A fluid diffusion resistant tube-encased fiber grating pressure sensor includes an optical fiber (10) having a Bragg grating (12) impressed therein which is encased within a sensing element, such as a glass capillary shell (20). A fluid blocking coating (30) is disposed on the outside surface of the capillary shell to prevent the diffusion of fluids, such as water molecules from diffusing into the shell. The fluid diffusion resistant fiber optic sensor reduces errors caused by the diffusion of water into the shell when the sensor is exposed to harsh conditions.
