Optical Sensor Applications Research Articles

Synthesis of cubic and tetragonal Ba2SmTaO6 and their optical properties after Sr doping

Ba2–xSrxSmTaO6 has attracted great attention due to its excellent dielectric performance and abundant crystal structures. Recent studies find the reflectance of Sr–doped Ba2SmTaO6 (Ba2–xSrxSmTaO6) significantly changes with the transition between its varied phases, indicating the potential applications in optical sensors. However, its phase transition temperature (Tt) and the preparation process are not clear. In this work, the Tt between the cubic and tetragonal phases of Ba2SmTaO6 was firstly confirmed to be 533 K using self–consistent phonon theory (SCP). Combining the experimental and calculation methods, we found that the cubic and tetragonal phases of Ba2–xSrxSmTaO6 can be obtained by reacting at 1200 °C for 8 h and 1200 °C for 96 h with a low cooling rate of 2 °C/min, using the solid state reaction method, respectively. With characterizing the reflectance of different phase structures Ba2–xSrxSmTaO6, the largest reflectance difference between the tetragonal phase and cubic phase was found to be 59.22% at a wavelength of 1064 nm (wavelength commonly used in laser emitters) when x is 1.5, indicating it has great potential using in the optical sensor area. This research provides a guidance for the preparation of complex perovskite with different crystal structures of similar A2BB'O6 structure materials and is of great significance for the application of Ba2–xSrxSmTaO6 in optical sensors.

Low threshold photon avalanche upconversion emission for temperature sensing based on Yb(III)/Er(III) Co-doped NdVO4 with sphere 3D self-assembled structure microparticles

Upconversion luminescent microcrystals (UCMs) due to their optical characteristics have been applicated in temperature detecting fields. However, the accuracy of traditional temperature probes based on UCMs is limited by the low intensity of upconversion luminescence (UCL). Herein, Yb3+ and Er3+ ions co-doped NdVO4 (NdVO4:Yb/Er) UCMs with a 3D self-assembled structure were designed via a hydrothermal method. This innovative structure enables the realization of a photon avalanche (PA) emission process. The Yb3+ and Er3+ co-doping in NdVO4:Yb/Er UCMs significantly reduces the PA threshold compared to NdVO4:Er UCMs. Obvious PA process produced by Yb3+/Er3+ doping is observed at low excitation threshold (～13 mW) in NdVO4:Yb/Er UCMs, enhancing the whole UCL intensity. Additionally, the NdVO4:Yb/Er UCMs exhibit a high temperature sensitivity of 3.5% K−1 at low pump power, indicating that UCMs have the potential application in optical temperature sensor.

Effects of the change of isomers on room-temperature phosphorescence, thermally activated delayed fluorescence, and long persistent luminescence of organic hole-transporting materials with the selective potential for the application in electronic devices and optical sensors of oxygen

Competition of room-temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF) was investigated on the example of four newly synthesised organic isomeric compounds containing two electron-donating triphenylamine moieties and single electron-accepting dibenzothiophene-2-yl(phenyl)methanone unit by numerous theoretical and experimental approaches. The different emission origin (RTP or TADF) of the isomeric compounds was caused by the different energy gaps between the lowest singlet and triplet states locally exited and charge transfer in nature. Very different external quantum efficiencies ranging from 2.8 to 13.9% were observed for green phosphorescent organic light-emitting diodes fabricated using the isomeric compounds as the hosts. Such device efficiency differences were related to the different hole mobility values. The hole mobilities of ca. 1 × 10−3 cm2V−1s−1 were observed at an electric field of 6.4 × 105 V/cm for the derivatives having triphenylamine moieties at C-2, C-4, and at C-3, C-5 positions of the central benzene ring. Considerably lower hole mobilities of ca. 1 × 10−5 cm2 V−1 s−1 were recorded at the same electric field for the compounds with triphenylamine groups at C-2, C-3, and at C-2, C-6 positions. Depending to the great extent on RTP and TADF processes, different efficiencies of long persistent luminescence (LPL) of the exciplex-forming solid-state mixtures of the isomers and bis[2-(diphenylphosphine)phenyl] ether oxide (DPEPO) were detected. The compound with triphenylamine groups at C-3, and C-5 positions as RTP emitter and its molecular mixture with DPEPO as LPL emitter the active layers of optical sensors of oxygen were prepared. They showed the Stern–Volmer constant of 4.55 × 10−4 ppm in the range of oxygen concentrations up to 10000 ppm.

