Lighting the Way: Quantum Research for Higher-End Chip Lasers

They consist of III-V QW/QD DFB lasers and SiN microring resonators. Credits: Emad Alkhazraji, Weng W. Chow, Frdric Grillot, John E. Bowers and Yating Wan

Laser diodes based on Quantum Well (QW) and Quantum Dot (QD) semiconductor materials integrated with SiN microresonators show promising potential due to their high energy efficiency and compact size. A study led by Professor Yating Wan has explored the design and functionality of these composite cavity lasers, offering valuable insights into the future development of laser diode technology.

Quantum Dot and Quantum Well laser diodes: the future of microresonators

On-chip laser diodes based on Quantum Well (QW) and Quantum Dot (QD) semiconductor materials are now prime candidates in various applications. Their attractive features include high energy efficiency, the ability to operate at high temperatures and compact size. While QWs have been widely implemented in commercial products, QDs, with their unique zero-dimensional state density and[{” attribute=””>atom-like degeneracy, are a promising alternative.

The heterogeneous integration of III-V lasers with silicon nitride (SiN) microresonators, facilitated by self-injection locking, adds intrinsic benefits. These include compactness, high-volume production potential, and enhanced stability. This technology allows for superior linewidth narrowing performance compared to III-V lasers grown on native platforms.

a,b Linewidth FWHM of the III-V/SiN QD laser as a function of the injection current density for different QD layers (a) and QD densities (b). c,d Colormaps of the output power (left) and wall-plug efficiency (right) as functions of the QD layers (c) and QD density (d). Credit: Emad Alkhazraji, Weng W. Chow, Frdric Grillot, John E. Bowers, and Yating Wan

New Study Explores Quantum Well and Quantum Dot Devices

A study recently published in the journal Light Science & Application dove into a parametric investigation of the design of the active medium of composite cavity lasers. This research was headed by Professor Yating Wan from the Integrated Photonics Lab at King Abdullah University of Science and Technology (KAUST), Saudi Arabia, Dr. Weng W. Chow from Sandia National Laboratories, Albuquerque, USA, Prof. Frdric Grillot from LTCI, Tlcom Paris, Institut Polytechnique de Paris, France, and Prof. John Bowers from the University of California Santa Barbara, USA.

The team focused on the impact of carrier quantum confinement on the dynamic and spectral characteristics of the locked composite cavity device. Their specific emphasis was on emission spectral refinement, or linewidth narrowing, when integrating III-V QW or QD distributed feedback (DFB) lasers with SiN microring resonators. Emad Alkhazraji, the research papers first author, clarified the principle behind the improvement. When properly tuned and locked to one or more of the microrings whispering gallery modes, optical feedback in the form of Rayleigh backscattering can enable drastic reductions in the lasing linewidth of a laser diode to the Hz-level, Alkhazraji explained.

It shows the 4D design space and the optimal points for each device. Credit: Emad Alkhazraji, Weng W. Chow, Frdric Grillot, John E. Bowers, and Yating Wan

Findings and Implications for Future Design

The parametric investigation was concluded with a multi-objective design-operation optimization analysis of both QW and QD devices via a genetic algorithm. A multi-decision algorithm was then employed to determine the optimal design-operation points for each optimization variable.

These findings provide guidance for more comprehensive parametric studies that can produce timely results for engineering design, Professor Yating Wan concluded. The study highlights the potential for improvement and further developments in the field of laser diode technology.

Reference: Linewidth narrowing in self-injection-locked on-chip lasers by Emad Alkhazraji, Weng W. Chow, Frdric Grillot, John E. Bowers and Yating Wan, 28 June 2023, Light Science & Applications.
DOI: 10.1038/s41377-023-01172-9

Funding: Advanced Research Projects Agency-Energy (ARPA-E), the U.S. Department of Energy, the American Institute for Manufacturing (AIM) Integrated Photonics.