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Abstract
A photonic crystal fiber utilizing surface plasmon resonance (PCF-SPR) sensor based on refractive index (RI) control of magnetic fluid (MF) is designed. The air holes of the sensor are arranged in a hexagonal shape, and the optical field transmission channels on both sides of the central air hole can effectively confine the energy of the optical field. We use MF as the sensing medium, and coat the inner wall of the central air hole with gold. It can effectively stimulate the SPR effect to achieve the purpose of magneto-refractive modulation. We study the sensing characteristics of the proposed sensor by finite element analysis. The results show that the highest refractive index sensitivity reaches 19520 nm/RIU in the RI range of 1.42-1.435 and the maximum figure of merit (FOM) is 374.3 RIU-1. In addition, the magnetic field and the temperature response characteristics of the designed sensor are also investigated. In the magnetic field range of 50-130 Oe, the magnetic field sensitivity is 590 pm/Oe. In the temperature range of 24.3-144.3 °C, the temperature sensitivity is only -29.7 pm/℃. The proposed sensor has significant advantages such as stable structure, high sensitivity, easy integration, resistance to electromagnetic interference and can be used for weak magnetic magnitude detection. It has wide application prospects in industrial production, military, and medical equipment.
© 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. Introduction
The measurement of magnetic field plays a significant role in industrial production [1], medical [2,3], navigation [4,5], resource exploration [6], and construction of national defense [7]. In order to accurately detect magnetic fields, magnetic field sensors have emerged and became an important branch of the sensor industry. Early sensors usually convert magnetic signals into electrical signals for measurement. However, the electrical magnetic field sensors have some problems such as large size, high cost, complex structure, difficulty in integration, and susceptibility to electromagnetic interference [8–11]. Compared with electrical magnetic field sensors, the sensors based on optical devices not only overcome these problems, but also have many advantages such as high sensitivity, wide dynamic range, and large-area distributed sensing [12]. Therefore, optical fiber magnetic field sensors have become popular for current research.
According to the sensing mechanism, optical fiber magnetic field sensors can be classified into magnetostrictive effect, Faraday rotation, ampere force, magneto-refractive and atomic magnetometer [13–15]. Among them, the optical fiber sensors based on magneto-refractive are widely studied. They are designed by combining the magneto-refractive modulation of magnetic fluid (MF) with different structures of optical devices to achieve magnetic field sensing [16,17]. They have the advantages of simple structure, convenient fabrication, low cost and are expected to be used in geomagnetic navigation, earthquake early warning, environmental magnetic anomaly monitoring. At present, researchers have done a series of studies on the optical fiber sensor based on magneto-refractive, and its sensitivity is in the range of approximately 20-300 pm/Oe [18–21]. These studies provide the basis for the further development of relevant optical devices. However, in order to truly meet the application requirement of geomagnetic navigation, it is still necessary to further improve the sensitivity and solve the temperature crosstalk problem.
Compared with traditional fibers, photonic crystal fiber (PCF) has the advantages of flexibility and diversity in structure [22]. By changing the structure of PCF, the optical field transmission properties of the sensor can be improved to achieve excellent sensing performance. Therefore, PCF-based sensors have been widely used in various sensing applications, such as the PCF-based sensor for temperature sensing [23], the gas detection sensor based on microstructured-core PCF [24], the PCF-based refractive index sensor [25] and the single polarizing filter based on two-core PCF [26]. In recent years, PCF sensors based on surface plasmon resonance (SPR) have attracted extensive attention. SPR is sensitive to the change of refractive index (RI) in the surrounding medium, which is a phenomenon of oscillation caused by the interaction of free electrons and photons on the metal surface. At present, the research of optical fiber sensors based on PCF-SPR has made great progress. In 2021, V. S. Chaudhary et al. [27] proposed a PCF-SPR biosensor for malaria diagnosis in the human body. The maximum sensitivity in x-polarized and y-polarized reaches 13714.29 nm/RIU and 14285.71 nm/RIU, respectively. In 2022, V. S. Chaudhary et al. [28] also designed a blood composition detection sensor based on PCF and SPR. The proposed biosensor has maximum wavelength sensitivity of 12400 nm/RIU. The PCF sensor combined with SPR not only has high sensitivity, but also has the advantages of wide detection range and label-free detection [29–31]. Therefore, the magnetic field sensors based on PCF-SPR have also been continuously proposed [32–37]. However, these works still have the defect of low sensitivity in practical applications. Thus, further improvement of the sensing characteristics of the magnetic field sensor based on PCF-SPR should be required.
