Resolved quadrupolar transition in TiO2

We report an investigation of the direct forbidden absorption edge of TiO2. For the first time we have resolved the weak quadrupolar 1s exciton and measured its binding energy. Taking into account polaron effects, we estimated the bare electron effective mass in the Γ1 minimum of the conduction band and obtained a fairly reasonable value of 3m0

The influence of feedback intensity on longitudinal mode properties and optical noise in index-guided semiconductor lasers

\u3cp\u3eTheory and experiments on optical feedback effects in index-guided singlemode semiconductor lasers are presented. Evidence is found for the existence of a characteristic parameter C which indicates the relative strength of the optical feedback. Near the transition (C \approx 1.0) from low to high feedback, the feedback-induced low-frequency intensity noise shows a maximum. At higher feedback hysteresis and instabilities are dominant, whereas the feedback-induced noise is low again.\u3c/p\u3

Hot electron injection laser, controlled carrier-heating induced gain switching

The novel hot electron injection laser (HEL), a three-terminal vertically integrated transistor-laser structure, is designed to investigate and possibly utilize the effects of carrier-heating on the optical gain and wavelength chirp. Simulations show the potential of carrier heating assisted gain switching to directly modulate the optical field intensity at frequencies up to 100 GHz while maintaining control over the wavelength chirp. The HEL is designed to demonstrate these results through independent but complementary control over the concentration and the energy of the electrons injected into the active layer. Previous research has shown though that proper LIV behavior and a strong carrier heating efficiency requires a trade-off between electron heating and hole leakage current. Furthermore, stringent control over the epitaxial growth is crucial for these devices. Recent devices now show proper LIV behavior and strongly reduced threshold current densities around 2 kA/cm2 at room temperature. They also show the external `heating' voltage modulating the intensity of the lasing mode. The possible link between this modulation and carrier heating is further explore

Hot Electron Injection Laser controlled carrier-heating induced gain switching

The novel Hot Electron Injection Laser (HEL), a three-terminal vertically integrated transistor-laser structure, is designed to investigate and possibly utilize the effects of carrier-heating on the optical gain and wavelength chirp. Simulations show th