Phase-locked laser arrays through global antenna mutual coupling

Abstract

Phase locking of an array of lasers is a highly effective method in beam shaping because it increases the output power and reduces the lasing threshold. Here, we show a conceptually novel phase-locking mechanism based on ‘antenna mutual coupling’ in which laser elements interact through far-field radiations with definite phase relations. This allows a long-range global coupling among the array elements to achieve a robust phase locking in two-dimensional laser arrays. The scheme is ideal for lasers with a deep subwavelength confined cavity, such as nanolasers, whose divergent beam patterns could be used to achieve a strong coupling among the elements in the array. We demonstrated experimentally such a scheme based on subwavelength short-cavity surface-emitting lasers at terahertz frequencies. More than 37 laser elements that span over 8 λo were phase locked to each other, and delivered up to 6.5 mW (in a pulsed operation) single-mode radiation at 3 THz, with a maximum 450 mW A–1 slope efficiency and a near-diffraction-limited beam divergence.

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Figure 1: Mutual admittance and electric-field distribution of the QCL.
Figure 2: Magnetic (H) fields inside the laser cavity and far-field beam patterns from 3D FEM simulations.
Figure 3: The laser arrays.
Figure 4: The four quadrants of the laser array.
Figure 5: Type I and Type II grids.

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Acknowledgements

This work is supported by the National Aeronautics and Space Administration and National Science Foundation, and also performed at the Center for Integrated Nanotechnologies, a US Department of Energy, Office of Basic Energy Sciences user facility. Sandia National Laboratories is a multiprogram laboratory operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the US Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Author information

T.-Y.K. conceived the strategy, designed and fabricated the antenna mutual coupled laser arrays and performed the measurements and analysis, and J.L.R. provided the material growth. All the work was done under the supervision of Q.H.

Correspondence to Qing Hu.

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The authors declare no competing financial interests.

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Kao, T., Reno, J. & Hu, Q. Phase-locked laser arrays through global antenna mutual coupling. Nature Photon 10, 541–546 (2016). https://doi.org/10.1038/nphoton.2016.104

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