As is obvious in this equation, the wavelength shift is independent of the substrate refractive index (n3), and thus, Si was selected due to the moderate reflectivity in the visible spectral range, the very low roughness that minimize the diffuse reflectance, and of course the potential for mass fabrication of the chips at low cost. At the same time if n0 o n1 o n2, then δλ increases as n1 approaches n2 since in such a case r2 approaches zero.