Grating Period Research Articles

Design of a microstructured surface for infrared radiation regulation based on structural combinations

There has been an increased interest on the development of infrared radiation (IR) regulation based on microstructured surfaces with desired radiative properties. Here design of a microstructured surface is proposed in terms of structural combinations to mediate the IR characteristics of targets. The designed microstructured surface is a combined structure, which is a two-dimension periodic composite grating obtained by combining two periodic simple gratings with different parameters and taking the union. Remarkably, the simple grating is also a combined structure obtained by combining and taking the intersection of two different single structures, a dielectric/metal/dielectric (DMD) structure and a metal grating structure. The results show that on the premise of having the structural characteristics of both constituent structures, the designed combined structures can not only inherit the spectral characteristics of both constituent structures but also have some new effects. For the adjusted composite grating, it is found that three absorption peaks with the maximal absorbance up to 89% are achieved in 5–8 μm range. Additionally, the average reflectance is greater than 80% in 3–5 μm and 8–14 μm bands. The adjusted composite grating fulfills the requirement for multiband regulation and the method of structural combinations suggests a feasible means to regulate the IR characteristics of targets.

Optical Fermi level-tuned plasmonic coupling in a grating-assisted graphene nanoribbon system.

A novel graphene-based grating-coupled metamaterial structure is proposed, and the optical response of this structure can be obviously controlled by the Fermi level, which is theoretically regulated by the electric field of an applied voltage. The upper graphene monolayer can be intensely excited with the aid of periodic grating and thus it can be considered a bright mode. Meanwhile, the lower graphene monolayer cannot be directly excited, but it could be indirectly activated by the help of bright mode. The plasmonic polaritons resulting from the light-graphene interaction resonance can lead to a destructive interference effect, leading to a plasmonic induced transparency. This structure has a simple construction and retains the integrity of graphene. In the meantime, it can achieve a good tuning effect by adjusting the voltage regulation of microstructure array and it can obtain an outstanding reflection efficiency. Thus, this graphene-based metamaterial structure with these properties is very suitable for the plasmonic optical reflector. In contacting with the characteristics of material, the group delay of this device can reach to 0.3ps, which can well match the slow light performance. Therefore, the device is expected to make some contribution in optical reflection and slow light devices.

Plasmonic Refractive Index Sensors Based on One- and Two-Dimensional Gold Grating on a Gold Film

In this paper, we propose two kinds of composite structures based on the one- and two-dimensional (1D&2D) gold grating on a gold film for plasmonic refractive index sensing. The resonance modes and sensing characteristics of the composite structures are numerically simulated by the finite-difference time-domain method. The composite structure of the 1D gold semi-cylinder grating and gold film is analyzed first, and the optimized parameters of the grating period are obtained. The sensitivity and figure of merit (FOM) can reach 660RIU/nm and 169RIU−1, respectively. Then, we replace the 1D grating with the 2D gold semi-sphere particles array and find that the 2D grating composite structure can excite strong surface plasmon resonance intensity in a wider period range. The sensitivity and FOM of the improved composite structure can reach 985RIU/nm and 298 RIU−1, respectively. At last, the comparison results of the sensing performance of the two structures are discussed. The proposed structures can be used for bio-chemical refractive index sensing.

Temperature Self-Compensation Biosensor Based on LPG Concatenated With SNCS Structure

A biosensor based on long period grating (LPG) concatenated with single-mode-no-core-single-mode (SNCS) fiber structure is designed and demonstrated both theoretically and experimentally. By analyzing the opposite shift of transmission dips formed by LPG and SNCS, the RI and temperature variations can be demodulated to realize the temperature self-compensation. The RI sensitivity of 90.56 nm/RIU is obtained by experiment at 1.333-1.399 with temperature compensation coefficient of -1.33× 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> /°C. The biosensing performance of the sensor is evaluated by detecting porcine hemoglobin (Hb) solutions with different concentrations and the sensitivity of 0.0165 nm/mg/mL is obtained. The designed sensor with simple structure, high sensitivity, noninvasive and label-free detection capability shows great potential in biosensing applications.

