一维金属光栅的透射光学特性

利用时域有限差分法模拟了一维金属光栅的透射光场的分布及光栅厚度等因素对透射光谱的影响.结果表明:特定波长的光通过金属光栅中的亚波长狭缝时有异常大的透过率增强.分析其物理起源,认为是类FabryPerot(FP)腔作用的结果.基底介电常量对类FP腔长度的调制导致了对透射光谱的影响.金属光栅表面激发的表面等离子体激元波与多缝干涉一样,对透射光谱有一定的影响,但不是形成增强的原因 关键词： 金属光栅 透射光学特性     

基于SOI工艺的扭转式微机械扫描光栅设计及制作

为实现微型光谱仪在工程领域的广泛应用,研究了其核心器件扭转式微机械扫描光栅的结构与制作方法。利用SOI工艺,设计一种无需启动电极的静电梳齿驱动结构,可以使扭转式微机械扫描光栅具有低频驱动、制作工艺简单、扫描范围广等优点。通过设计的制作工艺方法,研制出了能够初步满足性能要求的扭转式微机械扫描光栅样件。测试结果表明:该微扫描光栅在驱动电压为25 V时最大转角可达到4.8,对应的光学扫描角为19.2。     

基于长周期光纤光栅的FBG解调方法北大核心CSCD

研究了基于长周期光纤光栅(long-period fiber gratings,LPFG)的光纤布拉格光栅(fiber Bragg gratings,FBG)解调方法,该方法利用LPFG的透射谱作为边沿滤波器解调FBG,其解调性能主要取决于LPFG的透射光谱深度。详细分析了CO_(2)激光写制法对透射光谱的影响,制作了透射光谱深度为25 dB的LPFG,并采用该光栅搭建了FBG解调装置,将FBG粘贴于金属应变片表面,测试了其静态与动态响应特征。实验结果表明:该方法制作简单,成本低,具有较好的线性动态范围,可以实现较高灵敏度的FBG解调。     

Raman lasing and other nonlinear effects based on ultrahigh-Q CaF2 optical resonator

The calcium fluoride (CaF₂) whispering gallery mode crystalline resonator is an excellent platform for nonlinear optical applications because of the decreasing in threshold caused by ultrahigh quality (Q) factor. In this paper, we achieved the observation of Raman lasing, first-order Raman comb, and second-order Raman lasing in a CaF₂ disk resonator with a diameter of 4.96 mm and an ultrahigh-Q of 8.43× 10⁸ at 1550-nm wavelength. We also observed thermal effects in CaF₂ disk resonator, and the threshold of thermo-optical oscillation is approximately coincident with Raman lasing, since the intracavity power increases rapidly when the power reaches the threshold, and higher input pump power results in longer thermal drift and higher Raman emission power. With a further increase in pump power, the optical frequency combs range is from 1520 nm to 1650 nm, with a wavelength interval of 4× m FSR. It is a promising candidate for optical communication, biological environment monitoring, spectral analysis, and microwave signal sources.     

随机性对部分随机介质激光器阈值的影响

基于速率方程和Maxwell方程相结合的模型，采用时域有限差分法(FDTD)研究了介质的随机性和层数对部分随机介质激光器阈值的影响.模拟结果显示，当抽运速率超过阈值时，出现一个或者多个振荡模；随机性或者系统的尺度增加时，振荡模数量也增加；部分随机介质激光器的阈值在一定的随机强度和层数下将达到最小值，它与完全随机情况下的结论有所不同.对所得到的结论给出了物理解释.这些结果对于制作随机激光器和光集成潜在应用价值. 关键词： 激光物理 随机激光器 阈值 时域有限差分法     

Investigation of transmission resonances on the one-dimensional metallic cylindrical gratings in THz frequency range

In the experiments of THz wave transmitting through the metallic cylindrical gratings fabricated by sub-wavelength brass wires, this paper reports that the discrepancy in the sharp resonances occurred as the grating perpendicular or parallel to the electric vector are observed. A simulation based on the finite difference time domain (FDTD) indicated that the enhanced transmission through the grating is attributed to the combined effects of surface plasmons and cavity modes in the perpendicular condition, while the cavity modes dominate the resonant transmission under the other conditions. Additional experimental data and calculated results show that ～1 enhanced coupling efficiency can be realized in some THz frequency, which could be applied to the design and improvement of various optoelectronic devices, or detection of biological molecule and powder samples, etc.     

Two-dimensional non-spatial filtering based on holographic Bragg gratings

The filter made up of two gratings performs as a two-dimensional non-spatial filtering. This paper reports that the volume Bragg gratings are fabricated by interfering two collimated coherent laser beams in photopolymer. Diffraction efficiency of a single grating is up to 78% in Bragg's condition, then a two-dimensional non-spatial filter, which consists of two volume Bragg gratings and a half-wave plate, enables the laser beam filtered in two dimensions with the diffraction efficiency of 54%. The Bragg's condition and effect of polarisation on performances of the two-dimension filter are also discussed.     

