Fabry-Perot Fiber Optic Sensors Research Articles

Accurate Strain Sensing With Fiber-Optic Fabry–Perot Sensors Based on CNN-LSTM Model

Accurate Strain Sensing With Fiber-Optic Fabry–Perot Sensors Based on CNN-LSTM Model

Miniaturized and highly sensitive fiber-optic Fabry–Perot sensor for mHz infrasound detection

Infrasound detection is important in natural disasters monitoring, military defense, underwater acoustic detection, and other domains. Fiber-optic Fabry–Perot (FP) acoustic sensors have the advantages of small structure size, long-distance detection, immunity to electromagnetic interference, and so on. The size of an FP sensor depends on the transducer diaphragm size and the back cavity volume. However, a small transducer diaphragm size means a low sensitivity. Moreover, a small back cavity volume will increase the low cut-off frequency of the sensor. Hence, it is difficult for fiber-optic FP infrasound sensors to simultaneously achieve miniaturization, high sensitivity, and extremely low detectable frequency. In this work, we proposed and demonstrated a miniaturized and highly sensitive fiber-optic FP sensor for mHz infrasound detection by exploiting a Cr-Ag-Au composite acoustic-optic transducer diaphragm and a MEMS technique-based spiral micro-flow hole. The use of the spiral micro-flow hole as the connecting hole greatly reduced the volume of the sensor and decreased the low-frequency limit, while the back cavity volume was not increased. Combined with the Cr-Ag-Au composite diaphragm, a detection sensitivity of −123.19 dB re 1 rad/μPa at 5 Hz and a minimum detectable pressure (MDP) of 1.2 mPa/Hz1/2 at 5 Hz were achieved. The low detectable frequency can reach 0.01 Hz and the flat response range was 0.01–2500 Hz with a sensitivity fluctuation of ±1.5 dB. Moreover, the size of the designed sensor was only 12 mm×Φ12.7 mm. These excellent characteristics make the sensor have great practical application prospects.

Optimized Cavity Length Demodulation via Error Analysis in Graphene Fiber-Optic Fabry–Perot Sensor

Optimized Cavity Length Demodulation via Error Analysis in Graphene Fiber-Optic Fabry–Perot Sensor

A Five-Hole Pressure Probe Based on Integrated MEMS Fiber-Optic Fabry-Perot Sensors.

The five-hole pressure probe based on Micro-Electro-Mechanical Systems (MEMS) technology is designed to meet the needs of engine inlet pressure measurement. The probe, including a pressure-sensitive detection unit and a five-hole probe encapsulation structure, combines the advantages of a five-hole probe with fiber optic sensing. The pressure-sensitive detection unit utilizes silicon-glass anodic bonding to achieve the integrated and batch-producible manufacturing of five pressure-sensitive Fabry-Perot (FP) cavities. The probe structure and parameters of the sensitive unit were optimized based on fluid and mechanical simulations. The non-scanning correlation demodulation technology was applied to extract specific cavity lengths from multiple interference surfaces. The sealing platform was established to analyze the sealing performance of the five-hole probe and the pressure-sensitive detection unit. The testing platform was established to test the pressure response characteristics of the probe. Experimental results indicate that the probe has good sealing performance between different air passages, making it suitable for detecting pressure from multiple directions. The pressure responses are linear within the range of 0-250 kPa, with the average pressure sensitivity of the five sensors ranging from 11.061 to 11.546 nm/kPa. The maximum non-linear error is ≤1.083%.

High-speed spectrum demodulation of fiber-optic Fabry–Perot sensor based on scanning laser

A high-speed spectrum demodulation method with a large dynamic range for fiber-optic Fabry–Perot sensor is presented. The demodulation system only consists of a near-infrared distributed Bragg reflector (DBR) laser, a fiber circulator, a photodetector and a signal processing circuit. By quickly cyclically setting the grating current and phase current of the DBR laser, the laser wavelength is scanned with a repetition frequency of 2 kHz. The signal processing circuit controls the current of the laser and performs spectrum demodulation simultaneously. Spectral demodulation mainly includes normalization of interference spectrum, fast Fourier transform, phase estimation and cavity length calculation. The displacement stage and piezoelectric ceramics were used to remove the static cavity length and dynamic cavity length of the Fabry–Perot cavity. Experimental results show that the demodulation resolution reaches 0.15 nm. Benefiting from the high spectral detection resolution, a large demodulation range is achieved to be 0.3–13 mm. Compared with the demodulation systems based on spectrum modules, this solution significantly reduces the cost, simplifies the algorithm and improves the dynamic range.

