Fiber Bragg gratings (FBG) are suitable for measurements in harsh environments, because they are inert to electromagnetic radiation, very small, robust and embeddable into different compound materials. But for high temperature regimes, especially for temperatures beyond 1000 °C conventional fibers made of silica cannot be used due to their lower softening point. For such high temperatures FBGs in sapphire are of great interest, since the crystalline sapphire material is stable for temperatures beyond 2000 °C. Sapphire has a very high refractive index of about 1.74, so that the grating period of the FGB has to be very small in the order of 440 nm for a reflection wavelength in the standard telecommunication C-band (1530-1565 nm). With the common inscription wavelength of 800 nm, this is not possible and until now the only gratings reported are of higher orders. For our inscription we used a frequency doubled Ti:Sa amplified laser system, which provides femtosecond laser pulses with a sufficiently short wavelength of 400 nm for first order FBGs. The inscription itself was done using a tunable, phase mask based, two beam interferometer. With the interferometer the grating period can be tuned easily by rotating the interferometer mirrors, and multiplexing becomes applicable with only one beam splitting phase mask in the interferometer. Multiplexed gratings have been realized and their temperature dependency up to more than 1000 °C was characterized in a furnace by evaluating their reflection spectra. The sapphire fibers used were realized by air clad monocrystalline sapphire rods of 100 µm diameter guiding several hundreds of modes. This makes a multimode interrogation concept necessary, which will also be presented.