Single-mode-multimode-single-mode Research Articles

An experimental analysis on the performance of single mode-multimode-single mode and multimode- single mode-multimode fiber optic sensor

A cost effective and simple fabrication process for Mach Zehnder Interferometer (MZI) fiber based sensor has been proposed based on single mode-multimode-single mode structure and multimode-single mode-multimode. These proposed structures employed a standard fusion arc splicing by varying the length of sensing region instead of the structures. This sensor has been experimentally demonstrated for three different concentration of solutions such as water, 1mol sucrose solution and oil with the refractive index of 1.333, 1.384 and 1.464 respectively. Furthermore, the intention of this experiment is to determine which structure that provides superior performance in terms of the sensitivity of the device. The operating wavelength of different structures corresponds to the different refractive index. It is observed that the shifting response was influenced by the length of the sensing-area and the best sensitivity achieved for is -10.45nm/RIU.

Power Loss Classification on Shifts Based on SMS (Singlemode-Multimode-Singlemode) Structured Fiber Optic Using Gaussian Naïve Bayes Method

Singlemode-multimode-singlemode based optical fiber can be used as a good communication medium, but energy or power carried by light will be weakened (losses) due to leakage or due to lack of clarity or shift in optical fibers. In this study, power losses in fiber optics based on SMS will be classified based on changes in the values of power losses to shifts and divided them according to three classes, there are good, average, and bad. The shift will be used as a classification variable that is between 0 μm to 450 μm with an increment of 50 µm for every interval. The SMS optical fiber structure used is 5.5 with 25 attempts on different optical fibers. The classification method used is Naïve Bayes with a Gaussian distribution. Gaussian distribution is used in Naïve Bayes because the dataset will be processed in the form of continuous values. From the results of testing based on TP+TN = 6, FP = 6 FN = 6 on confusion matrix, the classification accuracy value was 42.86%. This indicates that this classification method is still less effective for classifying fiber optic power losses with an SMS structure. For further study, another classification methods can be used in the power loss classification to get better results.

Fiber in-line magnetic field sensor based on Mach-Zehnder interferometer integrated with magnetic fluid

In this paper, magnetic fluid (MF), a new type of optical functional nanomaterial with interesting optical characteristics under the external magnetic field, is adopted to form a novel fiber-optic magnetic field sensor. The proposed sensor is based on Mach-Zehnder interferometer (MZI) and has a multimode-singlemode-multimode (MSM) fiber structure. The MSM structure was fabricated by splicing a section of uncoated single mode fiber (SMF) between two short sections of multimode fibers (MMFs) using a fiber fusion splicer. The magnetic field sensing probe was made by inserting the fiberoptic structure in an MF-filled capillary tube. Variations in an external magnetic field is seen to cause changes in the refractive index of MF. This tunable change in the refractive index with magnetic field strengths between 0.6 mT to 21.4 mT produces a shift in the peak position of the wavelength. The shift of the valley wavelength with magnetic field intensity has a good linearity of up to 99.6%. The achieved sensitivity of the proposed magnetic field sensor is 0.123 nm/mT, which is improved by several folds compared with those of most of the other reported MF-based magnetic field sensors. Furthermore, we build the corresponding circuit-based measurement system, and the experimental results show that the voltage change indirectly reflects the change of the external magnetic field strength. Therefore, this provides the potential to fiber-based magnetic field sensing applications.

Sensitivity enhancement of singlemode-multimode-singlemode fiber optic sensor based on macrobending effect for food composition monitoring

The paper analyzes the sensitivity enhancement of the Fiber Optic Sensor (FOS) based on the Singlemode-Multimode-Singlemode (SMS) structure for food composition monitoring. The enhancement method utilized in this refractive index sensor is the macrobending effect with bending diameter of 2.8, 3.3 and 4 cm. The sensitivity of the sensor were analyzed in different food liquids such as water, oil and 1.0 mol sugar, with the refractive index of 1.333, 1.384 and 1.464 respectively. The device was developed using the fusion arc splicing technique and etching process of the sensor’s area. The selected core diameter of the sensor’s area according to the etching process analysis was 55 µm at etching time of 15 minutes. The results of the sensor with and without the macrobending effect were observed. Meanwhile, the smallest bending diameter experienced the highest sensitivity. Overall, the experiment demonstrated an improved sensitivity of the macrobending sensor by 38.14%. This study broadens the potential of the simple sensor configuration for application in food composition monitoring.

