Optical phase modulator utilizing electroabsorption in a Fabry–Perot cavity

Abstract

By changing the absorption coefficient in a Fabry–Perot cavity from a point below to a point above the critical matching condition, the phase of the reflected beam at resonance can be changed. At a constant refractive index, the phase switches by 180°. We demonstrate a device fabricated with GaAs/AlGaAs quantum wells that uses a combination of index and absorption modulation to produce a 90° phase change in a vertical Fabry–Perot cavity with an insertion loss of about 6 dB. Similar phase measurements on a conventional normally on absorption modulator yielded a chirp parameter, αc<0.4, a value superior to that of waveguide electroabsorption devices.