Fiber Fabry-Perot Sensor Research Articles

Continuous Hue-Based Self-Calibration of a Smartphone Spectrometer Applied to Optical Fiber Fabry-Perot Sensor Interrogation.

Smartphone-based optical spectrometers allow the development of a new generation of portable and cost-effective optical sensing solutions that can be easily integrated into sensor networks. However, most commonly the spectral calibration relies on the external reference light sources which have known narrow spectral lines. Such calibration must be repeated each time the fiber and diffraction grating holders are removed from the smartphone and reattached. Moreover, the spectrometer wavelength scale can drift during the measurement because of the smartphone temperature fluctuations. The present work reports on a novel spectral self-calibration approach, based on the correspondence between the light wavelength and the hue features of the spectrum measured using a color RGB camera. These features are caused by the nonuniformity of camera RGB filters’ responses and their finite overlap, which is a typical situation for RGB cameras. Thus, the wavelength scale should be externally calibrated only once for each smartphone spectrometer and can further be continuously verified and corrected using the proposed self-calibration approach. An ability of the plug-and play operation and the temperature drift elimination of the smartphone spectrometer was experimentally demonstrated. Conducted experiments involved interrogation of optical fiber Fabry-Perot interferometric sensor and demonstrated a nanometer-level optical path difference resolution.

Breathing process monitoring with a biaxially oriented polypropylene film based fiber Fabry–Perot sensor

The breathing process monitoring with a biaxially oriented polypropylene (BOPP) film based fiber Fabry–Perot (F–P) sensor is presented. The fiber F–P sensor is fabricated with 3-D printing technology and fixed on a medical respirator for breathing process monitoring. Due to the low Young’s modulus of the BOPP film and its thinner thickness, the breathing sensor shows the high pressure sensitivity of -0.581 nm/Pa. By monitoring its intensity response to the pressure induced by breathing, the breathing process can be monitored accurately, including respiratory waveform, respiratory rate, inspiratory duration and amplitude, expiratory duration and amplitude, and inspiratory and expiratory rhythm. Since the sensor is all fiber design with the inherent advantages of small size, anti-electromagnetic interference, green environmental protection, pollution-free and no harm to body, it is expected to be widely used in respiratory disease monitoring.

Heart-Rate Monitoring With an Ethyl Alpha-Cyanoacrylate Based Fiber Fabry-Perot Sensor

Heart-rate monitoring with an ethyl alpha-cyanoacrylate (EtCNA) based fiber Fabry-Perot (F-P) sensor is presented. The fiber F-P sensor is fixed in a capillary tube by using the EtCNA binder. Due to the lower Young's modulus of the EtCNA, the sensor can detect low frequency vibration with a high sensitivity. The fiber sensor is attached in a specially designed bracket to obtain the stable data. When the sensor with bracket is put on the human body, the heart-rate can be monitored accurately by monitoring the laser intensity variation induced by the heartbeat. Experimental results show that the sensor has the strain sensitivity of 2.57 pm/μN with good responses to low frequency vibrations of 1 Hz, 2 Hz and 3 Hz. The maximum and the minimum mean square deviations of the volunteers' data are 4.434210 and 0.667499, respectively. Moreover, it has good adaptability to measure the heart-rate on different positions of human body, such as wrist, chest and neck. Due to the advantages of small size, low cost, good adaptability, pollution-free and no harm to body. Our proposed sensor is expected to be widely used in heart disease monitoring.

Least square fitting demodulation technique for the interrogation of an optical fiber Fabry-Perot sensor with arbitrary reflectivity.

A novel Fabry-Perot (F-P) demodulation technique based on least square fitting for arbitrary reflectivity F-P sensors is proposed. The demodulation method was simulated and analyzed to verify feasibility of the algorithm. Two different finesse F-P interferometers constructed with a reflector bracket were used to make the stability experiments and the stepping experiments. The results show that the demodulation technique can interrogate the cavity length of F-P interferometers with different fineness in a wide range, and the demodulation error is less than 12 nm.

