Fiber-optic Fabry-Perot Interferometer Research Articles

Investigation of optical force on magnetic nanoparticles with magnetic-fluid-filled Fabry-Perot interferometer

The optical force acting on the magnetic nanoparticles (MNPs) is investigated with the magnetic-fluid-filled fiber-optic Fabry-Perot interferometer. The shift of interference spectra is related with the local refractive index variation in the light path, which is assigned to the optical-force-induced outward movement of MNPs. The influence of magnetic fluid’s viscosity, ambient temperature, strength and orientation of the externally applied magnetic field on the optical-force-induced MNPs’ movement is studied in details. The results of this work provide a further understanding of interaction between light and MNPs and clarify the dynamic micro-processes of MNPs within magnetic fluid under external stimuli. It may have the potentials in the fields of light-controllable magnetic-fluid-based devices and vector magnetic field detection.

Optical fiber Fabry-Perot interferometer based on phase-shifting technique and birefringence crystals.

In this paper, the optical fiber Fabry-Perot (F-P) interferometer based on phase-shifting technique and birefringence crystals is proposed and demonstrated. We use the characteristics of birefringence and four birefringence crystals with different thicknesses to obtain the quadrature phase-shifted signals, which are demodulated by phase-shifting technique. Two types of sensing interferometers are used in the experiment. One is the optical fiber F-P sensor and the other is composed of the fiber end face and the glass surface fixed on the nanopositioning stage. The experimental results show that the normalized standard deviation (SD) of the calibration microphone centerline is 1.97 and 2.63 times larger than the optical fiber F-P interferometer under the sinusoidal sonic signals of 21 kHz and 40 kHz, and the interferometer is effective in avoiding phase ambiguity. The proposed interferometer has high stability and can adapt to a larger measurement range.

Multiwavelength Thulium-Doped Fiber Laser Using a Micro Fiber-Optic Fabry–Perot Interferometer

A compact, all-fiberized multiwavelength thulium-doped fiber laser based on a micro fiber-optic Fabry–Perot interferometer (FPI) and a nonlinear optical loop mirror (NOLM) has been demonstrated. The FPI with a free spectral range of ∼26 nm was used as an effective wavelength selective filter, which was constructed by splicing a ∼71.4- μ m long air-filled hollow-core fiber with single-mode fibers at both ends. An NOLM, served as an amplitude equalizer, was used for stabilizing multiwavelength laser operation. Besides switchable single-wavelength operations (1948.00 and 1972.24 nm), stable dual-wavelength operations (1948.02/1974.25 and 1974.16/1975.30 nm) and triwavelength operation (1947.94/1973.03/1974.14 nm) have been obtained. The optical signal-to-noise ratio of each emission laser line is larger than ∼47 dB.

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.

Elastic Optical Fiber Fabry–Perot Interferometer for Highly Sensitive AC Magnetic Field Measurement

We have proposed and demonstrated a novel elastic optical fiber Fabry–Perot interferometer (FPI)-based ac magnetic field sensor with high magnetic sensitivity and correction of temperature crosstalk. The elastic FPI is formed by soft splicing using low Young’s modulus polydimethylsiloxane material at the joint point of a hollow-core fiber and single-mode fibers and is fixed on a common supermendur rod, a kind of magnetostrictive material. AC magnetic field-induced length change of the magnetostrictive rod results in the obvious change of the FPI cavity length and finally is transduced to the intensity variation of the sensor signal, which makes the sensor highly sensitive to ac magnetic field. Taking advantage of the elastic FPI structure, the magnetic sensitivity (in terms of strain) is improved to 48 ppm/mT (75.01 pm/mT in terms of wavelength), compared with the low intrinsic sensitivity of the conventional magnetostrictive rod (usually below several ppm/mT and 0.39 ppm/mT in our case). Moreover, the impact of temperature cross-sensitivity is removed by retrieving the wavelength shift of the FPI interference spectrum based on the calibrated signal voltage versus wavelength shift. All the ac magnetic fields of different frequencies and intensities have been successfully detected and measured by our FPI sensor without the impact of temperature crosstalk. We believe such a simple, compact, and cost-effective sensor would be a promising candidate for accurate monitoring of ac magnetic field.

