Optical Transmission Characteristics Research Articles

Weak oxidant fraction in the microwave plasma influencing the evolution of nanocrystalline-diamond–imbedded diamond–like carbon network at low temperatures and its orbital hybridization dependent wide optical band gaps

The diamond-like carbon (DLC) thin films having intrinsic nanocrystalline diamond (NCD) components were synthesized on bare glass substrates at 300 °C, employing a (C2H2/CO2/H2/) gas mixture in MW-PECVD. Relevant influence of the weak oxidant fraction [F = CO2/(CO2 + C2H2)] in the plasma on the specific hybridized constituents (sp3 and sp2) in the C-network, optical transmission characteristics of the film, and its accomplished degree of nanocrystallinity were investigated. A substantial segment of the NCD was achieved in the DLC matrix. An optimized diamond-phase component corresponding to the minimized bond angle disorder in the matrix was accounted from the manifestation of the maxima of IDia/IG and IDia/ID simultaneous to the minimum of ID/IG ratio in Raman response, along with an allied diamond peak appearing near 1332 cm−1. The optimal DLC film at F = 0.23 revealed a wide optical band gap (Eg) of ∼3.60 eV, ∼59% sp3-hybridized C component of the diamond phase, and a significant sp3/sp2 ratio of ∼2.1. The film microstructure seemed homogeneous with uniformly distributed NCDs of average diameter ∼7.5 nm and dominant 〈111〉 crystallographic orientation. The sp3/sp2 fraction in the film matrix has been correlated directly to the IDia/IG and IDia/ID, and inversely to ID/IG ratios of the Raman data. Atomic-O, including atomic-H, remains instrumental in chemical reactions, facilitating the etching of graphitic and a-C phases while preserving the superior sp3-hybridized NCD component growing uninterruptedly in the DLC network that subsists shielded from the high-energy ion impact within secondary plasma under the shadow mask.

Optical transmission characteristics of Large-tolerance Fiber Collimator

A Large-tolerance Fiber Collimator (LTFC) consisting of a Thermally Expanded Core Fiber (TECF) and an aspherical lens is designed to solve the problems of low beam coupling efficiency and small coupling tolerance of conventional collimators. According to the Gaussian beam coupling theory, the beam deviation coupling model of the LTFC is established to analyze the effects of coupling deviation and fiber Mode Field Diameter (MFD) on the collimator coupling efficiency. Beam coupling simulations are carried out by ZEMAX, which analyzes the influence of the interaction of the three coupling deviations on the beam coupling efficiency. And the final experimental platform is built to test the performance of the designed LTFC in combination with simulation. The results show that the LTFC can achieve a beam coupling efficiency more than 80% with an angular deviation less than 0.06°, a radial deviation less than 0.06 mm, and an axial deviation less than 2 mm. The coupling efficiency can reach 97.24% when the collimator fiber MFD is 28μm and all the deviations are extremely small(close to 0). The LTFC has a large coupling tolerance while obtaining a high coupling efficiency, which reduces the difficulty of beam coupling.

Failure Analysis on OPGW Cable During Short Circuit Test

A new type of ground wire used for communication lines in high-voltage power transmission systems is called Optical Ground Wire cable (OPGW). In addition to serving as a communication optical cable and standard overhead ground wire, it may also prevent lightning strikes and carry short circuit currents. The OPGW cable must fulfil the specifications for both construction and performance for the ground wire to work, the optical fiber integrity, and the optical transmission characteristics to be appropriate for the intended use. It is anticipated that OPGW cables will safeguard the optical fiber and that the cable’s temperature won’t rise to the point where the fiber’s parameters could deteriorate. This paper examines the analysis and review of OPGW cable failure cases during short circuit tests.

Modeling and oblique transmission characteristics of an underwater wireless optical communication channel based on ocean depth layering.

