We report modulation of the absorption coefficient at $1.3\mathrm{\mu m}$ in Ge/SiGe multiple quantum well heterostructures on silicon via the quantum-confined Stark effect. Strain engineering was exploited to increase the direct optical bandgap in the Ge quantum wells. We grew $9\mathrm{nm}$ -thick Ge quantum wells on a relaxed ${\mathrm{Si}}_{0.22}{\mathrm{Ge}}_{0.78}$ buffer and a contrast in the absorption coefficient of a factor of greater than 3.2 was achieved in the spectral range $1290–1315\mathrm{nm}$ .