Abstract-Development of Terahertz Frequency Quantum Cascade Lasers for the Applications as Local Oscillators

Y. J. Han, L. H. Li, A. Valavanis, N. Brewster, J. X. Zhu, R. Dong, P. Dean, L. Bushnell, M. Oldfield, A. G. Davies, B. Ellison, Edmund Linfield

https://link.springer.com/chapter/10.1007/978-94-024-1093-8_15

We report the development of terahertz frequency quantum cascade lasers for applications as local oscillators. A range of active region designs and waveguide structures have been characterised in order to develop the devices for operation at high temperatures, with high output power and low dissipated power. Quantum cascade lasers based on a LO-phonon bound-to-continuum design emitting at 3.5 THz, suitable for the detection of hydroxyl, were fabricated with a double-metal (gold-gold) waveguide structure. These devices operated in continuous-wave up to 94 K, with an output power of 0.4 mW and dissipated power of 1.7 W at 10 K. A new, mechanically robust packaging and waveguide-integration scheme is also presented for operation outside laboratory environments, which further allows integration of quantum cascade lasers with terahertz waveguides, mixers and other system components. This integration scheme yielded a better beam quality, with a divergence of <20°, compared to standard double-metal devices. Its impacts on the device performance, such as operating temperature range, spectral emission, output power and electrical properties, are presented.

Abstract-Mechanically robust waveguide-integration and beam shaping of terahertz quantum cascade lasers

Valavanis, A. Han, Y. ; Brewster, N. ; Dean, P. ; Dong, R. ; Bushnell, L. ; Oldfield, M. ; Zhu, J. ; Li, L. ; Davies, A. ;Ellison, B. ; Linfield, E.
http://ieeexplore.ieee.org/xpl/abstractAuthors.jsp?reload=true&arnumber=7122466&filter%3DAND%28p_IS_Number%3A7122393%29

Terahertz-frequency quantum cascade lasers (THz QCLs) have numerous potential applications as 1–5 THz radiation sources in space science, biomedical and industrial sensing scenarios. However, the key obstacles to their wide-scale adoption outside laboratory environments have included their poor far-field beam quality and the lack of mechanically robust schemes that allow integration of QCLs with THz waveguides, mixers and other system components. A block integration scheme is presented, in which a continuous-wave ∼3.4 THz double-metal QCL is bonded into a precision-machined rectangular waveguide within a copper heat-sink block. This highly reproducible approach provides a single-lobed far-field beam profile with a divergence of ≲20°, and with no significant degradation in threshold current or in the range of operating temperatures.