# Integrated IR Modulator with a Quantum Cascade Laser
## 6 Conclusions  
This study presents the preliminary test of an integrated IR modulator. A unique characteristic of this study was the simulation of the electrical signals supplying the quantum cascade lasers, and the integration of the lasing structure and the current switching module. For this purpose, an electric circuit for the lasing structure was proposed. The simulated results defined the influence of impedance mismatching on both the current and voltage supply signals. It was shown that both signal interfaces and laser parameters form the shape of light pulses. The QCL impedance has non-Ohmic character. That is why it requires more advanced models to describe the behavior of the laser. A perfect impedance match is also impossible, because the QCL impedance changes with the modulation of the driving signal.  
Finally, the integrated IR modulator was constructed. The shapes of its light pulses were comparable to the driving current obtained during simulations. These results confirm  
Figure 6: Registered signals for different pulse durations: biasing voltage (**a**) and radiation pulses (**b**).  
Figure 7: Comparison of experimental results (laser biasing voltage and light pulse) with simulation results (laser current).  
the phenomenon of dynamic changes in QC laser impedance with current pulse duration. The electrical circuit emulation does not ensure the observation of these results. However, they provide new knowledge in the field of modeling QC lasing structures considering the laser-system approach.  
The practical result of the work is an IR modulator that generates MWIR pulses using a QC laser operated at room temperature. The light time parameters, time duration of few tens of ns and max. frequency of 1 MHz, are unique results considering the performance of the other available compact QC laser modules.  
Theoretically, the applied switching module also provides a bandwidth of 250 MHz and the generation of complex waveforms using six independently controlled current signals of up to 5 A, and a biasing voltage of 30 V. In the future, it will give new opportunities for many advanced applications. Such a modulator with combined optical signals is needed, e.g., in tunable direct laser absorption spectroscopy, multi-level optical signal transmission, and ultra-short pulse generation with a pre-biasing current.  
Conceptualization, [PERSON]; methodology, [PERSON] and D.S.; validation, J.M.; formal analysis, [PERSON]; investigation, [PERSON]; resources, [PERSON]; data curation, [PERSON]; writing--original draft preparation, [PERSON]; writing--review and editing, [PERSON] and D.S.; visualization, [PERSON] Both authors have read and agreed to the published version of the manuscript.  
Research funded by Narodowe Centrum Badari i Rozwoju Grant No MAZOWSE/0196/19-00) and by Military University of Technology (Grant no UGB/22-786/2020/ WAT).  
Not applicable.  
I would like to thank for technical support with [PERSON] from the Institute of Optoelectronics, MUT. Assistance of the Siec Badawcza Lukasiewicz--Instytut Technologii Elektronowej ([PERSON]) in providing support of quantum cascade lasers technology is gratefully acknowledged.  
The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.