In this paper, we propose a magnetic field sensor based on PCF-SPR. The designed sensor has four layers of air holes which are arranged in a hexagonal shape. The central air hole is filled with MF and the inner wall of the air hole is coated with gold film. The results show that the maximum refractive index sensitivity and FOM are 19520 nm/RIU and 374.3 RIU-1, respectively. We also investigate the magnetic field and the temperature response characteristics of the proposed sensor. In the magnetic field range of 50-130 Oe, the resonance wavelength is red-shifted as the magnetic field increases. When the temperature increases from 24.3 °C to 144.3 °C, the resonance wavelength is blue-shifted. The magnetic field sensitivity and the temperature sensitivity are 590 pm/Oe and -29.7 pm/°C, respectively. The proposed sensor is high-sensitive, stable and can meet the application requirements of miniaturization and low cost. It aims to optimize the function of magnetic anomaly detection and provides a reference for existing magnetic field sensor research. It has great potential in industrial production, military, medical and other fields.
2. Principle and structural design
Figure 1(a) shows the cross-section of the proposed sensor. The structure includes four layers of air holes, and the outer three layers of air holes are arranged in a hexagonal pattern. The air holes on both sides of the central air hole are missing. The central air hole is filled with MF and the inner wall of the central air hole is coated with gold. Employing the outermost layer of PCF with perfectly matched layer (PML) and scattering boundary conditions (SBC) to absorb the radiation energy from the surface. The diameters of the peripheral air holes and the central air hole are represented by d and D, respectively. Λ indicates the distance of the air holes and h represents the thickness of the gold layer. Figure 1(b) shows the 3D model of the PCF-SPR sensor. The fabrication of PCF preforms can be accomplished by stacking, punching, and drilling [38,39]. Besides, the filling of MF can be realized by the pressure injection method [40]. The inner wall of the central air hole is coated with gold using the magnetron sputtering or chemical deposition coating (CVD) method [41]. The experimental setup of the proposed sensor is shown in Fig. 1(c). A broadband light source (BBS) emits incident light and the incident light enters the sensing device through a polarization controller. Magnets are placed in the sensing area to produce a uniform magnetic field. Finally, the output spectrum is displayed on an optical spectrum analyzer (OSA). By observing the change in the output spectrum, the magnetic field response can be measured.
Fig. 1. (a) Cross section of the PCF-SPR sensor; (b) Schematic of three-dimensional (3D) model of the sensor; (c) Experimental device of the sensor.
The cladding material of the proposed sensor is SiO2, and its dispersion relation can be expressed by the Sellmeier equation [42]:
The relationship between the refractive index of MF and the external magnetic field can be expressed by the Langevin function [43]. The formula is as follows:
The permittivity of gold can be expressed by the Drude–Lorentz model [44]:
The confinement loss is related to the imaginary part of the effective refractive index of the core mode [45], which satisfies the following equation:
In this paper, we use the finite element analysis of COMSOL to study the sensing characteristics of the designed sensor. The cross-section of the PCF in Fig. 1(a) shows that the structure has two channels for optical field transmission. According to the theory of mode coupling, the dual-core PCF has four supermodes in fundamental mode (two even modes in x-polarized and two odd modes in y-polarized) [46]. Figures 2(a)–2(d) show the electric field distribution of four supermodes at the wavelength of 700 nm. The red arrow indicates the direction of the electric field.
Fig. 2. Electric field distribution of four supermodes in fundamental mode at 700 nm. (a) even mode in x-polarized, (b) odd mode in x-polarized, (c) even mode in y-polarized, (d) odd mode in y-polarized.
Figure 3 shows the loss spectrum of x-polarized and y-polarized even core modes. It can be obviously seen that the x-polarized core mode has a larger loss peak than the y-polarized core mode. It shows that the coupling strength of the x-polarized core mode is greater than that of the y-polarized. The x-polarized core mode can better excite SPR and has better sensing performance. Thus, we choose to analyze the sensing characteristics of the x-polarized fiber core mode in the proposed sensor.
Figure 4 depicts the dispersion relationship between the x-polarized core mode and the SPP mode, and the loss spectrum of the x-polarized core mode. Blue, black, and orange curves represent the loss spectrum, the real part of the effective refractive index of the x-polarized core mode and the real part of the effective refractive index of the SPP mode, respectively. It can be found that black and orange curves intersect at the wavelength of 899nm. At this point, the real part of the effective refractive index of the core mode and the SPP mode are equal, and the phase-matching condition is satisfied [47]. The energy of the core mode is transferred to the SPP mode, which excites the SPR and produces a loss peak in the spectrum. In addition, when the resonance occurs, the evanescent field can affect the propagation of free electrons and the oscillation of resonant electrons, so that the phase of the transmitted electromagnetic field changes [48]. Therefore, the real part of the effective refractive index of the core mode changes abruptly during the descent, as shown by the sudden change of the black curve in Fig. 4.
