Curvature Sensitivity Research Articles

High fringe visibility Mach-Zehnder interferometric sensor based on a Four-Core fiber

An in-line optical fiber Mach-Zehnder interferometer (MZI) sensor with high fringe visibility is reported. The sensor is formed by splicing a short section of four-core fiber (FCF) between two coupling sections. The coupling section is fabricated by cascading very short segment of few mode fiber, multimode fiber (MMF), and large core diameter MMF together. A maximum fringe visibility of approximately 30 dB is obtained in the transmission spectrum. The temperature and curvature sensing response were also experimentally investigated. The temperature sensitivities are 61 pm/°C and 49 pm/°C for dip A and dip B ranging from 30 °C to 80 °C, respectively. The curvature sensitivities for dip A and dip B are 20.77 nm/m−1 and 12.89 nm/m−1 in the range of 0.2983 m−1 to 0.7916 m−1, as well as 9.99 nm/m−1 and 5.38 nm/m−1 from the range of 0.7916 m−1 to 1.039 m−1, respectively. The proposed MZI sensor has the advantage of easy fabrication, compactness, higher fringe visibility, and low cost.

Quantitative Nano-Platforms for Interrogation of Curvature Sensitive Proteins

Membrane curvature is a defining parameter which mediates many critical cellular processes like endocytosis and exocytosis. This parameter is mainly mediated by several types of curvature-sensing domains, including N-BAR, F-BAR, I-BAR, and ENTH domain. Previous studies of these curvature-sensing domains lacking precise quantification of curvature sensitivity while maintaining the ease of use the assay. Herein, we design a concise platform to quantitatively determine the curvature-sensing range for several curvature-sensing proteins, which implies the role of these proteins in several membrane-associated processes. The core of our technology consists of simple nanofabrication and microfluidics, integrated with quick lipid bilayer engineering and protein lysate preparation. This design provides us with the flexibility to switch lipid compositions, manipulate lysate components, and engineer complex curvatures, which serves as a powerful tool to investigate curvature-dependent cellular processes.

Distributed curvature sensing based on a bending loss-resistant ring-core fiber

A theoretical and experimental study on curvature sensing using a Brillouin optical time-domain analyzer based on the ring-core fiber (RCF) is reported. The Brillouin gain spectrum of the RCF is investigated, and the Brillouin frequency shift (BFS) dependence on temperature and strain is calibrated. We theoretically analyze the fiber bending-induced BFS and peak Brillouin gain variation for the RCF through a numerical simulation method, and the RCF is revealed to have a high curvature sensitivity. Distributed curvature sensing is successfully demonstrated, with the bending radius ranging from 0.5 to 1.5 cm, corresponding to a BFS variation from 32.90 to 7.81 MHz. The RCF takes advantage of great bending loss resistance, and the maximum macrobending loss at the extreme bending radius of 0.5 cm is less than 0.01 dB/turn. Besides, the peak Brillouin gain of the RCF is discovered to vary significantly in response to fiber bending, which is expected to be another parameter for distributed curvature determination. The results imply that the RCF is a promising candidate for highly sensitive distributed curvature measurement, especially in sharp bending circumstances.

Stress-insensitive vector curvature sensor based on a single fiber Bragg grating

Abstract A stress-insensitive vector curvature sensor based on a single fiber Bragg grating (FBG) is proposed and experimentally demonstrated. The sensor is easily fabricated by encapsulating an FBG on a thin steel plate with ultraviolet glue. When the FBG deviates from the neutral plane, its effective refractive index and grating constant are changed by bending, therefore, the sensor can realize the curvature measurement. The sensitivity of the sensor in convex bending is 553.65 pm/m−1 in the range of 0.4798–1.3569 m−1. The sensor can realize vector measurement of curvature due to the opposite stress direction on the two sides of the neutral plane during bending. The concave curvature sensitivity of the sensor is −811.19 pm/m−1 in the range of 0.4798–1.3569 m−1. Due to the large stiffness of the thin steel plate, the package of the FBG makes it insensitive to small axial stress. The favorable stability of the sensor facilitates its practical application in the measurement of curvature and inclination. This sensor has the advantage of simple manufacture, low cost, and easy industrial production.

