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Double-waveguide quantum cascade laser
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View: Figures


Image of FIG. 1.
FIG. 1.

(Color online) Schematic of the waveguide structure and scanning electron microscope (SEM) image.

Image of FIG. 2.
FIG. 2.

(Color online) (a) Measured EL spectra at 80 K from the full double-waveguide structure (black curve) and from the lower waveguide only (red curve), with upper waveguide etched away. Calculated difference of the two spectra as an approximation of the EL from the upper waveguide only (blue curve). The measured spectra are taken for two cleaved mesas of similar sizes with similar current flowing through them. The corresponding bias for the full structure is , comparable to the 19 V bias used for the lasing spectra in (b). EL is shown at 80 K for direct comparison with the lasing spectrum at 80 K. (b) Lasing spectra at different temperatures for a 23 μm wide and 3 mm long laser, operated in pulsed mode (100 ns, 20 kHz). The laser is driven at a constant bias of 19 V (current ). A high-reflectivity coating was deposited on the back facet of the laser. The letters A and B allow identification of the two groups of modes.

Image of FIG. 3.
FIG. 3.

(Color online) (a) Light intensity (peak power) (red) and voltage (blue) versus current density for a representative device (with high-reflectivity coating) operated in pulsed mode (100 ns, 20 kHz) at room temperature. (b) Far-field of the representative device of Fig. 2(b), operated in the same conditions. In blue, without filter; in red, with a short-pass filter at 9.3 μm. In green, the calculated difference of the two previous curves (blue minus red), illustrating the far-field of modes A. In black, simulated far-field of the linear combination of the two lowest-order orthogonal TM waveguide modes fitting best to the experimental data. The simulations are done at the central wavelength of the group of modes B (8.85 μm). The far-fields are measured by scanning a mercury-cadmium-telluride detector located 10 cm away from the laser, along a direction perpendicular to the growth planes. (c) Instantaneous electric field (at a time maximizing field amplitude) across the structure, along the direction perpendicular to the layer planes. The two active regions are in light blue, the central plasmon layer in green and the top gold contact in yellow.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Double-waveguide quantum cascade laser