George Simpson

High extinction ratio in-fiber polarizers based on 45° tilted fiber Bragg gratings

We report a near-ideal in-fiber polarizer implemented by use of 45° tilted fiber Bragg grating structures that are UV inscribed in hydrogenated Ge-doped fiber. We demonstrate a polarization-extinction ratio of 33?dB over a 100-nm operation range near 1550?nm. We further show an achievement of 99.5% degree of polarization for unpolarized light with these gratings. We also theoretically investigate tilted grating structures based on the Greens function calculation, therein revealing the unique polarization characteristics, which are in excellent agreement with experimental data.

Blank beam fabrication of regenerated type IA gratings

We demonstrate an idealized method for the fabrication of regenerated type IA fibre Bragg gratings using commonly available apparatus. We use this technique to show that gratings written in the same fibre with the same period may have central wavelengths which are 14.4 nm apart and have an + 11.5% and - 1.2% difference in temperature and strain coefficients, respectively. We use these results to show that temperature compensated dual grating sensor heads, of an arbitrary length, may be quickly and consistently manufactured.

Annealing and temperature coefficient study of type IA fibre Bragg gratings inscribed under strain and no strain: implications to optical fibre component reliability

The annealing properties of Type IA Bragg gratings are investigated and compared with Type I and Type IIA Bragg gratings. The transmission properties (mean and modulated wavelength components) of gratings held at predetermined temperatures are recorded from which decay characteristics are inferred. Our data show critical results concerning the high temperature stability of Type IA gratings, as they undergo a drastic initial decay at 100°C, with a consequent mean index change that is severely reduced at this temperature However, the modulated index change of IA gratings remains stable at lower annealing temperatures of 80°C, and the mean index change decays at a comparable rate to Type I gratings at 80°C. Extending this work to include the thermal decay of Type IA gratings inscribed under strain shows that the application of strain quite dramatically transforms the temperature characteristics of the Type IA grating, modifying the temperature coefficient and annealing curves, with the grating showing a remarkable improvement in high temperature stability, leading to a robust grating that can survive temperatures exceeding 180°C. Under conditions of inscription under strain it is found that the temperature coefficient increases, but is maintained at a value considerably different to the Type I grating. Therefore, the combination of Type I and IA (strained) gratings make it possible to decouple temperature and strain over larger temperature excursions.

Impact of hydrogenation conditions on the temperature and strain coefficients of type 1 and type 1a dual grating sensors

We report experimental findings for tailoring the temperature and strain coefficients of Type 1 and Type 1A fibre Bragg gratings by influencing the photosensitivity presensitisation of the host optical fibre. It is shown that by controlling the level of hydrogen saturation, via hot and cold hydrogenation, it is possible to produce gratings with lower thermal coefficients. Furthermore, there is a larger difference between the Type 1 and Type 1A thermal coefficients and a significant improvement in the matrix condition number, which impacts the ability to recover accurate temperature and strain invariant data using the Type1-1A dual grating sensor.

Dependence of Type IA FBG Growth on Inscription Intensity

We present a study on the dependence of the rate of Type IA fiber Bragg grating formation on the inscription laser intensity with a view to ascertaining the optimum CW inscription conditions at 244nm.

Wavelength tuning, chirping and thermally induced decay of type IA FBGs using purely optical methods

We report experimental measurements of reversible wavelength tuning, chirping and permanent thermally induced decay of type1A fibre Bragg gratings using purely optical means. The grating properties are modified in a controlled manner by utilising the characteristics of the intrinsic 1400nm absorption band of the optical fibre and two tuneable lasers coincident with that band. It is shown that the type 1A grating can be selectively tuned in a grating network and that selective tuning can be attained in a common section of suitably prepared optical fibre. Applications of this approach for tuning fibre lasers or edge filter modification in sensing applications are discussed.