Application of hybrid Au@Ag nanostructures in fiber optic biosensor for rapid detection of C-reactive protein

Elevated levels of C-reactive protein (CRP) in the bloodstream are a well-established marker of systemic inflammation in humans. Research on the application of hybrid plasmon material for optical fiber sensor application to sensitively monitor C-reactive protein concentration based on the hybrid material particles has been proposed in this study. Specifically, Au@Ag nanoparticles are coated onto the optical fiber surface by a self-assembled monolayer using an NH2 bridge. CRP antigens are then immobilized onto the surface of Au@Ag NPs to selectively detect CRP and improve sensor sensitivity. The limit of detection for this fiber sensor is 2.4 × 10−5 mg/L. The selectivity of the sensor was also demonstrated in media containing bovine serum albumin (BSA) and glucose. These findings represent an important step toward the development of biosensors capable of monitoring extremely low concentrations of biomolecules in vivo, thereby supporting early disease detection and diagnosis.

Enhancement of the phase sensitivity with two-mode squeezed coherent state based on a Mach-Zehnder interferometer.

We theoretically study the phase estimation based on a Mach-Zehnder interferometer (MZI) with a two-mode squeezed coherent state. By maximizing the quantum Fisher information, we find that the quantum Cramér-Rao bounds (QCRB) can reach sub-Heisenberg limit under the phase-matched condition. The optimal phase sensitivity can reach the sub-shot noise limit (SNL) and approach the QCRB by employing the intensity difference detection. Meanwhile, compared with the MZI fed with a coherent plus a single-mode squeezed vacuum state, this scheme can have better performance by adjusting the squeezing parameter and the mean photon number. With the same parameter, our scheme shows more sensitive phase measurement than the SU(1,1) interferometer with a coherent plus a vacuum state. We also show that the phase sensitivity of our proposal can still reach the SNL when the loss of the photon is 36%. This scheme can provide potential applications in optical sensors.

Application of FWM-Based OFC for DWDM Optical Communication System with Embedded FBG Sensor Network

Abstract Four-wave mixing optical frequency comb fibre-based setups (FWM-OFCs) have the potential to improve the combined dense wavelength division multiplexed passive optical network (DWDM-PON) and fibre Bragg grating (FBG) temperature sensors network providing easier application, broader technological opportunities for network development, and energy efficiency by substituting a power-demanding laser array. In this research, OFCs are generated for the purpose of combined network application of DWDM-PON and FBG optical sensors. The paper also investigates compatibility scenarios with OFCs in such systems. The mathematical simulation model has been developed and the performance of FWM-OFC based 8-channel 50 GHz spaced non-return-to-zero on-off keying (NRZ-OOK) modulated DWDM-PON transmission system, operating at 50 km single-mode fibre (SMF) with a bit rate of at least 10 Gbps embedded with 7 FBG optical temperature sensors, has been studied. As it is shown, FWM application results in OFC source that has fluctuations of the individual comb tones of less than 3 dB in power, and with an extinction ratio of about 33 dB for operation range of 192.9–193.25 THz, acting as a unified light source for all the data transmission channels. Embedded FBG optical sensors network causes negligible 0.3 dB power penalty.

Noble-transition-metal dichalcogenides-emerging two-dimensional materials for sensor applications

In recent years, 2D noble-transition-metal dichalcogenides (NTMDs) have attracted significant attention for their unique structure and novel properties. Due to the almost full occupation of d orbitals, the 2D NTMDs exhibit strong layer-dependent and adjustable electronic structure and physical properties compared with other transition metal dichalcogenide materials. Therefore, the fascinating physical/chemical properties of 2D NTMDs, such as abundant valence electrons, high carrier mobility, and air stability, have afforded the materials with great prospects in application of optical, gas, and mechanical sensors. However, a comprehensive review on this topic is still missing. Herein, the recent progress in synthesis, characterization, functionalization, and application of 2D NTMDs in various sensors is discussed. Future prospects and perspectives of the emerging 2D NTMDs are proposed based on the existing research.

