Fiber-optic Interferometer Research Articles

Investigation of CO2 measurement of ZIF-8-based F–P interferometric optical fiber sensor

In this paper, a set of ZIF-8 (Zeolitic Imidazolate Framework-8)-based Fabry-Perot (F–P) interferometric optical fiber sensor was designed to measure the carbon dioxide gas with different concentrations. The optical path difference of our sensing element was mainly caused by the F–P cavity filled with ZIF-8 instead of gas cavity. We analyzed the operating principle and verified the feasibility of the sensor. We gave the exact relation between the concentration of carbon dioxide and each parameter of the F–P cavity. The experimental results show that the spectrum will be red-shifted with the increase of the adsorption of carbon dioxide by ZIF-8 at a certain concentration of carbon dioxide. In addition, after applying Fourier transform to the spectrum, the frequency spectrum displayed two main peaks which changed to the lager value with the increase of concentration of carbon dioxide. The sensor has linear wavelength and phase sensitivities with the concentration of carbon dioxide under 5 × 104 ppm. Besides, the response time becomes shorter as the concentration of carbon dioxide decreases. To sum up, we presented a fiber optic gas sensor that is both simple to manufacture and has high selectivity, making it an effective method for measuring carbon dioxide.

Highly sensitive optical fiber pressure sensor based on the FPI and Vernier effect via femtosecond laser plane-by-plane writing technology.

In this paper, a highly sensitive pressure sensor based on fiber-optic Fabry-Perot interferometers (FPIs) and the Vernier effect (VE) is proposed and experimentally demonstrated. We employ a closed capillary-based F P I s for the sensing cavity, and an F P I r created through femtosecond laser refractive index modulation for the reference cavity, which remains impervious to pressure changes. Connecting these two FPIs in series produces a VE-based cascaded sensor with a clear spectral envelope. The femtosecond laser micromachining technique provides precise control over the length of F P I r and facilitates adjustments to the VE's amplification degree. Experimental results reveal significant pressure sensitivities of -795.96p m/M P a and -3219.91p m/M P a, respectively, representing a 20-fold and 80-fold improvement compared to F P I s (-39.80p m/M P a). This type of sensor has good sensitivity amplification and, due to its all-fiber structure, can be a promising candidate for high-temperature and high-pressure sensing, especially in harsh environments.

Real-Time Measurement and Uncertainty Evaluation of Optical Path Difference in Fiber Optic Interferometer Based on Auxiliary Interferometer.

Optical interferometers are the main elements of interferometric sensing and measurement systems. Measuring their optical path difference (OPD) in real time and evaluating the measurement uncertainty are key to optimizing system noise and ensuring system consistency. With the continuous sinusoidal wavelength modulation of the laser, real-time OPD measurement of the main interferometer is achieved through phase comparison of the main and auxiliary interferometers. The measurement uncertainty of the main interferometer OPD is evaluated. It is the first evaluation of the impact of different auxiliary interferometer calibration methods on OPD measurements. A homodyne quadrature laser interferometer (HQLI) is used as the main interferometer, and a 3 × 3 interferometer is used as the auxiliary interferometer. The calibration of the auxiliary interferometer using optical spectrum analyzer scanning and ruler measurement is compared. The evaluation shows that the auxiliary interferometer is the most significant source of uncertainty and causes the total uncertainty to increase linearly with increasing OPD. It is proven that a high-precision calibration and large-OPD auxiliary interferometer can improve the real-time accuracy of OPD measurements based on the auxiliary interferometer. The scheme can determine the minimum uncertainty to optimize the system noise and consistency for vibration, hydroacoustic, and magnetic field measurements with OPDs of the ~m level.

Fiber-optic trace gas sensing based on graphite excited photoacoustic wave

A fiber-optic trace gas sensing system based on photoacoustic (PA) effect of solids is reported. The modulated laser light absorbed by the gas is incident on a graphite sheet. The graphite sheet and cantilever are enclosed together to form an optical power detector based on PA effect of solids. This scheme is different from the traditional PA trace gas detection, achieving the separation of the gas chamber and the PA detector, thereby isolating the interference of airflow and environmental noise. In addition, due to the large size of the graphite sheet, the laser incident on the graphite sheet does not need to be converged through a lens, which makes it much easier to adjust the optical path. The PA pressure wave generated by the graphite sheet leads to the vibration of the optical interferometric cantilever. A fiber-optic white-light interferometer is used for high-resolution cantilever readout to detect the PA signal generated by solid excitations. The trace acetylene gas is used to verify the system performance. The experimental results indicate that when the averaging time is 100 s, the minimum detection limit (MDL) is 24 ppb. The normalized noise equivalent absorption (NNEA) coefficient of the designed PA system is 5.4×10−9 cm−1·W·Hz−1/2. This gas sensing system has the characteristics of intrinsic safety and high sensitivity, which can realize remote measurement of corrosive, flammable and explosive gases.

