基于双层金属光栅的中波红外多通道滤光片结构

提出一种多通道平面窄带滤光片阵列结构，该结构由双层金属光栅及其两侧的分布式布拉格反射器（DBRs）组成。所设计的多通道滤光片中心波长范围超过200 nm，每一个通道的中心波长可以通过调节光栅狭缝宽度来调节，从而实现多通道窄带滤光阵列。该结果为中波红外多通道窄带滤光片的设计提供了一条新的路径。     

Design of Narrowband Optical Filters Using Binary Number Sequence Photonic Crystals

A theory to design narrow band optical filters by using a new photonic crystal structure is presented. This new photonic crystal structure is composed of low index layers and high index layers arranged in mod. 4 up and down binary number sequence. The new structure exhibits narrow transmission peaks in the forbidden frequency gap region with high optical transmission (greater than 99.98%) at C.W.D.M. (Coarse Wavelength Division Multiplexing) center wavelengths. The proposed filters use only 8 layers. These new binary number sequence photonic crystal narrowband optical filters are much smaller in size, lower in cost and easier to fabricate as compared to narrowband photonic crystal optical filters based on defect Fractal Cantor multilayers, suggested recently by a group of researchers.     

Acoustic and linguistic factors in the perception of bandpass-filtered speech

Speech can remain intelligible for listeners with normal hearing when processed by narrow bandpass filters that transmit only a small fraction of the audible spectrum. Two experiments investigated the basis for the high intelligibility of narrowband speech. Experiment 1 confirmed reports that everyday English sentences can be recognized accurately (82%-98% words correct) when filtered at center frequencies of 1500, 2100, and 3000 Hz. However, narrowband low predictability (LP) sentences were less accurately recognized than high predictability (HP) sentences (20% lower scores), and excised narrowband words were even less intelligible than LP sentences (a further 23% drop). While experiment 1 revealed similar levels of performance for narrowband and broadband sentences at conversational speech levels, experiment 2 showed that speech reception thresholds were substantially (>30 dB) poorer for narrowband sentences. One explanation for this increased disparity between narrowband and broadband speech at threshold (compared to conversational speech levels) is that spectral components in the sloping transition bands of the filters provide important cues for the recognition of narrowband speech, but these components become inaudible as the signal level is reduced. Experiment 2 also showed that performance was degraded by the introduction of a speech masker (a single competing talker). The elevation in threshold was similar for narrowband and broadband speech (11 dB, on average), but because the narrowband sentences required considerably higher sound levels to reach their thresholds in quiet compared to broadband sentences, their target-to-masker ratios were very different (+23 dB for narrowband sentences and -12 dB for broadband sentences). As in experiment 1, performance was better for HP than LP sentences. The LP-HP difference was larger for narrowband than broadband sentences, suggesting that context provides greater benefits when speech is distorted by narrow bandpass filtering.     

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。     

Stable single frequency Er-doped all-fiber ring laser with fiber Bragg grating Fabry-Perot filter

Using a fiber Bragg grating (FBG) and a Fabry-Perot cavity composed of two fiber Bragg gratings (FBGFP) as its frequency-selective components, a type of single frequency all-fiber ring laser permits oscillation only on one longitudinal mode of the main cavity without modehopping while the cavity length can be up to tens of meters. The salient feature is due to the single narrowband resonance of the FBGFP filter. Such a fiber ring laser is achieved experimentally, and the laser mode is limited inside the single resonance of the FBGFP.     

Single-longitudinal-mode erbium-doped fiber laser based on a fiber Bragg grating Fabry-Perot filter

A novel single-longitudinal-mode (SLM) erbium-doped fiber laser with a simple linear cavity based on a fiber Bragg grating Fabry-Perot filter (FBG-FPF) and a narrowband (～0.06 nm) FBG is proposed and demonstrated experimentally. Two uniform FBGs form the FBG-FPF, which has two ultranarrow transmission bands with a bandwidth of 0.12 pm and a wavelength spacing of 0.095 nm. By slightly tuning the central wavelength of the narrowband FBG, SLM lasing at 1549.658 or 1549.563 nm (corresponding to the two transmission peaks of the FBG-FPF) is achieved with a laser output power of ～4 mW, when the pump power is ～75 mW.     