Upconversion luminescence and temperature sensing performance of Er3+ ions doped self-activated KYb(MoO4)2 phosphors

In this work, a series of self-activated KYb(MoO4)2 phosphors with various x at% Er3+ doping concentrations (x = 0.5, 1, 3, 5, 8, 10, 15) was synthesized by the solid-state reaction method. The phase structure of the as-prepared samples was analyzed by X-ray diffraction (XRD), XRD Rietveld refinement and Fourier transform infrared (FT-IR) spectroscopy. The as-prepared samples retain the orthorhombic structure with space group of Pbcn even Er3+ doping concentration up to 15 at%. High-purity upconversion (UC) green emission with green to red intensity ratio of 55 is observed from the as-prepared samples upon the excitation of 980 nm semiconductor laser and the optimum doping concentration of Er3+ ions in the self-activated KYb(MoO4)2 host is revealed as 3 at%. The strong green UC emission is confirmed as a two-photon process based on the power-dependent UC spectra. In addition, the fluorescence intensity ratios (FIRs) of the two thermally-coupled energy levels, namely 2H11/2 and 4S3/2, of Er3+ ions were investigated in the temperature region 300–570 K to evaluate the optical temperature sensor behavior of the sample. The maximum relative sensitivity (SR) is determined to be 0.0069 K−1 at 300 K and the absolute sensitivity (SA) is determined to be 0.0126 K−1 at 300 K. The SA of self-activated KYb(MoO4)2:Er3+ is almost twice that of traditional KY(MoO4)2:Er3+/Yb3+ codoping phosphor. The results demonstrate that Er3+ ions doped self-activated KYb(MoO4)2 phosphor has promising application in visible display, trademark security and optical temperature sensors.

Deep Learning for Optical Sensor Applications: A Review.

Over the past decade, deep learning (DL) has been applied in a large number of optical sensors applications. DL algorithms can improve the accuracy and reduce the noise level in optical sensors. Optical sensors are considered as a promising technology for modern intelligent sensing platforms. These sensors are widely used in process monitoring, quality prediction, pollution, defence, security, and many other applications. However, they suffer major challenges such as the large generated datasets and low processing speeds for these data, including the high cost of these sensors. These challenges can be mitigated by integrating DL systems with optical sensor technologies. This paper presents recent studies integrating DL algorithms with optical sensor applications. This paper also highlights several directions for DL algorithms that promise a considerable impact on use for optical sensor applications. Moreover, this study provides new directions for the future development of related research.

Multistimuli‐Responsive Luminescence of o‐Carborane Dyads via Restriction of Electron Transfer and Molecular Motion

AbstractThe striking change in the emission color/intensity of piezochromic luminescent materials in response to external mechanical stimuli (e.g., pressure, grinding, and stretching) has attracted attention due to potential applications in optical data storage devices, pressure sensors, and optoelectronic devices. The majority of organic materials show redshifted and quenched emission with increasing pressure. Herein, covalently linked donor/acceptor (D/A) o‐carborane dyads that exhibit dual luminescence peaks due to the occurrence of photoinduced electron transfer (PET) are reported. Interestingly, an anomalous phenomenon of pressure‐induced blueshifted and enhanced luminescence is clearly observed. From 1 atm to 1.09 GPa, the restriction of intramolecular motion increases the luminescence of o‐carborane dyads. At high pressures, the compressed o‐carborane unit suppresses PET and decreases the energy gap between the upper excited states. Since the rate of the internal conversion (IC) process is higher than that of PET, the charge transfer (CT) emission gradually disappears, causing the o‐carborane dyads to exhibit blueshifted luminescence. Therefore, a novel strategy for achieving the pressure‐induced enhanced and blueshifted luminescence characteristics of organic materials is reported in this work.

Photoluminescence and Temperature Sensing Properties of Bi3+/Sm3+ Co-Doped La2MgSnO6 Phosphor for Optical Thermometer

The optical temperature sensor utilizing the fluorescence intensity ratio (FIR) has garnered significant attention in the past few years due to its rapid response, robust anti-interference capability, remote control feature, and other advantages. In this study, the high-temperature solid-phase approach was used to fabricate a variety of double perovskite-structured La2MgSnO6: Bi3+, Sm3+ (LMS: Bi3+, Sm3+) phosphors. The Rietveld refinement data of XRD and the Gaussian fitting of the emission peak of LMS: 0.02Bi3+ phosphor indicated Bi3+ occupies three lattice sites. The calculation and analysis of average lifetime and energy transfer efficiency substantiated the presence of energy transfer from Bi3+ to Sm3+, with a transfer efficiency of up to 59.07%. The emission intensity of LMS: 0.02Bi3+, 0.05Sm3+ at 403 K maintains 50.2% at the condition of room temperature. The FIR fitting and calculation demonstrated that LMS: 0.02Bi3+, 0.05Sm3+ phosphor possessed good optical temperature sensitivity, with a maximum absolute sensitivity Sa-max of 0.0055 K−1 and a maximum relative sensitivity Sr-max of 0.88% K−1, demonstrating its valuable potential applications for optical temperature sensors.

