Core Bragg Fiber Research Articles

Simultaneous Measurement of Gas Pressure and Temperature Sensor Based on F-P Interference using Hollow Core Bragg Fiber

Simultaneous Measurement of Gas Pressure and Temperature Sensor Based on F-P Interference using Hollow Core Bragg Fiber

Quasi-periodic layering of linear/nonlinear materials in hollow core Bragg fiber for all-optical diode action

A novel approach to achieving an inline all-optical diode action is presented using a quasi-periodic arrangement of titanium dioxide and polydiacetylene 9-BCMU in cladding region of hollow core Bragg fiber structure. The proposed quasi-periodicity is based on Fibonacci sequences. The reflectance formula and power transmission are derived using the transfer matrix method, and their spectra are plotted for two different Fibonacci sequences. The quasi-periodicity of the structures enables the formation of multiple photonic bandgaps. An optical asymmetry is introduced at both ends of the fiber by splicing two combinations of Bragg fibers. The all-optical diode action is investigated and simulated under two conditions: both spliced Bragg fibers have identical Fibonacci sequences (symmetric combination) and different Fibonacci sequences (asymmetric combination). In the symmetric structure, light propagation is reciprocal for both ends, while the asymmetric structure exhibits non-reciprocal propagation with significantly reduced backward light 92 % less at the output compared to forward propagation. The proposed structure demonstrates a high transmitted contrast over 97 % and exhibits a nonlinear response with increasing incident light intensity at a specific wavelength (λ = 1735 nm). Furthermore, by adjusting the refractive index of the fiber core, the all-optical diode action remains nearly constant. This suggests that the proposed structure can serve as a stable inline all-optical diode in higher wavelength regions with a variable core index.

Signal processing integrated with fiber-optic Vernier effect for the simultaneous measurement of relative humidity and temperature.

A novel inline Fabry-Perot interferometer (FPI) for simultaneous relative humidity (RH) and temperature monitoring is proposed. The sensing probe consists of a section of hollow core Bragg fiber (HCBF) spliced with a single-mode fiber pigtail. The end-face of the HCBF is coated with Chitosan and ultraviolet optical adhesive (UVOA), forming two polymer layers using a well-designed fabrication process. The surfaces of the layers and splicing point will generate multiple-beam interference and form Vernier-effect (VE) related envelopes in the reflection spectrum. A signal processing (SP) method is proposed to demodulate the VE envelopes from a complicated superimposed raw spectrum. The principle of the SP algorithm is analyzed theoretically and verified experimentally. The sensor's RH and temperature response are studied, exhibiting a high sensitivity of about 0.437 nm/%RH and 0.29 nm/ ∘C, respectively. Using a matrix obtained from experiment results, the simultaneous RH and temperature measurement is achieved. Meanwhile, the simple fabrication process, compact size and potential for higher sensitivity makes our proposed structure integrated with the SP algorithm a promising sensor for practical RH and temperature monitoring.

Polished hollow core Bragg fiber sensor for simultaneous measurement of cortisol concentration and temperature.

Disturbance of surrounding temperature inevitably affects the accuracy of fiber biosensors. To that end, we propose a compact label-free optofluidic sensor based on a polished hollow core Bragg fiber (HCBF) that can simultaneously measure the cortisol concentration and surrounding temperature in real-time. The sensor is comprised of fusion splicing single mode fiber (SMF), multimode fiber (MMF) and HCBF. HCBF is side polished to remove part of the cladding that the suspended inner surface of the fiber can contact the external environment. After the incident light passes through the MMF from the SMF, it enters the hollow area, high refractive index (RI) layers, respectively, where the anti-resonant reflecting optical waveguide (ARROW) guiding mechanism and Mach-Zehnder interferometer (MZI) are simultaneously excited. Taking advantage of the high RI layers of HCBF, compared to the fiber with uniform cladding, the light can be more confined in the cladding and more sensitive to inner surface medium. The inner surface of sensor is immobilized with cortisol aptamer for the sake of achieving high sensitivity and specific sensing of cortisol with the limit of detection (LOD) to be 4.303 pM. The proposed sensor has a compact structure, enables temperature compensation, and can be fabricated at low cost making it highly suitable for in-situ monitoring and high-precision sensing of cortisol and other biological analytes.