Temperature-independent curvature sensor based on in-fiber Mach-Zehnder interferometer using hollow-core fiber

An in-fiber Mach–Zehnder Interferometer (MZI), based on hollow core fiber (HCF), for measuring curvature is fabricated and experimentally demonstrated. The sensing part was fabricated by splicing a section of HCF between two sections of multimode fiber (MMF), and different HCF lengths were investigated in order to achieve the highest curvature sensitivity. These devices were tested in a transmission configuration using lead-in and lead-out single mode fibers (SMF). The sensor was attached to a steel sheet by using the polymer Polydimethylsiloxane (PDMS) for accurate control of the applied curvature. The modal analysis was carried out using a commercial software based on finite element method (FEM) and by incorporating some of the experimental data, it was feasible to determine the two dominant modes that interfere in this sensor. The devices were characterized by measuring the fringe contrast variations due to the curvature changes. The interferometer fabricated with a HCF 2.5 mm in length HCF showed the highest curvature sensitivity, −17.28 ± 2.30 dB/m−1, in a range from 1.84 m−1 to 2.94 m−1. Moreover, the sensor that exhibited a better performance was fabricated with a HCF length of 1 mm, combining the most extensive curvature range (from 0.95 m−1 to 2.68 m−1) and an adequate sensitivity (−11.80 ±1.30 dB/m−1). The analysis of the interferometric signal of this device in Fourier domain, allows us to establish a one to one relationship between the contrast and the curvature in a broader range (from 0 m−1 to 2.94 m−1). Moreover, the fringe contrast showed a very low dependency on temperature (from 30 °C to 90 °C), depicting that this device was not affected by temperate fluctuation.

Wearable respiration monitoring using an in-line few-mode fiber Mach-Zehnder interferometric sensor.

Continuous respiratory monitoring is extensively important in clinical applications. To effectively assess respiration rate (RR), tidal volume (TV), and minute ventilation (MV), we propose and experimentally demonstrate a respiration monitoring system using an in-line few-mode fiber Mach-Zehnder interferometer (FMF-MZI), which is the first to introduce in-line MZI into an optimal wearable design for respiration rate and volume monitoring. The optimal linear region of the proposed sensor is analyzed and positioned by a flexible arch structure with curvature sensitivity up to 8.53 dB/m-1. Respiration monitoring results are in good agreement with a standard spirometer among different individuals. The difference in TV estimation is ± 0.2 L, and the overall error of MV estimation is less than 5%.

A Large Measurement Range Bending Sensor Based on Microfiber Probe

A large measurement range bending sensor based on a microfiber probe is proposed and experimentally demonstrated. The microfiber probe is simply fabricated by snapping a multimode biconical microfiber in the nonadiabatic tapering process, forming a reflection-type sensing unit. Such probe-type sensor is operated as an in-line Michelson interferometer with compact size. Bending deformation applied on the sensor will affect the refractive index profile of microfiber probe, resulting in the wavelength shift of resonance dip. The experimental results indicate that the microfiber probe-based bending sensor has a large curvature range of 0-11.82m−1. Meanwhile, the maximum curvature sensitivity of 700pm/m−1 has been achieved in the range of 8.73-11.82m−1. The microfiber probe-based bending sensor has the excellent advantages of compact size, large curvature range and good flexibility, which is suitable to measure bending deformation in semi-enclosed spaces and provides a great application prospect in wearable sensing devices for human motion monitoring.

In-Line Hybrid Fiber Sensor for Curvature and Temperature Measurement

We proposed and demonstrated a compact inline optical fiber sensor for curvature and temperature measurement with low cross sensitivity. The device consists of a 5 mm long hollow-core fiber (HCF) spliced between two single-mode fibers. Two up-tapers were fabricated at each splicing joint forming a Mach-Zehnder Interferometer (MZI). The HCF acted as the anti-resonant reflecting optical waveguide (ARROW), giving periodic dips at resonant wavelengths in the optical transmission spectrum. The cross sensitivity of curvature and temperature problem is solved by demodulating the wavelength shift of the MZI for temperature sensing and intensity variation of ARROW dips for curvature sensing. The curvature and temperature sensitivities are experimentally measured to be -4.28 dB/m -1 and 25.76 pm/°C, respectively. The cross sensitivities for ARROW is measured to be 0.0056 m -1 /°C. The structure of the sensor is simple and compact, which can be used for structural health monitoring in a complex environment.

