Fig. 1 Light-Current-Voltage characteristics of a 3-mm-long single ICL emitter with HR/AR coatings in the CW regime at 20^oC; inset: the emission spectra at 2I_th.

Figure 1 shows the light-current-voltage (L-I-V) characteristics of a 3-mm-long ICL single emitter with HR/AR coatings. At 20℃, the threshold current density is 220 A/cm² and the slope efficiency near the threshold is 800 mW/A. The maximum WPE reaches 12.3%. These values are close to the previous report on ICLs with the highest CW output power [10]. The CW output power of the single ICL emitter was measured up to 320 mW at the injection current density of 1.35 kA/cm², where the WPE is 10.5%. There has been no obvious thermal rollover in the L-I characteristics. As shown in the inset of Fig. 1, the emission spectrum recorded at 2J_thinjection current density is centered at 3.39 μm, which is consistent with our design.

The three-emitter arrays were mounted epilayer-down on diamond submounts for efficient heat extraction from the laser chips, which were bonded on copper heat sinks. Figure 2 shows the CW L-I-V characteristics of an ICL array sample. Measurements were taken at the heat sink temperature of 10℃. The threshold current density and the slope efficiency near the threshold are 170 A/cm² and 880 mW/A, comparable to the values measured from a single emitter at 10℃. The output power was measured up to 1.01 W at an injection current of 1.7 A (1.15 kA/cm²). Again, there is no thermal rollover in the L-I characteristics, indicating a potentially higher maximum output power. The maximum WPE and the WPE at the maximum injection current are 14.4% and 12.9%, respectively.