Resonance Wavelength Shift Research Articles

Improved Resolution of Temperature Sensor Using Fast and Slow Light in a Fiber Resonator

A novel scheme for improving the resolution of temperature sensor using fast and slow light in a fiber resonator is proposed and demonstrated experimentally. In the measurement system, the shift of resonance wavelength produced by the temperature change can be converted into strong variations of delay time. By measuring the delay time, this sensor we proposed has high-temperature sensitivity. Different from the traditional method of tracing spectrum, the temperature detection is carried out using an oscilloscope, which results in the sensor with fast response and high resolution. Moreover, the sensitivity, resolution, and measurement range of the sensor can be easily tuned by changing the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}$ </tex-math></inline-formula> -factor of the resonator. Using this approach, we demonstrate temperature measurements at fiber resonators with low- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}$ </tex-math></inline-formula> and high- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}$ </tex-math></inline-formula> , respectively, as well as a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.76\times 10^{-{4}}\,\,^{\circ }\text{C}$ </tex-math></inline-formula> resolution and a 2706 ns/°C sensitivity of temperature sensing are obtained. The scheme is simple in structure and easy to implement, which is particularly suitable for detecting very small temperature changes.

Graphene-Coated Twisted Taper for Highly Sensitive Sensing and All-Optical Modulation

An ultracompact graphene-coated twisted silica taper is fabricated and applied for highly sensitive sensing and all-optical modulation. The coated graphene is used as functional material with excellent optical properties, such as fast thermal response to enhance the temperature sensing and surface plasmon polariton (SPP) effect to produce and confine more propagating modes in the twisted taper. Therefore, the enhanced multimode interference further improves the optical sensitivities as used for temperature and strain sensings. High sensitivities of −127.2 pm/°C for temperature sensing and −173.9 pm/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \varepsilon $ </tex-math></inline-formula> for tensile strain sensing are observed in sequence, comparatively, along with those sensitivities of only −73.7 pm/°C and −163.5 pm/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \varepsilon $ </tex-math></inline-formula> for the twisted taper without coated graphene. Furthermore, all-optical modulation of the proposed taper is also investigated, showing a resonant wavelength shift of about 0.9 nm with a pump wavelength of 1470 nm and a power of 2.07 mW, while nearly no wavelength shift for the comparative case without coated graphene.

Label-Free cancer cell biosensor based on photonic crystal ring resonator

A photonic crystal (PhC) biosensor is a compact device, which detects the changes of characteristic of the light due to binding the sample by the analyte. In this paper; we propose using ring resonator in two-dimensional (2D) photonic crystal biosensor. A periodic array of silicon rods with the refractive index of n = 3.46 in the air bacground formed a cubic lattice structure. The sensing mechanism occures when the the resonant wavelength shifts due to change in the the refractive index of analytes. The transmission spectrum shifts about 4.47 nm to the higher wavelengths by increasing the refractive index of analyte. This mechanism can recognize the normal, and cancerous cells. The average values of sensitivity, quality factor, FOM, and transmission for the designed structure are 308.5 (nm/RIU), 3803.55, 848.06 RIU-1 and 98.78 %, respectively. The reported structure has high quality promising applications for highly sensitive label-free optical biosensors.

Radiation Sensitive Long-Period Fiber Grating Based on Tb-Doped Silica Fiber

We demonstrate a radiation sensitive long-period fiber grating (LPG) based on terbium (Tb)-doped silica fiber, fabricated by dual-sided CO2 laser exposure. At a total dose of 6.0 ± 0.2 kGy of gamma radiation, the maximum radiation-induced resonance wavelength shift (RIRWS) of LPG in Tb-doped silica fiber is up to 3.98 nm, which is much higher than that of 1.14 nm in standard single-mode fiber. To characterize the degree of modification of fibers by radiation, we calculate the radiation-induced refractive index change (RIRIC), which is as high as <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.05\times 10^{-5}$ </tex-math></inline-formula> for Tb-doped silica fiber, approximately 276.3% of that of standard single-mode fiber. In addition, the growth of RIRWS with increasing cladding mode order is analyzed, and the theoretical and experimental RIRWS of LPG are compared. This new type of LPG has great promise in the field of high-dose radiation sensing, such as dose monitoring in nuclear reactors, particle collision experiments, and so on.

