Monolithic integration of normally-on and normally-off asymmetric Fabry–Perot modulators by selective antireflection coating

We present asymmetric Fabry–Perot quantum-well modulators which are overbalanced, so that at zero bias at the exciton wavelength reflectivity is high. As bias is applied and the quantum-well absorption decreases, the optical cavity balances, nulling reflection. By partially antireflection coating, at zero bias the optical cavity is balanced, so that the reflectivity is near zero, and increases with bias. Therefore, we can integrate normally-on and normally-off high-contrast modulators by selective AR coating. With 10 V bias, we obtain 11:1 contrast ratio for the normally-on devices and 8:1 for the normally-off devices.