Sensing characteristics of rocking filters fabricated in microstructured birefringent fibers

A rocking filter is a type of long period grating that rotates azimuth of a linearly polarized light launched into one polarization mode of a birefringent fiber. If the grating period equals a beat length of the birefringent fiber (Lambda=L_B), a resonant coupling between the modes of orthogonal polarization arises. In this paper, we demonstrate that in microstructured fibers (MSFs) the phase matching condition between polarization modes can be obtained simultaneously at several wavelengths, because the phase birefringence in MSFs is very dispersive and increases against wavelength. In Fig. 1b, we show the transmission characteristic for the excited polarization mode registered for the rocking filter fabricated in highly birefringent MSF consisting of 13 coupling points with a period of Lambda=8 mm. The measured positions of respective resonances arising at 855, 1271 and 1623 nm are in good agreement with the calculated values obtained using Jones matrix formalism.