Cascade pumping of type-I quantum well gain sections led to increase of the output power and efficiency of GaSb-based diode lasers operating in spectral region from 1.9 to 3.3 µm. The wide stripe multimode lasers based on cascade lasers heterostructures generate watt class output power levels up to 3 µm. The corresponding narrow ridge single spatial mode and single frequency mode distributed feedback devices generate tens of mW. The external cavity lasers utilizing gain chips based on cascade diode laser heterostructures demonstrate extra wide tuning range. The short pulse passively mode-locked lasers generate optical frequency combs.
Passively mode-locked type-I quantum well cascade diode lasers emitting in the methane absorption band near 3.25 μm were designed, fabricated and characterized. The deep etched ~5.5-μm-wide single spatial mode ridge waveguide design utilizing split-contact architecture was implemented. The devices with absorber to gain section length ratios of 11% and 5.5% were studied. Lasers with the longer absorber section (~300 μm) generated smooth bell-shape-like emission spectrum with about 30 lasing modes at full-width-at-half-maximum level. Devices with reverse biased absorber section demonstrated stable radio frequency beat with nearly perfect Lorentzian shape over four orders of magnitude of intensity. The estimated pulse-to-pulse timing jitter was about 110 fs/cycle. Laser generated average power of more than 1 mW in mode-locked regime.
Cascade pumping of type-I quantum well gain sections was utilized to increase output power and efficiency of GaSb-based diode lasers operating in spectral region from 1.9 to 3.3 μm. Two-step ridge waveguide design with shallow 5-μm-wide and deep 15-μm-wide etched sections yielded λ ~ 2 μm lasers generating 250 mW of continuous wave output power in nearly diffraction limited beam when mounted epi-down. The same device mounted epi-up demonstrated output power of about 180 mW. Lasers operating in the wavelength range above 3.2 μm with variable deep etched ridge width and two-step ridge design were fabricated and characterized. Two-step ridge waveguide design yielded the lowest threshold current and the highest slope efficiency. Tens of mW of continuous wave output power was obtained in nearly diffraction limited beams in the wavelength range from 3.2 to 3.3 μm near and above 20 °C in both epi-up and epi-down mounting configurations. Laterally-coupled 2-nd-order distributed feedback lasers operated near 3.22 μm in continuous wave regime at room temperatures with more than 10 mW of output power at room temperature in epi-up mounted configuration.
Cascade pumping of type-I quantum well gain sections was utilized to increase output power and efficiency of
GaSb-based diode lasers operating in spectral region from 3.1 to 3.3 μm. The experiment showed that the increase
of the number of cascades from two (previously used in record cascade 3 μm emitters) to three led to critical
enhancement of the differential gain and reduction of the threshold current density of λ > 3 μm lasers. Light p-doping
of the AlGaAsSb graded section did not introduce extra optical loss but aided hole transport as required for
realization of the efficient multi-stage cascade pumping scheme. Corresponding coated three-stage devices with
~100-μm-wide aperture and 3-mm-long cavity demonstrated CW output power of 500 mW near 3.18 μm at 17 °C –
more than twofold increase as compared to previous state-of-the-art diode lasers emitting only 200 mW. Three-stage
lasers with quantum wells designed to emit in the middle of methane absorption band near 3.25 μm demonstrated
record output power levels above 350 mW – nearly threefold improvement over previous non-cascade state-of-the-art
diodes. Utilization of the different quantum wells in cascade laser heterostructure was demonstrated to yield
wide gain lasers as often desired for tunable laser spectroscopy. Two step etching was applied in effort of
simultaneous minimization of both internal optical loss and the lateral current spreading in narrow ridge lasers.