GHz modulators in the midinfrared using ultrahigh-confinement waveguides

摘要

Abstract: A high speed modulator at low voltage is created in the mid-infrared at 10 $mu@m wavelengths by using field-induced absorption on otherwise forbidden intersubband transitions. The physical effects could scale to 1.5 $mu@m wavelength light. This modulator is packaged into a unique 350 $mu@m long ultra high confinement (UHC) waveguide for low capacitance and high speed. The modulator quantum wells are at the interface of a 2.1 $mu@m thick by 3.75 $mu@m wide UHC Ge waveguide and the GaAs substrate. The quantum wells have a 17% power coupling to the evanescent fields of the Ge waveguide. A connector to the UHC waveguides, with dimensions much smaller than a free space wavelength, has been developed and demonstrated using diffractive optical element arrays on the back side of the substrate and non-uniform grating couplers. Fields are applied across the modulator quantum wells via an ohmic contact to the side of the Ge waveguide on the top of the QWs. The ground is on the other side of the waveguide and lower towards the substrate. The 7 $mu@m wide mesa supporting the quantum wells on the bottom of the Ge waveguide is slightly wider to accommodate a gold electrode.!10