Polarization- and direction-independent defect modes in a wide incident-angle range within Bragg gaps by photonic heterostructures containing negative-index materials

We propose a type of photonic heterostructure by combining dielectric one-dimensional (1D) defective photonic crystals (PCs) and magnetic 1D defective PCs. Both of the two PCs consist of alternating positive-index-material (PIM) layers with a negative-index-material (NIM) defect layer. It is demonstrated by transfer matrix method that there is a polarization- and direction-independent defect mode in a wide incident-angle range within Bragg gaps in the heterostructure. The field distributions prove that the dielectric 1D defective PC benefits to achieve the approximately omnidirectional defect mode for TE waves while the magnetic 1D defective PC benefits for TM waves. Such a structure is useful for designing polarization-independent and omnidirectional or large incident angle narrow-passband filters in optical devices.     

Electrical characteristics of the waveguide grating system

Electromagnetic wave propagation is conside-red through a waveguide system consisting of arbitrary number of short-period gratings (i.e. whose period is much shorter than the wave-length). We assume that gratings are formed by ideal conductors having arbitrary cross-section. In order to "stitch" together the fields on gratings, equivalent boundary conditions are used.We have analyzed and studied experimentally the electrical characteristics of an adjustable frequency filter. The filter consists of three short-period gratings formed by conductors with circular cross-section.Experimental results are in good agreement with theory.     

Analytical model of a corrugated optical waveguide

An analytical model of the diffraction energy exchange between the radiative and the waveguide modes in a planar optical waveguide corrugated by a waveguide grating with an arbitrary form of teeth is developed on the basis of the coupled-wave method. It is shown that the mechanism of the energy exchange between the modes is determined by the partial interaction of all components of the spatial frequency spectrum of the waveguide modes with the corresponding components of the spatial frequency spectrum of the grating. It is established that gratings with an asymmetric tooth profile providing a shift of the peak of the spatial frequency spectrum toward matching are characterized by a higher diffraction efficiency α; however, at small thicknesses δ of the waveguide grating, the efficiency is almost independent of the tooth profile. It is shown that gratings with a symmetric profile give on average a decreasing dependence α(δ), while gratings with an optimized asymmetric profile yield a monotonically increasing saturating dependence α(δ).     

Broad omnidirectional high-precision filters design using genetic algorithm

An application of the genetic algorithm in designing omnidirectional optical filters is reported in this paper. Concerning different periodic numbers and thickness ratios in the heterostructure, we gave some optimization examples and finally achieved a photonic heterostructure with very broad omnidirectional filter bandwidth as well as a very narrow transmission window. And it is found that when the normal incident beam is tilted at a negligibly small angle, the perfect transmittance peak will vanish. Hence, this heterostructure can be regarded as omnidirectional high-precision filters with potential application in optical filters, optical switches, and many other optical telecommunication areas.     

Tunable zero-phase-shift omnidirectional filter consisting of single-negative materials

We theoretically design a heterostructure with which we can achieve a tunable zero-phase-shift omnidirectional filter. The results show that by simply adjusting the thickness of the defect layer of air, we can achieve adjustability of the tunneling mode. We further prove the omnidirectional tunneling modes in the heterostructure consisting of layered single-negative materials and one layer of defect. PACS 42.25.Dd; 42.79.Ci     

利用遗传算法设计可见光波段全能反射器

介绍了遗传算法在设计宽频带全能反射器中的应用.设计的关键是通过遗传算法寻找到不同一维准周期光子晶体间的最佳组合方式以及光学厚度以便形成一个光子晶体异质结.利用传输矩阵法分析了一维准周期系统中的电磁传输特性.计算结果表明,准周期光子晶体的全方向反射带宽受晶胞单元以及周期数的影响.根据这些规律,用遗传算法成功地优化了光子晶体异质结的结构并得到两种适用于可见光波段的高性能全能反射器.例如结构为(HLLHL)13(HL)13( LHL)15 ［注: nL=1.46,nH=2.6,dL=0.218λ0/nL且dH=0.201λ0/nH］的反射器在可见光波段内的全方向反射带宽达到了88.42% (446 nm~779 nm).     