High-performance Fabry-Perot fiber optic sensors from one-step laser side-polished platforms

A facile one-step non-contact process was developed for preparing the substrates for Fabry-Perot-based side-polished optical fiber sensors. A carbon dioxide (CO2) laser cladding removal technique was used to control the profile of the polished fiber surface and to introduce two reflective cavities. The substrates were characterized for a range of cavity lengths and their thermal response was studied. This device added a degree of freedom to the design of optical fiber based Fabry-Perot sensors and its potential was demonstrated by coating the substrate with polydimethylsiloxane (PDMS). The resulting sensors had a three-order of magnitude increase in sensitivity when compared to the substrate. The polished flat surface provided a route for the integration of novel materials for sensing applications, particularly those where polarization control was vital for light-matter interaction, for example, low dimensional materials such as graphene or MXene. The inherent simplicity, mechanical stability, and scalability of this approach are important steps for the realization of practical devices of this type.

An improved phase generated carrier demodulation algorithm of fiber optic fabry-perot sensor

An improved phase generated carrier demodulation algorithm of fiber optic fabry-perot sensor

Parallel Cross-Correlation Algorithm for the Fast Interrogation of High-Finesse Fiber-Optic Fabry-Perot Sensors

It is still a challenge to realize the absolute optical path difference (OPD) demodulation of the high-finesse fiber-optic Fabry-Perot (FP) sensors with a high resolution and high speed. This paper proposes an improved parallel cross-correlation (PCC) algorithm for the absolute OPD interrogation of the high-finesse FP sensors. The proposed demodulation algorithm is simulated and analyzed to verify the feasibility of the algorithm for sensors with different reflectivity or OPDs with large dynamic range. A high-finesse fiber-optic FP pressure sensor with a cavity length of about 1500 µm and reflectivity of 62.5% has been used to carry out the experiment. Results show that the measurement resolution of the PCC algorithm can reach the sub-nanometer level, the sensor' sensitivity is about 3.93 nm/KPa, which is similar to the theoretical value. By exploring the effect of reflectivity on the demodulation results, it is found out that accurate results are still obtainable even though the exact reflectivity is unknown. In addition, thanks to the multi-threading of computers and the parallel computing method proposed in this paper, the demodulation speed would be further improved.

Miniature and high-performance optical fiber relative humidity sensor based on Fabry-Perot structure interacting with hydroxyethyl cellulose

A miniature Fabry-Perot fiber-optic sensor is demonstrated for high-performance relative humidity (RH) detection. This sensor is constructed by fusing a single-mode fiber to a small section of capillary coating the end with a hydroxyethyl cellulose film (HEC). The effects of capillary length and hydroxyethyl cellulose concentration on the RH response are investigated to obtain the preferential condition with capillary length of 102 μm and HEC concentration of 0.03 g/ml. A testing RH sensitivity of 1.24 nm/%RH can be achieved in the range of 48%RH to 60%RH. Simultaneously, small hysteresis errors are demonstrated in the tests with increasing and decreasing RH values. The dynamic measurements reveal a response time of 1.61 s and a recovery time of 2.1 s. The high sensitivity, good stability and simple fabrication process of the sensor make it promising for practical applications of relative humidity sensors.

All-Silica diaphragm-based optical fiber fabry-perot pressure sensor fabricated by CO2 laser melting capillary end face

An all-silica Diaphragm-based miniature optical fiber pressure sensor based on the Fabry-Perot (FP) interferometric principle is proposed. The FP structure is composed of a single-mode fiber and a fiber capillary end face diaphragm by a CO2 laser welding. The fabrication process and parameter control of all-silicon diaphragm are introduced in detail, and the pressure performance test system of FP is set up. The experimental results show that the fiber optic FP sensor has good sensitivity and linearity to air pressure, the sensitivity can reach 9.48 pm/kPa when the pressure ranges from 0 to 200 kPa, and the linearity is 0.998. All-silica diaphragm-based fiber FP pressure sensor fabricated by CO2 laser melting capillary end face is more compact, easy to produce, and has great potential in the extreme harsh environment.

