Bragg waveguide grating as a 1D photonic band gap structure: COST 268 modelling task

Modal reflection, transmission and loss of deeply etched Bragg waveguide gratings were modelled by six European laboratories using independently developed two-dimensional (2D) numerical codes based on four different methods, with very good mutual agreement. It was found that (rather weak) material dispersion of the SiO₂/Si₃N₄ system does not significantly affect the results. The existence of lossless Floquet–Bloch modes in deeply etched gratings was confirmed. Based on reliable numerical results, the physical origin of out-of-plane losses of 1D or 2D photonic band gap structures in slab waveguides is briefly discussed.     

Bragg waveguide grating as a 1d photonic band gap structure: COST 268 modelling task

Modal reflection, transmission and loss of deeply etched Bragg waveguide gratings were modelled by six European laboratories using independently developed two-dimensional (2D) numerical codes based on four different methods, with very good mutual agreement. It was found that (rather weak) material dispersion of the SiO₂/Si₃N₄ system does not significantly affect the results. The existence of lossless Floquet-Bloch modes in deeply etched gratings was confirmed. Based on reliable numerical results, the physical origin of out-of-plane losses of 1D or 2D photonic band gap structures in slab waveguides is briefly discussed.     

New insights on amorphous silicon-nitride microcavities

All amorphous silicon-nitride planar optical microcavities operating in the visible range have been grown by plasma enhanced chemical vapor deposition. The luminescence intensity of the N-rich silicon-nitride layer from a microcavity with 6 period distributed Bragg reflectors (DBRs) is two order of magnitude higher than that of the luminescent layer without the cavity. Moreover, a strong directionality of the microcavities emission can be observed. Such results can be ascribed to the anisotropic optical density of states induced in the Fabry–Perot structure. The quality factors of the resonators are strictly correlated to the number of periods of the DBRs.     

Bragg diffraction of light in a restricted homogeneous system of tunnel-coupled waveguides

A system of tunnel-coupled rectilinear waveguides is studied. The dependence of the number of modes in this system on the number of waveguides N, the distance between the waveguides, and the number of modes in a separate waveguide is considered. It is shown that the modes of the m = N and N + 1 orders in such a system are Bragg modes; i.e., the angle between the direction of their propagation and the system axis is close to the Bragg angle. The effective refractive indices n ^* of these modes change stepwise. The step size Δn ^* is found to be dependent on the distance s between the waveguides and on the number of modes in a separate waveguide. A system of single-mode waveguides with the number of guided modes M = 34 < N = 50 is studied experimentally. It is shown that the Bragg modes of the system lie among the leakage modes of the system and have rather low losses. It is demonstrated that the localization of the Bragg modes among the leakage modes may be favorable for their selection upon light generation.     

Fabry–Perot interferometer using curved plates

Fabry–Perot interferometer with curved plates is described. It is found that the partially reflecting surfaces of the Fabry–Perot interferometer need not be necessarily flat. The pair of Fabry–Perot plates may be curved but the surfaces must be well matched with an accuracy better than λ/100.     

Compact Branched Optical Waveguides Using High-Index-Contrast Stacked Structure

We have developed a novel branched optical waveguide using a stacked directional coupler, which consists of two Si₃N₄ core layers (each 0.3 μm thick) stacked with a thin (0.2 μm) SiO₂ film in between. Using this stacked high-index-contrast system, the size of the multiple branched waveguides can be dramatically reduced compared with the conventional Y-shaped branches. A four-branch optical waveguide is designed and fabricated, and good performance of distribution power of 25 ± 4% to each branch has been achieved.     

