Surface Gratings Research Articles

Four‐Dimensional Design Space of High‐Q Second‐Order Distributed Feedback Perovskite Lasers

AbstractSecond‐order distributed feedback (DFB) resonators are widely used for thin‐film lasers as they combine low lasing thresholds with ease of manufacturing. Here, the grating design parameters are varied to map the lasing characteristics of lead halide perovskite films deposited on a single substrate that contains hundreds of high‐quality silicon nitride surface gratings. The lowest lasing threshold (≈130 µJ cm−2) is identified through the aid of near‐field and far‐field imaging spectroscopy in a four‐dimensional design space composed of grating period, duty cycle, active layer thickness, and cavity length. Moreover, it is shown that antisymmetric modes support high‐quality lasing (Q up to ≈10800) in the second‐order DFBs. The multi‐dimensional experimental analysis is accompanied by a thorough theoretical study with a semi‐empirical model based on coupled wave equations, which is used to investigate the lasing characteristics beyond the manufacturing range. The results can be applied to a broad range of thin‐film DFB resonators, enabling the design of more complex laser stack configurations including light‐emitting devices for current‐injection lasing.

Multilayer metal-coated fiber Bragg grating for high-temperature sensing

In this study, a copper coating was deposited on the surface of a fiber Bragg grating (FBG) via electroplating. We compared the temperature responses of the uncoated and copper-coated FBGs from 20 °C to 1000 °C. Under high-temperature conditions, copper diffused into the FBG to form copper crystals, and the copper coating gradually underwent high-temperature oxidation. This reduced the sensitivity and spectral consistency of the copper-coated FBG. A multilayer metal-coated FBG was prepared with an inner layer of nickel, outer layer of gold, and copper layer in the middle. The multilayer FBG exhibited a temperature sensitivity of 23.1–23.53 pm/°C. Furthermore, it showed the coating-enhancement effect and good linearity after multiple thermal cycles. The multilayer metal-coated FBG not only shows high-temperature sensitization but also solves the problem of bare FBGs being extremely fragile after experiencing high temperatures. This study provides a feasible solution for the application of FBGs in extremely high-temperature environments.

Single-mode InGaAsP/InP BH lasers based on high-order slotted surface gratings.

A single-mode InGaAsP/InP buried heterostructure (BH) laser based on high-order slotted surface gratings has been fabricated. The introduction of surface slotted grating can simplify the fabrication process of single-mode BH lasers notably. The laser shows a good single-mode emission performance, with larger than 30 dB side-mode suppression ratio (SMSR) when the current is between 200 and 400 mA. Calculations show that the gain coupling mechanism plays a key role for the slot grating to select the emission wavelength. The linewidth of the laser is measured. The fitted Gaussian and Lorentzian linewidths are 1500 and 550 kHz, respectively.

Detection of Envelope Glycoprotein Domain III (ED III) Based on Surface-Enhanced Raman Scattering for Dengue Diagnosis

Surface-enhanced Raman Scattering (SERS) based ED III protein detection has been conducted as a dengue virus diagnosis. ED III is one of the ectodomains of the envelope located along the surface of the dengue virus and acts as a receptor for the virus with its host cells. The SERS substrate used in this study is On-Spec-lite SERS by NECTEC and fabricated as a grating surface coated with gold. The imaging results from SEM show that the average radius of gold nanoparticles on OnSpec-lite SERS is 60 nm. On the grating-Au surface, the grating period is 588 nm with 50 nm thickness of gold thin film. OnSpec-lite SERS has a more significant increase in Raman intensity than the grating-Au surface when detecting ED III using Raman spectroscopy. The amino acids in the ED III Raman bands are Glycine, Alanine, Histidine, and Proline. The highest intensity Raman band that appears is 850 cm-1. Based on the research done in dengue virus detection, ED III has a typical Raman peak of 850 cm-1 which is the Raman band of Glycine and Alanine with CCN symmetry stretching vibration mode (𝑣(CCN)). This distinctive characteristic of ED III can be used as a diagnostic to detect dengue virus.

