Abstract

There has been much recent theoretical (1-3) and experimental (4-8) interest in the electrooptic effect in quantum well heterostructures. The size of the change in refractive index Δn and its quadratic dependence on applied electric field yield an advantage for quantum well phase modulators over bulk semiconductor devices in both power consumption and device length. We have shown that propagation loss and residual intensity modulation are minimized in quantum well phase modulators by operating below the bandedge at large wavelength detuning Δλ_X from the excitonic absorption peak (8). At Δλ_X = 400 Å, the propagation length required for pi phase shift $\left(l_{\pi }\equiv \frac{\lambda }{2\Delta n}\right)$ in a leaky waveguide structure containing two quantum wells was found to be 4.25 mm for a transverse field 9.5 × 10 ⁴ V/cm (8). In this letter we show that much shorter device lengths l_π can be acheived in a waveguide structure containing a larger number of quantum wells. For the same transverse field and detuning Δλ_X we obtain l_π = 220 μm. In addition, we demonstrate that the drive power required to produce a pi phase shift can be significantly reduced via the quadratic effect by appropriate DC biasing of the quantum well waveguide phase modulator. In this way, large phase shifts are obtained in lengths on the order of 100 μm for voltages under 5 V.

© 1988 Optical Society of America