Suppose you invest in existing fiber optic cables. Then you can rent it out to telecom providers that do not have their own fiber optic network. The leases are often for a longer period of time and therefore provide a constant source of income.
Another way of investing in infrastructure is investing in smaller companies that still want to grow. They do this through acquisitions and the construction of new infrastructure.
You can also rent out the new infrastructure, or even better, sell it on to larger partiers. The demand for new infrastructure is high.