Fig. 4. Dispersion relationship between x-polarized fiber core mode and SPP mode, and the loss spectrum of PCF-SPR sensor.
3. Performance optimization
By changing the structural parameters, the sensor performance can be further optimized. We discuss the influence of d, D, h and Λ on the proposed sensor. Besides, we summarize the general rule that the change of structural parameters leads to the change of sensitivity to obtain the optimal structure with high sensitivity.
Theoretically, the resonance wavelength of the loss spectrum varies with the refractive index of the MF. Therefore, this paper adopts the method of wavelength modulation to study the sensing performance. The refractive index sensitivity is calculated as follows [49]:
where Δλpeak represents the variation of resonance wavelength, and Δna represents the variation of the refractive index.The figure of merit (FOM) is also an important parameter in evaluating the sensing performance of the sensor [50]. Its expression is as follows:
where ${S_\lambda }$ is the refractive index sensitivity. FWHM represents the full width at half maximum. If the FWHM is too large, it will affect the accuracy of the detection.Figures 5(a)–5(e) show the loss spectrum of the designed sensor when the d of 3.8 µm, 3.9 µm, 4 µm, 4.1 µm, and 4.2 µm. In the RI range of 1.42-1.435, we calculate the average value of the loss peaks, which are 363.8 dB/cm, 364.8 dB/cm, 367.0 dB/cm, 361.0 dB/cm, and 366.7 dB/cm. It can be seen that the average values are almost the same. Therefore, we consider that the change in d has little effect on the transfer of coupling energy between the core mode and SPP mode. In addition, the resonance wavelength redshifts with the increase of d at the same refractive index, which causes the sensitivity of the sensor to increase [51]. At the same time, the increase of d will reduce the effective refractive index near the fiber core, so that the difference in effective refractive index between the core and the cladding increases [44]. It is more conducive to the propagation of incident light within the fiber core, which can also improve the sensitivity of the sensor. According to the relationship between the resonance wavelength and the refractive index in Fig. 5(f), the refractive index sensitivity can be calculated as 14320 nm/RIU, 14520 nm/RIU, 14720 nm/RIU, 14920 nm/RIU, and 15060 nm/RIU in different d. As d increases, the refractive index sensitivity of the sensor increases. Table 1 summarizes the effect of different d on the FOM of the proposed sensor. Although the FOM decreases with the increase of d, the amount of change is small. Therefore, d = 4.2 µm is finally selected as the optimized parameter.
Fig. 5. Influence of d on the loss spectrum. (a) d = 3.8 µm, (b) d = 3.9 µm, (c) d = 4.0 µm, (d) d = 4.1 µm, (e) d = 4.2 µm, and (f) the fitted results of resonant wavelength of x-polarized fiber core mode with different d.
Table 1. FOM of the proposed sensor with different d
The central air hole is filled with MF, so the size of the central air hole plays an important role in the optimization of the sensing performance. Figures 6(a)–6(e) plot the loss spectrum of the proposed sensor when the D of 3 µm, 3.1 µm, 3.2 µm, 3.3 µm, and 3.4 µm. The average values of loss peak at different D are 383.2 dB/cm, 373.6 dB/cm, 366.7 dB/cm, 359.0 dB/cm, and 349.9 dB/cm, respectively. It shows that the loss peak of the sensor decreases as D increases. Meanwhile, the resonance wavelength redshifts with increasing D. From the above two phenomena, the average values of loss peak show a decreasing trend, but the variation is not large. The resonance wavelength moves to a longer wavelength, so the sensitivity of the sensor still increases. From Fig. 6(f), the refractive index sensitivities in different D are 13320 nm/RIU, 14100 nm/RIU, 15060 nm/RIU, 15960 nm/RIU, and 17000 nm/RIU, respectively. The FOM of the sensor with different D is shown in Table 2. The FOM is relatively high when D = 3 µm, but the sensitivity of the sensor is too low at this point. After comparison, D = 3.4 µm is chosen in this paper.
Fig. 6. Influence of D on the loss spectrum. (a) D = 3.0 µm, (b) D = 3.1 µm, (c) D = 3.2 µm, (d) D = 3.3 µm, (e) D = 3.4 µm, and (f) the fitted results of resonant wavelength of x-polarized fiber core mode with different D.
