High power and tunable single-mode quantum cascade lasers

Quantum cascade (QC) lasers are a fundamentally new semiconductor laser source designed by methods of ‘bandstructure engineering’ and realized by molecular beam epitaxy (MBE). One of their most intriguing features is the cascading scheme, which results in the lasers’ intrinsic potential for high optical output power. QC-lasers with varying numbers, from one to 75, of cascaded active regions and injectors have been studied. Pulsed peak output power levels of ≥500 mW at room temperature and ≥1 W at 200 K have been obtained for a 2.25 mm long and≈12 μm wide Fabry–Perot laser-stripe with 75 cascades. In continuous wave operation, 200 mW have been measured from one facet at 80 K and still 60 mW at 110 K, both from lasers with 30 stages. These lasers have an InP top cladding layer grown by MBE using solid source phosphorous. Widely tunable single-mode QC-distributed feedback (DFB) lasers have been fabricated in the wavelength range around 8.5 μm. A side-mode suppression ratio of 30 dB and a 140 nm single-mode tuning range (thermal tuning between 10 and 320 K for lasers operated in pulsed mode) have been obtained. QC-DFB lasers driven in cw-mode display a tunability of ≈70 nm as a result of thermal tuning between 20 and 120 K.