Abstract

Microdisk lasers having a III–V core coated with a ${\mathrm{TiO}}_2$ shell are experimentally studied under optical pumping. Initial core microdisk lasers with a 5–10 μm diameter comprising five layers of $\mathrm{InAs}/{\mathrm{In}}_{0.15}{\mathrm{Ga}}_{0.85}\mathrm{As}$ quantum dots demonstrate room temperature lasing with excellent characteristics (threshold, quality factor) at the ground state optical transition in the 1.28–1.30 μm spectral range. Deposition of the ${\mathrm{TiO}}_2$ dielectric shell results in a decimation of the whispering gallery modes of the microdisk resonator and, for thicker ($>100\mathrm{nm}$) shells, in a blueshift of the lasing wavelength. Using numerical analysis, we demonstrate that coating a III–V core microdisk with a high-index shell causes strong penetration of the second and third radial modes into the shell, whereas the first radial mode remains nearly undisturbed. Though optical loss added by the ${\mathrm{TiO}}_2$ dielectric shell is low (it does not exceed $2{\mathrm{cm}}^{-1}$ even for a 250-nm-thick ${\mathrm{TiO}}_2$ layer), mode leakage to the ${\mathrm{TiO}}_2$ results in a decrease in the optical confinement factor and an increase in the threshold pump power. This effect is more pronounced in microlasers of the smallest diameter studied (5 μm). Thus, in addition to other applications, a ${\mathrm{TiO}}_2$ shell can be used for mode selection in microdisk lasers or for selective outcoupling of the emission to the waveguide structure, which requires proper adjustment of the ${\mathrm{TiO}}_2$ shell thickness and microdisk diameter.

© 2019 Optical Society of America

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