Transition of Fabry-Perot and antiresonant mechanisms via a SMF-capillary-SMF structure

Ultrahigh Extinction Ratio Leaky-Guided Hollow Core Fiber Mach-Zehnder Interferometer Assisted by a Large Core Hollow Fiber Beam Splitter

We proposed a novel fiber Mach-Zehnder interferometer (FMZI) that can perform an ultrahigh extinction ratio (ER), ultracompact, and ultra-broadband interference characteristics. The FMZI structure is based on an extremely tiny hollow core fiber (HCF) with a small diameter of 10 μm (named HCF10) connected with a beam splitter of a large core of 50 μm HCF (named HCF50). The refractive index (RI) of the air core is lower than that of the HCF cladding; a leaky-guided fiber waveguide (LGFW) occurs in such a short-section HCF10 waveguide to simultaneously have the core and cladding modes. To achieve better fringe visibility of the interference, the section of HCF50 assists in splitting the optical light into core and cladding beams launched into the HCF10 with appropriate intensities. Experimental and simulation results show that the optical characteristics of the proposed LGFW-FMZI are very similar. Based on the results of the study, the length of the HCF10 primarily influences the free spectral range (FSR) of the interference spectra, and the HCF50 splitter significantly controls the optimal extinction ratio (ER) of the interference fringes. By exactly adjusting the lengths of HCF10 and HCF50, the proposed fiber interferometers can perform the capability of an ultrahigh ER over 50 dB with the arbitrary FSR in the transmitted interference spectra over an ultra-broad wavelength range of 1250 nm to 1650 nm.

Balloon-like optical fiber sensor for simultaneous displacement and temperature measurement based on an anti-resonance mechanism

We propose and experimentally demonstrate a balloon-like optical fiber sensor with an anti-resonance mechanism for the simultaneous measurement of displacement and temperature. The sensor consists of a hollow-core fiber spliced between two single-mode fibers and bent into a balloon-like shape. The balloon-like structure not only increases the contrast of the spectral lines but also improves the displacement sensitivity. Theoretical and experimental results show that the incidence angle of light varies with the change in displacement, resulting in the variation of spectral intensity based on the anti-resonance mechanism. In addition, the temperature change causes the wavelength drift of the spectrum. Thus, by separately demodulating the intensity and wavelength of this sensor, it is possible to measure displacement and temperature simultaneously. The sensitivity of the displacement and temperature of the sensor is 0.043 dB/µm and 20.94 pm/°C, respectively. The proposed optical fiber sensor has a compact structure and simple preparation, making it an ideal choice for simultaneous measurement of displacement and temperature in the fields of micro-manufacturing and structural monitoring in the future.

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.

Alterable interferential fineness for high temperature sensing calibration based on Bragg hollow core fiber

We propose, what we believe to be, a novel method for high temperature sensing calibration based on the mechanism of alterable interferential fineness in Bragg hollow core fiber (BHCF). To verify the proof-of-concept, the fabricated sensing structure is sandwiched by two sections with different length of BHCF. Two interferential fineness fringes dominate the transmission spectrum, where the high-fineness fringes formed by anti-resonant reflecting optical waveguide (ARROW) plays the role for high temperature measurement. Meanwhile, the low-fineness fringes induced by short Fabry-Perot (F-P) cavity are exploited as temperature calibration. The experimental results show that the ARROW mechanism-based temperature sensitivity can reach 26.03 pm/°C, and the intrinsic temperature sensitivity of BHCF is 1.02 pm/°C. Here, the relatively lower magnitude of the temperature sensitivity is considered as the standard value since it merely relies on the material properties of silicon. Additionally, a large dynamic temperature range from 100 °C to 800 °C presents linear response of the proposed sensing structure, which may shine the light on the sensing applications in the harsh environment.

