Back Reflection Research Articles

Fibre Refractometry for Minimally Invasive Sugar Content Measurements within Produce

A minimally invasive needle refractometer is presented for sugar content measurements within produce. A passive sampling cap structure was developed that improves the reliability of the device by avoiding interfering back reflections from the flesh of the produce. It is explained that factory calibration may not be needed for this type of refractometer, potentially reducing production costs. Also demonstrated is an iterative method to correct for temperature variations without the need for an integrated model for how the refractive index changes with temperature for different levels of sugar concentration. The sensor showed a typical standard deviation of 0.4 °Bx for a 10-s-long measurement and was validated against a prism refractometer, showing an average offset of (0.0±0.1) °Bx. In addition, the potential for using the device to investigate sugar distributions within a single fruit sample is demonstrated.

Newest Methods and Approaches to Enhance the Performance of Optical Frequency-Domain Reflectometers.

In this review, we summarize the latest advances in the design of optical frequency-domain reflectometers (OFDRs), digital signal processing, and sensors based on special optical fibers. We discuss state-of-the-art approaches to improving metrological characteristics, such as spatial resolution, SNR, dynamic range, and the accuracy of determining back reflection coefficients. We also analyze the latest achievements in the OFDR-based sensors: the accuracy of spatial localization of the impact, the error in detecting temperatures, deformation, and other quantities, and the features of separate measurement of various physical quantities. We also pay attention to the trend of mutual integration of frequency-domain optical reflectometry methods with time-domain optical reflectometry, which provides completely new sensing possibilities. We believe that this review may be useful to engineers and scientists focused on developing a lab setup, complete measurement instrument, or sensing system with specific requirements.

High-efficiency dual-level heterogenous grating coupler on CMOS-compatible silicon-lithium niobate platform

We present the design and experimental demonstration of multilayer etched CMOS-compatible grating couplers with high efficiency on a heterogeneous silicon-lithium niobate platform. The dual-level grating coupler comprises 90 nm-thick Si waveguides and 220 nm-thick Si grating with a linear chirped structure without etching LN. The design changes the grating diffraction properties, which not only reduce back reflection but also improve directionality and fiber-to-chip mode match. In comparison with existing studies, this work achieves high coupling efficiency solely through CMOS-compatible etching without additional bottom reflectors or high-index overlays. Theoretical calculations predict a fiber-to-chip coupling efficiency of −1.76 dB and an off-chip diffraction efficiency of −1.1 dB for the TE mode. The experimental measurement of the peak coupling efficiency is −2.84 dB with the back reflection as low as −26 dB. The grating coupler paves the way for monolithic integration of Si and LN.

Polarization-Independent Perfect Absorption in Monolayer Black Phosphorus Metasurfaces at Terahertz Frequencies via Critical Coupling.

Two-dimensional (2D) materials, which possess rich underlying physical properties that can provide the potential for designing more efficient and compact optoelectronic devices, have attracted great interest among scientists. Due to the atomic-scale thickness and the anisotropy of in-plane conductivity, 2D black phosphorus (BP) exhibits a polarization-dependent absorption spectrum with low absorption, which limits its further development in polarization-independent applications such as light absorbers and sensors. In this paper, a polarization-independent perfect absorber in the terahertz band is proposed, which is composed of a patterned BP monolayer deposited on a lossless photonic crystal (PC) slab with a back reflection mirror. The absorption of the patterned BP monolayer can reach 100% at resonant frequencies through the critical coupling mechanism of guided resonance. Moreover, the absorber exhibits polarization-independent absorption characteristics for vertically incident light, which are attributed to the 4-fold rotational symmetry of the PC substrate and the patterned BP monolayer deposited on it. This work opens up the possibility of fabricating optically polarization-independent devices based on single-layer 2D anisotropic materials.

Silicon Subwavelength Grating Coupler With Ultra-High Reproducibility, Ultra-Wide Bandwidth, and Ultra-Low Back Reflection

Silicon Subwavelength Grating Coupler With Ultra-High Reproducibility, Ultra-Wide Bandwidth, and Ultra-Low Back Reflection

Inverter With Paralleled Modules to Extend Current Capacity and Combat Motor Overvoltage in SiC-Based Adjustable Speed Drives

