TL;DR: The finite element method (FEM) model was used to investigate the modal behavior in multicore Fiber and to predict the phase-matching curves of the long period grating inscribed into multicore fiber.
Abstract: Long period grating was UV inscribed into a multicore fiber consisting of 120 single mode cores. The multicore fiber that hosts the grating was fusion spliced into a single mode fiber at both ends. The splice creates a taper transition between the two types of fiber that produces a nonadiabatic mode evolution; this results in the illumination of all the modes in the multicore fiber. The spectral characteristics of this fiber device as a function of curvature were investigated. The device yielded a significant spectral sensitivity as high as 1.23 nm/m-1 and 3.57 dB/m-1 to the ultra-low curvature values from 0 to 1 m-1. This fiber device can also distinguish the orientation of curvature experienced by the fiber as the long period grating attenuation bands producing either a blue or red wavelength shift. The finite element method (FEM) model was used to investigate the modal behavior in multicore fiber and to predict the phase-matching curves of the long period grating inscribed into multicore fiber.
A series of simulations were conducted over a range of wavelengths to obtain the effective indices of the core and cladding modes.
Fig. 6 (a) shows the spectral sensitivity of the sensor when subjected to a range of curvatures in both of the convex and concave directions.
As previously mentioned, the full cross section of the MCF core region, ~ 180 µm, is significantly larger than the inscription beam diameter (~120 µm) resulting in LPG inscription in only 46 cores of the MCF.
As a result, the spectral sensitivity of LPG, for which the wavelengths shift of the central LPG peak is measured, for the convex curvature is almost half of the correspondent measured value for the concave bending.
TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.
Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …
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.
TL;DR: A compact and highly-sensitive curvature sensor based on a Mach-Zehnder interferometer created in a photonic crystal fiber that exhibited a high curvature sensitivity and a temperature sensitivity suitable for high-sensitivity curvature sensing in harsh environments is demonstrated.
Abstract: 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.
TL;DR: In this article, the use of long period gratings (LPGs) for the implementation of a directional curvature sensor has been studied and a set of three different LPGs were inscribed in a seven core optical fiber using a selective inscription technique.
Abstract: Multicore optical fibers are especially attractive for the fabrication of curvature and shape sensors due to the spatial distribution of the different cores. Fiber Bragg gratings have been used in the past for the implementation of these sensors, however, despite their inherent properties, they have a very limited sensitivity. In this paper, we study the use of long period gratings (LPGs) for the implementation of a directional curvature sensor. We inscribed a set of three different LPGs in a seven core optical fiber using a selective inscription technique. We inscribed a single LPG in the external cores and an array of three LPGs in the central core. We have characterized the proposed sensor for strain, torsion, and curvature magnitude and direction. The proposed sensor shows a linear response for curvature magnitudes from 0 to 1.77 m–1 with a maximum curvature sensitivity of –4.85 nm/m–1 and shows a near sinusoidal behavior in all the cores with curvature directions from 0° to 360°. The sensor shows a good insensitivity to strain. The torsion in the multicore optical fibers can be detected and measured using the maximum attenuation of the LPGs in the external cores.
79 citations
Cites background from "Long period grating in multicore op..."
...special shape fibers, cladding index modification and multicore optical fibers (MCF) [3]–[5]....
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.
"Long period grating in multicore op..." refers background in this paper
...There are many successful examples in the literature of employing standard LPGs in various radially asymmetric fibers [4-8] or inscribed asymmetric gratings in radially symmetric fiber [9-16] to create a directional bend sensor....
TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.
Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …
33,785 citations
"Long period grating in multicore op..." refers background in this paper
...LPGs have shown potentials in the field of telecommunications [2] and are a topic of research in environmental sensing through their sensitivity to strain, bending, temperature, and the refractive index of surrounding medium [3]....
TL;DR: A novel class of highly sensitive sensors based on long-period fiber gratings that can be implemented with simple and inexpensive demodulation schemes are presented.
Abstract: We present a novel class of highly sensitive sensors based on long-period fiber gratings that can be implemented with simple and inexpensive demodulation schemes. Temperature, strain, and refractive-index resolutions of 0.65 °C, 65.75 μ∈, and 7.69 × 10−5, respectively, are demonstrated for gratings fabricated in standard telecommunication fibers.
TL;DR: In this article, two complementary delineation criteria are presented which provide guidelines to the design of relatively short, low-loss tapered fibres and devices, which are used to explain anomalous loss effects in depressed-cladding and W-fibres, as well as the difficulty in fabricating low loss devices by tapering such fibres.
Abstract: Two complementary delineation criteria are presented which provide guidelines to the design of relatively short, low-loss tapered fibres and devices. They are used to explain anomalous loss effects in depressed-cladding and W-fibres, as well as the difficulty in fabricating low-loss devices by tapering such fibres. Practical application of the criteria to couplers, beam expanders and abrupt taper filters is summarised. The accompanying paper provides both experimental and theoretical justification for the delineation criteria.
Q1. What contributions have the authors mentioned in the paper "Long period grating in multicore optical fiber: an ultra-sensetive vector bending sensor for low curvatures" ?
In this paper, a multi-core fiber that hosts the grating was fusion spliced into single-mode fiber at both ends, creating a taper transition between the two types of fiber that produces a nonadiabatic mode evolution.