Phase-locked laser arrays through global antenna mutual coupling

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.

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.

Department of Electrical Engineering and Computer Science and Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, 02139, Massachusetts, USA

LongWave Photonics LLC, Mountain View, 94043, California, USA

Sandia National Laboratories, Center of Integrated Nanotechnologies, MS 1303, Albuquerque, 87185-130, New Mexico, USA

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.

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