This article proposes a quasi-three-level (Q3L) PWM-based module-parallel inverter to address two major issues of deploying SiC MOSFETs in high-power cable-fed adjustable speed drives. Firstly, the maximum output power of SiC inverters is limited due to the lack of high current rating SiC devices, which cannot satisfy the demand of high-power applications such as heavy-duty electric vehicles and more electric aeroplanes. The second issue comes from the fast-switching speed of SiC MOSFETs, where power cables act like transmission lines under steep rising/falling voltages (high <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$dv/dt$</tex-math></inline-formula> ), with back and forth voltage reflections that result in serious overvoltage oscillations at motor terminals. To address these issues, a SiC module-parallel inverter is adopted with elevated current capacity, where the phase voltage is maintained at the mid-point of a coupled inductor connected to the output nodes of each paralleled half-bridge module. By actively controlling the switching delay between the paralleled half-bridge-legs, Q3L PWM waveforms are generated at the inverter output nodes which can mitigate the motor overvoltage due to the voltage reflections through power cables. An active current control technique is also proposed to facilitate the current balance between the paralleled half-bridge-legs. The proposed Q3L PWM-based module-parallel inverter is experimentally verified using a SiC-based cable-fed motor drive system. The results show that the proposed approach can extend the current capabilities of SiC devices as well as mitigate the motor overvoltage, enabling the adoption of SiC devices in high-power motor drives.

Adaptive Optics Methods to Rat Eye Properties: Impact of Pupil Diameter on Wavefront Detection

Achieving a high-quality wavefront sensing light spot and accurate wavefront estimation of the rat eye is still challenging due to its large ocular aberrations and the back reflections from fundus multilayer. Simulation and experiments of rat eye wavefront sensing are conducted to improve the quality of sensing spot for accurate wavefront estimation. The simulation results show that a smaller pupil diameter leads to a high quality of wavefront sensing light spot, and the model rat eye reaches diffractive limitation when the pupil diameter is 0.8 mm. However, the experimental results indicate a different conclusion. Consistent with the simulation results, the quality of the sensing light spot significantly improves when the pupil diameter decreases from 3.6 mm to 1.8 mm. The full width at half maximum (FWHM) of the sensing light spots decreases from 77.36 ± 8.95 μm to 26.78 ± 3.25 μm, and the calculated Strehl ratio increases from 0.007 to 0.396. As the pupil diameter continues to decrease to 1.2 mm, the sensing spot and calculated Strehl ratio continue to improve, while the detected low-order aberrations exhibit a significant increase in both value and variance. This observation suggests that using a half-filled pupil for rat wavefront detection may be a more favorable choice, which assists in obtaining high-resolution retinal images in the rat eye using adaptive optics technology.

A multi-modal microscope for integrated mapping of cellular forces and Brillouin scattering with high resolution

Mechanical forces and stiffness play key roles in the health and development of cells and tissue, but despite the physical connection between these quantities, they cannot be monitored in parallel in most cases. Here, we introduce a fully integrated microscope that combines a method for high-resolution cell force imaging (elastic resonator interference stress microscopy, ERISM) with non-contact mapping of the elastic properties of cells (via Brillouin microscopy). In order to integrate both techniques, we had to account for the strong back reflection on the surface of the microcavity used for ERISM measurements as well as the local destruction of the cavity under illumination for Brillouin microscopy measurements. Therefore, we developed an elastic optical microcavity with minimal absorption that can perform ERISM measurements without sustaining laser damage during Brillouin microscopy. Furthermore, an unequal-arm Michelson interferometer was designed to suppress the back reflection of the laser on the ERISM microcavity surface using division by amplitude interference to reduce the reflected light and enhance the Brillouin signal. We show the utility of our integrated microscope by simultaneously mapping cellular forces and Brillouin shifts in cultures of fibroblast cells.

Amber rainbow ribbon effect in broadband optical metamaterials

Using the trapped rainbow effect to slow down or even stop light has been widely studied. However, high loss and energy leakage severely limited the development of rainbow devices. Here, we observed the negative Goos-Hänchen effect in film samples across the entire visible spectrum. We also discovered an amber rainbow ribbon and an optical black hole due to perfect back reflection in optical waveguides, where little light leaks out. Not only does the amber rainbow ribbon effect show an automatic frequency selection response, as predicted by single frequency theoretical models and confirmed by experiments, it also shows spatial periodic regulation, resulting from broadband omnidirectional visible metamaterials prepared by disordered assembly systems. This broadband light trapping system could play a crucial role in the fields of optical storage and information processing when being used to construct ultra-compact modulators and other tunable devices.