Colorimetric Plasmonic Hydrogen Gas Sensor Based on One-Dimensional Nano-Gratings

Plasmonic hydrogen gas sensors have become widely used in recent years due to their low cost, reliability, safety, and measurement accuracy. In this paper, we designed, optimized, and fabricated a palladium (Pd)-coated nano-grating-based plasmonic hydrogen gas sensor; and investigated using the finite-difference time-domain method and experimental spectral reflectance measurements, the calibrated effects of hydrogen gas exposure on the mechano-optical properties of the Pd sensing layer. The nanostructures were fabricated using DC sputter deposition onto a one-dimensional nano-grating optimized with a thin-film gold buffer to extend the optical response dynamic range and performance stability; the color change sensitivity of the Pd surface layer was demonstrated for hydrogen gas concentrations as low as 0.5 vol.%, up to 4 vol.%, based on the resonance wavelength shift within the visible band corresponding to the reversible phase transformation. Visual color change detection of even the smallest hydrogen concentrations indicated the high sensitivity of the gas sensor. Our technique has potential for application to high-accuracy portable plasmonic sensors compatible with biochemical sensing with smartphones.

Polyacrylic Acid/Polyaniline-Coated Multimode Interferometer for Ammonia Detection.

A coaxial optical fiber interferometer (COFI) is proposed here for ammonia sensing, which comprises two light-carrying single-mode fibers (SMF) fused to a section of no-core fiber (NCF), thus forming an optical interferometer. The outer surface of the COFI is coated with a layer of polyacrylic acid (PAA)/polyaniline (PAni) film. The refractive index (RI) of the sensitive layer varies when PAA/PAni interacts with ammonia, which leads to the resonance wavelength shift. The surface morphology and structure of the PAA/PAni composites were characterized by using a scanning electron microscope (SEM) and Fourier-transform infrared (FTIR) spectroscopy. When the sensor was exposed to an ammonia atmosphere of different concentrations at room temperature, the sensing performance of the PAA/PAni composite film was superior to that of a sensitive film formed by single-component PAA or PAni. According to the experimental results, the composite film formed by 5 wt% PAA mixed with 2 wt% PAni shows better performance when used for ammonia sensing. A maximum sensitivity of 9.8 pm/ppm was obtained under the ammonia concentration of 50 ppm. In addition, the sensor shows good performance in response time (100 s) and recovery time (180 s) and has good stability and selectivity. The proposed optical fiber ammonia sensor is adapted to monitor leakage in its production, storage, transportation, and application.

Highly Sensitive Plasmonic Sensor with Au Bow Tie Nanoantennas on SiO2 Nanopillar Arrays

We report on plasmonic sensors based on arrays of metallic bow tie nanoantennas with high sensitivity and an enhanced figure of merit. In the present sensing device, each gold nanoantenna is positioned on the upper surface of a SiO2 nanopillar that is placed on a quartz substrate. The presence of the nanopillar significantly reduces the coupling of the enhanced electromagnetic field generated at the plasmon resonance to the substrate. The simulated results show that the sensitivity of the device to refractive index sensing is 612 nm/RIU, calculated by the resonance wavelength shift per refractive index unit due to the change in the ambient medium index, while the full width at half maximum is calculated at around 10 nm with a figure of merit of 61. The proposed sensor thus has a great potential for sensing and detection applications.

