Resonance Wavelength Shift Research Articles

Magnetic Field Sensing Based on Whispering Gallery Mode with Nanostructured Magnetic Fluid-Infiltrated Photonic Crystal Fiber.

A kind of novel and compact magnetic field sensor has been proposed and investigated experimentally. The proposed sensor consists of a tapered single mode fiber coupled with a nanostructured magnetic fluid-infiltrated photonic crystal fiber, which is easy to be fabricated. The response of magnetic fluid to magnetic field is used to measure the intensity of magnetic field via whispering gallery mode. The magnetic field-dependent shift in resonance wavelength is observed. The maximum magnetic field intensity sensitivity is 53 pm/mT. The sensor sensitivity is inversely proportional to the thickness of the photonic crystal fiber cladding.

Optofluidic conical microresonator for precise displacement sensing

In the present work we report fabrication of a compact optical displacement sensor based on whispering gallery mode with common materials on Polydimethylsiloxane (PDMS) medium with mold master technique. Conical and hollow geometry of microcavity filled with Rhodamine B-doped Glycerol as active medium. The fabricated device can be utilized for sensing applications. Coupling junction can be tuned so that moving the conical microcavity of about 100 μm in the axial direction is equivalent to ∼1.5 nm shift in resonant wavelength. Also, a small change in concentration of active medium results in a shift in the resonant wavelength which provides the feasibility of sensing the refractive index. The proposed structure demonstrates the ability of considerably high-resolution sensing for fine displacement steps which is limited by the resolution of the spectrometer (0.6 nm).

Monitoring and identifying pendant droplets in microbottle resonators

Optofluidic resonators are capable of characterizing various fluidic media. Here, we propose an optofluidic microbottle resonator (OFMBR) that is applied to generate pendant droplets, whose maximum mass is related to the liquid surface tension. Mass and type of droplets forming along the OFMBR stem can be monitored in real time by spectrum variation. As a pendant droplet grows, increased droplet gravity introduces a decreased coupling gap and compressive force between the tapered fiber and OFMBR, leading to a resonance wavelength shift. The operation mechanism of the proposed sensors is validated by theoretical simulation and experimental results. From the experimental spectra, a liquid mass sensor with maximum sensitivity of − 3.34 pm / mg is obtained, and distilled water and alcohol can be identified. This scheme provides a new thread for droplet generation as well as fluidic properties characterization.

Monolithic Silicon-Based Photovoltaic-Nanoplasmonic Biosensor With Enhanced Limit of Detection and Minimum Detectable Power

On-chip, fully integrated electrical readout nanoplasmonic biosensors are suitable technology for the increasing demands of compact, portable, cost-efficient, and sensitive biosensors. In this paper, an ultra-compact photonic biosensor based on plasmonic nanostructure integrated with a PIN photovoltaic detector in a single chip is presented. The refractive index of different biosamples results in a shift in the surface plasmon resonance wavelength of the biosensor, and the PIN photovoltaic detector measures the intensity of transmitted light from the photonic structure at the plasmonic resonance wavelength. The biosensor shows a linear optical response of 354 nm/RIU and electrical sensitivity of about 16.9 mA/W.RIU for a wide range of biosamples. The PIN photovoltaic ultra-low dark current enables an extremely desirable limit of detection of 3 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−8</sup> RIU and minimum detectable power of −54 dBm for the biosensor. Moreover, a simple light-emitting diode is used as the light source in the biosensor's structure, which reduces its complexity and price by eliminating any extra optical setups and beam shapers. The presented structure is an important step forward for the realization of practical and handheld lab-on-chip nanophotonic biosensors, which leads to eliminating large clinical laboratories.

