Perot Fiber Research Articles

Easy-to-Fabricate UV-Glue-Based Cascaded Fabry–Perot Fiber Sensor Probe for Temperature Measurement

In this paper, we propose an in-line fiber sensor probe based on UV-glue-assisted cascaded Fabry–Perot cavities for temperature measurement. The UV-curable adhesive in the sensing cavity plays an important role due to its high thermo-optic coefficient. We show that the temperature sensitivity depends on the optical path length difference between both cavities. We report a maximum value of 12.57 nm/°C in the range of 20 to 30 °C. This original sensor architecture features a low cost and simple structure that can be straightforwardly manufactured with readily available materials and a short production time.

The Investigation of All-Sapphire Fabry–Perot Fiber Acoustic Sensor Operating Up to 800 °C

The Investigation of All-Sapphire Fabry–Perot Fiber Acoustic Sensor Operating Up to 800 °C

High-Resolution Optical Fiber Salinity Sensor With Self-Referenced Parallel Fabry–Perot Fiber Microcavity

A high-resolution salinity sensor based on a self-referenced parallel Fabry–Perot fiber microcavity is proposed. The sensor is fabricated by inserting a short piece of exposed-core microstructure fiber (ECF) between multimode fiber (MMF) and single-mode fiber (SMF). Due to the unique exposed-core fiber structure and the specially designed SMF-MMF-ECF-SMF structure, two prominent parallel Fabry–Perot interferometers (FPIs) are constructed. Besides, a self-referenced differential phase-demodulation technology is proposed to eliminate the wavelength uncertainty of the spectra measurement devices. Enhanced demodulation system stability and accuracy are achieved by analyzing the phase shift responses of the reflection spectrum. A high salinity-phase sensitivity of 17.36 deg/ ‰ in the range from 0 ‰ to 35 ‰ is obtained, and the corresponding refractive index (RI) sensitivity is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${1.04} \times {10} ^{{5}}$ </tex-math></inline-formula> deg/RIU. The salinity resolution and RI resolution are as low as 0.0058 ‰ and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${9.6} \times {10} ^{-{7}}$ </tex-math></inline-formula> RIU, respectively, which gives a great potential for harsh environmental monitoring and label-free biochemical analysis.

High resolution polymer/air double-cavity Fabry–Perot fiber temperature sensor based on exposed core microstructured fiber

This study proposes a high-resolution optical fiber Fabry–Perot (FP) temperature sensor and it is based on an exposed-core microstructured optical fiber (ECF) coated by a ultraviolet curing polymer adhesive. Then, a small piece of multimode fiber (MMF) with large core diameter is spliced in front of ECF to expand the input light beam, and the parallel polymer/air double-cavity FP in such single-mode fiber (SMF)-MMF-ECF-SMF structure is constructed. Additionally, by employing a mobilized demodulation module, the interference signal is analyzed by phase demodulation method. The experimental results show that the temperature sensitivity of the sensor is 30.8 ℃−1 and the resolution is up to 1.6 × 10−4 ℃ in a range of 20 ℃–50 ℃, which can achieve high resolution temperature measurement. Furthermore, to alleviate the wavelength uncertainty of the demodulation device, a double-cavity self-reference differential phase modulation method is explored in the proposed parallel double-cavity FP. It shows that the stability could be improved to five times when system temperature is unstable, which offers an alternative method to further improve the temperature sensing resolution.

Photoacoustic spectroscopy for detection of trace C2H2 using ellipsoidal photoacoustic cell

In this paper, a new type of ellipsoid photoacoustic cell was designed to enhance the photoacoustic effect for the first time. The COMSOL Multiphysics software was used to stimulate the acoustic characteristics of the traditional cylindrical photoacoustic (PA) cell and the ellipsoid PA cell. The resonance frequency, acoustic pressure distribution and acoustic pressure level size in the resonant cavity of the novel PA cell and traditional cylindrical PA cell were analyzed. The novel PA cell was used to detect the concentration of acetylene. In the experiment, the 1532.83 nm absorption spectral line was selected as the measurement spectral line, and the tunable Distributed Feedback (DFB) semiconductor laser was finally selected as the light source. Fabry–Perot (F-P) fiber optic acoustic sensor which has been reported in other paper was used to collect the sound pressure signal. The signal-to-noise (SNR) of the cylindrical photoacoustic spectral system for the detection of acetylene gas was 23 dB, and the detection limit sensitivity was 2.17 ppb. The SNR of the ellipsoid photoacoustic spectral system for the detection of acetylene gas was 34 dB, and the detection limit sensitivity was 1.47 ppb. The performance of the ellipsoidal photoacoustic cell is better than that of the cylindrical photoacoustic cell. The results shown that the novel PA cell can improve the PA effect significantly.

