Two chemical sensors based on the common principle of infrared spectroscopyusing thulium doped zirconium fluoride glass and quantum cascade lasers are described. Exploiting optically absorbing molecular vibrations, IR optical sensors offer highly selective in situ sensing in compact packages. The near infrared (NIR) fluorescence of the thulium doped zirconium fluoride (ZBLAN:Tm3+) glass was characterised. A relative humidity sensor was developed using ZBLAN:Tm3+ fluorescence as a modulatable infrared spectroscopic source. The optical components, NIR detector, and detector electronics were integrated in an industrial prototype device. Relative humidity measurements were carried out to characterise the sensor. Two quantum cascade lasers (QCLs) were used for sensing a number of analytes in the mid infrared (MIR,) spectral range in a common-base optical configuration. The first laser, a distributed feedback device emitting at 6/im, was integrated into a silver halide optical fibre and a hollow waveguide, for liquid water and gaseous propylene sensing, respectively. The second laser, a Fabry-Perot device emitting at 5.625/im, was used for acetone, acetic acid and formaldehyde sensing using open path optical cells and a hollow waveguide. The second QCL was also used for the development of a pulse averaging and referencing system to eliminate sensor noise due to laser amplitude fluctuations.