Underwater wireless optical communication is widely considered in the field of underwater communication due to its high bandwidth and low latency. In a real transmission link, the temperature and salinity of seawater, chlorophyll concentration, and bubble density vary with ocean depth. Therefore, the depth of the optical transmitter in seawater and the tilt angle of the beam will exhibit different beam transmission characteristics. In this paper, an underwater oblique-range layered channel model considering the combined effects of dynamic turbulence, absorption, and scattering is developed based on real data of seawater at different depths measured by the Global Ocean Observing Buoy Argo and the Woods Hole Oceanographic Institution BCO-DMO. The effects of transmission distance, transmitter tilt angle, and transmitter depth on the oblique-range transmission characteristics of the beam in seawater are discussed. The simulation results show that, at the same transmission distance, the beam centroid displacement increases with an increase in transmitter depth only when the transmitter is located above the interior of the thermocline. When the transmitter is located below the interior of the thermocline, the influence of the transmitter tilt angle on the beam centroid displacement decreases. This indicates that at different depths within the interior of the thermocline, the optical beam transmission characteristics exhibit significant variations.

Optimization design of mode-selective ring core photonic lantern based on coupled local mode theory

In this paper, optical field transmission characteristics of a mode-selective ring core photonic lantern (MSRCPL) are theoretically analyzed and its optimization design is also investigated. This MSRCPL is based on a tapered fiber bundle of coreless fiber and glass capillary with low refractive index. Mode evolution characteristics in the taper region and mode coupling characteristics at the splicing point are analyzed. The coupled local mode theory (CLMT) is used to optimize the structure of a 3-port MSRCPL and a 5-port MSRCPL. The impact of taper length, taper shape, taper waist, and geometric arrangement on mode selectivity are calculated. Calculation results indicate that the mode selectivities of the optimized 3-port and 5-port MSRCPL are higher than 23 dB and 18 dB, respectively.

Antireflective structured surface of chalcogenide glass fabricated using glass to glass molding

Chalcogenide (ChG) glasses with micro-nano structure arrays are increasingly demanded in infrared optical systems owing to their excellent antireflective properties, and can be mass-produced by precision glass molding (PGM). Nickel-phosphorus (Ni–P) plated molds are commonly used in the PGM process, but the Ni atoms tend to react with the ChG glass at high temperatures. In this study, we propose a novel two-step PGM process. A Ni–P mold is used to transfer antireflective micro-nano structure array to silicate glass. Then the silicate glass, which has a higher glass transition temperature (Tg) than the ChG glass, is used as the mold to replicate the antireflective structured surface to the ChG glass. The results show that the ChG glass micro-nano structure array has high forming accuracy and favorable infrared optical transmission characteristics. The silicate glass is proved to be an appropriate mold material for the ChG glass molding process. This work provides a novel type of the PGM techniques for ChG glass materials.

Transparent and conductive thin films of cadmium doped tin oxide fabricated by pulsed laser deposition technique

Transparent conducting thin films of cadmium doped tin oxide (CTO) were successfully fabricated on glass substrates by pulsed laser deposition technique. Several analytical tools were employed to explore the causes of changes in the structural, optical and electrical properties of these films as a function of doping concentration. The 3 wt % Cd doped films showed lowest electrical sheet resistance of 300.9Ω/□ with electrical resistivity of 2.407×10−3Ωcm. The CTO films are optically transparent with more than 80% transmission in the visible and near IR region of the electromagnetic spectrum. The optical energy gap of CTO films marginally varied from 3.40 eV to 3.49 eV for different doping amount. The AFM studies showed an increase in the surface smoothness of the film with Cd doping concentration. The X-ray diffraction study revealed the tetragonal structure of the film with lattice parameters a=4.742Å and c=3.177Å. The enhanced electrical conductivity and optical transmittance characteristics in these pulsed laser deposited Cd:SnO2 thin films, are suitable, for photo anode/electrode applications in solar cells and display panels.