Fiber-optic Fabry–Perot temperature sensor based on the ultraviolet curable glue-filled cavity and two-beam interference principle

Abstract An ultraviolet curable glue (UCG)-filled microprobe Fabry–Perot fiber temperature sensor, which based on the two-beam interference principle, is proposed and fabricated. In the range of 25.7–250 °C, the average sensitivity and average linear correlation coefficient of the sensor are −41.69 pm/°C and 0.98558, respectively. Under the same temperature, the maximum fluctuation (0.56 pm) of the trough’s wavelength and the standard error (0.0023 ± 0.04%) are obtained. The proposed interferometer exhibits excellent stability and has a potential application in the field of temperature monitoring.

CURRENT STATE OF METHODS AND MEANS OF REGISTRATION OF HIGH TEMPERATURES AND MECHANICAL STRESSES IN STRUCTURES

An analytical review of physically possible methods and available achievements in registering hydrostatic pressure or mechanical stresses using fiber optic fibers and sensors based on them based on published works that can be used in harsh environmental conditions is carried out. The results of the review show that fully distributed or quasidistributed fiber-optic systems for recording hydrostatic pressure or mechanical stress can be implemented on the following physical principles and apparatus with measures to compensate or suppress the influence of temperature: polarizing sensors on birefringent single- mode light guides and OTDR equipment; micro-flexible sensors with OTDR equipment on conventional multimode fibers; measuring systems on fiber Bragg gratings; on discrete sensors, in particular, on sealed fiber Fabry–Perot interferometers; Brillouin distributed sensors on single-mode fibers that are not sensitive to temperature changes. It is shown that single-mode birefringent fibers with hollow holes in the shell and fiber Bragg gratings written in the core have a good linear sensitivity to hydrostatic pressure and a weak dependence on temperature. Lattices in phosphorous-containing single-mode light guides have increased high-temperature properties up to ~500 C and higher. A number of discrete fiber sensors’ structures and pressure recorders are investigated. Various structures of sensitive elements of pressure sensors on sealed fiber Fabry–Perot interferometers and fiber gratings in spherical and cylindrical small-sized cases are investigated. Sensors based on Fabry–Perot fiber interferometers soldered into a glass capillary and protected from water by external high-temperature hermetic coatings showed good linearity in the pressure range of 0…540 ATM at temperatures up to ~200 C. The sensors are efficient at temperatures up to 600 °C and are promising for use in severe and special external conditions. The possibility of compensating the temperature sensitivity by selecting external coatings is shown. Pressure sensors were tested on local areas with microbends and it was shown that they can measure pressures up to ~24 МPа at temperatures up to ~450 C, but to compensate for the dependence of the readings on temperature, it must be measured by an independent sensor. The possibility of independent and simultaneous measurement of hydrostatic pressure and temperature along a single fiber using spontaneous Brillouin scattering is shown. Pressure is measured by the frequency shift of Brillouin scattering, and temperature by its intensity. The operation of the Brillouin recorder in the pressure range 0…34 MРа is demonstrated. The pressure resolution was ~0,2 МРа. New methods are proposed for detecting Brillouin scattering – a heterodyne signal with a high signal-to-noise ratio and based on frequency modulation of a semiconductor single-frequency distributed feedback laser. The measurement range has been increased by more than 10 km and the coordinate resolution has been increased. The Brillouin scattering method is promising for creating distributed systems for measuring hydrostatic pressure or mechanical stress for severe physical conditions, including temperatures of ≥3000 C.