Frequency response of the non-polarization-maintaining depolarized sagnac interferometer based on maximum fringe contrast

The Sagnac Interferometer offers a promising solution to the speckle problem in interferometric detection due to its insensitivity to environmental low-frequency interference, making it well-suited for applications such as laser ultrasonic detection. Control of the polarization state of light is imperative for achieving high sensitivity in optical fiber interferometer and ensuring optimal quiescent operating conditions. This study employed the coherence matrix method to analyze the theory of optimal polarization control in a non-polarization-maintaining depolarized Sagnac Interferometer, encompassing the deduction of the stable π/2 initial phase bias and the maximum fringe contrast of 50% in theory. In experimental observations during PZT simulated large amplitude ultrasound experiments, the fringe contrast reached 48.4%. Furthermore, the system's amplitude-frequency response was evaluated using an electro-optics phase modulator, demonstrating its capability to detect high-frequency signals within 100 MHz These findings provide essential insights into optimizing the Sagnac Interferometer's performance for laser ultrasonic detection and its potential applications in high-frequency signal detection and ultrasonic amplitude measurement.

Belt conveyor speed detection based on fiber-optic Sagnac interferometer vibration sensor

With their long transportation distance and high productivity, belt conveyors are characterized as the main equipment for bulk material transportation in coal mines and other key industries. However, its speed detection method has always been an engineering challenge under harsh working conditions. In this work, the elastic-optical effect of the polarization-maintaining fiber is used to design a fiber ring laser vibration sensing system based on a fiber-optic Sagnac interferometer vibration sensor and its packaging structure. The vibration detection is achieved by detecting the change in optical power at the working wavelength, and the belt conveyor speed measurement is completed by detecting the vibration frequency. With such a method, the belt conveyor speed measurement obtained a relative error of less than 1.88%. The proposed method bears the characteristics of anti-electromagnetic interference, intrinsic explosion-proof, and adapts to the harsh smoke and dust working environment, which has a wide range of application prospects in the fields of engineering, machinery, security, etc.

An ERPNS Technology Based on OFDR for Accurate Arm-Length Difference Measurement of Optical Fiber Interferometer Under Dynamic Environment

An ERPNS Technology Based on OFDR for Accurate Arm-Length Difference Measurement of Optical Fiber Interferometer Under Dynamic Environment

Ultrasensitive Hydrogen Sensor with Vernier Effect by Dual Parallel Structured Fiber-Optic Fabry-Perot Interferometers

Ultrasensitive Hydrogen Sensor with Vernier Effect by Dual Parallel Structured Fiber-Optic Fabry-Perot Interferometers

Fast Demodulated White-light Interferometry-based Measurement and Theoretical Verification of Mechanical Sensitivity of MEMS Biomimetic Microphone with Fiber-optic Fabry-Perot Interferometer

Fast Demodulated White-light Interferometry-based Measurement and Theoretical Verification of Mechanical Sensitivity of MEMS Biomimetic Microphone with Fiber-optic Fabry-Perot Interferometer

Fiber-optic semi-distributed Fabry-Perot interferometer for low-limit label-free detection of CCL5 cancer biomarker

Fiber-optic semi-distributed Fabry-Perot interferometer for low-limit label-free detection of CCL5 cancer biomarker

Frequency Down-Converted and Sensitivity Enhanced Fiber Optic Sensing System Based on Multi-Passband Microwave Photonic Filter by Cascaded Fiber Optic Interferometers

Frequency Down-Converted and Sensitivity Enhanced Fiber Optic Sensing System Based on Multi-Passband Microwave Photonic Filter by Cascaded Fiber Optic Interferometers

Corrections to “A Fabry-Perot Fiber-Optic Interferometer for Highly Sensitive CO2 Detection Based on the Nanoparticles Self-Assembly Technology”