A Compact Sensor Integrated in a Single Hollow Core Bragg Fiber for Simultaneous Measurement of Temperature and Strain

A compact sensor integrated in a single hollow core Bragg fiber is proposed and demonstrated for simultaneous measurement of strain and temperature. The sensor is manufactured by splicing a 3 mm long homemade Hollow Core Bragg Fiber (HCBF) sandwiched between two segments of Single Mode Fibers (SMFs) with a lateral offset at one end. Experimental results demonstrate that both Mach-Zehnder Interferometer (MZI) and Bragg resonant mechanism are coexisting in the HCBF-based sensor. Two sensing mechanisms have different strain and temperature sensitivities with good linearity. The axial strain sensitivities of -0.4 pm/με and 0.33 pm/με and the temperature sensitivities of 40.8 pm/ °C and 26.5 pm /°C are obtained by monitoring the wavelength shifts with axial strain and temperature in temperature range of 60-80°C. Therefore, simultaneous measurement of temperature and strain can be achieved by using a characteristic matrix approach. Due to the large refractive index difference between the core and cladding of the Bragg fiber, the length of HCBF for forming mode interference in the sensor could be greatly reduced. This makes the sensor more compact than most previous reports for simultaneous measurement of temperature and strain.

Highly sensitive gas pressure sensor based on the hollow core Bragg fiber and harmonic Vernier effect.

A highly sensitive inline gas pressure sensor based on the hollow core Bragg fiber (HCBF) and harmonic Vernier effect (VE) is proposed and experimentally demonstrated. By sandwiching a segment of HCBF between the lead-in single-mode fiber (SMF) and the hollow core fiber (HCF), a cascaded Fabry-Perot interferometer is produced. The lengths of the HCBF and HCF are precisely optimized and controlled to generate the VE, achieving a high sensitivity of the sensor. Meanwhile, a digital signal processing (DSP) algorithm is proposed to research the mechanism of the VE envelope, thus providing an effective way to improve the sensor's dynamic range based on calibrating the order of the dip. Theoretical simulations are investigated and matched well with the experimental results. The proposed sensor exhibits a maximum gas pressure sensitivity of 150.02 nm/MPa with a low temperature cross talk of 0.00235 MPa/ ∘C. All these advantages highlight the sensor's enormous potential for gas pressure monitoring under various extreme conditions.

Sensitivity-enhanced temperature sensor utilizing core offset and hollow core Bragg fiber

A novel sensitivity-enhanced optical fiber temperature sensor (OFTS) utilizing core offset and hollow core Bragg fiber (HCBF) is proposed and experimentally investigated. The OFTS was fabricated by sandwiching the HCBF between two single-mode fibers (SMFs). The operation principle of temperature sensitivity enhancement is to excite inter-modal interference by lateral offset splicing fibers. The four-cladding structure unique to HCBF induces periodic interference envelopes in the transmission spectrum, which can be used to monitor changes in the external environment. The experimental results show that the temperature and strain sensitivities of OFTS is 10.27 pm/°C and −4.03 × 10−4 nm/με, respectively. After introducing different core offsets, the temperature sensitivities are improved to 16.29 pm/°C, 18.29 pm/°C, and 30.03 pm/°C, respectively. The strain sensitivities are −1.98 × 10−4 nm/με, −4.33 × 10−4 nm/με, and −4.96 × 10−4 nm/με, respectively. Moreover, due to the high-temperature sensitivity, strain insensitivity, and compact structure, the proposed sensor has broad application prospects in complex environments such as aerospace.

Dual Fabry-Perot interferometers gas pressure sensor in a parallel configuration based on a hollow core Bragg fiber and the harmonic Vernier effect.

An ultra-high sensitivity parallel-connected Fabry-Perot interferometers (FPIs) pressure sensor is proposed and demonstrated based on hollow core Bragg fiber (HCBF) and harmonic Vernier effect. The HCBF functions as a micro Fabry-Perot cavity and possesses low transmission loss. One FPI acts as the sensing unit while the other FPI is used as the reference unit to generate the Vernier effect. The sensing FPI was prepared by fusion splicing a section of HCBF between a single-mode fiber (SMF) and a hollow silica tube (HST), and the reference FPI was fabricated by sandwiching a piece of HCBF between two SMFs. Two FPIs with very different free spectral ranges (FSRs) in the fringe pattern were connected to the 2 × 2 coupler parallelly, which realizes the harmonic Vernier effect and ensures the stability of the interference fringe. Laboratory results exhibited that the pressure sensitivity can be enhanced to 119.3 nm/MPa within 0-0.5 MPa by the proposed sensor. Moreover, low-temperature crosstalk of 0.074 kPa/° was achieved. Compared with the traditional optical fiber gas pressure sensor, the advanced sensor features high sensitivity, stability, easy fabrication, and fast response, which can be a promising candidate for real-time and high-precision gas pressure monitoring.