Digital synthesis of multistage etalons based upon unequal cavity lengths

Fabry–Perot fiber etalons (FPEs) built from three or more reflectors are attractive for a variety of applications, including communication and sensing. In order to realize a desired transmission profile, usually multistage FPEs are designed with equal cavity lengths followed by a determination of the required reflectivities. As seen in previous works, however, fabricated reflectors may slightly differ from the designs, leading to a departure from the desired transmission profile of the FPE. Here, we show a novel digital synthesis of multistage etalons with off-the-shelf reflectors and unequal lengths of involved cavities. We find that, in contrast to equal cavity lengths, unequal lengths provide more poles in the z domain and hence more flexibility to achieve a desired multicavity FPE transmission response. For given reflectivities and by determining correct unequal lengths of a multicavity FPE with our synthesis technique, we demonstrate two design examples involving free spectral range enhancement and passband shaping. This work is generalizable to ring resonators and mirror- and fiber-Bragg-grating-based cavities, enabling the design and optimization of cavity systems for a wide range of applications, including lasers, sensors, and filters.

High-temperature all-fiber non-destructive multi-parameter sensing system with consistent performance.

A high-temperature all-fiber non-destructive multi-parameter sensing system is developed. The system can operate consistently in a wide range of temperature changes by specially designed active signal generation and detection units. It is capable of monitoring temperature up to 600°C and cracks on metal pipes with an acoustic wave generation unit and an acoustic detection unit. A gold-coated multi-mode fiber is used to deliver a laser pulse for acoustic excitation while minimizing parasitic acoustic signals at high temperature. An in-fiber Fabry-Perot fiber Bragg grating (FP-FBG) is fabricated in another single-mode fiber and bonded to the test object for acoustic detection. The FP-FBG avoids strain redistribution inside the bonder at high temperature to ensure consistent operation. The feasibility of the system for temperature monitoring and crack detection in real-world applications is also demonstrated on an industry-standard P91 pipe.

A Fiber Optic Acoustic Pyrometer for Temperature Monitoring in an Exhaust Pipe of a Boiler

This letter presents a fiber optic acoustic pyrometer for temperature monitoring in an exhaust pipe of an industrial scale combustion test facility. The acoustic pyrometer consists of a fiber optic acoustic generator and a Fabry–Perot (FP) fiber sensor receiver. The proposed acoustic pyrometer was tested and verified at an exhaust pipe over the Industry Scale Burner Facility (ISBF) at GE’s Clean Energy Center, at a temperature of 320 °C. Further research on such fiber optic acoustic pyrometers will advance the study of 2D/3D temperature distribution reconstruction in industrial combustion facilities.

High-Sensitivity Gas Pressure Fabry–Perot Fiber Probe With Micro-Channel Based on Vernier Effect

In this paper, we propose and demonstrate a gas pressure fiber probe with high sensitivity magnified by Vernier effect. The probe is composed of two cascaded Fabry–Perot interferometers based on a SMF–SOHST–OFC structure (SMF: single-mode fiber; SOHST: side-opened hollow silica tube; OFC: optical fiber column). The high-frequency CO2 laser drilling method for hollow silica tube can effectively maintain the transient balance of the air pressure inside and outside the cavity without destroying the reflective ends of the optical fibers. Experimental results show that the prepared fiber probe with the SOHST length of 375.2 μ m and column length of 247.3 μ m has high gas pressure sensitivity of 80.3 pm/kPa by demodulating Vernier envelope, and it has relatively low temperature cross-sensitivity of –1.33 kPa/°C. This sensor is highly sensitive and of compact size, which not only can be applied in gas pressure sensing but also has the potential for application in microfluidic detection.

