Modeling and performance analysis of WDM transmission links employing semiconductor optical amplifiers

We theoretically explored the system limits of various single- and multichannel transmission links employing semiconductor optical amplifiers (SOAs). For this purpose, we developed an accurate model to describe the amplifier dynamics in the moderate and low saturation regimes. Our simulation results revealed the delicate balance between the level of saturation, the signal-to-noise ratio and the amount of gain per amplifier required for optimum system performance. The modeling results have been confirmed by recent experimental work in this area

Variation of kink power with cavity length in weakly index guided semiconductor lasers

A periodic dependence of kink power on laser length is observed and explained. Weakly-index guided high power stripe lasers in the AlGaAs, InGaAlP and InGaAlAs material systems are studied and periods of 100 to 350 µm are found. The observations indicate that phase locked fundamental and first order modes exist at certain laser lengths. This new model fully explains the oscillatory behaviour of the kink power and the correlated changes in lateral far field distributions at the front and rear mirror facet

Fabrication of short GaAs wet-etched mirror lasers and their complex spectral behaviour

A versatile fabrication technique for GaAs-AlGaAs wet-etched mirror lasers is presented. This technique works independently of the Al concentration in the cladding layers up to a value of 70%, and it requires four photolithography steps. Ridge waveguide lasers have been successfully processed using a double heterostructure (DHS) as well as graded index separate confinement heterostructures (GRINSCH) having different quantum-well (QW) active layers. This technique is used to fabricate short-cavity lasers in GRINSCH structures having GaAs multiple-quantum-well (MQW) or bulk active layers. Laser operation was obtained in a 29-µm-long device using a 5-QW structure. Short lasers with QW active layers show a complex spectral behavior. These lasers operate at higher current densities (~20 kA/cm2) and emit light at more than one wavelength. This implies that higher order transitions are involved which is not the case when using a bulk GaAs active layer. Besides the two peaks corresponding to the n=1 and n=2 transitions, we found an intermediate peak which corresponds presumably to the forbidden transition E1-HH

Low-loss, low-confinement GaAs-AlGaAs DQW laser diode with optical trap layer for high-power operation

A low-confinement asymmetric GaAs-AlGaAs double-quantum-well molecular-beam-epitaxy grown laser diode structure with optical trap layer is characterized, The value of the internal absorption coefficient is as low as 1.4 cm-1, while keeping the series resistance at values comparable cm with symmetrical quantum-well gradient index structures in the same material system. Uncoated devices show COD values of 35 mW/µm. If coated, this should scale to about 90 mW/µm. The threshold current density is about 1000 A/cm2 for 2-mm-long devices and a considerable part of it is probably due to recombination in the optical trap layer. Fundamental mode operation is limited to 120-180 mW for 6.5-µm-wide ridge waveguide uncoated devices and to 200-300 mW for 13.5-µm-wide ones, because of thermal waveguiding effects. These values are measured under pulsed conditions, 10 µs/l m

Polarization stabilization in vertical-cavity surface-emitting lasers through asymmetric current injection

We present experimental evidence that asymmetric current injection in intracavity contacted vertical-cavity surface-emitting lasers (VCSELs) stabilizes the polarization of the emitted light. Anisotropies in the gain and loss mechanisms introduced by asymmetric current injection are considered to explain this effect. The design scheme opens perspectives to obtain actual polarization control in VCSEL

Electric transport in N-type Fe2O3

Resistivity, Seebeck-coefficient, Hall-coefficient and magneto-resistance of n-type single crystal ferric oxide (hematite), containing Sn4+ as an impurity, are reported. The resistivity does not show important anisotropy. The Hall- and magneto-resistance effects are probably related to the parasitic ferromagnetism present in this material, their magnitude depends strongly upon the orientation of the magnetic field with respect to the c axis. The magneto-resistance is probably a consequence of magneto-striction. Some information concerning the mobility of the electrons at higher temperatures (T>400°K) is derive; at lower temperatures the conduction mechanism should be rather complicated, contributions from impurity conduction being also present

Electric transport in N-type Fe2O3

Resistivity, Seebeck-coefficient, Hall-coefficient and magneto-resistance of n-type single crystal ferric oxide (hematite), containing Sn4+ as an impurity, are reported. The resistivity does not show important anisotropy. The Hall- and magneto-resistance effects are probably related to the parasitic ferromagnetism present in this material, their magnitude depends strongly upon the orientation of the magnetic field with respect to the c axis. The magneto-resistance is probably a consequence of magneto-striction. Some information concerning the mobility of the electrons at higher temperatures (T>400°K) is derive; at lower temperatures the conduction mechanism should be rather complicated, contributions from impurity conduction being also present