Temperature-insensitive refractive index sensing by use of micro Fabry-Pérot cavity based on simplified hollow-core photonic crystal fiber

Ultra-High Sensitivity and Temperature-Insensitive Optical Fiber Strain Sensor Based on Dual Air Cavities

This study proposed an all-fiber Fabry-Perot interferometer (FPI) strain sensor with two miniature bubble cavities. The device was fabricated by writing two axial, mutually close short-line structures via femtosecond laser pulse illumination to induce a refractive index modified area in the core of a single-mode fiber (SMF). Subsequently, the gap between the two short lines was discharged with a fusion splicer, resulting in the formation of two adjacent bubbles simultaneously in a standard SMF. When measured directly, the strain sensitivity of dual air cavities is 2.4 pm/με, the same as that of a single bubble. The measurement range for a single bubble is 802.14 µε, while the measurement range for a double bubble is 1734.15 µε. Analysis of the envelope shows that the device possesses a strain sensitivity of up to 32.3 pm/με, which is 13.5 times higher than that of a single air cavity. Moreover, with a maximum temperature sensitivity of only 0.91 pm/°C, the temperature cross sensitivity could be neglected. As the device is based on the internal structure inside the optical fiber, its robustness could be guarantee. The device is simple to prepare, highly sensitive, and has wide application prospects in the field of strain measurement.

Optical Fiber Fabry-Pérot Microfluidic Sensor Based on Capillary Fiber and Side Illumination Method

In this paper, an optical fiber Fabry-Pérot (FP) microfluidic sensor based on the capillary fiber (CF) and side illumination method is designed. The hybrid FP cavity (HFP) is naturally formed by the inner air hole and silica wall of CF which is side illuminated by another single mode fiber (SMF). The CF acts as a naturally microfluidic channel, which can be served as a potential microfluidic solution concentration sensor. Moreover, the FP cavity formed by silica wall is insensitive to ambient solution refractive index but sensitive to the temperature. Thus, the HFP sensor can simultaneously measure microfluidic refractive index (RI) and temperature by cross-sensitivity matrix method. Three sensors with different inner air hole diameters were selected to fabricate and characterize the sensing performance. The interference spectra corresponding to each cavity length can be separated from each amplitude peak in the FFT spectra with a proper bandpass filter. Experimental results indicate that the proposed sensor with excellent sensing performance of temperature compensation is low-cost and easy to build, which is suitable for in situ monitoring and high-precision sensing of drug concentration and the optical constants of micro-specimens in the biomedical and biochemical fields.

Two-photon direct laser writing of micro Fabry-Perot cavity on single-mode fiber for refractive index sensing

Using the two-photon polymerization (TPP) lithography, here we propose and experimentally demonstrate a fiber-tipped Fabry-Perot interferometer (FPI) for liquid refractive index (RI) measurement. To fit the aqueous environment, the FPI is designed as an open-cell microstructure consisting of well-crafted surfaces together with supporting rods, where the major spectral interference occurs between the waveguide's facet and the printed surface. Subsequently, the sensing performances of the fiber FPI are comprehensively studied under various RI as well as temperature configurations. The RI sensitivity is obtained to be ∼1058 nm/RIU with a low detection limit of 4.5× 10^-6 RIU, which is comparable to that of previous reported FPIs. And the temperature cross-sensitivity reaches a value of 8.2 × 10^-5 RIU/°C, indicating the good reliability for RI monitoring. Compared to other fiber FPIs, our sensor exhibits substantial advantages such as ease of fabrication, highly smooth cavity surfaces, and sufficient mechanical strength, providing a practical and competitive solution for chemical and biological sensing.

High-temperature-sensitive and spectrum-contrast-enhanced sensor using a bullet-shaped fiber cavity filled with PDMS

Low temperature sensitivity and low spectral contrast are serious but common issues for most Fabry Perot (FP) sensors with an air cavity. In this paper, a high-temperature-sensitive and spectrum-contrast-enhanced Fabry Perot interferometer (FPI) is proposed and experimentally demonstrated. The device is composed of a hollow cylindrical waveguide (HCW) filled with polydimethylsiloxane (PDMS) and a semi-elliptic PDMS end face. The semi-elliptic PDMS end face increases the spectral contrast significantly due to the focusing effect. Experimentally, the spectral contrast is 11.97 dB, which is two times higher than the sensor without semi-elliptic PDMS end face. Ultra-high temperature sensitivity of 3.1501 nm/°C was demonstrated. The proposed sensor exhibits excellent structural stability, high spectral contrast and high temperature sensitivity, showing great potential in biomedicine, industrial manufacturing, agricultural production and other applications.

