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1.
We report the theory and experimental demonstration of two multiplexing schemes for addressing fiber grating sensor arrays consisting of multiple branches. In the first scheme, light in each branch is intensity modulated at different subcarrier frequencies and signals from different branches are separated in frequency domain by using bandpass filters. In the second scheme, the modulation frequency in each branch can be the same and signal separation is performed in time domain by using an electronic switch after photodetection. 相似文献
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The generation of amplitude and phase gratings in an absorbing medium is discussed, including the effects of light polarization, population kinetics and orientational relaxation. A theory is given which describes light diffraction by a combination of an amplitude and a phase grating. It is shown that the coherent coupling effect in transient absorption measurements is solely due to the amplitude grating. Weak absorption and a low triplet yield favour diffraction of the probing beam by the phase grating in triple-beam experiments. Phase grating experiments can be performed with highly soluble absorber dyes, the absorption maximum of which is far away from the laser wavelength. Due to photoselection, diffraction by an amplitude grating depends on the polarization of the probing beam while phase grating diffraction is insensitive to this. Perpendicular polarization of the two exciting pulses prevents the buildup of a phase grating and results in light diffracted by the amplitude grating that is proportional to the transient dichroism signal as known from the common absorption relaxation. 相似文献
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A two step light emission process becomes possible when atoms are placed near a metallic grating. The atoms can excite surface plasmons in the grating. The surface plasmons can then emit light. This light is emitted at certain angles determined by momentum conservation in the plane of the grating. Thus, the angles depend on the spacing of the grating. Our measurements on light from nitrogen atoms at distances, d, ranging from 10 to 100 nm from a silver grating are in agreement with a recent theory of Aravind, Hood and Metiu. We also report the effect of a nonsinusoidal grating profile and the emission of light at angles which can be predicted from a straightforward extension of the theory. 相似文献
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Na Chen 《Optics Communications》2006,259(2):587-591
A new type of fiber grating with only cladding index modulation is presented. Characteristics of both cladding index modulated short-period fiber grating (FBG) and long-period fiber grating (LPFG) are analyzed. The calculation of the modes involved in this paper is based on a model of three-layer step-index fiber geometry. Transmission of a mode guided by the core through a cladding index modulated grating when evanescent field coupling occurs is analyzed with couple-mode theory. Evanescent field coupling causes a power flowing from the core to the cladding, so the attenuation of the new grating is analyzed as well. Lower attenuation, flexible spectral characteristics are demonstrated in comparison with traditional fiber core index modulated grating. 相似文献
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An optically switchable, polarization-independent holographic polymer dispersed liquid crystal (H-PDLC) transmission grating
is demonstrated by adding azobenzene-LC and chiral molecules into the H-PDLC formulation. The optical switchable mechanism
is from the trans-cis photoisomerization of the doped azobenzene-LC, which modulates the refractive index of the LC rich area. The dependence of
the diffraction efficiency of the H-DPLC grating without chiral molecules on light polarization suggests that the orientation
of LC directors within the droplet is ellipsoidal and uniaxial. However, the addition of chiral molecules into the H-PDLC
formulation helps the formation of isotropic and non-uniaxial LC directors within the droplets. The polarization properties
of the grating are investigated and analyzed by the coupled and modified coupled wave theory with a model of sinusoidal dielectric
modulation. The results show that the addition of chiral molecules changes the LC phase from nematic to chiral-nematic, where
the grating efficiency, which is modulated by the photoinduced phase transition, is independent of the polarization of incident
light. Our findings may help improve optical systems that utilize non-polarized light. 相似文献