Study of the Surface Plasmon Refractive Index Nanosensor Based on Fanoresonance

In order to solve the problems of low sensitivity and complex structure of surface –plasmon- polariton (SPP) sensor at the present stage, a highly sensitive and stable SPP sensor composed of metal-insulator-metal (MIM) waveguide, a stub and a resonant cavity is proposed. The diameter of the MIM waveguide is chosen to be 50 nm so that only the single mode exists. The radius and refractive index of the cavity can vary, which is imbedded in silver background so that SPP phenomenon can be produced. The optical transmission characteristics and sensing characteristics of the designed sensor are studied by using finite element method. Experimental results show that the combination of the MIM waveguide and the stub can produce continuous state and the cavity can produce discrete state at the wavelength of 830 nm. At the same time, our research also demonstrates the sharp asymmetric Fano transmission spectrum is also sensitive to the surrounding medium. The application of the designed device in the field of refractive index sensing is also studied by calculating the shift of the resonant wavelength with the change of the refractive index of the medium in the resonator. The device can achieve refractive index sensing performance with the sensitivity of 803 nm/RIU and the figure of merit of 121.

Design and analysis of optical biosensor based on symmetric and asymmetric structured one-dimensional photonic crystal for tuberculosis detection

We looked into three distinct topologies, using a one-dimensional photonic crystal with a defect layer in two symmetrical and one asymmetrical configurations as an optical biosensor application for detection in tuberculosis (TB). In order to investigate the optical transmission characteristics of such structures, we used a well-known transfer matrix approach. A shift in resonant peak is estimated, when blood of healthy or TB infected human is infiltrated in defect layer. The impact of several parameters, including the thickness of the defect layer, the number of unit cells, and the angle of incidence for all three configurations, has been studied. The sensitivity, quality factor, figure of merit, and detection limit for all structures have been studied and it is found that asymmetric structure is the best suitable structure for optical sensor application in the present case.

Luminous Flux Utilization of Static Birefringent Fourier Transform Imaging Spectrometer with Zoomable Spectral Resolution

The optical displacement calculation formula for the dual Wollaston prism is derived for any incident plane and angle using the wave normal tracing method. The validity of the calculation is confirmed by comparing it with captured photographs. The relationship between the maximum incident aperture, incident angle, and incident surface angle is given when plane and spherical waves incident on the prism group. The aperture utilization of a novel static birefringent Fourier transform imaging spectrometer based on dual Wollaston prisms is also analyzed. The relationship of aperture utilization with the incident surface angle, incident angle, and prisms’ air gap thickness is given. The results provide a theoretical foundation for fully describing the optical transmission characteristics of the dual Wollaston prism group and developing a high-performance spatio-tempo hybrid modulated birefringent spectral zoom Fourier transform imaging spectrometer.

Multilevel transmission contrast in optical structures with thin films of GeTe

Analysis of the optical properties: refractive index n(λ) and extinction coefficient k(λ), of thin films of phase-change materials obtained by photometric and ellipsometric methods allows to optimize optical characteristics reflection R, transmission T and absorption A. The interference of an electromagnetic wave in an absorbing thin film on a dielectric substrate significantly affects the values of the optical characteristics. Optimization of the optical characteristics is possible through the use of additional layers of dielectric materials, which are used to compensate for the difference in the refractive indices of the film with the substrate and air and minimize the reflection. This approach will increase the contrast of the transmission levels for the modulated optical signal in near infrared range. Calculations of the optical characteristics of thin films of germanium telluride in multi-layer structures are performed. Experimental samples of structures with antireflection layers of zinc sulfide have been prepared and their optical transmission characteristics have been investigated. The combination of multilayer structures for the implementation of contrast levels of transmission have been determined.

The Low-Temperature Sol-Gel Synthesis of Metal-Oxide Films on Polymer Substrates and the Determination of Their Optical and Dielectric Properties.

Photoactive, optically transparent heterostructures from silver nanowires and titanium dioxide were obtained by the sol-gel method on the surface of a polyethylene terephthalate film. The characteristics of optical transmission on the wavelength and those of dielectric permittivity, conductivity and dissipation on frequency in the range of 25-1,000,000 Hz were investigated.

Nonreciprocal transmission in a nonlinear coupled heterostructure.

