Design of guided-mode resonance filters with an antireflective surface at oblique incidence

A design approach of guided-mode resonance filter (GMRF) with an antireflective surface at oblique incidence is presented. For a given incident angle or grating filling factor, the required grating filling factor or incident angle can be expressed by the analytical forms of the quadratic equations at quarter-wavelength thickness. Long-range, low sidebands are obtainable for a single-layer GMRF under the TM mode wave illumination at oblique incidence. The reflection properties such as the symmetry of the lineshape and the sideband level in the logarithm scale can be further improved by slightly varying both the grating period and the grating thickness. Magnetic field enhancement occurs in these structures due to the coupling between the evanescent diffracted order and the waveguide mode.     

Relationship between linewidth and electric field intensity of guide-mode resonance filter

In this paper, relationship between linewidth and maximum electric field intensity (MEFI) at resonance of guided-mode resonance filter (GMRF) is investigated. It is demonstrated that the linewidth will vary inversely with the MEFI as one of some of the parameters of the GMRF increasing (e.g. period, thickness, and filling factor of the grating in the GMRF and cover refractive index) and with others maintained. Also it is demonstrated that resonant wavelength will shift to longer wavelength as any one of the parameters of the GMRF increasing. Moreover, the changes of period and thickness of grating have good linear relation with wavelength shifting. This will be of interest for optical sensor systems.     

A method to accurately control the period of subwavelength planar holographic grating in the fabrication process of guided mode resonance filter

Subwavelength optical element such as guided-mode resonance filter has gained much interest recently due to its properties and applications. It is very hard to fabricate an ideal guided-mode resonance filter with the same parameters as the designed one. The reason is that the resonance wavelength of guided-mode resonance filter is susceptible to the fabrication errors of its parameters, such as the period, the groove depth, the thickness of a guided-wave layer, and the refraction indexes of materials, etc. In this article, a method to accurately control the period of subwavelength planar holographic grating which was used as a sub-layer of the guided mode resonance filter is investigated. Results show that utilizing a convex lens placed in the exposure position can cause the adjusting of the period of subwavelength planar grating more convenient in the holographic optical path during the fabrication process. Accuracy controlling the period of grating which was used as the sub-layer of guided-mode resonance filter has great significance in the fabrication of guided-mode resonance filter.     

紫外固化型聚合物高阶布拉格波导光栅滤波器

利用紫外固化材料SU-82005与热交联聚合物甲基丙烯酸甲酯一甲基丙烯酸缩水甘油酯[P（MMA—GMA）]分别作为波导芯层和包层材料,通过直接光刻技术,成功实现了厚度为5μm,宽度为9μm,光栅高度为4μm的起伏型高阶布拉格波导光栅滤波器。对光栅器件的谐振波长,光透射率等重要参数进行了模拟设计。测得制备的聚合物高阶布拉格波导光栅滤波器的谐振波长为1550．4nm,消光比为23dB,3-dB带宽为2nm。     

带缓冲层的导模共振滤光片反射光谱特性

将均质多层膜系设计中的缓冲层概念引入到反射导模共振滤光片的设计中,以研究缓冲层的增加对导模共振滤光片反射光谱特性的影响.设计并通过严格的耦合波理论计算了一、二、三、四通道导模共振反射滤光片光谱特性.在膜系设计中增加缓冲层后.随着其厚度的逐渐增加.反射光谱中依次出现二、三、四个窄带反射峰;缓冲层厚度为796.35 nm时.当滤光片光栅层占空比在0.2～O.9范围内、光栅深度在100～200 nm变化时,共振峰的位置、反射率峰值高度几乎不变,保持了很好的多通道滤光片特性.     

Design of internal Brewster guided-mode resonance filter

An internal Brewster guided-mode resonance （GMR） filter is designed. For this kind of GMR filter, the Brewster reflection occurs at the interface of grating/waveguide layers rather than at the interface of air/grating layers. At Brewster angle of 60~, the GMR filter owns almost 100% reflection at the resonance wavelength of 800 nm with the full-width at half-maximum （FWHM） of 0.2 nm. Its angle response changing with the fabrication deviation is also discussed.     