Thermo-optic phase shifter based on amorphous silicon carbide

We report the preliminary experimental results for an amorphous silicon carbide (a-SiC) thermo-optic phase shifter (TOPS). This device is based on microring resonator (MRR) structure with a titanium (Ti) heater placed on the top of the device, separated by 1.5 μm thick SiO2 to reduce the optical loss. The proposed a-SiC microring has a thickness and a radius of 1.1 μm and 33 μm, respectively. By applying an electrical power in the Ti heater, a resonance wavelength shift at an optical wavelength of λ=1550 nm is shown, and the extracted thermal tunability is 52.2 pm/mW.

Quantitative Insights into a Plasmonic Ruler Equation from the Perspective of Enhanced Near Field.

The plasmonic shift of resonance wavelength induced by near-field coupling enables one to measure nanoscale distances optically. Empirically, the well-known ruler equation correlating plasmon shift with interparticle spacing was proposed. Though it has been widely used in analyzing simulation and experimental outcomes, little is known about the underlying physical mechanism of the characteristic exponential form of the plasmon ruler equation and the universal decay constant therein. In this work, we attempt to decrypt these from the perspective of plasmon near-field enhancement. Based on an analytical quasi-normal mode formula for plasmon shifts, we proved that the exponential decaying electric field is the critical reason that results in the exponential form of the plasmon ruler equation and quantitatively, we found that the universal decay constant in the plasmon ruler equation actually reflects the range of the enhanced near field. This work hopefully helps to deepen the understanding of the mechanism of light-matter interaction in corresponding plasmonic processes.

Multiparametric Guided-Mode Resonance Biosensor Monitoring Bulk and Surface-Film Variations

A guided-mode resonance (GMR) sensor with multiple resonant modes is used to measure the collection of biomolecules on the sensor surface and the index of refraction of the sensor environment (bulk). The number of sensor variables that can be monitored (biolayer index of refraction, biolayer thickness, and bulk, or background, index of refraction) is determined by the number of supported resonant modes that are sensitive to changes in these variable values. The sensor we use has a grating and homogeneous layer, both of which are made of silicon nitride (Si3N4), on a quartz substrate. In this work, we simulate the sensor reflection response as a biolayer grows on the sensor surface at thicknesses from 0 to 20 nm and biolayer indices of refraction from 1.334 to 1.43 RIU; simultaneously, we vary the bulk index of refraction from 1.334 to 1.43 RIU. In the specified span of sensor variable values, the resonance wavelength shifts for 2023 permutations of the biolayer index of refraction, biolayer thickness, and bulk index of refraction are calculated and accurately inverted. Inversion is the process of taking resonant wavelength shifts, for resonant modes of a sensor, as input, and finding a quantitative variation of sensor variables as output. Analysis of the spectral data is performed programmatically with MATLAB. Using experimentally measured resonant wavelength shifts, changes in the values of biolayer index of refraction, biolayer thickness, and bulk index of refraction are determined. In a model experiment, we deposit Concanavalin A (Con A) on our sensor and subsequently deposit yeast, which preferentially bonds to Con A. A unique contribution of our work is that biolayer index and biolayer thickness are simultaneously determined.