Multi-wavelength mode-locked thulium-doped fiber laser based on a fiber-optic Fabry–Perot interferometer and a nonlinear optical loop mirror

An all-fiberized multi-wavelength mode-locked thulium-doped fiber laser (TDFL) based on fiber-optic Fabry–Perot interferometer (FPI) and nonlinear optical loop mirror (NOLM) has been presented. The fiber-optic FPI played the roles of wavelength selective filter and output mirror, which constructs by a single mode-hollow core-single mode fiber structure (SMF-HCF-SMF). A NOLM with wavelength-dependent cavity loss was employed to alleviate the mode competition in thulium-doped fiber and enabled the multi-wavelength mode-locking. With proper manipulation of the polarization controller and the pump power, besides the single-wavelength (~1948 nm) fundamental and high orders harmonic mode-locked operations, switchable dual-wavelength (1924.67/1949.16 nm and 1949.64/1972.68 nm) and stable three-wavelength (1924.80/1951.42/1972.14 nm) mode-locked operations are obtained. The multi-wavelength mode-locked TDFL exhibits a good stability with maximum peak power fluctuations of less than 0.5 dB in 2 h.

Fiber-optic Fabry-Perot interferometer based high sensitive cantilever microphone

We demonstrate a high sensitive cantilever microphone based on fiber-optic Fabry-Perot interferometer. A stainless steel cantilever is manufactured by laser micro-machining technique. The size of the cantilever is 2 mm × 1 mm, and the thickness is 10 μm. The air gap between the fiber endface and the cantilever forms the Fabry-Perot cavity. Acoustic sensing test demonstrates high sensitivities in the frequency range from 100 Hz to 3 kHz. The pressure sensitivity and the noise-limited minimum detectable acoustic pressure level are measured to be 364 nm/Pa and 8.5 μPa/Hz1/2 at the frequency of 1 kHz, respectively. The Fabry-Perot interferometer based cantilever microphone shows advantages of high sensitivity, small size, easy to install and immune to electromagnetic interference.

Ultrasonic imaging of seismic physical models using a fringe visibility enhanced fiber-optic Fabry-Perot interferometric sensor.

A fringe visibility enhanced fiber-optic Fabry-Perot interferometer based ultrasonic sensor is proposed and experimentally demonstrated for seismic physical model imaging. The sensor consists of a graded index multimode fiber collimator and a PTFE (polytetrafluoroethylene) diaphragm to form a Fabry-Perot interferometer. Owing to the increase of the sensor's spectral sideband slope and the smaller Young's modulus of the PTFE diaphragm, a high response to both continuous and pulsed ultrasound with a high SNR of 42.92 dB in 300 kHz is achieved when the spectral sideband filter technique is used to interrogate the sensor. The ultrasonic reconstructed images can clearly differentiate the shape of models with a high resolution.

Thin-film-based optical fiber Fabry-Perot interferometer used for humidity sensing.

A thin-film-based optical fiber Fabry-Perot interferometer that consists of ZrO2 and SiO2 porous thin films is designed and fabricated by electron beam physical vapor deposition. Since the SiO2 porous thin film has the capability of water adsorption, the proposed Fabry-Perot interferometer is appropriate to detect humidity. Experimental results show that the prepared sensor has a humidity detection range from 0.06% RH to 70% RH. A cycling test shows that the humidity sensor has a responding or recover time of 4s and good repeatability among different humidity environments. Especially, the proposed humidity sensor is insensitive to temperature variation and suitable for the detection of low relative humidity.

Flexible Optical Fiber Fabry–Perot Interferometer Based Acoustic and Mechanical Vibration Sensor

We have proposed and demonstrated a novel flexible optical fiber Fabry–Perot interferometer (FPI) based vibration sensor with broadband frequency response. The sensor consists of a flexible FP cavity formed by soft splicing using polydimethylsiloxane (PDMS) material with low Young's Modulus and a compact fiber cantilever of low moment inertia as the vibration receiver. Acoustic or mechanical waves experienced by the fiber cantilever can result in obvious change of the FPI cavity length and finally be transduced to the intensity variation of the sensor signal, which makes the sensor highly sensitive to external acoustic or mechanical vibrations. Taking advantage of the superior elasticity of PDMS and compact structure of cantilever, a broadband frequency response for vibration detection has been achieved together with high sensitivity without extra external vibration receiver. The vibration detection is theoretically analyzed, and acoustic vibrations up to 20 kHz and damped mechanical vibrations from tens of hertz to tens of kilohertz, covering both the sound and part of ultrasound range, have been experimentally detected. Moreover, each event of the ball hitting and rebounding has been accurately identified by our sensor, showing excellent vibration sensing only by a thin optical fiber. We believe such a broadband, compact and cost-effective sensor would be a promising candidate for monitoring both acoustic and mechanical vibrations.

Five-step phase-shifting white-light interferometry for the measurement of fiber optic extrinsic Fabry-Perot interferometers.

