We have proposed and experimentally demonstrated optical fiber strain sensor with a extended dynamic range based on a coupled optoelectronic oscillator (COEO). The oscillation frequency equals to the mode spacing of the laser that is affected by the axial strain applied to the cavity. Thus, we can evaluate the strain by measuring the oscillation frequency shift. A proof-of-concept experiment is carried out. The dynamic range is up to 10000 με. The sensitivity is 13.8 Hz/με for 2700 MHZ. The COEO has a maximum frequency drift range of ±303.907 Hz for 2700 MHz within 90 minutes, and the corresponding measurement error is ±20 με . The scheme has the advantages of high precision and high speed.
Magnetic field as a kind of objective substance contains abundant physical information, so high sensitivity and resolution measurement for the magnetic field has great significance in scientific and industrial fields. In this work, we verify a highly sensitive cascaded Mach-Zehnder interferometer (C-MZI) sensor based on optical Vernier effect for the magnetic field measurement, which is composed of a reference MZI (R-MZI) without magnetic fluids (MFs) connected in series with a sensing MZI (S-MZI) with MFs. An evident envelope and shift induced by the external magnetic field is observed in the transmission spectra of the C-MZI, resulting in the sensitivity being elevated by an amplification factor. The experimental results reveal a wavelength sensitivity of -5.148 nm/mT in the range of 10.15~30.44 mT, being ~4.77 of that in the single S-MZI. In order to further improve the detection resolution of the magnetic field, a magnetic field measurement system based on the combination of the above S-MZI and an optoelectronic oscillator (OEO) is proposed, and the spectral response is tested in a small magnetic field range of 1.45~1.90 mT, obtaining a spectral sensitivity of 3.18 kHz/mT, which proves the detection of less than 1 Oe. The designed sensor and system possess the merits of high sensitivity, high resolution, simple fabrication, fast response and low phase noise, having broad prospects in the fields of magnetic field measurement.
Magnetic field as a kind of objective substance contains abundant physical information, so high sensitivity and resolution measurement for the magnetic field has great significance in scientific and industrial fields. In this work, we propose a novel fiber-optic magnetic field sensor by using an etched fiber Bragg grating (FBG) in conjunction with an OEO. A commercial FBG was firstly dipped into mixed hydrofluoric acid solution to remove cladding layer, and then was embedded with Fe3O4 magnetic fluid as sensing element. Incorporating the microwave photonic filter (MPF) in the OEO sensor, the oscillation frequency is determined by the magnetic field. Experimental results show that the oscillation frequency decreases with the increment of the magnetic field with sensitivity of 15.2Hz/Oe ranging from 3mT to 10mT, mainly because the refractive index of magnetic fluid was reduced sharply in this range. Since the proposed method transfers the measurement from the optical domain to electric domain, the interrogation speed, sensing sensitivity and resolution are significantly increased, offering potentials in many fields where the magnetic field measurement is required.
KEYWORDS: Frequency modulation, Signal to noise ratio, Sensing systems, Pulsed laser operation, Optical filters, Signal detection, Data acquisition, Phase shift keying, Fiber optics sensors, Radar signal processing, Compressed sensing
We reported a new method based on additive random sampling (ARS) and non-linear frequency modulation (NLFM) to enhance the frequency response of long-range phase-sensitive optical time-domain reflectometry (φ-OTDR) system. Using the NLFM interrogation pulse, the side-lobe suppression ratio (SLSR) and signal-to-noise ratio (SNR) of the demodulated traces are improved, and phase signal detection with less than 3m spatial resolution is achieved over 50 km sensing range. By modulating the NLFM laser pulse intervals, we realize the ARS and the uniform sampling alternately for every sensing point of the long interrogation fiber, and therefore the frequency domain aliasing is avoided. We test the proposed system by detected a 20 kHz harmonic signal, and this signal is well identified and reconstructed over 50 km sensing range.
