We demonstrate the first application of the periodic damage tracks in optical fibers formed by the fiber fuse. A refractive index sensor with a sensitivity of 350 nm/refractive index unit (RIU) is experimentally demonstrated. This technique can allow mass production by incorporating small sections of the damaged fiber into each device. It can also be applied widely in different types of sensing systems by coating sensing material on the damaged fiber’s cladding surface.
In this paper we propose and demonstrate two forms of a device for sensing cladding modes efficiently. The cladding modes, generated by an untilted and tilted fibre Bragg grating (TFBG) written in SMF28 fibre are captured by splicing it to an in-line double-clad fibre coupler (DCFC). A comaprison is made of the capture efficiency of the cladding modes in two configurations; one in which the TFBG is taper spliced to the DCF, or in the other in which an FBG in an SMF28 is etched down to match the outer core of the DCF. In both cases the cladding modes are captured efficiently, but with significantly improved results for the former configuration. We demonstrate surrounding refractive index sensing using a new signal analysis scheme based on the extinction of each cladding mode resolved over a bandwidth of over ~60nm. This robust device has the advantage of faithfully transmitting the cladding modes over a long distance and is therefore suitable for remote sensing over long distances. The sensitivity of the device is discussed. This device may be used in a variety of applications such as for bend, strain, temperature and surrounding refractive index sensing.
We report the fabrication and characterisation of near perfect ultra-long fibre Bragg gratings for applications in signal
processing. Narrow bandwidth down to ~few pm FWHM have fabricated using an electro-optic modulation technique,
and characterised for their transfer functions and dispersion. Near perfect characteristics have been achieved with
symmetric group-delay and transmission spectra. 30cm-long, ultra-high reflectivity gratings are also reported. We
discuss prospects for making complex gratings with very low residual noise, opening unprecedented possiblities for
signal processing in the RF, microwave and the THZ regions.
In this paper, it is demonstrated for the first time to our knowledge the use of a novel high-repetition rate 224 nm
nanosecond Q-switched laser source for fiber Bragg grating fabrication. Results are compared with 213 nm a nanosecond
laser source, recently reported for grating inscription. High index change are rapidly obtained using a phase mask
technique in B/Ge doped fiber with a maximum average writing power of only 280 mW at 224 nm and 100 mW at 213
nm. Strong gratings can also be written in standard SMF28 fiber. Photosensitivity is shown to be due to single and two-photon
absorption for SMF28 and B/Ge doped fiber, respectively.
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