Abstract

Coherent sources in the mid-infrared spectral range are of great interest due to the large number of scientific and industrial applications [1–2]. Many of these can benefit greatly from the development of electrical tunable devices. In the talk, we will present novel solutions for electrical tuning of the laser emission. In particular, we will show a novel generation of devices that allow for local control of the laser active region temperature using an integrated heating element [3]. This buried resistor is compatible with the BH QCL and diode laser technology and can be applied to many sources, e.g. laser combs, DFBs, multi-terminal DBRs. In particular, the integrated heater concept can be applied to Vernier devices with peculiar advantages. In fact, it has been often shown that the tuning of conventional DBR lasers can be sensibly expanded exploiting the Vernier effect [4-7]. Typically the optical cavity of these sources is fractioned in multiple contacts, e.g. front mirror, back mirror, phase section, in order to control the refractive index and therefore tune the optical emission. Unfortunately, partial reflections along the waveguide result generally in unpredictable tuning behavior and require extensive post-fabrication characterization. In addition the tuning is generally obtained changing the current in the multiple electrodes at the same time, resulting in difficult pumping schemes. The application of integrated heaters has permitted the fabrication of vernier based DBR lasers with a single laser contact, see Fig. 1 (a). Two integrated heaters can be used to modify the mirror’s temperature without changing the current injected in the active medium. No phase section is necessary and only one of the resistor contacts is pumped at the time. The devices present different stable channels, colored in Fig. 1 (b), defined by the current in the heaters. The tuning inside each channel is obtained simply changing the laser current. We have applied this technique to both the 7–9 µm range, see Fig. 1 (b), and the 4–5 µm range resulting in gapless tuning of ~ 25 cm⁻¹ and 40 cm⁻¹. The integrated heater concept has also been applied to conventional DFB QCLs allowing for up to 15 cm⁻¹ of electrical tuning at 2000 cm⁻¹ in cw operation. Due to the proximity of the heaters from the active region, emission can be modulated at kHz frequencies and the absence of moving parts guarantees the mechanical stability of the system. As mentioned, these integrated heaters are compatible with all the BH processes and can be applied also to standard diode lasers and not only in the Mid-IR range.

© 2015 IEEE