A nonlinear coupled heterostructure, metal-nonlinear-metal-insulator-metal, is proposed. The heterostructure is a non-Hermitian system that possesses reciprocal and nonreciprocal optical transmission characteristics. With low incident power, linear optical characteristic is observed whereas at high incident power, nonlinear optical characteristics is observed. Under the low incident power there is no nonlinear effect, the forward and backward transmission are reciprocal. With appropriate geometric parameters, for forward propagation two exceptional points where the reflection coefficients equal zero can be obtained simultaneously. With high power incident nonlinear effect becomes significant, leading to reciprocity broken and optical bistability observed. We investigated the behaviours of forward and backward transmission as well as the optical bistability under different incident powers using nonlinear coupled mode theory. There is excellent agreement between the simulation results and theoretical modelling. The theoretical study of proposed heterostructure shows it has several novel optical responses under different incident conditions. The proposed heterostructure is relatively simple to fabricate and therefore can be experimentally verified with ease. These unique optical characteristics allow more possibilities for the design of multifunctional devices.

Optical Field Transmission Analysis of an All-Fiber Signal Combiner With a Dumbbell Shape

In this paper, the optical field transmission characteristics of an all-fiber signal combiner with a dumbbell shape and its application in laser beam combining are analyzed theoretically. Based on the three-layer waveguide model, the mode characteristics of a tapered multi-core fiber and a tapered single core fiber are analyzed respectively. On this basis, the working principle of an all-fiber signal combiner with a dumbbell shape is introduced from the perspective of mode evolution. The finite-difference beam propagation method is used to numerically analyze optical field envolution process in the combiner. Influences of the waist diameter, taper length and geometric arrangement are analyzed in detail. The calculation results show that an all-fiber signal combiner with a dumbbell shape can realize high brightness laser beam combining and the beam quality can reach the theoretical limit.

Mid-Infrared Hollow-Core Fiber Based Flexible Longitudinal Photoacoustic Resonator for Photoacoustic Spectroscopy Gas Sensing

Photoacoustic spectroscopy (PAS) has received extensive attention in optical gas sensing due to the advantages of high sensitivity, gas selectivity, and online detection. Here, a mid-infrared hollow-core fiber (HCF) based flexible longitudinal photoacoustic resonator for PAS-based gas sensing is proposed and theoretically demonstrated. A mid-infrared anti-resonant HCF is designed to innovatively replace the traditional metallic acoustic resonator and obtain a flexible photoacoustic cell in PAS. Optical transmission characteristics of the HCF are analyzed and discussed, achieving single mode operation with below 1 dB/m confinement loss between 3 and 8 μm and covering strong absorptions of some hydrocarbons and carbon oxides. With varied bending radii from 10 mm to 200 mm, the optical mode could be maintained in the hollow core. Based on the photoacoustic effect, generated acoustic mode distributions in the HCF-based flexible photoacoustic resonator are analyzed and compared. Results show that the PAS-based sensor has a stable and converged acoustic profile at the resonant frequency of around 16,787 Hz and a favorable linear response to light source power and gas concentration. The proposed novel photoacoustic resonator using HCF presents bring potential for advanced flexible PAS-based gas detection.

Novel View Synthesis Of Transparent Object From a Single Image

AbstractWe propose a method for converting a single image of a transparent object into multi‐view photo that enables users observing the object from multiple new angles, without inputting any 3D shape. The complex light paths formed by refraction and reflection makes it challenging to compute the lighting effects of transparent objects from a new angle. We construct an encoder–decoder network for normal reconstruction and texture extraction, which enables synthesizing novel views of transparent object from a set of new views and new environment maps using only one RGB image. By simultaneously considering the optical transmission and perspective variation, our network learns the characteristics of optical transmission and the change of perspective as guidance to the conversion from RGB colours to surface normals. A texture extraction subnetwork is proposed to alleviate the contour loss phenomenon during normal map generation. We test our method using 3D objects within and without our training data, including real 3D objects that exists in our lab, and completely new environment maps that we take using our phones. The results show that our method performs better on view synthesis of transparent objects in complex scenes using only a single‐view image.

Exact optical path difference and complete performance analysis of a spectral zooming imaging spectrometer.