LNOI photonic wire switch based on phase transition material

An on-chip switch based on lithium-niobate-on-insulator (LNOI) photonic wire (PW) is proposed. The switch consists of a pulley LNOI PW and a microring resonator (MRR) coupled with a 160° LNOI PW arc loaded with a temperature phase transition material (PTM). A pulley PW is adopted to promote coupling efficiency. The PTM is used to control the mode guided in the MRR and realize the switching function by utilizing its amorphous and crystalline states. As the PTM is in the amorphous state, the coupling between the PTM-loaded LNOI PW arc and the MRR occurs, resulting in that mode in the MRR is destructive and cannot keep resonant, the light power in the pulley LNOI PW has little loss, and hence the switching on is realized. As the PTM is crystalline, the coupling does not happen due to phase mismatch. The mode in the MRR keeps constructive and resonant. As a result, light power is highly lossy there and the switch is off. We have carried out design and optimization of the proposed device, and presented an optimal geometry. The study shows that the optimal device has a smaller size of 24 × 23 μm2 and excellent switching performances, including larger extinction ratio of 14.2 dB, lower insertion loss of 1.8 dB in the state of switching on, and smaller shift of resonance wavelength < 0.5 nm in the conversion procedure of the on/off state. The ultra-compact device may find its application in on-chip high-density photonic integrated circuits.

Field-Effect Transistor with a Plasmonic Fiber Optic Gate Electrode as a Multivariable Biosensor Device.

A novel multivariable system, combining a transistor with fiber optic-based surface plasmon resonance spectroscopy with the gate electrode simultaneously acting as the fiber optic sensor surface, is reported. The dual-mode sensor allows for discrimination of mass and charge contributions for binding assays on the same sensor surface. Furthermore, we optimize the sensor geometry by investigating the influence of the fiber area to transistor channel area ratio and distance. We show that larger fiber optic tip diameters are favorable for electronic and optical signals and demonstrate the reversibility of plasmon resonance wavelength shifts after electric field application. As a proof of principle, a layer-by-layer assembly of polyelectrolytes is performed to benchmark the system against multivariable sensing platforms with planar surface plasmon resonance configurations. Furthermore, the biosensing performance is assessed using a thrombin binding assay with surface-immobilized aptamers as receptors, allowing for the detection of medically relevant thrombin concentrations.

Micro-Tapered Fiber Few-Mode Interferometers Incorporated by Molecule Self-Assembly Fiber Grating for Temperature Sensing Applications

We demonstrate fiber few-mode interferometers based on a self-assembly surface corrugated grating using charged nano-particles. Initially, an abrupt taper (AT) was first created using a micro flame. The AT was then further outwardly stretched to make an elongated uniformed taper until the tapered diameter achieved a micron scale. The high order core modes (HOCMs) were excited at the AT and the optical path difference (OPD) among the modes was enlarged through the uniformed taper to achieve the few-mode interference effects seen. However, to significantly enhance the interference effects with higher extinction ratios (ER) over such a short length of interferometer, an external assisted grating was made using charged nanoparticles to form surface corrugated grating with a period, Λ, of approximately 14 μm. This intermediate period of the fiber grating was helpful in scattering and attenuating some unwanted high-order modes to change the optical characteristics of the few-mode interferometer (FMI). This FMI with a self-assembly fiber grating (SAFG) was further used to make fiber temperature sensors, with a maximum resonant wavelength shift of 4.6 nm, over a temperature range from 20–60 °C. The temperature sensitivity achieved was 112.6 pm/°C and the coefficient of determination, R2, was as high as 0.99, which revealed the high linearity of the results.

Wavelength-Tunable Vortex Beam Emitter Based on Silicon Micro-Ring with PN Depletion Diode.

Herein we propose a design of a wavelength-tunable integrated vortex beam emitter based on the silicon-on-insulator platform. The emitter is implemented using a PN-depletion diode inside a microring resonator with the emitting hole grating that was used to produce a vortex beam. The resonance wavelengths can be shifted due to the refractive index change associated with the free plasma dispersion effect. Obtained numerical modeling results confirm the efficiency of the proposed approach, providing a resonance wavelength shift while maintaining the required topological charge of the emitted vortex beam. It is known that optical vortices got a lot of attention due to extensive telecommunication and biochemical applications, but also, they have revealed some beneficial use cases in sensors. Flexibility in spectral tuning demonstrated by the proposed device can significantly improve the accuracy of sensors based on fiber Bragg gratings. Moreover, we demonstrate that the proposed device can provide a displacement of the resonance by the value of the free spectral range of the ring resonator, which means the possibility to implement an ultra-fast orbital angular momentum (de)multiplexing or modulation.