Modeling of grating assisted standing wave,microresonators for filter applications in integrated optics

A wide, multimode segment of a dielectric optical waveguide, enclosed by Bragg reflectors and evanescently coupled to adjacent port waveguides, can constitute the cavity in an integrated optical microresonator. It turns out that the device can be described adequately in terms of an approximate coupled mode theory model which involves only a few guided modes as basis fields. By reasoning along the coupled mode model, we motivate a simple design strategy for the resonator device. Rigorous two dimensional mode expansion simulations are applied to verify the predictions of the approximate model. The results exemplify the specific spectral response of the standing wave resonators. As refinements we discuss the single resonance of a device with nonsymmetrically detuned Bragg reflectors, and the cascading of two Fabry–Perot cavities, where the coupling across an intermediate shorter grating region establishes a power transfer characteristic that is suitable for an add-drop filter.     

Si3N4的晶体化和ZrN/Si3N4纳米多层膜的超硬效应

研究了Si₃N₄层在ZrN/Si₃N₄纳米多层膜中的晶化现象及其对多层膜微结构与力学性能的影响. 一系列不同Si₃N₄层厚度的ZrN/Si₃N₄纳米多层膜通过反应磁控溅射法制备. 利用X射线衍射仪、高分辨透射电子显微镜和微力学探针表征了多层膜的微结构和力学性能. 结果表明，由于受到ZrN调制层晶体结构的模板作用，溅射条件下以非晶态存在的Si₃N₄层在其厚度小于0.9 nm时被强制晶化为NaCl结构的赝晶体，ZrN/Si₃N₄纳米多层膜形成共格外延生长的柱状晶，并相应地产生硬度升高的超硬效应. Si₃N₄随层厚的进一步增加又转变为非晶态，多层膜的共格生长结构因而受到破坏，其硬度也随之降低.     

Variational analysis of Er:Ti:LiNbO3 waveguide lasers based on Gaussian/two-half Gaussian mode field distribution

Starting with two dimensional, scalar wave equation, a variational equation was established for the fundamental TE and TM modes guided in Ti:LiNbO₃ waveguides on the basis of assuming a symmetric Gaussian mode field function in the width direction and two-half Gaussian trial functions in the depth direction. The controllable waveguide fabrication parameters, including channel width, diffusion temperature, initial Ti-strip thickness and diffusion time, dependent of fundamental mode size, effective pump area, coupling efficiency between pump and laser modes, and the coupling loss between a Ti:LiNbO₃ waveguide and a fiber were numerically calculated for Z-cut Er:Ti:LiNbO₃ channel waveguide lasers at three possible emission wavelengths 1532,1563 and 1576 nm and two possible pump wavelengths 1480 and 980 nm. The calculated results were compared with those of Gaussian/Hermite–Gaussian mode field distribution in detail.     

Crystallization of amorphous Si3N4 and superhardness effect in HfC/Si3N4 nanomultilayers

HfC/Si₃N₄ nanomultilayers with various thicknesses of Si₃N₄ layer have been prepared by reactive magnetron sputtering. Microstructure and mechanical properties of the multilayers have been investigated. The results show that amorphous Si₃N₄ is forced to crystallize and grow coherently with HfC when the Si₃N₄ layer thickness is less than 0.95 nm, correspondingly the multilayers exhibit strong columnar structure and achieve a significantly enhanced hardness with the maximum of 38.2 GPa. Further increasing Si₃N₄ layer thickness leads to the formation of amorphous Si₃N₄, which blocks the coherent growth of multilayer, and thus the hardness of multilayer decreases quickly.     

Observation of strong light-matter coupling by spectroscopic ellipsometry

We report on the observation of strong coupling between excitons and cavity photons in a ZnO-based microresonator up to room temperature. The ZnO-based resonator was grown by means of pulsed laser deposition (PLD) on c-sapphire substrate and consists of a half-wavelength ZnO-cavity between two Bragg reflectors, each made of 10.5 layer pairs of yttria stabilized zirconia and Al₂O₃. Angle-resolved spectroscopic ellipsometry revealed the resonator to be in the strong coupling regime at room temperature. This was confirmed for temperatures between 10 K and 290 K by means of angle-resolved photoluminescence and reflection experiments. Prior studies on a Fabry–Perot resonator containing a half-wavelength YSZ-cavity (empty resonator) demonstrate the ability of ellipsometry to gain comprehensive information on mode-structure properties of resonators without coupling effects.     