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.     

Multiband processing of multimode light: combining 3D photonic lanterns with waveguide Bragg gratings

The first demonstration of narrowband spectral filtering of multimode light on a 3D integrated photonic chip using photonic lanterns and waveguide Bragg gratings is reported. The photonic lanterns with multi‐notch waveguide Bragg gratings were fabricated using the femtosecond direct‐write technique in boro‐aluminosilicate glass (Corning, Eagle 2000). Transmission dips of up to 5 dB were measured in both photonic lanterns and reference single‐mode waveguides with 10.4‐mm‐long gratings. The result demonstrates efficient and symmetrical performance of each of the gratings in the photonic lantern. Such devices will be beneficial to space‐division multiplexed communication systems as well as for units for astronomical instrumentation for suppression of the atmospheric telluric emission from OH lines.     

Analysis and design of grating couplers

Based on an accurate perturbation analysis of the guiding properties of dielectric gratings, simple design criteria are developed for grating couplers which transfer the energy of a beam into or out of an optical waveguide. Gratings having arbitrary groove shapes are considered and explicit formulae are given for the leakage parameters of gratings with symmetric profiles. The results cover TE_v and TM_v modes and they apply to both shallow and deep grating grooves. The variation of the leakage parameter α in rectangular gratings is examined in detail; these rectangular gratings are then used as basic configurations for predicting the characteristics of other grating profiles. Particular attention is given to trapezoidal and triangular profiles and gratings with asymmetric profiles are also discussed.     

Fabrication of integrated waveguide grating in azo polymers

In this Letter, we have introduced a technique, new to our knowledge, to fabricate gratings on a waveguide of azo-functionalized polymeric films using a slit mask and a fast, direct-writing method. To prevent the destruction of the waveguide by the grating formation on the waveguide, we placed a slit mask on the waveguide. By properly adjusting the resonance, this grating can be used as an integrated wavelength filter. We have produced an attenuation of 13.4?dB at 1562?nm with a FWHM of 3.45?nm. The grating has been fabricated as narrow as the width of the waveguide to couple filtered light into the waveguide by using a slit mask. Any light shifted from the resonance will pass through the waveguide undisturbed.     

Diffractionless flow of light in all-optical microchips

We introduce the concept of a hybrid 2D-3D photonic band gap (PBG) heterostructure which enables both complete control of spontaneous emission of light from atoms and planar light-wave propagation in engineered wavelength-scale microcircuits. Using three-dimensional (3D) light localization, this heterostructure enables flow of light without diffraction through micron-scale air waveguide networks. Achieved by intercalating two-dimensional photonic crystal layers containing engineered defects into a 3D PBG material, this provides a general and versatile solution to the problem of "leaky modes" and diffractive losses in integrated optics.     

Development of a Fourier-transform waveguide spectrometer for space applications

We describe the development of a waveguide Fourier-transform spectrometer for space-borne high-resolution sensing. A prototype device is designed to monitor the water vapor absorption band near 1,364?nm with a resolution of 0.05?nm. It has no moving parts and is based on a unique concept of arrayed interferometers implemented in silicon-on-insulator planar waveguide chip. The optical input is formed by many independent waveguides, providing a significantly increased light gathering capability (étendue) compared to single-waveguide input configurations. Enhancements of the spectrometer capabilities are achieved by stacking planar waveguide layers and by using surface gratings to couple light into the waveguides.     

Realization of quantum efficiency enhanced PIN photodetector by assembling resonant waveguide grating

We demonstrate an InP/InGaAs PIN photodetector with enhanced quantum efficiency by assembling silicon resonant waveguide gratings for the application of polarization sensitive systems. The measured results show that quantum efficiency of the photodetector with silicon resonant waveguide gratings can be increased by 31.6% compared with that without silicon resonant waveguide gratings at the wavelength range of 1500 to 1600 nm for TE-polarization.     

