Single-mode-multimode-single-mode Fiber Structure Research Articles

Magnetic field sensing based on singlemode–multimode–singlemode fiber structures using magnetic fluids as cladding

Magnetic field sensing based on magnetic fluid (MF) and a singlemode-multimode-singlemode (SMS) fiber structure is proposed. The sensitivity of the proposed sensing system can be enhanced by corroding the cladding of the multimode fiber of the SMS fiber structure. The achieved maximum magnetic field sensitivity of our experimental structures is -16.86 pm/Oe as the fiber is corroded for 1680 s. The visibility of the interference dip for the MF-clad SMS fiber structure decreases with corrosion time. Considering the trade-off between sensitivity and visibility, the figure of merit of the sensing system is employed to evaluate the sensing performance comprehensively. In our experiments, the structure corroded for ~1620 s is found to have maximum sensing performance.

Sensitivity enhancement in a multimode interference-based SMS fibre structure coated with a thin-film: Theoretical and experimental study

Multimode interference in a single-mode–multimode–single-mode (SMS) fibre structure leads to the generation of transmission bands and attenuation bands in the optical spectrum. In this work, the progressive deposition, with layer-by-layer assembly technique, of a high refractive index thin-film onto the SMS structure permits to observe the evolution of the bands as a function of the coating thickness. The results show that it is possible to increase the sensitivity of the device to variations of the coating thickness, what indicates the adequateness of this structure as a sensing platform. The experimental results are corroborated with a numerical method based on coupled-mode theory. As a practical application, a sensitivity improvement has been obtained a pH sensor by increasing the coating thickness.

Relative humidity sensor based on SMS fiber structure with polyvinyl alcohol coating

A novel relative humidity (RH) sensor based on single-mode–multimode–single-mode (SMS) fiber structure is presented. The sensors are created through coating a thin layer of polyvinyl alcohol (PVA) on the multimode fiber deleted the cladding trough HF solution cauterization as the sensitive cladding film, whose refractive index varies as a function of humidity level. Due to the SMS fiber structure's sensitivity to ambient refractive index, the transmission spectra of SMS fiber structure coated PVA film are modified under exposure to different ambient humidity levels ranging from 30% to 80% RH. The related numerical simulations of transmission spectra of SMS fiber structure with different surrounding refractive index are also proposed. The sensitive of the RH measurement of 0.09nm/% RH in the range from 30% to 80% RH is experimentally achieved. Meanwhile the intensity of wavelength at 1543nm is decreasing as the humidity increasing. The experimental results obtained are consistent with the conclusion obtained by numerical simulating.

SMS fiber structure for temperature measurement using an OTDR

A singlemode-multimode-singlemode (SMS) fiber structure for temperature measurement using an optical time domain reflectometer (OTDR)-based interrogation system is proposed. A temperature measurement range of 40 °C–195 °C with a resolution of 0.12 °C and a linearity of 0.992 could be achieved for the multimode fiber (MMF) graded index with a length of 60 mm. It was also demonstrated that two-point temperature measurement with two SMS fiber structures as temperature sensors could be made. The proposed temperature measurement system offered a high resolution and also benefited from a simple configuration with a capability of multi-point temperature measurement.

Detection of liquid-level variation using a SMS fiber structure

A novel liquid-level sensor based on a single-mode-multimode-single-mode (SMS) fiber structure is proposed and demonstrated. The transmission spectra of the SMS fiber structure are dependent on the fraction of the length of the multimode fiber that is surrounded by the liquid. Both experimental and numerical results with different liquid levels are presented. The experiment results show that the resonance wavelength exhibits a total blue-shift 4nm with the variation of liquid-level 4mm. Meanwhile transmission optical power is obviously decreases in the wavelength range from 1523nm to 1534nm with the increase of the liquid-level. A measurement sensitivity of 1.02nm/mm and 1.03dB/mm is achieved, respectively.

侧边抛磨SMS光纤传感器

A new type of optical fiber refractive index sensor was reported.The partial multimode fiber of Singlemode-Multimode Singlemode(SMS)fiber structures were side polished,and then the refractive index sensing properties were analyzed.The results show that multiple loss peaks can be observed in the spectrum of the SMS fiber structures because of the mutual interference by the high order modes of multimode fiber.The spectrum of the SMS fiber structures just drift a few nanometres when the SMS fiber structures are polished to close to the core;but when being side polished to the core of the fiber,the spectrum changes dramatically.After being side polished,the refractive index resolution of the SMS fiber structures will be higher.When the polishing depth is 10μm and the polishing length is 10mm,the refractive index sensitivity of the SMS fiber structure is 703.2nm/RIU.When the polishing depth is 15μm,the refractive index sensitivity of the SMS fiber structure is 798nm/RIU.When the polishing depth is 20μm,the refractive index sensitivity of the SMS fiber structure is up to 1 190nm/URI.A new type of optical fiber refractive index sensor can be realized with a single side polished SMS fiber structure,and the sensitivity of the sensor can be improved by increasing the depth of polishing area.

