Abrupt Taper Research Articles

A liquid lever sensor based on an abrupt taper and micro‐arc Michelson interferometer in single‐mode fiber

AbstractA novel two‐parameter sensor is proposed based on the abrupt taper and micro‐arc Michelson interferometer (MI) in single‐mode fiber. When there is a regular change in the liquid level or temperature, the phase difference changes, and the spectral intensity or wavelength of the interfering valleys of this sensor is directionally shifted. This study enriches the construction of MI and provides a new perspective on liquid level measurement. We experimentally explored the sensor's sensing performance over temperature and liquid level: this sensor's temperature sensitivity and liquid level sensitivity were up to 62.9 pm/°C and 0.2896 dB/mm, respectively. In addition, this sensor is characterized by compactness, simplicity, low cost, and high reliability, and it is suitable for measurement of liquid level and temperature, expanding the application field of MI.

Abrupt Discontinuation Versus Taper of Hydrocortisone in Patients With Septic Shock.

Although not mentioned in the most recent guidelines, the 2016 Surviving Sepsis Campaign guidelines recommend to taper corticosteroids once vasopressors are no longer needed; however, at the time of publication, there were no studies comparing taper versus abrupt discontinuation of corticosteroids. The purpose of this study was to further evaluate the impact of abrupt versus taper discontinuation of corticosteroids in septic shock. This was a retrospective cohort study that included patients who received an initial dose of 200 to 300 mg of hydrocortisone for septic shock. Participants were then divided into "abrupt" and "taper" groups. The primary outcome assessed was hemodynamic instability during taper or within 72 hours of the last corticosteroid dose. Secondary outcomes included intensive care unit (ICU) and hospital length of stay, incidence of hyperglycemia or hypernatremia, and in-hospital mortality. The primary outcome of reinitiation of vasopressor therapy occurred in a larger proportion of patients in the taper group compared with the abrupt group (21.9% vs 10.7%). The ICU length of stay (7.6 days abrupt vs 9 days taper) and hospital length of stay (14.9 vs 15.3 days) were similar between groups. There was a statistically significant increase in patients who experienced hyperglycemia within 24 hours of the last corticosteroid dose in the abrupt group. All other secondary outcomes were similar between groups. The abrupt discontinuation of hydrocortisone in the treatment of septic shock was associated with a nonstatistically significant 50% absolute reduction in the need for vasopressor reinitiation.

High Sensitivity Fiber Interferometric Strain Sensors Based on Elongated Fiber Abrupt Tapers.

We demonstrate high-sensitivity fiber strain sensors based on an elongated abrupt taper. The fiber abrupt taper, with a tapered diameter ranging from 40–60 μm, was made by using a hydrogen microflame to break the waveguide adiabaticity so as to convert the fundamental mode into cladding modes. The abrupt taper was further uniformly tapered by using a normal moving flame with a torch diameter of 7 mm to elongate the tapered region until the tapered diameter was down to 2.5–5 μm. The excited high-order modes were confined to propagate along the cladding and then recombined at the rear edge of the fiber taper to produce interferences with extinction ratios of up to 16 dB. The tapered region was pulled outwardly to change the optical path difference (OPD) between modes to measure the tensile strain with all the interfering wavelengths blue-shifted. The measured best strain sensitivity was 116.21 pm/με and the coefficient of determination R2 of linear fitting exhibits high linearity. This strain sensor based on elongated abrupt taper is several times higher than that of most of the fiber strain sensors ever reported.

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.

Orientation-dependent fiber-optic accelerometer based on eccentric fiber Bragg grating.

A highly localized eccentric fiber Bragg grating (EFBG) accelerometer was proposed, and its orientation-dependent measurement results were demonstrated experimentally. An EFBG was inscribed point-by-point (PbP) in a single-mode fiber (SMF) using a femtosecond laser, and the cladding mode was recoupled to excite the ghost mode through an abrupt taper. Owing to the asymmetry caused by the lateral offset of the EFBG, the ghost mode showed a significant directional response to acceleration. Furthermore, monitoring the fundamental core mode resonance can help calibrate accidental power perturbation or cross-sensitivity.