Molecularly Imprinted Polymer-Based Biomimetic Systems for Sensing Environmental Contaminants, Biomarkers, and Bioimaging Applications

Molecularly imprinted polymers (MIPs), a biomimetic artificial receptor system inspired by the human body’s antibody-antigen reactions, have gained significant attraction in the area of sensor development applications, especially in the areas of medical, pharmaceutical, food quality control, and the environment. MIPs are found to enhance the sensitivity and specificity of typical optical and electrochemical sensors severalfold with their precise binding to the analytes of choice. In this review, different polymerization chemistries, strategies used in the synthesis of MIPs, and various factors influencing the imprinting parameters to achieve high-performing MIPs are explained in depth. This review also highlights the recent developments in the field, such as MIP-based nanocomposites through nanoscale imprinting, MIP-based thin layers through surface imprinting, and other latest advancements in the sensor field. Furthermore, the role of MIPs in enhancing the sensitivity and specificity of sensors, especially optical and electrochemical sensors, is elaborated. In the later part of the review, applications of MIP-based optical and electrochemical sensors for the detection of biomarkers, enzymes, bacteria, viruses, and various emerging micropollutants like pharmaceutical drugs, pesticides, and heavy metal ions are discussed in detail. Finally, MIP’s role in bioimaging applications is elucidated with a critical assessment of the future research directions for MIP-based biomimetic systems.

Modeled predictions of human-associated and fecal-indicator bacteria concentrations and loadings in the Menomonee River, Wisconsin using in-situ optical sensors.

Human sewage contamination of waterways is a major issue in the United States and throughout the world. Models were developed for estimation of two human-associated fecal-indicator and three general fecal-indicator bacteria (HIB and FIB) using in situ optical field-sensor data for estimating concentrations and loads of HIB and FIB and the extent of sewage contamination in the Menomonee River in Milwaukee, Wisconsin. Three commercially available optical sensor platforms were installed into an unfiltered custom-designed flow-through system along with a refrigerated automatic sampler at the Menomonee River sampling location. Ten-minute optical sensor measurements were made from November 2017 to December 2018 along with the collection of 153 flow-weighted discrete water samples (samples) for HIB, FIB, dissolved organic carbon (DOC), and optical properties of water. Of those 153 samples, 119 samples were from event-runoff periods, and 34 were collected during low-flow periods. Of the 119 event-runoff samples, 43 samples were from event-runoff combined sewer overflow (CSO) influenced periods (event-CSO periods). Models included optical sensor measurements as explanatory variables with a seasonal variable as an interaction term. In some cases, separate models for event-CSO periods and non CSO-periods generally improved model performance, as compared to using all the data combined for estimates of FIB and HIB. Therefore, the CSO and non-CSO models were used in final estimations for CSO and non-CSO time periods, respectively. Estimated continuous concentrations for all bacteria markers varied over six orders of magnitude during the study period. The greatest concentrations, loads, and proportion of sewage contamination occurred during event-runoff and event-CSO periods. Comparison to water quality standards and microbial risk assessment benchmarks indicated that estimated bacteria levels exceeded recreational water quality criteria between 34 and 96% of the entire monitoring period, highlighting the benefits of high-frequency monitoring compared to traditional grab sample collection. The application of optical sensors for estimation of HIB and FIB markers provided a thorough assessment of bacterial presence and human health risk in the Menomonee River.

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.

Effective splicing technique of different cladding diameter-based optical fibers and performance evaluation.

In this work, the fabrication and sensing performance of fusion structures based on single-mode fiber (SMF) and multimode fiber (MMF) with different cladding diameters are discussed, and the effects of different lengths of MMF and fiber etching on sensing performance are analyzed. First, the transmitted intensity measurement experiment is performed, and the results indicate that the performance of the SMF-MMF-SMF(SMS)-based structure is better for sensing purposes. In addition, the results demonstrate that the performance of etched fiber is better than that of non-etched fiber. The etched fiber structure with lower fiber diameters produces more evanescent waves and is better for sensing purposes. Therefore, the proposed structure has certain development potential as an application of future optical fiber sensors.