Multimode interference based fiber-optic sensor for temperature measurement

A new fiber-optic sensor was demonstrated for temperature measurement using multimode interference effect in single mode multimode single mode (SMS) fiber structure. Interference fringes were found to red-shift as the temperature increased and vice versa due to the thermo-optic effect, which changed the phase of the core and cladding modes inside the structure. The sensor probes were shown to measure temperature stably with a linearity of more than 99%. The temperature sensitivity of the SMS sensor was 21 pm/?C, which is twice the sensitivity of the conventional fiber Bragg grating sensor. Our proposed sensor is simple, cost-effective, and could operate at high temperatures.

Highly sensitive strain sensor based on composite interference established within S-tapered multimode fiber structure.

In this paper, a novel strain sensor based on composite interference established within an S-tapered multimode (STM) fiber structure is proposed and experimentally demonstrated. The STM fibre structure is simply realized by non-axially tapering a traditional single-mode-multimode-single-mode (SMS) fiber into S-shape using a fusion splicer. This fabricated S-tapered structure provides an extra Mach-Zehnder interferometer (MZI) that is introduced within the multimode fibre (MMF) section; therefore, composite interference based on the inherent multimode interference (MMI) of an SMS and the introduced MZI is successfully established. This resultant composite interference greatly enhances the performance of traditional SMS fibre structures for strain sensing, with a maximum strain measurement sensitivity as high as -103.8 pm/με achieved with a detectable strain resolution of 0.2 με. Benefiting from the experimentally determined high sensitivity and good repeatability, this low-cost strain sensor can be realistically applied in many areas where high accuracy strain measurement is required.

Efficient humidity sensor based on an etched no-core fiber coated with copper oxide nanoparticles

We report on a humidity sensor based on passband spectrum resulting due to self-imaging effect in single-mode–multimode–single-mode fiber structure experimentally. The sensor performance with varying NCF diameter was investigated to find appropriate size of maximized evanescent fields. Different tuned diameters of NCF of 100, 80, 60, and 40 μm were obtained by chemical etching process based on hydrofluoric (HF) acid immersion. The experimental results reveal that almost a threefold increase in sensitivity was obtained at the proposed optimum NCF diameter of 60 μm coated with copper oxide nanoparticles embedded in poly polyvinyl alcohol. The highest wavelength and intensity sensitivity of −0.581 nm / RH % and −0.456 dB / RH % were obtained, respectively, in the RH range of 30% to 100% with 8.11-s response time. To the best of our knowledge, this is the first demonstration of RH sensor based on NCF coated with CuO NPs thin film.

Optical fiber sensor based on Mach–Zehnder interferometer combined with a fiber Bragg grating for simultaneous measurement of refractive index and temperature

An optical fiber sensor based on fiber Bragg grating (FBG) and Mach–Zehnder interferometer (MZI) is experimentally demonstrated for simultaneous measurement of refractive index (RI) and temperature. The MZI is formed by a single-mode–multimode–single-mode fiber structure and a spherical-shape structure. The temperature sensitivities of FBG and MZI are 0.0098 and 0.093 nm / ° C, respectively. Simultaneous measurement of RI and temperature can be realized using the sensitivity coefficient matrix. The sensor has the advantages of easy fabrication, good robustness, and high sensitivity.

Performance comparison of high temperature sensor based on non‐adiabatic silica microfiber and single mode‐multimode‐single mode fiber structure

AbstractA fiber‐based temperature sensor operating at high temperature was demonstrated using multimode interference effect and its performance was compared with that of two different probes based on a non‐adiabatic microfiber and singlemode‐multimode‐singlemode (SMS) fiber structure. Interference fringes of the output red‐shifted as the temperature increased due to the change in the effective refractive index of the multiple modes inside both structures. The sensor probes were able to measure the temperature variation up to 400°C with a linearity of more than 90%. The temperature sensitivity of the microfiber and SMS sensors is 6.0 pm/°C and 11.1 pm/°C, respectively. Our proposed sensors are simple, relatively cheap to be fabricated, and could operate at high temperatures above 300°C.