Fabry-Perot interferometers for highly-sensitive multi-point relative humidity sensing based on Vernier effect and digital signal processing.

A highly sensitive relative humidity (RH) sensor based on Fabry-Perot interferometers (FPI) is proposed and experimentally demonstrated. The sensor is fabricated by splicing a segment of hollow core Bragg fiber (HCBF) with single mode fiber (SMF) and functionalized with chitosan and ultraviolet optical adhesive (UVOA) composite at the end of HCBF to form a hygroscopic polymer film. The reflection beams from the splicing point and the two surfaces of the polymer film generate the Vernier effect in the reflection spectrum, which significantly improves the humidity sensitivity of the sensor. To demodulate the envelope based on the Vernier effect and realize multi-point sensing, a digital signal processing (DSP) algorithm is proposed to process the reflection spectrum. The performance of the DSP algorithm is theoretically analyzed and experimentally verified. The proposed sensor demonstrates a high sensitivity of 1.45 nm/% RH for RH ranging from 45% RH to 90% RH. The compact size, high sensitivity and multiplexing capability make this sensor a promising candidate for RH monitoring. Furthermore, the proposed DSP can potentially be applied to other sensors based on the Vernier effect to analyze and extract valuable information from the interference spectrum.

Simultaneous Measurement of Humidity and Temperature Based on ZnO-Coated Hollow Core Bragg Fiber

An optical fiber sensor for simultaneous measurement of relative humidity (RH) and temperature is proposed, which is constructed by sandwiching one section of hollow core Bragg fiber (HCBF) between two sections of single mode fiber (SMF). The ultrathin ZnO film is coated on the outer surface of HCBF as humidity-sensitive material. The dips in the transmission spectrum caused by different anti-resonant (AR) modes of HCBF have different sensitivities to the RH and temperature, and then the simultaneous measurement of above two parameters can be realized by solving a cross matrix. For the two dips monitored in the experiments, the sensitivities of the proposed sensor to RH are 0.7 pm/%RH and 16.95 pm/%RH in the range of 46–73 %RH, and the sensitivities to temperature are 25 pm/°C and 26.8 pm/°C in the range of 20-60 °C, respectively. Taking advantage of compact structure, good stability, easy fabrication and the proposed sensor exhibits great potential application in fields of chemical sensors and biochemical detection.

Hollow Core Bragg Fiber-Based Sensor for Simultaneous Measurement of Curvature and Temperature.

In this paper, the hollow core Bragg fiber (HCBF)-based sensor based on anti-resonant reflecting optical waveguide (ARROW) model is proposed and experimentally demonstrated for simultaneous measurement of curvature and temperature by simply sandwiching a segment of HCBF within two single-mode fibers (SMFs). The special construction of a four-bilayer Bragg structure provides a well-defined periodic interference envelope in the transmission spectrum for sensing external perturbations. Owing to different sensitivities of interference dips, the proposed HCBF-based sensor is capable of dual-parameter detection by monitoring the wavelength shift. The highest curvature sensitivity of the proposed sensor is measured to be 74.4 pm/m−1 in the range of 1.1859–2.9047 m−1 with the adjusted R square value of 0.9804. In the meanwhile, the best sensitivity of temperature sensing was detected to be 16.8 pm/°C with the linearity of 0.997 with temperature range varying from 25 to 55 °C. Furthermore, with the aid of the 2 × 2 matrix, the dual demodulation of curvature and temperature can be carried out to realize the simultaneous measurement of these two parameters. Besides dual-parameter sensing based on wavelength shift, the proposed sensor can also measure temperature-insensitive curvature by demodulating the intensity of resonant dips.

Design and analysis of hollow core Bragg fibers array for space division multiplexing

The space division multiplexing system is helpful to break through the transmission limitations of traditional optical communication systems. Inter-fiber separation and the number of alternating dielectric layers of Bragg fibers array (BFA) are considered with view to applying BFA to space division multiplexing system. The simulation results indicate that BFA with improper inter-fiber separation will result in topological edge state, thus leading to strong crosstalk and high confinement loss, and its crosstalk is hard to decrease with the increase of alternating dielectric layers. The confinement loss of each Bragg fiber in BFA with proper inter-fiber separation is greatly lower than that of traditional Bragg fiber with the same parameters. Our optimized BFA can be realized with low crosstalk of below −30 dB for 55.4 km propagation. In addition, the arrangement analysis of BFA in this paper provides some constructive suggestions for the application of traditional Bragg fiber in optical devices design such as BFA laser and omnidirectional emitting laser.

