Quantum Noise and Polarization Fluctuations in Vertical Cavity Surface Emitting Lasers

We investigate the polarization fluctuations caused by quantum noise in quantum well vertical cavity surface emitting lasers (VCSELs). Langevin equations are derived on the basis of a generalized rate equation model in which the influence of competing gain-loss and frequency anisotropies is included. This reveals how the anisotropies and the quantum well confinement effects shape the correlations and the magnitude of fluctuations in ellipticity and in polarization direction. According to our results all parameters used in the rate equations may be obtained experimentally from precise time resolved measurements of the intensity and polarization fluctuations in the emitted laser light. To clarify the effects of anisotropies and of quantum well confinement on the laser process in VCSELs we therefore propose time resolved measurements of the polarization fluctuations in the laser light. In particular, such measurements allow to distinguish the effects of frequency anisotropy and of gain-loss anisotropy and would provide data on the spin relaxation rate in the quantum well structure during cw operation as well as representing a new way of experimentally determinig the linewidth enhancement factor alpha.Comment: 16 pages and 3 Figures, RevTex, to be published in Phys. Rev.

Broadband detection of methane and nitrous oxide using a distributed-feedback quantum cascade laser array and quartz-enhanced photoacoustic sensing

Here we report on the broadband detection of nitrous oxide (N2O) and methane (CH4) mixtures in dry nitrogen by using a quartz-enhanced photoacoustic (QEPAS) sensor exploiting an array of 32 distributed-feedback quantum cascade lasers, within a spectral emission range of 1190−1340 cm−1 as the excitation source. Methane detection down to a minimum detection limit of 200 ppb at 10 s lock-in integration time was achieved. The sensor demonstrated a linear response in the range of 200−1000 ppm. Three different mixtures of N2O and CH4 in nitrogen at atmospheric pressure have been analyzed. The capability of the developed QEPAS sensor to selectively determine the N2O and CH4 concentrations was demonstrated, in spite of significant overlap in their respective absorption spectra in the investigated spectral range

STRAIN COMPENSATED INGAAS-GAASP-INGAP LASER

The performance characteristics of InGaAs-GaAsP-InGaP strain compensated laser emitting near 1 mu m are reported, The ridge waveguide lasers have room temperature threshold current of 18 mA and differential quantum efficiency of 0.45 W/A/facet. The linewidth enhancement factor is smaller and gain coefficient is larger for these strain compensated lasers compared to that for conventional strained layer laser, This may be due to higher effective compressive strain in the light emitting layer of these devices which reduces the effective mass, The observed larger gain coefficient is consistent with the measured larger relaxation oscillation frequency of these lasers compared to that for a conventional strained layer laser.X1126sciescopu

980 NM SPREAD INDEX LASER WITH STRAIN COMPENSATED INGAAS/GAASP/INGAP AND 90% FIBRE COUPLING EFFICIENCY

Single transverse and lateral mode InGaAs/GaAsP/InGaP 980 nm SPIN (spread index) ridge waveguide lasers (3 mu m x 750 mu m) with symmetric far fields of theta(perpendicular to) x theta(parallel to) = 17 degrees x 15 degrees, slope efficiency of eta(ext) = 0.9W/A and threshold current of I-th = 24mA have been demonstrated. 90% coupling to singlemode lensed fibre and 52% direct buttcoupling to cleaved fibre has been achieved.X119sciescopu