Polarization-independent guided-mode resonance filter with cross-integrated waveguide resonators

A cavity-resonator-integrated guided-mode resonance filter (CRIGF) has been proposed and investigated in order to realize high-efficiency narrowband reflection with a small aperture. The CRIGF consists of a grating coupler integrated in a cavity resonator constructed by a pair of distributed Bragg reflectors on a thin-film waveguide. This time, orthogonally crossed integration of two CRIGFs was demonstrated in order to obtain polarization-independent reflection spectrum. An SiO₂-based device with 10?μm aperture was designed and fabricated for around 850?nm wavelength operation, and narrowband polarization-independent reflection was confirmed experimentally.     

角度调谐滤光片特性分析及膜系设计

对窄带滤光片的倾斜入射特性作了分析.斜入射时其透射通带和峰值会向短波方向移动,透射曲线的稳定性跟滤光片的间隔层结构相关,多腔间使用相同的间隔层可以保证斜入射时有稳定的峰值透射率和带宽,利用该特点可以制备角度调谐窄带滤光片.透射光S和P偏振分量的中心波长随入射角度的增大出现分离现象,产生较大的偏振相关损耗.通过搭配不同厚度的高低折射率材料作为间隔层,改变其有效折射率,使其两个偏振分量的中心波长实现重合.设计了符合密集波分复用(Dense Wavelength Division Multiplexing,DWDM)系统要求的低偏振相关损耗四腔窄带角度调谐滤光片膜系,其可调谐范围达20 nm以上,并评估了所设计角度调谐滤光片的调谐性能.     

Planewave remittances of an axially excited chiral sculptured thin film with gain

Reflectances and transmittances of chiral sculptured thin films (STFs) with gain qualitatively differ from those of lossless and lossy chiral STFs, chiefly at the edges of the Bragg regime, for normally incident plane waves. The difference is explained in terms of the photonic density of states. A chiral STF with a central twist defect exhibits a reflection hole if there is no gain and emits narrowband radiation if there is gain, provided the thickness is not large. This narrowband feature diminishes as the thickness increases, and is replaced by an ultranarrowband transmission hole only if the chiral STF has neither gain nor loss.     

Stable high-power continuous-wave Yb(3+)-doped silica fiber laser utilizing a point-by-point inscribed fiber Bragg grating

We report on a narrowband 5 W cw fiber laser incorporating a point-by-point fiber Bragg grating inscribed into the core of a Yb(3+)-doped double-clad fiber. The laser featured excellent long-term wavelength and power stability (0.3%), as well as a very narrow (15 pm) linewidth, when passive temperature stabilization of the grating was implemented.     

Performance of conformal guided mode resonance filters

Guided mode resonance (GMR) filters are highly functional micro-optics capable of narrowband spectral filtering. GMR devices have previously been demonstrated on flat substrates using a wide range of materials and configurations. In this Letter, we apply a soft lithographic technique followed by the deposition of dielectric layers to generate GMR filters on a concave lens surface. Resonances of the resulting conformal GMR filters are experimentally measured and characterized, and the results are compared to the performance of similar GMR filters fabricated on flat surfaces.     

Single-mode fiber laser based on core-cladding mode conversion

A single-mode fiber laser based on an intracavity core-cladding mode conversion is demonstrated. The fiber laser consists of an Er-doped active fiber and two fiber Bragg gratings. One Bragg grating is a core-cladding mode converter, and the other Bragg grating is a narrowband high reflector that selects the lasing wavelength. Coupling a single core mode and a single cladding mode by the grating mode converter, the laser operates as a hybrid single-mode laser. This approach for designing a laser cavity provides a much larger mode area than conventional large-mode-area step-index fibers.     

光纤光栅传感信号解调技术研究进展

光纤光栅传感器是一种新型传感器,有着非常广泛的应用前景。限制光纤光栅传感器大量实际应用的主要障碍是传感信号解调,因而,光纤光栅传感信号解调是光纤光栅传感器应用的关键技术之一。本文对现有已报道的光纤光栅传感信号的解调方法进行综述,并归类为:边缘滤波法、匹配滤波法、可调谐滤波法、光源波长可调谐扫描法、射频探测法、光栅啁啾法、CCD分光仪法、干涉法。对各种方法的原理及相关改进方法进行了阐述,并对其优缺点做了比较分析,最后,对光纤光栅传感信号的解调技术发展进行了展望。     