Hollow-Core Microstructured Optical Fiber Based Refractometer: Numerical Simulation and Experimental Studies

In this paper, we numerically and experimentally propose a novel hollow-core microstructured optical fiber (HC-MOF) biosensor for refractive index determination. The sensing mechanism of the proposed sensor is based on photonic bandgap effect and the location of transmission maxima of the fiber, which is strongly depend on the liquid analyte RI filled in the fiber core. The proposed HC-MOF biosensor demonstrates the spectral sensitivity of 5636.3 nm/RIU with a RI detection range of 1.333 to 1.3385 for different ratios of plasma in blood serum in our experimental studies. The HC-MOF proposed here can detect similar liquid analytes with RI close to 1.33. The proposed sensor with a high sensitivity, ease of operation and the possibility of real-time sensing has a strong potential for detection of liquid analytes and biomolecules with possible applications in medicine, chemistry, and biology.

Optical Fiber Sensors by Direct Laser Processing: A Review

The consolidation of laser micro/nano processing technologies has led to a continuous increase in the complexity of optical fiber sensors. This new avenue offers novel possibilities for advanced sensing in a wide set of application sectors and, especially in the industrial and medical fields. In this review, the most important transducing structures carried out by laser processing in optical fiber are shown. The work covers different types of fiber Bragg gratings with an emphasis in the direct-write technique and their most interesting inscription configurations. Along with gratings, cladding waveguide structures in optical fibers have reached notable importance in the development of new optical fiber transducers. That is why a detailed study is made of the different laser inscription configurations that can be adopted, as well as their current applications. Microcavities manufactured in optical fibers can be used as both optical transducer and hybrid structure to reach advanced soft-matter optical sensing approaches based on optofluidic concepts. These in-fiber cavities manufactured by femtosecond laser irradiation followed by chemical etching are promising tools for biophotonic devices. Finally, the enhanced Rayleigh backscattering fibers by femtosecond laser dots inscription are also discussed, as a consequence of the new sensing possibilities they enable.

Hollow-Core Photonic Crystal Fiber Mach-Zehnder Interferometer for Gas Sensing

A novel and compact interferometric refractive index (RI) point sensor is developed using hollow-core photonic crystal fiber (HC-PCF) and experimentally demonstrated for high sensitivity detection and measurement of pure gases. To construct the device, the sensing element fiber (HC-PCF) was placed between two single-mode fibers with airgaps at each side. Great measurement repeatability was shown in the cyclic test for the detection of various gases. The RI sensitivity of 4629 nm/RIU was demonstrated in the RI range of 1.0000347-1.000436 for the sensor with an HC-PCF length of 3.3 mm. The sensitivity of the proposed Mach-Zehnder interferometer (MZI) sensor increases when the length of the sensing element decreases. It is shown that response and recovery times of the proposed sensor inversely change with the length of HC-PCF. Besides, spatial frequency analysis for a wide range of air-gaps revealed information on the number and power distribution of modes. It is shown that the power is mainly carried by two dominant modes in the proposed structure. The proposed sensors have the potential to improve current technology's ability to detect and quantify pure gases.

Enhancing Temperature Sensitivity of the Fabry-Perot Interferometer Sensor with Optimization of the Coating Thickness of Polystyrene

The exploration of novel polymers for temperature sensing with high sensitivity has attracted tremendous research interest. Hence, we report a polystyrene-coated optical fiber temperature sensor with high sensitivity. To enhance the temperature sensitivity, flat, thin, smooth, and air bubble-free polystyrene was coated on the edge surface of a single-mode optical fiber, where the coating thickness was varied based on the solution concentration. Three thicknesses of the polystyrene layer were obtained as 2.0, 4.1, and 8.0 μm. The temperature sensor with 2.0 μm thick polystyrene exhibited the highest temperature sensitivity of 439.89 pm °C^-1 in the temperature range of 25-100 °C. This could be attributed to the very uniform and thin coating of polystyrene, along with the reasonable coefficient of thermal expansion and thermo-optic coefficient of polystyrene. Overall, the experimental results proved the effectiveness of the proposed polystyrene-coated temperature sensor for accurate temperature measurement.