A Demodulation Model of Dynamic Low-Finesse Fabry-Perot Cavity Based on the Instantaneous Frequency

If the measurand changes during the spectrum acquisition process, it easily leads to the failure of the classic demodulation algorithms of low-finesse optical fiber Fabry-Perot (FP) sensors. To address this problem, a novel demodulation model is proposed based on the definition of the instantaneous frequency. The proposed model establishes the relationship between the optical path length (OPL) of the FP cavity and the instantaneous frequency distribution of the FP interference spectrum. The link between the classic FFT algorithm and this model is discussed, and it is found that this model can be viewed as a generalized form of the FFT algorithm. Based on this model, the Doppler-induced demodulation error is analyzed. The analysis uncovers that the average frequency of the FP interference spectrum should be used for the evaluation of the error, and the error is proportional to the variation of OPL during the spectrum acquisition period. Further, numerical simulation and an experiment were carried out to verify the proposed model, and results show that the proposed model is effective for the dynamic low-finesse FP cavity. It is the first time that the idea of instantaneous frequency is introduced for the FP demodulation, and this model provides us a new way to cope with the FP sensing signal.

Long-Sensing-Length Strain Sensor Based on Optical Fiber Fabry-Perot Interferometer With HCF-SMF Structure

We proposed and demonstrated an optical fiber Fabry-Perot (F-P) sensor with long sensing length for strain measurement. The structure of the sensor was fabricated with a simple process by splicing a long single mode fiber (SMF) with a short section of hollow-core fiber (HCF). The end of the SMF was cleaved with smooth reflective surface which hence allows the sensing length of the proposed sensor can achieve several centimeters with good visibility. Sensors with different sensing lengths were fabricated and experimentally analyzed in this paper. The relationship between the optical path difference (OPD) of the sensor and strain is found to be linear. With the sensing length of ∼10 mm and ∼49 mm, the sensor can achieve the OPD strain sensitivity of 20.42 nm/ μϵ and 115.57 nm/ μϵ at 1550 nm over the range of 1000 μϵ respectively. Besides, with the sensing length of ∼10 mm, the OPD temperature sensitivity of the sensor was 187.64 nm/°C. With the advantages of easy making, low cost and long sensing length, it is anticipated that the proposed sensor has great potential in measuring the strain with a large distribution.

On-Line Monitoring of Power Transformer Core Vibration Test System Based on Optical Fiber Fabry-Perot Sensor and Photodetector

Transformer fault is a common problem in power system safety. In the situation of major failure of severe power transformers (PTF), the entire power grid system can be crashed and collapsed. In this study, by analyzing the causes of the vibration of transformer core (vTFC), it was found that the magnetostriction of the silicon steel sheet (SSS) is the main cause of vTFC. The magnetostrictive effect and principle of SSS was analyzed, and the relationship between core magnetostriction and exciting voltage, current, core vibration acceleration and core magnetostriction were discussed. Based on the optical fiber Fabry-Perot sensor (FFPs) and photodetector, vTFC signal testing system was designed as a whole. The system was built and the system was used to measure and analyze the vTFC signal. It is verified that the higher harmonic components of the vTFC signal are mainly distributed around the natural frequency of the core and will vary with the load. The test results showed that the system designed in this study is stable, it is capable of online monitoring and extracting effective vTFC signals, and is easy to optimize and upgrade.

Trace Gas Detection System Based on All-Optical Quartz-Enhanced Photoacoustic Spectroscopy.

An all-optical quartz-enhanced photoacoustic spectroscopy system (QEPAS) with quadrature point stabilization for trace gas detection was reported. The extrinsic interferometry-based optical fiber Fabry-Perot sensor with quadrature point self-stabilization for detection of quartz prong vibration was used to replace the conventional one. The optimal coefficient of the modulation depth was ∼2.2 theoretically and experimentally, corresponding to the modulation depth of ∼0.1795 cm-1 at an acetylene (C2H2) absorption line of 6534.36 cm-1. Furthermore, the enhancement of QEPAS signal was obtained by using different microresonators. The minimum detectable limit of ∼580 parts per billion by volume (ppbv) was obtained. A normalized noise equivalent absorption coefficient for C2H2 of 2.95 × 10-7 cm-1·W·Hz-1/2 was obtained. The detection sensitivity was enhanced by a factor of ∼2.1 in comparison to the conventional QEPAS system. The linear correlation coefficient of the QEPAS signal response to the C2H2 concentration was 0.998 within the range from 10 parts per million by volume (ppmv) to 500 ppmv. Finally, the long-term stability of the QEPAS system was evaluated using Allan deviation analysis, and the ultimate detection limit of ∼130 ppbv was reached for an optimum averaging time of ∼108 s at atmospheric pressure and ambient temperature.