Highly sensitive optical fiber curvature sensor based on a seven-core fiber with a twisted structure.

A highly sensitive Mach-Zehnder interferometer based on a twisted structure in seven-core fiber (SCF) for curvature measurement is investigated both theoretically and experimentally. The device is fabricated by splicing a segment of a twisted SCF with single-mode fibers by the over fusion method. An interference pattern of the straight sensor appears in the transmission spectra. When the sensor is bent, the wavelength shift of the interference pattern is induced, which may be used for curvature measurement through wavelength shift. In the experiment, SCFs with and without the twisted structure are tested, and the results are compared with wavelength-based sensitivities. The proposed twisted-SCF sensor offers a maximum curvature sensitivity of $ - {25.16}\,\,{{\rm nm/m}^{ - 1}}$-25.16nm/m-1 within the measurement range of ${0.5201 - 1.0071}\,\,{{\rm m}^{ - 1}}$0.5201-1.0071m-1, which is a 37-fold improvement compared with the previous works. The results also indicate that this highly sensitive all-fiber sensor offers great potential for realization of curvature measurement in the field of structural health monitoring.

A Self-Referencing Intensity-Based Fabry–Perot Cavity for Curvature Measurement

In this article, a self-referencing intensity-based fiber optic sensor relying on the principle of Fabry-Perot interference is proposed and demonstrated to measure curvature. The sensor is manufactured producing an air bubble cavity between two sections of multimode fiber. By detecting optical power variations at specific wavelengths, it was possible to measure curvature, enabling this sensor as a self-referencing system. For this setup, the achieved curvature sensitivity was 0.561 ± 0.014 dB/m -1 , with a correlation factor up to 0.997, within the measurement range of 0.0-0.8 m -1 . The proposed system has several features, including the self-referencing characteristic and its structure simplicity in terms of measuring procedure, making it a useful system.

Temperature-insensitive curvature sensor based on anti-resonant reflection guidance and Mach–Zehnder interferometer hybrid mechanism

A temperature-insensitive optical fiber curvature sensor based on hollow-core fiber is proposed. The hybrid guidance mechanism is a combination of anti-resonant reflecting guidance and the Mach–Zehnder interferometer. The curvature can be detected through the wavelength interval between the two kinds of lossy dips resulting from the two above-mentioned guidance mechanisms. The curvature sensitivity is −0.54 nm/m−1 and −2.02 nm/m−1 in the curvature range of [0 m−1, 7.04 m−1] and [7.04 m−1, 11.87 m−1], respectively. And the temperature cross-sensitivity of the sensor is only 5.54 pm °C−1, which makes the device attractive for potential applications in curvature measurements.

Vernier effect of two cascaded in-fiber Mach-Zehnder interferometers based on a spherical-shaped structure.

The Vernier effect of two cascaded in-fiber Mach-Zehnder interferometers (MZIs) based on a spherical-shaped structure has been investigated. The envelope based on the Vernier effect is actually formed by a frequency component of the superimposed spectrum, and the frequency value is determined by the subtraction between the optical path differences of two cascaded MZIs. A method based on band-pass filtering is put forward to extract the envelope efficiently; strain and curvature measurements are carried out to verify the validity of the method. The results show that the strain and curvature sensitivities are enhanced to -8.47 pm/με and -33.70 nm/m-1 with magnification factors of 5.4 and -5.4, respectively. The detection limit of the sensors with the Vernier effect is also discussed.

