Low dissipation integrated frequency combs are ideal candidates to realize miniaturized spectrometers without moving parts and hence are of great interest for integrated photonics.
After reviewing frequency comb generation in interband cascade lasers (ICLs), the nonlinear dynamics and performance limiting mechanisms of ICLs will be discussed. A newly developed k-space resolved non-equilibrium carrier transport model combined with experimental studies enables us to explore different loss mechanisms, as well as to explore the reasons, why passive mode-locking of ICLs for short pulse generation remains challenging.
We present GaSb based interband cascade lasers with a center emission wavelength of 6170 nm that emit in cw operation up to a temperature of 40°C. While the pulsed threshold current density for a broad area laser is as low as 500 A/cm² at a temperature of 20°C a ridge waveguide laser with 23µm ridge width reaches more than 25mW of output power, the results were achieved by careful optimizations of the active region design, the waveguide design and epi down mounting of the laser chips.
We report on the development of Quartz-Enhanced Photoacoustic Spectroscopy (QEPAS) technology to detect 8 different air pollutants, namely CH4, NO2, CO2, N2O, CO, NO, SO2 and NH3, with the same acoustic detection module and interchangeable laser sources, to prove the modularity of the technique as well as the adaptability to different lasers. For each gas species, the fine structure of the infrared absorption bands has been simulated by using HITRAN database. Each gas species was detected with an ultimate detection limit well below their typical natural abundance in air even with signal integration time as low as 0.1 s.
Interband cascade lasers (ICLs) are attracting more and more attention, being established as reliable mid-infrared laser sources. In particular, their low threshold current densities and low power consumption qualify them for a multitude of applications aiming for portable, miniaturized sensing systems. ICLs show a performance sweet spot around 3-4 μm and continuous-wave (cw) operation at room temperature has been shown at wavelengths from 2.8-5.6 μm in the GaSb material system. When trying to extend this range towards even longer wavelengths, several difficulties are inevitably faced. Some can partly be traced back to a still insufficient understanding of the internal device physics.
Here, we report on our latest findings showing the impact of intersubband transitions in the valence band band of ICL active regions on the performance of these devices.
Using a numerical model employing the eight-band k·p method, we calculate the electronic band structure of the active W-quantum well (QW) in an ICL. We then use a generalized momentum matrix element model to determine the wavelength-dependent absorption between subbands in the valence band. This model can explain all contributions to the absorption in the W-QW, regardless of the nature of the transitions, whether they are interband or intersubband.
We experimentally observe a clear dependence of performance metrics on the thickness and composition of the GaInSb hole-QW. Specifically, the threshold current density Jth, and its dependence on the operating temperature, described by the characteristic temperature T0, are influenced. This is in good agreement with our model. By carefully adjusting the design of the active W-QW the intersubband absorption in the valence band can be modified and even sufficiently avoided, allowing us to enhance the ICL performance outside of the sweet spot 3-4 μm region.
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