Reviewed by Lexie CornerFeb 12 2025
Researchers from the Institute of Electrical and Electronic Engineers developed a numerical simulation technique to analyze light wave interactions within Photonic Crystal Surface-Emitting Lasers (PCSELs). The study was published in the IEEE Journal of Selected Topics in Quantum Electronics.
Laser diodes, a type of semiconductor, generate light using optical feedback. Repeated reflections amplify the light until the desired optical gain is reached. The amplified light is then emitted as a strong laser beam.
PCSELs, an advanced class of laser diodes, distribute optical gain laterally within a photonic crystal (PC) structure. By separating gain, feedback, and emission functions, they enable scalable single-mode power and innovative designs, distinguishing them from conventional lasers. This structural separation enhances performance and expands application possibilities.
The researchers examined light wave interactions in a triangular-lattice PCSEL, where the PC forms a triangular grid pattern. They found that triangular-lattice PCSELs exhibited stronger two-dimensional light wave coupling than square-lattice PCSELs. This increased coupling provides greater optical feedback, improving lasing efficiency.
The study focused on six-plane light waves propagating through the crystal, coupled by Bragg diffraction. The researchers numerically simulated the two-dimensional coupling of these plane waves in triangular-lattice PCSELs and compared them with square-lattice PCSELs.
To support the design of transverse magnetic (TM) triangular-lattice PCSELs, the team derived analytical formulas for mode frequencies and coupling constants, which can be used alongside experimental band structure measurements.
These equations improve in-plane 2D coupling for TM-mode triangular-lattice PCSELs, which is particularly beneficial for low-index contrast devices.
Stephen John Sweeney, Professor and Study Co-Author, James Watt School of Engineering
Stephen John Sweeney is a Senior Member of the Institute of Electrical and Electronics Engineers.
The researchers also determined the general form of the coupled wave equations for unit cells in the crystal lattice, which can assist in the experimental design of more efficient PCSELs. Additionally, they identified the "fundamental lasing mode" in triangular-lattice PCSELs, referring to the electromagnetic field pattern that optimizes laser output.
The findings indicate similarities between transverse electric (TE) and TM polarization behaviors while highlighting the specific advantages of TM modes in certain configurations, particularly in low-index contrast devices.
The derived analytical models and coupling equations facilitate the experimental optimization of photonic crystal structures, enabling targeted improvements in device performance and efficiency.
With enhanced scalability, single-mode operation, and broader industrial applicability, these advancements could significantly influence the design of next-generation PCSELs.
Journal Reference:
Robinson, M. N., et al. (2024) Two-dimensional coupled Wave Theory for Triangular Lattice TM-polarised Photonic Crystal Surface Emitting Lasers. IEEE Journal of Selected Topics in Quantum Electronics. doi.org/10.1109/jstqe.2024.3502794.