Вплив тонких плівок Se на ефективність збудження поверхневих плазмон-поляритонів в срібних та алюмінієвих голографічних решітках

In this paper, we study the effect of thin selenium layers up to 3 nm thick on the efficiency of excitation of surface plasmon polaritons (SPPs). The Se layers were deposited by thermal evaporation in vacuum on the surface of silver and aluminum gratings. Gratings with a groove profile close to sinusoidal and a period equal to а = 694 nm were formed on chalcogenide photoresist films using interference lithography. Then they were coated with layers of the above metals with a thickness of 80–85 nm using thermal evaporation. Registration of SPP excitation on the gratings was carried out by measuring the angular dependences of the intensity of specularly reflected or diffracted p-polarized He-Ne laser radiation on a stand mounted on the basis of a G5M goniometer and a Fedorov table. An atomic force microscope was used to determine the shape of the groove profile and the depth of the grating relief. It has been found that for silver gratings with a relief modulation depth h/a less than the optimal value (which ensures maximum plasmon absorption, i.e., the maximum efficiency of SPP excitation), selenium deposition causes significant degradation of the plasmon resonance: a decrease in the depth of the minimum of the total reflection Rpt (i.e., a decrease in the efficiency of plasmon absorption), a shift of the Rpt minimum towards larger angles, and its widering. For silver gratings with h/a greater than the optimal value, a similar shift and widering of the plasmon resonance is also observed. However, at the same time, a significant deepening of the Rpt minimum is recorded, that is, an increase in the efficiency of SPP excitation. Such changes in the plasmon characteristics also appear on aluminum gratings, however, in this case the effect of the selenium layers is weaker by an order of magnitude. The obtained results allow us to propose a method of correcting the plasmonic characteristics of silver gratings in which the value of h/a is higher than optimal.

Low-Threshold 795 nm Oxide-Confined Distributed Feedback Lasers With Surface Gratings

Low-Threshold 795 nm Oxide-Confined Distributed Feedback Lasers With Surface Gratings

High performance sensor based on phase difference induced quasi-BIC and Fermi energy

We propose a dielectric corrugated structure surrounded by two monolayer graphene and find that the structure supports bound states in the continuum (BIC). By introducing a phase difference between the upper and lower surface of dielectric grating, the symmetry of the structure is broken, and the BIC turns into quasi-BIC. In addition, we find that the Fermi energy of graphene strongly affect the spectral line. By controlling phase difference and Fermi energy of graphene, the ultrahigh Q-factor can be achieved. Finally, introducing a sensing medium at the incident side, the high performance sensor is realized.

Synthesis, Properties, Applications, and Future Prospective of Cellulose Nanocrystals.

The exploration of nanocellulose has been aided by rapid nanotechnology and material science breakthroughs, resulting in their emergence as desired biomaterials. Nanocellulose has been thoroughly studied in various disciplines, including renewable energy, electronics, environment, food production, biomedicine, healthcare, and so on. Cellulose nanocrystal (CNC) is a part of the organic crystallization of macromolecular compounds found in bacteria's capsular polysaccharides and plant fibers. Owing to numerous reactive chemical groups on its surface, physical adsorption, surface grating, and chemical vapor deposition can all be used to increase its performance, which is the key reason for its wide range of applications. Cellulose nanocrystals (CNCs) have much potential as suitable matrices and advanced materials, and they have been utilized so far, both in terms of modifying and inventing uses for them. This work reviews CNC's synthesis, properties and various industrial applications. This review has also discussed the widespread applications of CNC as sensor, acoustic insulator, and fire retardant material.

Nanometer flat blazed x-ray gratings using ion beam figure correction.

