Abstract
We report gain-guided broad area quantum cascade lasers at 4.55 μm. The devices were processed in a buried heterostructure configuration with a current injector section much narrower than the active region. They demonstrate 23.5 W peak power at a temperature of 20°C and duty cycle of 1%, while their far field consists of a single symmetric lobe centered on the optical axis. These experimental results are supported well by 2D numerical simulations of electric currents and optical fields in a device cross-section.
Highlights
Quantum cascade lasers (QCLs) have become the sources of choice for chemical sensing and directional infrared countermeasure applications in the mid-infrared spectral range (3-15 μm). #267948Received 8 Jun 2016; revised 19 Jul 2016; accepted 29 Jul 2016; published 9 Aug 2016Continuous-wave output powers up to ≈ 5 W at room temperature have been reported [1,2].While cw power is limited by heat dissipation due to the relatively low wall plug efficiency (≤20%) [3] of QCLs, much higher peak powers can be reached in pulsed mode operation by scaling the size of the device
Broad active region configurations are interesting for QCLs, because, unlike diode lasers, they do not suffer from filamentation and, can operate stably in a single transverse mode at currents well above threshold [4]
If no special precaution is taken, because of the TM polarization facet reflectivity increases with mode index and broad area QCLs lase on a high-order mode with a far field profile consisting of 2 lobes propagating at large angles from the optical axis [4]
Summary
Quantum cascade lasers (QCLs) have become the sources of choice for chemical sensing and directional infrared countermeasure applications in the mid-infrared spectral range (3-15 μm). For the active region much wider than in conventional index-guided QCLs, the current density in it could not be assumed uniform anymore, and the local dependency of conductivity in growth direction on electric field was accounted for. Inset: half width at half maximum (HWHM) of current density distribution as function of applied voltage (solid curve) for 1 μm of cladding thickness left unetched as in fabricated devices. If etching depth parameter was increased to reproduce the usual QCL geometry with etched active region, horizontal index guiding and zero order mode selection were observed again as expected, which became an additional proof of reliability of our model. The resulting device geometry corresponded to the one simulated (Fig. 1) Both narrow ridge-waveguide and gain guided QCLs were cleaved in 6 mm-long chips and mounted epitaxial-side up on Cu carriers with In solder.
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