SiGe alloys present a large Infra-Red transparency window and a full compatibility with the standard Complementary Metal Oxide Semiconductor processing making them suitable for applications in integrated optics. In this paper we report on Mlines characterization of Si(1-x)Ge(x) graded index waveguides at 2.15 µm. First, a law giving the refractive index of a Si(1-x)Ge(x) alloy as a function of the Ge content x: n = 1.342x(2) + 0.295x + 3.451, has been experimentally established in the 0 < x < 0.4 range. Then, we have demonstrated that our methodology based on Mlines measurements can be used as short-loop non-destructive technique to provide feedback for sample growth.