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Low-cost Custom Fabrication and Mode-locked Operation of an All-normal-dispersion Femtosecond Fiber Laser for Multiphoton Microscopy

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Anomalous Mode Transitions in High Power Distributed Bragg Reflector Quantum Cascade Lasers.

Feng-Min Cheng^1,2, Jin-Chuan Zhang³, Zeng-Hui Gu^1,2

¹Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, Beijing Key Laboratory of Low Dimensional Semiconductor Materials and Devices, P.O. Box 912, Beijing, 100083, China.

Nanoscale Research Letters

|October 24, 2019

Summary

Distributed Bragg reflector (DBR) quantum cascade lasers (QCLs) exhibit anomalous spectral data, where modes unexpectedly shift to shorter wavelengths with increased temperature or current. This behavior is explained by modal analysis of refractive index changes.

Keywords:

Anomalous mode transitions Distributed Bragg reflector Quantum cascade laser

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Area of Science:

Quantum optics
Semiconductor lasers
Infrared spectroscopy

Background:

Distributed Bragg reflector (DBR) quantum cascade lasers (QCLs) are crucial for mid-infrared applications.
Understanding their spectral behavior under varying operational conditions is essential for device optimization.
Anomalous spectral shifts can impact laser performance and application fidelity.

Purpose of the Study:

To present and explain anomalous spectral data observed in DBR QCLs.
To investigate the underlying physical mechanisms responsible for unexpected mode transitions.
To provide insights into the thermal and current-dependent behavior of QCLs.

Main Methods:

Experimental characterization of two-section DBR QCLs emitting around 7.6 μm.
Continuous wave (CW) operation at room temperature with output power measurements.
Modal analysis to interpret the observed anomalous spectral shifts.

Main Results:

DBR QCLs demonstrated output power exceeding 0.6 W in CW mode.
Anomalous spectral data observed: longitudinal modes shifted to shorter wavelengths with increasing temperature or injection current.
These transitions were explained by thermal-induced changes in refractive index, leading to nearly periodic cavity mode transitions.

Conclusions:

The study successfully presented and explained anomalous spectral behavior in DBR QCLs.
Modal analysis confirmed that refractive index changes drive unexpected mode hops.
Findings contribute to a deeper understanding of QCL spectral dynamics for improved laser design.