Showing papers on "Quantum dot laser published in 1974"

Photon recycling in semiconductor lasers

Abstract: In a suitably designed semiconductor laser, spontaneously emitted photons with energies above the absorption edge can be reabsorbed in the active layer and can decrease the current density that must be supplied to reach the lasing threshold. The magnitude of the threshold reduction is estimated to be about 20% in a GaAs double‐heterostructure laser at room temperature.

GaAs–AlxGa1−xAs heterostructure laser with separate optical and carrier confinement

Abstract: Heterostructure injection lasers in which the GaAs active region is the center layer of a five‐layer dielectric slab waveguide have been investigated. The GaAs active layer is bounded on each side by an AlxGa1−xAs layer to confine the carriers. The two outside layers which are AlyGa1−yAs(y > x) confine the optical field. Lasers with this structure have been fabricated and room‐temperature threshold current densities Jth300 as low as 650 A/cm2 have been obtained for 1‐mm cavity lengths. Differential quantum efficiencies ηD for these separate optical and carrier confinement heterostructure (SCH) lasers were higher than generally encountered for double‐heterostructure (DH) lasers with values as high as 65% for [inverted lazy s]300−μ−long cavities. The external quantum efficiency of several typical units was determined as a function of input current, and for one representative unit a maximum value of 39% was obtained at about four times Jth300. Emission in the fundamental TE mode was obtained for symmetrical ...

Threshold reduction in Pb1−xSnx Te laser diodes through the use of double heterojunction geometries

Abstract: A systematic study has been made of the effect of the middle active region width in double heterojunction Pb1−xSnx Te/PbTe laser diodes on the lasing threshold. A fourfold reduction in pulsed threshold over that of comparable single heterojunction lasers is demonstrated in lasers having 4‐μm‐wide middle regions. A comparison is also made between lasers fabricated by liquid phase epitaxy using undoped melts and substrates, and using thallium‐doped p ‐type PbTe layers; the latter is shown to yield thresholds as much as two times lower.

Analysis of ring distributed‐feedback lasers

Abstract: Here a structure for ring distributed feedback (DFB) lasers is proposed and analyzed. The threshold condition for such lasers is derived and compared with that for plain DFB lasers. It is shown that the etalon and feedback effects provided by the uniform section of a ring DFB laser should narrow the laser bandwidth and lower the threshold gain.

Luminosity control system employing semiconductor lasers

Abstract: A luminosity control device comprises a first semiconductor laser operable in a spontaneous mode to emit noncoherent light and in a laser mode different from its inherent laser mode to emit coherent light. The first semiconductor laser is electrically biased into its spontaneous laser mode. A second semiconductor laser is operated in a laser mode to emit coherent light which is applied to the first semiconductor laser to optically bias the first semiconductor laser into the laser mode of the second semiconductor laser. The second semiconductor laser is electrically biased into operating in its laser mode and the optical coupling between the two semiconductor lasers is such that the coherent light output from the first semiconductor laser varies exponentially with respect to the electrical energy input into the second semiconductor laser.

The Reproducibility of 633-nm Lasers Stabilized by 127I2

Abstract: The experiments investigate the performance of iodine-stabilized lasers under a variety of conditions. In particular, the influences of offsets in the control electronics, the magnitude of the frequency modulation necessary to stabilize the laser, and the effects of laser power and iodine pressure variations are considered. The results demonstrate a reproducibility of better than 1 × 10-10.

6190‐Å emission at 77 K of Ga1−xAlxAs double heterostructure lasers

Abstract: The Ga1−xAlxAs laser diodes which emit a wavelength of 6190 A at 77 K with threshold current densities as low as 300 A/cm2 were fabricated using a double heterostructure with lightly doped active regions. This lasing wavelength is the shortest ever attained in Ga1−xAlxAs lasers for such a low threshold current density. The maximum external quantum efficiency of these diodes was found to be about 35% at 77 K. The extensive studies made of the properties of these visible‐light‐emitting lasers, especially of the spectral distributions, are described in full detail.

Configurational coordinates model in the alkali-halide exciton laser

Abstract: A configurational coordinates model in the fully quantum theoretical treatment of the alkali-halide exciton laser is used. The theory predicts a correlation between threshold pumping power and the Stokes shift. The predictions of the theory are compared with the observed characteristics of laser action on the first exciton peak of KBr. The observed spectral narrowing is in good agreement with theoretical prediction.