December 19, 2024
Researchers derive 2D coupled wave equations for photonic crystal surfaces, aiding the development of efficient laser devices
Photonic crystal surface-emitting lasers or PCSELs are laser diodes that generate laser beams through controlled light wave interaction within a photonic crystal structure. In a recent study, researchers developed a method to study the two-dimensional interaction of light waves in PCSELs and measure their efficiency. The findings suggest that triangular-lattice PCSELs may be more efficient at converting electricity into laser light compared to square-lattice PCSELs, providing mathematical modelling tools for designing efficient laser diodes.
Laser diodes are semiconductors that generate light and amplify it using repeated reflection or ‘optical feedback’. Once the light has achieved desirable optical gain, laser diodes release it as powerful laser beams. Photonic crystal surface-emitting lasers (PCSELs) are advanced laser diodes where the optical gain is typically distributed laterally to the propagating light within a photonic crystal (PC) structure. They differ from traditional lasers by separating gain, feedback, and emission functions, offering scalable single-mode power and innovative designs. This leads to enhanced performance and new application possibilities.
In a paper that was recently published in Volume 31, Issue 2 of the IEEE Journal of Selected Topics in Quantum Electronics on 20 November, 2024, researchers have developed a method to numerically simulate the interaction of light waves within PCSELs. The researchers examined how light waves interact within a triangular-lattice PCSEL, where the PC forms a triangular grid structure. They found that the two-dimensional light wave interaction or ‘coupling’ within triangular-lattice PCSEL was stronger than that in square lattice PCSEL. This increased coupling offers greater optical feedback, which is beneficial for efficient lasing.
The researchers focused on six plane light waves propagating through the crystal and coupling through a process called Bragg diffraction. They then performed numerical simulations of 2D coupling of these plane wave in triangular-lattice PCSEL. Finally, they compared the 2D coupling with those seen in square lattice PCSEL.
The team derived analytical equations for both mode frequencies and coupling constants, which can be used alongside experimental band structure measurements to aid the design of transverse magnetic (TM) triangular lattice PCSELs. ‘These equations improve in-plane 2D coupling for TM-mode triangular-lattice PCSELs, which is particularly beneficial for low-index contrast devices’, notes Professor Stephen John Sweeney, a senior IEEE member and co-author of the study.
The researchers also derived the general form of the coupled wave equations for unit cells in the crystal lattice, which can further aid the experimental design of PCSELs with superior efficiency. Additionally, the team identified the ‘fundamental lasing mode’ of triangular-lattice PCSEL, which is the pattern of the electromagnetic field that offers the most efficient laser output.
The findings establish parallels between TM and transverse electric (TE) polarisation behaviours, while emphasizing the unique advantages TM modes offer in certain configurations, particularly in low index contrast devices.
The derived analytical models and coupling equations provide a foundation for experimental optimization of photonic crystal structures, enabling targeted enhancements in device efficiency and performance. They have the potential to significantly influence the next generation of PCSEL designs, offering enhanced scalability, single-mode operation, and broader applicability across industries.
Reference
Authors Title of original paper Journal | Matthew N Robinson1,2, Stephen John Sweeney1, and Richard A Hogg3 Two-Dimensional Coupled Wave Theory for Triangular Lattice TM-Polarised Photonic Crystal Surface Emitting Lasers IEEE Journal of Selected Topics in Quantum Electronics |
DOI Affiliations | 10.1109/JSTQE.2024.3502794 1James Watt School of Engineering, University of Glasgow, G12 8QQGlasgow, U.K., 2Centre for Quantum Materials and Technologies, Queen’s University Belfast, BT7 1NNBelfast, U.K. 3Aston Institute of Photonic Technologies, Aston University, B4 7ET Birmingham, U.K. |
Additional Information for EurekAlert
Latest article publishing date: 20 November 2024
Method of research: Computational simulation/modeling
Subject of research: Not Applicable
COI Statement: NA

Image Title: Advances in photonic crystal laser technology
Image Caption: Researchers have developed a method to numerically assess the efficiency of photonic crystal surface-emitting lasers
Image Credit: FastLizard4 fromOpenverse
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