Reflection behaviour of SH0 from small defects in thin sheets, with application to EMAT inspection of titanium

ABSTRACT Defects can arise within the weld during the laser welding process of thin titanium sheets, and it is critical that these defects are detected. Shear horizontal (SH) waves offer good potential for defect detection, but require an understanding of how the ultrasonic waves interact with defects, in order to develop an optimised inspection setup, increasing the probability of defect detection. The geometry of a defect strongly affects the reflected signal magnitude, with finite element simulations showing that defect width and length determine the maximum SH0 wave reflection. Experiments confirm this behaviour. The defect width is shown to affect the reflection behaviour due to wave interference. Phase differences between the front face reflection and back face reflection cause a shift in the peak position. In addition, the experimental work presented in this paper also shows the potential for electromagnetic acoustic transducers to be used for the inspection of titanium components.

WDM C-band four channel demultiplexer using cascaded multimode interference on SiN strip waveguide structure

Back reflection challenges significantly constrain the efficiency of optical communication networks employing dense wavelength division multiplexing (DWDM) technology, particularly those based on Silicon (Si) Multimode Interference (MMI) waveguides. To mitigate this limitation, we present a novel 1×4 optical demultiplexer design using MMI within a Silicon-Nitride (SiN) strip waveguide configuration, operating within the C-band spectrum. Our design was optimized using AI-enhanced RSoft-CAD simulations that combined the Beam Propagation Method (BPM) and Finite-Difference Time-Domain (FDTD) techniques, integrated with convolutional neural network (CNN) machine learning algorithms. The simulation results demonstrate that the proposed device efficiently transmits four channels with 10 nm spacing in the C-band, showing low power loss ranging from 1.98-2.35 dB, a broad bandwidth of 7.68-8.08 nm, and excellent crosstalk suppression between 20.8-23.4 dB. Leveraging the low refractive index of SiN, we achieve ultra-low back reflection of 40.58 dB without requiring specialized angled MMI designs, which are often necessary in Si-based MMI technology. Consequently, this SiN-based MMI demultiplexer provides an effective solution for DWDM systems, enabling high data transmission rates with minimal back reflection in optical communication networks.

ЛИНЕЙНАЯ ОЦЕНКА БЫКОВ ГОЛШТИНСКОЙ ПОРОДЫ ПО ЭКСТЕРЬЕРНОМУ ТИПУ ИХ ДОЧЕРЕЙ В ТОО «БЕК+»

The article presents the characteristics of linear evaluation of exterior of the first calving heifers of different lineage in the conditions of dairy complex of Beck+ LLP located in the Fyodorov district of the Kostanay region. Three experimental groups of cows were formed based on the different lineage of their first calving: Vis Back Ideal, Reflection Sovereign, and Osborndale Ivanhoe. The assessment of first-calving cows' exterior traits was conducted using 24 indicators and 9-point scale from day 30 to day 150 of lactation. Throughout the study, cows from the Vis Back Ideal and Reflection Sovereign lines demonstrated their superiority in overall body conformation, dairy type, and limb structure compared to their herd mates from the Osborndale Ivanhoe line. Across most of the evaluated traits such as hip height, rear width, udder depth, udder attachment, and hind leg posture, first-calving cows from the Vis Back Ideal line exhibited an advantage over those from the Reflection Sovereign and Osborndale Ivanhoe lines. A comprehensive evaluation of exterior traits was conducted, revealing that first-calving cows from the Vis Back Ideal and Reflection Sovereign lines are classified as "good," while their herd mates from the Osborndale Ivanhoe line are classified as "satisfactory." These finding confirm that servicing bulls significantly influence the expression of linear exterior traits in offspring.

Increasing the productive potential of large and small cattle breed resources in the South of Russia based on modern breeding methods

The results of the genetic characteristics research of large and small cattle populations grown in the Southern Russia are stated. Breed-specific DNA patterns have been identified in three of the most common cattle breeds of meat productivity in arid conditions. The milk productivity of Holstein cows of different breeding lines has been studied. It was found that increasing the frequency of animals of Vis Back Ideal and Reflection Sovering lines in the parent pairs could be able to increase the level of milk productivity of offspring and improve the quality indicators of dairy raw materials. The adaptive abilities and milk productivity of imported foreign Holstein cows depending on their origin were estimated. In comparison with Australian and Danish Holstein cows, American and German analogues have a higher level of milk productivity. However Australian and Danish animals have a more flexible adaptive capacity. As a result of the comparative study of the economic and biological characteristics of two generations of Aberdeen-Angus cattle (parental foreign generation, and the first generation - obtained under breeding conditions in Southern Russia), tendencies to increase productive values are revealed. The features of the meat productivity formation in Kalmyk steers different exterior and constitutional types are investigated. It was found that the Kalmyk steers of the tall body type have a higher meat productivity compared with their analogues of medium and compact body types. However, the beef of compact steers has a higher fat percentage, more attractive taste characteristics, culinary and technological indices. The features of polymorphism of CAST, GH, GDF9, CLPG, FABP4 and MC4R genes in populations of sheep of different breeds grown in the Republic of Kalmykia, Volgograd and Rostov regions, Kabardino-Balkaria Republic were also studied. As a promising method of early diagnosis of presence economically useful traits in sheep during ontogenesis, the effectiveness of DNA analysis in young lambs and the further selection of animals with desirable genotypes according to these genes were justified.

