Abstract
We will examine the waveguide mode losses in ridge-guided quantum cascade lasers. Our analysis illustrates how the low-loss mode for broad-ridge quantum cascade lasers (QCLs) can be a higher-order lateral waveguide mode that maximizes the feedback from the sloped ridge-wall regions. The results are in excellent agreement with the near- and far-field data taken on broad-ridge-guided quantum cascade lasers processed with sloped ridge walls.
Highlights
Quantum cascade lasers (QCLs) are being used in applications requiring mid-infrared sources.For many of these applications, narrow-ridge devices can provide adequate power and beam quality.For applications requiring higher powers, broadening the ridge has led to higher-order lateral modes.These effects are displayed in recent experiments on broad-ridge quantum cascade lasers [1,2,3].These near- and far-field studies of QCLs processed with sloping ridge walls have shown that as the ridge widths are increased, the lasing power is concentrated in just a few higher-order lateral waveguide modes
The lateral extent of the sloped ridge-wall regions, B, proves to be the critical parameter. It determines the lowest-loss mode as a function of ridge width, and most importantly, demonstrates that the angular separation of the two lobes in the far-field is essentially independent of ridge width for the broad-ridge QCLs
Perhaps for the broad-ridge QCLs, the effects at QCLs, the sloping ridge at the sloping ridge walls can be viewed as only a small part of the overall waveguide, so that the walls can be viewed as only a small part of the overall waveguide, so that the perturbation is of order perturbation is of order
Summary
Quantum cascade lasers (QCLs) are being used in applications requiring mid-infrared sources. For many of these applications, narrow-ridge devices can provide adequate power and beam quality. For applications requiring higher powers, broadening the ridge has led to higher-order lateral modes These effects are displayed in recent experiments on broad-ridge quantum cascade lasers [1,2,3]. These near- and far-field studies of QCLs processed with sloping ridge walls have shown that as the ridge widths are increased, the lasing power is concentrated in just a few higher-order lateral waveguide modes. Photonics 2016, 3, 11 illustrates this ideal model for the QCL waveguide
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