复合式光纤法布里-珀罗传感器非扫描相关解调系统

复合式光纤法布里-珀罗传感器非扫描相关解调系统

Two-Parameter Elliptical Fitting Method for Short-Cavity Fiber Fabry⁻Perot Sensor Interrogation.

To solve the cavity interrogation problem of short cavity fiber Fabry–Perot sensors in white light spectral interrogation with amplified spontaneous emissions (ASEs) as the white light sources, a data processing method, using an improved elliptical fitting equation with only two undetermined coefficients, is proposed. Based on the method, the cavity length of a fiber Fabry–Perot sensor without a complete reflection spectrum period in the frequency domain can be interrogated with relatively high resolution. Extrinsic fiber Fabry–Perot air-gap sensors with cavity lengths less than 30 μm are used to experimentally verify the method, and are successfully interrogated with an accuracy better than 0.55%.

Miniature probe for all-optical double gradient-index lenses photoacoustic microscopy.

A novel all-optical double gradient-index (GRIN) lens optical-resolution photoacoustic microscopy (OR-PAM), termed as DGL-PAM, is demonstrated. The miniature probe consists of a single-mode fiber and double GRIN lenses for optical focusing and a miniature fiber Fabry-Perot sensor for ultrasound detection. The new design is simple and realizes high resolution with long working distance (WD) by virtue of the double GRIN lenses. The overall size of the probe is 2.7 mm in diameter. High lateral resolution of 3.7 μm (at 532 nm laser wavelength) and long WD of 5.5 mm are achieved. In vivo OR-PAM of mouse ear demonstrates the imaging ability of DGL-PAM. Since precise alignment of optical and acoustic foci is not needed, the proposed DGL-PAM is relatively easy to implement. It has potential to be developed as a low-cost, disposable OR-PAM probe and for endoscopic applications. The proposed double GRIN lenses for making miniature endoscopic probes can also be applied to other modalities, such as optical coherence tomography and confocal fluorescence microscopy, to enable high resolution and long WD.

Temperature Insensitive and Integrated Differential Pressure Sensor for Liquid Level Sensing Based on an Optical Fiber Fabry–Perot Interferometer

We propose a temperature insensitive optical fiber Fabry-Perot (FP) sensor for liquid level measurement. The sensor is based on a silicon diaphragm and borosilicate glass ferrules. Through the combination of different ferrules, the FP cavity is fabricated without a seal to eliminate the influence of the residual air in the FP cavity, thereby the temperature cross-sensitivity is significantly reduced. The opened FP cavity constitutes a differential pressure sensing structure at the same time. To verify the performance of this sensor, an experiment with an optical fiber pressure and temperature experiment system is carried out. The measuring range is 0.5-1.3 MPa. The sensor has a good monotonic linear response with an accuracy less than 0.4% F.S. (full scale). The measuring error caused by the temperature drift is lower than 0.0007 MPa/K, i.e., 0.09% F.S./K.

光楔式光纤法布里-珀罗传感器相关干涉信号特性分析

光楔式光纤法布里-珀罗传感器相关干涉信号特性分析

MEMS-based Optic Fiber Fabry-Perot Sensor for Underwater Acoustic Measurement with A Wavelength-switched System

In this paper, a MEMS-based extrinsic Farby-Perot Interferometric (EFPI) acoustic pressure acoustic sensor is presented. The diaphragm structure is used as the second reflected surface, and the sensitive surface to acoustic pressure. A wavelength-switched phase demodulation system for EFPI sensors is used for acoustic signal recovery. The modified phase demodulation system has been demonstrated to recover the signal to a stable intensity fluctuation level of ±0.5 dB at the test frequency of 2000 Hz. In the test depth of 50cm, the sensor has a resonant frequency of 3.7 kHz, a flat frequency range of 10-800Hz, and a corresponding acoustic pressure sensitivity of -159 dB re. 1/μPa.