Vernier effect-based optical fiber sensor for dynamic sensing using a coarsely resolved spectrometer

Vernier effect-based optical fiber sensors have been demonstrated for high-sensitivity measurements of a diverse array of physical and chemical parameters. The interrogation of a Vernier sensor typically needs a broadband source and an optical spectrum analyzer to measure amplitudes over a broad wavelength window with dense sampling points, facilitating accurate extraction of the Vernier modulation envelope for sensitivity-improved sensing. However, the stringent requirement on the interrogation system limits the dynamic sensing capability of Vernier sensors. In this work, the possibility of employing a light source with a small wavelength bandwidth (35 nm) and a coarsely resolved spectrometer (∼166 pm) for the interrogation of an optical fiber Vernier sensor is demonstrated with the assistance of a machine learning-based analysis technique. Dynamic sensing of the exponential decay process of a cantilever beam has been successfully implemented with the low-cost and intelligent Vernier sensor. This work represents a first step towards a simpler, faster, and cheaper way to characterize the response of optical fiber sensors based on the Vernier effect.

Compact highly sensitive Fabry-Perot temperature and gas pressure sensing probe fabricated by a femtosecond laser and PDMS

A high sensitivity optical fiber temperature and gas pressure sensor with integrated micro-cavity is proposed. First, a single-mode optical fiber (SMF) is spliced with a section of capillary, and then the sensitive material polydimethylsiloxane (PDMS) is filled into the capillary to form a Fabry-Perot interferometer (FPI). Finally, a femtosecond laser is used to ablate the fiber core of the SMF to form the third reflecting surface, constituting two cascaded FPIs. When two FPIs have a similar free spectral range, a Vernier effect is produced. The temperature and gas pressure sensitivity of the sensor reached 14.41 nm/°C and 113.82 nm/MPa, respectively, after using the sensitive material and Vernier effect double sensitization technology. In addition, a fiber Bragg grating is cascaded with the sensor, which can realize the simultaneous measurement of temperature and gas pressure and eliminate cross-sensitivity.

Machine learning for a Vernier-effect-based optical fiber sensor

In recent years, the optical Vernier effect has been demonstrated as an effective tool to improve the sensitivity of optical fiber interferometer-based sensors, potentially facilitating a new generation of highly sensitive fiber sensing systems. Previous work has mainly focused on the physical implementation of Vernier-effect-based sensors using different combinations of interferometers, while the signal demodulation aspect has been neglected. However, accurate and reliable extraction of useful information from the sensing signal is critically important and determines the overall performance of the sensing system. In this Letter, we, for the first time, propose and demonstrate that machine learning (ML) can be employed for the demodulation of optical Vernier-effect-based fiber sensors. ML analysis enables direct, fast, and reliable readout of the measurand from the optical spectrum, avoiding the complicated and cumbersome data processing required in the conventional demodulation approach. This work opens new avenues for the development of Vernier-effect-based high-sensitivity optical fiber sensing systems.

Construction of multiple anti-resonant light guidance mechanisms in a hollow-core fiber structure for simultaneous measurement of multiple parameters

The construction of multiple light guidance mechanisms in a hollow-core fiber (HCF) structure is a popular way to realize the simultaneous measurement of multiple parameters. In this work, a partial coating method to excite multiple anti-resonant light guidance mechanisms (ARLGMs) in an HCF structure for the simultaneous measurement of multiple parameters is proposed. As an example, a double ARLGM based on a partially polyimide (PI)-coated HCF structure for the simultaneous measurement of relative humidity (RH) and temperature is demonstrated theoretically and experimentally. The dip (dip II) produced by the PI-coated HCF section shifts linearly with surrounding RH changes with a sensitivity of circa 58.6 ± 0.77 pm/%RH, while the dip (dip I) produced by the bare HCF section (with an air coating layer) is insensitive to RH changes. In addition, both types of dips have linear responses to temperature variations, with similar sensitivities of ∼ 17 pm/°C. Hence, the proposed sensor structure can be used as an RH sensor that is also capable of compensating for local temperature fluctuations. More importantly, the simultaneous measurement of multiple parameters (such as biomarkers) is possible using the proposed method provided the proper sensing materials are partially coated onto the HCF surface.