With the development of nanometer accuracy stitching interferometry, ion beam figuring (IBF) of x-ray mirrors can now be achieved with unprecedented performance. However, the process of producing x-ray diffraction gratings on these surfaces may degrade the figure quality due to process errors introduced during the ruling of the grating grooves. To address this challenge, we have investigated the post-production correction of gratings using IBF, where stitching interferometry is used to provide in-process feedback. A concern with ion beam correction in this case is that ions will induce enough surface mobility of atoms to cause smoothing of the grating structure and degradation of diffraction efficiency. In this study we found however that it is possible to achieve a nanometer-level planarity of the global grating surface with IBF, while preserving the grating structure. The preservation was so good, that we could not detect a change in the diffraction efficiency after ion beam correction. This is of major importance in achieving ultra-high spectral resolution, and the preservation of brightness for coherent x-ray beams.

Nonequilibrium Plasma Cleaning of Organic Contaminants on the Surface of Diffraction Gratings

Nonequilibrium Plasma Cleaning of Organic Contaminants on the Surface of Diffraction Gratings

Embedded silicon gratings for high-efficiency light-chip coupling to thin film silicon nitride waveguides.

Thin film silicon nitride (<150 nm) waveguide has emerged as a dominant ultra-low-loss platform for many loss-critical applications. While thin-film silicon nitride propagation loss is a crucial characteristic, coupling light between an optical fiber and the waveguide is still challenging. While the larger mode size of the decoupled thin waveguide offers better coupling than a highly-confined waveguide, the coupling efficiency is still sub-optimal. The poor diffraction efficiency of such thin films limits the scope of implementing standalone surface gratings. We demonstrate an efficient way to couple into thin film silicon nitride waveguides using amorphous silicon strip gratings. The high contrast gratings provide an efficient means to boost the directionality from thin films leading to an enhanced coupling performance. In addition, we incorporate a bottom reflector to further improve the coupling. We present an optimal design for uniform strip gratings with a maximum coupling efficiency of -1.7 dB/coupler. We achieved a maximum coupling efficiency of -0.28 dB/coupler by engineering the scattering strength along the grating through apodization. We have experimentally shown the highest coupling efficiency reported yet of -2.22 dB/coupler and -1.84 dB/coupler for uniform and apodized grating couplers in the C-L band. We present a detailed design strategy, simulation, fabrication and characterization data on the effect of various parameters on the coupling efficiency.

Enhancement of longitudinal mode characteristic of quantum cascade laser by high-order tilted asymmetric surface grating

The high-order tilted asymmetric surface grating (TASG) is firstly investigated and applied to quantum cascade lasers (QCLs) here. Due to the tilted grating of 16°in the middle of ridge, the longitudinal mode loss difference of TASG is about 4% higher than that of the uniform grating (UNG), which results in better single mode selectivity in reflectance spectrum. Further experimental results indicate that the TASG distributed feedback (DFB) QCL maintains more stable single longitudinal mode performance with increasing the current and temperature because that TASG have a larger longitudinal mode loss difference. While the UNG QCL with the equivalent coupling coefficient exhibits mode jumping. Hence, the drift coefficient of 0.311 nm/K of TASG QCL is 60% lower than that of the UNG device and the maximum side-mode suppression ratio (SMSR) achieves 30 dB. The characteristic temperature of TASG QCL device is 36K, which is higher than 32K of UNG device. This study showcases the feasibility and superiority of the TASG in mid-infrared active devices.

Advanced low blaze angle x-ray gratings via nanoimprint replication and plasma etch.

We developed a new method of making ultra-low blaze angle diffraction gratings for x-ray applications. The method is based on reduction of the blaze angle of a master grating by nanoimprint replication followed by a plasma etch. A master blazed grating with a relatively large blaze angle is fabricated by anisotropic wet etching of a Si single crystal substrate. The surface of the master grating is replicated by a polymer material on top of a quartz substrate by nanoimprinting. Then a second nanoimprinting is performed using the 1st replica as a mold to replicate the saw-tooth surface into a resist layer on top of a Si grating substrate. A reactive ion etch is used to transfer the grating grooves into the Si substrate. The plasma etch provides reduction of the groove depth by a factor defined by the ratio of the etch rates for the resist and Si. We demonstrate reduction of the blaze angle of a master grating by a factor of 5 during fabrication of a 200 lines/mm blazed grating with a blaze angle of 0.2°. We investigated the quality and performance of the fabricated low blaze angle gratings and evaluate process accuracy and reproducibility. The new blaze angle reduction method preserves the planarity of the optical surface of the grating substrate and at the same time provides improvement in the grating groove quality during the reduction process.

