A Microlaser Emitting Helical Light

Chiral objects are ubiquitous in nature, from rotating galaxies to the DNA double helix. Chirality of light can be defined when its phase winds along its propa­gation axis. In the 1990s, it was recognized that harnessing such a chiral feature of light fields, the orbital angular momentum (OAM), could be techno­logically advan­tageous. Indeed OAM represents an unbounded degree of freedom, as the phase front can theoreti­cally wind an arbitrary large number of times within an optical period. It therefore offers a drasti­cally enlarged basis for encoding information in comparison to the commonly used polari­zation states of light, which are limited to a two-dimensional basis.

Scheme of an integrated microlaser based on a novel design that allows emitting light in chiral modes, thus producing corkscrews of light. (Source: C2N, CNRS, U. Paris-Sud)

Multi­plexing information in such a higher-dimensional basis would offer the possibility to drasti­cally enhance the efficiency of both classical and quantum information protocols. Furthermore, transferring such large values of angular momentum to massive particles is a powerful asset for optical mani­pulation schemes at the atomic scale (i.e. atomic tweezers). Researchers from the Centre de Nanosciences et de Nano­technologies (C2N) in Palaiseau, together with collaborators from Labora­tory Phlam in Lille and from Institut Pascal in Clermont-Ferrand, have reported the demons­tration of a novel integrated laser architec­ture, where light is emitted in a chiral state, thus producing corkscrews of light. The disruptive advantage of this microlaser lies in the possibility of controlling the orien­tation of the corkscrew – from clockwise to counter clockwise – by simple optical means.

In order to generate these chiral states of light, the researchers have used an approach based on two main ingredients. First, they fabri­cated a hexagonal laser cavity formed from six coupled micro­pillars. As a result of the rota­tional symmetry of their device, the resonating modes present OAM with well-defined values. Secondly, in order to favour emission from either clockwise or counter-clockwise optical modes, which requires breaking time-reversal symmetry in the system, they took benefit of an engineered inter­action between the polarization and OAM of light.

This inter­action couples the OAM and the polarization of the photon modes. This coupling allows generating a lasing emission with a net chirality by using a circularly polarized optical pump. As a result, this novel micro­laser emits clockwise or counter-clockwise coherent light depending on the circular polari­zation of the optical pump. The very general scheme proposed and implemented in this work paves the way to the realization of novel genera­tions of micro­lasers emitting chiral light that could be used for encoding infor­mation in the orbital angular momentum basis. (Source: C2N)

Reference: N. Carlon Zambon et al.: Optically controlling the emission chirality of microlasers, Nat. Phot. 13, 283 (2019); DOI: 10.1038/s41566-019-0380-z

Link: Centre de Nanosciences et de Nanotechnologies (C2N), CNRS – Université Paris-Sud – Université Paris-Saclay, Palaiseau, France

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