Fabry-Perot腔谐振对横电波激励下亚波长一维金属光栅的异常透射性的作用

利用时域有限差分法,对横电波(TE波)激励带电介质的亚波长一维金属光栅的光场分布进行了模拟分析,发现TE波在所研究的模型下具有异常透射现象.探究其物理本质,确定类导模共振理论是第一个峰和第二个峰产生的主要原因.在此基础上,从麦克斯韦方程出发,通过有效折射率法,确定了类Fabry-Perot(F-P)腔谐振是产生第三个峰的主要原因.从而完善了TE波在所研究的模型下产生异常透射现象的物理本质.为进一步研究TE波异常透射性的物理本质提供了一种完整的理论依据. 关键词： 金属光栅 横电波 异常透射 类Fabry-Perot腔谐振     

双光栅测速

双光栅的多普勒频移正比于动光栅的速度,所以测出了多普勒频移就可以定出动光栅的速度.通过对不确定度的分析,得出的结论是:速度测量的相对不确定度等于光栅常数的相对误差.     

Optical filter based on subtractive dispersion planar reflective gratings

We have successfully designed, fabricated, and tested an optical filter based on cascaded planar reflective gratings. The device uses a combination of two grating elements arranged in a subtractive dispersion configuration. The first grating demultiplexes a 300 nm wide band and drops optical channels at 1490 and 1550 nm, commonly used in passive optical networks. The second grating completely counter-balances the dispersion properties of the first grating and ultimately yields zero dispersion in the output waveguide. Such a configuration allows the transmission of optical signals though the device in an ultra-wide band spanning 1250-1410 nm. The filter was manufactured using an industry standard silica-on-silicon process which was augmented with grating facet formation and metallization. In spite of using low refractive index contrast waveguides (0.82%), the device had a remarkably low footprint of only 0.21 cm². Applications of the device in passive optical networks are discussed.     

Self-imaging with curved gratings

We analyze the near field behavior of binary amplitude gratings which present a curved profile. This configuration has an important application in rotary optical encoders. This kind of encoders is used to measure the angular displacement between two different parts of the devices. To our knowledge, its behavior in the near field has not been analyzed yet. We have found that Talbot effect is produced but the period of the self-images and Talbot distances change as we separate from the grating. We have fabricated a curved grating and have performed the experiment to corroborate the behavior theoretically found. This fact could be useful in systems that use Talbot effect to measure displacements, since the mechanical tolerances grow.     

横电波激励下亚波长一维金属光栅的异常透射性

针对一维亚波长金属光栅异常透射现象实现的问题,利用时域有限差分法,对横电波（TE波）激励带电介质的亚波长一维金属光栅的光场分布进行了模拟分析,得到了TE波的透射率与电介质折射率的变化关系,从而发现TE波在所研究的模型下具有异常透射现象.基于导模共振理论建立了类导模共振理论,并应用该理论较好地解释了TE波在所研究模型下的异常透射现象,确定类导模共振是TE波产生异常透射性的主要原因.应用所建立的理论解决了传统透射理论无法解决的问题.类导模共振理论揭示了异常透射现象的物理本质,为进一步研究异常透射性的物理本质提 关键词： 金属光栅 横电波 异常透射 类导模共振     

Mechanically induced long-period fiber gratings on tapered fibers

The characteristics of a mechanically induced long-period fiber grating (MLPFG) made by pressing a pair of grooved plates over single-mode fiber tapers are analyzed. Fiber tapers with a waist length of 80 mm and diameter ranging from 90 to 125 μm, fabricated using the heating and puling method, were used. We observed that the resonance wavelengths shift toward shorter wavelengths as the fiber taper waist diameter is reduced. A maximum shift of 254 nm in the position of the resonance peaks was observed when the fiber diameter was reduced to 90 μm. This technique is particularly suitable for tuning the resonance wavelengths to shorter wavelengths below the limit imposed by the grooved plate period.     

Configurable coarse wavelength division demultiplexers based on planar reflective gratings

Configurable coarse wavelength division multiplexing filters were realized using a planar reflective grating architecture utilizing small diffraction angles. The novel architecture yielded a 10-fold reduction in the chip size compared to previously reported filter configurations. The proposed design was manufactured using a standard silica-on-silicon process with a waveguide refractive index contrast of 0.82%. Polarization dependent losses of less than 0.2 dB were achieved without any post-processing steps. Fabricated filters showed insertion losses of 2.4 dB and remarkably broad free spectral ranges of more than 500 nm. The combination of single-mode input and multi-mode output guides resulted in box-like passband responses with bandwidth of 14.2 nm. Applications of the filters for integrated coarse wavelength division receivers and monitors are discussed.     

