The wavelength of the carrier waves in a modern optical fiber communication network is close to:

In optical fibre communication, we prefer those wavelengths at which the loss (attenuation) inside the silica fibre is minimum and the signal can travel the longest possible distance without needing too many repeaters. Experimental studies of attenuation spectrum for silica show three important low-loss windows. These are commonly named as the first window at $$\lambda \approx 850\ \text{nm}$$, the second window at $$\lambda \approx 1310\ \text{nm}$$ and the third window, which is the best, at $$\lambda \approx 1550\ \text{nm}$$.

Among these, the third window around $$1.55\ \mu\text m$$ gives the smallest attenuation, typically less than $$0.2\ \text{dB km}^{-1}$$. Therefore, almost all modern long-distance and high-capacity optical fibre communication systems choose carrier waves whose wavelength lies very close to $$1550\ \text{nm}$$ (in practical design the range $$\text{C-band}\; 1530\text{-}1565\ \text{nm}$$ and $$\text{L-band}\; 1565\text{-}1625\ \text{nm}$$ are used).

Looking at the given options, $$1500\ \text{nm}$$ is the value that is nearest to this preferred third-window wavelength of $$1550\ \text{nm}$$, while the other listed wavelengths $$600\ \text{nm},\; 900\ \text{nm},\; 2400\ \text{nm}$$ do not correspond to any low-loss window employed in present-day commercial systems.

Hence, the correct answer is Option D.