光纤法布里-珀罗传感器偏振互相关解调系统的复消色差光路设计

光纤法布里-珀罗传感器偏振互相关解调系统的复消色差光路设计

Fiber fabry-pero micro pressure sensor

A new fiber fabry-perot pressure sensor is designed. It is made by photolithography, silicon wafer etching, anode bonding, microelectromechanical system technology and so on. It is suitable for the pressure measurement of micro-pressure environment under harsh environment and small space. The structure of the transmitter and the way to make it are described in detail. The design smartly uses the Fiber optic flange, the optical fiber end face is parallel to the sensitive film, thus a high-quality Fabry-Pero-cavity is formed. The structure also contributes to the stability of the initial cavity, the sensor error is reduced. The experimental demodulation system is established, the pressure, temperature and other characteristics are tested in detail. The experiment result shows that within the pressure range of 0~0.1MPa, the sensor has a good linearity, high repeatability and a sensitivity of 61.6 μm/MPa.

Wavelet phase extracting demodulation algorithm based on scale factor for optical fiber Fabry-Perot sensing.

Optical fiber Fabry-Perot (F-P) sensors have been used in various on-line monitoring of physical parameters such as acoustics, temperature and pressure. In this paper, a wavelet phase extracting demodulation algorithm for optical fiber F-P sensing is first proposed. In application of this demodulation algorithm, search range of scale factor is determined by estimated cavity length which is obtained by fast Fourier transform (FFT) algorithm. Phase information of each point on the optical interference spectrum can be directly extracted through the continuous complex wavelet transform without de-noising. And the cavity length of the optical fiber F-P sensor is calculated by the slope of fitting curve of the phase. Theorical analysis and experiment results show that this algorithm can greatly reduce the amount of computation and improve demodulation speed and accuracy.

Temperature measurements and multi-physical field simulations of micro-sized metal film bridge

To measure the temperature of micro-sized metal film bridge under constant current excitations, by the Fabry–Perot interferometric technology, a new optical fiber sensor was designed for high temperature measurements and quick temperature response. A matched spectrum demodulation system was independently designed and manufactured, including advantage such as a response frequency up to 1.5–5kHz, wide measuring range between ambient temperature and 1500K, and sensor spatial resolution of 125μm. For comparison, the temperature distributions under different current excitation values were obtained by multi-physical field simulations. Experimental values and simulation results have a maximum deviation of 7.6%, indicating the reliability and credibility of the results. In addition, the critical ignition current was evaluated as 182mA, for the micro-sized metal film bridge charged with lead styphnate. The self-designed optical fiber Fabry–Perot sensor provides effective techniques for ignition safety and reliability, when used for precise temperature measurements of micro zones. Furthermore, it is of vital importance to assess the electrothermal conversion efficiency of heating devices in micro-electromechanical system.

Design of Optical Fiber Fabry-Perot Sensors Based on Intensity and Phase with Parallel Processing

Design of Optical Fiber Fabry-Perot Sensors Based on Intensity and Phase with Parallel Processing

Crosstalk Reduction and Demodulation Stability Promotion in Inline Fiber Fabry–Pérot Sensor Array Using Phase Generated Carrier Scheme

An inline time-division multiplexing (TDM) fiber Fabry–Perot sensor array based on the low-reflectivity fiber Bragg gratings (FBGs) is promising for lots of sensing applications. The intrinsic multireflection (MR) between the FBGs with the same Bragg wavelength is a serious problem, which induces crosstalk and generates false detection information. Furthermore, the amplitude of the demodulated signal cannot reach a stable state due to the MR. Here, we presented a full theoretical demonstration of the MR-induced crosstalk fluctuation and demodulation instability, where the phase generated carrier method was used as the interrogation scheme. An interference synthesis method was presented to reduce the MR-induced crosstalk and to promote the demodulation stability simultaneously. The experimental results showed that a crosstalk reduction of 18 dB and a demodulation stability promotion of 1.42 dB could be achieved with the FBG reflectivity of 5%. The principle of the method can be extended to the array with more TDM channels.