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Peak optical power and voltage vs current density characteristics of a ring and FP QCL at a temperature of 10 K. The geometry of the FP emitter is , which gives an area comparable to ring QCLs. The inset shows scanning electron microscopy images of a processed ring emitter holding a 42-period DFB grating to allow for surface emission.
(a) mode (electric field), calculated by means of a three-dimensional finite element solver for a emitter with 42 grating periods. (b) Computed surface losses (open circles) and measured spectrum (line) for the same device. Insets illustrate the resonances (left) and (right) with the lowest surface losses.
Surface emission single-mode spectra for different grating periods at 10 K. The upper inset indicates a SMSR higher than 30 dB for a 42-period device. The lower inset illustrates the frequency tuning of a device with 43 periods with temperature.
Two-dimensional surface emission far-field plot for a 42-period device recorded at a current density of . The circular symmetry of the interference pattern is diminished by the cryostat window and the instability of the Golay cell.
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