Design and implementation of an acoustic wave measuring system based on a fiber optic sensor using multimodal interference

An integrated fiber-optic displacement sensor based on multimode interference is characterized through analysis of experimental performance in comparison to the expected behavior that is theoretically predicted. Multimode interference and re-imaging theory applied to the specific fiber properties and geometry of the device can be used to design and predict the performance of the device. Essentially, the sensor consists of a multimode fiber of a specific length fusion spliced to a single mode fiber used in conjuction with an 80/20 splitter, source, and detector that are used to inject and detect reflected signals from targets. The sensor is fabricated into a robust, compact, and single arm device capable of operating as a calibrated displacement sensor over a large displacement range. This is achieved through analysis of power reflected off of a surface and back through the device over a finite wavelength range.

Highly sensitive and real-time detection of acetone biomarker for diabetes using a ZnO-coated optical fiber sensor.

Fiber-optic temperature sensor based on a thinner no-core fiber

We review our recent work on optical biosensors based on microring resonators (MRR) integrated with 4x4 multimode interference (MMI) couplers for multichannel and highly sensitive chemical and biological sensors. The proposed sensor structure has advantages of compactness, high sensitivity compared with the reported sensing structures. By using the transfer matrix method (TMM) and numerical simulations, the designs of the sensor based on silicon waveguides are optimized and demonstrated in detail. We applied our structure to detect glucose and ethanol concentrations simultaneously. A high sensitivity of 9000 nm/RIU, detection limit of 2x10-4 for glucose sensing and sensitivity of 6000nm/RIU, detection limit of 1.3x10-5 for ethanol sensing are achieved.
 Keywords
 Biological sensors, chemical sensors, optical microring resonators, high sensitivity, multimode interference, transfer matrix method, beam propagation method (BPM), multichannel sensor
 References
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Optical fiber sensor with a lateral-offset structure assisted by virtual vernier effect for stretching strain measurement

This paper reports on the refractometric detection of water-adulterated milk using an optical fiber sensor whose principle of operation is based on multimode interference (MMI). The device is manufactured in a simple way by splicing a segment of coreless multimode fiber (NC-MMF) between two single-mode fibers (SMFs); neither functionalization nor deposition of a sensing material is required. MMI takes place in the NC-MMF and, when fed with a broadband spectrum, a transmission peak appears at the output of the MMI device due to its inherent filter-like response, whose position depends on the effective refractive index (RI) of the medium surrounding the NC-MMF. Therefore, when the sensor is immersed in different milk–water mixtures, the peak wavelength shifts according to the RI of the mixture. In this way, adulterated milk can be detected from the wavelength shift of the transmission peak. The system was tested with two commercial brands of milk, and adulterations were clearly distinguished in both cases. In the range of interest, from no dilution up to 50% dilution, the sensor exhibits a linear response with a sensitivity of −0.04251 and −0.03291 nm/%, respectively, for the two samples tested. The measurement protocol is repeatable and allows for locating the peak wavelength within <0.34 nm over several repetitions using different samples with the same concentration. A thermal sensitivity of 0.85 nm/°C was obtained, which suggests that the temperature needs to be maintained as fixed during the measurements. The approach presented can be extended to other scenarios as a quality control tool in beverages for human consumption, showing the advantages of simple construction, high sensitivity, and the potential for real-time monitoring.

The bending deformation and matrix cracking were investigated by conducting a four-point bending test for a cross-ply composite beam with an embedded fiber optic Michelson sensor. The fiber optic Michelson interferometric sensor was constructed and embedded in the composite beam. The failure of composite beam, due to the matrix cracking, was successfully detected by the fiber optic sensor and the matrix crack in the composite beam was confirmed by an edge replica method. The characteristics of the failure signals from the fiber optic sensor were studied. The strain and failure signals of the composite beam were separated by digital filtering of the signal from the fiber optic sensor. The failure was obviously detectable by the failure signal filtered from the optical signal.

Strain measurements on pipelines provide a nondestructive means to evaluate their in-service conditions. They have been proposed to detect abnormal operating pressures, pipe wall problems, or intrusive pipeline events. For such applications, optical fiber sensors are especially appealing because of their hazard and electromagnetic interference-free nature. In this work, two different types of optical fiber sensors are compared for use to monitor the hoop strain on a pressurized pipe, the well-developed fiber Bragg grating (FBG) sensor and a proposed simple fiber sensor based on multimode interference (MMI). The FBG sensor shows a better linearity of strain measurement, while the MMI sensor provides a larger wavelength shift with strain at relatively low pressures. An intensity-based detection of vibrations, simulating an intrusive pipe drilling event, was achieved using the proposed MMI sensor.