Design of single-material guided-mode resonance filter

In this letter, a guided-mode resonance （GMR） filter with the same material for both the grating layer and the waveguide layer is designed, and its optical properties are investigated. The GMR filter owns almost 100% reflection at the resonance wavelength of 800 nm with the full-width at half-maximum （FWHM） of 20 nm, and its sideband reflection from 700 to 1000 nm is less than 5%. As the resonance wavelength is influenced by more than one parameter during the fabrication process, GMR filter with the same resonance wavelength can be obtained by adjusting other parameters or even one parameter to deviate from the design value.     

Design and analysis of nano-deep corrugated waveguide grating-based dual-resonant filters in visible and infra-red regions

A theoretical analysis of nano-deep corrugated long-period waveguide gratings on a SU-8 polymer-based channel waveguide with NOA61 optical epoxy coated upper- and lower cladding is presented. The transmission spectra of the gratings show strong rejection bands both at visible (at wavelength region of 450?460 nm) and infra-red (at wavelength region of 1530?1540 nm) regions when a grating period of ?68 μm with optimized grating tooth height is considered. Phase-matching graphs are studied to find the relationship between resonance wavelength and grating period. These results show that the grating parameters significantly affect the characteristics of transmission spectra as well as the resonance wavelength of the grating. Long-period waveguide grating-based band pass filter made by use of same polymer materials are also designed and analyzed. These types of waveguide grating-based filters can widely be used for visible and infra-red wavelength sensing applications.     

Design and analysis of multilayered structures with metal-dielectric gratings for reflection resonance and color generation

A multilayered structure incorporating a metal-dielectric subwavelength grating, with the characteristic of polarization separation for visible light and the capability of creating reflection resonance and distinctive polarization-dependent color effects, is proposed. Its reflection resonance and color for TE and TM polarizations are discussed, as well as the influence of its structural parameters on them. Moreover, a reflection filter with characteristics of red for TE-polarized light, green for TM-polarized light, and yellow for daylight is designed and fabricated by replacing its grating region with a sinusoidal grating, and its related characteristics also are verified. The structure and its properties can achieve practical applications in various fields, such as color security, image reproduction, color filtering, and polarization-based information hiding.     

Color filters featuring high transmission efficiency and broad bandwidth based on resonant waveguide-metallic grating

A one-dimensional transmission color filter based on a resonant waveguide-metallic subwavelength grating was numerically investigated by employing rigorous coupled-wave analysis (RCWA) and genetic algorithm (GA). The hybrid numerical method is used to determine the optimal parameters (the grating period, filling factor, grating thickness, and waveguide thickness) of two waveguide-grating structures, namely a double-layer resonant waveguide-metallic grating and a triple-layer resonant waveguide-metallic grating. The optical responses of these structures are evaluated and compared in terms of the ideal transmission efficiency aiming at the central wavelengths of 645 nm, 546 nm, and 455 nm of red (R), green (G), and blue (B) lights, respectively, over the visible region (380–780 nm). The results show that the optical performance of the double-layer with silver grating achieves the highest transmission efficiency of 82% (R), 81% (G), and 66% (B); and the largest bandwidth of about 125 nm (R), 118 nm (G), and 85 nm (B). Compared with existing color filters, the proposed device not only obtains a higher transmission and broader bandwidth, but it also suppresses redundant spectral peaks and transmission sidebands.     

Guided-mode resonance Brewster filter

A new type of optical filter is predicted theoretically and verified experimentally. The filter operates under guided-mode resonance conditions in a thin-film waveguide grating. A high-efficiency reflection filter response is produced at the Brewster angle at which TM reflection is classically prohibited. Low-reflectance sidebands are obtained that are adjacent to the resonance peak induced by the Brewster effect in the neighborhood of the resonance peak. A double-layer waveguide grating yields 94% experimental reflectance at the thin-film Brewster angle for a Gaussian laser beam with TM polarization at the 1064-nm wavelength.     