High sensitivity gas pressure sensor based on different inner diameter quartz capillary cascading and Vernier effect

In this paper, a highly sensitive optical fiber gas pressure sensor is proposed and experimentally verified. The sensor is composed of two Fabry-Pérot (F-P) cavities, and two F-P cavities are fabricated by a single-mode fiber and two quartz capillaries with different inner diameters splicing. Among them, the small inner diameter capillary is used as a gas channel connecting the large inner diameter capillary and the external environment. The manufacturing process of the sensor only involves capillary cleaver and splicing and does not involve other complex manufacturing technologies. By correctly adjusting the length of the two quartz capillaries, when the free spectral range of the two F-P cavities is very close, the optical Vernier effect will be observed and used as a sensitive probe for detecting gas pressure. The experimental results show that, in the pressure range of 0-0.8 MPa, the gas pressure sensitivity of the sensor reaches -81.73 nm/MPa with a linearity of 99.7%, and the temperature cross-sensitivity is only 1.82 kPa/°C. Due to its easy manufacture, high sensitivity, compact structure, and small volume, the sensor has become one of the preferred structures for large-scale use in the field of gas sensing.

Simultaneous measurement of displacement and temperature using a balloon-like hybrid fiber sensor

A fiber sensor based on a silica capillary in a balloon-like shape for simultaneous measurement of displacement and temperature is proposed and experimentally demonstrated. The sensor is fabricated by splicing a segment of a hollow-core fiber between two single-mode fibers (SMF) and by creating a balloon shape with the capillary at the top-center position. The SMF-capillary-SMF configuration excites an antiresonant (AR) guidance, and the balloon shape enhances the Mach-Zehnder interferometer (MZI). Experimental results show that, for a balloon length of 4.0 cm and a capillary length of 1.2 cm, the AR is insensitive to displacement and its sensitivity to temperature is 14.3 pm/°C, while the MZI has a sensitivity to displacement of 1.68 nm/mm in the range between 0 and 5 mm and a sensitivity to temperature of 28.6 pm/°C, twice the value of the AR. The proposed fiber sensor has only one sensing element in one configuration, which makes it simple to fabricate as well as low cost.

Machine learning boosts performance of optical fiber sensors: a case study for vector bending sensing

The spectral response produced when a high-sensitivity optical fiber sensor (OFS) is subject to an external perturbation has recently been shown to contain rich information that can be potentially exploited for multi-dimensional sensing. In this article, we propose the use of machine learning to directly and statistically learn the relation between the complex spectral response from an OFS and a measurand of interest, without knowing if there are distinct and tractable features in the spectrum. As a proof-of-concept demonstration, it is shown that a simple heterostructure-based device with a capillary tube sandwiched between two single-mode fibers without any fiber modification and complicated fabrication steps, is able to achieve directional bending sensing in a broad dynamic range with machine learning as a tool for signal analysis. It is also demonstrated that stringent requirements of the sensor interrogator, such as the wavelength and bandwidth of the light source, can be greatly relaxed due to the direct spectral mapping between the sensor and the measurand of interest, and importantly, without sacrificing the performance of the sensor. The proposed technique is highly generalizable and can be extended to any OFSs with regular or irregular characteristic spectra for sensing any measurands.

Light transmission mechanisms in a SMF-capillary fiber-SMF structure and its application to bi-directional liquid level measurement

Capillary fiber (CF) has been extensively investigated in a singlemode fiber (SMF)-CF-SMF (SCS) sensing structure since multiple light guiding mechanisms can be easily excited by simply tuning the air core diameter (cladding diameter) and length of the CF. Understanding the light guiding principles in an SCS structure is essential for improved implementation of a CF based fiber sensor. In this work, light guiding principles in a relatively large air core diameter (≥ 20 µm) and long length of CF (> 1 mm) are investigated theoretically and experimentally. It is found that both multimode interference (MMI) and Anti-Resonant Reflecting Optical Waveguide (ARROW) light guiding mechanisms are excited in the SCS structure in the transmission configuration. However, MMI dips are not observed in the spectrum for the air core diameters of CF smaller than 50 µm in the experiment due to large transmission loss in small air core CFs. Further experimental results demonstrate that a CF with a bigger air core diameter shows a higher sensitivity to curvature, and the highest sensitivity of -16.15 nm/m^-1 is achieved when an CF-100 was used. In addition, a SMF-CF-20-CF-30-SMF (SCCS) structure is proposed for high sensitivity bi-direction liquid level measurement for the first time, to the best of our knowledge. Two types of ARROW dips (Dip-20 and Dip-30) are simultaneously excited in transmission, hence both liquid level and liquid flow direction can be detected by tracing the dip strength changes of Dip-20 and Dip-30, respectively.

