Abstract
In this work design, fabrication and characterization of mid-infrared AlInAs/InGaAs/InP QCLs taper quantum cascade lasers are presented. In order to increase output power while keeping good beam quality, taper design of resonator was used. We have studied devices emitting at 4.5 μm with different shapes (linear, concave and convex) and angles of taper waveguide section, to optimize the output beam parameters, namely M2 and brightness. Experimental results demonstrate that convex geometry taper laser with 1.7° taper shows the best performance, the highest output power up to 5 W and the smallest horizontal beam divergence of 5.6° in the fundamental mode. This design is also characterized by the highest brightness.
Highlights
Q UANTUM cascade lasers (QCL) have a well-established position as mid-infrared sources with a large number of applications such as free space communication [1]–[3], absorption spectroscopy-based molecular sensing [4], breath analysis for medical diagnostics [5]
In numerical simulations the following parameters were assumed for the geometry of tapered QCLs; straight, narrow ridge section of 5 μm width and tapered section widths at the output mirror of 25, 50 and 100 μm, which correspond to taper angles of 0.6°, 1.7° and 3.6°, respectively
Comparison of light-current-voltage (LIV) characteristics for convex, concave and linear designs of investigated QCLs with taper angle change in the range from 0.4° to 3.6° is shown in the Fig. 6
Summary
Q UANTUM cascade lasers (QCL) have a well-established position as mid-infrared sources with a large number of applications such as free space communication [1]–[3], absorption spectroscopy-based molecular sensing [4], breath analysis for medical diagnostics [5]. In most of the applications, lasing on the fundamental lateral transverse mode with narrow beam width and high output power is desirable. Such qualities are especially required by applications requiring precise collimation for beam delivery over long distances (e.g., free space optics – FSO systems). The straightforward solution of increasing the output power by increasing the ridge width results in drastic deterioration of beam quality, as the QC laser tends to operate on very high order transverse mode. Color versions of one or more of the figures in this article are available online at http://ieeexplore.ieee.org
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