Curvature and Temperature Discrimination Using Multimode Interference Fiber Optic Structures—A Proof of Concept

Singlemode-multimode-singlemode fiber structures (SMS) based on distinct sections of a pure silica multimode fiber (coreless-MMF) with diameters of 125 and 55 μm, were reported for the measurement of curvature and temperature. The sensing concept relies on the multimode interference that occurs in the coreless-MMF section and, in accordance with the length of the MMF section used, two fiber devices were developed: one based on a bandpass filter (self-image effect) and the other on a band-rejection filter. Maximum sensitivities of 64.7 nm·m and 13.08 pm/°C could be attained, for curvature and temperature, respectively, using the band-rejection filter with 55 μm-MMF diameter. A proof of concept was also explored for the simultaneous measurement of curvature and temperature by means of the matrix method.

Sensitivity enhancement of RI sensor based on SMS fiber structure with high refractive index overlay

We propose a novel way to enhance the sensitivity of single-mode-multimode-single-mode (SMS) fiber structure in the measurement of surrounding refractive index (RI), which is realized by depositing the multimode fiber section with a high RI overlay. First, as an essential basis of the analysis of the novel structure, characteristics of mode reorganizations in the deposited multimode fiber are discussed. Second, based on full-vector mode expansion, a theoretical analysis of transmission characteristics of the deposited SMS fiber structure is presented. Third, aimed at RI measurement ranges which are of common interest in liquid and gas sensing, the transmission spectra of the structure in response to the surrounding RI are investigated by simulations. To well utilize the collective effect of multiple interference modes in mode reorganizations, the monitoring based on wavelength shifts of valleys and the optimization of the overlay are analyzed for various application requirements. Lastly, largely enhanced sensitivities for RI measurements are demonstrated with properly designed overlay. For RI ranges from 1.31 to 1.35 and 1.0 to 1.03, average sensitivities of 900 and 206 nm/RIU are achieved with overlay thicknesses of 340 and 470 nm, respectively.

Evanescent field coupling between two parallel close contact SMS fiber structures

We proposed a novel optical coupling technique based on two parallel singlemode-multimode-singlemode (SMS) fiber structures. This technique utilizes one SMS structure to excite multiple cladding modes within an output singlemode fiber. The excited multiple cladding modes will be coupled to the input SMF in the second SMS structure by placing the two SMS fiber structures in parallel and in close contact each other. The coupled cladding modes will be re-coupled to a guided core mode by the second SMS fiber structure. Theoretical analysis for such technique was provided and experimentally we have achieved a pass band spectral response with an extinction ratio higher than 20 dB and a maximum coupling efficiency of 5.9%.

Temperature and strain-independent curvature sensor based on a singlemode/multimode fiber optic structure

This work describes a fiber optic sensing structure that is sensitive to curvature, and features a low temperature- and strain cross-sensitivity. It is based on multimode interference, and relies on a singlemode–step index multimode–singlemode fiber structure. It was observed that the transmitted optical power in such a layout is highly sensitive to the wavelength of operation, and to the length of the multimode fiber. The optical spectrum exhibits two dominant loss bands, at wavelengths that have similar responses both to temperature and strain, but different responses to curvature. Based on this result, an interrogation approach is proposed that permits substantial sensitivity to curvature (8.7 ± 0.1 nm m) and residual sensitivities to temperature and strain (0.3 ± 0.1 pm °C−1 and (−0.06 ± 0.01) × 10−6 m m−1, respectively). The beam-propagation method was employed for modeling the propagation of light along the optical fiber sensing device proposed.

Single‐mode–multimode–single‐mode fiber structures for simultaneous measurement of strain and temperature

AbstractThis article presents two related techniques for the simultaneous measurement of strain and temperature: (1) using two single‐mode–multimode–single‐mode (SMS) fiber structures accompanied with an optical spectral analyzer (OSA); (2) using three SMS fiber structures and a ratiometric power measurement system.Experimental results show that (1) the technique accompanied with an OSA has a resolution of 1.64 με for strain in the range from 0 to 1000 με and 0.11°C for temperature and (2) the technique based on ratiometric system offers a resolution of better than 2 με for strain measurements in the range from 0 to 1000 με and a resolution better than 0.84°C for temperature. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26205

Fiber refractometer based on a fiber Bragg grating and single-mode–multimode–single-mode fiber structure

A refractive index (RI) sensor based on a novel fiber structure that consists of a single-mode-multimode-single-mode (SMS) fiber structure followed by a fiber Bragg grating was demonstrated. The multimode fiber in the SMS structure excites cladding modes within output single-mode fiber (SMF) and recouple the reflected cladding Bragg wavelength to the input SMF core. By measuring the relative Bragg wavelength shift between core and cladding Bragg wavelengths, the RI can be determined. Experimentally we have achieved a maximum sensitivity of 7.33 nm/RIU (RI unit) at RI range from 1.324 to 1.439.