Polarization dynamics in spin‐VCSELs with integrated surface grating for high birefringence splitting

AbstractPolarization dynamics in spin‐polarized vertical‐cavity surface‐emitting lasers (spin‐VCSELs) with high birefringence have recently been demonstrated to offer very high potential for optical data‐transmission systems that outperform their counterparts based on conventional direct current modulation by far. For polarization dynamics in spin‐VCSELs, the birefringence determines the resonance frequency and thus the modulation bandwidth. In previous work, birefringence was controlled using mechanical strain, which lacks the ability to be integrated in standard VCSEL manufacturing processes. In this work the polarization dynamics of a VCSEL with an integrated birefringence control mechanism is demonstrated based on custom designed integrated surface gratings. It is found that, despite the surface grating which is commonly known to stabilize the polarization, the presented spin‐VCSELs are able to generate polarization oscillations with frequencies corresponding to the birefringence induced by the surface grating and show polarization dynamics up to 68 GHz.

High-efficiency upward radiation in a slow-light grating beam scanner.

Slow-light grating (SLG) is used as a solid-state optical beam scanner, but the efficiency of conventional SLGs has been constrained by unwanted downward radiation. In this study, we developed a high-efficiency SLG consisting of through-hole grating and surface grating, which selectively radiates upward. Via the optimization using the covariance matrix adaptation evolution strategy, we designed a structure showing a maximum upward emissivity of 95% as well as moderate radiation rates and beam divergence. Experimentally, the emissivity was enhanced by 2-4 dB and the roundtrip efficiency was improved by 5.4 dB, which is significant in applications to light detection and ranging.

PULM3: The Effects of a Two-step Coating Process and Flow on Artificial Lung Fiber Fouling.

The densely packed fiber bundle design of the artificial lung increases the gas exchange efficiency of the device by dramatically increasing its surface area to volume ratio. However, the close arrangement of the lung’s fibers is a significant source for blood coagulation, and therefore the effectiveness of their in-situ coating for effective protein antifouling activity requires a process that uniformly applies the coating across the bundle thickness. In this study, polydopamine/polysulfobetaine methacrylate (pDOPA/pSBMA) was grafted onto the artificial lung circuit using a two-step surface modification process consisting of an ultraviolet-oxygen plasma surface activation followed by surface grating in pDOPA/pSBMA dissolved in tris(hydroxymethyl)aminomethane (TRIS, pH 8.5) buffer. The antifouling activities of coating on fiber mats at the surface or buried in the bundle, on fiber bundle exposed to 24hr phosphate buffered saline (pH 7.34, temp. ~37C) flow (1.22L/min), and uncoated controls were analyzed. Fibrinogen (Fg) and platelet (plt) fouling on fibers were used as metrics of antifouling activity. Ultimately, the utility of fully priming the lung circuit with pDOPA/pSBMA coating solution with a side-to-side positioning of the primed device every 10 minutes for 2 hrs was evaluated for coating uniformity across bundle thickness. Fg and plt fouling on uncoated controls, coated bundle surface fibers, coated bundle buried fibers, coated bundle surface fibers after 24hr flow, and coated bundle buried fibers after 24hr flow were respectively (0.83±0.01, 0.20±0.003) (0.36±0.01 pval=0.026, 0.36±0.01 pval=8.740E-11), (0.38±0.004 pval=0.026, 0.01±0.02 pval=8.740E-11), (2.64±0.53 pval=0.077, 0.02±0.003 pval=0.218), and (2.70±0.72 pval= 0.077, 0.03±0.01 pval=0.218). The data indicated that while the pDOPA/pSBMA coating significantly reduced fouling, not only did its appearance vary across the bundle thickness but so did its antifouling activity. This warrants the optimization of the coating process.

