By introducing air holes with different diameters, the mechanical properties of the fiber can be changed. The fabrication of MOFs allows easy introduction of different air hole structures into the coating and breaks the circular symmetry of the fiber. Therefore, the arrangement of the structure of the air hole is important, which transmits the external disturbances optically in the core.
Since the structure of the air hole is different, the birefringence of the fibers is not the same. The sensing information of the Sagnac interferometer is encoded in the wavelength shift of the interference spectrum.
Sensing applications of MOFs in the oil and gas industry
However, the pressure sensitivity of FBG inscribed in the fiber was measured to be 8.2 pm/MPa, which is higher than that of SMFs, which is ~3.1 pm/MPa [60]. The single-ring suspended fiber differs from SMF due to the large air area within the fiber, resulting in a high air filling ratio (AFR). The different pressure responses obtained from the fast and slow axis peaks are due to the asymmetric air hole structure, which breaks the uniformity of the pressure-induced stress.
However, the temperature dependence of the two polarized states is the same, approx. 10 pm/C, as shown in Figure 8(b). The change in pressure and temperature can be calculated according to the total wavelength shift of the fast and slow axis grating tip via the following equation.
Conclusion
Intermodal coupling of supermodes in a dual-core photonic crystal fiber and its application as a pressure sensor. Dependence of measurement accuracy on birefringence of PANDA fiber Bragg gratings in simultaneous distributed strain and temperature sensing. Femtosecond laser-induced ultrafast fiber Bragg gratings in microstructured fibers with air holes for high-temperature pressure sensing.
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Background
Optical fiber interferometric sensors have been widely used for various sensing applications and characterization of physical quantities. The advantages of optical fibers have been recognized and exploited in interferometric sensor applications, which include compactness, alignment freedom from free-space optics, high sensitivity, high reliability, etc. These fibers have shown superior properties in many applications and created significant scientific and industrial impact in recent years.
In the past decade, PCFs have received intensive and continuous attention and have undergone rapid development from. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Various PCF structures, such as polarization maintaining (PM) PCFs, photonic bandgap (PBG) PCFs, including hollow core (HC) PCFs and all-solid PBG PCFs, Bragg fibers, large mode area (LMA) PCFs and highly nonlinear PCFs have been demonstrated with good potential in the development of interferometric fiber sensors.
PCFs can provide a platform for the integration of materials such as gas, liquid or metals for additional functionality. For example, PCFs have been used for optofluidic sensing and gas sensing applications that utilize the selective or non-selective infiltration of liquid or gas into the hole structures [3]. In addition, they are a desirable platform for the integration of plasmonic structures that can improve application capabilities in terms of performance and versatility.
Integration of plasmonic structures such as metal nanoparticles, metal nanowires and metal thin films into PCF structures has proven to significantly improve sensor performance, e.g. The continuous development and maturation of PCF technologies and PCF-based interferometric sensors are expected to make more contributions to optical fiber technology and real-world applications [ 5 ].
Overview of PCF-based interferometric sensors
The sensitivity to temperature is often based on the thermal-optical effect of silica and is therefore proportional to the length of the PCF cavity [18]. These MZI configurations make useful refractometers as the effective refractive index of the cladding modes will be affected by the surrounding environment [21, 23]. It is also possible to replace the second LPG by collapsing the holes of the PCF [46].
MZI used a method of detecting two parameters, namely the change in signal strength and the shift in wavelength. The dependence of PCF length, temperature, and ambient RI on device interference fringes has been investigated for sensing applications [58]. The PCF voids completely collapsed in the joining process, and the collapsed area between the SMF and the PCF was about 300 μm.
The PCF end plane acted as the reflective surface for the core mode and cladding modes of the PCF, which were combined and mixed into the collapsed region at the return path. The end facet of the PCF is coated with a gold film as the reflective mirror. One side of the PM-PCF is fixed and the other side is stretched with a precision translation stage, for strain measurement.
The temperature sensitivity of the sensor was measured to be 0.29 pm/C, as shown in Fig. 8(c) , which is much lower than the reported value of 0.99 nm/C for a conventional fiber optic Sagnac interferometer [67]. The sensitivity of strain measurement using PM-PCF is also affected by the ratio of the detectable PM-PCF over the entire length of the PM-PCF in the Sagnac loop [70]. The C-shaped fibers provided openings for fluid flow into and out of the PCF.