窄带有机光电探测器的优化设计

针对基于无机材料的光电探测器需要借助滤光器或棱镜耦合实现窄带响应,提出了一种通过有机材料制备窄带光电探测器并提高吸收峰值和降低半高全宽的方法和结构。该器件由分布布拉格反射器和有机光电二极管构成。有机光电二极管的顶电极和底电极之间构成光学微腔。采用传输矩阵法,详细分析了分布布拉格反射器的中心波长、有机光电二极管透明顶电极和光敏感层的厚度对有机光电探测器吸收性能的影响。研究结果表明,Tamm等离激元共振波长接近光敏感层的光学带隙时,可获得半高全宽小于20 nm的窄带响应,并且吸收峰值在70%以上。基于PTB7∶PC~(71)BM和PTB7-Th∶IEICO-4F的有机光电探测器分别可用于探测红光和近红外光。该研究从基本物理机制出发,结合材料和器件结构可将有机光电探测器的响应窗口从可见光拓展至近红外光。     

Optimization of multiplexed holographic gratings in PQ-PMMA for spectral-spatial imaging filters

Holographic gratings formed in thick phenanthrenquinone- (PQ-) doped poly(methyl methacrylate) (PMMA) can be made to have narrowband spectral and spatial transmittance filtering properties. We present the design and performance of angle-multiplexed holographic filters formed in PQ-PMMA at 488 nm and reconstructed with a LED operated at approximately 630 nm. The dark delay time between exposure and the preillumination exposure of the polymer prior to exposure of the holographic area are varied to optimize the diffraction efficiency of multiplexed holographic filters. The resultant holographic filters can enhance the performance of four-dimensional spatial-spectral imaging systems. The optimized filters are used to simultaneously sample spatial and spectral information at five different depths separated by 50 microm within biological tissue samples.     

Production and characterization of refractive index gratings in high-birefringence fibre optics

In this work, we report production and modelling of both Bragg gratings and rocking filters in high birefringence fibre optics. Bragg gratings are produced by UV (257.0 nm) external interferometric exposition of a frequency-doubled Ar⁺ ion laser, whereas for rocking filters formation the visible Ar⁺ ion laser lines in 488.0 and 514.5 nm are used in an internal method. The spectral characteristics due to the birefringence properties are studied through numerical methods and experimental techniques. The spectral responsivity of the structures under temperature changes and stress application is presented.     

Fiber optic liquid leak detection technique with an ultrasonic actuator and a fiber Bragg grating

We present a technique for liquid leak detection in which ultrasonic and optical waves are introduced into a fiber simultaneously. The system is based on an ultrasonic technique using an ultrasonic actuator and a fiber Bragg grating receiver. A fiber-guided ultrasonic wave is utilized to stress the fiber Bragg grating, which is remote from the ultrasonic transmitter. When the traveling ultrasonic wave encounters a liquid, part of the wave will leak out from the fiber, which results in an ultrasonic strain decrease in the fiber Bragg grating. The ultrasonic wave and its attenuation are detected by the light variation of a narrowband laser source reflected and transmitted from the fiber Bragg grating, and the amplitude variation of the ultrasound can eventually be correlated with the fiber area coupled with the liquid.     

Tunable all-optical negative multitap microwave filters based on uniform fiber Bragg gratings

We present a novel and simple technique for obtaining transversal filters with negative coefficients by using uniform fiber Bragg gratings. We demonstrate a wide tuning range, good performance, low cost, and easy implementation of multitap filters in an all-optical passive configuration in which negative taps are obtained by use of the transmission of a broadband source through uniform Bragg gratings.     

Compact middle-wave infrared Fabry-Perot interferometer with double metallic subwavelength gratings

We demonstrate a compact middle-wave IR (MWIR) Fabry-Perot (FP) interferometer by replacing the traditional distributed Bragg reflectors consisting of thick multilayer films with two identical metallic subwavelength gratings. The transmission efficiency, resonance peak position, and finesse of the FP interferometer can be controlled by tuning the structural parameters. The performance of the MWIR FP interferometer is verified by experiment, which shows its potential application as, for example, narrowband MWIR filter for gas detection.     

Tunable All-Optical Microwave Filters Based on Fiber Loop and Chirped Fiber Bragg Gratings

All-optical microwave filters are important parts of fiber-optic microwave/millimeter wave processing systems. In this paper, two novel passive tunable all-optical microwave filters based on fiber loop and chirped fiber Bragg gratings (CFBGs) are demonstrated, where the frequency response of the both filters can be continuously tuned by adjusting the wavelength of the input light. The required free spectral range (FSR) of the filters can be obtained by carefully controlling the length of fiber loop and the positions of the CFBGs in the fiber loop. Experimental results prove the feasibility of the proposed filtering structures.