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(a) Scanning electron microscopy (SEM) images of a typical device with a 50% duty-cycle grating. (b) Top-view SEM image of the metallic grating. (c) Calculated profile intensity for mode 2 (solid line) and real part of the refractive index (dashed line) for a 50% duty cycle DFB. Mode 2 exhibits field maxima below the metal fingers, therefore the reported one dimensional (1D) index profile corresponds to the metalized regions of the grating. (d) Calculated profile intensity for mode 1 (solid line) and real part of the refractive index (dashed line) for a 50% duty cycle DFB. Mode 1 exhibits field maxima below the air gaps, therefore the reported 1D index profile corresponds to the nonmetalized regions of the grating.
(a) Calculated photonic band structure around the band edge for 70% (black continuous line), 50% (blue dashed line), and 25% (red dot-dashed line) grating duty cycles, showing the opening of a stop band. The grayed regions mark the zone above the substrate light line, where the calculated modes are not confined in the active region. (b) Calculated losses per unit of length as a function of the grating duty cycle for the band edge states of panel (a). The refractive indexes of the layers composing the QC laser and used for the calculation are , , , and . These values are obtained using a Drude model at a wavelength of and with a constant scattering time of . The active region is considered as a bulk layer, whose refractive index is averaged between the InGaAs wells and the AlInAs barriers.
(a) Typical spectra of a SP DFB QC laser (50% grating duty cycle) at three heatsink temperatures. The spectra have been acquired in pulsed mode ( at ), using a Fourier transform infrared spectrometer operated in rapid-scan mode and equipped with a liquid-nitrogen-cooled MCT detector. We measure a wavelength shift with heatsink temperature of . (b) Peak output power as a function of injected current for a DFB QC laser operated at 240, 280, and , respectively. Inset: corresponding RT laser spectrum in semilogarithmic scale. The device exhibits a side mode suppression ration of .
Laser threshold current density as a function of the heatsink temperature for a typical unpatterned surface-plasmon QC laser (red symbols) and for 25% (black symbols), 50% (blue symbols), 70% (dark yellow symbols) duty-cycle DFB lasers. The dotted lines are fits to the data with the fitting function . is the heatsink temperature and and are fitting parameters. The values obtained for the unpatterned, 70%, 50%, and 25% grating duty cycle devices are, respectively, , , , and .
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