Design, Modeling, and Fabrication of High-Speed VCSEL with Data Rate up to 50 Gb/s.

We have studied the characteristics of frequency response at 850-nm GaAs high-speed vertical-cavity surface-emitting lasers (VCSELs) with different kinds of oxide aperture sizes and cavity length using the PICS3D simulation program. Using 5-µm oxide aperture sizes, the frequency response behavior can be improved from 18.4 GHz and 15.5 GHz to 21.2 GHz and 19 GHz in a maximum of 3 dB at 25 °C and 85 °C, respectively. Numerical simulation results also suggest that the frequency response performances improved from 21.2 GHz and 19 GHz to 30.5 GHz and 24.5 GHz in a maximum of 3 dB at 25 °C and 85 °C due to the reduction of cavity length from 3λ/2 to λ/2. Consequently, the high-speed VCSEL devices were fabricated on a modified structure and exhibited 50-Gb/s data rate at 85 °C.

Polarized photoluminescence from single GaN nanorods: effects of optical confinement.

By measuring linearly polarized photoluminescence (PL) from single, isolated gallium nitride (GaN) nanorods with the rod diameters in the subwavelength regime (30-90 nm), we present clear evidence for size dependence of polarization anisotropy. The maximum polarization ratio at room temperature (approximately 0.9 with emission and excitation light polarized parallel to the long axis of nanorod) occurs at the rod diameter of approximately 40 nm. The experimental data are compared with the recent theoretical model proposed for thick semiconductor nanowires. It is concluded that the optical confinement effects in this size regime play an important role in the observed giant polarization anisotropy. Furthermore, we have performed a temperature-dependent study of polarized PL to show the importance of internal emission anisotropy at low temperatures.

Gallium nitride nanorod arrays as low-refractive-index transparent media in the entire visible spectral region.

Vertically aligned gallium nitride (GaN) nanorod arrays grown by the catalyst-free, self-organized method based on plasma-assisted molecular-beam epitaxy are shown to behave as subwavelength optical media with low effective refractive indices. In the reflection spectra measured in the entire visible spectral region, strong reflectivity modulations are observed for all nanorod arrays, which are attributed to the effects of Fabry-Pérot microcavities formed within the nanorod arrays by the optically flat air/nanorods and nanorods/substrate interfaces. By analyzing the reflectivity interference fringes, we can quantitatively determine the refractive indices of GaN nanorod arrays as functions of light wavelength. We also propose a model for understanding the optical properties of GaN nanorod arrays in the transparent region. Using this model, good numerical fitting can be achieved for the reflectivity spectra.