A label-free fiber optic biosensor for Salmonella Typhimurium detection

A label-free fiber optic biosensor based on single mode-tapered multimode-single mode (SMS) structure for bacteria detection has been reported. The main aim of the present study was the sensitive detection of Salmonella Typhimurium in phosphate buffer saline (PBS) and spiked samples of milk. The multimode interference based SMS sensor was developed for biosensing application by removal of cladding region of the multimode fiber, followed by modification of the etched region with anti-S. Typhimurium monoclonal antibodies. The antibodies functionalized SMS biosensor provided S. Typhimurium detection in a wide linear range (500 CFU/mL − 5000 CFU/mL) to attain limit of detection (LOD) of 247 CFU/mL. The complete analysis process for each sample including regeneration was completed in less than 20 min. A comprehensive theoretical study of the developed biosensor regarding beam propagation and power distribution has been presented. The developed biosensor showed high selectivity in the presence of Escherichia coli and Staphylococcus aureus. It provides an alternative platform for rapid and specific detection of S. Typhimurium without any prior sampling processes. The proposed biosensing technique could be used for sensitive detection (275.86 nm/RIU) of the broad spectrum of pathogens.

Optical fibre sensors for monitoring phase transitions in phase changing materials

A platinum coated singlemode-multimode (SM) structure is investigated in this paper as an optical fibre sensor (OFS) to monitor the phase transition of a phase change material (PCM). Paraffin wax has been used as an example to demonstrate the sensor’s performance and operation. Most materials have the same temperature but different thermal energy levels during the phase change process, therefore, sole dependency on temperature measurement may lead to an incorrect estimation of the stored energy in PCM. The output spectrum of the reflected light from the OFS is very sensitive to the bend introduced by the PCM where both liquid and solid states exist during the phase transition. The measurement of strain experienced by the OFS during the phase change of the PCM is utilized for identifying the phase transition of paraffin wax between the solid and liquid states. The experimental results presented in this paper show that the OFS with a shorter multimode fibre section has better performance for monitoring the phase transition of paraffin wax with a measured phase transition temperature range of 41.5 °C–57.7 °C for the SM based OFS with a 5 mm long multimode fibre section.

Mach–Zehnder interferometer based on a cross-type microchannel in SMS fiber structure for gas pressure sensing with high sensitivity

An inline fiber Mach–Zehnder interferometer (MZI) based on a cross-type microchannel in single mode–multimode–single mode fiber structure was proposed. The cross-type microchannel was fabricated in the fiber material directly using femtosecond laser-induced breakdown in water. The horizontal part of the cross-type microchannel along the fiber direction results in enough phase difference for the interference, and the cross-type shape makes the whole structure more robust because a smaller part of fiber material is etched. In addition, the proposed MZI shows high-pressure sensitivity (−14.27 nm / MPa), low-temperature cross sensitivity (0.043 nm/°C), and low strain force cross sensitivity (0.257 nm/N), which makes it a promising candidate for applications in gas pressure sensing field.

A novel optical fiber magnetic field sensor based on Mach-Zehnder interferometer integrated with magnetic fluid

In this paper, a novel Magnetic fluid-filled optical fiber sensor consisting of a multimode-single mode-multimode (MM-SM-MM) fiber structure has been proposed and experimentally demonstrated. The proposed sensor is based on a Mach-Zehnder interferometer, which is fabricated by splicing a section of uncoated single mode fiber between two short sections of multimode fibers with a fiber fusion splicer. The micro-structure is sealed in a Magnetic fluid-filled capillary tube and the magnetic field sensing probe is formed. Variations in an external magnetic field is seen to cause changes in the refractive index of MF. This tunable change in the refractive index with magnetic field strengths between 0.6 mT to 21.4 mT produces a shift in the position of the peak of the wavelength. The shift of the valley wavelength with magnetic field intensity has a good linearity of up to 99.586%. The achieved sensitivity of the proposed magnetic field sensor is 0.12306 nm/mT. Furthermore, we also proposed the corresponding building methods of the measurement system based on the MM-SM-MM structure. It turned out that a voltage change indirectly reflects the change of the external magnetic field strength. This therefore provides the potential to fiber-based magnetic field sensing applications.