Curvature Sensing Setup Based on a Fiber Laser and a Long-Period Fiber Grating

In this letter, a curvature sensing setup based on a fiber ring laser containing a long-period fiber grating (LPFG) is presented. The LPFG operates as a wavelength selective filter and as a curvature sensing head. The LPFG consists of a periodically tapered fiber section written by a CO2-laser glass processing system. The experimental results show that by increasing the curvature values from 0 to 0.266 $\text{m}^{-1}$ , the laser wavelength emission shifts linearly from 1572 to 1560 nm, and a curvature sensitivity of −42.488 nm/ $\text{m}^{-1}$ is achieved. In addition, the laser emission has a linewidth of 0.05 nm, a slope laser efficiency of 0.43%, and a high single-mode suppression ratio (SMSR) of 60 dB. Finally, this fiber laser offers output power stability at room temperature, compactness, and robustness.

Molecular Mechanisms of Membrane Curvature Sensing by a Disordered Protein.

The ability of proteins to sense membrane curvature is essential for the initiation and assembly of curved membrane structures. Established mechanisms of curvature sensing rely on proteins with specific structural features. In contrast, it has recently been discovered that intrinsically disordered proteins, which lack a defined three-dimensional fold, can also be potent sensors of membrane curvature. How can an unstructured protein sense the structure of the membrane surface? Many disordered proteins that associate with membranes have two key physical features: a high degree of conformational entropy and a high net negative charge. Binding of such proteins to membrane surfaces results simultaneously in a decrease in conformational entropy and an increase in electrostatic repulsion by anionic lipids. Here we show that each of these effects gives rise to a distinct mechanism of curvature sensing. Specifically, as the curvature of the membrane increases, the steric hindrance between the disordered protein and membrane is reduced, leading to an increase in chain entropy. At the same time, increasing membrane curvature increases the average separation between anionic amino acids and lipids, creating an electrostatic preference for curved membranes. Using quantitative imaging of membrane vesicles, our results demonstrate that long disordered amino acid chains with low net charge sense curvature predominately through the entropic mechanism. In contrast, shorter, more highly charged amino acid chains rely largely on the electrostatic mechanism. These findings provide a roadmap for predicting and testing the curvature sensitivity of the large and diverse set of disordered proteins that function at cellular membranes.

Highly sensitive vector curvature sensor based on a triple-core fiber interferometer

A highly sensitive vector curvature sensor based on a triple-core fiber (TCF) interferometer is proposed and demonstrated. The TCF interferometer is composed of a piece of TCF that is fusion spliced to a standard single mode fiber (SMF). A taper is fabricated at the TCF near the TCF-SMF junction to couple the light from the input SMF into the three cores of the TCF and recouple the reflected light from the end of the TCF back to the SMF, which forms a three-beam Michelson interferometer in the TCF. Such a three-beam interferometer has the unique characteristic that its sensitivity is greatly affected by the optical path differences (OPD) and light intensities of the light transmitted in the cores of the TCF. As a result, choosing a TCF with proper refractive index differences between three cores or designing a proper splitting ratio of the TCF taper can effectively enhance the sensitivity of the TCF interferometer. The bending responses of the TCF interferometer were tested in the curvature range of 0-1.305 m−1. Experimental results show that the curvature sensitivities at the opposite bending directions along the cores’ connection are about 91.61 nm/m−1 and -95.22 nm/m−1, respectively.

Simultaneous Curvature and Temperature Sensing Based on a Novel Mach-Zehnder Interferometer

A novel fiber inline Mach-Zehnder interferometer (MZI) is proposed for simultaneous measurement of curvature and temperature. The sensor composes of single mode-multimode-dispersion compensation-multimode-single mode fiber (MMF-DCF-MMF) structure, using the direct fusion technology. The experimental results show curvature sensitivities of −12.82 nm/m−1 and −14.42 nm/m−1 in the range of 0–0.65 m−1 for two resonant dips, as well as temperature sensitivities of 57.6 pm/°C and 74.3 pm/°C within the range of 20 °C–150 °C. In addition, the sensor has unique advantages of easy fabrication, low cost, high fringe visibility of 24dB, and high sensitivity, which shows a good application prospect in dual-parameters of sensing of curvature and temperature.