Prospects of Photonic Crystal Fiber as Physical Sensor: An Overview

Photonic crystal fiber sensors have potential application in environmental monitoring, industry, biomedicine, food preservation, and many more. These sensors work based on advanced and flexible phototonic crystal fiber (PCF) structures, controlled light propagation for the measurement of amplitude, phase, polarization and wavelength of spectrum, and PCF-incorporated interferometry techniques. In this article various PCF-based physical sensors are summarized with the advancement of time based on reported works. Some physical PCF sensors are discussed based on solid core as well as hollow core structures, dual core fibers, liquid infiltrated structures, metal coated fibers, grating incorporated fibers. With the advancement of sensing technology the possibilities of temperature, pressure, strain, twist, curvature, electromagnetic field, and refractive index sensing are discussed. Also, limitations as well as possible solutions and future hopes are outlined.

High-sensitivity refractive index and temperature sensor based on cascaded dual-wavelength fiber laser and SNHNS interferometer

A novel differential intensity-measurement high-sensitivity refractive index (RI) sensor based on cascaded dual-wavelength fiber laser and single-mode-no-core-hollow-core-no-core-single-mode (SNHNS) structure is proposed and demonstrated. The sensing unit consists of one uniform fiber Bragg grating (FBG) and an SNHNS structure as all-fiber interferometer filter. The dual-wavelength fiber laser has a ring cavity composed of two FBGs with central wavelengths of 1550.10nm and 1553.61nm. Through monitoring the wavelength shift and the output power difference of the dual-wavelength fiber laser, the simultaneous measurement for RI and temperature is realized. In our experiment, the proposed fiber laser sensor exhibits high RI sensitivities of -193.1dB/RIU and 174.8dB/RIU in the range of 1.334-1.384. The relative variation of output power at the two FBG wavelengths shows a higher RI sensitivity of -367.9dB/RIU with better stability, which is greater than the traditional modal interferometer structure. Meanwhile, the temperature sensitivity of the proposed sensor is 8.53 × 10^-3nm/°C, and the changes of laser output power caused by temperature are -0.223dB/°C and 0.215dB/°C.

Birefringent Bragg Grating in C-Shaped Optical Fiber as a Temperature-Insensitive Refractometer

We demonstrate a simple-to-fabricate refractometer based on the inscription of fiber Bragg gratings in a special C-shaped optical fiber. The C-shaped fiber was drawn into shape using a quarter cladding removed preform of a commercial standard single-mode fiber by simple machining. The sensor did not suffer from cross-sensitivity of the refractive index with ambient temperature fluctuations, commonly occurring with many optical fiber refractometers. A refractive index sensitivity of 1300 pm per refractive index unit (RIU) was achieved without employing any additional sensitization techniques such as tapering or etching.

A Simplified Hollow-Core Photonic Crystal Fiber SERS Probe with a Fully Filled Photoreduction Silver Nanoprism

In this paper, a simplified hollow-core photonic crystal fiber surface-enhanced Raman scattering (SERS) probe is presented. Silver nanoprisms are grown with a photoreduction method and account for the SERS, which have better electromagnetic enhancement than spherical silver nanoparticles at 785 nm. Due to the antiresonant reflecting guidance mechanism, the excited laser and SERS signal are effectively guided in such a fully filled hollow-core photonic crystal fiber SERS probe and complicated selective filling with target sample is avoided. Rhodamine 6G molecules are used as probe molecules and the simplified hollow-core photonic crystal fiber SERS probe is test. Detection of low concentration Rhodamine 6G down to 10⁻⁸ M is achieved with a short integration time of 300 ms.

Ultrasensitive sensing in air based on graphene-coated hollow core fibers

The mismatching between permittivities of guided mode and air limits the operation of accurately monitoring the change in the refractive index of the surrounding air. To solve it, we propose a platform using a hollow core fiber with the integration of graphene coating. Experimental results demonstrate that the anti-resonant reflecting guidance has been enhanced while it induces sharply and periodically lossy dips in the transmission spectrum. We conclude a sensitivity of -365.9 dB/RIU and a high detection limit of 2.73 × 10^-6 RIU by means of interrogating the intensity of the lossy dips. We believe that this configuration opens a direction for highly sensitive sensing in researches of chemistry, medicine, and biology.

