February 1, 2023

The effects of exceptional point (EP) singularities can naturally be seen in many applications in physical problems: mechanics, electromagnetism, atomic and molecular physics, quantum phase transitions, quantum chaos, and much more. Researchers from Switzerland have developed a more practical and robust method for studying these effects. As lasers provide an ideal system for direct observation and engineering of spectral singularities, two dual section distributed feedback (DFB) quantum cascade lasers (QCLs) were designed with Fabry-Perot modes and quarter wave shifted (QWS) DFB modes.


By varying the physical location of the QWS defect as well as the injection current, researchers were able to observe and study EPs based on the coupling parameters of the system. These results show that the developed QCL is a perfect platform to study and further the knowledge of EPs and the effects they have between the weak and strong coupled regime of a laser.

Due to the temperature dependence on the injection current of the QCL, researchers upgraded the electronic drive equipment to utilize the high performance capabilities of Wavelength Electronics’ QCL2000 OEM driver. This critical component enables the sensitive measurements and analysis of EP degeneracy in QCLs and other non-Hermitian systems.


Because the EP degeneracy is lifted at only a certain applied current, ultra-low noise laser drivers were needed. Wavelength Electronics’ driver limits noise produced to as low as 1.3 μA RMS up to 100 kHz and an average current noise density of 4 nA/√Hz. With an output of up to 2 A and stability around 10 ppm long-term, the QCL2000 provided the stability and flexibility needed. This stability allowed researchers to discover the precise applied current at which the EP degeneracy was lifted.
 

The complete case study is available as CS-LD06.
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