Study on guided-mode resonance characteristic of multilayer dielectric grating with broadband and wide using-angle

Guided-mode resonance in a diffraction band of multilayer dielectric gratings may lead to a catastrophic result in laser system, especially in the ultrashort pulse laser system, so the inhibition of guided-mode resonance is very important. In this paper the characteristics of guided-mode resonance in multilayer dielectric grating are studied with the aim of better understanding the physical process of guided-mode resonance and designing a broadband multilayer dielectric grating with no guided-mode resonance. By employing waveguide theory, all guided-wave modes appearing in multilayer dielectric grating are found, and the incident conditions, separately, corresponding to each guided-wave mode are also obtained. The electric field enhancement in multilayer dielectric grating is shown obviously. Furthermore, from the detailed analyses on the guided-mode resonance conditions, it is found that the reduction of grating period would effectively avoid the appearing of guided-mode resonance. And the expressions for calculating maximum periods, which ensure that no guided-mode resonance occurs in the requiring broad angle or wavelength range, are first reported. The above results calculated by waveguide theory and Fourier mode method are compared wit each other, and they are coincident completely. Moreover, the method that relies on waveguide theory is more helpful for understanding the guided-mode resonance excited process and analyzing how each parameter affects the characteristic of guided-mode resonance. Therefore, the effects of multilayer dielectric grating parameters, such as period, fill factor, thickness of grating layer, {\it et al.}, on the guided-mode resonance characteristic are discussed in detail based on waveguide theory, and some meaningful results are obtained.     

High spectral resolution analysis of tunable narrowband resonant grating waveguide structures

A high spectral resolution analysis of narrowband reflection filters based on resonant grating waveguide structures is presented. A tunable high-performance dye laser with ∼ 0.15 cm^-1 line width and a beam analyzing system consisting of three simultaneously controlled CCD cameras were used to investigate grating waveguide resonances at wavelengths in the 694 nm and 633 nm ranges. A reflectivity of ∼ 91% and a line width of ∼ 0.55 nm were measured and theoretically modeled for a resonant reflection filter specifically designed for the ruby laser wavelength 694.2 nm. For a second grating waveguide structure, designed for the helium-neon laser emission wavelength 632.8 nm, we observed a thermal shift of its spectral resonance position of several nanometers, when increasing the sample temperature by some degrees. An inverse thermal shift was observed when the structure was subsequently cooled down to room temperature. Our results suggest implementation of grating waveguide devices combining a narrow line width with a tunability of the resonant response into innovative concepts for reflection filter and sensor applications. PACS 42.62.-b; 42.79.Dj; 42.79.Gn     

级联亚波长平面介质栅偏振分束器研究

提出了一种纳米厚度金属层连接的级联亚波长平面介质光栅三明治结构,利用该结构中纳米金属连接层上下界面处的表面等离子共振的互作用形成多波长共振的特点设计了适用于光通信波段（1 300～1 600nm）高性能的宽带偏振器和宽带偏振分束器。利用严格耦合波理论分析发现偏振分束器带宽主要由金属连接层厚度控制,光栅厚度基本不影响偏振分束器带宽,只影响共振深度和共振波长。该结论为后续的制备提供了理论指导和借鉴作用。     

Analysis of a widely tunable long-period grating by use of an ultrathin cladding layer and higher-order cladding mode coupling

A widely tunable long-period grating in single-mode fiber is analyzed by use of an ultrathin cladding layer and higher-order cladding mode coupling. The numerical simulation shows that a 225-nm tuning range in the newly designed ultrathin long-period grating (cladding thickness, 35 microm) with third-order cladding mode coupling can be obtained. The analyzed tuning range is seven times wider than those of the other known long-period gratings. We believe that the proposed highly sensitive long-period grating will be widely used as a gain-flattening filter for ultrawideband optical amplifiers and fast tunable filters in dynamic optical communication systems.     