All-Fiber Curvature Sensor Based on Multimode Interference

A fiber-optic curvature sensor based on the single-mode-multimode-single-mode (SMS) fiber structure is developed. Several notches in the transmitted spectrum of the SMS fiber structure are generated due to the multimode interference effect. The dependence of the wavelength shifts and intensity changes of three transmission notches on the applied curvature are different from each other. The maximum sensitivities of wavelength-curvature and intensity-curvature relationships are - 10.38 nm/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and - 130.37 dB/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> respectively. By properly choosing to measure wavelength shifts or intensity changes, high sensitivity measurement of curvature over a large scale can be obtained. The wavelength of the second notch is insensitive to the curvature change, offering the possibility for simultaneous measurement of curvature and other parameters such as temperature or strain.

Experimental demonstration of a simple displacement sensor based on a bent single-mode–multimode–single-mode fiber structure

A simple displacement sensor based on a bent single-mode–multimode–single-mode (SMS) fiber structure is proposed and experimentally investigated. The sensor offers a wider displacement range, not limited by the risk of fiber breakage, as well as a three-fold increase in displacement sensitivity by comparison with a straight SMS structure sensor. This sensor can be interrogated by either an optical spectral analyzer (OSA) or a ratiometric interrogation system: (1) if interrogated by an OSA assuming a resolution of 1 pm, it has a sensitivity of 28.2 nm for a displacement measurement range from 0 to 280 µm; (2) if interrogated by a ratiometric interrogation system, it has worst and best case resolutions of 556 and 38 nm, respectively, for a displacement measurement range from 0 to 520 µm.

A voltage sensor based on a singlemode–multimode–singlemode fiber structure

AbstractA voltage sensor based on a singlemode–multimode–singlemode (SMS) fiber structure, attached to a piezoelectric (PZT), used in a ratiometric optical power measurement scheme is proposed. The elongation of the PZT due to an applied voltage induces a strain on the SMS fiber structure and in turn results in a change in the transmission loss response of the SMS fiber structure. It is found that at selected wavelengths, a strong voltage dependence for the transmission loss of the SMS fiber structure can be achieved. The voltage information can be obtained from the power ratio of the system, assuming the system is calibrated. The proposed voltage sensor offers a simpler configuration when compared to other fiber optic voltage sensors. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1887–1890, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25339

Polarization dependence of an edge filter based on singlemode–multimode–singlemode fibre

The polarization dependent loss (PDL) of a singlemode–multimode–singlemode (SMS) fibre structure used as an edge filter is presented. Minor errors in the fabrication process for the SMS fibre structure can introduce SMS fibre core offsets. The PDL due to lateral and rotational core offsets is investigated numerically and experimentally. It is shown that small core offsets are necessary to achieve low PDL for an SMS fibre based edge filter. It is also demonstrated that when lateral core offsets are unavoidable, the PDL of a SMS edge filter can still be minimized by introducing a rotational core offset of 90 °.

Bent SMS fibre structure for temperature measurement

A temperature sensor fabricated using a bent singlemode-multimode-singlemode (SMS) fibre structure is presented. Experimental results show, that compared to a sensor based on a straight SMS fibre structure, this temperature sensor has a much higher sensitivity of 31.97 pm/°C over a temperature range from 20 to 80°C, based on the measurement of the mean 3 dB wavelength shift, and offers a resolution of 0.1°C for a temperature range from 45 to 80°C when demodulated by a simple ratiometric interrogation technique.

Analysis of temperature dependence for a ratiometric wavelength measurement system using SMS fiber structure based edge filters

Temperature dependence of an edge filter based on singlemode–multimode–singlemode (SMS) fiber structure is investigated numerically and experimentally. The experimental results and numerical results are in good agreement within an operational temperature range from 10 °C to 40 °C. It is found that the thermo-optic coefficient (TOC) has a more significant effect on the temperature dependence of an SMS edge filter compared to the thermal expansion coefficient (TEC). In the ratiometric wavelength measurement using two SMS edge filters, a small temperature variation can induce the ratio variation and in turn the wavelength measurement error. It is found the SMS edge filter’s response to both wavelength and temperature is linear. It is proposed that self-monitoring of temperature can be carried out using an updated ratiometric scheme. Self-monitoring of the temperature reduces temperature induced wavelength error to ±0.7 pm at 1545 nm, regardless of the ambient temperature variation.

SMS fibre structure for temperature measurement using a simple intensity-based interrogation system

A singlemode–multimode–singlemode (SMS) fibre structure for temperature measurement that utilises a simple intensity-based interrogation system is proposed. The temperature dependence of the SMS fibre structure utilised as a sensor is investigated numerically and experimentally. It is found that a strong temperature dependence for the SMS fibre structure exists at selected wavelengths. The temperature characteristic at such wavelengths is linear in nature and can be used for temperature measurements. The proposed temperature sensor offers a high resolution and accuracy, and also benefits from a simple configuration and low cost when compared to other fibre-optic temperature sensors.