Enlargement of omnidirectional electronic gap in the graphene superlattice heterostructures with Gaussian profile potential voltages

A valid method is used to extend the omnidirectional electronic gap (OEG) of Gaussian gapped graphene superlattices (GSLs) heterostructure. The heterostructure consists of two superlattices with different width ratios of potentials. Each superlattice comprises a periodic repetition of a unit cell consisting of 21 layers with the potential voltages varying according to a Gaussian function and another layer with a fixed potential voltage. The potential width ratios of constituent Gaussian gapped GSL are established utilizing the lower and upper energy edges of omnidirectional electronic gap depending on the width ratio of potentials. Moreover, it is shown that the width of OEG of the heterostructure is sensitive to lattice constant, which can be applicable to the development of graphene-based electronics.     

Broad omnidirectional reflectors design using genetic algorithm

A application of genetic algorithm in designing omnidirectional reflectors is reported in this paper. Based on different quasi-periodic dielectric multilayer stacks, we give some optimization examples concerning both quart-wave and non quart-wave systems, and finally we achieve a photonic heterostructure with very broad omnidirectional reflection bandwidth.     

Subwavelength lithography using metallic grating waveguide heterostructure

We present subwavelength periodic gratings achieved by employing a metallic grating waveguide heterostructure (MGWHS). The mask can be designed to make one of its diffraction order (±mth) waves resonate with the surface plasmon wave supported by the MGWHS. With a finite-difference time-domain method, we numerically demonstrate that one-dimensional periodic structure of about 60 nm feature, which is far beyond the diffraction limit, can be patterned with the interference of the 3rd diffraction order waves of the mask at a wavelength of 546 nm. The technique can also be extended to two-dimensional patterns using circularly polarized incidence and for the incidence with an angle θ.     

Nonpolarizing and tunable perpendicular dual-grating guided-mode resonance filter

A perpendicular dual-grating (PDG) guided-mode resonance filter was constructed by placing two identical waveguide gratings close to and their grooves perpendicular to each other. Multilayer waveguide theory was used to estimate the resonant wavelength for the TE and TM polarization incidences, and the rigorous coupled wave analysis (RCWA) was used to investigate the resonant wavelength, the lineshape and linewidth of the resonant peaks for arbitrary polarization incidences. The filter presents identical spectral characteristics for normally incident wave with arbitrary polarization. The separation of the resonant reflection peaks corresponding to the TE₀ and TM₀ split modes were realized by properly selecting the geometrical and material parameters of the grating layers and the waveguide layers. Measurement of the nano air gap between 0 and 0.4 p by determining one of the two resonant reflection peaks of the TE₀/TM₀ split modes was achieved without being interfered by the TM₀/TE₀ split modes.     

Improved implanted,planar buried heterostructure lasers through enhanced optical confinement

We fabricated and tested implanted, planar-buried heterostructure, graded-index, separate confinement heterostructure (IPBH-GRINSCH) lasers in various waveguide geometries. These devices were also numerically simulated with a two-dimensional waveguide model. We report improved laser performance that results from a reduced overlap of the optical field with the absorbing regions produced by residual implant damage.     

Quantum well intermixed waveguide grating

A waveguide grating have been designed suitable for Coarse Wavelength Division Multiplexing applications in which the refractive index is perturbed by the spatial tailoring of the band gap with fluorine ion implanted quantum well intermixing of the In_0.95Ga_0.05As_0.10P_0.90/InP multi quantum well structure. The gratings have been modeled using coupled mode theory and diffusion equations and Schr?dinger wave equations are used to model quantum well energy while interdiffusion. A four channel waveguide grating from 1,550 to 1,610?nm at a span of 20?nm have been simulated with a channel bandwidth of 13?nm and a cross talk of ?5 to ?10 dB.     

Grating polarizers in waveguide miter bends

Rectangular grooved gratings have been fabricated on mirrors of waveguide miter bends. When the HE₁₁ mode was propagated in corrugated waveguide with diameter equal to approximately 12 wavelengths, these gratings performed in the same manner as predicted using plane wave theory. Two gratings with different groove depths in successive miter bends are sufficient to generate a rather wide range of polarizations. These gratings are particularly convenient in waveguide, which offers ease of alignment, compact transverse dimensions, and the possibility of vacuum operation.