Abstract
Bifunctional active regions, capable of light generation and detection at the same wavelength, allow a straightforward realization of the integrated mid-infrared photonics for sensing applications. Here, we present a high performance bifunctional device for 8 μm capable of 1 W single facet continuous wave emission at 15 °C. Apart from the general performance benefits, this enables sensing techniques which rely on continuous wave operation, for example, heterodyne detection, to be realized within a monolithic platform and demonstrates that bifunctional operation can be realized at longer wavelength, where wavelength matching becomes increasingly difficult and that the price to be paid in terms of performance is negligible. In laser operation, the device has the same or higher efficiency compared to the best lattice-matched QCLs without same wavelength detection capability, which is only 30% below the record achieved with strained material at this wavelength.
Highlights
Integrated photonics is a growing research field and is often connected to silicon photonics at telecommunication wavelength,[1] aiming for high speed optical data links or quantum computing.[2,3] integrated photonics enables a much wider field of fascinating applications, for example, the realization of extremely compact chemical sensing systems
The demonstration of a monolithically integrated sensor using plasmonic waveguide demonstrated that such bifunctional active regions allow a straightforward realization of integrated photonics.[23]
Thereby, we show that the flexibility due to the engineerable wavelength known from quantum cascade laser (QCL) to address a variety of different sensing applications applies to bifunctional devices
Summary
Continuous wave operation requires two main ingredients: A temperature insensitive gain medium with a low threshold and a low loss waveguide with a low thermal resistance. In the first bifunctional designs, wavelength matching was achieved using thicker barriers and reduced energy splittings between the extraction levels, but with the drawback of a reduced laser performance These devices showed relatively high threshold currents and were restricted to short pulse operation. Aiming for continuous wave operation (in contrast to pulsed operation), it is not useful to optimize the device at the bias where the injector state is aligned with the upper laser level. It is capable to emit 1 W single facet output power in continuous wave at 15 °C cooling water temperature and achieves a maximum wallplug efficiency of 7% Both the pulsed and continuous wave performance are excellent when compared to record values from literature. The optimization of the resistance is very limited for bifunctional devices, as the typical strategy of using larger barriers would not allow for laser operation
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