Fig. 1. (a) Schematic of device cross section from the facet direction. (b) SEM image of the device facet; region enclosed by the yellow line denotes the regrown InP:Fe.

Fig. 2. Measured (solid) and simulated (red dashed) lateral far-field radiation patterns for the coupled ridge waveguide QCL chirped devices. The driving currents changed from 2.1 to 3.3 A with a step of 0.3 A at a 5 kHz repetition frequency and 1% duty cycle pulsed mode operation.

Fig. 3. (a) Losses of different order supermodes for five-element QCL chirped and uniform arrays of coupled ridge waveguide with different geometry. The ridge width of the chirped array elements is 4, 6, w, 6, 4 μm with w changing from 7 to 11 μm at a step of 1 μm; the interspace of chirped arrays is 2 μm. The uniform arrays center-to-center space is 8, and the interspace is 2 μm. (b) Losses of the fundamental and high-order supermodes and loss difference as a function of the centered ridge width w for the chirped arrays. (c) Calculated near-field profile of five-element chirped structure taken with finite element method; red lines illustrate the current distribution in the QCL array showing the InP:Fe region without current distribution. The simulation is based on the finite element software COMSOL.

Fig. 4. Total peak power change as a function of the current at 298 K for a 2  mm long×36  μm wide chirped array (blue line) and a 2  mm long×13  μm wide single laser (green line). The current driver is maintained at 5 kHz with a duty cycle of 1%. Inset is the lasing spectrum of the chirped arrays at 1.3 times threshold current, which peaks at ∼7.6  μm.