Interaction of Confined Polaritons in Microcavity Structures

Morteza Navadeh Toupchi
EPFL, 2021
EPFL thesis

Abstract

A polariton is a quasiparticle formed from the coupling of a confined photon in a cavity to electronic excitation, like exciton in a semiconductor. This dissertation reports on series of experiments in confined polariton interaction by design, fabrication, and characterization of semiconductor microcavity structures operating in strong or weak coupling regime.

In the first part of the thesis, we mainly concentrate on the optical study of the 2D microcavity sample, including spin-dependent lower-upper polariton cross interactions by pump-probe spectroscopy technique, supported by theoretical analyses and numerical simulations based on Gross-Pitaevskii equations. In particular, we present a scattering resonance behavior via an exciton molecule (biexciton) when polaritons from both the upper and lower branches with anti-parallel spins are involved through a polaritonic cross Feshbach resonance. This demonstration will permit the control of the polariton interbranch scattering.

The second part of the thesis is dedicated to the design and fabrication of the potentials where the photonic part of polaritons is confined laterally by adjusting the thickness of the cavity layer locally in so-called mesa structures. By engineering a periodic lattice of mesas on a two-dimensional microcavity, it is possible to couple confined polariton modes of nearby mesas to establish an optical lattice analogous to the crystalline semiconductorsâ electronic band structures. We especially demonstrate the localization of light with a lasing mode at the edge of the Brillouin zone in a two-dimensional triangular lattice. We produce a self-trapping of light by optically inducing a local breaking of the strong-coupling regime of excitons to photons. In the weak coupling regime, we control the confined modes by the shape of the generated defect. We also reveal a controllable localization degree and experimental signature of the Anderson localization in microcavity polaritons by inducing positional disorder in the triangular lattice.

The last part is devoted to the fabrication of sub-micron size mesas to enhance polariton interaction by confining them tightly and discuss the quantum correlation of polaritons by a Hanbury Brown and Twiss (HBT) setting toward polariton blockade.

Official source

https://infoscience.epfl.ch/record/283984?ln=en

About this result

This page is automatically generated and may contain information that is not correct, complete, up-to-date, or relevant to your search query. The same applies to every other page on this website. Please make sure to verify the information with EPFL's official sources.

Related concepts

Related publications

Morteza Navadeh Toupchi
EPFL, 2021
EPFL thesis

Abstract

Official source

https://infoscience.epfl.ch/record/283984?ln=en

About this result

Related concepts (21)

Related concepts

Related publications (30)

Related publications

Localized Photon Lasing in a Polaritonic Lattice Landscape

Fauzia Jabeen, Morteza Navadeh Toupchi, Daniel Oberli, Marcia Portella Oberli

Periodic photonic structures have attracted much interest due to their versatility for controlling light propagation. The dispersion of photon modes in photonic lattices exhibits an energy band structure analo-gous to the electronic one in crystals. An important consequence of the photonic band structure is the localization of light in a band gap, which can be engineered by breaking the translational symmetry introducing a defect in the lattice. Here, we demonstrate experimentally the localization of light in a two-dimensional periodic system of polaritons confined in a patterned microcavity. We generate a self-trapping of light by optically inducing a local breaking of the strong-coupling regime of excitons to photons. In the photon lasing regime we show the existence of confined modes that can be controlled by the shape of the generated defect. We demonstrate single on-site localization with lasing mode at the edge of the Brillouin zone similar to a gap soliton. Our results pave the way for useful tools to optically control localization and propagation of light towards the generation of microlasers.

AMER PHYSICAL SOC2020

III-nitride waveguides featuring AlInN claddings and GaN/AlGaN quantum wells (QWs) offer promising perspectives for applications in many fields of short-wavelength photonics. Thanks to their nearly lattice-matched nature, these structures exhibit an excellent material quality, leading, e.g., to strong light-matter interaction in such QWs, and several promising phenomena. In the low carrier density regime, the strong coupling between QW excitons and waveguide photons results in propagating hybrid light-matter particles, called (exciton-)polaritons, which combine photon-like propagation and exciton-like interactions. These interactions lead to a strong optical nonlinearity, which could be useful for integrated all-optical devices. Due to their strong exciton binding energy (~40 meV in the present structures), III-nitride devices have the potential to maintain these nonlinearities up to room temperature. In the high carrier density regime, a GaN/AlGaN QW electron-hole plasma can provide gain to an optical field in the UV, which can be useful for realizing near-UV laser diodes and semiconductor optical amplifiers. The performance of current UV devices featuring AlGaN claddings is limited by poor material quality. The improved structural quality of waveguides with lattice-matched AlInN claddings could therefore circumvent these issues. This study aims at an in-depth investigation of the optical properties of III-nitride waveguides with AlInN claddings and GaN/AlGaN QWs grown on freestanding GaN substrates. In a sample with an active region that was optimized for strong exciton-photon coupling, we observe propagating polaritons in the low-density regime. A sample with an active region that was optimized for homogeneous near-resonant excitation with a 355 nm laser shows elevated optical gain in the high-density regime. The nearly lattice-matched nature of the entire structure leads to a high structural and optical quality. We found inhomogeneous broadening values between 8 and 11 meV, and a standard deviation in the QW emission energy well below 1 meV over a 50 × 50 µm