Simultaneous measurement of magnetic field and temperature based on two anti-resonant modes in hollow core Bragg fiber

A simple and compact magnetic field and temperature dual-parameter sensor is proposed, which is based on a sandwich structure consisting of a section of hollow core Bragg fiber (HCBF) filled with magnetic fluid (MF) and two sections of single-mode fiber (SMF). The corresponding relationship between the resonant dip with different periods in the transmission spectrum and specific anti-resonant (AR) mode in the HCBF is determined. The resonant dips based on different AR modes shift differently when the magnetic field intensity and temperature change. Then, the simultaneous measurement of the magnetic field intensity and temperature can be achieved by utilizing a cross matrix. The experimental results show that the maximum magnetic field sensitivity in the range of 0-12 mT is 86.43 pm/mT, and the maximum temperature sensitivity in the range of 20-60 ℃ is 17.8 pm/℃. The proposed sensor has the advantages of compact structure, easy fabrication and low cost, thus, it has great potential applications in the field of simultaneous sensing of magnetic field intensity and temperature in complex environments.

Hollow Core Bragg Fiber Integrated With Regenerate Fiber Bragg Grating for Simultaneous High Temperature and gas Pressure Sensing

We have proposed and experimentally demonstrated a novel optical fiber sensor for simultaneous measurement of high temperature and gas pressure based on a Regenerated Fiber Bragg grating (RFBG) cascaded with a homemade hollow core Bragg fiber (HCBF). The HCBF functions as an anti-resonant reflecting waveguide and acts as a pressure and temperature sensing unit. The sample was fabricated and tested in our lab, exhibiting a high linear pressure and temperature sensitivity of −3.747 nm/MPa and 25.925 pm/°C in a large-dynamic range of 2 MPa and 600 °C, respectively. The RFBG, as a temperature monitor, was integrated to compensate the temperature cross-correspondence of the HCBF. By utilizing a 2 × 2 matrix obtained with the experimental results, simultaneous measurement of temperature and gas pressure can be achieved. Besides, compact size, low cost and high sensitivity make the sensor more competitive in harsh environment application.

Temperature and curvature insensitive all-fiber sensor used for human breath monitoring.

In this paper, an all-fiber sensor based on hollow core Bragg fiber (HCBF) is proposed and successfully manufactured, which can be used for human breath monitoring. Benefiting from the identical outer diameters of HCBF and single mode fibers (SMFs), the sensor can be directly constructed by sandwiching a segment of HCBF between two SMFs. Based on optical propagation properties of HCBF, the transmission light is sensitive to specific environmental change induced by human breath. Thus, the breath signals can be explicitly recorded by measuring the intensity of the transmitted laser. The sensor presents a rapid response time of ∼0.15 s and recovery time of ∼0.65 s. In addition, the HCBF-based sensor shows good insensitivity to the variation of temperature and curvature, which enables its reliable sensing performance in the dynamic and changeful environment.

Simultaneous measurement of temperature and strain based on a hollow core Bragg fiber.

A novel, to the best of our knowledge, reflective sensor fabricated by simply sandwiching a homemade hollow core Bragg fiber (HCBF) between two single-mode fibers is proposed and demonstrated for the simultaneous measurement of the temperature and the strain. Different from traditional Fabry-Perot interferometer (FPI) sensors that can achieve only one-parameter sensing with inevitable cross-correspondence to other parameters, the proposed sensor based on the HCBF, which functions as an FPI-inducing FPI spectrum pattern and a weak waveguide confining light-inducing periodic envelope in reflection spectrum, ensures double-parameter sensing. For the HCBF-based reflective sensor, different sensing mechanisms lead to the various sensitivity values of temperature and strain (2.98 pm/°C, 19.4 pm/°C, 2.02 pm/µε, -0.36pm/µε), resulting in a different shift of the confining spectrum envelope and the FPI spectrum fringe. Experimental results indicate that our proposed sensor can measure temperature and strain simultaneously by utilizing a 2×2 matrix. Taking advantage of the compact size, easy fabrication, and low cost, this sensor has an applicable value in harsh environment for simultaneous strain and temperature sensing.

