Quantum cascade lasers monolithically integrated on germanium.

Silicon (Si) photonics can have a major impact on the development of mid-IR photonics by leveraging on the reliable and high-volume fabrication technologies already developed for microelectronic integrated circuits. Germanium (Ge), already used in Si photonics, is a prime candidate to extend the operating wavelength of Group IV-based photonic integrated circuits beyond 8 µm, and potentially up to 15 µm. High performance quantum cascade lasers (QCLs) and interband cascade lasers grown on Si have been demonstrated, whereas no QCLs monolithically integrated on Ge have been reported yet. In this work, we present InAs-based QCLs directly grown on Ge by molecular beam epitaxy. The lasers emitting near 14 µm exhibited threshold current densities as low as 0.8-0.85 kA/cm2 at room temperature.

Interband cascade Lasers with AlGaAsSb cladding layers emitting at 3.3†µm.

We investigate the impact of the growth conditions of AlGaAsSb cladding layers on the properties of interband cascade lasers (ICLs). For an optimized structure emitting at 3.3 µm, we achieve an internal quantum efficiency of 65% per stage in good agreement with conventional ICL using InAs/AlSb superlattice cladding layers, in spite of internal losses of 15 cm-1 due to higher optical losses in the n-type AlGaAsSb alloys. Finally, we report a narrow ridge ICL emitting at 3.33 µm operating in continuous wave up to 80°C that produces 1 mW/uncoated facet at 80 °C, 10 mW at 40 °C and more than 12 mW at 20°C.

High temperature operation of far infrared (λ ≈20 µm) InAs/AlSb quantum cascade lasers with dielectric waveguide.

We demonstrate the high temperature operation, up to 80°C, of quantum cascade lasers emitting at a wavelength of 20 µm. The lasers are based on the InAs/AlSb materials and take benefit of a low loss plasmon-enhanced dielectric waveguide. The waveguide consists of doped InAs cladding layers and low-doped InAs spacers. For 2.9-mm-long devices, the threshold current density is 4.3 kA/cm2 and the measured peak output power is 7 mW at room temperature. The cavity length dependence of the threshold currents also indicates that very large optical gain is achieved and effectively overcome the strong free carrier absorption.

Demonstration of air-guided quantum cascade lasers without top claddings.

We report on quantum cascade lasers employing waveguides based on a predominant air confinement mechanism in which the active region is located immediately at the device top surface. The lasers employ ridge-waveguide resonators with narrow lateral electrical contacts only, with a large, central top region not covered by metallization layers. Devices based on this principle have been reported in the past; however, they employed a thick, doped top-cladding layer in order to allow for uniform current injection. We find that the in-plane conductivity of the active region - when the material used is of high quality - provides adequate electrical injection. As a consequence, the devices demonstrated in this work are thinner, and most importantly they can simultaneously support air-guided and surface-plasmon waveguide modes. When the lateral contacts are narrow, the optical mode is mostly located below the air-semiconductor interface. The mode is predominantly air-guided and it leaks from the top surface into the surrounding environment, suggesting that these lasers could be employed for surface-sensing applications. These laser modes are found to operate up to room temperature under pulsed injection, with an emission spectrum centered around l (1/4) 7:66 mum.