Chemical sensors based on optical sensitivity of metal oxide materials deposited on multimode interference couplers

An optical sensor based on MMI structures has been studied. We have used the optical parameters of a new hybrid material deposited by sol-gel method leading to waveguide structures after UV-photoinscription, and of ZnO, sensitive material characterised in previous studies. The variation of optical properties such as the refractive index of the covering sensitive material leads to a modification of waveguiding conditions in the MMI. A gas sensor can be developed by measuring the variation of light intensity at the output of the MMI structure under gas exposure. Simulations have been performed in order to optimise the output light intensity variations to increase sensitivity. We have shown that these structures are more sensitive than Mach-Zehnder interferometers, and that the relation between dimensions and sensitivity of the MMI is not trivial. Computations have to be performed to optimise the structure for given parameters.