Conclusions and outlook
Temperature insensitive refractive index detection using micro Fabry-Pérot cavity based on simplified hollow-core photonic crystal fiber. High-pressure and high-temperature characteristics of a Fabry-Perot interferometer based on photonic crystal fiber. Temperature and index insensitive voltage sensor based on an inline Mach-Zehnder interferometer of photonic crystal fibers.
In-line Mach-Zehnder fiber interferometer based on photonic crystal fiber with near-elliptical core for temperature and strain sensing. Compact and highly sensitive temperature sensor with a photonic crystal fiber interferometer fully filled with Mach–Zehnder fluids. A fiber-based in-line Mach–Zehnder interferometer strain sensor in dual-core photonic crystal fiber.
Highly sensitive strain and bending sensor based on in-line fiber Mach-Zehnder interferometer in solid core photonic crystal fiber with large area. In-fiber modal Mach-Zehnder interferometer based on the locally postprocessed core of a photonic crystal fiber. Temperature insensitive torsion sensor with improved sensitivity using a highly birefringent photonic crystal fiber.
Pore water pressure sensor based on Sagnac interferometer with polarization preserving photonic crystal fiber for geotechnical engineering. A highly sensitive temperature sensor using a Sagnac loop interferometer based on metal-filled side hole photonic crystal fibers.
Dual-Core Transversally Chirped Microstructured
Optical Fiber for Mode-Converter Device and Sensing Application
- Introduction
- Fabrication methodology
- Mode converter device
- Refractive index sensor
- Conclusion
The tuning of the wavelength in the S + C + L + U bands is performed by changing the refractive index (RI) of the fill fluid. In the first option, the analyte is located in the evanescent field of the waveguide [39, 40]. Then the refractive index of the sample modulates the device transmission through its influence on the coupling between the cores.
The first alternative consists of implementing the standard stacking and drawing technique [49, 50]. The cross-section of the proposed dual-core transversely chirped MOF MSC is shown in Figure 2. Since the right core supports two modes (LP01 and LP11), supermode analysis [57] was used to investigate the behavior of the temperature-driven mode. converter.
Almost 100% of the power is observed to be coupled between the nuclei with the stroke length L. The refractive index of the sensor layer and α-streptavidin is 1.45 (we neglect the dispersion of the biomolecule layer). The refractometric sensor derives its sensitivity from the fact that only the mode of the right nucleus has substantial overlap with the analyte.
Therefore, the proposed configuration was classified as a modal interferometer in the sense that two modes of the dual-core structure interfere between them. We only apply this variation to the first ring of vents around the right core to determine the impact on the sensitivity of the proposed sensor. The effective refractive index of the fundamental modes for both polarizations as a function of the refractive index of the analyte.
Transmittance of MOF with two core transverse chirping for L = 50 mm and L = 70 mm as a function of analyte refractive index: (a) RI sensor without biomolecule layers; (b) RI sensor with layers of biomolecules in the first ring of air holes around the right core. In Fig. 11(a) , we can see that the sensitivity of the two-core cross-chirped MOF structure scales with the device length.
Acknowledgements
Finally, the sensing possibilities enabled by the transversely chirped microstructure concept, which can be exploited for refractive index sensing in an interferometric setup, have been demonstrated. The sensor can be operated over a wide range of analyte refractive index values with higher sensitivity compared to other selectively charged MOF sensors.
Author details
In general, this kind of mode selective coupler has potential applications in MDM optical fiber communication as it can increase the channel capacity. Liu, Jianxiang Wen, and Tingyun Wang, Mode converter based on the long period fiber gratings written in dual-mode fiber, in 2015 Opto-Electronics and Communications Conference (OECC) (IEEE, 2015), Vol. All-optical ultrafast wavelength and mode converter based on inter-modal four-wave mixing in few-mode fibers.
Understanding birefringence effects in an all-fiber device based on photonic crystal fibers with integrated electrodes. Effect of filler metal on birefringent optical properties of photonic crystal fiber with integrated electrodes. Mode-selective characteristics of an optical fiber with a high-index core and a photonic bandgap cladding.
A mode-selective coupler based on a dual-core photonic crystal fiber with non-identical cores for spatial mode conversion, in Latin American Conference on Optics and Photonics (OSA, 2016), p. Simultaneous measurement of stress, temperature and refractive index based on multimode interference, tapered fibers and fiber Bragg gratings.