In this paper, a magnetic field sensor based on a multilongitudinal mode fiber laser has been proposed by employing a rotary apparatus modulated by an external magnetic field. Due to the remarkable birefringence change caused by the fiber twist, the polarimetric mode beat frequency (PMBF) of the laser is sensitive to the applied magnetic field intensity. Experimental results show that the PMBF linearly shifts with the variation of the magnetic field intensity and the sensitivity reaches up to 10.4 KHz/Oe in the range of 0 - 270Oe.
Tilt sensor is becoming more and more popular in many engineering fields. With the development of the sensor, tilt sensor with high sensitivity and directional is required in these fields. A simple, compact and high sensitivity fiber-optic directional tilt angle sensor is proposed and experimentally demonstrated in this paper. This novel structure is based on an asymmetrical in-line M-Z inclinometer, as a result, the structure is very compact. At the same time, the structure is easy to fabricate. Because of the asymmetrical structure, different changes happened to the sensor and the sensor can recognize the tilt direction. The tilt angle is obtained by monitoring the resonant wavelength shift and the tilt direction can be obtained from the redshift or blueshift. This structure got a very high sensitivity of 0.935nm/° in a range from -3° to 3°.
An in-fiber whispering gallery mode resonator fabricated by femtosecond laser micromaching is demonstrated. The cylinder resonator cavity is fabricated by scanning the D-fiber cladding with infrared femtosecond pulses along a cylindrical trace with radius of 25μm and height of 20μm. Quality factor on the order of 103 is achieved by smoothing the cavity surface with ultrasonic cleaner, which is mainly limited by the surface roughness of hundreds nanometers. Resonant characteristics and polarization dependence of the proposed resonator is also studied in detail. Our method takes a step forward to the integration of whispering gallery mode resonators.
We propose a tunable optical switching based on thermo-optic nonlinear effect in an electro-microtube ring resonator (EMRR) made by a capillary embedded with a heating wire. The significant modes shift in the EMRR for nonlinear switching are attributed to a huge joule heat generated by the heating wire, leading to the resonant wavelength shifts over 0.9nm when using 250mA current. In our viewpoints, with such a significant performance, the EMRR may be practically applied to switching, optical filter, sensing and optical network process.
An interferometric microfluidic sensor is proposed by perpendicularly coupling light into/out from a glass capillary with a pair of collimators. Light trapped in the wall of a capillary with inner and outer radius of 245μm and 413.5μm travels along different paths and interferes at the output, resulting in a multiple modes interferometer. By successively injecting salt solutions with different concentrations into the capillary air hole, red shift happens in the interferometric spectra with a sensitivity of 42.75nm/RIU. Such a sensing head offers potentials in identifying solutions in real time, especially for those not transparent for light.
A core-cladding-mode interferometer (CCMI) is fabricated by splicing a single-mode fiber (SMF) to an endlessly singlemode photonic crystal fiber (ESM-PCF). The optimum collapsed length of ESM-PCF is investigated to ensure a higherorder cladding mode of ESM-PCF to be excited, serving as a sensing beam. At the end of ESM-PCF, a spherical endfacet with big radius is proposed to ensure from where the higher-order cladding mode to be reflected and then it interferes with the core mode serving as a reference beam. Such a device has an enhanced refractive index sensitivity of ~199 nm/RIU, offering potentials in biological and chemical applications.
We propose and experimentally demonstrate a low-cost, compact temperature-insensitive inclinometer, which is constructed by connecting a chemically etched fiber Bragg grating to a hollow-core fiber filled with tin. The optical power reflected from the grating is linearly proportional to the inclination angle of the grating and can provide a real-time measure of the inclination angle. Our experimental sensor can measure the inclination angle from 0° to 20° with an uncertainty of ± 0.35º and negligible temperature interference.
A novel peanut-shape fiber structure which can realize the coupling and re-coupling between the fiber core mode
and the cladding modes is proposed in this paper. Based on the peanut-shape structure, two kinds of simple and
low-cost interferometers are fabricated in single-mode fiber (SMF). Experimental results show that the temperature
sensitivities of the Mach-Zehnder and Michelson interferometers were ~46.8pm/°C and ~0.096 nm/°C, respectively.
In particular, the Michelson interferometer could be heated up to 900°C, which is suitable for the high temperature
sensing applications.
