We present a study of high-power quantum-cascade lasers (QCL) for 8 μm spectral range with active regions of latticematched to InP substrate and strain-balanced designs. The use of the strained quantum well/barrier pairs made it possible to increase the energy barrier between the upper laser level and continuum by ~ 200 meV. Our experiments show that utilization of the strain-balanced design of the active region makes it possible to more than double the characteristic temperature T0 to 253 K from 125 K for the lattice-matched design. In pulsed mode, QCLs with strain-balanced active region demonstrated high efficiency of 12% and high output optical power of 21 W (over 10 W per facet). This is the highest value of the optical power demonstrated to date in 8 μm spectral region to the best of our knowledge.
We present a study of quantum cascade laser dynamical properties accounting for the Joule heating released in the active region. In particular, we study the QCL emitting at 8 μm in the pulsed pumping mode and present experimental measurements, as well as a theoretical description of the QCL build-up time, showing the features appearing due to the Joule heating released inside the active region.
We study high-power high bit rate single-mode 1550 nm vertical-cavity surface-emitting lasers fabricated using wafer-fusion. The optical cavity was grown on an InP wafer, and the two AlGaAs/GaAs distributed Bragg reflectors were grown on GaAs wafers, all three by molecular-beam epitaxy. The active region is based on thin InGaAs/InAlGaAs quantum wells and a composite InAlGaAs tunnel junction. To confine current and optical radiation, we use a lateral-structured buried tunnel junction with ≈ 6 µm diameter and an etching depth of ≈ 20 nm. These VCSELs demonstrate up to 5 mW single-mode continuous-wave output power and a threshold current of ≈ 2 mA at 25 °C. Even at an ambient temperature of 85 °C, the maximum optical output power is larger than 1 mW. The lasers demonstrate a 34 Gbps non-return-to-zero data transfer rate and 42 Gbps (21 GBaud) using 4-level pulse amplitude modulation at 25 °C back-to-back conditions with ≈ 934 fJ/bit power consumption per bit, which is amongst the lowest values reported for this wavelength range and bit rate.
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