Magnetic tuning of optical fibre long period gratings utilizing ferrofluids

Results are presented on the magnetic tuning of optical fibre long period gratings utilizing water and hydrocarbon based ferrofluids as outcladding overlayers. Two approaches are adopted for modifying the ambient refractive index at the position of the long period grating. In the first, a water based ferrofluid is controllably translated along the length of the grating via a magnetic field. Changes as high as 7.5 nm and 6.5 dB are monitored in the wavelength and strength, respectively, of the attenuation bands of the grating. The repeatable performance of this device for forward and backward translation verifies that no ferrofluidic residue is left on the clear fibre section, due to silanization pre-processing. In the second approach the refractive index of a hydrocarbon based ferrofluidic overlayer is modified through the magneto-optical effect. For an applied static magnetic field in the order of 400 Gauss the strength of the attenuation band of the grating is modified by more than 10% while its spectral position remains unaffected.