Enhanced sensitivity of heterocore structure surface plasmon resonance sensors based on local microstructures

A method to improve the refractive index (RI) and temperature sensitivities of optical fiber based on surface plasmon resonance (SPR) sensors is proposed and experimentally demonstrated. It is realized by using a precision femtosecond laser system to manufacture microstructures on a heterocore optical fiber structure (multimode single-mode multimode fiber, MSM). The microstructured MSM structure fiber-optic sensors were coated with 60-nm gold (Au) film to test and verify RI sensing, obtaining an enhancement of the maximum sensitivity range from 2845.18 to 3313.15 nm/RIU. The fabricated sensors were additionally coated with a layer of polydimethylsiloxane, which has a high negative thermos-optic coefficient, to conduct a series of temperature sensing experiments. Experimental results showed that the maximum sensitivity increased from 1.1998 to 1.5646 nm/°C. Compared with nonmicrostructured sensors, the RI and temperature sensitivity of the proposed sensor has increased 16.4% and 30.2%, respectively. The simply fabricated, low-cost, and high-sensitivity SPR sensor has promising applications in many areas, especially in the biochemical field.

Multimode interference in single mode‐multimode‐single mode fiber structure for steel beam compressive strain measurement

AbstractA simple optical sensor based on singlemode‐multimode‐singlemode (SMS) optical fiber structure is proposed and demonstrated for the measurement of steel beam compression strain. The SMS sensor probe is fabricated by splicing both ends of a short multimode fiber with two pieces of standard single‐mode fibers using a fusion splicer. The strain sensitivity stems from the difference in the effective refractive index of the core, which induces resonant wavelength shift against the strain. In the experiment, parallel measurements were also made using an electrical resistance (ER) strain gauge for comparison purpose. The SMS sensor was also able to detect the elastic limit of the steel beam from the abrupt shift in the interference wavelength as the compressive strain was increased above 5.351 mm/mm. The sensor showed that the steel beam had an elastic limit at a compressive load of 130 kN, which was in good agreement with the ER strain gauge measurement. Furthermore, the SMS sensor exhibited a compressive strain sensitivity of 0.0323 nm/kN from the initial load until it reached the elastic limit.

Sensitivity enhancement of optical fiber vibration sensor through encapsulation of acoustic Helmholtz resonator

Optical fiber sensors should be encapsulated to prevent the possible damage in practical applications. Moreover, the encapsulation should be optimized to increase the sensitivity of the sensor as much as possible. Herein three different Helmholtz resonators are designed to encapsulate the singlemode-multimode-singlemode (SMS) fiber vibration sensor. Finite element analyses exhibit the acoustic pressure distributions in the resonators. The SMS fiber structures are fixed in the resonators with different schemes. Experiments demonstrate that the encapsulations increase the sensitivity of the sensors, which are determined by the fixing schemes, the acoustic pressure distributions, and the structures of the resonators. The combined resonator with two coaxially attached cavities renders the sensor a response range from 20 to 1000 Hz, which possesses a higher sensitivity and wider frequency response range than the sensor with a single cavity of resonator. The sensitivity of the encapsulated sensor with the combined resonator is 2.11 times of the sensitivity of the un-encapsulated sensor at 120 Hz. The SMS sensor encapsulated by the combined resonator exhibits a higher sensitivity than a commercial microphone, which indicates a favorable practicability of the Helmholtz resonator to the encapsulation of various kinds of fiber vibration sensors.

