Abstract
The Mach–Zehnder interference (MZI) structure has
played a significant role in research and development of the optical
modulator/switch and silicon-on-insulator (SOI) waveguides have been
increasingly developed to implement highly integrated photonic devices. In
this paper, for the SOI-waveguide MZI-type electro-optic (EO) switch with
free-carrier dispersion (FCD) effect, the extra optical absorption (EOA)
loss caused by the FCD effect is analyzed and modeled. An intrinsic
limitation factor existing in this device is found to be the tension between
the EOA loss and the interaction length, resulting in a negative impact upon
the device performance. The numerical calculations show that the
millimeter-order interaction length has the lowest optical on-chip (OC) loss
of about 0.8 and 1.8 dB at the OFF- and ON-state, respectively, and even a
lowest OC imbalance of 1.0 dB between the two switching states. The
influence of the coupling ratio of 3 dB waveguide directional coupler used
in the MZI structure upon the switch performance is also studied, and a
push–pull modulation scheme is proposed as an efficient solution to
leveraging this intrinsic limitation caused performance decay with a
combination of injection and depletion processes for the FCD effect. As a
result, the optical OC loss is reduced to 1.0 dB, its imbalance is
compressed to 0.2 dB, and the crosstalk at the OFF-state is also better than
-21 dB. The relationship between
the switching speed and the interaction length is also analyzed. As a vital
condition for the FCD-based EO modulation of the switch, the dependence of
free-carrier concentration modulation on the drive voltage and electrode gap
is simulated via MEDICI software.
© 2011 IEEE
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