Five-step phase-shifting white-light interferometry is presented for interrogating the absolute cavity length of the fiber optic extrinsic Fabry-Perot interferometer (EFPI). It combines ideas of phase-shifting interferometry and white-light interferometry (WLI) to extend the measurement range of fiber optic WLI. Five sub-interferograms intercepted from the white-light optical spectrum are used to recover the optical path difference (OPD) of the EFPI. This method is demonstrated to interrogate a wider range of OPD. The experimental results show that the measurement resolution ranges from 0.5μm to 5μm with cavity length ranges from 16μm to 12,402μm, and it has a great advantage in measuring EFPIs with short cavity lengths.

High‐temperature Fabry–Perot interferometer based on mode analysis

An optical fibre Fabry–Perot interferometer (FPI) is proposed and experimentally demonstrated in this work. In the fast Fourier transform spectrum of the FPI transmission spectrum, a higher order model is separated from the transmission spectrum and the spatial frequency spectrum of the higher order model is detected. As the temperature changes, the shifts of the spatial frequency spectrum will be observed. The sensitivity of the temperature is 0.128 µm−1 K−1. The proposed sensor features the advantages of easy fabrication, compact structure and stable chemical property, and exhibits great potential in high-temperature measurement.

Fiber-Optic Biological/Chemical Sensing System Based on Degradable Hydrogel

To improve the sensitivity and shorten the testing time of hydrogel-based bio-toxin sensors, we introduce an optical fiber Fabry–Perot interferometer (FPI) to detect the changes in the optical properties induced by the reactions between the target agent and the hydrogel. The concept is demonstrated by a polyacrylamide hydrogel filled into a cavity of an optical fiber FPI with a length of 150 $\mu \text{m}$ . Dithiothreitol (DTT) solutions with different concentrations were used as target agent. The degradation of the hydrogel by the DTT solution leads to a long and indistinct change in optical properties, which is difficult to be observed by conventional microscopy methods, but which can be detected by measuring the unique shifting process of the interfering spectrum caused by the hydrogel cleavage in the FPI cavity. Compared to our previous hydrogel-based sensor based on the microscopy observation, the sensitivity of the optic fiber FPI is improved by 2000 times, and the testing time is shortened from hundreds of hours to a few hours. Our approach opens up an avenue for highly sensitive, high-speed in-field detection of bio-toxins in live samples.

Fe3O4-decorated graphene assembled porous carbon nanocomposite for ammonia sensing: study using an optical fiber Fabry-Perot interferometer.

A porous graphene-coated optical fiber Fabry-Perot interferometer (G-FPI) and Fe3O4-graphene nanocomposite coated Fabry-Perot interferometer (FG-FPI) have been investigated and compared for the detection of ammonia gas at room temperature. The sensor probes were subjected to ammonia concentrations varying from 1.5 ppm to 150 ppm. An increased sensitivity was observed for FG-FPI (36 pm ppm-1) when compared with that of G-FPI (25 pm ppm-1). The observed sensor detection limits for FG-FPI and G-FPI were around 7 and 10 ppb, respectively. The sensing mechanism was based on the change in refractive index/dielectric constant of the material; which changed the conductivity of coated material in presence of NH3. It was observed that the modified refractive index induced a wavelength shift in the FPI. The highly porous structure of graphene and the uniform dispersion of Fe3O4 nanoparticles into this framework effectively facilitated the target gas diffusion and hence improved the sensing performance. The sensing was correlated to the oxygen vacancies on the Fe3O4 surfaces and the depletion region manipulations with the ammonia interactions along with Schottky-type electron conductivity via the conducting graphene assembled porous carbon framework. The mathematical evaluation of the phenomenon also justified the excellent repeatability and reversibility of this sensitive, room temperature sensor.

Fiber-Optic Fabry-Perot Phase Shifted Interferometer Using Modal Demultiplexing

A fiber-optic phase-shifted Fabry-Perot interferometer (PS-FPI) using a modal phase shifter (MPS) and modal demultiplexing is demonstrated. The PS-FPI is used as a temperature sensor to obtain two output fringe sets as a result of a 6°C rise in temperature. A controllable phase shift between the fringe sets is obtained using the MPS and is beneficial in quadrature demodulation of measurand induced sensor signals which can extend the unambiguous range beyond half a fringe. Located before the sensing cavity, the MPS introduces a phase shift between the LP01 and LP11 modes. These modes travel to the FP cavity to produce interference fringes. This results in a few-mode sensor system having 2 orders of magnitude higher sensitivity than conventional few-mode systems, with a worst case voltage signal to noise ratio of 16.9 dB for a 0.5°C rise in temperature.

