Direct Generation of Radially Polarized Vector Vortex Beam with an Exciton-Polariton Laser

Jiaqi Hu, Seonghoon Kim, Christian Schneider, Sven Höfling, and Hui Deng

Phys. Rev. Applied 14, 044001 – Published 1 October 2020

Abstract

Vector vortex beams are a class of optical beams with singularities in their space-variant polarization. Vector vortex beam lasers have applications in many areas including imaging and communication, where vertical-cavity lasers emitting Gaussian beams have been most widely used so far. Generation of vector vortex beams from vertical-cavity lasers has required external control or modulation. Here, by utilizing a polarization-selective subwavelength grating as one of the reflectors in a vertical semiconductor microcavity, we design the spin textures of the polariton mode and demonstrate polariton lasing in a single-mode, radially polarized vector vortex beam. Polarization and phase distributions of the emission are characterized by polarization-resolved imaging and interferometry. This method of vector vortex laser beam generation allows low threshold power, stable single-mode operation, scalability, and on-chip integration, all of which are important for applications in imaging and communication.

Received 30 June 2020
Revised 29 August 2020
Accepted 2 September 2020

DOI:https://doi.org/10.1103/PhysRevApplied.14.044001

Physics Subject Headings (PhySH)

Exciton polariton Integrated optics Optical vortices Optoelectronics Polarization of light Semiconductor lasers Spatial profiles of optical beams

VCSELs

Atomic, Molecular & OpticalCondensed Matter, Materials & Applied Physics

Authors & Affiliations

Jiaqi Hu ^1,*, Seonghoon Kim², Christian Schneider^3,4, Sven Höfling^4,5, and Hui Deng^1,6,†

¹Applied Physics Program, University of Michigan, Ann Arbor, Michigan 48109, USA
²Department of Electrical Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA
³Institute of Physics, University of Oldenburg, Oldenburg, D-26129 Germany
⁴Technische Physik, Universität Würzburg, Am Hubland, Würzburg 97074, Germany
⁵SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews KY16 9SS, United Kingdom
⁶Department of Physics, University of Michigan, Ann Arbor, Michigan 48109, USA

^*hujiaqi@umich.edu
^†dengh@umich.edu

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Vol. 14, Iss. 4 — October 2020

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Images

Figure 1
Polariton laser device with concentric circular grating mirror. (a) Schematic of the SWG-based microcavity, showing the SWG-based top mirror, QWs in cavity and part of the bottom DBR mirror. (b) Top view SEM image of a fabricated device. Inset: design of the concentric circular pattern. The black regions are the etched grating grooves. (c) Real-space reflection spectrum across the center of the device, $y$ polarized. Here, the light is incident from the air side of the grating, where most energy goes into first diffraction order of transmission [28]. The reflectivity is much lower than 1 and the resonances appear as peaks. (d) Real-space PL spectrum at low excitation power with emission intensity normalized to the maximum value in this spectrum, $y$ polarized. In (c),(d) the dashed lines mark the energy of the exciton resonance that strongly couples to the cavity, and the lower polartiton (LP) and upper polariton (UP) energies about $1 μ m$ away from the center of the device.
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Figure 2
Ground-state lasing properties. (a) $k$ -space emission spectrum at 30.8 mW excitation power. The intensity is normalized to the maximum value in this spectrum. (b) Emission intensity. (c) Energy. (d) Linewidth. In (b)–(d) the gray dashed line marks the lasing threshold.
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Figure 3
Polarization properties of the emission at 40-mW excitation power. Spatial distribution of (a) normalized emission intensity and (b) degree of polarization. (c) Profiles of total intensity (blue circles) and DOP (orange squares) along $y = 0$ [marked with dashed lines in (a),(b)]. (d)–(f) Stokes parameters $S_{1}$ - $S_{3}$ . (g) Azimuthal profiles of $S_{1}$ - $S_{3}$ at $r = 1.5 μ m$ [marked with dashed circles in (d)–(f)]. In (a),(b) and (d)–(f) the solid gray circles mark the boundary of the device. In (a),(c) the intensity is normalized to the maximum value in this image.
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Figure 4
Polarization-resolved interferograms at 40-mW excitation power. (a) Interferogram of $σ +$ component, with the extracted phase map in (b). The two solid circles mark the device boundary in the two interfering images and the dashed circle marks one of the fork patterns. (c),(d) Similar to (a),(b) but for $σ -$ polarization. (e) Azimuthal profiles of the phase at $r = 0.8 μ m$ [dashed circles in (b),(d)]. (f),(g) Similar to (a),(b) but for vertical linear polarization. The dashed ellipse in (f) marks the dislocation of fringes. (h) Phase profile along the dashed line in (g). In (a), (c), and (f) the intensity is normalized to the maximum value in the corresponding image.
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