Low Temperature Sensor Based on Etched LPFG with Different Materials Coating

A low temperature sensor based on etched Long Period Fiber Grating LPFG is proposed and demonstrated. A chemically etched LPFG sensor coated with (Indium In, Aluminum Al, Silver Ag, Palladium Pd and Titanium Ti) embedded within a build low temperature setup. The sensor investigation was carried out under temperature range of 20℃ to -150℃; and the resonance wavelength shift was collected with different cooling rates of (10, 15, 20, 25℃/min) in order to investigate the effect of cooling rates on the sensor performance. However, the experimental results show that 10 mm LPFG sensor with grating period of 400 µm offer temperature sensitivity of 1.5 times, 2 times, 2.5 times, 3 times and 3.5 times higher than bare LPFG for Ti-coated LPFG, Pd-coated LPFG, Ag-coated LPFG, Al-coated LPFG and In-coated LPFG respectively. The maximum measuring error is less than ±0.5℃, which confirms the effectively using of LPFG sensor in cryogenic application. Moreover, the overall resonance wavelength shifts are 1.213 nm, 1.532 nm, 1.935 nm, 2.015 nm, 2.397 nm and 2.671 for bare LPFG, Ti-coated LPFG, Pd-coated LPFG, Ag-coated LPFG, Al-coated LPFG and In-coated LPFG sensors respectively. According to the cooling rates, the results illustrate that as cooling rate increase, the sensor sensitivity decrease due to the sensor response. For more investigations, simulation work is carried out using MATLAB and the sensor shows a good agreement results between experimental and simulation measurements. It is worth to mention that the main findings will essentially contribute to choose suitable materials for coating LPFG for low temperature sensing purposes and will increase the existing knowledge about optical fiber sensor applications.

Protein conformation characterization via a silicon resonator-based optical sensor based on the combination of wavelength interrogation and dual polarization detection.

Protein conformational abnormality causes cell malfunction. Conformational change of amyloid protein causes neuron malfunction, which renders "protein conformational disease" Alzheimer's disease. Dual polarization interferometry enables to provide one-dimensional structure of a protein biolayer via deconvolution of interference patterns, which in turn is interpreted as the protein molecule conformation. However, it is still challenging to avoid interference patterns becoming faint and obscure sometimes. Resonance wavelength response to the biolayer structure can achieve a very low detection limit due to inherent high Q factor of an optical resonator. Here, we introduce the concept of combining dual polarization detection with wavelength interrogation via a simple and compact resonator-based optical biosensor. Biolayer were probed by the wave of dual polarization and its opto-geometrical parameters were resolved into resonance wavelength shift. Because protein molecule with distinct conformation produced a biolayer with unique thickness and mass density. Amyloid proteins in monomeric and dimeric morphology were respectively characterized. This concept enables protein conformation characterization in an easy and direct paradigm and provides a desirable sensing performance due to sensitive resonance response in the form of the sharp resonance profile occurring in a nonoverlapping spectrum.

Multifield Coupling of Local Surface Plasmon Resonance‐Assisted Au–TiO2 Photocatalysis Considering Bimodal Resonance and Superposition Effect

This study concerns the improvement of the synergetic catalytic efficiency of Au–TiO2 nanorods considering the local surface plasmon resonance (LSPR) effect of different Au nanoparticles (NPs). The absorption spectrum and selective absorption efficiency for visible light, the local electric field, and the generated thermal effect are specifically analyzed based on the multifield decoupling of LSPR‐assisted Au–TiO2 catalysts. The simulation results show that the extinction spectra of both spherical and ellipsoidal Au particles are consistent with the experimental data. Interestingly, the latter is characterized by significant bimodal resonance modes. Comparatively, the simulation results show that the longitudinal mode, which is sensitive to the aspect ratio, is more favorable for the improvement of the photocatalytic activities. It is found that the resonance peaks are highly controllable, and are linear to the particle size and aspect ratio. Meanwhile, the electric field mode of TiO2 is significantly increased under the resonance wavelength. It is worth mentioning that the superposition effect makes a non‐negligible impact on the actual catalysts, leading to a relative shift of resonance wavelength. The consideration of the hot spots caused by the superposition effect influence the photocatalytic results significantly, providing values in diminishing the inadaptability of the theory in near‐touching regions of plasma particles.

