Nikolai Plougmann

Efficient iterative technique for designing Bragg gratings

We present a new iterative method for designing Bragg gratings based on the Levenberg-Marquardt method of minimizing a chi-squared merit function. It is effective for designing both weak and strong gratings and is particularly well suited for unchirped gratings.

Polarization control method for ultraviolet writing of advanced Bragg gratings

We present a flexible and simple method for UV writing of Bragg gratings with advanced apodization profiles including discrete phase shifts. The method is based on a p phase shift between the refractive-index modulation profiles induced by s and p polarization of UV light. By changing the ratio of UV intensity in the two polarizations we are able to control the modulation strength and to induce phase shifts while keeping a constant effective refractive index throughout the Bragg grating. We demonstrate strong UV-written Bragg gratings with Gaussian or sinc apodizations with spectral shapes, in good agreement with theoretical predictions.

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.

New iterative approach for designing bragg gratings

We present a new iterative method for designing Bragg gratings based on the Levenberg-Marquardt method of minimizing a chi-squared merit function. It is effective and suitable for designing both weak and strong unchirped gratings.

Polarization controlled UV writing of Bragg gratings

In conclusion the polarization control method is superior to any double scan method since it allows much more flexible apodization and inclusion of phase shifts, and since only one exposure is required. In many cases the method performs just as well as the most sophisticated phase mask jitter methods, while still remaining very simple and robust.

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

A flexible approach for the apodization of planar waveguide Bragg gratings

A novel single-step technique for the apodization of planar waveguide Bragg gratings based on the polarization control method is proposed. First results are presented, showing successful side-lobe suppression in the reflection spectrum of the gratings.