Optical fiber Fabry-Perot interferometer coupled to a 3-D integrated waveguide for 3-D position sensing

Optical fiber extrinsic Fabry-Perot interferometers (EFPIs) have been extensively demonstrated for the measurement of displacement and displacement-related physical quantities, e.g., acceleration, pressure, with high sensitivity and resolution. Despite its wide and successful applications, a conventional EFPI is limited to measuring only one-dimensional (out-of-plane) movement of its external reflector. In this Letter, a new strategy for optical fiber sensing, particularly for EFPI sensing, is proposed and demonstrated, allowing for three-dimensional (3-D) measurements based on a hybrid and compact EFPI device. A 3-D integrated optical waveguide array is aligned against a lead-in optical fiber with an air gap, where an EFPI is formed by the end facet of the optical fiber and the end facet of the waveguide array. As a proof of concept, we experimentally demonstrate that 3-D positioning can be achieved from the EFPI with sub-micron resolution by simultaneously measuring the reflection and transmission of the device. The proposed strategy of using an optical waveguide as an external reflector for an optical fiber EFPI, combined with machine learning-based analysis, opens new avenues in the development of compact yet multi-dimensional sensors.

Coexistence of transmission mechanisms for independent multi-parameter sensing in a silica capillary-based cascaded structure

The coexistence of transmission mechanisms, including Fabry-Perot (FP), Mach-Zehnder (MZ), and anti-resonant (AR), is demonstrated via a silica capillary-based cascaded structure. The analysis for MZ shows that one pathway is formed by the beam refracted into the silica capillary cladding from the air core, rather than being transmitted into the cladding directly at the splicing interface. Using the ray optics method, the two coexistence conditions are derived for FP and MZ, and for FP, MZ and AR, respectively. The existence percentages of the three mechanisms can be obtained using the fast Fourier transform. Finally, the coexistence of multiple transmission mechanisms is applied for independent multi-parameter sensing with the FP-based temperature sensitivity of 10.0 pm/°C and AR-based strain sensitivity of 1.33 nm/N. The third mechanism MZ interference can assist in verifying changes in both the temperature and axial strain. This shows the possibility to optimize the transmission spectra for independent multi-parameter sensing by tailoring the existence percentages of different mechanisms.

Microwave photonics interrogation for multiplexing fiber Fabry-Perot sensors

A microwave photonics interrogation system for multiplexing fiber Fabry-Perot (FP) sensors is demonstrated in this paper. Different from previous FP demodulation schemes, this system aims at quasi-distributed sensing networks composed of FP sensors with a short effective cavity length less than 1 mm. With the help of a dispersion element, the superimposed reflected spectrum from FP sensors based on a hollow core fiber (HCF) can be converted into separate response passbands in the frequency domain simultaneously, whose center frequency will shift linearly with the variations of environment. The experimental results exhibit high linearity and interrogation ability for both the all-FP multiplexing system and hybrid multiplexing system. A strain interrogation sensitivity of 0.938 kHz/µɛ and temperature sensitivity of -0.699 MHz/°C have been realized, corresponding to a FP cavity length demodulation sensitivity of 1.563 MHz/µm. Furthermore, numerical studies about the impacts of the HCF-FP spectrum envelope on the RF response passband, as well as the theoretical minimum detectable cavity length and multiplexing capacity of the system, are also carried out.

Recent Advancement of Anti-Resonant Hollow-Core Fibers for Sensing Applications

Specialty fibers have enabled a wide range of sensing applications. Particularly, with the recent advancement of anti-resonant effects, specialty fibers with hollow structures offer a unique sensing platform to achieve highly accurate and ultra-compact fiber optic sensors with large measurement ranges. This review presents an overview of recent progress in anti-resonant hollow-core fibers for sensing applications. Both regular and irregular-shaped fibers and their performance in various sensing scenarios are summarized. Finally, the challenges and possible solutions are briefly presented with some perspectives toward the future development of anti-resonant hollow-core fibers for advanced sensing.