Highly Sensitive Refractive Index-Based Sensor for DNA Hybridization Using Subwavelength Grating Waveguide

A biosensor for detecting DNA hybridization via refractive index sensing has been demonstrated using a subwavelength grating (SWG) waveguide. Waveguide dimensions are selected by parametric optimizations to increase the mode-analyte overlap with considerations of typical silicon-on-insulator fabrications technology. DNA layer is added with a linker layer on silicon pillars of the SWG waveguide to optimize and detect the DNA hybridization. Some essential characteristics such as mode overlap factor, change in effective refractive index, waveguide sensitivity, and shift in resonance wavelength are computed for the different dimensional parameters of the SWG waveguide in DNA hybridization along with mode field intensity and normalized power using the finite element method. The DNA hybridization is shown by variation in normalized power of interacting light in cladding region of the waveguide for 0% to 100% fractional change of dsDNA and ssDNA. Waveguide sensitivity, shift in resonance wavelength, device sensitivity, and intrinsic limit of detection are obtained to ∼ 0.157, 7.01, 605 nm/RIU, and 1.30 × 10−4 RIU, respectively, for the optimized structure of SWG waveguide in sensing of DNA hybridization, which could be suitable aspects for detecting DNA hybridization.

Strain measurements by FBG-based sensors embedded in various materials manufactured by different technological processes

The paper presents a study devoted to the registration and analysis of experimental results obtained from fiber-optic sensors based on Bragg gratings embedded in samples made of various materials at the technological stage of their manufacture. As the materials into which the fiber-optic sensors were embedded, such polymeric materials as epoxy resin, poured plastic, thermoplastics used in 3D printing, as well as an important structural material - cement were considered. The evolution of the reflected spectra of fiber-optic sensors based on Bragg gratings and the measured resonant wavelength shift are shown during the technological processes of fabrication and under loading of finished samples in different directions relative to sensor orientation axis. The paper notes the features associated with the embedment of fiber-optic sensors in various materials, which must be taken into account to ensure the sensor integrity. Recommendations are given for the embedment of fiber-optic sensors into the material to improve the operability of the sensors.

A combined fiber sensor for simultaneous measurement of directional torsion and displacement

A combined sensor for simultaneous measurement of directional torsion and displacement is proposed and experimentally demonstrated. The sensor is constructed with a helical long-period fiber grating (H-LPG) and an air-cavity fiber-optic Fabry–Perot interferometer (FPI) in series. By investigating the resonant wavelength shift of the H-LPG and the FSR variation of the FPI in the transmission spectra of the sensor, the applied torsion and displacement can be unambiguously discriminated and determined simultaneously. The experimental results show that the sensor achieves to the directional torsion responsivity of −2.693 nm/rad/m, and the displacement responsivity of 0.0275 nm/μm in ranges of −240 to 240 degrees and 0 to 200μm, respectively.

Study of a MOEMS XOR gate based on optical ring resonator

Based on ring resonator with Microelectromechanical systems, optical XOR logic gate is proposed in this paper to realize the optical logic gate application. The proposed gate is basically structured on an optical ring resonator with 7 μm radius and resonance wavelength of 1.55 μm which is placed on the edge of a thin SiC circular diaphragm. In order to apply input voltages to electrodes, two very thin circular gold layers with 50nm air gap spacing are deposited under the diaphragm. Input voltages are considered as logic inputs and resonance wavelength shift as logic output. When an input DC voltage is applied across the diaphragm, an attractive electrostatic force is created between two electrodes. As a result, the diaphragm is deformed and an internal stress is created. This in turn changes the resonator refractive index due to the photoelastic effect and thus shifts its resonance wavelength about 35nm. COMSOL Multiphysics and MATLAB are carried out to verify FEA and numerical analysis of the designed structure, respectively. A good agreement between the simulations and analytical results is obtained. Enhancement of the wavelength shift and FSR are resulted. The proposed structure is used as an optical XOR gate for the first time.

