Compact fiber-optic curvature sensor based on super-mode interference in a seven-core fiber.
TL;DR: A compact, low loss, and highly sensitive optical fiber curvature sensor is presented, which allows for using either visibility or spectral shift for sensor interrogation when the device is bent.
Abstract: A compact, low loss, and highly sensitive optical fiber curvature sensor is presented. The device consists of a few-millimeter-long piece of seven-core fiber spliced between two single-mode fibers. When the optical fiber device is kept straight, a pronounced interference pattern appears in the transmission spectrum. However, when the device is bent, a spectral shift of the interference pattern is produced, and the visibility of the interference notches changes. This allows for using either visibility or spectral shift for sensor interrogation. The dynamic range of the device can be tailored through the proper selection of the length of the seven-core fiber. The effects of temperature and refractive index of the external medium on the response of the curvature sensor are also discussed. Linear sensitivity of about 3000 nm/mm−1 for bending was observed experimentally.
Citations
More filters
TL;DR: The authors' MCF bending sensor was found to be highly sensitive (4094 pm/deg) to small bending angles and it is capable of distinguishing multiple bending orientations.
Abstract: In this Letter, we demonstrate a compellingly simple directional bending sensor based on multicore optical fibers (MCF). The device operates in reflection mode and consists of a short segment of a three-core MCF that is fusion spliced at the distal end of a standard single mode optical fiber. The asymmetry of our MCF along with the high sensitivity of the supermodes of the MCF make the small bending on the MCF induce drastic changes in the supermodes, their excitation, and, consequently, on the reflected spectrum. Our MCF bending sensor was found to be highly sensitive (4094 pm/deg) to small bending angles. Moreover, it is capable of distinguishing multiple bending orientations.
113 citations
TL;DR: A review of optical fiber bending sensors is presented in this article, where the authors mainly focus on the measurement methods of the structure bending and the existing problems of the bending measurement methods and the future prospects of different bending sensors.
88 citations
TL;DR: A bending sensor is demonstrated using the combination of a mode-selective photonic lantern (PL) and a multicore fiber, which reveals a high sensitivity to bending curvature and differential power distributions according to bending direction, without the need for spectral measurements.
Abstract: A bending sensor is demonstrated using the combination of a mode-selective photonic lantern (PL) and a multicore fiber. A short section of three-core fiber with strongly coupled cores is used as the bend sensitive element. The supermodes of this fiber are highly sensitive to the refractive index profiles of the cores. Small bend-induced changes result in drastic changes of the supermodes, their excitation, and interference. The multicore fiber is spliced to a few-mode fiber and excites bend dependent amounts of each of the six linearly polarized (LP) modes guided in the few-mode fiber. A mode selective PL is then used to demultiplex the modes of the few-mode fiber. Relative power measurements at the single-mode PL output ports reveal a high sensitivity to bending curvature and differential power distributions according to bending direction, without the need for spectral measurements. High direction sensitivity is demonstrated experimentally as well as in numerical simulations. Relative power shifts of up to 80% have been measured at radii of approximately 20 cm, and good sensitivity was observed with radii as large as 10 m, making this sensing system useful for applications requiring both large and small curvature measurements.
70 citations
TL;DR: In this article, a simple and compact optical fiber sensor based on multipath Mach-Zehnder interferometer (m-MZI) is proposed and experimentally demonstrated, which consists of a segment of four-core fiber (FCF) spliced between two single-mode fibers (SMFs).
Abstract: A novel, simple and compact optical fiber sensor based on multipath Mach-Zehnder interferometer (m-MZI) is proposed and experimentally demonstrated. The device consists of a segment of four-core fiber (FCF) spliced between two single-mode fibers (SMFs). When the m-MZI is kept straight, an obvious interference pattern appears in the transmission spectrum. Compared with previously reported optical fiber modal interferometers, higher phase sensitivity can be obtained in our scheme due to the multipath interference configuration embedded in one fiber. The maximum fringe visibility of the interference resonance dips exceeds 23 dB. The interference fringe of the FCF would shift with the variation of strain, temperature, refractive index (RI) and curvature. So it is possible to measure these parameters by simply monitoring the wavelength shifts. Experimental results show that the sensitivities of the sensor in strain, temperature, RI and curvature are 1.78 pm/μe, 209 pm/°C, 91.39 nm/RIU and 20.18 nm/m↙1, respectively. To the best of our knowledge, the multi-purpose sensing applications of the sensor have been experimentally investigated for the first time. Moreover, the proposed sensor has the advantages of high fringe visibility and simple fabrication process.
61 citations
TL;DR: In this article, a novel fiber Bragg grating (FBG) structure based on an eccentric core fiber (ECF) and a singlemode fiber (SMF) was proposed and experimentally demonstrated for distinguishing the bending effect from the axial strain effect and measuring the pure directional bending.