Quantification of training load distribution in mixed martial arts athletes: A lack of periodisation and load management.

The aim of this study was to quantify typical training load and periodisation practices of MMA athletes. MMA competitors (n = 14; age = 22.4 ± 4.4 years; body mass = 71.3 ± 7.7 kg; stature = 171 ±9.9 cm) were observed during training for 8 consecutive weeks without intervention. Seven athletes were training for competitive bouts whilst the remaining 7 were not. Daily training duration, intensity (RPE), load (sRPE and segRPE), fatigue (short questionnaire of fatigue) and body region soreness (CR10 scale) were recorded. Using Bayesian analyses (BF10≥3), data demonstrate that training duration (weekly mean range = 3.9-5.3 hours), sRPE (weekly mean range = 1,287-1,791 AU), strain (weekly mean range = 1,143-1,819 AU), monotony (weekly mean range = 0.63-0.83 AU), fatigue (weekly mean range = 16-20 AU) and soreness did not change within or between weeks. Between weeks monotony (2.3 ± 0.7 AU) supported little variance in weekly training load. There were no differences in any variable between participants who competed and those who did not with the except of the final week before the bout, where an abrupt step taper occurred leading to no between group differences in fatigue. Training intensity distribution corresponding to high, moderate and low was 20, 33 and 47%, respectively. Striking drills accounted for the largest portion of weekly training time (20-32%), with MMA sparring the least (2-7%). Only striking sparring and wrestling sparring displayed statistical weekly differences in duration or load. Athletes reported MMA sparring and wrestling sparring as high intensity (RPE≥7), BJJ sparring, striking sparring and wrestling drills as moderate intensity (RPE 5-6), and striking drills and BJJ drills as low intensity (RPE≤4). We conclude that periodisation of training load was largely absent in this cohort of MMA athletes, as is the case within and between weekly microcycles.

Analytical and experimental study on a bent abrupt taper.

This work presents an analytical coupling model for perturbed abrupt fiber tapers in single-mode fibers. In addition to LP0m modes, the modeling predicts the presence of LP11 and LP12 modes for a bent taper. Our model also introduces a perturbation function that can match most cases of bending variations on a taper. We have shown that the tapering and bending effect can be treated separately within one abstract formulation. Agreement amongst the model predictions and experimental results support the viability of our method.

Error estimation in the analytical modeling of abrupt taper Mach-Zehnder interferometers

In-line fiber interferometers based on abrupt tapers have been shown as a promising low-cost platform for various sensing applications. Many variations have been demonstrated experimentally using combinations and permutations of novel photonic devices such as photonic crystal fibers or multimode fibers. In this manuscript, an analytical model for light propagation in an abrupt taper Mach-Zehnder Interferometer in commercial single-mode fiber based on coupled-mode theory is detailed. The model calculates the mode propagation process, and the result is compared with previous numerical simulations. For experimental verification, an in-line Mach-Zehnder interferometer based on an abruptly tapered fiber is fabricated and tested. The spectrum calculated by the model matches well with the measured spectrum. To reduce the computational complexity, a method for step size estimation and the corresponding error accumulation is discussed and verified. This can serve as a basis to estimate the optical responses of this class of abrupt taper based fiber sensors. With the right packaging, these sensors can play a vital role in rugged and hostile environments.

Practical interrogation scheme for the abrupt taper Mach-Zehnder interferometer refractive index sensor.

A practical interrogation scheme of a refractive index (RI) sensing system based on the abrupt fiber taper Mach-Zehnder interferometer sensor is designed, implemented, and demonstrated by experiment. The broadband light source and optical spectrum analyzer in the conventional design are replaced by two single-wavelength laser diodes modulated by a periodical square waveform and a simple photodetector (PD), which can significantly lower the cost and lead to easier integration. The photocurrent of the PD output signal is used as the indicator of the surrounding RI. Automatic data acquisition and processing is realized by LabVIEW programming. The experiment proves the feasibility of the new scheme and shows a high sensitivity (2371 mV/RIU) and high stability.