Table 2. FOM of the proposed sensor with different D
The thickness of the gold layer affects the excitation of SPR. Figures 7(a)–7(e) plot the loss spectrum when the h of 35 nm, 40 nm, 45 nm, 50 nm, and 55 nm. It can be seen that the resonance wavelength redshifts as h increases. This is because the phase-matching condition changes, causing the resonance wavelength to shift. The average values of the loss peak in different h are 283.0 dB/cm, 349.9 dB/cm, 376.5 dB/cm, 311.8 dB/cm, and 223.4 dB/cm, respectively. Obviously, the loss peak increases at first and starts to decrease when h = 50 nm. The thicker the gold layer, the more free-electrons will be generated on the gold surface, so the loss peak will increase. However, if the gold layer is too thick, it is difficult for the core mode of the fiber to penetrate the dielectric layer in the form of an evanescent wave. It will hinder the interaction between the evanescent wave and MF, resulting in a weakening of the SPP mode on the gold surface [52]. In Fig. 7(f), the refractive index sensitivities in different h are 16460 nm/RIU, 17000 nm/RIU, 17340 nm/RIU, 17380 nm/RIU, and 17320 nm/RIU, respectively. Table 3 shows the influence of different h on the FOM of the sensor. When the h is 50 nm, the FOM achieves the maximum value. Therefore, we chose h = 50 nm as the optimized value.
Fig. 7. Influence of h on the loss spectrum. (a) h = 35 nm, (b) h = 40 nm, (c) h = 45 nm, (d) h = 50 nm, (e) h = 55 nm, and (f) the fitted results of resonant wavelength of x-polarized fiber core mode with different h.
Table 3. FOM of the proposed sensor with different h
Figures 8(a)–8(e) show the loss spectrum of the proposed sensor when the Λ of 4.8 µm, 4.9 µm, 5 µm, 5.1 µm, and 5.2 µm, respectively. As the Λ increases, the effective refractive index of the core mode increases, while the effective refractive index of the SPP mode is almost unchanged. It will make the phase-matching point to blueshift. The average loss peaks with different Λ are 361.4 dB/cm, 329.7 dB/cm, 311.8 dB/cm, 299.7 dB/cm, and 268.8 dB/cm, respectively. It is evident that the average values of loss peak decrease with the increase in Λ. This is because the excessive increase in Λ leads to energy leakage in the core mode, resulting in less energy transfer from the x-polarized core mode to the SPP mode. In general, with the increase in Λ, the resonance wavelength moves to the short-wave direction and the loss peak decreases, which will eventually reduce the sensitivity of the sensor. The relationship between the refractive index and wavelength with different Λ is shown in Fig. 8(f). The refractive index sensitivities are 19520 nm/RIU, 18300 nm/RIU, 17380 nm/RIU, 16620 nm/RIU, and 16040 nm/RIU respectively. The FOM of the sensor in different Λ is shown in Table 4. It can be found that when Λ = 5 µm, the sensor has both high sensitivity and large FOM. Therefore, the optimized value of Λ is 5 µm.
Fig. 8. Influence of Λ on the loss spectrum. (a) Λ = 4.8 µm, (b) Λ = 4.9 µm, (c) Λ = 5.0 µm, (d) Λ = 5.1 µm, (e) Λ = 5.2 µm, and (f) the fitted results of resonant wavelength of x-polarized fiber core mode with different Λ.
Table 4. FOM of the proposed sensor with different Λ
In summary, the structural parameters d, D, h and Λ can influence the shift of the resonance wavelength and the change of the loss spectrum, which in turn affects the sensing performance of the sensor. The final structural parameters of the optimized sensor are determined as d = 4.2 µm, D = 3.4 µm, h = 50 nm, and Λ = 5 µm, respectively. The sensor proposed in this paper allows more energy transfer between the x-polarized core mode and the SPP mode, which can easily excite SPR to obtain excellent sensing performance.
4. Sensing performance analysis
4.1 Analysis of magnetic field sensing characteristics
Based on the structure of the above-mentioned optical fiber, we continue to investigate the magnetic field sensing characteristics of the proposed sensor. When the external magnetic field changes, the refractive index of the magnetic fluid in the central air hole also changes, which makes the resonance wavelength shift. The magnetic field sensitivity can be obtained by calculating the shift of the resonance wavelength, which is expressed as [53]:
where Δλpeak represents the variation of resonance wavelength and ΔH represents the variation of external magnetic field.The loss spectrum of the x-polarized fiber core mode at the magnetic field of 50-130 Oe is shown in Fig. 9(a). It can be seen that as the magnetic field increases, the resonance wavelength redshifts. This is because the refractive index of MF increases with the increase in the external magnetic field so that the effective refractive index of the x-polarized fiber core mode increases. Figure 9(b) depicts the relationship between the magnetic field and the resonance wavelength. In the magnetic field range of 50-130 Oe, the magnetic field sensitivity of the PCF-SPR sensor is 590 pm/Oe. In addition, the resolution of the OSA is set to 0.1 nm, and the magnetic field detection resolution of the sensor is about 10 uT, allowing for weak magnetic detection.
