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Poly-cyclooctatetraene framework (PCF)-graphene, an emerging all-sp2 hybridized two-dimensional (2D) carbon allotrope, possesses an intrinsic direct bandgap (0.77 eV) and excellent mechanical properties, indicating great potential in nanoelectronics. Understanding the thermal transport behavior of PCF-graphene is of vital importance for determining the reliability of related devices based on it. In this work, the thermal transport in PCF-graphene is systematically studied using the Boltzmann transport theory combined with first-principles calculations. The results show that the room-temperature thermal conductivity of PCF-graphene with only considering three-phonon scattering is as high as 1587.3 W/m K along the zigzag direction, and decreases by 27.1% (1157.4 W/m K) when including four-phonon scattering, indicating the four-phonon scattering plays a non-negligible role in in thermal transport. Although the thermal conductivity of PCF-graphene is not as large as that in graphene, it still exceeds most common 2D materials and makes it suitable for applications in the thermal management of microelectronics. Analyses of phonon group velocity and phonon scattering rates are conducted to reveal the high thermal conductivity of PCF. Moreover, as the temperature increases to 800 K, the reduction of thermal conductivity is close to 50% after including four-phonon scattering. The analysis of phonon group velocity and phonon scattering rates are conducted to reveal the underlying mechanism. Our results provide insights for constructing high-thermal-conductivity materials based on 2D carbon allotropes.

Self-starting harmonic frequency combs in quantum cascade lasers exhibit skipping of several tens of longitudinal modes of the cavity, producing widely spaced frequency combs which may be used for a number of applications, such as the generation of high-spectral-purity microwave and terahertz tones. Under pure electrical injection, the spacing of such combs is fixed by fundamental laser parameters and can hardly be controlled. Here, we demonstrate that harmonic frequency combs in quantum cascade lasers can be induced by optical injection of an external seed provided by a tunable source. This scheme enables wide tunability of the harmonic comb spacing, allowing the skipping between 44 and 171 longitudinal modes in a single device.Self-starting harmonic frequency combs in quantum cascade lasers exhibit skipping of several tens of longitudinal modes of the cavity, producing widely spaced frequency combs which may be used for a number of applications, such as the generation of high-spectral-purity microwave and terahertz tones. Under pure electrical injection, the spacing of such combs is fixed by fundamental laser parameters and can hardly be controlled. Here, we demonstrate that harmonic frequency combs in quantum cascade lasers can be induced by optical injection of an external seed provided by a tunable source. This scheme enables wide tunability of the harmonic comb spacing, allowing the skipping between 44 and 171 longitudinal modes in a single device.

Distributed feedback (DFB) interband cascade lasers (ICLs) with a 1st order top surface grating were designed and fabricated. Partially corrugated sidewalls were implemented to suppress high order lateral modes. The DFB ICLs have 4 mm long and 4.5 μm wide ridge waveguides and are mounted epi-up on AlN submounts. We demonstrated a continuous-wave (CW) DFB ICL, from a first wafer which has a large detuning of the gain peak from the DFB wavelength, with a side mode suppression ratio of 30 dB. With proper matching of grating feedback and the gain peak wavelength for the second wafer, a DFB ICL was demonstrated with a maximum CW output power and a maximum wall plug efficiency reaching 42 mW and 2%, respectively, at 25 °C. The lasing wavelengths of both lasers are around 3.3 μm at 25 °C.

Here, we present results of quantum cascade laser lifetime tests under various aging conditions including an accelerated life test. The total accumulated life time exceeds 1.5 × 106 device hours. The longest single device aging time was 46 500 hours without failure in the room temperature aging test. Four failures were found in a group of 19 devices subjected to the accelerated life test with a heat-sink temperature of 60 °C and a continuous-wave current of 1 A. Failure mode analyses revealed that thermally induced oxidation of InP in the semi-insulating layer is the cause of failure. An activation energy of 1.2 eV is derived from the dependence of the failure rate on laser core temperature. The mean time to failure of the quantum cascade lasers operating at a typical condition with the current density of 5 kA/cm2 and heat-sink temperature of 25 °C is expected to be 809 000 hours.

High temperature continuous-wave (CW) operation of a distributed Bragg reflector (DBR) quantum cascade laser is demonstrated up to a heat sink temperature of 80 °C. A CW output power of 2 W and a single mode operation with side mode suppression ratio of 30 dB around wavelength of 4.48 μm were achieved at 20 °C. The maximum pulsed and CW wall-plug-efficiencies reached 14.7% and 10.3% at 20 °C, respectively. A large tuning range of 5 cm−1 between mode hopping was observed and attributed to the thermal cross-talk from the gain section to the DBR section.

Continuous-wave operation of a distributed-feedback quantum-cascade laser in a packaged module is demonstrated up to a heat sink temperature of 80 °C with an output power of greater than 10 mW and a power consumption of less than 3.8 W. Single longitudinal mode emission near 5.24 μm is observed over a temperature range from 10 to 80 °C with a side mode suppression ratio greater than 20 dB limited by the instrumentation. A single spatial mode is determined with far-field pattern measurement. The above performance is achieved using a buried heterostructure and a small cavity of 7.6 μm×1.5 mm.

We report on our progress in the development of a terahertz quantum cascade laser source based on intracavity terahertz difference-frequency mixing in a dual-wavelength mid-infrared quantum cascade laser with the active region engineered to possess giant second-order nonlinear susceptibility. In this letter, we demonstrate devices that operate in mid-infrared at λ1=8.9μm and λ2=10.5μm and produce terahertz output at λ≈60μm via difference-frequency generation with 7μW output power at 80K, 1μW output at 250K, and still approximately 300nW output at 300K.

The authors demonstrate a quantum cascade laser design with an integrated resonant nonlinearity for second-harmonic generation. Its nonlinear power conversion efficiency is strongly dependent on the injected current density due to an electric field and current dependent nonlinear susceptibility. This dependence produces an observed tenfold increase of the conversion efficiency over the current density range of 2.7–7.5kA∕cm2. Furthermore, bidirectional lasing at widely different wavelengths is a side effect for this active region design.