^2

area. We calculated the band structure and transition energies of the QWs using self-consistent Schrödinger-Poisson k ·p calculations and found an excellent agreement with experiments. The waveguide polaritons feature a normal mode splitting as large as 60 meV at low temperature, thanks to the large overlap between the optical mode and the active region, a polariton decay length up to 100 µm for photon-like polaritons and a lifetime of 1-2 ps. These decay lengths and lifetimes are limited by residual absorption occurring in the waveguide. The large normal mode splitting and elevated in-plane homogeneity are important assets for the realization of polaritonic integrated circuits. We also demonstrate optically-pumped waveguides exhibiting narrow bandwidth (3.8 nm) optical gain around 370 nm. Due to the high refractive index contrast between the cladding layers and the active region, the confinement factor is as high as 48% and net modal gain values in excess of 80 cm

{¿1}

are measured. The results agree well with self-consistent calculations accounting for built-in electric field effects and high carrier density related phenomena. As such, these results open interesting perspectives for the realization of more efficient near-UV laser diodes and semiconductor optical amplifiers.

EPFL2018

Dynamics of Interactions of Confined Microcavity Polaritons

Taofiq Paraïso

The present Ph.D. thesis consists in a series of experiments carried out in the Laboratory of Quantum Optoelectronics under the direction of professor Benoît Deveaud-Plédran between April 2006 and April 2010. We study the effect of lateral confinement on the dynamics of microcavity polaritons according to two important subjects. On the one hand, we study the polariton relaxation, on the other hand, we study the role of the spin in polariton mutual interactions. We first introduce microcavity polaritons, their optical properties and present the polariton pseudospin formalism. In our sample, polaritons are trapped through their photonic component in cylindrical extensions of the cavity length called mesas. Polariton relaxation is studied in the linear and nonlinear regimes. In the linear regime, we demonstrate that polariton interactions with acoustic phonons are enhanced under lateral confinement. Thermalization, which is forbidden in planar microcavities, is facilitated by confinement, and is very efficient in small diameter mesas. We develop for the first time a comprehensive model of polariton relaxation dynamics under confinement, and highlight the role of polariton states with large exciton content. This work will be profitable to the design of future samples dedicated to the study of Bose-Einstein condensation. In the nonlinear regime, we study the impact of polariton-polariton collisions on the spatial dynamics of microcavity polaritons. In the low-density regime, when the mesa is excited in a coherent superposition of the three lowest energy states, the polariton dynamics is characterized by dipole oscillations. In the high-density regime, we observe a continuous damping of the dipole oscillation. This is due to multiple parametric scattering processes, which redistribute the energy to the benefit of the ground state. Moreover, we demonstrate that the collisional damping is more efficient for collisions between polaritons of the same spin than between polaritons of opposite spins. We investigate in detail the influence of polariton spin in the interactions between polaritons. We first consider the case of planar polaritons. We observe that optical bistability is strongly reduced, or even suppressed, when the system contains polaritons of opposite spins. This results from a pairing of polaritons of opposite spins to form biexciton states. We demonstrate the polarization control of the different optical instability regimes. We then study the case of confined polaritons. As the system is cleaner (we work with a single polariton energy level), we achieve full optical control over the spinor interactions. We demonstrate the first realization of multi-valued switching with a coherent spin ensemble in the solid state. This is a very important step in the research on spin manipulation for the development of spin optoelectronic devices. Finally, we show the influence of the polariton spin on the coupling between planar and confined polaritons and on the control of the polariton fluid dynamics. All our experiments are confirmed by theoretical models. We propose perspectives for the next studies on the dynamics of polaritons and on the coherent spin manipulation in microcavities.

EPFL2010

^2

{¿1}

EPFL2018

Dynamics of Interactions of Confined Microcavity Polaritons

Taofiq Paraïso

EPFL2010