AlN/Si3N4纳米多层膜的外延生长与力学性能

采用射频磁控溅射方法制备单层AlN, Si₃N₄薄膜和不同调制周期的AlN/Si₃N₄纳米多层膜.采用X射线衍射仪、高分辨透射电子显微镜和纳米压痕仪对薄膜进行表征.结果发现,多层膜中Si₃N₄层的晶体结构和多层膜的硬度依赖于Si₃N₄层的厚度.当AlN层厚度为4.0nm、 Si₃N₄层厚度 关键词： 3N₄纳米多层膜')" href="#">AlN/Si₃N₄纳米多层膜 外延生长 应力场 超硬效应     

Si3N4在h-AlN上的晶体化与AlN/Si3N4纳米多层膜的超硬效应

采用反应磁控溅射法制备了一系列具有不同Si₃N₄层厚度的AlN/Si₃N₄纳米多层膜,利用X射线衍射仪、高分辨透射电子显微镜和微力学探针表征了多层膜的微结构和力学性能.研究了Si₃N₄层在AlN/Si₃N₄纳米多层膜中的晶化现象及其对多层膜生长结构与力学性能的影响.结果表明,在六方纤锌矿结构的晶体AlN调制层的模板作用下,通常溅射条件下以非晶态存在的Si₃N₄层在其厚度小于约1nm时被强制晶化为结构与AlN相同的赝形晶体,AlN/Si₃N₄纳米多层膜形成共格外延生长的结构,相应地,多层膜产生硬度升高的超硬效应.Si₃N₄随层厚的进一步增加又转变为非晶态,多层膜的共格生长结构因而受到破坏,其硬度也随之降低.分析认为,AlN/Si₃N₄纳米多层膜超硬效应的产生与多层膜共格外延生长所形成的拉压交变应力场导致的两调制层模量差的增大有关. 关键词： 3N₄纳米多层膜')" href="#">AlN/Si₃N₄纳米多层膜 外延生长 赝晶体 超硬效应     

Effect of SiO2/Si3N4 dielectric distributed Bragg reflectors (DDBRs) for Alq3/NPB thin-film resonant cavity organic light emitting diodes

In this article, we report on the effect of SiO₂/Si₃N₄ dielectric distributed Bragg reflectors (DDBRs) for Alq₃/NPB thin-film resonant cavity organic light emitting diode (RCOLED) in increasing the light output intensity and reducing the linewidth of spontaneous emission spectrum. The optimum DDBR number is found as 3 pairs. The device performance will be bad by further increasing or decreasing the number of DDBR. As compared to the conventional Alq₃/NPB thin-film organic light emitting diode (OLED), the Alq₃/NPB thin-film RCOLED with 3-pair DDBRs has the superior electrical and optical characteristics including a forward voltage of 6 V, a current efficiency of 3.4 cd/A, a luminance of 2715 cd/m² under the injection current density of 1000 A/m², and a full width at half maximum (FWHM) of 12 nm for emission spectrum over the 5-9 V bias range. These results represent that the Alq₃/NPB thin-film OLED with DDBRs shows a potential as the light source for plastic optical fiber (POF) communication system.     

Light Squeezing in a Fabry–Perot Cavity

A quantum mechanical model for the study of quadrature squeezing in radiation coming out of Fabry–Perot cavity containing nonlinear Kerr medium has been proposed. We have incorporated the vacuum fluctuations entering in the cavity through unused ports. The analysis has been applied to a sample of GaAs filled in the Fabry–Perot cavity and irradiated by an off-resonant Co:MgF₂ laser. Limitations on achievable squeezing due to incident pump power, interaction time, nonlinear coupling parameter and facet reflectivities have been discussed and it is seen that low reflectivity of front facet and high reflectivity of rear facet of the cavity produces substantial squeezing.     