Optical fiber sensors in infrastructure monitoring: a comprehensive review

Abstract The purpose of this article is to review and further promote the application of optical fiber sensor technology in infrastructure monitoring. Compared with traditional sensors, optical fiber sensors have low maintenance costs and are small in size; consequently, they have gradually become a future development direction of sensors. This paper introduces the basic principles of several commonly used optical fiber sensors and the progress of optical fiber sensors in the monitoring of physical, mechanical, and chemical parameters and demonstrates the applications of optical fiber sensors in infrastructure.

Dynamically tunable single-/dual-band of the graphene absorber with a resonant asymmetric grating based on lithium niobate on insulator

We propose a tunable single-/dual-band of graphene absorber with a resonant asymmetric grating based on lithium niobate on insulator (LNOI). The single-/dual-band of the absorber can be dynamically switched by changing the incident angle, and the increase of the spacing between the two peaks reduces the crosstalk in adjacent channels as the incident angle increase. Meanwhile, the resonant wavelength is adjusted by applying a voltage to lithium niobate (LN), changing the refractive of LN. The wavelength shifts caused by a slight change in incident angle can be regulated back through the electro-optical effect of LN. Furthermore, the effects of the structural parameters and the incident angle on the bandwidth are investigated by the finite element method (FEM). This structure has promising applications in optical filters, sensors, thermal emitters, and spatial optical measurements.

Strong field enhancement and hot spot manipulation based on anapole state in Si disk-ring metasurface

In this work, a metasurface consisting of disk-ring Si nanostructures on a SiO2 substrate is proposed and numerically simulated. The Si disk-ring structure can excite and manipulate anapole state, and periodic array supports lattice resonance simultaneously, which can improve the near-field enhancement in the gap region. The maximum E-field enhancement can be up to 346 times, and a transmission dip with an ultra-narrow bandwidth of 0.34 nm and a Q-factor of 4460 is shown. When the central disk has an offset, the near-field enhancement can be affected. In the case of y-direction offset, the maximum E-field enhancement can be up to 468 times. The near field energy is concentrated in the gap region, easy to interact with probing molecule in surrounding environment. Meanwhile, the designed metasurface shows a sensing performance of 387 nm/RIU. The strong energy confinement and high Q-factor of the proposed structure give an opportunity to enhance the interaction between light and matter, which may have potential applications in nonlinear optics, optical sensors and surface enhanced Raman scattering.

Giant Switchable Persistent Photoconductivity in Soft Chemistry Reduced SrTiO3

AbstractHigh tunability of photoconductivity is highly desired for applications in optical memories, sensors, and bioelectronics. Recently, room temperature persistent photoconductivity (PPC) in SrTiO3 (STO) has been revealed and has attracted great attention. However, reversible switching of the PPC in STO with a large on/off ratio remains challenging to date. Here, a giant switchable PPC in soft chemistry reduced STO is reported. An initial insulator‐to‐metal transition with on/off ratio up to 7 orders of magnitude is observed and about 5 orders of magnitude transition is found to be reversible. Via nuclear magnetic resonance measurements, it is uncovered that such unusual PPC is driven by the generation of excess carriers accompanied with a configuration evolution of the incorporated hydrogen from hydridic HO+ to protic Hi+ upon illumination. The work demonstrates giant switchable PPC transition in soft chemistry reduced perovskite oxides, providing a new platform for pursuing high performance sensors and nonvolatile optoelectronic memory devices.

Evolutionary selection growth of silver films for low-loss nanophotonic devices

When talking about nanophotonics, quantum computing and sensing high-quality factor plasmonic devices are playing crucial role. In most cases for making such devices one has to use non-lattice matched or transparent amorphous substrates. Plasmonic devices quality factor is mainly determined by ohmic losses, scattering losses at grain boundaries, and in-plane plasmonic scattering losses of a metal – substrate system. We demonstrate here the e-beam evaporation method to deposit ultralow-loss silver thin films on transparent lattice-mismatched substrates. This process corresponds to evolutionary selection growth mode. The key feature of our approach is a precise control during the whole process consisting of film deposition on a cold substrate, self-crystallization and subsequent annealing for stress relaxation. In particular, the stress relaxation leads to further grains growth. We are able to deposit 100 nm thick polycrystalline silver films with micrometer-scale grains, low roughness and ultralow optical losses. Finally, we show ultrahigh-quality factor plasmonic silver nanostructures on transparent lattice-mismatched substrate. This can be of the great interest for high performance and single-molecule optical sensors applications.