Highly sensitive balloon-like fiber interferometer based on GO nanomaterial coated for humidity measurement

A highly sensitive balloon-like fiber interferometer based on Graphene Oxide (GO) nanomaterial coated for humidity measurement is proposed in this paper. The Mach-Zehnder interferometer (MZI) is formed by bending single-mode optical fiber. Then GO nanomaterials, which are sensitive to environmental humidity, are coated in the sensing region of the balloon-like fiber interferometer by physical deposition method. When ambient environmental relative humidity (RH) changes, GO nanomaterials will interact with water molecules, thus changing the refractive index (RI) around the sensing region of the balloon-like fiber interferometer, resulting in the shift of resonant wavelength. The measurement of different RH in the environment can be realized by evaluating the spectral drift. By comparing the RH sensitivity of the balloon-like fiber structure with different sensitive lengths, it can be found that the RH sensitivity of the balloon-like fiber structure is enhanced with the increase of the sensitive length. The experimental results of thickness optimization show that when the thickness of GO nanomaterial coating is about 250 nm, the sensitivity of 0.449 nm/%RH with a linearity of 0.992 can be achieved in the range of low humidity (less than 50 %RH). The response time and recovery time are about 4.8 s and 7.8 s. Moreover, the temperature sensitivity of the sensing structure with 250 nm GO nanomaterial is 0.102 nm/°C. Compared with the sensing structure without GO nanomaterial, the cross-influence of temperature can be effectively reduced by GO nanomaterial coating, so as to be better applied to humidity measurement. The balloon-like fiber sensors coated with GO nanomaterial possess good repeatability and stability, and offer broad application prospects for RH monitoring such as in the fields of biochemistry and medicine in the future.

Optimum Design of Surface Plasmon Resonance (SPR) Tapered Fiber Optic Biosensing Probe With Graphene–MoS2 Over Layers for DNA Hybridization

A novel graphene/MoS2-coated tapered fiber optic surface plasmon resonance (SPR) biosensing probe is presented for the first time to analyze the deoxyribonucleic acid (DNA) hybridization working in the near-infrared region (IR) of the electromagnetic spectrum with improved performance. A proper optimization mechanism is devised to study DNA hybridization concerning the taper ratio. A transfer matrix method (TMM) has been envisaged to study various performance parameters such as the figure of merit (F.O.M.), detection accuracy (D.A.), full width at half maximum (FWHM), and sensitivity. The proposed biosensor is very effectively able to distinguish between DNA hybridization and single-nucleotide polymorphisms (SNPs) by observing a considerable shift in SPR resonance wavelength and transmission dip. Due to the effect of optimized graphene/MoS2 nanostructured and tapering section of fiber, the proposed SPR biosensor work in the near-IR region is very much advantageous for further scope of sensing technology.

Design and Implementation of a Dual-Region Self-Referencing Fiber-Optic Surface Plasmon Resonance Biosensor.

The need for self-referencing is extremely important in the field of biosensing. In this manuscript, we report on the study, design, and validation of a dual-region self-referencing fiber-optic surface plasmon resonance biosensor. One region is intended to measure and monitor the binding events of the biological sample under test, while the other one is designed to be used as a reference channel to compensate for external factors, such as bulk refractive index modifications and temperature oscillations, that can negatively affect the biomolecular interaction measurement. Two different configurations for the biosensor probe are presented and investigated here, both theoretically and experimentally. First, the theoretical performance of the proposed biosensor probes, in terms of surface plasmon resonance wavelength shift, was simulated using a numerical model. Afterward, they were experimentally validated in sucrose-water solutions and showed a response to refractive index and temperature changes with sensitivities up to 2000 nm/RIU and 1.559 nm/°C, respectively. Finally, an aptamer-based bioassay and a high-resolution melting assay were successfully implemented on the two proposed configurations, demonstrating the feasibility of analyzing the binding events and measuring other external signal modifications simultaneously using the same biosensor probe.

