Jung-Hoon Ser

Polarization stabilization of vertical‐cavity top‐surface‐emitting lasers by inscription of fine metal‐interlaced gratings

The polarization of vertical‐cavity top‐surface‐emitting lasers (VCSELs) is stabilized by inscribing a fine metal‐interlaced grating into the topmost λ/4 layer of the distributed Bragg reflector (DBR). In this scheme, thin Al/AuZn films are deposited on the sidewalls of the grating defined by the ion milling technique. These metal films enhance polarization anisotropy of the top DBR. Grating periods of 0.9, 1.2, and 1.5 μm are tested and VCSELs with the 1.2‐ or 1.5‐μm grating show good polarization selectivity over the entire range of operating current. The direction of the dominant polarization is orthogonal to the grating line, and the polarization extinction ratio exceeds 40:1 on the average. This polarization discrimination scheme works well for all sizes of VCSELs tested.

Square-lattice photonic-crystal vertical-cavity surface-emitting lasers

The single mode square lattice photonic-crystal vertical-cavity surface-emitting lasers (PC-VCSELs) are proposed and demonstrated. Square-lattice photonic-crystal patterns of various lattice constants are introduced on top mirrors of VCSELs having two different current apertures. The maximum single mode output power of about 1 mW is obtained from the device with lattice constant of 5.0 m and current aperture of 16 m. The PC-VCSEL operates in a single transverse mode in an entire operating current range with a side-mode suppression ratio of over 20 dB. The asymmetric introduction of smaller air holes improves the polarization selectivity.

High-finesse AlxOy/AlGaAs nonabsorbing optical cavity

We report the measured finesse value of ∼390 in nonabsorbing AlxOy/AlGaAs cavities. The nonabsorbing cavity consisting of a bottom AlxOy/AlGaAs distributed Bragg reflector (DBR), an AlxOy spacer layer, and a top AlxOy/AlGaAs DBR is prepared by a wet-oxidation process. The measured resonance linewidth agrees well with that of calculation, indicating very small overall losses in the cavity. The wet-oxidation process does not seem to degrade the interface of the epitaxial layers significantly. The lower bound of maximum achievable reflectivity from the AlxOy DBR is estimated to be >99.95%, assuming an average interface roughness of about 0.6 nm. The maximum achievable finesse of this type of cavity is expected to be larger than that of the all-epitaxial counterpart assuming the same roughness.

Analysis of metal-interlaced-grating vertical-cavity surface-emitting lasers using the modal method by modal expansion

It is analyzed by the modal method by modal expansion (MMME) that the strong polarization discrimination of a vertical-cavity surface-emitting laser (VCSEL) can be effectively obtained by using the metal-interlaced grating on the topmost layer of the VCSEL. The MMME is used to overcome the problems coming from the large permittivity discontinuities at GaAs-Al-air-Al interfaces. The analyses predict the correct direction of dominant polarization and the mode-suppression ratio. The calculated transmission efficiencies explain the characteristics of the VCSELs below threshold. It is found that the difference in phase and amplitude between the two orthogonal polarization generated by the grating plays important roles for the selection of a dominant polarization through mirror reflectivities and mirror losses. In addition, the influence of various thin metal layers on polarization stabilization is demonstrated.

Direct Observation of Strong Quantum-Confined Stark Effect in Vertically-Stacked Quantum Dots at Room Temperature

Strong quantum-confined Stark effect of vertically-stacked quantum dots (VSQDs) is observed by electroabsorption spectroscopy at room temperature. Contrary to single-layer QDs, the VSQDs show a large red shift of 9.4 meV with electric-field change of 60 kV/cm.

Reliability in the oxide vertical-cavity surface-emitting lasers exposed to electrostatic discharge

Electrostatic discharge(ESD) damage is known as a major source affecting the lifetime of oxide VCSEL. We investigated how ESD damage threshold voltage depends on the size, thickness, and composition of the oxide aperture by measuring the change of output power and reverse leakage current after ESD. ESD damage threshold voltage increased with the size of the oxide aperture, regardless of the thickness and the composition of the oxide aperture. However, damaged devices with thinner oxide layers showed relatively longer lifetime in the reliability test. The reliability data also showed that the VCSELs exposed to ESD have steeper power declines in reliability test than normal devices. This may be due to the defects formed in the active medium by ESD.

Enhanced quantum-confined Stark effect of vertically coupled quantum dots at room temperature

Summary form only given.Quantum confined Stark effect (QCSE) of vertically-coupled QDs (VCQDs) are investigated by modulation spectroscopy of absorption itself. The selfaligned column of VCQDs forms a coupled electronic system and effective dimension of QDs along vertical electric field is much enlarged, resulting in the increased Stark shift. Unlike electroreflectance spectra, electroabsorption spectra of VCQDs are strong enough to clearly determine the Stark shift of QDS.