Self-Organized Nanogratings for Large-Area Surface Plasmon Polariton Excitation and Surface-Enhanced Raman Spectroscopy Sensing

Surface plasmon polaritons (SPP) are exploited due to their intriguing properties for the fabrication and miniaturization of photonic circuits, for surface-enhanced spectroscopy and imaging beyond the diffraction limit. However, excitation of these plasmonic modes by direct illumination is forbidden by energy/momentum conservation rules. One strategy to overcome this limitation relies on diffraction gratings to match the wavevector of the incoming photons with that of propagating SPP excitations. The main limit of the approaches so far reported in the literature is that they rely on highly ordered diffraction gratings fabricated by means of demanding nanolithographic processes. In this work, we demonstrate that an innovative, fully self-organized method based on wrinkling-assisted ion-beam sputtering can be exploited to fabricate large-area (cm2 scale) nanorippled soda lime templates, which conformally support ultrathin Au films deposited by physical deposition. The self-organized patterns act as quasi-one-dimensional (1D) gratings characterized by a remarkably high spatial order, which properly matches the transverse photon coherence length. The gratings can thus enable the excitation of hybrid SPP modes confined at the Au/dielectric interfaces, with a resonant wavelength that can be tuned by modifying the grating period, photon incidence angle, or, potentially, the choice of the thin-film conductive material. Surface-enhanced Raman scattering experiments show promising gains in the range of 103, which are competitive, even before a systematic optimization of the sample fabrication parameters, with state-of-the art lithographic systems, demonstrating the potential of such templates for a broad range of optoelectronic applications aiming at plasmon-enhanced photon harvesting for molecular or biosensing.

Chirped-grating spectrometer-on-a-chip.

We demonstrate an on-chip spectrometer readily integrable with CMOS electronics. The structure is comprised of a SiO2/Si3N4/SiO2 waveguide atop a silicon substrate. A transversely chirped grating is fabricated, in a single-step optical lithography process, on a portion of the waveguide to provide angle and wavelength dependent coupling to the guided mode. The spectral and angular information is encoded in the spatial dependence of the grating period. A uniform pitch grating area, separated from the collection area by an unpatterned propagation region, provides the out-coupling to a CMOS detector array. A resolution of 0.3 nm at 633 nm with a spectral coverage tunable across the visible and NIR (to ∼ 1 µm limited by the Si photodetector) by changing the angle of incidence, is demonstrated without the need for any signal processing deconvolution. This on-chip spectrometer concept will cost effectively enable a broad range of applications that are beyond the reach of current integrated spectroscopic technologies.

Terahertz time-domain spectroscopy of two-dimensional plasmons in AlGaN/GaN heterostructures

Two-dimensional plasmons were investigated by terahertz time domain spectroscopy observing experimentally the distinctive minima and inflection points in the transmission power amplitude and phase spectra, respectively. Gratings of different periods (600, 800, and 1000 nm) and filling factors (50 and 80%) were provided to the two-dimensional electron gas in AlGaN/GaN heterostructures in order to measure the plasmon dispersion and the coupling efficiency with THz radiation. Comparative analysis of experimental data revealed that the resonant plasmon features in the amplitude spectrum are related to those in the phase spectrum by a simple integral relation, paving the way for phase spectroscopy of the plasmon phenomena in fields of THz physics and engineering.

High-efficiency broadband fiber-optic mechanical intermodal converter

We demonstrate a highly efficient, broadband fiber-optic intermodal converter. The technique relies on a long period grating mechanically induced in a two-mode fiber. A compact, portable apparatus was designed and fabricated, where period-variable metallic corrugation is implemented to form periodic micro-bends along the fiber. The coupling strength between the interacting fiber modes and the grating period can be tuned continuously and individually using two control knobs in the apparatus. Experimental results show that the complete coupling between the LP01 and LP11 modes is achieved, which is confirmed by an observed over-coupling while increasing the grating strength. For the short fiber length of <1.9 cm (33 grating periods), large band-rejection of −32.5 dB was obtained at resonance. The band rejection efficiency over 98.6% have been achieved in the entire communication C-band. As the grating strength increased, two over-couplings were observed at resonance, which indicates the high efficiency of the device. Experimental results are confirmed by our numerical simulations.

