PMMA based optical fiber Bragg grating for measuring moisture in transformer oil

Water contamination can cause serious problems that compromise in transformer's safe operation and reduce its lifetime. Online monitoring of moisture concentration in transformer oil would permit the control of moisture buildup. This letter presents a direct optical measurement of moisture concentration in transformer oil using a poly(methyl methacrylate) (PMMA)-based optical fiber Bragg grating (POFBG). The refractive index and volume of PMMA-based optical fiber vary with the moisture in the surrounding transformer oil, changing the reflecting wavelength of the grating. A sensitivity of POFBG wavelength change to moisture content of 29 pm/ppm is demonstrated in this letter, indicating detectable water content better than 0.05 ppm.

Microchanneled chirped fiber Bragg grating formed by femto-second laser aided chemical etching for refractive index and temperature measurements

In this work, a microchanneled chirped fiber Bragg grating (MCFBG) is proposed and fabricated through the femtosecond laser-assisted chemical etching. The microchannel (~550 µm) gives access to the external index liquid, thus inducing refractive index (RI) sensitivity to the structure. In the experiment, the transmission bands induced by the reduced effective index in the microchannel region were used to sense the surrounding RI and temperature changes. The experimental results show good agreement with the theoretical analysis. The proposed MCFBG offers enhanced RI sensitivity without degrading the robustness of the device showing good application potential as bio-chemical sensors.

Tunable compensation of second and third order dispersion by non-uniformly strained chirped fibre Bragg grating

A novel fibre grating device is demonstrated with tuneable chromatic dispersion slope. The tuning range is 70 to 190 ps/nm and 0 to 25 ps/nm2 for the second and third order dispersion, respectively.

The interrogation and multiplexing of long period grating curvature sensors using a Bragg grating based, derivative spectroscopy technique

A long period grating is interrogated with a fibre Bragg grating using a derivative spectroscopy technique. A quasi-linear relationship between the output of the sensing scheme and the curvature experienced by the long period grating is demonstrated, with a sensitivity of 5.05 m and with an average curvature resolution of 2.9 × 10-2 m-1. In addition, the feasibility of multiplexing an in-line series of long period gratings with this interrogation scheme is demonstrated with two pairs of fibre Bragg gratings and long period gratings. With this arrangement the cross-talk error between channels was less than ± 2.4 × 10-3 m-1.

Extended range interrogation of wavelength division multiplexed fibre Bragg grating sensors using an arrayed waveguide grating

A technique for interrogating multiplexed fibre Bragg grating (FBG) sensors using an arrayed waveguide grating (AWG) is described. The approach considerably extends the sensing range from that achieved previously, while providing a strain resolution of 17nevHz at 30 Hz.

High-resolution, wavelength-division-multiplexed in-fibre Bragg grating sensor system

A novel wavelength-division-multiplexed in-fibre Bragg grating sensor system combined with high resolution drift-compensated interferometric wavelength-shift detection is described. This crosstalk-free system is based on the use of an interferometric wavelength scanner and a low resolution spectrometer. A four element system is demonstrated for temperature measurement, and a resolution of ±0.1°C has been achieved.

Wavelength-division and spatial multiplexing using tandem interferometers for Bragg grating sensor networks

We present a new method for the interrogation of large arrays of Bragg grating sensors. Eight gratings operating between the wavelengths of 1533 and 1555 nm have been demultiplexed. An unbalanced Mach—Zehnder interferometer illuminated by a single low-coherence source provides a high-phase-resolution output for each sensor, the outputs of which are sequentially selected in wavelength by a tunable Fabry-Perot interferometer. The minimum detectable strain measured was 90 ne-vHz at 7 Hz for a wavelength of 1535 nm.

