Anomalous splitting in microwave mode-beating spectra of semiconductor ring lasers

Mode-beating spectra are investigated in long-perimeter (1.028 cm) monolithically integrated multiple-quantum-well semiconductor ring lasers. The beating line near 8 GHz is found to be split into two components. With increasing pumping current, a normal component shifts to lower frequencies, while an anomalous higher-frequency component shifts in the opposite direction. It is suggested the anomalous blue-shifting line results from power-induced perturbation of the refractive index in the vicinity of a strong mode.     

Heat-source distribution in etched-well surface-emitting semiconductor lasers

The authors report on the development of a comprehensive self-consistent thermal-electrical model of etched-well vertical-cavity surface-emitting lasers. The analysis provides valuable insight into distribution of heat sources in these devices. Two-dimensional current- and heat-spreading analysis is used to determine in a self-consistent manner a realistic distribution of heat sources in etched-well vertical-cavity surface-emitting lasers. Strong nonuniformities of heat-source and temperature distributions are revealed. The relative contributions of various heat sources are evaluated. The Joule heating of the p-AlGaAs cladding layer is identified as a major cause of intense heating above threshold.<>     

Low-threshold single-quantum-well InGaAs/GaAs lasers grown bymetal-organic chemical vapor deposition on structure substrates

Low-threshold current (as low as 3.0 mA) and high-external efficiency (≈88%) InGaAs/GaAs lasers emitting at 1 μm under a stable fundamental transverse mode were obtained by using the temperature engineered growth technique for the growth on prepatterned substrates     

A semi-empirical algorithm for flow balancing in multi-cavity transfer molding

Multi-cavity transfer molding is an important process step in several electronic and photonic technologies. In some applications, uniform filling of the cavities of the mold, or mold balancing, is required. A semi-empirical flow model to predict mold filling patterns was developed. The algorithm is a one-dimensional network flow simulation that uses experimental pressure drop data to determine the volumetric flow rate through the gates and runners. A comprehensive experimental program was undertaken to determine these hydraulic resistances for different flow rates and mold geometries. A theoretical treatment is also described to compute hydraulic resistance from gate geometry. Uniform gate resistances provide unbalanced filling and higher velocities in the cavities. Balanced filling can significantly reduce the molding compound velocity and the flow induced stresses, but imperfect balancing compromises the benefits. Experimental filling patterns were obtained for two sets of gates. The agreement between the model and the experiments was satisfactory, and the discrepancies were attributed to correctable phenomena.     

Picosecond pulse analysis of gain-switched 1.55 µm InGaAsP laser

Results of computer simulation of gain-switched pulses from InGaAsP lasers emitting at 1.55 μm are reported. Multimode rate equations are solved for short triangular current pulses of large amplitude superimposed on a dc bias close to threshold. Lasers of conventional length (200μm) and with short cavity (50 μm) are analyzed. The effect of wavelength chirp on time-resolved and the time-averaged multimode spectra is demonstrated. Optical pulses as short as 10 ps are predicted for short-cavity lasers with reflective coatings. While the number of longitudinal modes in gain-switched spectrum is efficiently reduced for short-cavity lasers, the dynamic linewidth of each mode remains of a similar magnitude (up to 140 GHz) as for standard-cavity lasers. It is expected that gain saturation effects could reduce the calculated values of dynamic linewidth.     

Multiple feedback effects in asymmetric external cavitysemiconductor lasers

Multiple feedback effects on the output power and spectral characteristics of an external cavity semiconductor laser with asymmetric feedback induced by misalignment of an external mirror are discussed. The external mirror tilt modifies the round-trip phase condition as well as the coupling efficiency. Undulation in power as a function of external mirror tilt have been observed. At particular tilt angles where strong interaction between odd-order round-trip beams and even-order round-trip beams occurs, unique optical spectra featuring double peaks within a compound-cavity mode spectrum or uneven compound-cavity mode spacings have been observed. A quasi-static model for asymmetric external cavity systems explains qualitatively the power undulations and complex spectral characteristics. The model also predicts the existence of two nearby phase-matched mode groups, which may result in complex and chaotic instabilities     

Enhancement of the antineoplastic effect of local hyperthermia by induced hyperglycemia

It is shown that the antitumour effect of local hyperthermia (2450 MHz, 43 degrees C, 60 min) is enhanced essentially if it follows immediately after i. v. infusion of 20% glucose solution at a rate of 80 mg X kg-1 X min-1 for 90 min in experiments on rats bearing the Guerin carcinoma. Under such a combined treatment the rate of tumour growth decreases by a factor of 2. An assumption is advanced that such an enhancement of the hyperthermia effect is caused mainly by low pH values of the tumour which are observed under hyperglycemia.     

Reformulation of the coupled-mode theory of multiwaveguide systems

We show that by proper reformulation the coupled-mode theory of Hardy and Streifer can be reconciled with that of Haus et al based on a variational principle. The new formulation has the merit of leading to simpler coupled-mode equations while giving marginally more accurate results.