Optofluidic in-fiber interferometer based on hollow optical fiber with two cores

We demonstrate a novel integrated optical fiber interferometer for in-fiber optofluidic detection. It is composed of a specially designed hollow optical fiber with a micro-channel and two cores. One core on the inner surface of the micro-channel is served as sensing arm and the other core in the annular cladding is served as reference arm. Fusion-and-tapering method is employed to couple light from a single mode fiber to the hollow optical fiber in this device. Sampling is realized by side opening a microhole on the surface of the hollow optical fiber. Under differential pressure between the end of the hollow fiber and the microhole, the liquids can form steady microflows in the micro-channel. Simultaneously, the interference spectrum of the interferometer device shifts with the variation of the concentration of the microfluid in the channel. The optofluidic in-fiber interferometer has a sensitivity of refractive index around 2508 nm/RIU for NaCl. For medicine concentration detection, its sensitivity is 0.076 nm/mmolL^-1 for ascorbic acid. Significantly, this work presents a compact microfluidic in-fiber interferometer with a micro-channel which can be integrated with chip devices without spatial optical coupling and without complex manufacturing procedure of the waveguide on the chips.

Dual-wavelength highly-sensitive refractive index sensor

We report and demonstrate a highly-sensitive refractive index (RI) sensor based on a linear-cavity dual-wavelength erbium-doped fiber laser (DWEDFL). The optical spectrum of the laser varies as the external environmental RI changes from 1.3 to 1.335. The DWEDFL has a linear-cavity configuration with two fiber Bragg gratings (FBGs) with central wavelengths < 1 nm apart. Since both FBGs share the same EDF gain medium, gain competition occurs in the cavity. Optical loss of one wavelength can be introduced by immersing the sensing component, a 15 mm micro-fiber (MF), in a solution under test. Experimental results demonstrate a high sensitivity of -231.1 dB/RIU (refractive index unit) and 42.6 dB/RIU in the range from 1.300 to 1.335. The relative power change at the two FBG wavelengths reveals a higher sensitivity of -273.7 dB/RIU with better stability due to reduced light source jitter and external perturbation. Due to its high sensitivity and simple structure, the dual wavelengths gain competition RI sensor has potential applications in chemical and biochemical sensing fields.

Highly sensitive temperature sensor using a Sagnac loop interferometer based on a side-hole photonic crystal fiber filled with metal

A highly sensitive temperature sensor based on an all-fiber Sagnac loop interferometer combined with metal-filled side-hole photonic crystal fiber (PCF) is proposed and demonstrated. PCFs containing two side holes filled with metal offer a structure that can be modified to create a change in the birefringence of the fiber by the expansion of the filler metal. Bismuth and indium were used to examine the effect of filler metal on the temperature sensitivity of the fiber-optic temperature sensor. It was found from measurements that a very high temperature sensitivity of -9.0  nm/°C could be achieved with the indium-filled side-hole PCF. The experimental results are compared to numerical simulations with good agreement. It is shown that the high temperature sensitivity of the sensor is attributed to the fiber microstructure, which has a significant influence on the modulation of the birefringence caused by the expansion of the metal-filled holes.

Lab-on-fiber electrophoretic trace mixture separating and detecting an optofluidic device based on a microstructured optical fiber

We report an in-fiber integrated electrophoretic trace mixture separating and detecting an optofluidic optical fiber sensor based on a specially designed optical fiber. In this design, rapid in situ separation and simultaneous detection of mixed analytes can be realized under electro-osmotic flow in the microstructured optical fiber. To visually display the in-fiber separating and detecting process, two common fluorescent indicators are adopted as the optofluidic analytes in the optical fiber. Results show that a trace amount of the mixture (0.15 μL) can be completely separated within 3.5 min under a high voltage of 5 kV. Simultaneously, the distributed information of the separated analytes in the optical fiber can be clearly obtained by scanning along the optical fiber using a 355 nm laser. The emission from the analytes can be efficiently coupled into the inner core and guides to the remote end of the optical fiber. In addition, the thin cladding around the inner core in the optical fiber can prevent the fluorescent cross talk between the analytes in this design. Compared to previous optical fiber optofluidic devices, this device first realizes simultaneously separating treatment and the detection of the mixed samples in an optical fiber. Significantly, such an in-fiber integrated separating and detecting optofluidic device can find wide applications in various analysis fields involves mixed samples, such as biology, chemistry, and environment.