Integrating Vernier spectrum with Fano resonance for high sensitivity of an all-optical sensor

Vernier and Fano resonances are promising approaches for enhancing the sensitivity of an all-optical sensor. A theoretical analysis was performed to integrate a Fano-like resonance shape with a Vernier resonance by considering the presence of partially reflective end facets at a double microring resonator waveguide. The system was developed based on scattering matrix and optical transfer function. The all-pass racetrack microring resonator (ARMRR) and the double racetrack microring resonator (DRMRR) were compared with and without the end facet at the waveguide to analyze the dynamic change of the output resonance spectrum. The spectrum was analyzed based on the free spectral range and resonance pattern. The resonator systems were applied to a refractive index-based sensing protocol, which was operated by a resonance wavelength shift with a refractive index change. The sensitivity was optimized by varying the configuration parameters such as the radius of the ring, the distance between the end facet, and the coupling coefficients. Integrating Vernier spectrum with Fano resonance improved the sensitivity for ARMRR configuration by 5.16% and the sensitivity for DRMRR configuration by 6.31%. The recorded limit of detection (LOD) of the DRMRR was 3.30 × 10-5.

Suppressing the spectral shift of a polarization-independent nanostructure with multiple resonances.

Resonances are the cornerstone of photonic applications in many areas of physics and engineering. The spectral position of a photonic resonance is dominated by the structure design. Here, we devise a polarization-independent plasmonic structure comprising nanoantennas with two resonances on an epsilon-near-zero (ENZ) substrate in order to loosen this correlation to obtain less sensitivity to geometrical perturbations of the structure. Compared with the bare glass substrate, the designed plasmonic nanoantennas on an ENZ substrate exhibit a nearly three-fold reduction only in the resonance wavelength shift near the ENZ wavelength as a function of antenna length.

Optical fiber hydrogen sensor based on self-assembled PDMS/Pd-WO3 microbottle resonator

In this paper, a new optical fiber hydrogen(H2) sensor based on a self-assembled microbottle resonator was proposed. The self-assembled microbottle was simply obtained by coating the single-mode fiber (SMF) with an internal composite material layer of palladium-tungsten trioxide (Pd-WO3) that was sensitive to H2 and an outer organic polymer material layer of polydimethylsiloxane (PDMS) with a significant thermal response. The microbottle resonator was further fabricated by coupling a tapered fiber with the self-assembled microbottle to excite whispering gallery mode (WGM). When the WGM resonator is exposed to H2, H2 molecules penetrate the PDMS and undergo redox reaction with the Pd-WO3. After the PDMS absorbs the reaction heat, its volume and refractive index will change, along with the wavelength shift of the WGM resonator. Therefore, a simple and low-cost H2 sensor is realized by observing the shift of resonance wavelength. Experimental results showed that the hydrogen sensor had a maximum sensitivity of − 3.091 nm/% at 25 ℃. And the resonance wavelength just shifted a small distance when the relative humidity increased from 22.87 % to 84.59 % or the temperature rose from 20.2 ℃ to 30 ℃, which indicated the sensor had preferable resistance to disturbances of external humidity and temperature.

Surface plasmon resonance sensor based on MXene coated PCF for detecting the cancer cells with machine learning approach

This article presents a highly sensitive gold/Ti3C2Tx coated photonic crystal fiber (PCF)-based surface plasmon resonance (SPR) sensor for cancer cells detection. The hybrid gold/Ti3C2Tx layer is coated circularly over PCF for occurrence of SPR by coupled mode theory. The simulations and numerical analysis are done by the finite element method. The resonance wavelength shift is measured between normal and cancerous cell samples to estimate the wavelength sensitivity and resolution. In results, the maximum wavelength sensitivity for breast cancer MCF-7 cells is achieved as 10,714 nm/RIU in x-polarization mode and 13,071 nm/RIU in y-polarization mode with very low resolution of 10−6 RIU. The impact of the MXene (Ti3C2Tx) thin film on sensitivity is also observed. In addition, the optimization of parametric variation is analyzed with machine learning technique with low mean squared error of 0.01525. <2% error is obtained in sensitivity analysis with multilayer perceptron regressor. Due to the advanced results and machine learning application, this sensor can be used as a fast, efficient and low-cost cancer disease detection device.