The Leap from Organic Light-Emitting Diodes to Organic Semiconductor Laser Diodes

In recent years, organic light-emitting device technology has expanded from organic light-emitting diodes (OLEDs) to organic semiconductor laser diodes (OSLDs) with the progress of sophisticated mo...

Розвиток дослідницьких здібностей учнів при вивченні оптики в умовах дистанційної освіти

An important aspect of the application of information and communication technologies (ICT) in the study of physics is the organization of a virtual experiment using appropriate software modeling tools (SMT). Such programs allow both monitor the progress of the experiment, and easily change its parameters. This is especially true when working with real equipment in the school physics classroom becomes impossible due to quarantine measures and the corresponding transition of domestic education to distance learning. The article considers the peculiarities of the use of the virtual laboratory Wolfram Demonstration Project in the study of optics by high school students in distance education. Examples of research of the phenomena of wave, geometric and quantum optics are given. The program allows students to more clearly present the studied phenomena and objects, in a matter of minutes to trace the processes that take place over a big duration in real life, or their demonstration requires complex and expensive equipment. The relevance of the development of PMZ in optics is also caused by the fact that light waves and objects with which these waves interact due to their small size (wavelength, elementary particles, the periodicity of the diffraction grating) can not be directly observed. We learn about their properties indirectly: interference and diffraction pattern, inelastic light scattering on microparticles, Photoeffect, etc.) Conducting appropriate virtual demonstrations and experiments, the teacher by increasing the component of research activities and visibility increases the activity and interest of students, improves understanding of educational material, which is especially important in distance education. The use of the virtual laboratory Wolfram Demonstration Project can significantly help the teacher in studying the optics of students in the mode of distance education, in particular, conducting laboratory work in physics. Each student, if connected to the Internet, has the opportunity to conduct their own research, following the instructions of the teacher. The described PMZ makes it possible not only to record the results of the experiment (interference and diffraction patterns, instrument readings), but also to visually observe the dynamics of motion of objects inaccessible to real observations (wave front motion, photoelectron flux, etc.). The proposed virtual demonstrations and experiments promote the development of research abilities of students, increase their activity and interest in acquiring knowledge, improve the understanding of educational material.

Optimization methods for achieving high diffraction efficiency with perfect electric conducting gratings.

This work presents the implementation, numerical examples, and experimental convergence study of first- and second-order optimization methods applied to one-dimensional periodic gratings. Through boundary integral equations and shape derivatives, the profile of a grating is optimized such that it maximizes the diffraction efficiency for given diffraction modes for transverse electric polarization. We provide a thorough comparison of three different optimization methods: a first-order method (gradient descent); a second-order approach based on a Newton iteration, where the usual Newton step is replaced by taking the absolute value of the eigenvalues given by the spectral decomposition of the Hessian matrix to deal with non-convexity; and the Broyden-Fletcher-Goldfarb-Shanno (BFGS) algorithm, a quasi-Newton method. Numerical examples are provided to validate our claims. Moreover, two grating profiles are designed for high efficiency in the Littrow configuration and then compared to a high efficiency commercial grating. Conclusions and recommendations, derived from the numerical experiments, are provided as well as future research avenues.

Wearable Wrist Movement Monitoring Using Dual Surface-Treated Plastic Optical Fibers

