattering wavelengths plays a key role in determining the magnitude of the SERS EF. Finally, the optimum near-field generating optical structure with controlled dielectric cavity is suggested for a tunable SERS platform, and its dynamic SERS switching performance is confirmed by demonstrating information encryption through liquid immersion.     

A newly designed high-spectral-resolution Rayleigh temperature lidar based on two-stage Fabry–Perot interferometer

A two-stage Fabry–Perot interferometer (FPI)-based high-spectral-resolution (HSR) Rayleigh temperature lidar technology is proposed that is capable of simultaneously detecting tropospheric temperature and aerosol optical properties with high-precision. The system structure is designed and the measurement principle is analysed. A two-channel integrated FPI used forming a two-stage FPI ensures the relative stability of the two FPI spectrums. The first-stage FPI with high spectral resolution can effectively separate Mie and Rayleigh signals to derive the signal components. Two adjacent-order transmission spectrums of the second-stage FPI are just located in the two wings of Rayleigh–Brillouin (R–B) scattering spectrum to measure temperature. Two multimode polarization insensitive optical circulators used in receiver system can achieve high-efficiency utilization of signals. A narrow linewidth semiconductor laser at 852 nm is used as light source. Using the selected and optimized system parameters, the lidar performance simulation results show that in the sunny weather conditions for 0.15WSr^–1 m^–2 nm^–1 sky brightness, with 0.3 W laser power, a 30 cm diameter telescope, 60 m range resolution and 30 min observation time, the temperature measurement errors are below 0.4 K in night-time and below 1.6 K in daytime; the relative measurement errors of backscatter ratio are below 0.04% in night-time and below 0.13% in daytime respectively up to 6 km height. Compared with the traditional FPI-based HSR technique, the technique we proposed can improve the detection accuracy of temperature by 2.5 times and can also significantly improve the detection accuracy of backscatter ratio.     

High-sensitive transmission type of gas sensor based on guided-mode resonance in coupled gratings

A new type of high-sensitive transmission gas sensor based on the coupled gratings (CGs) and the corresponding Fabry–Pérot-like (FP-like) model for evaluating the resonance peaks are presented. The estimated locations of the FP-like resonance obtained by this theoretical model are well agreed with those of the exact results. It is shown that a narrow FP-like channel with high transmissivity occurs in the opaque background of the CGs, and its location is shifted linearly with the variation of the refractive index (RI) of the gaseous analyte. The transmission peak of the sideband can be selected as a reference, and it remains nearly fixed as the RI of the analyte is varied. Good sensing properties of the CGs sensor can be maintained, regardless of whether the two grating membranes are laterally aligned or not. The sensitivity of the CGs sensor is immune to the variation of the RI of the substrate. By selecting the higher order FP-like mode (m = 4), sensitivity as high as 748 nm/RIU with the figure of merit of 374 can be achieved.     

Bandwidth‐enhancement of circularly‐polarized fabry‐perot antenna using single‐layer partially reflective surface

In this article, we investigate bandwidth‐enhancement of a circularly‐polarized (CP) Fabry‐Perot antenna (FPA) using single‐layer partially reflective surface (PRS). The FPA is composed of a single‐feed truncated‐corner square patch antenna, which is covered by the PRS formed by a square aperture array. We revealed that the finite‐sized PRS produces extra resonances and CP radiations for the antenna system, which broadened the impedance matching and axial ratio (AR) bandwidths significantly. For verification, a broadband CP FPA prototype operating near 5.8 GHz was realized and tested. The fabricated antenna with overall size of 125 mm × 125 mm × 23.5 mm achieves a |S₁₁| < ?10 dB bandwidth of 31.7% (5.23‐7.2 GHz), an AR < 3‐dB bandwidth of 13.7% (5.45‐6.25 GHz), the peak gain of 13.3 dBic, a 3‐dB gain bandwidth of 22.38% (5.0‐6.26 GHz), and a radiation efficiency of >91%.     

Dual‐polarized low sidelobe Fabry‐Perot antenna using tapered partially reflective surface

A novel dual‐polarized Fabry‐Perot (FP) cavity antenna with low sidelobes is proposed. Low sidelobes are obtained by using a tapered partially reflective surface (PRS) in the form of circular lattice instead of the conventional rectangular lattice. As the PRS can be regarded as a 2D leaky wave surface on which cylindrical waves propagate outward radially in the form of concentric rings, so arranging the PRS elements in the form of circular lattice and then applying tapering on it yields low sidelobes in both the E‐ and H‐planes. The performance of the proposed PRS is validated by fabricating a dual‐polarized FP antenna and measuring its radiation patterns. Peak realized gains of 18.6 and 18.5 dBi are obtained for horizontal and vertical polarizations respectively, giving an aperture efficiency of around 42%. Measured sidelobe levels are reduced to lower than ?21.3 dB in both the E‐ and H‐planes for the two orthogonal polarizations.     

Modular Design for Versatile Broadband Polarizing Metasurfaces with Freely Switching Functions

Polarization is a fundamental property of electromagnetic waves that plays a key role in many physical phenomena and applications. Schemes to manipulate it are revisited with the emergence of metasurfaces, which have brought multi-functionalities straightforwardly. However, this has come at the expense of design complexity that relies strongly on field theory. Here, an ingenious strategy of modular design is proposed to construct subwavelength multifunctional polarization control devices. Chiral metasurfaces with different handedness are first proposed and regarded as modules. The versatile polarization controller can thus be obtained with the combination of different modules. These experiments demonstrate that the well-designed polarization controller possesses reconfigurable functionality, and various broadband polarization and amplitude regulation functions with high efficiency including arbitrary linear polarization rotation, asymmetric transmission effect, neutral-density-like filter, polarization beam splitter, etc., can be readily realized just by changing the cascaded modules. The physical mechanisms of the versatile polarization controller and chiral metasurface modules are both guaranteed by the Fabry–Pérot-like resonances, which are theoretically verified via the transfer matrix method. It is envisioned that the modular concept will be of great benefit to designing compact multifunctional polarization controllers.