Fig. 9. (a) Influence of different magnetic field intensity on the loss spectrum, and (b) the fitted results of resonant wavelength of x-polarized fiber core mode with different magnetic field intensity.
4.2 Analysis of temperature response characteristics
In addition to the magnetic field, temperature is also a factor that affects the sensing performance according to Eq. (2), so we continue to investigate the temperature response characteristics of the designed sensor. Figure 10(a) shows the loss spectrum of the sensor at different temperatures. As the temperature increases from 24.3 °C to 144.3 °C, the resonance wavelength blue shifts. According to the relationship between temperature and resonance wavelength in Fig. 10(b), the temperature sensitivity is calculated as -29.7 pm/°C. The error of magnetic field detection due to temperature interference is only 5%.
Fig. 10. (a) Influence of different temperature on the loss spectrum, and (b) the fitted results of resonant wavelength of x-polarized fiber core mode with different temperature.
4.3 Discussion
Finally, we also compare our sensor with other optical fiber sensors based on magneto-refractive as shown in Table 5. It can be found that our magnetic field sensor has a higher sensitivity than previous work. The magnetic field sensitivities of sensors are significantly improved after applying the SPR effect. At the same time, the temperature sensitivity of our sensor is low, which has little effect on magnetic field detection. The proposed sensor can be cascaded with fiber Bragg grating to realize temperature compensation and demodulation, thus enabling the simultaneous sensing of magnetic field and temperature. Besides, the magnetic field response of the proposed sensor also reaches weak magnetic field magnitude, which meets the application requirements of geomagnetic detection. In addition, the central air hole in this structure can be filled with other sensitive media, which is expected to realize functions of gas or biological sensing.
Table 5. Performance comparison of the proposed sensor with earlier reported sensors
5. Conclusion
A high-sensitivity magnetic field sensor based on PCF and SPR is designed. We discuss the effects of d, D, h and Λ on the sensing performance of the proposed sensor. By optimizing these four structural parameters, the refractive index sensitivity of our sensor is further improved to seek the optimal magnetic field sensing performance. The simulation results show that different structural parameters have different influences on the shift of resonance wavelength, the value of loss peak and optical field energy. Therefore, the optimization of structural parameters is important to obtain better sensing performance. In the RI range of 1.42-1.435, the highest refractive index sensitivity of the optimized sensor is 19520 nm/RIU. The maximum FOM of the sensor is 374.3 RIU-1. In the magnetic field range of 50-130 Oe, the magnetic field sensitivity reaches 590 pm/Oe. Meanwhile, in the temperature range of 24.3-144.3 °C, the temperature sensitivity of the sensor is -29.7 pm/°C. Compared with other sensors, the designed sensor is of high sensitivity, excellent sensing characteristics, and stable structure, which can be used in environmental monitoring, geomagnetic navigation and many other fields. It provides an alternative platform for physical parameters based on refractive index sensing.
Funding
National Natural Science Foundation of China (Grant Nos. 61661004, Grant Nos. 61775238, Grant Nos. 61805278); Project of State Key Laboratory of Transducer Technology of China (No. SKT2001); Guangdong Guangxi joint Science Key Fundation (2021GXNSFDA076001); Science and Technology Major Project of Guangxi (2020AA21077007, 2020AA24002AA).
Acknowledgments
The authors would like to thank the support of the laboratory and university.
Disclosures
The authors declare no conflicts of interest.
Data availability
Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.
References
1. M. Lara-Castro, A. L. Herrera-May, R. Juarez-Aguirre, F. López-Huerta, C. A. Ceron-Alvarez, I. E. Cortes-Mestizo, E. A. Morales-Gonzalez, H. Vazquez-Leal, and S. M. Dominguez-Nicolas, “Portable signal conditioning system of a MEMS magnetic field sensor for industrial applications,” Microsyst. Technol. 23(1), 215–223 (2017). [CrossRef]
2. K. Ishiyama, M. Sendoh, and K. I. Arai, “Magnetic micromachines for medical applications,” J. Magn. Magn. Mater. 242-245, 41–46 (2002). [CrossRef]
3. L. P. Ichkitidze, N. A. Bazaev, D. V. Telyshev, R. Y. Preobrazhensky, and M. L. Gavrushina, “Magnetic Field Sensors in Medical Diagnostics,” Biomed. Eng. 48(6), 305–309 (2015). [CrossRef]
4. M. H. Afzal, V. Renaudin, and G. Lachapelle, “Magnetic field based heading estimation for pedestrian navigation environments,” in 2011 International Conference on Indoor Positioning and Indoor Navigation (IEEE, 2011), pp. 1–10.