Fabry-Perot İnterferometre Tabanlı Sensörlerde Mesa Boyutlarının MEMS Diyaframlar Üzerine Etkisi

In this study, the effects of mesa dimensions on sensor response in diaphragm-based Fabry-Perot fiber optic sensors (FOSs) were investigated in detail. Mesa diaphragms, also called center-embossed diaphragms, have been discussed sufficiently in the literature, but the effect of mesa thickness on sensor performance has not been discussed in detail. Moreover, there is no precise analytical solution for such diaphragms. For this reason, diaphragms with different thicknesses and radii were selected, and the deflection and frequency responses of the diaphragm according to the applied acoustic pressure were analyzed using the ANSYS software, depending on whether the mesa is thinner or thicker than the diaphragm. If the thickness of the mesa is smaller than the thickness of the diaphragm, the center deflection changes drastically. However, if the thickness of the mesa is two times greater than the thickness of the diaphragm, there is no significant change in the deflection results. Similarly, if the mesa thickness is thinner than the diaphragm, the sensor’s frequency response changes drastically with increasing mesa radius. In cases where the mesa thickness is larger than the diaphragm thickness, the frequency response changes less. According to the results, mesa dimensions should be considered when designing a mesa diaphragm-based Fabry-Perot FOS.

Design and Demodulation of a Fiber-Optic Fabry-Perot Sensor Applied in a High- Frequency Pneumatic System

This study proposes a high-frequency pneumatic system and demodulation method based on polydimethylsiloxane (PDMS) film-embedded fiber-optic Fabry-Perot sensor to meet the conflicting requirements of small sizes and wide frequency-response range not achieved by conventional pneumatic probes. The high modulus of elasticity of PDMS films provides the potential for an upper limit of a pneumatic frequency response up to 20 kHz, and the new demodulation algorithm, based on the ability of the F-P cavity to return to its initial length from the maximum cavity length change, is utilized to analyze its variation. The process of recovering F-P cavity corresponds with the sparse part of the signal, which takes advantage of the unique characteristics of interference fringes in this part. Moreover, the relationship between the relative change of the F-P cavity length and pneumatic pressure, as well as the relationship between the duration of the relative change of the F-P cavity length and the frequency are analyzed comprehensively. The rationality of the proposed demodulation scheme is verified from the angle-error analyses. These analyses could be helpful for integrated and high-frequency response pneumatic detection.

Nano-strain resolution fiber-optic Fabry-Perot sensors compatible with moderate/low resolution VIS-NIR spectrometers.

This paper reports on nano-strain resolution fiber-optic Fabry-Perot sensors produced by an improved selective etching method. The presented sensors exhibit high spectral sensitivity, low intrinsic temperature response, small size and mounting comparable to conventional Fiber Bragg gratings. Furthermore, the proposed sensors can be read-out by a combination of cost-efficient and widely available VIS/NIR spectrometers and LEDs used in lighting/automotive applications. A strain resolution of 1 nɛ was demonstrated when using a high-end FBG signal interrogator, while the application of a cost-efficient VIS spectrometer still yielded a strain resolution of about 20-70 nɛ. When applying suitable temperature compensation, absolute measurements with the nano-strain range are also plausible.

Microbubble end-capped fiber-optic Fabry-Perot sensors.

We report on a simple fabrication technique for Fabry-Perot (FP) sensors formed by a microbubble within a polymer drop deposited on the tip of an optical fiber. Polydimethylsiloxane (PDMS) drops are deposited on the tips of standard single-mode fibers incorporating a layer of carbon nanoparticles (CNPs). A microbubble inside this polymer end-cap, aligned along the fiber core, can be readily generated on launching light from a laser diode through the fiber, owing to the photothermal effect produced in the CNP layer. This approach allows for the fabrication of microbubble end-capped FP sensors with reproducible performance, showing temperature sensitivities as large as 790 pm/°C, larger than those reported for regular polymer end-capped devices. We further show that these microbubble FP sensors may also prove useful for displacement measurements, with a sensitivity of ∼5.4 nm/µm.

Fundamental and high-order cross-correlation combined demodulation method for absolute cavity length measurement of fiber-optic Fabry–Perot sensors

For the accurate cavity-length demodulation of fiber-optic Fabry–Perot (FP) sensors, a combined correlation method based on the fundamental cross-correlation and a higher-order one is proposed, simulated, and experimentally verified. By extending the reflection spectrum eightfold through continuous frequency-doubling three times, cross-correlation using both the original and eightfold spectra, and determination of the main peak of the fundamental cross-correlation coefficient function with the assistance of the eighth-order cross-correlation coefficient, the cavity-length demodulation resolution for fiber-optic FP sensors can be significantly improved even when the spectral bandwidth of the source is limited or the cavity length is relatively short. A cavity length resolution better than 1.8 nm is achieved for an FP sensor with a cavity length of ∼162 μm. The proposed demodulation method can effectively reduce the bandwidth requirement of the light source for the cavity-length extraction of fiber-optic FP sensors, particularly those with relatively short cavity lengths.

Microbubble-based optical fiber Fabry-Perot sensor for simultaneous high-pressure and high-temperature sensing.