Dynamical measurement of refractive index distribution using digital holographic interferometry based on total internal reflection

We present a method for dynamically measuring the refractive index distribution in a large range based on the combination of digital holographic interferometry and total internal reflection. A series of holograms, carrying the index information of mixed liquids adhered on a total reflection prism surface, are recorded with CCD during the diffusion process. Phase shift differences of the reflected light are reconstructed exploiting the principle of double-exposure holographic interferometry. According to the relationship between the reflection phase shift difference and the liquid index, two dimensional index distributions can be directly figured out, assuming that the index of air near the prism surface is constant. The proposed method can also be applied to measure the index of solid media and monitor the index variation during some chemical reaction processes.

All-glass extrinsic Fabry-Perot interferometer thermo-optic coefficient sensor based on a capillary bridged two fiber ends

An all-glass extrinsic Fabry-Perot interferometer (EFPI) is demonstrated for thermal-optic coefficient (TOC) of water, glycerol, and their mixture (volume ratio of 1:1). The compensation for the thermal expansion of Fabry-Perot (FP) cavity is realized by assembling a glass capillary and optical fibers through a CO₂ laser welding. The thermal responses of EFPIs are tested in air at different cavity lengths of 578.6 μm, 911.7 μm, and 1520.3 μm, respectively. The corresponding refractive index errors induced by thermal expansion of FP cavity are negligible, which are demonstrated to be 4.33×10^-6  RIU/°C, 4.13×10^-6  RIU/°C, and 3.45×10^-6  RIU/°C when temperature increases from 20.03°C to 60.78°C. The thermal-optic coefficients of water, glycerol, and their mixture are measured to be -1.5×10^-4  RIU/°C, -2.3×10^-4  RIU/°C, and -2.0×10^-4  RIU/°C, respectively. Our study suggests a potential use of this sensor for TOC measurements of liquids with the advantages of low costs and robustness.

High-sensitivity strain sensor based on in-fiber rectangular air bubble

We demonstrated a unique rectangular air bubble by means of splicing two sections of standard single mode fibers together and tapering the splicing joint. Such an air bubble can be used to develop a promising high-sensitivity strain sensor based on Fabry-Perot interference. The sensitivity of the strain sensor with a cavity length of about 61 μm and a wall thickness of about 1 μm was measured to be up to 43.0 pm/με and is the highest strain sensitivity among the in-fiber FPI-based strain sensors with air cavities reported so far. Moreover, our strain sensor has a very low temperature sensitivity of about 2.0 pm/°C. Thus, the temperature-induced strain measurement error is less than 0.046 με/°C.

Single mode tapered fiber-optic interferometer based refractive index sensor and its application to protein sensing

We demonstrate refractive index sensors based on single mode tapered fiber and its application as a biosensor. We utilize this tapered fiber optic biosensor, operating at 1550 nm, for the detection of protein (gelatin) concentration in water. The sensor is based on the spectroscopy of mode coupling based on core modes-fiber cladding modes excited by the fundamental core mode of an optical fiber when it transitions into tapered regions from untapered regions. The changes are determined from the wavelength shift of the transmission spectrum. The proposed fiber sensor has sensitivity of refractive index around 1500 nm/RIU and for protein concentration detection, its highest sensitivity is 2.42141 nm/%W/V.

Temperature-insensitive optical fiber refractometer based on multimode interference in two cascaded no-core square fibers

A temperature-insensitive optical fiber refractometer, based on multimode interference in no-core square fibers, has been proposed and experimentally demonstrated. The refractometer is formed by a single-mode fiber sandwiched between two segments of no-core square fibers through cleaving and fusion splicing. The transmission spectra characteristic of refractive index (RI) and environmental temperature have been investigated. Experimental results show that a transmission dip exhibits a redshift as large as about 25 nm when the ambient RI increases from 1.3424 to 1.4334. Within the RI range of 1.4033 to 1.4334, the RI sensitivity reaches 474.8189  nm/RIU. A temperature sensitivity of 0.00639  nm/°C is experimentally acquired between 20°C and 85°C, showing a low temperature cross-sensitivity of about 1.35×10⁻⁵  RIU/°C. The proposed refractometer has several advantages, such as low cost, simple structure, and compact size. Therefore, it is also expected to be employed in chemical and multi-parameter sensing applications.

