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(a) Simulated eigenfrequency as a function of the grating duty cycle with a periodicity of 1.43 μm. (b) The losses ( , and ) change with duty cycle . (c) The coupling coefficient (grating depth = 130 nm) changes with duty cycle . Gray area indicates the optimized coupling strength range ( = 1–2).
(a) Schematic for the cross section of surface emitting DFB quantum cascade laser. (b) Scanning electron microscope image of buried grating after regrowth by MOVPE.
cw operation spectra at different temperature from 10 °C to 75 °C. Upper panel inset: Extracted threshold current density and emission spectrum at different temperatures. The black dotted curve is exponential fitted by expression Jth = J0 exp(T/T0) for temperature range of 10–75 °C. The red dotted line shows the linearly fitted tuning characteristics of the wavelength with temperature for the same device. Lower panel inset: single mode emission spectra at various cw injection currents at 15 °C. The spectra are obtained at injection current of 0.3–0.5 A with a step of 0.05 A.
L-I-V characterization at different heat sink temperatures of 10–30 °C operated in cw mode.
(a) The far-field profile of symmetric mode in cavity-length direction. (b) The far-field profile of asymmetric mode in cavity-length direction. (c) The far-field profile in ridge-width direction.
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