Visible Raman and Brillouin lasers from a microresonator/ZBLAN-fiber hybrid system

Raman and Brillouin lasers based on a high-quality (high-Q) whispering gallery mode microresonator (WGMR) are usually achieved by employing a tunable single-frequency laser as a pump source. Here, we experimentally demonstrate visible Raman and Brillouin lasers using a compact microresonator/ZrF4−BaF2−LaF3−AlF3−NaF (ZBLAN)-fiber hybrid system by incorporating a WGMR with a fiber-compatible distributed Bragg reflector/fiber Bragg grating to form a Fabry–Perot (F-P) fiber cavity and using a piece of Pr:ZBLAN fiber as gain medium. The high-Q silica-microsphere not only offers a Rayleigh-scattering-induced backreflection to form the ∼635 nm red laser oscillation in the F-P fiber cavity, but also provides a nonlinear gain in the WGMR itself to generate either stimulated Raman scattering or stimulated Brillouin scattering. Up to six-order cascaded Raman lasers at 0.65 μm, 0.67 μm, 0.69 μm, 0.71 μm, 0.73 μm, and 0.76 μm are achieved, respectively. Moreover, a Brillouin laser at 635.54 nm is clearly observed. This is, to the best of our knowledge, the first demonstration of visible microresonator-based lasers created by combining a Pr:ZBLAN fiber. This structure can effectively extend the laser wavelength in the WGMR to the visible waveband and may find potential applications in underwater communication, biomedical diagnosis, microwave generation, and spectroscopy.

Development and analysis of a model based on chirped fiber Bragg gratings employed for cracks characterization in materials

In this work a model was developed that allows to understand the behavior of a chirped fiber Bragg grating for the detection and characterization of cracks in materials. In addition to the amplitude response, we show that the group delay of the grating provides useful information for the characterization of the crack. The position of the crack can be determined thanks to the linear chirp of the grating that fixes a correlation between the spatial position and both, the wavelength and the group delay. However, our analysis shows that this simple approach has a source of error, which can be overcome if a controllable external strain can be applied to the embedded grating, additional to the strain generated by the embedding process. Thus, the width of the crack can be also estimated. The effect of the appearance of a crack on the grating generates simple o multiple transmission peaks that are analyzed considering the behavior of a Fabry–Perot fiber cavity. This simple model was experimentally tested and preliminary results were in good agreement with the simulations.

Optical fiber F–P magnetic field sensor based on magnetostrictive effect of magnetic fluid

Abstract magnetic field sensor of air-gap Fabry–Perot fiber interferometersis proposed based on magnetostrictive effect. The sensor is consisted of single-model fiber (SMF), air-gap, no-core fiber (NCF) and magnetic fluid. Those are sealed in the capillary, SMF and NCF are connect with air chamber and magnetic fluid column. With the presence of an external magnetic field, air chamber cavity length changes because of the magneto-volume variation of magnetic fluids. This situation causes a change in the optical path difference. Detection of the drift of interference spectrum leads to the detection of the change in magnetic field. When the magnetic field is parallel to the direction in which the capillary is placed, the sensitivity is 0.2347 nm/mT; when the magnetic fluid is perpendicular to the direction in which the capillary is placed, the sensitivity is 0.325 nm/ mT. In addition to this new magnetic fluid sensor, a practical detection system is built, which relative error rate is less than 2%.

Refractive Index and Temperature Sensing Based on an Optoelectronic Oscillator Incorporating a Fabry–Perot Fiber Bragg Grating

An ultrafast high-sensitivity refractive index (RI) and temperature-sensing system based on an optoelectronic oscillator (OEO) is proposed and demonstrated in this paper. A Fabry–Perot fiber Bragg grating (FP-FBG), which combines a gap with two FBGs in a silica V-shaped slot and characterizes a narrow notch in the reflection spectrum, is incorporated in the OEO to implement a microwave photonic filter and perform oscillating frequency selection. A microwave signal is generated by the OEO, whose oscillating frequency is determined by the center frequency of the FP-FBG notch, which varies with the surrounding environments. The RI or the temperature change can be accordingly measured by monitoring the frequency shift of the microwave signal using an electrical spectrum analyzer or a digital signal processor. An experiment is performed to verify the proposal. An RI sensitivity of 413.8 MHz/0.001RIU and a temperature sensitivity of 2516 MHz/°C are successively demonstrated.