Corrections to “A Fabry-Perot Fiber-Optic Interferometer for Highly Sensitive CO₂ Detection Based on the Nanoparticles Self-Assembly Technology”

Measurement of refractive index and temperature using a balloon-like interferometer with an inner embedded waist-enlarged structure

A balloon-like composite optical fiber interferometer, integrated with a waist-enlarged structure, is presented for measuring refractive index (RI) and temperature. The waist-enlarged fusion tapers (WEFTs) are spliced to the single-mode fiber (SMF) to form a Mach-Zehnder interferometer (MZI). Meanwhile, the WEFTs structure is curved into a balloon-like structure. When the two structures are integrated, a larger evanescent field is formed, which can interact with the external environment better. The experiment results indicate that the best sensitivity of RI and temperature can achieve 340.9 nm/RIU and −0.162 nm/℃, respectively. In addition, the interferometer is small, easy to manufacture, and can be widely applied in various measurement applications.

Optimal fiber-optical sensing element selection on multimode interferometer

The paper presents the results of model and experimental search for optimal configuration of sensing element based on fiber-optical multimode interferometer with intermode interference in the phase-amplitude filter. Simulation results are presented. Based on them, combinations of multimode fiber light guides with single-mode ones are selected, the most suitable for constructing the sensitive part. Laboratory tests of the selected configurations were carried out. The requirements for the necessary components have been developed. The dynamic characteristics of the sensing elements are obtained depending on the variable parameters for different methods of welding fiber light guides.

Optimizing the sensitivity of a fiber optic-based Sagnac interferometer for high-performance human voice sensing

This article presents a theoretical and experimental study aimed at enhancing the sensitivity of the fiber optic Sagnac interferometer, specifically designed for efficient detection of human voice signals. The study focuses on optimizing various factors that influence the sensitivity, including the frequency response of the Sagnac interferometer, the structure of the sensing fiber, and the sensor noise. Several fiber sensing structures were investigated both theoretically and experimentally within this framework to enable high-performance human voice sensing. The measurement results validate the theoretical findings, particularly highlighting the directional sensitivity influenced by the geometry of the sensing fiber structure. Notably, we succeeded in recording and intelligible listening to a human conversation at a distance of 5 m using a multi-layer fiber coil with a total length of 50 m. The measured Minimum Detectable Pressure (MDP) is approximately 337 μPa/Hz1/2 at 1 kHz, which can be reduced by increasing the fiber length.

Optimization of nanoparticles for application in optical sensors

This study explored the influence of crystallite size on a nanoparticle-coated fiber optic Mach-Zehnder Interferometer (MZI). The primary aim was to enhance the magnetic properties of the nanoparticles for application in fiber optic sensors designed for magnetic field sensitivity. The motion of the nanoparticles within the magnetic field induced alterations in the sensor's transmission, creating an imbalance in the optical signals between the interferometer arms. Nickel ferrites (NiFe2O4) with average crystallite sizes of 3.3 nm, 51.9 nm, and 74.3 nm were used. The nanoparticles were identified by X-ray diffraction, VSM magnetic measurements, and Mössbauer spectroscopy. Structural parameters obtained from X-ray diffraction underwent refinement using the Rietveld method, and the Scherrer equation was applied to determine the average crystallite size. Magnetic sensor performance was assessed for sensitivity, precision, and accuracy for different nanoparticle sizes. The relationship between output power and applied magnetic field exhibited linearity between 87.6% and 99.2%. Sensitivity varied from 1.65 dB/Oe to 3.17 dB/Oe for different particle sizes, indicating an increase in sensitivity with nanoparticle magnetization. This study establishes a correlation between crystallite size and nanoparticle magnetization, enhancing sensor responsiveness. This optimization facilitates the development of tailored electric current and magnetic field sensors, considering nanoparticle size and their distinctive magnetic properties. Although the primary focus was on the optical sensor, a comprehensive nanoparticle characterization was crucial as it directly influenced sensor performance.

