Direct writing of plane-by-plane tilted fiber Bragg gratings using a femtosecond laser

In this Letter, we report a flexible, plane-by-plane direct write inscription method for the development of tailored, tilted fiber Bragg gratings using a femtosecond laser. Compared to ultraviolet or femtosecond laser inscription
based on the phase mask, interferometric, or point-by-point methods, the presented approach is far more flexible and offers several advantages. Laser inscription is made through the fiber coating, while the grating planes are controlled
to minimize birefringence, with precise control over the wavelength location and strength of cladding modes. Tenth-order gratings were produced in the C + L bands so that higher-order gratings could be studied at shorter wavelengths. In particular, we show that the refractometric sensitivity depends on the grating order, ranging from ∼28 nm∕refractive index unit (RIU) at ∼1510 nm to ∼13 nm∕RIU at ∼1260 nm.