Plasmonic leaky‐mode lasing in active semiconductor nanowires

Leaky modes are below‐cutoff waveguide modes that lose part of their energy to the continuum of radiation modes during propagation. In photonic nanowire lasers, leaky modes have to compete with almost lossless above‐cutoff modes and are therefore usually prevented from crossing the lasing threshold. The situation is drastically different in plasmonic nanowire systems where the above‐cutoff plasmonic modes are very lossy because of their strong confinement to the metal surface. Due to gain guiding, the threshold gain of the hybrid electric leaky mode does not increase strongly with reduced wire diameter and stays below that of all other modes, making it possible to observe leaky‐mode lasing. Plasmonic ZnO nanowire lasers operating in the gain‐guided regime could be used as coherent sources of surface plasmon polaritons at the nanoscale or as surface plasmon emitting diodes with an emission angle that depends on the nanowire diameter and the color of the surface plasmon polariton.

     

Tunable two-wavelength lasing of Ti: Al_2O_3 and its two-wave mixing in β-BaB_2O_4

A tunable Ti: sapphire laser with a symmetric two-channel dispersive resonator operated simultaneously at two wavelengths was obtained. The delay between λ_1 and λ_2 pulses did not exceed a few nanosecond. Independent tunable range of each output wavelength is 720-820nm, and the maximum wavelength difference was about 55nm. The competition and connectivity between two waves have been observed. The frequency suming and doubling of the two waves generated in BBO were also obtained.     

基于光纤叠栅的全光纤声光可调谐滤波器的特性分析

本文提出了一种基于光纤叠栅的全光纤声光可调谐滤波器, 与普通光纤布拉格光栅型全光纤声光可调谐滤波器相比, 该滤波器能够对光纤叠栅的两个中心波长进行同步调制. 理论分析了声波频率和声致应变幅度对基于光纤叠栅的全光纤声光可调谐滤波器的传输光谱的影响, 结果表明, 各阶次反射峰分别以两个主反射峰为中心呈对称关系, 且主反射峰与其所调制出的次反射峰之间的波长间隔与声波频率成正比, 而两个主反射峰所调制出的同阶次反射峰之间的波长间隔与声波频率无关; 声致应变幅度主要影响主反射峰及次反射峰的反射率的变化. 实验中, 分别测试声波频率为390 kHz和710 kHz的基于光纤叠栅的全光纤声光可调谐滤波器的传输光谱, 实验结果的变化趋势与仿真分析结果相一致.     

Surface plasmon resonance spectroscopy on rotated sub-micrometer polymer gratings generated by UV-laser based two-beam interference

Two-beam interference method was applied to generate gratings having periods of 416 nm and 833 nm by the forth harmonic of a Nd:Yag laser on thin poly-carbonate films spin-coated onto silver layer-covered substrates. The dependence of the modulation depth on the fluence and number of laser pulses was investigated by atomic force microscopy. A secondary pattern appeared on very thin polymer layers thanks to the “p” polarized laser beam illumination induced self-organized processes. The conditions of the emergence of grating-coupling caused additional plasmon resonance peak were determined for the sub-micrometer periodic polymer gratings. Surface plasmon resonance measurements were performed in attenuated total reflection arrangement to determine the effect of the angle between the plasmon propagation direction and the polymer groves on the grating-coupling. The effect of the modulation depth on the grating-coupling caused additional resonance minimum was also analyzed. We found coupling phenomena according to our calculations, the differences between the measured and theoretically predicted resonance curves were explained by the scattering on the complex surface structure.     

Different kinds of band-pass filters based on one-dimensional photonic crystal heterostructures

Three kinds of band-pass filters (BPFs), termed a TE BPF, a TM BPF and a BPF at oblique incidence, are designed by crossing the band edges of two different one-dimensional (1D) photonic crystals (PCs). The TE BPF, fulfilling the function of high reflectivity for p-polarization and high transmittance in a narrow pass-band for s-polarization, is constructed by two subPCs, one of which is obtained by decreasing the lattice constant of the other one while the other parameters keep the same. The TM BPF also comprises two subPCs, but the materials of one subPC are quite different with those of the other one. Similarly, the BPF at oblique incidence, from which both polarization waves can transmit in a narrow pass-band at oblique incidence, is composed of two different subPCs. Note that, the distribution of the wave impedance of material in each BPF should be periodic to prevent unexpected defect modes. The new filters not only provide narrow pass-bands and wide non-transmission bands, but also have simple structures. This is a result of the fact that the wave impedance ratio between composites is enlarged by introducing magnetic materials. The new designs have potential applications in optical filters and optical integrated circuits.     

Characteristics of light emission from surface plasmons based on rectangular silver gratings

We investigated the characteristics of transmitted light from propagating surface plasmons based on rectangular silver gratings. The results calculated by rigorous coupled-wave analysis presented that silver diffraction gratings can produce significant transmittance and conversion efficiency, comparable to the case of dielectric gratings. Especially, silver gratings optimized at a wide range of grating thickness and period may lead to an improved diffraction efficiency larger than 64%. Moreover, the effect of silver oxide layer on the transmittance was examined and a bimetallic structure with a thin gold coating was introduced to prevent an oxidation of silver substrates. As a practical sensor application, silver grating-based surface plasmon resonance (SPR) configuration showed an enhanced sensitivity associated with an increase of surface reaction area and strong excitations of local plasmon fields, outperforming a conventional thin-film-based SPR structure.