All-sapphire-based optical fiber pressure sensor with an ultra-wide pressure range based on femtosecond laser micromachining and direct bonding

An all-sapphire extrinsic Fabry-Perot interferometer (EFPI) optical fiber pressure sensor with ultra-wide pressure range and high temperature resistance is proposed and experimentally demonstrated. The sensor is fabricated by direct bonding three sapphire wafers, including the sapphire substrate, the sapphire wafer with a through hole, and the sapphire pressure-sensitive diaphragm. A femtosecond (fs) laser is used to inscribe a through hole in the center of the sapphire wafer and roughen the outer surface of the sapphire pressure-sensitive diaphragm. By using original polished surfaces of sapphire wafers with low surface roughness as reflective surfaces of the Fabry-Perot (FP) cavity, the high-quality interference signal can be obtained, thereby improving the measurement accuracy of the sensor. The optical cavity length (OCL) of the proposed sensor changes linearly with the applied pressure in the wide range of 0 - 50 MPa at room temperature, and the pressure sensitivity is 0.0921 µm/MPa. The pressure measurement accuracy reaches 0.31%FS (full scale). High temperature experiments show that the sensor can work stably at 1000 ℃.

Temperature compensation of fiber optic unbalanced interferometers for high resolution static strain sensing

Accurate temperature compensation challenges the use of fiber optic unbalanced interferometers in static strain sensing. We propose a temperature compensation theory and scheme of unbalanced interferometers using sensing fibers with different temperature coefficients, aiming at resolving the temperature disturbance of optical fibers and achieving high strain resolution. For the first time, we comprehensively analyze the thermal response of interferometers due to different temperature coefficients, different thermal behaviors, and inconsistent temperature disturbances in the optical fiber arms. A sensing combination and a reference combination are designed. The sensing combination measures a strain and compensates for the temperature disturbance of the sensing arm, and the reference combination provides a reference to compensate for the temperature disturbance of the reference arm and frequency drift of the interferometer in the sensing combination. The proposed scheme can compensate for the temperature disturbances of interferometers in the sensing combination completely. To verify the theory and scheme, bend-insensitive single-mode fibers and Boron/Germanium co-doped fibers are used as sensing fibers in the experiment. The experimental results show that the temperature resolution of the sensing arm is about 3.43 × 10−4 °C, and the static strain resolution of the unbalanced interferometer within 24 h after temperature compensation is about 2.55 nε. The temperature-compensated strain resolution of ∼nε indicates that the proposed temperature compensation theory and scheme can be used in high-resolution, long-term, low-frequency, and static strain sensing, such as crustal deformation observation in geophysical applications.

Ameliorted algorithm for PGC to eliminate the influence of carrier phase delay with FFT

In the real environment, the carrier phase delay (θ) is difficult to accurately maintain at nπ (n is an integer), which results in the demodulation error of the phase generation carrier (PGC) demodulation algorithm. In this paper, the fast Fourier transform (FFT) technique is used to extract 1θ0, 2θ0, 3θ0, 4θ0 from the first to fourth harmonic signals of the interference signal, then introduce 1θ0, 2θ0, 3θ0, 4θ0 into the mixed signal as the initial phase, and finally perform a mixing operation to real time eliminate the carrier phase delay. The experiments show that when the carrier delay is in the range of 0 to π, the SINAD of the ameliorated algorithm reaches 43.66 dB, which is 19.31 dB higher than the PGC-Arctan algorithm on average. The THD of the ameliorated algorithm can be stabilized at 0.183 %, which always maintains the best level of the PGC-Arctan algorithm. The ameliorated algorithm eliminates the carrier phase delay and does not have the phase singularity, thus expanding the application range of the fiber optic interferometer sensor.

Miniature fiber-optic near-surface gap-coupled cladding waveguide Mach-Zehnder interferometric refractive index sensor inscribed by femtosecond laser

A miniature fiber-optic gap-coupled cladding waveguide Mach-Zehnder interferometer (MZI) is proposed and demonstrated for high-sensitive refractive index measurement. Two straight cladding waveguides respectively coupled with the fiber core are inscribed by a femtosecond laser (fs) to form the MZI structure. At their far ends, the two cladding waveguides are very close to the cladding surface, and a short separation was intentionally designed for the coupling of light between them and generating light field with evanescent wave expanded outside the cladding surface, which makes the MZI structure very sensitive to ambient refractive variations. In a refractive index range of 1.34–1.42, a high sensitivity of −59.90238 nm/RIU is achieved simultaneously with good linearity. The sensing structure also shows good characteristic of temperature insensitivity, which may find practical applications in chemical or biological sensing.