5. S. A. Rahok, Y. Shikanai, and K. Ozaki, “Navigation using an environmental magnetic field for outdoor autonomous mobile robots,” Advanced Robotics 25(13-14), 1751–1771 (2011). [CrossRef]
6. A. Tsukamoto, T. Hato, S. Adachi, M. Motoori, M. Sugisaki, and K. Tanabe, “Development of Magnetic Prospecting System with HTS SQUID Gradiometer for Exploration of Metal Resources,” (IEEE, 2015), pp. 1–3.
7. I. Diallo, M. Auffret, L. Attar, E. Bouvard, J. Rousset, and D. B. Salem, “Magnetic Field Interactions of Military and Law Enforcement Bullets at 1.5 and 3 Tesla,” Military Medicine 181(7), 710–713 (2016). [CrossRef]
8. N. A. Stutzke, S. E. Russek, D. P. Pappas, and M. Tondra, “Low-frequency noise measurements on commercial magnetoresistive magnetic field sensors,” Journal of Applied Physics 97(10), 10Q107 (2005). [CrossRef]
9. C. Reig, M. Cubells-Beltrán, and D. Ramírez Muñoz, “Magnetic Field Sensors Based on Giant Magnetoresistance (GMR) Technology: Applications in Electrical Current Sensing,” Sensors 9(10), 7919–7942 (2009). [CrossRef]
10. V. K. Shah and R. T. Wakai, “A compact, high performance atomic magnetometer for biomedical applications,” Phys. Med. Biol. 58(22), 8153–8161 (2013). [CrossRef]
11. R. Weiss, R. Mattheis, and G. Reiss, “Advanced giant magnetoresistance technology for measurement applications,” Meas. Sci. Technol. 24(8), 082001 (2013). [CrossRef]
12. S. Qin, J. Lu, Y. Yu, M. Li, J. Yang, Z. Zhang, Y. Lu, and Z. Meng, “Magnetic field and temperature two-parameter sensor based on optical microfiber coupler interference (OMCI) wrapped with magnetic fluid and PDMS,” Opt. Express 29(18), 29492 (2021). [CrossRef]
13. M. Yang, J. Dai, C. Zhou, and D. Jiang, “Optical fiber magnetic field sensors with TbDyFe magnetostrictive thin films as sensing materials,” Opt. Express 17(23), 20777–20782 (2009). [CrossRef]
14. A. Masoudi and T. P. Newson, “Distributed optical fiber dynamic magnetic field sensor based on magnetostriction,” Appl. Opt. 53(13), 2833 (2014). [CrossRef]
15. L. Sun, S. Jiang, and J. R. Marciante, “All-fiber optical magnetic field sensor based on Faraday rotation,” (IEEE, 2010), pp. 1–2.
16. Y. Zhao, R. Lv, Y. Zhang, and Q. Wang, “Novel optical devices based on the transmission properties of magnetic fluid and their characteristics,” Optics and Lasers in Engineering 50(9), 1177–1184 (2012). [CrossRef]
17. R. Lv, Y. Zhao, H. Li, and H. Hu, “Theoretical Analysis and Experimental Measurement of Birefringence Properties in Magnetic Fluid Subjected to Magnetic Field,” IEEE Trans. Magn. 51(7), 1–5 (2015). [CrossRef]
18. F. Shi, Y. Luo, J. Che, Z. Ren, and B. Peng, “Optical fiber F–P magnetic field sensor based on magnetostrictive effect of magnetic fluid,” Optical Fiber Technology 43, 35–40 (2018). [CrossRef]
19. W. Wang, H. Zhang, B. Li, Z. Li, and Y. Miao, “Optical fiber magnetic field sensor based on birefringence in liquid core optical waveguide,” Optical Fiber Technology 50, 114–117 (2019). [CrossRef]
20. F. Wei, D. Liu, A. K. Mallik, G. Farrel, Q. Wu, G. Peng, and Y. Semenova, “Magnetic field sensor based on a tri-microfiber coupler ring in magnetic fluid and a fiber Bragg grating,” Sensors 19(23), 5100 (2019). [CrossRef]
21. Y. Zheng, X. Dong, C. C. Chan, P. P. Shum, and H. Su, “Optical fiber magnetic field sensor based on magnetic fluid and microfiber mode interferometer,” Optics Communications 336, 5–8 (2015). [CrossRef]
