Figure 1

(a) Spectra of a QCL with a $12\mathrm{\text{−}}\mu \mathrm{m}$-wide active region. (b) Fourier transform of the spectra. The laser is driven by pulsed current $I=1.0\mathrm{A}$ (upper panel) and 0.75 A (lower panel) at a repetition rate of 80 kHz. The pulse duration is 125 ns.Reuse & Permissions

Figure 2

(a) SEM image of the facet of a QCL with a $12\mathrm{\text{−}}\mu \mathrm{m}$-wide active region, and simulations showing from top to bottom the electric field of ${\mathrm{TM}}_{00}$, ${\mathrm{TM}}_{01}$, and ${\mathrm{TM}}_{02}$ modes for the device; the arrows in the figure indicate the polarization of the field. (b) Measured far-field intensity distributions of the device (open circles) and their fits (solid lines) at driving currents of 1.7, 1.5, 1.35, 1.2, 1, 0.75, 0.70, and 0.68 A (from top to bottom). The curves are shifted vertically for clarity. (c) Electric-field amplitude (upper panel) and phase (lower panel) of the transverse modes used to fit the far-field data in (b). Open circles: ${\mathrm{TM}}_{00}$ mode; open triangle: ${\mathrm{TM}}_{01}$ mode; open squares: ${\mathrm{TM}}_{02}$ mode; open diamonds: ${\varphi }_{\mathrm{TM}00}+{\varphi }_{\mathrm{TM}02}-2{\varphi }_{\mathrm{TM}01}$. Dotted lines are used to guide the eyes. Error bars indicate the range of individual parameter changes that will lead to a root mean square deviation of 0.05 between the experimental data and the fits. (d) Light output versus current (LI) curve for the device. The LI curve is free of kinks, indicating a smooth growth of all the mode components. The dots indicate the operating conditions at which the near- and far-field measurements were performed.Reuse & Permissions

Figure 3

(a) NSOM images of the laser modes on the facet of the $12\mathrm{\text{−}}\mu \mathrm{m}$ QCL at driving currents of 1.7, 1.0, 0.75, and 0.68 A (from top to bottom). Image size: $18\mu \mathrm{m}\times 5\mu \mathrm{m}$. The dashed trapezoidal frame in the first panel indicates the laser active region. (b) Line scans of the NSOM images (solid lines) and near-field mode profiles (dashed line) calculated using the amplitudes and phases extracted from the far-field fits [Fig. 2c] at driving currents of 1.7, 1.5, 1.35, 1.2, 1, 0.75, 0.70, and 0.68 A (from top to bottom). The near-field mode profiles are shifted vertically for clarity.Reuse & Permissions

Figure 4

(a) SEM image of the facet of a QCL with a $22\mathrm{\text{−}}\mu \mathrm{m}$-wide active region, and simulations showing from top to bottom the electric field of ${\mathrm{TM}}_{00}$, ${\mathrm{TM}}_{02}$, and ${\mathrm{TM}}_{04}$ modes of the device; the arrows in the figure indicate the polarization of the field. (b) Measured far-field intensity distributions of the device (open circles) and their fits (solid lines) at driving currents of 1.7, 1.4, 1.2, and 1.0 A (from top to bottom). The curves are shifted vertically for clarity. (c) Electric-field amplitude (upper panel) and phase (lower panel) of the transverse modes used to fit the far-field data in (b). Open circles: ${\mathrm{TM}}_{00}$ mode; open triangles: ${\mathrm{TM}}_{02}$ mode; open squares: ${\mathrm{TM}}_{04}$ mode; open diamonds: ${\varphi }_{\mathrm{TM}00}+{\varphi }_{\mathrm{TM}02}-2{\varphi }_{\mathrm{TM}04}$. Dotted lines are used to guide the eyes. Error bars indicate the range of individual parameter changes that will lead to a root mean square deviation of 0.05 between the experimental data and the fits. (d) Light output versus current curve for the device. The dots indicate the operating conditions at which the different near- and far-field measurements were performed.Reuse & Permissions

Figure 5

(a) NSOM images of the laser modes on the facet of the $22\mathrm{\text{−}}\mu \mathrm{m}$ QCL at driving currents of 1.7, 1.4, 1.2, and 1.0 A (from top to bottom). Image size: $25\mu \mathrm{m}\times 6.9\mu \mathrm{m}$. The dashed trapezoidal frame in the first panel indicates the laser active region. (b) Line scans of the NSOM images (solid lines) and near-field mode profiles (dashed lines) calculated using the amplitudes and phases extracted from the far-field fits [Fig. 4c] at driving current 1.7, 1.4, 1.2, and 1.0 A (from top to bottom). The near-field mode profiles are shifted vertically for clarity.Reuse & Permissions