Transistor Based Quantum Well Optical Modulator and Its Performance in RF Links

摘要

A novel transistor based quantum well modulator structure is presented and analyzed for applications in RF photonic links. The modulator has been realized in the GaAs epitaxial system using both GaAs/AlGaAs and InGaAs/AlGaAs modulation-doped quantum wells. The modulator operates on the principle of charge filling of a quantum well to shift the absorption edge to shorter wavelengths (blue shift). A generalized absorption model is presented for the modulator in which the relaxed k-selection rule and Lorentzian weighting function are used to represent the absorption coefficient in terms of the carrier Fermi energy. Then the blue shift of the absorption edge is determined by the channel charge density in which the Fermi level is controlled by the applied gate-to-source voltage. From this charge control model the transmission of the modulator is determined to be an increasing function of gate-to-source voltage. Absorption spectra and relative transmission curve for both devices are then calculated and validated by comparison to measurement data. It is found that the enhancement interface offers better performance. It is also found that deionization of charge sheet sets the upper limits on input optical power. The analytical T(V) response enables full distortion analysis. Thus RF link performance is studied based on calculation results and SFDR of 120 dB·Hz~(273) and 127 dB·Hz~(273) are predicted for the two modulators respectively.