Abstract
The characteristics of whispering-gallery modes (WGMs) in 3-D cylindrical,
square, and triangular microcavities with vertical optical confinement of
semiconductors are numerically investigated by the finite-difference time-domain
(FDTD) technique. For a microcylinder with a vertical refractive index 3.17/3.4/3.17
and a center layer thickness 0.2 $\mu{\hbox
{m}}$, $Q$-factors
of transverse electric (${\hbox {TE}}$) WGMs around wavelength 1550 nm are smaller than ${\hbox {10}} ^{3}$, as the radius ${R} < 4~\mu{\hbox {m}}$ and reach the orders of ${\hbox {10}} ^{4}$ and ${\hbox {10}} ^{6}$ as $R = 5~{\hbox {and }}~6 ~\mu{\hbox {m}}$,
respectively. However, the ${\hbox {Q}}$-factor of transverse magnetic (${\hbox
{TM}}$) WGMs at wavelength 1.659 $\mu {\hbox {m}}$ reaches 7.5$\,\times {\hbox {10}} ^{5}$ as $R = 1~\mu{\hbox {m}}$. The mode coupling between the
WGMs and vertical radiation modes in the cladding layer results in vertical
radiation loss for the WGMs. In the microcylinder, the mode wavelength of ${\hbox {TM}}$ WGM is larger than
the cutoff wavelength of the vertical radiation mode with the same mode numbers,
so ${\hbox {TM}}$ WGMs
cannot couple with the vertical radiation mode and have high $Q$-factor. In contrast, ${\hbox {TE}}$ WGMs can couple with the corresponding
vertical radiation mode in the 3-D microcylinder as $R < 5~\mu{\hbox {m}}$. However, the mode wavelength
of the ${\hbox {TE}}$ WGM
approaches (is larger than) the cutoff wavelength of the corresponding radiation
modes at $R = 5~\mu{\hbox {m}}$ (6 $\mu{\hbox {m}}$), so ${\hbox {TE}}$ WGMs have high ${\hbox {Q}}$-factors in such microcylinders too. The
results show that a critical lateral size is required for obtaining high $Q$-factor ${\hbox {TE}}$ WGMs in the 3-D microcylinder. For 3-D
square and triangular microcavities, we also find that the ${\hbox {Q}}$-factor of ${\hbox {TM}}$ WGM is larger than that of ${\hbox {TE}}$ WGM.
© 2008 IEEE
PDF Article
More Like This
Cited By
You do not have subscription access to this journal. Cited by links are available to subscribers only. You may subscribe either as an Optica member, or as an authorized user of your institution.
Contact your librarian or system administrator
or
Login to access Optica Member Subscription
Add to BibSonomy