Fig. 2 | Nature Communications

Fig. 2

From: High power surface emitting terahertz laser with hybrid second- and fourth-order Bragg gratings

Fig. 2

Comparison of hybrid DFB and second-order DFB for terahertz QCLs. a Illustration of a metallic cavity for terahertz QCLs in which slits are opened in the top metal cladding to implement a periodic grating18. A fourth-order grating is superimposed at an offset of length d to the original second-order grating with periodicity Λ to realize a hybrid grating structure as in Fig. 1c. b Mode-spectrum for a 1.4 mm long and infinitely wide cavity with DFB gratings (Λ = 27 μm, slit-width ~3 μm) computed with finite-element modeling method. Radiative surface-losses for various resonant modes for cavity with second-order gratings are plotted in red (thin-lines), and that for cavity with hybrid gratings (d/Λ = 3/8) in blue (thick-lines). The insets show electric field profiles for lower and upper band-edge modes respectively, of the photonic bandstructure for each type of gratings (the color-bar shown in this figure applies to all the plots of electric field profiles). The radiative loss is effectively determined by the amplitude and phase of the in-plane electric field (E x ) in the slits

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