Fiber-optic sensor implanted with seven-core helical structure for measurement of tensile strain and extrusion bending

We proposed a fiber-optic sensor implanted with helical seven-core structure based on Mach–Zehnder interference, which can be used for the measurement of tensile strain and extrusion bending. The sensor consisted of a section of seven-core optical fiber with helical structure, which can be described as the SMF-Taper-HSCF-Taper-SMF (HSCF, helical seven-core fiber) sensor. When stretching or bending is applied, the sensor will undergo certain deformation, which will lead to the changes of interference modes in the optical fiber. The tensile strain and extrusion bending can be measured accurately according to the response of transmission spectrum to mode change. The helical seven-core structure can effectively stimulate higher order modes and induced deformation changes. In the experiment, three sensors with different helical periods were fabricated and their spectral characteristics were analyzed. Finally, we selected the sensor with a helical period of 190 μm to conduct a strain and bending test. The results show that the strain sensitivity of the sensor is −21.31 pm / μe in the range of 0 to 500 μe, and the curvature sensitivity of the sensor is −6.36 nm / m − 1 in the range of 0.16 to 1.6 m − 1. This sensor can detect strain and bending and has stable sensing performance and high sensitivity.

Highly Sensitive Vector Curvature Sensor Based on Two Juxtaposed Fiber Michelson Interferometers With Vernier-Like Effect

In this paper, a highly sensitive vector curvature sensor based on two juxtaposed fiber Michelson interferometers (MI) with Vernier-like effect has been proposed and verified. Different from the structures of the conventional Vernier effect which are composed of the cascaded elements, the proposed configuration consists of two juxtaposed MIs. A triple-core fiber (TCF) is connected with a quite short piece of dual-side-hole fiber (DSHF), and the core of the DSHF and the two eccentric cores of the TCF are respectively constituted two juxtaposed MIs. The Vernier-like effect is caused by the very small refractive index difference between the two eccentric cores of the TCF. The most outstanding feature of the proposed structure is that the two MIs are both sensitive to curvature with opposite sensitivities, which makes the curvature sensitivity magnification factor twice that of the conventional Vernier effect structure. Experimental results show that the curvature sensitivity of the structure can reach $-60.84~{\mathrm {nm/m}}^{-1}$ .

A cascaded fiber sensor for measuring different curvature ranges based on the cladding mode resonance in double-cladding fiber

Abstract A cascaded fiber sensor for measuring different curvature ranges based on the cladding mode resonance in double-cladding fiber is proposed. It is formed by double-cladding fiber and single-mode fiber. Based on the evanescent wave coupling principle, the cladding mode resonance phenomenon in double-cladding fiber is illustrated. The transmission spectrum with different length are also analyzed. The experimental results show that the resonance wavelength changes with the length of double-cladding fiber. When the fiber length is 22 mm, the transmission spectrum is blue-shifted as the curvature increases in minor range of 0–0.204 m−1, the corresponding curvature sensitivity can be up to −19376.48 pm/m−1. When the fiber length is 20 mm, the corresponding curvature sensitivity can be up to −4161.73 pm/m−1 as the curvature increases in large range of 0–1.06 m−1. The proposed curvature sensor has the characteristics of simple structure and high sensitivity, so it has a good application prospects in large bridges, industrial buildings and other curvature measurement situations.

Membrane reshaping by micrometric curvature sensitive septin filaments

Septins are cytoskeletal filaments that assemble at the inner face of the plasma membrane. They are localized at constriction sites and impact membrane remodeling. We report in vitro tools to examine how yeast septins behave on curved and deformable membranes. Septins reshape the membranes of Giant Unilamellar Vesicles with the formation of periodic spikes, while flattening smaller vesicles. We show that membrane deformations are associated to preferential arrangement of septin filaments on specific curvatures. When binding to bilayers supported on custom-designed periodic wavy patterns displaying positive and negative micrometric radii of curvatures, septin filaments remain straight and perpendicular to the curvature of the convex parts, while bending negatively to follow concave geometries. Based on these results, we propose a theoretical model that describes the deformations and micrometric curvature sensitivity observed in vitro. The model captures the reorganizations of septin filaments throughout cytokinesis in vivo, providing mechanistic insights into cell division.