A Highly Sensitive Magnetic Field Sensor Based on a Tapered Microfiber

A compact all-fiber magnetic field sensor based on the combination of a magnetic fluid and a nonadiabatic microfiber is experimentally demonstrated. By using a fusion splicer combined with an additional flame brushing, the nonadiabatic microfiber, with an abrupt taper, a small waist diameter and a long region, provides a strong evanescent field and a long sensitive distance. The result indicates that a sensitivity as high as 309.3 pm/Oe can be achieved in the range from 0 to 200 Oe. The designed nonadiabatic microfiber sensing structure suggests potential application as a tunable all-in-fiber photonic and other newly fashioned magneto-optical photonic devices.

Selective and sensitive Escherichia coli detection based on a T4 bacteriophage-immobilized multimode microfiber.

Escherichia coli bacteria have been found to be responsible for various health outbreaks caused by contaminated food and water. Accurate and rapid test of E. coli is thus crucial for protecting the public health. A fast-response, label-free bacteriophage-based detection of E. coli using multimode microfiber probe is proposed and demonstrated in this article. Due to the abrupt taper and subwavelength diameter, different modes are excited and guided in the microfiber as evanescent field that can interact with surrounding E. coli directly. The change of E. coli concentration and corresponding binding of E. coli bacteria on microfiber surface will lead to the shift of optical spectrum, which can be exploited for the application of biosensing. The proposed method is capable of reliable detection of E. coli concentration as low as 103 cfu/mL within the range of 103 to 107 cfu/mL. Owing to the advantages of high sensitivity and fast response, the microfiber probe has great potential application in the fields of environment monitoring and food safety.

Immobilized optical fiber microprobe for selective and sensitive Escherichia coli detection.

Escherichia coli (E. coli) bacteria have been found to be responsible for various health outbreaks caused by contaminated food and water. Accurate and rapid test of E. coli is thus crucial for protecting the public health. A fast-response, label-free bacteriophage-based detection of E. coli using multimode microfiber probe is proposed and demonstrated in this paper. Due to the abrupt taper and subwavelength diameter, different modes are excited and guided in the microfiber as evanescent field that can interact with surrounding E. coli directly. The change of E. coli concentration and corresponding binding of E. coli bacteria on microfiber surface will lead to the shift of optical spectrum, which can be exploited for the application of biosensing. The proposed method is capable of reliable detection of E. coli concentration as low as 103 cfu/mL within the range of 103 to 107 cfu/mL. Owing to the advantages of high sensitivity and fast response, the microfiber probe has great potential application in the fields of environment monitoring and food safety.

Temperature independent refractive index measurement using a fiber Bragg grating on abrupt tapered tip

A fiber Bragg grating was inscribed in an abrupt fiber taper using a femtosecond laser and phase-mask interferometer. The abrupt taper transition allows to excite a broad range of guided modes with different effective refractive indices that are reflected at different wavelengths according to Bragg’s law. The multimode-Bragg reflection expands over 30 nm in the telecom-C-band. This corresponds to a mode-field overlap of up to 30% outside of the fiber, making the device suitable for evanescent field sensing. Refractive index and temperature measurements are performed for different reflection peaks. Temperature independent refractive index measurements are achieved by considering the difference between the wavelength shifts of two measured reflection peaks. A minimum refractive index sensitivity of 16 ± 1 nm/RIU was obtained in a low refractive index regime (1.3475–1.3720) with low influence of temperature (−0.32 ± 0.06 pm/°C). The cross sensitivity for this structure is 2.0 × 10−5 RIU/°C. The potential for simultaneous measurement of refractive index and temperature is also studied.

Asymmetric structured microfiber-based temperature sensor

A temperature sensor formed by a cascaded sphere and an abrupt taper, together in a standard single-mode fiber, was developed. The dip of the measured spectrum signal shifted obviously when the surrounding temperature changed. Measurement sensitivity to 18.36 pm/°C was shown with the surrounding temperature ranging from 35°C to 395°C. Due to its compact size and all-fiber configuration, the proposed sensor has the advantages of simplicity and low-cost fabrication, thus the device would find potential applications in sensing fields.