22. A. A. Rifat, R. Ahmed, A. K. Yetisen, H. Butt, A. Sabouri, G. A. Mahdiraji, S. H. Yun, and F. R. M. Adikan, “Photonic crystal fiber based plasmonic sensors,” Sensors and Actuators B: Chemical 243, 311–325 (2017). [CrossRef]
23. V. S. Chaudhary, D. Kumar, R. Mishra, and S. Sharma, “Twin core photonic crystal fiber for temperature sensing,” Mater. Today: Proc. 33, 2289–2292 (2020). [CrossRef]
24. G. P. Mishra, D. Kumar, V. S. Chaudhary, and S. Kumar, “Design and Sensitivity Improvement of Microstructured-Core Photonic Crystal Fiber Based Sensor for Methane and Hydrogen Fluoride Detection,” IEEE Sensors J. 22(2), 1265–1272 (2022). [CrossRef]
25. G. P. Mishra, D. Kumar, V. S. Chaudhary, and S. Sharma, “Terahertz refractive index sensor with high sensitivity based on two-core photonic crystal fiber,” Microw Opt Technol Lett 63(1), 24–31 (2021). [CrossRef]
26. V. S. Chaudhary, D. Kumar, and S. Kumar, “SPR-Assisted Photonic Crystal Fiber-Based Dual-Wavelength Single Polarizing Filter With Improved Performance,” IEEE Trans. Plasma Sci. 49(12), 3803–3810 (2021). [CrossRef]
27. V. S. Chaudhary, D. Kumar, and S. Kumar, “Gold-Immobilized Photonic Crystal Fiber-Based SPR Biosensor for Detection of Malaria Disease in Human Body,” IEEE Sensors J. 21(16), 17800–17807 (2021). [CrossRef]
28. V. S. Chaudhary, D. Kumar, G. P. Mishra, S. Sharma, and S. Kumar, “Plasmonic Biosensor with Gold and Titanium Dioxide Immobilized on Photonic Crystal Fiber for Blood Composition Detection,” IEEE SENS J, 1.
29. A. Rifat, G. Mahdiraji, D. Chow, Y. Shee, R. Ahmed, and F. Adikan, “Photonic Crystal Fiber-Based Surface Plasmon Resonance Sensor with Selective Analyte Channels and Graphene-Silver Deposited Core,” Sensors 15(5), 11499–11510 (2015). [CrossRef]
30. R. K. Gangwar and V. K. Singh, “Highly Sensitive Surface Plasmon Resonance Based D-Shaped Photonic Crystal Fiber Refractive Index Sensor,” PLASMONICS 12(5), 1367–1372 (2017). [CrossRef]
31. H. Nguyen, J. Park, S. Kang, and M. Kim, “Surface Plasmon Resonance: A Versatile Technique for Biosensor Applications,” Sensors 15(5), 10481–10510 (2015). [CrossRef]
32. H. Liu, C. Chen, H. Wang, and W. Zhang, “Simultaneous measurement of magnetic field and temperature based on surface plasmon resonance in twin-core photonic crystal fiber,” OPTIK 203, 164007 (2020). [CrossRef]
33. H. Liu, Y. Wang, S. Wei, C. Zhu, C. Tan, M. Wang, and D. Cheng, “Simultaneous dual-parameter measurement based on dual-channel surface plasmon resonance in photonic crystal fiber,” OPTIK 145, 582–588 (2017). [CrossRef]
34. H. Liu, H. Li, Q. Wang, M. Wang, Y. Ding, C. Zhu, and D. Cheng, “Temperature-compensated magnetic field sensor based on surface plasmon resonance and directional resonance coupling in a D-shaped photonic crystal fiber,” OPTIK 158, 1402–1409 (2018). [CrossRef]
35. X. Mo, J. Lv, Q. Liu, X. Jiang, and G. Si, “A Magnetic Field SPR Sensor Based on Temperature Self-Reference,” Sensors 21(18), 6130 (2021). [CrossRef]
36. L. Zhu, N. Zhao, Q. Lin, L. Zhao, and Z. Jiang, “Optical fiber SPR magnetic field sensor based on photonic crystal fiber with the magnetic fluid as cladding,” Meas. Sci. Technol. 32(7), 075106 (2021). [CrossRef]
37. J. N. Dash and R. Das, “SPR based magnetic-field sensing in microchannelled PCF: a numerical approach,” J. Opt. 20(11), 115001 (2018). [CrossRef]
38. D. M. Chow, S. R. Sandoghchi, and F. M. Adikan, “Fabrication of photonic crystal fibers,” in 2012 Ieee 3rd international conference on photonics(IEEE, 2012), pp. 227–230.