Humidity Sensor Based on Fabry–Perot Interferometer and Intracavity Sensing of Fiber Laser

A humidity sensor based on Fabry–Perot interferometer (FPI) and intracavity sensing of a fiber ring laser is proposed and experimentally demonstrated. A compact humidity-sensitive fiber-optic FPI is developed and inserted in a fiber ring laser. Because the output power of the fiber laser is modulated by the reflection loss of the FPI at different ambient humidity, intracavity humidity sensing is induced. The experiment shows that the relative output power of the fiber laser has a good linear response to ambient humidity from 25%RH to 95%RH and the humidity sensitivity of 0.202 dB/%RH is obtained with a narrow 3-dB bandwidth and high signal-to-noise ratio. Furthermore, the excellent performance of the sensor for remote humidity detection is demonstrated. The sensor also shows a low temperature cross-sensitivity, fast time response, and good stability. The proposed sensor has a great potential in high-capacity sensor network and remote detections.

Multi-mode all Fiber Interferometer based on Fabry-Perot Multi-cavity and its Temperature Response

We present the use of conventional arc discharge technique for manufacturing an optical fiber Fabry-Perot interferometer using hollow core photonic crystal fiber and conventional single-mode fiber. The interferometric structure is composed by several intrinsic Fabry-Perot cavities, here the excitation of several fiber optic modes generates a high frequency interference reflection spectrum with special properties such as a free spectral range of 0.1nm and visibility near to 6dB. Thermal analysis has been conducted to demonstrate a sensing application, hence several modal Fabry-Perot interferometers were immersed in liquid and controlled temperature increments were applied. The thermal variations show a linear phase shifting to a shorter wavelength. The analysis exhibits a sensitivity and resolution of 27pm/°C and 0.7°C respectively. The proposed fiber structure offers compactness, robustness, low-cost fabrication, simple manufacturing process and remote sensing operation. Moreover, it was demonstrated for real sensor applications: suitable sensitivity, good resolution, and long dynamic range.

CO$_{2}$ Gas Sensing Using Optical Fiber Fabry–Perot Interferometer Based on Polyethyleneimine/Poly(Vinyl Alcohol) Coating

An optical fiber Fabry–Perot interferometer (FPI) based on poly (ethyleneimine) (PEI)/ poly (vinyl alcohol) (PVA) blend membrane is proposed and realized experimentally as a sensor for the pressure of CO $_{2}$ in the atmosphere. The functional material layer based on PEI/PVA blend polymer exhibits reversible optical path difference change because of absorption and release of CO $_{2}$ gas molecules. The cavity of the FPI is fabricated by coating a 15- $\mu$ m PEI/PVA blend film on the end-face of a cleaved single-mode fiber. An interference spectrum with fringe contrast of 19.5 dB and free spectra range of 33.15 nm is obtained. The proposed FPI sensor is sensitive to the changes of concentration of CO $_{2}$ , as well as a sensitivity of 0.281 nm/ $\%$ within an interval which ranges from 7.6 $\%$ to 86.9 $\%$ .

Ultrasonic Sensitivity-Improved Fabry–Perot Interferometer Using Acoustic Focusing and Its Application for Noncontact Imaging

An easily multiplexed fiber-optic Fabry–Perot interferometer (FPI)-based ultrasonic wave (UW) sensor has been proposed and used to experimentally demonstrate ultrasound wave imaging of seismic-physical models. The sensor probe comprises an interferometer formed by a free-standing gold foil and a cleaved optic-fiber tip. An acoustic focusing lens enhances the sensor's ultrasound sensitivity and assists with capability to multiplex multiple probes. Theoretical modeling of the focusing effect of the acoustic lenses and the ultrasonic responses of the probes are presented and analyzed. We present an experimental demonstration of time-division multiplexing of three fiber-optic Fabry–Perot sensors operating in air to reconstruct the shapes of physical models. The compact sensor has a symmetrical structure so that it presents a good directionality of ultrasound detection, making it valuable as an effective sensor for ultrasound scanning of physical models in air.

Highly sensitive and selective fiber-optic Fabry-Perot volatile organic compounds sensor based on a PMMA film

A compact fiber-optic Fabry-Perot interferometric (FFPI) volatile organic compounds (VOCs) sensor is fabricated based on a single mode fiber (SMF) and a polymethyl methacrylate (PMMA) film. The VOCs induce the swelling effect and refractive index changes of PMMA film. The swelling of PMMA film affects the cavity length of Fabry-Perot interferometer resulting in shift of resonant dip, while the change in refractive index influences reflection resulting in change of extinction ratio (ER). The sensitivities of 2.7 pm/ppm for ethanol and 2.17 pm/ppm for acetone are achieved. Moreover, this sensor is insensitive to the inorganic gases. In addition, it has the advantages of ease of fabrication and high sensitivity to VOCs.