Ultrahigh-sensitivity displacement sensing enabled by the Vernier effect with inhibited antiresonance

We demonstrate an optical fiber displacement sensor based on the Vernier effect, consisting of a single-mode fiber (SMF) and a section of capillary with an internal movable microsphere freely controlled forward and backward by a half-taper. The antiresonance is inhibited to purify the reflectance spectra by optimizing the capillary length. The interference of three beams reflected from the splicing interface, front and rear surfaces of the microsphere, respectively, hence results in the Vernier effect due to combined cavities. By adjusting the distance between the splicing interface and front surface, an appropriate Vernier effect can significantly enhance the displacement sensitivity up to 344.8 pm/nm, with a subnanometer resolution of 0.058 nm. The proposed device has advantages such as simple fabrication process, compact size, and ultrahigh sensitivity, showing a great potential in displacement sensing applications.

Negative curvature hollow core fiber sensor for the measurement of strain and temperature

Three different types of strain and temperature sensors based on negative curvature hollow core fiber (NCHCF) are proposed. Each sensor is produced by splicing a small section of the NCHCF between two sections of single mode fiber. Different types of interferometers are obtained simply by changing the splicing conditions. The first sensor consists on a single Fabry-Perot interferometer (FPI). The remaining two configurations are attained with the same sensing structure, depending on its position in relation to the interrogation setup. Thus, a double FPI or a hybrid sensor, the latter being composed by an FPI and a Michelson interferometer, are formed. The inline sensors are of submillimeter size, thus enabling nearly punctual measurements.

Liquid level sensor based on dynamic Fabry-Perot interferometers in processed capillary fiber

In this work, a novel optical fiber sensor capable of measuring both the liquid level and its refractive index is designed, manufactured and demonstrated through simulations and experimentally. For this, a silica capillary hollow-core fiber is used. The fiber, with a sensing length of 1.55 mm, has been processed with a femtosecond laser, so that it incorporates four holes in its structure. In this way, the liquid enters the air core, and it is possible to perform the sensing through the Fabry–Perot cavities that the liquid generates. The detection mode is in reflection. With a resolution of 4 μm (liquid level), it is in the state of the art of this type of sensor. The system is designed so that in the future it will be capable of measuring the level of immiscible liquids, that is, liquids that form stratified layers. It can be useful to determine the presence of impurities in tanks.

High-sensitivity temperature sensor based on anti-resonance in high-index polymer-coated optical fiber interferometers

Compared to the multimode interference (MMI) effect, the anti-resonance (AR) effect does not rely on the multimode property of the optical waveguide. This Letter shows that fiber bending can suppress the MMI and can break the superposition of AR spectra of multiple modes in a high-index polymer-coated optical fiber interferometer based on a single-mode fiber-polymer-coated no-core fiber-single-mode fiber hetero-structure. This results in the dominance of the AR spectrum of an individual mode and consequently in periodic sharp transmission dips. As a result of this phenomenon and large thermo-optical and thermal expansion coefficients of the polymer, a compact, high-sensitivity and linear response temperature sensor with the sensitivity as high as -3.784nm/^∘C has been demonstrated experimentally.

Three-parameter measurement optical fiber sensor based on a hybrid structure

We have proposed a hybrid-structured optical fiber sensor that can measure curvature, temperature, and transverse load. The hybrid structure is made by fusing a section of hollow-core fiber (HCF) between an air bubble and an up-taper. The air bubble acts as a Fabry-Perot interferometer (FPI) and at the same time serves as excitation for a Mach-Zehnder interferometer (MZI). HCF is used as an anti-resonant reflected optical waveguide (ARROW), which periodically decreases in the resonant wavelength of the optical transmission spectrum. The transverse load can be measured by demodulating the reflection spectrum of the FPI. By demodulating the wavelength shift of the MZI for temperature sensing and the intensity change of ARROW inclination for curvature sensing, the curvature and temperature can be measured simultaneously. The experimental results show that the transverse load sensitivity of the FPI is 1.53 nm/N. The curvature and temperature sensitivities are 33.23dB/m^-1 and 20.3 pm/°C, respectively, and the cross-sensitivity is 0.0003m^-1/^∘C. Due to its ease of manufacture, low crosstalk, and high sensitivity, the hybrid-structured optical fiber sensor is suitable for multi-parameter measurement applications.