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We present a simple model for surface enhanced Raman (SER) scattering, in which enhanced surface charge densities and fields, coupled to light through a metallic grating, are modulated by vibrating molecular potentials. The modulated charge densities produce radiation at the Stokes shifted frequency. 相似文献
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We have constructed a low-cost, double-cavity erbium-doped fiber ring laser with a fiber Bragg grating and a 2×2 coupler. A high output power of 8.7 dBm and a signal-to-noise-floor ratio of 43 dB were demonstrated. This fiber grating ring laser is used as the light source for the 2.488 Gb/s transmission experiment through a 100 km single mode fiber. To our knowledge, this is the first time a fiber grating ring laser is being used as an externally modulated source for digital transmission. 相似文献
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N. Garcia 《Optics Communications》1983,45(5):307-310
Exact calculations of the interaction of p-polarized light from grating surfaces are presented by using the theory of Toigo, Marvin, Celli and Hill. New features for the scattered field are found for light resonating with surface plasmon polaritons; the reflectivity present maxima for large amplitude gratings. The electromagnetic field is calculated on a fine grid near the grating. We find enhancements of the order of 200 to 300 for the square of the field that could partly explain SERS. 相似文献
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杂散光是平面光栅的重要性能指标,光栅杂散光的测量一直是光栅研制领域的难题。为实现仪器自身杂光低于10-8量级,以满足对平面光栅杂散光10-7量级的精确测量要求,基于标量衍射理论和经典Fresnel-Kirchhoff衍射理论,对光谱仪器中的光栅杂散光进行了理论分析,设计了平行光照射条件下光栅杂散光测试仪的光机模型。利用杂散光分析软件ASAP建立紫外单色光入射下光栅杂散光测试仪的散射模型并对其进行仿真计算,分析仪器杂光的主要来源及散射路径,据此提出了用于降低仪器散射光和光栅多次衍射光的挡光环、叶片、光阑、光学陷阱等四种杂光抑制结构。最后,采用ASAP软件对增加抑制结构前后的仪器杂光相对强度进行了对照分析。仿真及分析结果表明,仪器杂光在测试波长±100 nm范围内的最大值由采用杂光抑制结构前的10-6量级以上降低至10-8量级以下,已满足光栅杂散光测试仪的设计需求,即可实现刻线密度为300~3 600 gr·mm-1的光栅杂散光10-7量级精确测量。该研究方法及结果将为平面光栅杂散光测试仪研制提供理论依据。 相似文献
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采用简化的三层光纤模型,从模式理论和耦合模理论出发,分析了长周期光纤光栅的耦合特性及功率透射谱,给出了长周期光栅的主要特性参数。利用计算机建模,采用Matlab软件对实用的SMF 28单模光纤加以特定的光栅折射率调制参数进行数值计算,并采用振幅掩模法刻写长周期光纤光栅进行实验验证,计算结果与实验结果相吻合。 相似文献
18.
Cladding-mode-assisted recouplings in concatenated long-period and fiber Bragg gratings 总被引:1,自引:0,他引:1
We investigate new types of mode recouplings in a concatenated grating structure comprising a long-period grating and a fiber Bragg grating. It is demonstrated that the light coupled out to the cladding mode by one of these gratings can be recoupled back to the guided mode by the other grating. Theoretical analysis based on the coupled-mode theory is presented, together with experimental results. 相似文献
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Rui Zhang Xiaomin Zhang Zhan Sui Jianjun Wang Honghuan Lin Mingzhong Li Jingqin Su Feng Jing Xiaofeng Wei Ping Li Huaiting Jia 《Optics & Laser Technology》2008,40(8):1018-1024
Precise physical experiments place strict requirements on target illumination uniformity. A new smoothing technology aimed at indirect-drive laser fusion is studied, which uses linearly modulated light and angular spectral dispersion (ASD). Simulation indicates that the best smoothing effect could be obtained when number of color cycles (Nc) is chosen to be 0.5 at 1.2 nm bandwidth. A table-top setup aimed at the experimental study of the beam smoothing method has been established. When the linearly modulated light generated by pulse stacking is dispersed by a grating with Nc=2.6, periodical undulations are found on the far-field focal spot, which agrees with the simulation results. To improve illumination uniformity, the Nc adopted should be decreased to 0.5. Simulation also indicates that the combination of linearly modulated light, angular spectral dispersion and a continuous phase plate could considerably improve the irradiation nonuniformity. 相似文献
20.
Holographic gratings are recorded and thermally fixed in iron-doped photorefractive lithium-niobate crystals. A spatially
modulated concentration of filled and empty electron traps (Fe2+ and Fe3+) yields a modulated dark conductivity. As a consequence, dark diffusion currents and dark drift currents arise. Space–charge
fields and electro-optic refractive-index changes build up. An additional refractive-index grating, which may originate from
a modulated proton concentration, as well as a pronounced absorption grating arising from the modulated Fe2+ concentration are also observed. The dark development has practical advantages: thermally fixed holograms can be used in
devices without the need to develop them freshly from time to time by illumination. Although with dark development diffraction
efficiencies up to 50% are demonstrated, in general the efficiencies are smaller compared to those achieved by development
with light.
Received: 28 June 2000 / Published online: 8 November 2000 相似文献