2.6 Assume that, in the manufacture of a single-mode fiber, the tolerance in the core radius a is ±5% and the tolerance in the normalized refractive index difference ? is ±10%, from their respective nominal values. If the nominal value of ? is specified to be 0.005, what is the largest nominal value that you can specify for a while ensuring that the resulting fiber will be single moded for ? > 1.2 ?m even in the presence of the worst-case (but within the specified tolerances) deviations of a and ? from their nominal values? Assume that the refractive index of the core is 1.5.