Design and analysis of low-chirp electroabsorption modulators using bandstructure engineering

The design principle for completely negative-chirp operation of an electroabsorption (EA) modulator in the 1.55 /spl mu/m window is studied theoretically in InGaAsP strained quantum well (QW) structures for strain ranging from compressive to tensile. The small-signal chirp parameter for TE polarization is evaluated from calculated EA spectra based on k/spl middot/p theory and their Kramers-Kronig transformed refractive index changes. It is found that both compressive and tensile strain in the well layer reduce the chirp parameter The compressive-strained QW lowers the chirp parameter to nearly zero or negative values, the amount of the reduction being proportional to strain amount. In a tensile-strained QW, almost continuously negative values irrespective of applied electric fields occur at an optimized amount of strain.