Metasurfaces-Integrated VCSELs Enable Remarkable Laser Beam-Shaping Applications

Posted Feb 13, 2020 by

Apart from the indispensable contributions of vertical cavity surface-emitting lasers (VCSELs) to the development of modern optoelectronic technologies, their problem of arbitrary beam shaping within a compact system is still the same. But now a new research, led by Patrice Genevet of the Centre de Recherche sur l’Hétéro-Epitaxie et ses Applications (CRHEA) at the University Côte d’Azur and collaborators at the key laboratory of Optoelectronics Technology at the Beijing University of Technology, has demonstrated a wafer-level non-intrusive and monolithic integration that solves these issues of arbitrary beam shaping of VCSELs by directly sculpturing their emitting surfaces into metasurfaces.

VCSEL has experienced a soaring development over the last 30 years, becoming the most versatile laser technology for applications in optical communication, instrumentation, manufacturing, and sensing. Their integration with metasurfaces enables wafer-scale wave front shaping, offering exciting new opportunities.

The exploding development of modern optoelectronic technologies places stringent requirements for lower power consumption devices with high efficiency and more compact integrated system. The current operational principle of VCSELS relies on an active region, consisting of only a few pairs of quantum wells (gain region), sandwiched in between two distributed Bragg reflector mirrors parallel to the wafer surface. In this configuration, the laser radiation is emitted directly from the laser surfaces, i.e. perpendicular from wafer. These devices feature several advantages for both practical application and mass production: 1) the short axial length of the gain region and high reflectivity mirrors leads to small threshold current and thus low-power consumption, 2) they can be tested on-wafer before being cleaved into individual devices, increasing the fabrication yield, 3) they can be made into large-scale two-dimensional arrays, enabling tens of thousands of VCSELs processed simultaneously on a three-inch wafer, thus greatly reducing their fabrication cost.

However, due to the narrow aperture of the laser, their emission is generally highly divergent, spreading the signal after only few hundreds of microns from the laser source. Moreover, the arbitrary beam shaping of VCSELs within a compact system still remains inaccessible until now.

The emerging ultra-thin flat optical structures, namely metasurfaces, offer a powerful technique to manipulate electromagnetic fields with exceptional spectral and spatial controllability. In comparison with conventional bulky optical components, the ultra-thin thickness, unique planar configuration, and complementary-metal-oxide-semiconductor processing compatibility of metasurfaces make them promising candidates for ultra-compact optoelectronic integration. The operational principle of metasurfaces relies on local -sub-wavelength- addressing of the phase, amplitude and polarization of light using arrangements of nanostructures, disposed precisely one with respect to each other to arbitrary modify the incoming light.

In this regard, plasmonic metasurfaces have been previously integrated on VCSELs to improve the laser performance, such as the beam quality, light transmission, and control polarization. With respect to plasmonic metasurfaces, recent high-index dielectric metasurfaces have demonstrated advantages of low absorption loss and the ability to engineer both the electric and the magnetic optical responses, predominantly considered for realistic applications.

The newly developed monolithic approach, which enables arbitrary laser shaping, has been named Metasurface integrated Vertical Cavity Surface Emitting Lasers (MS-VCSELs). It offers a new avenue for programmable laser-on-chip arrays, and enables the realization of independent laser sources with fully-arbitrary beam profiles. Integrating passive metasurfaces, i.e. beam shaping elements that do not alter the laser cavity, MS-VCSELs provide a new degree of freedom of beam shaping VCSELs without the risk of compromising the laser performances such as the operation mechanism, threshold, current distribution, lasing wavelength, high-speed modulation, etc.

It thus remains fully compatible with existing state-of-the-art VCSEL technologies, including the wafer-level fabrication process, the standard packaging process, electrical injection solutions, and theoretical analysis. The arbitrary wavefront control directly at the wafer-level and the programmability of MS-VCSELs would significantly promote applications in various wide-field applications, such as optical fibre communications, laser printing, smartphones, optical sensing, face recognition, directional displays, and ultra-compact light detection and ranging (LiDAR).

Read the complete paper: Metasurface-Integrated Vertical Cavity Surface-Emitting Lasers for Programmable Directional Lasing Emissions