SERS-active WO3-x thin films with tunable surface plasmon resonance induced by defects from thermal treatment

A series of WO3-x thin films with defects were obtained by thermal treatments from laser irradiation and annealing, respectively. The corresponding tunability of localized surface plasmon resonance properties and the enhancement of Raman scattering intensity were realized due to the defects in the WO3-x thin films after thermal treatments. With the changes of either laser power or annealing temperature, the crystalline quality of WO3-x thin film was declined with a red shift of the surface plasmon resonance wavelength from 464 nm to 482 nm. The as-treated WO3-x film shows good uniformity and reproducibility in Surface-enhanced Raman spectroscopy measurement, the detection limit for dye methylene blue can reach 10−8 mol/L, and enhancement factor is 1.38 × 106. Furthermore, the simulation result of finite-difference time-domain showed a substantial agreement with experimental results.

Ultrahigh Sensitivity of a Plasmonic Pressure Sensor with a Compact Size.

This study proposes a compact plasmonic metal-insulator-metal pressure sensor comprising a bus waveguide and a resonator, including one horizontal slot and several stubs. We calculate the transmittance spectrum and the electromagnetic field distribution using the finite element method. When the resonator’s top layer undergoes pressure, the resonance wavelength redshifts with increasing deformation, and their relation is nearly linear. The designed pressure sensor possesses the merits of ultrahigh sensitivity, multiple modes, and a simple structure. The maximum sensitivity and resonance wavelength shift can achieve 592.44 nm/MPa and 364 nm, respectively, which are the highest values to our knowledge. The obtained sensitivity shows 23.32 times compared to the highest one reported in the literature. The modeled design paves a promising path for applications in the nanophotonic field.

Wavelength and sensitivity tunable long period gratings fabricated in fluid-cladding microfibers

We report the fabrication of long period gratings in fluid-cladding microfibers by directly focusing a femtosecond laser beam on the microfibers surface to induce periodical modification a long one side of the microfibers. A long period grating is fabricated in a water-cladding microfiber with a diameter of ~ 5 μm, which demonstrates a resonant attenuation of 28.53 dB at wavelength of 1588.1 nm with 10 pitches. When water cladding is changed to be refractive index oil of n= 1.33 and alcohol solution with concentration of 5%, the resonance wavelength shifts to 1575.1 nm with resonant attenuation of 24.91 dB and 1594.1 nm with resonant attenuation of 35.9 dB, respectively. The long period grating demonstrates different temperature sensitivities of–0.524 nm/°C,–0.767 nm/°C and–1.316 nm/°C for water, alcohol solution and refractive index oil cladding microfibers, respectively, which means the alterable liquid cladding allows the availability of tunable wavelength and sensitivity. The fluid-cladding protects the microfibers from external disturbance and contamination and allows more flexibility in controlling the transmission property and sensing characteristics of long period gratings, which can be used as fiber devices and sensors for chemical, biological, and environmental applications.

Analysis of thermo-plasmonic lab-on-fiber probes in liquid environments

Lab-on-fiber (LOF) optrodes are recently emerging not only as valid platforms for biosensing, but also as promising light-controlled actuators in drug-delivery, optical trapping and thermo-ablation systems. In this regard, the thermo-plasmonic effect has been recognized as an intriguing tool for conferring to the optical fiber the capability of interacting with the external environment through the fine control of local overheating actuated by light in the range of few mW. However, the evaluation of the thermo-plasmonic overheating on small areas such as that of a standard single mode fiber tip is not trivial, especially in liquid solutions, where these probes typically operate. Here we demonstrate that by functionalizing the metallic nanostructure of LOF devices with a thermoresponsive smart materials, it is possible to measure the light-induced overheating on the fiber tip. Specifically, we monitored the plasmonic resonance wavelength shift induced by the temperature-dependent swelling dynamics of different microgel films deposited on the nanostructure. We find a local overheating of about 8 °C mW−1, i.e. also in line with our theoretical predictions based on numerical simulations. Our results demonstrate that the proposed approach is a valid methodology for the direct and continuous monitoring of the temperature changes in LOF devices induced by the input optical power in liquid environment. Our findings lay the basis for the analysis of thermo-plasmonic optical fiber probes exploitable in many applications, especially for the life science sector.