Cascaded-cavity Fabry–Perot interferometer for simultaneous measurement of temperature and strain with cross-sensitivity compensation

We propose and demonstrate a fiber sensor for simultaneous temperature and strain measurements. The proposed sensor is implemented by a cascaded-cavity Fabry–Perot (FP) fiber interferometer. The two cascaded FP cavities comprise a micro-air-cavity in a hollow-core tube fiber and a micro-silica-cavity in a standard single-mode fiber. To separate the interference spectrum of each FP cavity, the total spectrum is filtered in the frequency domain through band-pass filters, whose central frequencies were predesigned based on the relationship between the spatial frequency and free spectral range of each FP cavity. The different cross-sectional areas and thermal-optic coefficients of the two FP cavities confer different sensitivities to temperature and strain. Both parameters were measured simultaneously by tracking the wavelength shifts in the filtered interference spectra of the FP cavities. Moreover, the temperature–strain cross-sensitivity was compensated by solving a sensitivity-coefficient matrix equation for the two cavities, using the calibrated temperatures and strains. Other advantages of the proposed sensor are simple fabrication and an all-fiber structure. Owing to these properties, the proposed sensor is potentially applicable to real sensing applications.

Diaphragm based long cavity Fabry–Perot fiber acoustic sensor using phase generated carrier

A diaphragm based long cavity Fabry–Perot interferometric fiber acoustic sensor is proposed. The Fabry–Perot cavity is formed by a flat fiber facet and an ultra-thin silver diaphragm with a 6-meter long fiber inserted in the cavity. A narrow-linewidth ring-cavity erbium-doped fiber laser is applied to demodulate the sensing signal in the phase generated carrier algorithm. Experimental results have demonstrated that the phase sensitivity is about −140dB re 1rad/μPa at 2kHz. The noise equivalent acoustic signal level is 60.6μPa/Hz1/2 and the dynamic range is 65.1dB-SPL at 2kHz. The sensor is suitable for sensing of weak acoustic signals.

Photonic-Crystal-Based Fiber Hydrophone With Sub-&lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$100~\mu $ &lt;/tex-math&gt;&lt;/inline-formula&gt;Pa/&lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$\surd $ &lt;/tex-math&gt;&lt;/inline-formula&gt;Hz Pressure Resolution

A Fabry–Perot fiber hydrophone with improved fluidics over a previous design to increase the pressure sensitivity by two orders of magnitude and the response at low frequencies is reported. The interferometer is made of a photonic-crystal diaphragm placed at the tip of a single-mode fiber coated with a dielectric reflector. To increase the sensitivity, the water that fills the sensor head is connected to the surrounding environment through holes in the protective housing. The response extends below 100 Hz, with a measured average sensitivity of $\sim 0.23$ Pa $^{\mathrm {-1}}$ and a record average minimum detectable pressure of $\sim 90~\mu $ Pa/ $\surd $ Hz from 100 Hz to 2.5 kHz.

Polymer Microbubble-Based Fabry–Perot Fiber Interferometer and Sensing Applications

A polymer microbubble-based Fabry–Perot fiber interferometer (FPI) for pressure and temperature measurement is proposed and demonstrated. By splicing a small segment of photonic bandgap fiber to a single-mode fiber and immersing such a fiber tip into an optical adhesive, a micro air bubble could be buried into the formed polymer diaphragm. Size of air bubble and polymer diaphragm thickness can be controlled by adjusting arc discharge intensity at the fiber splice point. In order to achieve the wide dynamic range and high-resolution measurement, a demodulation algorithm based on absolute phase analysis is adopted and present high sensitivity for simultaneous pressure and temperature sensing. This simple and reproducible fabrication method of such a sensor gives an alternative way to construct FPI-based biomedical and microfluidic sensors.

Study on high temperature Fabry–Perot fiber acoustic sensor with temperature self-compensation

A Fabry–Perot (F-P) fiber acoustic sensor, which can work under high-temperature harsh environment with temperature self-compensation, is designed and prepared. A condenser was used to maintain the sensor to work in a stable temperature environment. Because of the special structure of the sensor and the function of the condenser, the cavity variation of the sensor caused by changes of external temperature from −10°C to 500°C would not exceed 8 nm. The experimental results show that the sensor has a good frequency response in a range of 1 to 5 kHz and the field experiment results show that it could be used for hydraulic decoking online monitoring by judging the acoustic frequency spectrum.