Humidity Sensor Based on Hybrid Fiber Bragg Grating/Abrupt Fiber Taper

A novel fiber humidity sensor based on fiber Bragg grating (FBG) cascaded with an abrupt fiber taper is proposed and demonstrated. The evanescent wave around the abrupt fiber taper varies with humidity around the sensor, so that the power of the FBG core reflection is affected by the ambient humidity. Experimental results show that the sensor has a linear response to humidity with sensitivity of 0.10-dB/%RH in the humidity range of 50%–90% RH. Such a cost-effective, compact, and reflection power detection-based humidity sensor could be a good candidate in applications.

In-fiber modal interferometer for simultaneous measurement of curvature and temperature based on hollow core fiber

An in-fiber modal interferometer is presented and experimentally demonstrated for simultaneous measurement of curvature and temperature. The sensing part is fabricated by splicing single mode fiber (SMF) and hollow core fiber (HCF) via two abrupt tapered joints. Light couples to the wall of HCF due to the collapse in abrupt taper region and then modal interference occurs among multiple modes. Not only intensity but also wavelength of the dip around 1556nm linearly responses to the curvature and temperature change thus a sensitivity matrix could be built to demodulate both curvature and temperature simultaneously. In addition, the interference dip around 1540nm performs a decrease trend and the highest curvature sensitivity of 5.05dB/m−1 is achieved in a wide range from 0.765m−1 to 3.423m−1.

Optical Fiber Inclinometer Based on a Fiber Taper Cascading a Peanut-Shape Structure

An optical fiber inclinometer applying modal interference based on an abrupt tapering cascading a peanut-shape configuration is proposed. The abrupt taper splits part of the core mode into cladding modes and the interference occurs when the peanut-shape recombines the cladding modes and core mode together. Four inclinometers with different lengths have been fabricated and characterized, and the high sensitivities of -1.76 and -4.49 nm/° are obtained in the angle range of 0°-3° and 3°-6.66°, respectively.

Asymmetrical in-fiber Mach-Zehnder interferometer for curvature measurement.

We demonstrated a compact and highly-sensitive curvature sensor based on a Mach-Zehnder interferometer created in a photonic crystal fiber. Such a Mach-Zehnder interferometer consisted of a peanut-like section and an abrupt taper achieved by use of an optimized electrical arc discharge technique, where only one dominating cladding mode was excited and interfered with the fundamental mode. The unique structure exhibited a high curvature sensitivity of 50.5 nm/m-1 within a range from 0 to 2.8 m-1, which made it suitable for high-sensitivity curvature sensing in harsh environments. Moreover, it also exhibited a temperature sensitivity of 11.7 pm/°C.

Compact bending sensor based on a fiber Bragg grating in an abrupt biconical taper

We propose and experimentally demonstrate a compact bending sensor. The head of the sensor is only 0.8 mm in length, and consists of an abrupt biconical fiber taper formed using a conventional fusion splicer, in which a fiber Bragg grating (FBG) is inscribed using a femtosecond laser. The biconical taper incorporating the FBG can couple light from the cladding to the backward-propagating core mode, which realizes an interferometer in reflection-mode. Bending of the structure can be detected from the contrast change of interference fringes. A configuration to measure curvature is investigated to demonstrate the sensing characteristics. The temperature cross-sensitivity of the sensor is studied, and the results demonstrate that it is insensitive to temperature.

Abrupt Taper Michelson Interferometer Using Heterodyne for Measuring Refractive Index

A method is proposed for measuring the refractive index (RI) of aqueous solutions using an abrupt taper Michelson interferometer and a synthetic heterodyne detection scheme. In the proposed approach, the abrupt taper Michelson interferometer is implemented with a Fabry-Perot cavity in a path-matching differential interferometer. The RI of the aqueous solution is then extracted from the phase shift of the heterodyne demodulated interferometric signal. The experimental results show that a change in the RI of 0.0001 prompts a phase shift of sim 1.35° in the demodulated signal given the use of an abrupt taper Michelson interferometer with a sensing length of 20 cm.