There is provided a system for measuring temperature and strain simultaneously utilizing Brillouin Scattering within an optical fiber. The system has a cladding, a first optical core within the cladding and a second optical core within the cladding and having a different refractive index profile and/or composition than the first core. Means to couple light into and out of said individual optical cores and/or from one optical core to the other within the fiber is provided along with means for calculating strain and temperature characteristics based on measured Brillouin frequencies for said optical cores.