Spatially-multiplexed fibre-optic Bragg grating strain and temperature sensor system based on interferometric wavelength-shift detection

A prototype fibre-optic system using interferometric wavelength-shift detection, capable of multiplexing up to 32 fibre-optic Bragg grating strain and temperature sensors with identical characteristics, has been demonstrated. This system is based on a spatially multiplexed scheme for use with fibre-based low-coherence interferometric sensors, reported previously. Four fibre-optic Bragg grating channels using the same fibre grating have been demonstrated for measuring quasi-static strain and temperature.

Implementation of microwave photonic filtering using a profiled superstructured fiber Bragg grating and dispersive fiber

The microwave photonic response of a superstructured fiber Bragg grating is investigated. A bandpass response is achieved with the optical taps controlled by the combination of superstructured fiber grating characteristics and fiber dispersion. A rejection level of >45 dB is demonstrated.

Smart structure sensors based on embedded fibre Bragg grating arrays in aluminium alloy matrix by ultrasonic consolidation

Smart structure sensors based on embedded fibre Bragg grating (FBG) arrays in aluminium alloy matrix by ultrasonic consolidation (UC) technique have been proposed and demonstrated successfully. The temperature, loading and bending responses of the embedded FBG arrays have been systematically characterized. The embedded FBGs exhibit an average temperature sensitivity of ~36 pm °C-1, which is three times higher than that of normal FBGs, a bending sensitivity of 0.73 nm/m-1 and a loading responsivity of ~0.1 nm kg-1 within the dynamic range from 0 kg to 3 kg. These initial experimental results clearly demonstrate that the UC produced metal matrix structures can be embedded with FBG sensor arrays to become smart structures with capabilities to monitor the structure operation and health conditions in applications.

Fiber Bragg grating structures inscribed using 800nm femtosecond laser in single- and multi-core mid-IR glass fibers with their spectral, thermal and strain properties

Single- and multi-core passive and active germanate and tellurite glass fibers represent a new class of fiber host for in-fiber photonics devices and applications in mid-IR wavelength range, which are in increasing demand. Fiber Bragg grating (FBG) structures have been proven as one of the most functional in-fiber devices and have been mass-produced in silicate fibers by UV-inscription for almost countless laser and sensor applications. However, because of the strong UV absorption in germanate and tellurite fibers, FBG structures cannot be produced by UVinscription. In recent years femtosecond (fs) lasers have been developed for laser machining and microstructuring in a variety of glass fibers and planar substrates. A number of papers have been reported on fabrication of FBGs and long-period gratings in optical fibers and also on the photosensitivity mechanism using 800nm fs lasers. In this paper, we demonstrate for the first time the fabrication of FBG structures created in passive and active single- and three-core germanate and tellurite glass fibers by using 800nm fs-inscription and phase mask technique. With a fs peak power intensity in the order of 1011W/cm2, the FBG spectra with 2nd and 3rd order resonances at 1540nm and 1033nm in a single-core germanate glass fiber and 2nd order resonances between ~1694nm and ~1677nm with strengths up to 14dB in all three cores of three-core passive and active tellurite fibers were observed. Thermal and strain properties of the FBGs made in these mid-IR glass fibers were characterized, showing an average temperature responsivity of ~20pm/°C and a strain sensitivity of 1.219±0.003pm/µe.

Simultaneous interrogation of fiber Bragg grating sensors using an acoustooptic tunable filter

We describe a novel technique to provide demultiplexing of fiber Bragg grating sensors, interrogated using interferometric wavelength shift detection. Amplitude modulation of multiple radio frequency driving signals allows an acoustooptic tunable filter to provide wavelength demultiplexing. We demonstrated a noise limited strain resolution of 150 nanostrain/v(Hz) and a crosstalk better than -50 dB.

Fast and widely tunable Bragg grating reflection filter

A fiber Bragg grating filter device linearly tunable over 45 nm is presented. The device has a maximum tuning speed of 19 nm/ms with a wavelength setting time below 1.5 ms.

Wideband tuneable fibre Bragg grating filters

A fibre Bragg grating filter device, tunable over 45 nm, is reported. The device has a wavelength setting time below 1.5 ms and a maximum tuning speed of 21 nm/ns.