Continuous tuning of unidirectional emission wavelength by bending a notched-elliptical polymer microdisk

An approach of continuously tunable unidirectional emission through bending a notched-elliptical polymer microdisk is proposed. The characteristics of the bending-dependent action are carefully analyzed, and the resonance wavelength for unidirectional emission can be tuned continuously through bending the device. Such a whispering-gallery-mode microresonator enables unidirectional emission with ultra-low divergence, of which the emission efficiency and Q factor are stabilized, demonstrating the whole structure is robust and relatively insensitive within a certain bending angle range. A maximum resonance wavelength shift of ∼100 nm and Q factor of 1500 can be achieved with the total size of the microdisk less than 10 μm. This kind of microresonator is promising for applications in multilevel integrated photonics circuits and may open the door to new functionalities of resonator devices, from sensing to optical amplification.

Modeling and analysis of all‐optical pressure sensor using photonic crystal based micro ring resonator

AbstractThe paper illustrates a photonic crystal micro ring resonator based pressure sensor utilizing the variation of refractive index of the material and the structural deformation. FEM is employed for reformed structure analysis. Structural deformation and change in refractive index are taken as input variables in FDTD simulation and the external pressure is measured by analyzing shift in resonance wavelength. A comparative study of the rod type and the hole type photonic crystal micro ring resonator based pressure sensor is reported in this paper. Both the structures are ultra compact and can be used for compact photonic integrated circuits.

Polymeric microsphere enhanced surface plasmon resonance imaging immunosensor for occult blood monitoring

Occult blood testing is a routine screening method for evaluating the function of the urinary system and digestive tract. The hemoglobin (Hb) content in human excreta is an important indicator of the presence of occult blood. In this study, a surface plasmon resonance imaging (SPRi)-based immunosensor with high sensitivity was developed for the detection of Hb. The immunosensor was constructed by physically immobilizing anti-Hb antibodies on the detection channels. Samples for evaluation were pre-incubated with the polymeric microsphere-antibody conjugate. The shift in resonance wavelength induced by the specific binding of microsphere-antibody-antigen and immobilized antibodies was monitored in real time. Owing to the amplification effect of microspheres, the detection limit of the immunosensor was reduced 42-fold to 4.8 ng/mL under the optimized concentration of immobilized antibody (10 μg/mL) with microsphere-antibody conjugate dilution ratio of 1:200 and incubation time of the microsphere-antibody conjugate and samples (10 min). The immunosensor displayed a good linear response to Hb ranging from 10 ng/mL to 500 ng/mL in both test solutions and in 1:30 urine sample, as well as a good specificity toward Hb and an acceptable recovery rate for spiked Hb solution in urine sample. The immunosensor was also exploited to detect the Hb concentration in 50 clinical urine samples. Therefore, the proposed SPRi immunosensor developed in this study provides a simple, rapid, high-throughput, and sensitive immunology strategy for the detection of occult blood.

Optimization of second harmonic generation in Au/Si core-shell nanoparticles

This study numerically investigated second harmonic generation (SHG) and the linear optical responses in core–shell nanoparticles comprising a gold core and silicon shell. The effects of the core radius and shell thickness were studied based on the resonance wavelength shifts, linear responses, and SHG efficiency in numerical simulations. By accurately setting the shell thickness, a model was designed where the resonance wavelength was almost constant relative to variations in the core radius for a specific shell thickness (i.e., the resonance wavelength did not shift). Thus, it was possible to optimize the efficiency of the linear optical responses and SHG in the core–shell nanoparticles by only changing the core radius. The desired efficiency can be achieved for this nanoparticle in specific applications by first tuning the resonance wavelength by changing the shell thickness and then by optimizing the efficiency by changing the core radius. The results obtained in this study may facilitate the development and optimization of optical nanodevices for different applications in nanophotonics and nano-optics, such as nanolasers and nanosensors.