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(Color online) Scanning electron microscope image of the grating on top of the active region after MOVPE re-growth.
(Color online) Light-current-voltage of HR coated 14-μm-wide lasers with 1.5-, 2-, 2.5-, and 3-mm-long cavities at 20 °C in cw mode.
(Color online) (a) Cw lasing spectra at a different currents from 0.24 to 0.54 A with a step of 0.05 A and (b) Lasing frequency change as a function of input electrical power for the temperature range of 10-30 °C. The dotted lines is the fitting result using the function ν = ν0 + βνTsubmount + βνRthPelec.
(Color online) Output power of the uncooled DFB QCLs with 1.5-, 2-, 2.5-, and 3-mm-long cavities at 20 °C in cw mode. The inset shows the heat sink temperature as a function of injection current density for different cavity length devices after lasing in uncooled cw mode.
(Color online) Maximum average optical power as a function of the duty cycle at 20 °C for uncooled operation of DFB QCLs with 1.5-, 2-, 2.5-, and 3-mm-long cavities.
(Color online) The maximum wall-plug efficiency as a function of cavity length for thermoelectrically cooled and uncooled device in cw mode.
(Color online) Quasi-cw far-field patterns parallel to the epitaxial layers of HR coated 14 μm-wide and 3-mm-long lasers without cooling. The upper panel shows the far-field measured at different injection currents from 0.35 to 0.5 A with a step of 0.05 A at a fixed duty cycle of 1% with a pulsed width of 2 μs and the repetition frequency of 5 kHz. The lower panel shows the far-field measured with different duty cycles at a fixed current of 0.4 A. The duty cycle is 1%, 10%, 30%, and 50%, respectively.
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