An optical fiber-based sensor is described that is suitable for operation in a gas-rich environment. The sensor comprises a chamber into which are mounted one or more segments of optical fiber, into which are inscribed a plurality of sensor gratings. Each of the plurality of sensor gratings is configured to have the same wavelength shift over time in response to a change in gas diffusion, such that gas diffusion parameters are excluded in the determination of the respective amount of change in temperature, applied strain, and gas diffusion. Also described is a fiber, and techniques for making same, comprising of cores extend through a common cladding. The cores are doped so as to create, in conjunction with the cladding, a plurality of waveguides having the same wavelength shift over time is response to a change in gas diffusion, but different wavelength shifts in response to changes in other parameters.