Hole-Assisted Solid Core Bragg Fibers With a High-Index-Contrast Cladding for Broadband Single-Polarization Operation

We propose a hole-assisted solid core Bragg fiber (SCBF) with a high-index-contrast cladding for near-infrared broadband single-polarization transmission in this article. The circular symmetry of a common SCBF is broken by the introduced air holes in the solid core for increasing the modal birefringence and polarization-dependent loss (PDL). In the proposed single-polarization SCBF, the confinement of guided modes predominantly depends on the photonic bandgap effect from the high-index-contrast cladding, and simultaneously rests with the total internal reflection from the interface between the solid core and air holes. The numerical results show that both the enhanced modal birefringence and PDL are strongly related to the refractive index, size and locations of air holes. We demonstrate that the modal birefringence for the fundamental mode can be up to the order of 10−3, and the difference in confinement losses between both polarized fundamental modes is no less than an order of magnitude, which is sufficiently large to support single-polarization operation. Moreover, the single-polarization bandwidth with the transmission loss lower than 0.1 dB/m is as high as 277 nm and the critical bend radius is as low as 1 cm, indicating the excellent performances of high bandwidth and bending resistance in the hole-assisted single-polarization SCBF.

Enhancement of modal birefringence in solid core Bragg fibers with high-index-contrast claddings

Abstract We present two types of highly birefringent solid core Bragg fibers (SCBFs) with high-index-contrast claddings by asymmetrically introducing low index parts (LIPs) into the solid core. The characteristics of their modal birefringence and confinement loss are numerically investigated by using a full-vector finite element method. The simulation results reveal that the modal birefringences in such highly birefringent SCBFs essentially depend not only on the difference in electric field boundary condition between the orthogonal-polarized modes, but also on the photonic bandgap effect. Both types of highly birefringent SCBFs have higher modal birefringence than those with low-index-contrast claddings, owing to the large refractive index (RI) modulation ranges of the LIPs. The modal birefringence of the fundamental mode at the targeted 1550 nm is strongly dependent on the size, RI and location of LIPs. Notably, the linear relationship between the modal birefringence and the RI of LIPs in the y-direction in a highly birefringent SCBF with four LIPs included can serve as a new sensing mechanism for the RI measurement of liquid analytes. We believe that the results would be beneficial to the design and application of highly birefringent SCBFs with high-index-contrast claddings.

Analysis of Bragg fiber waveguides having a defect layer for biosensing application

A novel hollow core Bragg fiber waveguides having a defect layer are proposed and analyzed theoretically for sensing application. Matching the electric and magnetic fields at various interfaces, a relation between fields of first layer with final layer has been stabilized; hence, the equations for reflectance and transmittance of proposed structure are derived. Due to periodicity of concentric cylindrical structure, a perfect photonic band gap is observed in considered wavelength range. The presence of defect layer in cylindrical periodic structure shows a peak corresponding to defect mode in perfect photonic band gap region. The full width at half maxima of this peak depends on the periodicity of the cladding layers. Also, the spectral position and shift of peak of defect mode depend on the angle of incidence of light, refractive index of core material and design wavelength of structure. Therefore, it is more appropriate to consider this peak of defect mode as sensing signal instead of considering whole photonic band gap as sensing signal.

Liquid-Filled Hollow Core Bragg Fiber Sensors Using Different Bandgaps for High-Refractive-Index Sensing

Liquid-filled hollow core Bragg fibers (HCBFs) provide an excellent platform for refractive index (RI) sensing. The capacity for high-RI sensing based on higher order bandgaps of an HCBF is explored for higher sensitivity. We numerically compare the performances of an As2S3/PEI-based HCBF RI sensor using first-order and second-order photonic bandgaps (PBGs) for high-RI sensing. The influences of material dispersion and structural parameters on the sensing performance for both PBGs are investigated comparatively. Similar to the first-order PBG, the modification of the bandgap structure induced by material dispersion can also help to improve the linearity of an RI sensor using the second-order PBG of a conventional HCBF. For first-order and second-order PBGs including material dispersion, both a reduction in confinement loss and an improvement in sensitivity can be achieved by increasing the cladding period. In contrast, the influence of the period number on the sensitivity for a first-order PBG is contrary to that for a second-order PBG, which may be attributed to their different reflection characteristics. Furthermore, the comparative results show that a liquid-filled defect HCBF RI sensor using the second-order PBG can achieve high sensitivity and high linearity by optimizing the structural parameters of the defect layer. The proposed RI sensor would have great potential in the real-time measurement of high-RI liquid analytes.