Negative Curvature Hollow Core Fiber Based All-Fiber Interferometer and Its Sensing Applications to Temperature and Strain

Negative curvature hollow core fiber (NCHCF) is a promising candidate for sensing applications; however, research on NCHCF based fiber sensors starts only in the recent two years. In this work, an all-fiber interferometer based on an NCHCF structure is proposed for the first time. The interferometer was fabricated by simple fusion splicing of a short section of an NCHCF between two singlemode fibers (SMFs). Both simulation and experimental results show that multiple modes and modal interferences are excited within the NCHCF structure. Periodic transmission dips with high spectral extinction ratio (up to 30 dB) and wide free spectral range (FSR) are produced, which is mainly introduced by the modes coupling between HE₁₁ and HE₁₂. A small portion of light guiding by means of Anti-resonant reflecting optical waveguide (ARROW) mechanism is also observed. The transmission dips, resulting from multimode interferences (MMI) and ARROW effect have a big difference in sensitivities to strain and temperature, thus making it possible to monitor these two parameters with a single sensor head by using a characteristic matrix approach. In addition, the proposed sensor structure is experimentally proven to have a good reproducibility.

Bragg labeled wavelength calibrates interferometric sensors in hollow core fiber

A Bragg labeled wavelength (BLW) employed to the sensitivity calibration in an interference pattern has been proposed and experimentally demonstrated. According to the critical condition of Fabry-Perot (FP) interference and the antiresonant (AR) effect, the length of hollow core fiber (HCF) is artificially controlled to form a FP microcavity by collapsed fusion splicing. Dual-spectral features of the BLW and inline multimode interference (IMMI) dominate the transmission spectrum of the collapsed Bragg HCF (BHCF). The location of the BLW remains unchanged once the air-core diameter is selected. Sensing performance is investigated to validate the calibration function of the proposed BHCF. In particular, the temperature sensitivity of the BLW and multimode interference are 12.8 pm/°C and 87.1 pm/°C, respectively, corresponding to the reference sensitivity induced by the Bragg structure and the measurement sensitivity of the IMMI. All these findings highlight the calibration of HCF-based interferometric sensors in practical applications.

Antiresonant mechanism based self-temperature-calibrated fiber optic Fabry-Perot gas pressure sensors

A self-temperature-calibrated gas pressure sensor with a sandwich structure made of single-mode fiber (SMF)-hollow core fiber (HCF)-SMF is proposed and experimentally demonstrated. A Fabry-Perot interferometer (FPI) is formed by the SMF-HCF-SMF structure along the axial direction, and an antiresonant reflecting optical waveguide (ARROW) is formed by the ring-cladding of the HCF along the radial direction. A micro-channel is drilled on the ring-cladding of the HCF using a femtosecond laser to facilitate air entering/exiting the HCF. The FPI functions as the pressure sensor, and the ARROW functions as the temperature sensor. The initial wavelength and pressure sensitivity of the FPI can be calibrated from the temperature obtained by measuring the optical thickness of the ARROW. The experimental results show that the ARROW exhibits a temperature sensitivity of ~0.584 nm/°C, and the pressure sensitivity of the FPI ranges from 3.884 to 0.919 nm/MPa, within the temperature range of 37-1007 °C. The simplicity and durability of the sensor make it suitable for reliable gas pressure measurement in high-temperature environments.

Antiresonant Reflecting Guidance and Mach-Zender Interference in Cascaded Hollow-Core Fibers for Multi-Parameter Sensing

We propose and demonstrate a cascaded hollow-core fiber (HCF) device for multi-parameter sensing based on the combination of antiresonant reflecting guidance (ARRG) and Mach-Zender interference (MZI). The device was fabricated by splicing two sections of HCF together. Two sets of fringes, which have different free spectral ranges, were generated from ARRG and MZI, respectively, and were aliasing in the transmission spectrum. The two sets of fringes were then separated using a band pass filter and a Gaussian fitting technique. The wavelengths at two transmission loss dips formed by ARRG and MZI exhibit a temperature sensitivity of 14.1 and 28.5 pm/°C, and a strain sensitivity of 0.4 and −0.8 pm/με, respectively. By using a crossing matrix with differences sensitivities, the cross-sensitivity between temperature and strain can be solved. The gas pressure response of the cascaded HCF device was also tested up to 300 °C, and linear relationships between the gas pressure sensitivities and temperature were found, which can be used in gas pressure application in various temperatures. Moreover, the proposed cascaded HCF sensor is compact, low cost, and simple for fabrication, and hence offers a promising way for the simultaneous measurement of multiple parameters, such as temperature, strain, and gas pressure.