Plasmonic grating H2S sensor based on a chitosan-polyaniline-nano-composite

In this study, a plasmonic sensor was designed based on the grating coupling to detect the low concentration of H2S as a toxic chemical. The polyaniline nanostructure was prepared using the laser ablation technique in a chitosan solution and the final products were tested using analytical methods. The chitosan-polyaniline nanocomposite layer was used as a sensing layer and coated on the surface of 1D polydimethylsiloxane grating. The variation of reflectivity with different concentrations of H2S was registered from the surface of the grating for evaluating the sensor’s response. Finally, it was explained using the Langmuir isotherm absorption model. The limit of detection and the sensitivity of chitosan-polyaniline-nanocomposite were about 1 ppm and 0.10767 for the detection of H2S, respectively.

Least-squares phase-shifting algorithm of coherence scanning interferometry with windowed B-spline fitting, resampled and subdivided phase points for 3D topography metrology

3D topography metrology of optical micro-structured surfaces is critical for characterizing surface texture and form errors. The coherence scanning interferometry (CSI) faces many challenges for improving the accuracy of 3D topography metrology. In this paper, the least-squares (L-S) phase-shifting algorithm of coherence scanning interferometry with windowed B-spline fitting, resampled and subdivided phase points is proposed, which provides high accuracy of 3D surface topography. The proposed algorithm avoids the introduction of complex judgment criterion of fringe orders, and tedious phase unwrapping. Comparison with generalized phase-shifting algorithm, the wrong textures do not appear on the reconstructed 3D surfaces and 2D profiles for optical grating and Micro-lens array (MLA) surfaces using the proposed algorithm. Experimental results show that a VLSI step surface has high repeated measurement accuracy with a standard deviation of 1.6 nm, the periodic error of the proposed algorithm for PMMA MLA sub-aperture units is about 20 nm, and the mean value of PMMA MLA four random sub-aperture units are 6.66 nm (Sq), 77.63 nm (Sp), 36.38 nm (Sv), 114.18 nm (Sz) and 4.90 nm (Sa), respectively.

A two-dimensional grating surface made of quaternary Huygens elements excited by a real source

In this article, a new method to create an anomalous reflection in the desired direction is proposed. Two-dimensional grating surfaces consisting of four particles with the properties of a Huygens source are employed in each period. Then, this method is extended to the problem in which the grating surface is illuminated by a real source such as a horn. In this case, the designed grating surface has different periods in both directions to collimate the reflected wave and give an in-phase wavefront. Using our method, a high-efficiency reflectarray (RA) based on quaternary Huygens grating is designed. This RA is distinguished from common RAs due to its beam squint capability. This array offers more aperture efficiency and thus more gain in comparison to the leaky waves that inherently have low aperture efficiency. Therefore, our designed RA can compete with leaky wave antennas in many applications. The mentioned RA is designed to have the main beam in the direction of left( {{theta _0} = {{68}^{circ }},{varphi _0} = {{225}^{circ }}} right), at the frequency of 12 GHz. The simulation results show the realized gain and SLL of this antenna are 24.8 dB and -15.5 dB, respectively. Also, by changing the frequency in the range of 12–15 GHz, the direction of the main beam varies from left( {{{68}^{circ }}, {{225}^{circ }}} right) to left( {{{39}^{circ }}, {{225}^{circ }}} right).

An Efficient Method for Light Beaming from Subwavelength Slits Surrounded by Surface Gratings

This paper investigates the directional beaming of metallic subwavelength slits surrounded by dielectric gratings. The design of the structure for light beaming was formulated as an optimization problem for the far-field angular transmission. A vertical mode expansion method was developed to solve the diffraction problem, which was then integrated into a genetic algorithm and an active set method to obtain the optimal result. By using the proposed method for a two-slit structure, we demonstrate that both the single- and dual-beaming effects can be efficiently achieved. Moreover, the beaming directions can be flexibly adjusted and precisely controlled.