Polarisation effects in an In0.53Ga0.47As/InP quantum well waveguide modulator operating in the 1.57 μm wavelength region

A single-mode waveguide quantum confined Stark effect modulator has been fabricated from In_0.53Ga_0.47As/InP quantum well material. Polarisation effects in the modulator are dominated by the selection rules governing optical absorption of the TE and TM polarisations. For the TE polarisation, a modulation depth of 19 dB has been measured on the application of a reverse bias of 3 V at a wavelength of 1.568 μm, accompanied by an estimated absorption loss of only 2.5 dB within the device. The structure of the guide is such that it is potentially suitable for direct monolithic integration with a quantum well laser although the use of large bandgap InP barriers may result in carrier injection problems within a laser. A major obstacle to the simple integration of quantum well lasers with modulators is the long absorption tail seen in long wavelength material systems-in this case the heavy hole exciton at zero bias occurred at 1.48 μm, whilst the modulator exhibited rapidly increasing propagation losses as the wavelength was reduced below 1.567 μm, an energy difference of 46 meV