Regarding high-sensitivity human wrist joint motion monitoring in exercise rehabilitation; we develop a pair of novel wearable and sensitivity-enhanced plastic optical fiber (POF) strain sensors consisting of an etched grating fiber and a side-polished fiber stitched into a polyamide wrist brace. The two flexible and surface-treated fibers are; respectively; featured with an etched periodic gratings with a pitch of 6 mm and a depth of 0.5 mm and a D-shaped side-polished zone of ~300 µm depth and ~30 mm length; which, correspondingly, show the sensitivities of around 0.0176/° and 0.0167/° in a normalized bending angle by far larger than a conventional commercial POF, because it achieves a more sensitive strain-induced evanescent field interaction with the side-machined fibers. Moreover, in terms of the sensor response to bending deformation in the range of −40°~+40°, the former exhibits a better sensitivity in lower angle change, while the latter is superior as the bending angle increases; thereby arranging the two modified POFs separately at the side and back of the human wrist, in order to decouple the wrist joint behaviors induced by typical flexion-extension or abduction-adduction movements. Then, the circular and pentagonal wrist motion trajectory patterns are investigated, to demonstrate the maximum average single-axis motion error of 2.94° via the transformation of spatial angle to plane coordinate for the fabricated couple of POF sensors, which is lower than a recognized standard of 5°, thus suggesting the great potential in wearable exercise rehabilitation of human joints in the field of medical treatment and healing.

Estimation of carrier mobilities and recombination lifetime in halide perovskites films using the moving grating technique

Pulsed excitation methods followed by time-resolved measurements have been questioned as a valid procedure to deduce transport properties of halide perovskites (HaPs). Measurements of both the majority and minority carrier’s phototransport properties, under illumination conditions as close as possible to one sun, are needed to obtain reliable information on recombination mechanisms. In this work, we show that the moving photocarrier grating technique (MGT) fulfills the above-mentioned conditions. In this method, both carriers mobilities and the common recombination lifetime are deduced from the DC short circuit current induced by the movement of an interference pattern along the sample surface. We show that the method, originally developed to measure the transport parameters of amorphous semiconductors, can be fully applied to HaPs films. We briefly describe the technique, we perform measurements as a function of the grating period and the light intensity, and we discuss the best approach to extract the transport parameters from MGT measurements. Finally, we find the exponents that describe the intensity dependence of the transport parameters of majority and minority carriers in a HaP sample.

Novel High-Resolution Lateral Dual-Axis Quad-Beam Optical MEMS Accelerometer Using Waveguide Bragg Gratings

A novel lateral dual-axis a-Si/SiO2 waveguide Bragg grating based quad-beam accelerometer with high-resolution and large linear range has been presented in this paper. The sensor consists of silicon bulk micromachined proof mass suspended by silica beams. Three ridge gratings are positioned on the suspending beam and proof mass to maximize sensitivity and reduce noise. Impact of external acceleration in the sensing direction on the Bragg wavelength of gratings and MEMS structure has been modelled including the effects of strain, stress and temperature variation. Acceleration induces stress in the beam thus modifying the grating period and introducing chirp. The differential wavelength shift with respect to reference grating on the proof mass is the measure of acceleration. To compensate for the effect of the weight of the proof mass and increase the sensitivity of the sensor, electrostatic force of repulsion is applied to the proof mass. For the chosen parameters, the designed sensor has a linear response over a large range and a sensitivity of 30 pm/g. The temperature of surroundings, which acts as noise in sensor performance is compensated by taking differential wavelength shift with respect to reference grating. By design and choice of material, low cross-axis sensitivity is achieved. The proposed design enables a high-resolution well below 1 μ g/ Hz and is suitable for inertial navigation and seismometry applications.

Tunable Plasmonic Talbot Effect Based on Graphene Monolayer

In this article, the plasmonic Talbot effect supported by a graphene monolayer is investigated theoretically when surface plasmon polaritons (SPPs) are excited on the graphene. The Talbot effect distance is studied by varying the chemical potential, wavelength and the period of grating. The Talbot distance increases with the period in a parabolic way, and exhibits the opposite trends with respect to the chemical potential and wavelength. Moreover, the full width at half maximum (FWHM) of the Talbot image is recorded as a function of chemical potential and the wavelength. This study provides a new approach for sub-wavelength scale imaging and extends the applications of Talbot effect as well as graphene-based plasmonic devices.

Band structure formation in magnonic Bragg gratings superlattice

The features of spin-wave propagation in a magnonic superlattice are investigated theoretically and experimentally. This superlattice consists of periodic metallic gratings, having two non-equal periods located at the surface of the ferromagnetic film. It is shown that two band gaps are formed in the spin-waves spectrum within the first Bragg zone. A theoretical model using a coupled waves model and equating magnetic permeabilities at the surface boundaries demonstrating the mechanism of band structure formation was developed. Experimental data obtained with microwave and Brillouin light scattering techniques are in good agreement with theoretical results.