金属光栅的非对称透射现象研究

提出一种利用表面等离子体耦合的金属光栅结构,该光栅结构因入射光的方向和耦合表面等离子体的条件不同,从不同方向入射时会有不同的透射率。周期为500 nm、填充因子为0.7的Au-SiO₂光栅结构在565~589 nm波段具有单向透射性。当填充因子为0.662时,最大透射对比率达3×10⁴。当光栅厚度为60 nm时,入射波长在570~630 nm之间的透射对比率均可达到5以上,最高透射率为43%。当光栅周期为1 100 nm时,1 530~1 590 nm波段的透射对比率均大于5,可以满足中红外波段的应用。     

介质光栅导模共振耦合波分析

导模共振是由于光栅介质内高级次子波耦合进光栅所支持的泄漏模中,导致传播波能量重新分布的结果.采用严格的耦合波方法,通过分析波导的导波模式,正确估计出弱调制介质光栅导模共振的位置.并对导模共振与光栅厚度、基底厚度以及入射角的关系作了讨论.通过采用抗反射设计,获得了具有对称、低旁带特点的窄带共振峰 关键词： 导模共振 耦合波     

Adjustable plasmon resonances through an H-shaped metallic grating

We propose an H-shaped metallic grating and investigate its surface plasmon resonance properties. The result shows the formation process of the transmission spectra of the H-shaped grating by adjusting the depths of the arm cuts, and a band gap is formed on the region of short wavelength. It is also presented that the transmission of the H-shaped grating sensitively depends on the width and position of the arm slit, noticeable magnitude modification, redshift and blueshift, meld and split of the resonance peaks are found. In addition, the resonance peaks exhibit dips in the transmission spectrum when the two slit widths are different, and the dips are tunable by changing any one slit width for fixed another slit. To understand its physical origin, a field-interference mechanism, the Fabry–Pérot-like resonance theory and the phase resonance mechanism have been suggested, respectively. By selecting appropriate structural parameters, an H-shaped metallic grating for optical filter and channel selecting devices can be constructed.     

基于PDMS薄膜的等离子体光栅仿真分析

为了实现对等离子体光栅共振波长的测量,研究光栅参数对应力的响应敏感程度,提出了一种新型的应力敏感型聚二甲基硅氧烷（polydimethylsiloxane,PDMS）薄膜等离子体光栅。基于时域有限差分（finite difference time domain,FDTD）法的原理,构造了一种结构仿真模型,即周期性等离子体光栅模型。借助周期边界条件,通过对光栅施加应力,改变等离子体光栅参数（即周期、占空比及Au膜厚度）来实现共振波长的测量,研究光栅参数对应力的响应敏感程度。最后将仿真结果与理论数值作对比,并得出相对误差大小。仿真结果表明,当光栅周期p=0.7 μm,占空比f=55%,金膜厚度b=0.02 μm时,对应力的响应最敏感。其次,将仿真所得不同周期时的共振波长与理论值相比较,可知二者结果相吻合;周期为0.7 μm时,共振峰的波长为1.251 μm,仿真结果与理论数值比较得到,其相对误差都不超过2%,结果较为准确。此方法在单色仪、光谱仪和传感等领域中具有重要作用。     

Theoretical investigation of a notch filter using a long-period grating based on the sampling theorem

A notch filter using a different grating scheme is investigated theoretically. The grating is the thermo-optic index change induced by individually controllable heaters that are periodically arranged on the filter surface. If the index change pattern induced by the heaters is in the form of sampling a periodic index change, the transmission spectrum of the filter has the same resonance band as that generated by the periodic index change. Simulation results show that the attenuation, bandwidth, and center wavelength of a resonance band are independently adjustable. In addition, it is shown that the transmission spectrum may be tailored to arbitrary predictable shapes. Finally, the realization of the filter is discussed.