Abstract
We report novel design considerations for graded separate
confinement heterostructure (SCH) cavities of oxide-confined
vertical-cavity surface-emitting lasers (VCSELs). Using a self-consistent
effective-index method, we have analyzed ungraded, linearly and
exponentially graded SCH cavities of an 850-nm VCSEL. An ungraded SCH
gives the best optical-confinement factor, while linear and exponential
gradings reduce the factor by 18% and 9%, respectively. Grading the SCH
cavities of oxide-confined VCSELs leads to both a shift in the resonant
wavelength as well as a decrease in the optical-confinement factor. The
resonant-wavelength shifts in graded SCH cavities are attributed to two
competing effects: the formation of an effective-index step that redefines
the λ cavity, and larger optical-field leakage, which relaxes the
confinement. We have also demonstrated that wavelength shifts can be
easily compensated by optimized width extensions of the aperture layers
which sandwich the graded SCH cavity, without further reducing the
optical-confinement factor. Based on a revised understanding of the
resonances for graded SCH cavities,we can therefore control the design of
graded SCH VCSELs to obtain a desired resonant wavelength with great
precision.
[IEEE ]
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