A fiber optic sensor based on Mach‐Zehnder interferometer structure for food composition detection

AbstractIn this article, fiber optic sensor (FOS) has been employed for food composition detection by using a Mach–Zehnder Interferometer (MZI) structure. The Single Mode–Multimode–Single Mode configuration with varied length of the sensing region with 4 cm and 8 cm were designed and analyzed. The FOS has been developed by using a fusion arc splicing technique. The sensor device has been tested with the major components of food compositions such as water, 1.0 mol sucrose solution and oil with the refractive index (RI) of 1.333, 1.384, and 1.464, respectively. The sensor device experienced a wavelength redshift as the RI increases. Meanwhile, it is also observed that the sensitivity of FOS is linearly proportional to the length of the sensor region. The best sensitivity achieved is 4.413 nm/RIU for 8 cm length of sensor region. The findings of this article can serve as a reference for improved sensitivity by manipulating the sensor's length.

Magnetic field sensor based on the magnetic-fluid-clad combined with singlemode–multimode–singlemode fiber and large core-offset splicing structure

A simple, compact optical fiber magnetic field sensor is proposed and experimentally demonstrated in this paper. It is based on the magnetic-fluid-clad combined with singlemode–multimode–singlemode fiber structure and large core-offset splicing structure. It was protected by a section of capillary tube and was sealed by UV glue. A sensing property study of the combined optical fiber structure and the proposed sensor were carried out. The experimental results show that the sensitivity of the refractive index of the optical fiber sensing structure is up to 156.63 nm/RIU and the magnetic field sensitivity of the proposed sensor is up to −97.24 pm/Oe in the range from 72.4 Oe to 297.8 Oe. The proposed sensor has several other advantages, such as simple structure, small size, easy fabrication and low cost.

Liquid level and temperature sensing by using dual-wavelength fiber laser based on multimode interferometer and FBG in parallel

Abstract The detection of liquid level and temperature based on a fiber ring cavity laser sensing configuration is presented and demonstrated experimentally. The sensing head contains a fiber Bragg grating (FBG) and a single-mode–cladding-less–single-mode multimode interferometer, which also functions as wavelength-selective components of the fiber laser. When the liquid level or temperature is applied on the sensing head, the pass-band peaks of both multimode interference (MMI) filter and FBG filter vary and the two output wavelengths of the laser shift correspondingly. In the experiment, the corresponding sensitivities of the liquid level with four different refractive indices (RI) in the deep range from 0 mm to 40 mm are obtained and the sensitivity enhances with the RI of the liquid being measured. The maximum sensitivity of interferometer is 106.3 pm/mm with the RI of 1.391. For the temperature measurement, a sensitivity of 10.3 pm/°C and 13.8 pm/°C are achieved with the temperature ranging from 0 °C to 90 °C corresponding to the two lasing wavelengths selective by the MMI filter and FBG, respectively. In addition, the average RI sensitivity of 155.77 pm/mm/RIU is also obtained in the RI range of 1.333–1.391.

Acoustic frequency vibration sensor based on tapered SMS fiber structure

The propagation of light from a singlemode fiber (SMF) to a multimode fiber (MMF) arouses a series of eigenmodes, which interference together along the MMF where the positions of the local maximum intensity are the self-imaging points (SIPs). When the light in the MMF propagates to a SMF, the maximum coupling efficiency is obtain when the SMF and MMF connect at a SIP. However the connection generally deviates the SIPs for the accurate connection is difficult to be achieved, which decreases the accuracy of the sensor severely. Herein a novel vibration sensor based on the singlemode multimode singlemode (SMS) fiber is developed, in which the MMF is etched, which turns the SIP to the connection of the MMF and the output SMF accurately. The etched SMS structure dispenses with the requirement of highly accurate connection at a SIP and provides a succedaneous scheme that is sensitive to vibration. The etched sensor responses to the vibration more easily comparing to the un-etched one. Experimental results demonstrate that the sensitivity of the SMS sensor with the both ends etched is respectively over 5 and 40 times as that of the middle etched and un-etched one. When the MMF length decreases from 8 to 2 cm, the vibrating sensitivity of the sensor increases 13.5 times. Experimental results demonstrate that the etched structure with MMF length of 2 cm responses well to the acoustic wave from 20 to 300 Hz, where a pressure sensitivity of 1.49 mV/mPa and linear correlation index of 0.9980 can be attained at 120 Hz.