An in-fiber integrated optofluidic device based on an optical fiber with an inner core

A new kind of optofluidic in-fiber integrated device based on a specially designed hollow optical fiber with an inner core is designed. The inlets and outlets are built by etching the surface of the optical fiber without damaging the inner core. A reaction region between the end of the fiber and a solid point obtained after melting is constructed. By injecting samples into the fiber, the liquids can form steady microflows and react in the region. Simultaneously, the emission from the chemiluminescence reaction can be detected from the remote end of the optical fiber through evanescent field coupling. The concentration of ascorbic acid (AA or vitamin C, Vc) is determined by the emission intensity of the reaction of Vc, H2O2, luminol, and K3Fe(CN)6 in the optical fiber. A linear sensing range of 0.1-3.0 mmol L(-1) for Vc is obtained. The emission intensity can be determined within 2 s at a total flow rate of 150 μL min(-1). Significantly, this work presents information for the in-fiber integrated optofluidic devices without spatial optical coupling.

High-sensitivity strain sensor based on in-fiber improved Fabry-Perot interferometer

We demonstrated a high-sensitivity strain sensor based on an in-fiber Fabry-Perot interferometer (FPI) with an air cavity, which was created by splicing together two sections of standard single-mode fibers. The sensitivity of this strain sensor was enhanced to 6.0  pm/με by improving the cavity length of the FPI by means of repeating arc discharges for reshaping the air cavity. Moreover, such a strain sensor has a very low temperature sensitivity of 1.1  pm/°C, which reduces the cross sensitivity between tensile strain and temperature.

Anti-resonant reflecting guidance in alcohol-filled hollow core photonic crystal fiber for sensing applications

Mechanism and sensing applications of antiresonant reflecting guidance in an alcohol-filled simplified hollow-core (SHC) photonic crystal fiber (PCF) are demonstrated. By filling one air hole in the air cladding of the PCF with alcohol, anti-resonant reflecting guidance of light can be achieved and energy leakage of the core modes can be induced at resonant wavelengths of the Fabry-Pérot (F-P) resonator formed by the alcohol-filled layer combined with the silica cladding in the cross-section of the PCF. The proposed structure exhibits periodic lossy dips in the transmission spectrum, of which the visibilities are sensitive to the refractive index of surrounding medium due to the reflectivity variation of the F-P resonator. Water level sensing is experimentally realized with this principle and the lossy dip exhibits a linear decrease against water level with a sensitivity of 1.1 dB/mm. The sensor is also sensitive to environmental temperature and a temperature sensitivity of -0.48 nm/°C is obtained between room temperature and 60 °C.

In-fiber integrated chemiluminiscence online optical fiber sensor

We report an in-fiber integrated chemiluminiscence (CL) sensor based on a kind of hollow optical fiber with a suspended inner core. The path of microfluid is realized by etching microholes for inlets and outlets on the surface of the optical fiber without damaging the inner core and then constructing a melted point beside the microhole of the outlet. When samples are injected into the fiber, the liquids can be fully mixed and form steady microflows. Simultaneously, the photon emitted from the CL reaction is efficiently coupled into the core and can be detected at the end of the optical fiber. In this Letter, the concentration of H2O2 samples is analyzed through the emission intensity of the CL reaction among H2O2, luminol, K3Fe(CN)6, and NaOH in the optical fiber. The linear sensing range of 0.1-4.0 mmol/L of H2O2 concentration is obtained. The emission intensity can be determined within 400 ms at a total flow rate of 150 μL/min. Significantly, this work presents the information of developing in-fiber integrated online analyzing devices based on optical methods.

Compressible fiber optic micro-Fabry-Pérot cavity with ultra-high pressure sensitivity

We propose and demonstrate a pressure sensor based on a micro air bubble at the end facet of a single mode fiber fusion spliced with a silica tube. When immersed into the liquid such as water, the air bubble essentially acts as a Fabry-Pérot interferometer cavity. Such a cavity can be compressed by the environmental pressure and the sensitivity obtained is >1000 nm/kPa, at least one order of magnitude higher than that of the diaphragm-based fiber-tip sensors reported so far. The compressible Fabry-Pérot interferometer cavity developed is expected to have potential applications in highly sensitive pressure and/or acoustic sensing.