transmission issues. Then, the basics of modulators based on phase and absorption
changes and the associated physical mechanisms are treated, followed by an in depth
discussion of state-of-the-art traveling-wave (TW) electroabsorption modulators
(EAMs) based on indium phosphide (InP)-related materials. Novel or emerging
modulator types are the subject of Section 7.7, notably intersubband (IS) as well as
silicon-based modulators. Section 7.8 gives a summary and outlook.
7.2 PRINCIPLES AND MECHANISMS OF EXTERNAL
OPTICAL MODULATION
In general, amplitude (intensity), phase, and polarization modulation are readily
implemented with external modulators, thus they can be seen as basic light-field
transformation devices. An input field
^
E =
^
xA
x
sinð!tÞ (7.1)