An all-silica Fabry-Perot interferometer (FPI) based on a microbubble for high-pressure and high-temperature measurements is proposed and demonstrated. The microbubble-based air cavity is fabricated using a hollow silica tube and a single-mode optical fiber for pressure sensing. The suitable thickness between the two end faces of the microbubble enables the silica cavity to be used for temperature sensing. The wavelength shift of the reflection spectrum versus pressure is linear, and the sensitivity reaches -5.083 nm/MPa at room temperature (20 °C) within the range of 0 - 4 MPa. The temperature sensitivity reaches 12.715 pm/°C within the range of 20 - 700 °C. The very low temperature-pressure cross-sensitivity of the two cavities indicates that the proposed FPI sensor offers great potential for simultaneous high-pressure and high-temperature measurements in harsh environments.

High-Precision Cavity Length Demodulation Method for Fiber-Optic Fabry-Perot Sensors Based on Dual Superluminescent Diodes.

A high-precision cross-correlation cavity length demodulation method for fiber-optic Fabry–Perot (F–P) sensors based on two different wavelength superluminescent diodes (SLDs) was proposed. This method can solve the problem of low demodulation accuracy caused by the difficulty in identifying the maximum cross-correlation coefficient when the cavity length of the fiber-optic F–P fiber sensor is too short, or when the spectral bandwidth of the illuminating single-light source is too narrow. This demodulation method is based on the principle that the two main peaks of the two cross-correlation curves corresponding to two different spectral ranges should match, and the average value of the two calculated cavity lengths corresponding to the two matched peaks is determined as the real cavity length. The cavity length demodulation of fiber-optic F–P sensors in the range of 20–200 μm shows a maximum measurement deviation of 0.008 μm, which is significantly smaller than the demodulation result obtained with a single light source, and the standard deviation of the measurement results is only approximately 0.0005 μm, indicating the high precision and stability of a dual SLD cross-correlation demodulation method.

Optical Fiber Probe Microcantilever Sensor Based on Fabry-Perot Interferometer.

Optical fiber Fabry–Perot sensors have long been the focus of researchers in sensing applications because of their unique advantages, including highly effective, simple light path, low cost, compact size, and easy fabrication. Microcantilever-based devices have been extensively explored in chemical and biological fields while the interrogation methods are still a challenge. The optical fiber probe microcantilever sensor is constructed with a microcantilever beam on an optical fiber, which opens the door for highly sensitive, as well as convenient readout. In this review, we summarize a wide variety of optical fiber probe microcantilever sensors based on Fabry–Perot interferometer. The operation principle of the optical fiber probe microcantilever sensor is introduced. The fabrication methods, materials, and sensing applications of an optical fiber probe microcantilever sensor with different structures are discussed in detail. The performances of different kinds of fiber probe microcantilever sensors are compared. We also prospect the possible development direction of optical fiber microcantilever sensors.

Cavity Length Sequence Matching Algorithm Based on Combined Valley Peak Positioning for Fiber-Optic Fabry-Perot Sensors

To solve the problem of low demodulation accuracy of conventional peak-to-peak algorithm for fiber-optic Fabry-Perot (FP) sensors due to failure of determining the interference order, a novel cavity length sequence matching demodulation algorithm based on a combined valley peak positioning is proposed. Firstly, a pair of a peak and its neighboring valley in the reflection spectrum is selected and positioned, and two groups of interference orders are supposed to generate two groups of cavity length sequences. Finally, these cavity lengths are compared to find the real interference order of the peak and valley for the extraction of the accurate cavity length. In order to verify the feasibility and performance of the proposed algorithm, simulations and experiments were carried out for fiber-optic FP sensors with cavity lengths in the range of 15–115 μm. A demodulation accuracy better than 8.8 nm was found. The proposed algorithm can achieve highly accurate cavity length demodulation of fiber-optic FP sensors.

Valley-positioning-assisted discrete cross-correlation algorithm for fast cavity length interrogation of fiber-optic Fabry–Perot sensors

This study proposes a valley-positioning-assisted discrete cross-correlation algorithm for the fast cavity length interrogation of fiber-optic Fabry–Perot (FP) sensors. Because the number of template cavity lengths that require to be cross-correlated with the spectral function of the FP sensor is dramatically decreased by considering the interference order and discretization of the template function, the computation amount can be effectively reduced without sacrificing the interrogating resolution. The feasibility and performance of the proposed algorithm were successfully verified through simulations and experiments. In the cavity length range of 20–130 μm, fiber-optic FP sensors were successfully interrogated with high performance. The maximum error is 3.97 nm, and the resolution reaches a value of 2.62 nm.