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An in-line Mach-Zehnder interferometric refractive index (RI) sensor is demonstrated by concatenating two single-mode fiber (SMF) half-tapers separated by one section of SMF. The cladding modes excited at the first half-taper interferes with the core mode at the second half-taper to generate the interference fringe. Theoretical and experimental results consistently show that the interference fringe...
A multiwavelength random fiber laser based on stimulated Brillouin scattering (SBS) with odd and even order Stokes output separated is proposed and demonstrated experimentally. The gain is provided by the SBS and erbium doped fiber amplifier, while the Rayleigh scattering in single mode fiber (SMF) provides random distributed feedback. With a two-branch structure, we successfully make the laser output...
The sensing performance in Brillouin-based distributed fiber sensors is ultimately depends on the signal-to-noise ratio (SNR) of the received signal. In order to enhance the SNR, thus improve the sensing performance, several wavelength diversity techniques have been proposed. This paper presents the current wavelength diversity techniques employed in both Brillouin optical time-domain reflectometry...
Ballistocardiography (BCG) is a non-invasive method for measuring the reaction force of the human body to the ejection of blood at each cardiac cycle. It is now being the subject of renewed research interest due to recent technological advancement in the field of sensors. In this paper, we summarize our work on BCG with optical fiber sensors for various applications in the past 6 years. These include...
Ballistocardiography (BCG) is a non-invasive method for measuring the reaction force of the human body to the ejection of blood at each cardiac cycle. It is now being the subject of renewed research interest due to recent technological advancement in the field of sensors. In this paper, we summarize our work on BCG with optical fiber sensors for various applications in the past 6 years. These include...
We demonstrated femtosecond laser inscription of fiber Bragg gratings (FBGs) in a twin-core few-mode fiber (TC-FMF) for directional bend sensing. An FBG was selectively inscribed in one core of the TC-FMF by using an 800 nm femtosecond laser through a phase mask. Three resonance peaks at the wavelengths of 1549.05, 1547.65, and 1546.08 nm were observed in the reflection spectrum of the TC-FM FBG,...
We demonstrate a novel polyvinyl chloride (PVC) diaphragm-based fiber-tip Fabry-Perot interferometer for gas pressure measurements with ultra-high sensitivity. The PVC diaphragm has been coated to the end facet of a well-cut standard single-mode fiber by use of a plastic welder. Ultrahigh pressure sensitivity of ∼66.07 nm/MPa at 1565 nm and a low temperature cross-sensitivity of —5.5 KPa/°C have been...
We demonstrated an optical fiber sensor with high sensitivity of temperature and refractive index, we can use it to measure temperature and refractive index simultaneously. The sensing head consists of a section of multimode fiber (MMF) and a section of multi-core fiber (MCF), which is connected between two segments of single-mode fibers to form a Mach-Zehnder interferometer (MZI). A short section...
Ultrasound technique has been widely applied in various areas such as diagnostic applications, structure health monitoring, etc. Most advanced applications require novel ultrasonic transmitters, where fiber optic technique has been proved to be a great candidate due to its compact dimension, high frequency, and highly harsh environment survivability. Therefore, extensive research has been conducted...
Characteristic of two cascaded Mach-Zehnder interferometers based on spherical-shape structures is investigated. When the light in the fiber core is excited into high-order cladding mode, part of the light can propagate along the fiber cladding for a long distance. By cascading two identical interferometers formed by dual spherical-shape structures, it proves that the high-order cladding modes are...
A magnetic field sensor based on a novel phase-shifted fiber Bragg grating with magnetic fluid is proposed and experimentally demonstrated. It is fabricated by cleaving a uniform fiber Bragg grating at the center point, introducing a micrometre gap as a phase-shift and then filling the gap with magnetic fluid. External applied magnetic field changes refractive index of the magnetic fluid, leading...
A random phase-shifted fiber Bragg grating has been theoretically analysed by the transfer matrix method. Numerical predictions of the effects of phase-shifted points on the reflection spectra of such a grating are calculated. This fiber Bragg grating with 10 random phase-shifted points distributed has been fabricated. These predictions are compared with experimentally measured spectra of the random...
A new method to modify excessively titled fiber gratings (Ex-TFGs) with 20 nm gold nanoparticles (GNPs) through 3-mercapt-otrimethoxysilane(MPTMS) was proposed. By monitoring the wavelength shift of Ex-TFGs for every modified step and using the scanning electron microscope (SEM), it proves that GN Ps are firmly combined on the surface of Ex-TFGs. Finally, by using different concentration of NaCl solutions...
A methylcellulose (MC) coated humidity sensor by using photonic crystal fiber (PCF) based Mach-Zehnder interferometer (MZI) is proposed and experimentally demonstrated. It is fabricated by sandwiching a PCF between two standard single mode fibers (SMFs) with the air holes of the PCF in the fusion splicing region being fully collapsed. Experimental results show that this structure can not only carry...
Recently, some fiber sensing applications by coating graphene oxide or reduce graphene oxide have been proposed. In this paper, a novel humidity sensor based on core-offset fiber Mach-Zehnder interferometer coated graphene oxide film has been carried out. Here, we use the chemical method to deal with the surface of the fiber first, and then coated graphene oxide on the surface of the optical fiber...
The comb filters consist of few mode fiber and standard single mode fiber suffer from low extinction radio. Replacing standard single mode fiber with small-mode-area fiber can better the balance excitation in few mode fiber, thus improve the extinction radio. A lab-made small-mode-area single mode fiber was utilized to a commercial few mode fiber and increase the extinction radio from 2.5dB to 6.5dB...
A tadpole-shape fiber sensor, with S-bend fiber cascading spherical shape, has been proposed and experimentally realized in this work. In our experiments, the output spectrum of the proposed sensor was found to be shifted with the changing of the refractive index and the temperature. Experiments results showed that the highest sensitivity of the refractive index was up to −114.845nm/RIU with a wide...
We propose a refractive index (RI) sensor based on a liquid-filled defect hollow core Bragg fiber (DHCBF) for high index sensing, in which a resonant wavelength resulted from the transverse resonant coupling effect between core modes and defect modes is utilized as the characteristic wavelength. The linearity and sensitivity strongly depend on structural parameters of defect layer. Accordingly, we...
We developed a new technique for constructing humidity sensor comprised of two cascaded peanut-shape structure which were coated with polyvinyl alcohol (PVA) and in between was also coated with PVA. The coating changes with the humidity which resulting in the change of the effective refractive index, and lead to the change of the interference wavelength. Experiments show that, with the humidity changes...
The applications of specklegram analysis techniques have been developed recently. In this paper, we represent a fiber-optic method to measure the temperature through the analysis of output specklegrams. The proposed all-fiber device excites higher-order modes through splicing a multimode fiber (MMF) to a single-mode fiber (SMF) with a core offset. The basic principle of the sensor is based on determining...
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