Lasing action in active dielectric nanoantenna arrays (1803.09993v1)

Abstract: Directional lasing, with a low threshold and high quality factor, in active dielectric nanoantenna arrays is demonstrated. This is achieved through a leaky resonance excited in coupled gallium arsenide (GaAs) nanopillars. The leaky resonance is formed by partially breaking a bound state in the continuum (BIC) generated by the collective, vertical electric dipole resonances excited in the nanopillars for sub-diffractive arrays. By opening an unprotected, diffractive channel along one of the periods of the array one can control the directionality of the emitted light without sacrificing the high Q associated with the BIC mode, thus achieving directional lasing. A quality factor Q = 2750 is achieved at a controlled angle of emission of ~ 3 degrees with respect to the normal of the array with a pumping fluence as low as 10 uJ/cm^2. We demonstrate the possibility to control the lasing directivity and wavelength by changing the geometrical parameters of the nanoantenna array, and by tuning the gain spectrum of GaAs with temperature. Lasing action is demonstrated at different wavelengths and emission at different angles, which can be as large as 25 degrees to the normal. The obtained results provide guidelines for achieving surface emitting laser devices based on active dielectric nanoantennas that are compact and highly transparent.

• The paper introduces a novel method for achieving directional lasing by partially breaking a bound state in the continuum in GaAs nanoantenna arrays.
• It achieves a high Q-factor of 2750 at a 3° emission angle and operates with an exceptionally low pump fluence of 10 μJ/cm² using a 2D nanopillar design.
• Combining experimental back focal plane imaging with finite-element simulations, the study offers actionable insights for integrating efficient nanophotonic devices.

Overview of Lasing in Active Dielectric Nanoantenna Arrays

The research investigated in "Lasing Action in Active Dielectric Nanoantenna Arrays" explores a novel approach to achieving directional lasing with low threshold and high-quality factors in dielectric nanoantenna arrays, particularly focused on gallium arsenide (GaAs) nanopillars. This paper effectively leverages bound states in the continuum (BIC) to create leaky resonances, which facilitate lasing action through GaAs nanoantenna arrays, overcoming previous challenges of low Q-factors and poor directionality.

Key Findings

The paper introduces an approach to maintaining a high Q-factor in lasing by partially breaking a BIC. The research highlights the capability to control the directionality of light emission through adjustment of the array's geometry, achieving an impressive quality factor of Q = 2750 at a mere 3° emission angle with respect to the normal. Furthermore, the lasing operation is undergone with a remarkably low pumping fluence of 10 μJ/cm².

The structural arrangement of a 2D array of GaAs nanopillars allows manipulation of both the lasing wavelength and directivity by varying temperature and the geometric parameters of the nanoantennas. The research demonstrates lasing at variable wavelengths and angles, with emission angles reaching up to 25° to the normal.

Experimental and Theoretical Insights

High-index dielectric GaAs nanopillars, with a diameter of ~100 nm and a height of 250 nm, are employed in this paper, forming the central components of the laser device. The structure harnesses collective vertical electric dipole resonances, with experimental demonstrations displaying emissions at controlled angles by choosing specific periods in the arrays that support diffraction orders. Spectrally resolved back focal plane imaging is used to investigate resonant modes, confirming the emergence of the BIC and its associated high Q-factor.

Simulation techniques using finite-element methods corroborate experimental results, elucidating the behavior of two main resonant modes: a horizontal in-plane electric dipole and a vertical electric dipole. Significantly, the vertical electric dipole mode is carefully controlled to minimize radiation loss, formulating a BIC with increased Q at normal incidence angles and reinforcing the potential for effective lasing.

Implications and Future Developments

This research provides valuable insights into the use of dielectric nanoantennas for optical applications, offering a compact, highly transparent device that may be integrated into multilayered photonic systems without considerable optical losses. It invites further exploration into other active semiconductor materials compatible with typical semiconductor fabrication processes, potentially enabling on-chip integration.

The demonstrated ability to maintain high transparency (e.g., >85% over the 700-900 nm range) indicates significant applicability in surface-emitting laser devices, retaining efficiency even in low gain environments. By exploring further material enhancements or employing surface passivation techniques, the potential to achieve lasing at higher temperatures, including room temperature, is conceivable.

Conclusion

The paper marks a pivotal step in realizing dielectric-based lasing for photonic applications, bypassing limitations prevalent with conventional methods, and underscoring the practicality of vertical dipole resonances in dielectric nanoantenna systems. These findings chart a course toward novel applications in nanophotonics, specifically heralding advancements in compact, efficient, and directionally enhanced laser technology.