High speed electroabsorption modulator by integration of a RTD with an optical waveguide

High speed Optoelectronic modulation using the resonant tunnelling characteristics by interaction of a resonant tunnelling diode (RTD) in the middle of an unipolar ridge optical waveguide based on the GaAs/AlGaAs system is investigated. This interaction of an RTD within an optical waveguide introduces high non-linearities into the electrical characteristics of the waveguide by inducing large electric field changes on the collector region which give rise to a band-edge shift via the Franz-Keldysh effect that can be used for electroabsorption modulation up to millimeter-wave frequencies of light at photon energies close to the bandgap energy of the semiconductor, in this case around 900 nm. The device allows efficient high speed intensity modulation requiring a few hundreds of mV as drive voltage. Streak camera studies have shown around 4 dB modulation depth at 14 GHz for an applied voltage at 1 GHz of around 0.4 V, implying a bandwidth-to-voltage ratio of 33 GHz/V.