Development and evaluation of optical fiber NH3 sensors for application in air quality monitoring

In the last few years, the nuclear industry has experienced some problems with the performance of pressure transmitters and has been interested in new sensors based on new technologies. Fiber optic pressure sensors offer the potential to improve on or overcome some of the limitations of existing pressure sensors. Up to now, research has been motivated towards development and refinement of fiber optic sensing technology. In most applications, reliability studies and failure mode analyses remain to be exhaustively conducted. Fiber optic sensors have currently penetrated certain cutting edge markets where they possess necessary inherent advantages over other existing technologies. In these markets (e.g. biomedical, aerospace, automotive, and petrochemical), fiber optic sensors are able to perform measurements for which no alternate sensor previously existed. Fiber optic sensing technology has not yet been fully adopted into the mainstream sensing market. This may be due to not only the current premium price of fiber optic sensors, but also the lack of characterization of their possible performance disadvantages. In other words, in conservative industries, the known disadvantages of conventional sensors are sometimes preferable to unknown or not fully characterized (but potentially fewer and less critical) disadvantages of fiber optic sensors. A six-month feasibility study has been initiated under the auspices of the US Nuclear Regulatory Commission (NRC) to assess the performance and reliability of existing fiber optic pressure sensors for use in nuclear power plants. This assessment will include establishment of the state of the art in fiber optic pressure sensing, characterization of the reliability of fiber optic pressure sensors, and determination of the strengths and limitations of these sensors for nuclear safety-related services.

We have developed a simple, high-sensitivity optical-fiber temperature sensor based on multimode interference (MMI). The fabricated MMI structure comprises three segmented fibers: a single-mode fiber (SMF); a large-core multimode fiber (MMF), whose outer surface is coated with a temperature-sensitive material; and another SMF. Fluoroacrylate and silicone rubber are tested as temperature-sensitive cladding materials. The silicone rubber coating exhibits a large shift in interference wavelength with temperature, producing a very fine temperature resolution as low as 0.01 °C.

A novel ultrasensitive fiber-optic refractive index (RI) sensor is proposed and experimentally demonstrated for solute concentration measurement. To realize higher RI sensitivity, we insert a fiber-optic multimode interference sensor into a fiber-loop configuration to produce a steeper spectrum. The interaction with multimode interference is repeated and enhanced by the fiber loop, resulting in an output spectrum steeper than that obtained without a fiber loop. An ultrahigh RI resolution of 3.06 × 10−7 refractive index unit (RIU) is obtained in the steepest RI range, and it is higher by approximately 53.6 times. We apply this sensor to the measurement of the concentration of a sodium chloride solution and obtain a resolution of 1.87 × 10−4 wt %. This result agrees well with the RI measurement result. The results show that this ultrasensitive RI sensor has the potential for detection applications in the chemical and biomedical fields.

Fiber optic sensors (FOSs) have transformed industrial applications with their high sensitivity and precision, especially in real-time monitoring. This study presents a fiber optic sensor based on multimodal interference (MMI) applied to detect honey adulteration. The sensor is built using a non-core multimode fiber (NC-MMF) segment spliced between two standard single-mode fibers (SMFs). We focus on reporting the detection of two main adulterants in honey that modify its refractive index (RI): the presence of glucose and moisture content. Detailed testing was performed with two commercially approved honey brands, named A and B. The sensor successfully detected glucose concentrations from 1% to 5% and moisture content from 0% to 20% for both brands. For glucose detection, we obtained sensitivity values −0.55457 nm/% for brand A and −2.61257 nm/% for brand B. In terms of moisture content in honey, we observed a sensitivity around −0.3154 nm/% and −0.3394 nm/% for brands A and B, respectively. Additionally, temperature tests were performed, showing that the sensor works optimally up to 30 °C. The results were validated using a conventional refractometer, showing a close agreement with the data obtained and confirming the reliability and accuracy of the proposed sensor. Compared to other refractometers, the MMI sensor offers advantages such as real-time monitoring, ease of assembly, cost-effectiveness, and minimal maintenance. Furthermore, the sensor represents an alternative tool to guarantee the quality and authenticity of honey, overcoming the limitations of conventional measurement techniques.

We introduced a fiber-optic sensor, based on multimode interference, in a fiber-loop technique to realize ultrasensitive refractive index measurement. The multiplied interaction of multimode interference in the fiber-loop enlarged the spectral contrast, resulting in a sensitivity several tens of times higher than that of the sensor without the fiber-loop.

In this paper, an underwater fiber-optic sensor based on surface plasmon resonance (SPR) and multimode interference (MMI) is presented for simultaneous measurement of salinity and pressure. This sensor is based on a single-mode-multimode-single-mode-multimode-single-mode structure with a gold film deposited on the middle single-mode fiber and the fiber structure is wrapped around an elastic cylinder to constitute a sensing head. In the fiber structure, the SPR region produces a resonance dip to measure salinity, and the independent MMI region achieves narrow and salinity-insensitive interference dips to measure pressure. Performance of the sensor is predicted by calculation, and the MMI spectrum is simulated by using the finite-difference beam propagation method. By experimental tests for salinity and pressure, the sensitivities of 0.36 nm/‰ and -1.42nm/MPa are achieved, respectively, and the cross talk is also proved to be insignificant. This study provides an important application direction for SPR-MMI sensors and a prospective method for ocean detection.