微结构窄带滤光片设计及制备工艺研究

为了提升微结构窄带滤光片的光谱透过率,增大微结构单元的制备精度,提出一种新的膜系镀制方法和微结构单元的制备方法。基于法布里-珀罗(F-P)多光束干涉仪原理设计了3种不同中心波长的窄带滤光片,采用光化学掩模分离法和PECVD技术相结合,制备出3种中心波长分别为480 nm、520 nm和590 nm,峰值透过率均大于80%,半宽度30 nm~50 nm,微结构单元的通道面积为50 μm×50 μm的窄带滤光片。光谱透过率得到了提升的同时微结构单元边缘整齐、分界线清晰,精度也得到了有效地增加,达到μm量级。     

Design of non-polarization angle-tuned narrowband thin film filter

Angle-tuned thin film bandpass filter is widely used in DWDM system. In oblique incidence, the bandwidths and central wavelengths of the P-polarization and S-polarization light will separate obviously, which will cause serious polarization dependent loss. These phenomena of the polarization sensitivities are analyzed and a novel non-polarization 100 GHz four-cavity narrowband dielectric thin film stack used in oblique incidence is proposed. The simulation results show that it can eliminate the polarization bandwidths and central wavelengths separation within the incident angle from 0° to 25°, and its tunable range can cover the whole C-band.     

新型内反射旋光光学滤波器研究

基于氯酸钠晶体的各向同性和旋光色散特性,利用线偏振光以Brewster角内反射时P分量反射率为零的特性,研制出一种新型内反射旋光光学滤波器,该光学滤波器仅需采用单个偏振片,即可达到良好的滤波效果.利用Mueller矩阵对该滤波器的滤波特性进行理论分析以及实验测试,结果表明对含有532 nm和632.8 nm谱线的线偏振光,改变起偏器角度即可连续调制出射红、绿光的光强,当起偏器较初始位置旋转过133.36°和173.06°时,绿光和红光分别消光,绿光和红光的隔离度可达10 dB. 关键词： 光学滤波器 各向同性 旋光色散 偏振     

Widely tunable monolithic narrowband grating filter for near-infrared radiation

We propose a monolithic narrowband guided-mode grating filter in fused silica that is widely tunable in the near-IR wavelength region. Based on a recently demonstrated approach for a monolithic reflector comprising an encapsulated grating, we theoretically investigate such a device by means of rigorous modeling aimed at a narrow linewidth. It is demonstrated that upon a spatial variation of the filter's grating period its resonance wavelength can be tuned in a remarkably wide range of near-IR radiation with 800 nm<λ(res)< 1600 nm by translating the laser beam relative to the grating area. The filter performance in terms of linewidth and contrast is essentially preserved over the entire tuning interval.     

Tunable narrowband filter based on a combination of Fabry-Perot etalon and volume Bragg grating

A new type of tunable narrowband filter is proposed. This filter is a combination of a Fabry-Perot etalon, which permits the selection of a comb of discrete narrow bands, and a high-efficiency rotating volume Bragg grating recorded in photo-thermo-refractive glass, which permits tuning between the Fabry-Perot resonances. A tunable filter for fixed wavelengths in the region of 1.5 mum with a spectral width of 220 pm (FWHM), separation between channels of 800 pm, and throughput of 95% (losses <0.2 dB) is demonstrated.     

Demonstration of Faraday anomalous dispersion optical filter with reflection configuration

A narrow linewidth Faraday anomalous dispersion optical filter(FADOF)with reflection configuration is achieved for the first time based on the cesium(Cs)ground state 6S_1/2 to the excited state 6P_3/2 transition at 852 nm.Compared with the conventional FADOF with transmission configuration,reflection-type FADOF can greatly improve the transmittance of optical filter under the same experimental parameters,because it allows signal light to go and return through the atomic vapor cell.In our experiment,peak transmittance at Cs 6S_1/2 F=4-6P_3/2 transition is 81%for the reflection-type FADOF,and while 54%for the transmission-type FADOF when the temperature of Cs vapor cell and the axial magnetic field are 60℃and 19 G.The idea of this reflection-type FADOF design has the potential to be applied to the FADOF operating between two excited states to obtain higher transmittance.     

基于古斯-汉欣位移的双通道窄带滤波器

本文利用光束在对称金属包覆波导表面反射得到的异常大的古斯-汉欣(Goos-Hänchen)位移,通过实验实现了双通道窄带滤波.当入射激光波长为859.60 nm时,两通道滤波的峰值位置分别为859.604 nm和859.688 nm,峰值半宽(FWHM)为0.036 nm,而消光比达到15.3 dB.峰值波长可通过改变入射角或小孔位置实现调谐. 关键词： 古斯-汉欣(Goos-Hä nchen)位移 光波导 双通道 滤波器     

Tunable multilayer narrowband filter containing an ultrathin metallic film and a lithium niobate defect

By using lithium niobate (LiNbO₃) as a defect layer, a tunable multilayer narrowband reflection-and-transmission filter containing an ultrathin metallic film is proposed. Due to the voltage dependence of the refractive index for LiNbO₃, tunable optical filtering properties have been theoretically investigated based on the calculated wavelength-dependent reflectance and transmittance. The dependences of peak wavelength on the applied voltage and the angle of incidence are numerically illustrated. The results reveal that in addition to working as a tunable filter, it can also be expected to act as a refractometric optical sensor.     