Measurement of the electro-optic coefficient of polymer thin films with better spatial resolution

A method for measuring the electro-optic coefficient of polymer films on the basis of an asymmetry Fabry–Perot cavity is introduced. The sample layer is located between two aluminium layers, which are deposited on glass substrates by thermal evaporation. This layer structure is objected to a laser beam, and a variable voltage is applied to the aluminium films resulting in a modulation of the transmitted laser power. The electro-optic coefficient γ₁₃ of the poled polymer film can be calculated by evaluating the Fabry–Perot equation. The spatial resolution is tested with a polymer film that was poled by a needle corona discharge in air through a metal grating with a period of 120 μm. By scanning the sample plate in the direction perpendicular to the grating lines, the spatial resolution is also demonstrated according to the spacing of the poled structure.     

Experimental investigation of the line center of Hg intercombination spectral line 253.7 nm perturbed by Kr

The collision broadening and shift of the Hg intercombination spectral line 253.7 nm (6¹S₀–6³P₁) perturbed by Kr has been investigated using a high-resolution scanning Fabry–Perot interferometer. The values of the pressure broadening and shift coefficients β and δ, respectively, for the studied line have been obtained. The obtained coefficients β and δ are compared with their corresponding published experimental values and also those calculated using Lindholm–Foley impact theory.     

Surface electromagnetic waves at the interface between a homogeneous medium and a system of coupled waveguides

An analysis is made of the experimental investigations of the surface waves existing at the interface between a homogeneous medium and a periodically stratified medium that represents a bounded system of coupled waveguides. It is shown that, in all cases of the observation of surface waves, the bounded system of coupled waveguides has its own spectrum of guided modes and a spectrum of leaky modes that become surface waves of the system. It is also demonstrated that a biosensor can successfully operate when two surface waves serve as leaky modes of a Bragg waveguide in which the periodic system of waveguides is used as a distributed Bragg mirror of this waveguide. A structure supporting surface waves is designed on the basis of ten pairs of Nb₂O₅-SiO₂ layers and implemented experimentally. The surface waves are detected with a K8 glass prism according to the Kretschmann scheme.     

Effect of processing parameters on the deposition rate of Si3N4/Si2N2O by chemical vapor infiltration and the in situ thermal decomposition of Na2SiF6

Silicon nitride (Si₃N₄) and oxynitride (Si₂N₂O) were deposited by chemical vapor infiltration (CVI) through a novel route involving the in-situ thermal decomposition of Na₂SiF₆ in commercial nitrogen precursors containing impurity oxygen. In addition, the quantitative effect of processing time (30, 60, 90, 120 min), temperature (1000, 1100, 1200 and 1300 °C), nitrogen precursor (N₂ or N₂-5%NH₃) and gas flow rate (46.5, 93, 120 and 240 cm³/min) on phase percentage and deposition rate of Si₃N₄ and Si₂N₂O was investigated. Analysis of variance shows that the parameter that most significantly impacts the total amount of deposited phase is the processing temperature, followed by processing time and nitrogen precursor. Regardless of the nitrogen precursor, at 1300 °C, Si₃N₄ and Si₂N₂O depositions follow an S-like and parabolic behavior, respectively. The incubation period shown by Si₃N₄ in N₂-5%NH₃ is associated to a decrease in the O₂ partial pressure during Si₂N₂O formation while the rapid increase at long processing times is attributed to the enhanced effect of hydrogen. PACS 81.15.Gh; 81.05.Je; 81.15.-z; 81.05.Rm; 47.85.L-     

Minimization of thermal effects in a waveguide structure optical switch

Many studies have been performed on III–V semiconductor all-optical switches with a Fabry–Perot or a waveguide structure. Nonlinear effects have been observed in these devices but fast thermal effects occur which often limit their performances, especially their speed. We report a theoretical study of a waveguide device experimentally studied elsewhere, made of a III–V active material film with a grating coupler and epitaxied on a Bragg reflector.