We demonstrated a novel method of low-loss splicing photonic crystal fiber (PCF) and single-mode fiber (SMF) by
conventional electric arc fusion splicer, in which the air with proper pressure is injecting into the PCFs holes to control
the collapse ratio and then an optimum mode field match at the joint of SMF/PCF is realized. The experimental results
show that the splice loss at 1550nm is ~0.40 dB and ~1.05dB for solid-core PCF/SMF and hollow-core PCF/SMF,
respectively. This method could be widely used to fabricate PCF Devices.
We present a refractive index (RI) sensor based on a fiber Mach-Zehnder interferometer, which is realized by two
cascaded special long period gratings with rotary refractive index modulation (C-RLPFG). The wavelength shift of the
refractometer behaves good linear response in a RI range of 1.3342 to 1.3362, and the sensitivity of 14.5pm/mm for
0.01SRI change has been obtained. The sensitivity is 4 times higher than that of M-Z interferometer formed by using
normal long period fiber gratings. Such kind of high sensitivity, easy fabrication and simple structure interferometer may
find applications in chemical or biochemical sensing field.
We report the fabrication of a highly sensitive refractive-index sensor based on three cascaded single-mode fiber tapers,
in which a weak taper is sandwiched between the two tapers to improve the sensitivity of the sensor. Experimental
results show that the sensitivity of the device is 0.286 nm for a 0.01 RI change, which is about eleven times higher than
that of the normal two cascaded tapers MZ interferometer. Such kind of low-cost and highly sensitive fiber-optic
refractive index sensors will find applications in chemical or bio-chemical sensing fields.
Two kinds of novel in-line all-fiber interferometers, including tip Farby-Perot interferometer and compact Mach-Zehnder
interferometer, are proposed and demonstrated by automatically fusion splicing a short section of hollow fiber to the end
of a single-mode fiber (SMF) and sandwiching a section of hollow fiber in two section of SMF with a tiny intentional
lateral offset that induces the optical path difference (OPD) required to form the two interferometers, respectively.
Temperature responses of both the two interferometers are studied experimentally. It is anticipated that such an easy
making, compact and low cost fiber-optic interferometers could find important applications in practice.
An in-line fiber F-P sensor is formed by splicing a section of hollow-core photonic bandgap fibers in between two
single mode fibers. Such a F-P sensor can be used under high temperature of up to 600 °C, and has a low temperature
sensitivity of ~1.05nm/°C, while it has a relatively high strain sensitivity of ~5.93nm/με. Moreover, this F-P sensor is
insensitive to bend or transverse load. Furthermore, the long cavity length (>1cm) of the sensor makes it suitable for
multiplexing. These characteristics would make this F-P sensor to be an excellent strain gauge for use in high
temperature environments.
We present a novel fiber-optic refractive-index (RI) sensor based on F-P interferometer, formed by splicing an
endlessly photonic crystal fiber to a single-mode fiber. This type of RI sensor can be used to simultaneously measure
RI and temperature by determination of its fringe visibility and cavity length change, respectively. The RI resolution is
~2x10-5 in the linear range and the cavity-length-temperature sensitivity is 18.72nm/ C o from 20°C to 100°C. In
addition, the RI measurement based on the fringe visibility with such a miniature in-line fiber-optic tip sensor is
independent on temperature change, making it suitable for practical applications.
This paper, for the first time to the best of our knowledge, presents a novel fiber-optic refractive-index sensor which is based on an intrinsic Fabry-Perot interferometer (IFPI) formed by a section of endlessly single-mode photonic crystal fiber (EPCF) and conventional single-mode fiber. Such an IFPI sensor has the advantages of easy fabrication, low joint and transmission losses, low-cost and good fringe visibility due to the use of the EPCF. Simultaneous measurement of refractive index (RI) and temperature can be realized by determination of the cavity length change and the fringe visibility of such a PCF-based IFPI, respectively. In addition, it is found that the fringe visibility of the IFPI is insensitive to temperature change, providing a practical way to measure refractive index with self temperature compensation. Such a miniature fiber-optic sensor is demonstrated for the measurement of the refractive index change of glycerin solution by measuring its fringe visibility change solely.
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