The optical path difference (OPD) equations of the dual Wollaston prisms (DWP) with an adjustable air gap (AG) are derived by the wave normal tracing method, which is suitable for arbitrary incidence plane and angle. The spatial distribution of the OPD for various AG is presented. The validity of the OPD equation is verified by comparing the calculated interferograms with experimentally observed one. The performance of a novel static birefringent Fourier transform imaging spectrometer (SBFTIS) based on the DWP is investigated. The spectral resolution can be adjusted by changing the AG and the field of view can reach 10.0°, which is much larger than that predicted by our previous work. The results obtained in this article provide a theoretical basis for completely describing the optical transmission characteristic of the DWP and developing the high-performance birefringent spectral zooming imaging spectrometer.

New approach for designing an underwater free-space optical communication system

Ocean observation system that involves multiple underwater vehicles and seafloor nodes plays an important role in better learning the ocean, where underwater wireless communication is mandatory for massive data interaction. Optical communication that has wide bandwidth and comprehensive working distance is the preferred method compared to acoustic and other methods. However, the presence of directionality makes the optical method difficult to use especially when the transceiver is equipped on a motive vehicle. In this study, an underwater free-space optical communication method of transmitting information is proposed. Characteristics of underwater optical transmission, as well as the photoelectric signal processing and modulation and demodulation algorithms, are studied and modeled. New approach for realizing underwater free-space optical communication is proposed and simulated. A prototype including a free-space optical transmitter and a receiver is developed; tests in different scenarios were carried out, and the results were observed: (1) by using the minimum number of LEDs, the effect of uniform lighting in space is achieved, and the transmitter coverage reaches 160°. (2) When the power of the transmitter is 10 W and the communication rate is 1 Mbps, the maximum communication distance reaches 13 m.

Model of a multilayer coating for an artificial optical synapse

Optical characteristics of germanium telluride (GeTe) thin films in multilayer structures are calculated. A model of a multilayer optical coating with a four-level transmission coefficient is developed. Based on the calculated data, thickness values are determined at which the transmittance change is greatest for 1550-nm modulated optical radiation. Experimental samples coated with antireflection GeTe films are synthesized and their optical transmission characteristics are investigated. Combinations of parameters of the multilayer structures for the implementation of contrast transmittance levels are determined. The results of the study represent the implementation of a multilevel artificial optical synapse for neuromorphic processors.

A Finite Element Mesh Regrouping Strategy-Based Hybrid Light Transport Model for Enhancing the Efficiency and Accuracy of XLCT.

X-ray luminescence computed tomography (XLCT) is an emerging hybrid imaging modality in optical molecular imaging, which has attracted more attention and has been widely studied. In XLCT, the accuracy and operational efficiency of an optical transmission model play a decisive role in the rapid and accurate reconstruction of light sources. For simulation of optical transmission characteristics in XLCT, considering the limitations of the diffusion equation (DE) and the time and memory costs of simplified spherical harmonic approximation equation (SPN ), a hybrid light transport model needs to be built. DE and SPN models are first-order and higher-order approximations of RTE, respectively. Due to the discontinuity of the regions using the DE and SPN models and the inconsistencies of the system matrix dimensions constructed by the two models in the solving process, the system matrix construction of a hybrid light transmission model is a problem to be solved. We provided a new finite element mesh regrouping strategy-based hybrid light transport model for XLCT. Firstly, based on the finite element mesh regrouping strategy, two separate meshes can be obtained. Thus, for DE and SP N models, the system matrixes and source weight matrixes can be calculated separately in two respective mesh systems. Meanwhile, some parallel computation strategy can be combined with finite element mesh regrouping strategy to further save the system matrix calculation time. Then, the two system matrixes with different dimensions were coupled though repeated nodes were processed according to the hybrid boundary conditions, the two meshes were combined into a regrouping mesh, and the hybrid optical transmission model was established. In addition, the proposed method can reduce the computational memory consumption than the previously proposed hybrid light transport model achieving good balance between computational accuracy and efficiency. The forward numerical simulation results showed that the proposed method had better transmission accuracy and achieved a balance between efficiency and accuracy. The reverse simulation results showed that the proposed method had superior location accuracy, morphological recovery capability, and image contrast capability in source reconstruction. In-vivo experiments verified the practicability and effectiveness of the proposed method.