Abstract: A novel fiber Bragg grating (FBG) structure based on an eccentric core fiber (ECF) and a single-mode fiber (SMF) was proposed and experimentally demonstrated for distinguishing the bending effect from the axial strain effect and measuring the pure directional bending The structure is fabricated by writing a FBG on the fusion splice junction between an ECF and a SMF The FBG formed on the ECF-SMF junction has two different resonant peaks because of the different refractive indices of the two fibers The peak relating to the ECF is sensitive to both directional bending and axial strain, while the peak corresponding to the SMF is only sensitive to strain By using the unique FBG structure, one can directly know whether a bending is accompanied by an axial strain, and can obtain both the direction and curvature of the bending Experimental results show that the bending sensitivities of the FBG in the ECF part are 493 and −503 ${\rm{pm}}/{{\rm{m}}^{ - 1}}$ at directions of 0° and 180°, respectively, and the strain sensitivities of the FBG in the ECF and SMF are 074 and 070 pm/μϵ, respectively
56 citations
Cites background from "Compact fiber-optic curvature senso..."
...[4], [5], gratings written in specific fibers [6]–[9], and a variety of inline interferometers [10]–[13]....
[...]
References
More filters
TL;DR: In this article, the curvature loss for optical fibers with constant radius of curvature of their axes is derived by expressing the field outside of the fiber in terms of a superposition of cylindrical outgoing waves.
Abstract: The loss formula for optical fibers with constant radius of curvature of their axes is derived by expressing the field outside of the fiber in terms of a superposition of cylindrical outgoing waves. The expansion coefficients are determined by matching the superposition field to the field of the fiber along a cylindrical surface that is tangential to the outer perimeter of the curved fiber. This method is a direct extension of my derivation of the curvature-loss formula for slab guides.
620 citations
TL;DR: A simple and compact modal interferometer for applications in refractometry that is highly stable over time, has low temperature sensitivity, and is suitable for measuring indices in the 1.330-1.440 range is reported.
Abstract: We report a simple and compact modal interferometer for applications in refractometry. The device consists of a stub of large-mode-area photonic crystal fiber (PCF) spliced between standard single-mode fibers. In the splice regions the voids of the PCF are fully collapsed, thus allowing the coupling and recombination of PCF core and cladding modes. The device is highly stable over time, has low temperature sensitivity, and is suitable for measuring indices in the 1.330-1.440 range. The measure of the refractive index is carried out by monitoring the shift of the interference pattern.
245 citations
TL;DR: In this paper, a fiber Michelson interferometer refractive index (RI) sensor with a single core-offset attenuator and a layer of ~ 500-nm gold coating was demonstrated.
Abstract: Mach-Zehnder and Michelson interferometers using core-offset attenuators were demonstrated. As the relative offset direction of the two attenuators in the Mach-Zehnder interferometer can significantly affect the extinction ratio of the interference pattern, single core-offset attenuator-based sensors appear more robust and repeatable. A novel fiber Michelson interferometer refractive index (RI) sensor was subsequently realized by a single core-offset attenuator and a layer of ~ 500-nm gold coating. The device had a minimum insertion loss of 0.01 dB and maximum extinction ratio over 9 dB. The sensitivity (0.333 nm) of the new sensor to its surrounding RI change (0.01) was found to be comparable to that (0.252 nm) of an identical long period gratings pair Mach-Zehnder interferometric sensor, and its ease of fabrication makes it a low-cost alternative to existing sensing applications.
213 citations
TL;DR: In this article, an effective method of realizing optical bend sensing based on the measurement of bending-curvature encoded resonance mode splitting of long-period fiber grating was proposed.
Abstract: We report an effective new method of realizing optical bend sensing based on the measurement of bending-curvature encoded resonance mode splitting of long-period fiber grating. The bending induced mode splitting exhibits a near-linear response and the bending sensitivity achieved by this method is nearly four times higher than the previously reported wavelength shift detection method. The evolution of the transmission loss under bending appears dependent on the initial mode coupling strength.
181 citations
TL;DR: A novel high temperature sensor based on customized multicore fiber (MCF) spliced between two standard single-mode fibers is proposed and experimentally demonstrated, enabling temperature measurements with high sensitivity and accuracy.
Abstract: A novel high temperature sensor based on customized multicore fiber (MCF) is proposed and experimentally demonstrated. The sensor consists of a short, few-centimeter-long segment of MCF spliced between two standard single-mode fibers. Due to interference effects, the transmission spectrum through this fiber chain features sharp and deep notches. Exposing the MCF segment to increasing temperatures of up to 1000°C results in a shift of the transmission notches toward longer wavelengths with a slope of approximately 29 pm/°C at lower temperatures and 52 pm/°C at higher temperatures, enabling temperature measurements with high sensitivity and accuracy. Due to its compact size and mechanical rigidity, the MCF sensor can be subjected to harsh environments. The fabrication of the MCF sensor is straightforward and reproducible, making it an inexpensive fiber device.
158 citations