Use of photonic quantum well as tunable defect in multilayer narrowband reflection-and-transmission filter

By using a photonic quantum well (PQW) as a tunable defect layer, a theoretical analysis on the optical properties in a multilayer narrowband reflection-and-transmission filter can be given. It is found that the resonant peaks in the reflection and transmission spectra are shifted to shorter wavelengths as the number of periods in the PQW increases. The shifting feature is more salient if the QW is deeper, that is, the refractive index contrast in the constituents of the PQW is increased. This novel design provides an alternative for achieving a tunable filter instead of using the usual electrooptical defect.     

Experimental demonstration of a narrowband, angular tolerant, polarization independent, doubly periodic resonant grating filter

Resonant grating filters are promising components for free-space narrowband filtering. Unfortunately, due to their weak angular tolerance, their performances are strongly deteriorated when they are illuminated with a standard collimated beam. Yet this problem can be overcome by resorting to a complex periodic pattern known as the doubly periodic grating [Lemarchand et al., Opt. Lett.23, 1149 (1998)]. We report what we believe to be the first experimental fabrication and characterization of a bidimensional doubly periodic grating filter. We obtained a 0.5 nm bandpass polarization independent reflection filter for telecom wavelengths (1520-1570 nm) that presents a transmittivity minimum of 18% with a standard incident collimated beam.     

边带耦合光子晶体滤波器反射谱特性分析

 为研究边带耦合光子晶体滤波器的性质,利用耦合模理论（CMT）和传输矩阵方法（TMM）分析了谐振器腔体的周期,Q值和腔体的个数对滤波器反射谱的影响。仿真结果表明：相移为nπ/2,反射谱才具有对称性;Q值增加,反射峰带宽减小;N增大,反射峰带宽相应增大,旁瓣也随之出现。针对为实现增加带宽而出现的旁瓣增加的现象,采用了类似一维光子晶体滤波器的方法啁啾和级联技术实现了旁瓣的抑制。为设计具体光子晶体滤波器提供指导和依据。     

A tunable narrowband optical filter via phase conjugation by nondegenerate four-wave mixing in a doppler-broadened resonant medium

The formulation of phase conjugation via nondegenerate four-wave mixing in a Doppler-broadened resonant medium is generalized to include nondegenerate pump frequencies. This process is shown capable of yielding a tunable optical band-pass filter whose central frequency can be tuned over the entire Doppler profile with only a small degradation of the filter efficiency while still maintaining a bandwidth limited by the homogeneous linewidth.     

Mechanically switchable photonic crystal filter with either all-pass transmission or flat-top reflection characteristics

We theoretically introduce a new type of optical all-pass filter based on guided resonance in coupled photonic crystal slabs. The filter exhibits near-complete transmission for both on- and off-resonant frequencies and yet generates large resonant group delay. We further show that such a filter can be mechanically switched into a flat-top band rejection filter.     

Variable spectral filter based on optically saturated selective reflection

We have studied the selective reflection from glass-rubidium vapor interface at a large incidence angle in pump-probe experiment. The linear reflectivity can be more than 0.9 in a narrow spectral range (several GHz) at the blue side of the atomic resonance. The effect can be called the reduced total selective reflection. The reflectivity has been decreased two times due to the optical saturation. The obtained results can be used to develop a variable optical filter or optical switcher. Our estimations show that switching time can be less than the natural lifetime of the excited state. We suggested a multi-reflection scheme to increase the contrast of the variable spectral filter.     

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.     

Multi-wavelength fiber source based on double-pass superfluorescent fiber source and a reflection Mach-Zehnder filter

A spectrum-sliced multi-wavelength fiber source (SS-MWFS) based on double-pass superfluorescent fiber source (SFS) with a reflection Mach-Zehnder filter (RMZF) as the reflected comb filter is demonstrated.With backward pumped configuration, MWFS with 50 wavelength channels of extinction ratio (ER) of 16.7 dB is obtained over the almost total C-band gain region. Total output power of the MWFS is 16.2 mW which shows that a power of about 0.3 mW of per channel is achieved. The SS-MWFS with forward pumped configuration is also discussed for comparing. The backward pumped configuration can provide a larger output power while only a little smaller ER than that of the forward pumped configuration.     

Variable single-passband narrowband optical filter based on forward stimulated interpolarization scattering in photonic crystal fiber

A variable transmission spectrum single-passband narrowband optical filter is proposed and experimentally demonstrated. It is based on forward stimulated interpolarization scattering (SIPS) in a photonic crystal fiber by applying a differential quadrature phase-shift keying modulation to the pump wave to broaden and shape the SIPS gain spectrum. By choosing the bit rate of the modulation data pattern, a flat-top steep-cutoff optical bandpass filter with a 3?dB bandwidth of 70?MHz and a 10?dB bandwidth of 90?MHz is realized. In addition, a variable narrowband optical notch filter is also realized by attenuation of the pump wave.     

Accurate lidar temperatures with narrowband filters

At daytime, metal resonance lidars need narrowband spectral filtering in the receiver to measure Doppler temperatures in the mesopause region. For our K lidar equipped with a Faraday anomalous dispersion optical filter we demonstrate that the derived resonance temperatures can be shifted by 10 K because of the wavelength dependence of the filter transmission for the Rayleigh scattered light when this filter transmission is used for normalization. We show that, if all filter effects are considered correctly, temperature measurements at daytime can be as accurate as at nighttime without such filters.