Abstract
Quasi-crystal distributed feedback lasers do not require any form of mirror cavity to amplify and extract radiation. Once implemented on the top surface of a semiconductor laser, a quasi-crystal pattern can be used to tune both the radiation feedback and the extraction of highly radiative and high-quality-factor optical modes that do not have a defined symmetric or anti-symmetric nature. Therefore, this methodology offers the possibility to achieve efficient emission, combined with tailored spectra and controlled beam divergence. Here, we apply this concept to a one-dimensional quantum cascade wire laser. By lithographically patterning a series of air slits with different widths, following the Octonacci sequence, on the top metal layer of a double-metal quantum cascade laser operating at THz frequencies, we can vary the emission from single-frequency-mode to multimode over a 530-GHz bandwidth, achieving a maximum peak optical power of 240 mW (190 mW) in multimode (single-frequency-mode) lasers, with record slope efficiencies for multimode surface-emitting disordered THz lasers up to ≈570 mW/A at 78 K and ≈720 mW/A at 20 K and wall-plug efficiencies of η ≈ 1%.
Highlights
The photonic engineering of semiconductor laser cavities has been extensively investigated in recent years as a versatile approach to control the spectral, spatial and temporal emission of lasers operating in different regions of the electromagnetic spectrum[1,2].Patterned resonators can be exploited to create miniaturised and efficient laser sources by using onedimensional (1D)[3] or two-dimensional (2D)[4,5,6] patterning to modulate the optical properties of a cavity spatially, directly controlling the feedback and extraction mechanisms
The contour plot (Fig. 4e) of the quality factor of the resonating modes, simulated for the device with W = 160 μm and L = 1.9 μm, at mirror distances of 10 μm < d < 150 μm shows that the three-dimensional quality factor is strongly enhanced when the mirror is positioned, so that the bare external cavity frequency is resonant with a laser eigenmode frequency; the results show good agreement with the experimental coupling retrieved for the spectral peaks located at 3.25 THz and 3.39 THz
In conclusion, we have demonstrated highly efficient surface-emitting semiconductor lasers operating at THz d a Mirror distance
Summary
The photonic engineering of semiconductor laser cavities has been extensively investigated in recent years as a versatile approach to control the spectral, spatial and temporal emission of lasers operating in different regions of the electromagnetic spectrum[1,2].Patterned resonators can be exploited to create miniaturised and efficient laser sources by using onedimensional (1D)[3] or two-dimensional (2D)[4,5,6] patterning to modulate the optical properties of a cavity spatially, directly controlling the feedback and extraction mechanisms. Periodic patterning has been successfully exploited in combination with miniaturized quantum cascade laser (QCL) semiconductor heterostructures operating at midIR9 and terahertz (THz) frequencies[10], where unconventional resonator architectures have been used to tailor the emission frequency[11,12,13] optical power[14] beam divergence[14,15,16,17] and direction[18]. This approach has been exploited to target relevant technological applications in spectroscopy, imaging, sensing and metrology. This approach has been exploited to target relevant technological applications in spectroscopy, imaging, sensing and metrology19–21. 1D
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