A micro resonator quantum well intensity modulator for operation in the wavelength band around 1μm is described.
High efficiency 90° bends are used to form the resonator and also provide optimal coupling to the external
waveguide. The benefits are to reduce loss, to relax the lithography requirements and to provide more flexible
contact designs to the modulator. The characteristics of modulator are analyzed using optical simulation tools and
based on measured absorption parameters. The modulator operates with two distinctly different electrode
configurations which are both based on the index change calculated using Kramers-Kronig relations. A model
including parasitic is developed for HSPICE transient simulations and run in the AGILENT ADS environment. The
performance parameters are determined to be an extinction ratio of 10.4dB, a bandwidth of 33GHz, and a dc power
less than 1mW for device dimensions of 16×6μm2.
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·Hz2/3 and 127 dB·Hz2/3 are predicted for the two
modulators respectively.
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