Highly-chirped Bragg gratings for integrated silica spectrometers.

A blazed chirped Bragg grating in a planar silica waveguide device was used to create an integrated diffractive element for a spectrometer. The grating diffracts light from a waveguide and creates a wavelength dependent focus in a manner similar to a bulk diffraction grating spectrometer. An external imaging system is used to analyse the light, later device iterations plan to integrate detectors to make a fully integrated spectrometer. Devices were fabricated with grating period chirp rates in excess of 100 nm mm-1, achieving a focal length of 5.5 mm. Correction of coma aberrations resulted in a device with a footprint of 20 mm×10 mm, a peak FWHM resolution of 1.8 nm, a typical FWHM resolution of 2.6 nm and operating with a 160 nm bandwidth centered at 1550 nm.

Non-spherical aluminum nanoparticles fabricated using picosecond laser ablation

We report the picosecond laser ablation of aluminum targets immersed in a polar organic liquid (chloroform, CHCl3) with ∼2 ps laser pulses at an input energy of ∼350 µJ. The synthesized aluminum nanoparticles exhibited a surface plasmon resonance peak at ∼340 nm. Scanning electron microscopy images of Al nanoparticles demonstrated the spherical morphology with an average size of (27 ± 3.6) nm. The formation of smaller spherical Al nanoparticles and the diminished growth could be from the formation of electric double layers on the Al nanoparticles. In addition to spherical aluminum nanoparticles, triangular/pentagonal/hexagonal nanoparticles were also observed in the colloidal solution. Field emission scanning electron microscopy images of ablated Al targets demonstrated laser induced periodic surface structures (LIPSSs), which were the high spatial frequency LIPSSs (HSF-LIPSSs) since their grating period was ∼280 nm. Additionally, coarse structures with a period of ∼700 nm were observed.

Dynamics of Diffraction Efficiency of Superimposed Volume Reflection Holograms at Their Simultaneous Recording in Photopolymer Material

The new experimental data on the dynamics of diffraction efficiency (DE) of superimposed volume reflection holograms with a grating period of $${\sim}$$ 250 nm is obtained at their simultaneous recording in the photopolymer material BAYFOL HX TP. The character and parameters of their interaction are established when exposure of one hologram is delayed relative to the other one. It is revealed that the DE dynamics is practically not affected by variations in diffusion time of monomer in the range $$0.12<t_{D}<0.17$$ s, but the transient behavior of the photopolymerization parameter $$\tau_{p}$$ , which increased in our experiments from 5 to 15 s, becomes considerably visible. The well-known equations of the photoinduced variation in the photopolymer refraction index are improved with account for the character of variation in the parameter $$\tau_{p}$$ . The calculated dependences of DE dynamics obtained with refined formulas are in good agreement with experimental data (mean square deviation is $${\sim}2\%$$ ).

Radiative cooling with multilayered periodic grating under sunlight

Radiative cooling is an energy-saving cooling technology and is achieved when the grating structure emits infrared radiant heat energy into outer space through an atmospheric window (8∼13μm). The radiation cooling effect is low for the simple grating structure due to its low absorptivity, thus was a novel multilayered composite grating structure proposed in the paper, an aluminum substrate composite whose top layer is polycarbonate coating and intermediate layers are composed of SrTiO2, SiO and Al2O3. The influencing factors of the absorptivity of the simple grating structure were analyzed by rigorous coupled wave analysis (RCWA), which consider grating period (1∼5μm), grating height (1∼20μm), duty cycle (0.75∼1) and angle of incidence (0∼75°), it was found that grating height is the crucial factor and increasing grating height can improve the absorptivity of the grating structure Hence, the proposed composite grating structure was studied with 20μm grating height and 0.5 to 2μm thickness of the polycarbonate (PC) coating, 1μm thickness polycarbonate structure was found to have good absorptivity, most is over 0.9, and the net cooling power of this grating structure could reach 71.39 W/m2 at ambient temperature.