A novel approach to interface high-Q Fabry–Pérot resonators with photonic circuits

The unique benefits of Fabry–Pérot resonators as frequency-stable reference cavities and as an efficient interface between atoms and photons make them an indispensable resource for emerging photonic technologies. To bring these performance benefits to next-generation communications, computation, and time-keeping systems, it will be necessary to develop strategies to integrate compact Fabry–Pérot resonators with photonic integrated circuits. In this paper, we demonstrate a novel reflection cancellation circuit that utilizes a numerically optimized multi-port polarization-splitting grating coupler to efficiently interface high-finesse Fabry–Pérot resonators with a silicon photonic circuit. This circuit interface produces a spatial separation of the incident and reflected waves, as required for on-chip Pound–Drever–Hall frequency locking, while also suppressing unwanted back reflections from the Fabry–Pérot resonator. Using inverse design principles, we design and fabricate a polarization-splitting grating coupler that achieves 55% coupling efficiency. This design realizes an insertion loss of 5.8 dB for the circuit interface and more than 9 dB of back reflection suppression, and we demonstrate the versatility of this system by using it to interface several reflective off-chip devices.

Study the effect of adding buffer layer and back reflection on the performance of Chalcogenide compounds

Solar energy is one of the most important methods used worldwide to provide some of the global energy requirements. It is easily available and free from negative effects on the environment. In this research, the possibility of increasing the efficiency of solar cells is investigated. The SCAPS-D simulation is used to investigate the ZnO/ZnS/CNTS solar cell. The practical research is compared with the program, showing that the program simulates the reality due to the high convergence between the practical and theoretical results of the program. By changing the doping ratios of the theoretical cell layers, the cell efficiency shifts from )3.19%( to )9.41%(. The theoretical cell is improved by adding various back reflection layers (BSL), increasing the conversion efficiency from )9.41%( to )11.59%(. After adding more matching layers, the cell's structure becomes ZnO/ZnS/V2O5/CNTS, increasing the conversion efficiency to (14.25%). The ratio of conversion efficiency of ZnS/V2O5/CNTS/CFTS is (17.22%), the filling factor (67.74%), the short circuit current (23.247mA/cm2), and the open circuit voltage (1.0937 V).

High-performance grating couplers on 220-nm thick silicon by inverse design for perfectly vertical coupling

Efficient grating couplers (GCs) for perfectly vertical coupling are difficult to realize due to the second-order back reflection. In this study, apodized GCs (AGCs) are presented for achieving perfectly-vertical coupling to 220 nm thick silicon-on-insulator (SOI) waveguides in the C-band. We compare the performance of the AGCs to that of uniform GCs (UGCs) and demonstrate the superiority of the former. The AGCs were obtained through inverse design using gradient-based optimization and were found to effectively suppress back reflection and exhibit better matching to the Gaussian beam profile. The design and measurement results show that AGCs have a 3 dB lower coupling loss than UGCs. We fabricated focusing AGCs by electron beam lithography with a single, 70 nm shallow etch and a minimum feature size of 100 nm, which makes them compatible with CMOS technology. The AGCs achieved a coupling efficiency of −5.86 dB for perfectly vertical coupling. Overall, our results demonstrate the potential of AGCs for achieving high-performance coupling in the C-band on the SOI platform.

Anti-reflection grating-assisted contra-directional coupler with large corrugation width

The grating-assisted contra-directional coupler (contra-DC) is one of the commonly used add-drop filters serving for coarse wavelength-division-multiplexing (CWDM) systems due to its flat-top and wide-band response. However, the free-spectral-range (FSR) of contra-DC is limited by the back reflection to the input port caused by the intra-waveguide coupling. In this paper we propose an anti-reflection grating-assisted contra-DC by simply increasing the sidewall corrugation width. The intra-waveguide coupling coefficient can be decreased to 0 when the corrugation width is increased to a certain value. The simulation result shows that the transmission at drop port is −0.42 dB, while the back reflection to the input port is only −22.0 dB. The 4-channel cascaded contra-DCs with wavelength range of ∼60 nm are also simulated, all the channels are not affected by the intra-waveguide coupling. We believe the proposed contra-DC with large corrugation width can be applied to the CWDM system requiring a broad spectrum range.

