Henrik Rokkjær Sørensen

Control of the wavelength dependent thermo-optic coefficients in structured fibres

By controlling the fibre geometry, the fraction of optical field within the holes and the inserted material of a photonic crystal fibre, we demonstrate that it is possible to engineer any arbitrary wavelength-dependent thermo-optic coefficient. The possibility of making a fibre with a zero temperature dependent thermo-optic coefficient, ideal for packaging of structured fibre gratings, is proposed and explored.

Ultraviolet-induced birefringence in hydrogen-loaded optical fiber

A precision phase-shifting approach to fabricate various phase-shifted gratings using different combinations of polarized ultraviolet (UV) light is demonstrated. In doing so, the difference between s- and p-polarized light reported by others is confirmed. However, we reveal added complexity for the role of hydrogen and deuterium in the UV-induced process. Previous arguments for the origins are systematically ruled out by reviewing existing literature. We note that the birefringence is made up of at least two components with different thermal stabilities, one consistent simply with molecular hydrogen being present in the system. Overall the birefringence, by deduction, is associated with anisotropy in hydrogen reactions within the fiber. As a result they lead, through known mechanisms of dilation in glass, to anisotropic stress relaxation that can be annealed out, with or without hydrogen remaining, at low temperatures close to 125u2009°C.

Thermal hypersensitisation and grating evolution in Ge-doped optical fibre

Low temperature (sub 1000 degrees C) thermal hypersensitisation is reported in germanosilicate optical waveguides. Gratings are written using a CW 266nm laser source. In contrast to laser hypersensitisation, thermal excitation is generally dispersive involving a range of specific glass sites. More complex grating profiles presenting evidence of solid-state autocatalysis and bistability at increasingly high sensitisation temperatures are observed. More specifically, at 500 degrees C, a behaviour resembling type IIA grating response is observed.

Direct UV written Michelson interferometer for RZ signal generation using phase-to-intensity modulation conversion

An integrated Michelson delay interferometer structure making use of waveguide gratings as reflective elements is proposed and fabricated by direct ultraviolet writing. Successful return-to-zero alternate-mark-inversion signal generation using phase-to-intensity modulation conversion is demonstrated up to 40 Gb/s using the device. Compared to other implementations, the device is compact, inherently stable, and allows for easy customization of the pulsewidth by proper positioning of the gratings on a single coupler structure.

Fabrication of advanced Bragg gratings with complex apodization profiles by use of the polarization control method

The polarization control method offers a flexible, robust, and low-cost route for the parallel fabrication of gratings with complex apodization profiles including several discrete phase shifts and chirp. The performance of several test gratings is evaluated in terms of their spectral response and compared with theoretical predictions. Short gratings with sidelobe-suppression levels in excess of 32 dB and transmission dips lower than 80 dB have been realized. Finally, most of the devices fabricated by the polarization control method show comparable quality to gratings manufactured by far more complex methods.

Thermal stability of UV-written gratings in low- and high Ge content fibers

A systematic study of the thermal decay of Bragg gratings in high and low Ge-content fibers is presented. The resulting annealing curves are discussed in the framework of three different models of UV-induced index changes.

Efficient Bragg grating fabrication in germanium-rich fibre by high-intensity femtosecond 264 nm irradiation

In this work we study FBG recording in a highly-nonlinear fibre (HNLF), employing 264 nm 220 fs (FWHM) pulses with a peak intensity of around 180 GW/cm2. For comparison, FBG inscription was also done with a conventional 248 nm KrF excimer laser with an incident pulse intensity of 4 MW/cm2 and a pulse duration of 25 ns. The lengths of the recorded gratings were 3 and 5 mm for 264 and 248 nm radiations, respectively

Polarization control method for UV writing of advanced Bragg gratings

We report the application of the polarization control method for the UV writing of advanced fiber Bragg gratings (FBG). We demonstrate the strength of the new method for different apodization profiles, including the Sinc-profile and two designs for dispersion-free square filters. The method has been tested for advanced FBGs with various strengths up to 65 dB.