39. G. Amouzad Mahdiraji, D. M. Chow, S. R. Sandoghchi, F. Amirkhan, E. Dermosesian, K. S. Yeo, Z. Kakaei, M. Ghomeishi, S. Y. Poh, and S. Yu Gang, “Challenges and solutions in fabrication of silica-based photonic crystal fibers: an experimental study,” Fiber and Integrated Optics 33(1-2), 85–104 (2014). [CrossRef]
40. J. Yin, S. Ruan, T. Liu, J. Jiang, S. Wang, H. Wei, and P. Yan, “All-fiber-optic vector magnetometer based on nano-magnetic fluids filled double-clad photonic crystal fiber,” Sensors and Actuators B: Chemical 238, 518–524 (2017). [CrossRef]
41. Y. Fu, M. Liu, P. Shum, and L. Chu, “An ultrahighly sensitive photonic crystal fiber based surface plasmon resonance sensor,” OPTIK 212, 164649 (2020). [CrossRef]
42. S. Singh and Y. K. Prajapati, “TiO2/gold-graphene hybrid solid core SPR based PCF RI sensor for sensitivity enhancement,” OPTIK 224, 165525 (2020). [CrossRef]
43. Y. F. Chen, S. Y. Yang, W. S. Tse, H. E. Horng, C. Hong, and H. C. Yang, “Thermal effect on the field-dependent refractive index of the magnetic fluid film,” Appl. Phys. Lett. 82(20), 3481–3483 (2003). [CrossRef]
44. W. Liu, Y. Shi, Z. Yi, C. Liu, F. Wang, X. Li, J. Lv, L. Yang, and P. K. Chu, “Surface plasmon resonance chemical sensor composed of a microstructured optical fiber for the detection of an ultra-wide refractive index range and gas-liquid pollutants,” Opt. Express 29(25), 40734 (2021). [CrossRef]
45. M. M. Rahman, M. A. Molla, A. K. Paul, M. A. Based, M. M. Rana, and M. S. Anower, “Numerical investigation of a highly sensitive plasmonic refractive index sensor utilizing hexagonal lattice of photonic crystal fiber,” Results in Physics 18, 103313 (2020). [CrossRef]
46. M. A. Mollah, M. Yousufali, I. M. Ankan, M. M. Rahman, H. Sarker, and K. Chakrabarti, “Twin core photonic crystal fiber refractive index sensor for early detection of blood cancer,” Sensing and Bio-Sensing Research 29, 100344 (2020). [CrossRef]
47. S. Singh and Y. K. Prajapati, “Highly sensitive dual-core symmetrical side-polished modified D-shaped SPR based PCF refractive index sensor with deeply etched micro openings,” OPTIK 235, 166657 (2021). [CrossRef]
48. Z. Tan, X. Hao, Y. Shao, Y. Chen, X. Li, and P. Fan, “Phase modulation and structural effects in a D-shaped all-solid photonic crystal fiber surface plasmon resonance sensor,” Opt. Express 22(12), 15049 (2014). [CrossRef]
49. W. Liu, F. Wang, C. Liu, L. Yang, Q. Liu, W. Su, J. Lv, S. An, X. Li, T. Sun, and P. K. Chu, “A hollow dual-core PCF-SPR sensor with gold layers on the inner and outer surfaces of the thin cladding,” Results in Optics 1, 100004 (2020). [CrossRef]
50. C. Liu, W. Su, Q. Liu, X. Lu, F. Wang, T. Sun, and P. K. Chu, “Symmetrical dual D-shape photonic crystal fibers for surface plasmon resonance sensing,” Opt. Express 26(7), 9039 (2018). [CrossRef]
51. S. Cao, Y. Shao, Y. Wang, T. Wu, L. Zhang, Y. Huang, F. Zhang, C. Liao, J. He, and Y. Wang, “Highly sensitive surface plasmon resonance biosensor based on a low-index polymer optical fiber,” Opt. Express 26(4), 3988 (2018). [CrossRef]
52. M. R. Islam, M. A. Jamil, M. S. Zaman, S. A. H. Ahsan, M. K. Pulak, F. Mehjabin, M. M. I. Khan, J. A. Chowdhury, and M. Islam, “Design and analysis of birefringent SPR based PCF biosensor with ultra-high sensitivity and low loss,” OPTIK 221, 165311 (2020). [CrossRef]
53. H. Huang, Z. Zhang, Y. Yu, L. Zhou, Y. Tao, G. Li, and J. Yang, “A Highly Magnetic Field Sensitive Photonic Crystal Fiber Based on Surface Plasmon Resonance,” Sensors 20(18), 5193 (2020). [CrossRef]