Tunable magnetic phase transition in thulium–samarium orthoferrite single crystals

Spintronics and condensed matter physics are in pursuit of materials that can serve as carriers for novel quantum devices. Antiferromagnetic rare earth orthoferrites (RFeO3, where R is rare earth or Y), are potential functional materials for magnetic information processing. They exhibit temperature-controlled spin reorientation transition (SRT) and magnetic field/temperature-induced spin switching (SSW) properties. As such, RFeO3 is expected to be used in spintronic devices that can easily control the spin. With the advancement of research, the co-doping of rare earth ions has emerged as a prominent area of investigation in RFeO3. In this work, we have grown a series of Tm1-xSmxFeO3 (TSFO, x = 0, 0.2, 0.3, 0.4) single crystals via a four-mirror optical floating zone furnace. Crystal axes and single phase of these single crystals were determined using Laue back reflection camera and X-ray diffractometer. We observed that the doping of Sm ions can effectively regulate the spin reorientation temperature of the parent material TmFeO3. Both type-I and type-II SSW have been observed when the doping rate x is 0.2 or 0.4, perfectly integrating the magnetic properties of TmFeO3 and SmFeO3 single crystals. Furthermore, the spin switching in TSFO (x = 0.2, 0.3, 0.4) can be manipulated by applying low magnetic fields with tens of Oe. On the other hand, when the doping rate x reaches 0.4, the magnetic compensation phenomenon and the Néer temperature of rare earth ions occurred. The super-exchange interaction between R3+ and Fe3+ magnetic sublattices leads to these interesting phenomena.

O-Band Grating Couplers Using Silicon Nitride Structures

To test silicon photonics component performances, a silicon (Si) grating coupler (GC) is used to couple the light from a single-mode fiber (SMF) into the chip. However, silicon nitride (Si3N4) waveguides have recently become more popular for realizing photonic integrated circuits (PICs), which may be attributable to their exceptional characteristics, such as minimal absorption and low back reflection (BR) in the O-band spectrum. Thus, to test the photonic chip, a waveguide converter from Si3N4 to Si needs to be added to the photonic circuit, which can lead to more power losses and BR. To avoid this conversion, we propose in this manuscript a configuration of a GC based on Si3N4 structures, which can be employed to minimize the footprint size and obtain better performance. The achievement of high efficiency was possibly obtained by optimizing the structural properties of the waveguide and the coupling angle from the SMF. The results demonstrated high efficiency within the O-band spectrum by using a wavelength of 1310 nm. Notably, at this specific wavelength, the findings indicated a coupling efficiency of −5.52 db. The proposed design of the GC consists of a uniform grating that offers improvements regarding affordability and simplicity in manufacturing compared to other GC models. For instance, using a reflector or a GC with non-uniform grooved teeth introduces challenges in fabrication and incurs higher costs. Thus, the proposed design can be useful for improving the testing abilities of the Si3N4 photonic chips used in transceiver systems.

An Optical 1×4 Power Splitter Based on Silicon-Nitride MMI Using Strip Waveguide Structures.

This paper presents a new design for a 1 × 4 optical power splitter using multimode interference (MMI) coupler in silicon nitride (Si3N4) strip waveguide structures. The main functionality of the proposed design is to use Si3N4 for dealing with the back reflection (BR) effect that usually happens in silicon (Si) MMI devices due to the self-imaging effect and the higher index contrast between Si and silicon dioxide (SiO2). The optimal device parameters were determined through numerical optimizations using the beam propagation method (BPM) and finite difference time domain (FDTD). Results demonstrate that the power splitter with a length of 34.6 μm can reach equal distribution power in each output port up to 24.3% of the total power across the O-band spectrum with 0.13 dB insertion loss and good tolerance MMI coupler parameters with a shift of ±250 nm. Additionally, the back reflection range over the O-band was found to be 40.25-42.44 dB. This demonstrates the effectiveness of the incorporation using Si3N4 MMI and adiabatic input and output tapers in mitigating unwanted BR to ensure that a good signal is received from the laser. This design showcases the significant potential for data-center networks, offering a promising solution for efficient signal distribution and facilitating high-performance and reliable optical signal routing within the O-band range. By leveraging the advantages of Si3N4 and the MMI coupler, this design opens possibilities for advanced optical network architectures and enables efficient transmission of optical signals in the O-band range.