450 research outputs found
Photonic Crystal Architecture for Room Temperature Equilibrium Bose-Einstein Condensation of Exciton-Polaritons
We describe photonic crystal microcavities with very strong light-matter
interaction to realize room-temperature, equilibrium, exciton-polariton
Bose-Einstein condensation (BEC). This is achieved through a careful balance
between strong light-trapping in a photonic band gap (PBG) and large exciton
density enabled by a multiple quantum-well (QW) structure with moderate
dielectric constant. This enables the formation of long-lived, dense 10~m
- 1~cm scale cloud of exciton-polaritons with vacuum Rabi splitting (VRS) that
is roughly 7\% of the bare exciton recombination energy. We introduce a
woodpile photonic crystal made of CdMgTe with a 3D PBG of 9.2\%
(gap to central frequency ratio) that strongly focuses a planar guided optical
field on CdTe QWs in the cavity. For 3~nm QWs with 5~nm barrier width the
exciton-photon coupling can be as large as \hbar\Ome=55~meV (i.e., vacuum
Rabi splitting 2\hbar\Ome=110~meV). The exciton recombination energy of
1.65~eV corresponds to an optical wavelength of 750~nm. For 106 QWs
embedded in the cavity the collective exciton-photon coupling per QW,
\hbar\Ome/\sqrt{N}=5.4~meV, is much larger than state-of-the-art value of
3.3~meV, for CdTe Fabry-P\'erot microcavity. The maximum BEC temperature is
limited by the depth of the dispersion minimum for the lower polariton branch,
over which the polariton has a small effective mass where
is the electron mass in vacuum. By detuning the bare exciton
recombination energy above the planar guided optical mode, a larger dispersion
depth is achieved, enabling room-temperature BEC
High-occupancy effects and stimulation phenomena in semiconductor microcavities
This paper describes recent work on high-occupancy effects in semiconductor microcavities, with emphasis on the variety of new physics and the potential for applications that has been demonstrated recently. It is shown that the ability to manipulate both exciton and photon properties, and how they interact together to form strongly coupled exciton-photon coupled modes, exciton polaritons, leads to a number of very interesting phenomena, which are either difficult or impossible to achieve in bulk semiconductors or quantum wells.
The very low polariton density of states enables state occupancies greater than one to be easily achieved, and hence stimulation phenomena to be realized under conditions of resonant excitation. The particular form of the lower polariton dispersion curve in microcavities allows energy and momentum conserving polariton-polariton scattering under resonant excitation. Stimulated scattering of the bosonic quasi-particles occurs to the emitting state at the center of the Brillouin zone, and to a companion state at high wave vector. The stimulation phenomena lead to the formation of highly occupied states with macroscopic coherence in two specific regions of k space. The results are contrasted with phenomena that occur under conditions of nonresonant excitation. Prospects to achieve "polariton lasing" under nonresonant excitation, and high-gain, room-temperature ultrafast amplifiers and low-threshold optical parametric oscillator under resonant excitation conditions are discussed
Collective coherence in planar semiconductor microcavities
Semiconductor microcavities, in which strong coupling of excitons to confined
photon modes leads to the formation of exciton-polariton modes, have
increasingly become a focus for the study of spontaneous coherence, lasing, and
condensation in solid state systems. This review discusses the significant
experimental progress to date, the phenomena associated with coherence which
have been observed, and also discusses in some detail the different theoretical
models that have been used to study such systems. We consider both the case of
non-resonant pumping, in which coherence may spontaneously arise, and the
related topics of resonant pumping, and the optical parametric oscillator.Comment: 46 pages, 12 figure
Polariton condensates at room temperature
We review the recent developments of the polariton physics in microcavities
featuring the exciton-photon strong coupling at room-temperature, and leading
to the achievement of room-temperature polariton condensates. Such cavities
embed active layers with robust excitons that present a large binding energy
and a large oscillator strength, i.e. wide bandgap inorganic or organic
semiconductors, or organic molecules. These various systems are compared, in
terms of figures of merit and of common features related to their strong
oscillator strength. The various demonstrations of polariton laser are
compared, as well as their condensation phase diagrams. The room-temperature
operation indeed allows a detailed investigation of the thermodynamic and
out-of-equilibrium regimes of the condensation process. The crucial role of the
spatial dynamics of the condensate formation is discussed, as well as the
debated issue of the mechanism of stimulated relaxation from the reservoir to
the condensate under non-resonant excitation. Finally the prospects of
polariton devices are presented.Comment: 22 pages, 3 figures, 1 tabl
Propagating Polaritons in III-Nitride Slab Waveguides
We report on III-nitride waveguides with c-plane GaN/AlGaN quantum wells in
the strong light-matter coupling regime supporting propagating polaritons. They
feature a normal mode splitting as large as 60 meV at low temperatures thanks
to the large overlap between the optical mode and the active region, a
polariton decay length up to 100 m for photon-like polaritons and lifetime
of 1-2 ps; with the latter values being essentially limited by residual
absorption occurring in the waveguide. The fully lattice-matched nature of the
structure allows for very low disorder and high in-plane homogeneity; an
important asset for the realization of polaritonic integrated circuits that
could support nonlinear polariton wavepackets up to room temperature thanks to
the large exciton binding energy of 40 meV
Exciton-photon hybridisation in ZnSe based microcavities
This thesis presents the design, fabrication and experimental analysis of ZnSe based
microcavities. Semiconductor microcavities are micro-structures in which the exciton
ground state of a semiconductor is coupled to a photonic mode of an optical cavity.
The strong light matter coupling mixes the character of excitons and photons, giving
rise to the lower and upper cavity polaritons, quasiparticles with an unusual dispersion
due to the extreme mass contrast between the composite exciton and photon. In particular,
the dispersion of the lower polariton forms a dip around the lowest energy state
with zero in-plane momentum. In this dip, which can be seen as a trap in momentum
space, the polaritons are efficiently isolated from dephasing mechanisms involving
phonons. The features of these quasiparticles promise a variety of applications, for
instance lasing without inversion and micro-optical parametric amplifiers, and an environment
to study fundamental physics, such as Bose-Einstein condensation in the
solid state.
By overcoming the longstanding fabrication problems of ZnSe-based microcavities,
the enlarged exciton binding energy in combination with the use of highly reflective
dielectric mirrors makes this material system ideally suited to the realisation of
polariton-based devices operating at room temperature. An epitaxial liftoff technology
is developed that relies on the high etch selectively between the ZnSe heterostructure
and a novel II-VI release layer, MgS.
Three hybrid microcavities are fabricated with the liftoff technique and spectroscopically
characterised. Angle resolved transmission experiments reveal strong hybridization
of the ZnSe/Zn0:9Cd0:1Se quantum well excitons and cavity photons in a fixed
microcavity. A completely length tunable microcavity is presented and shown to exhibit
similar dispersion as for the fixed microcavity, with the addition of evidencing the
cavity polariton bottleneck effect. The nonlinear optical features are discussed. Photoluminescence
data is presented that evidences the first observation of the build up
of cavity polaritons at the edge of the momentum space trap in the lower polariton
branch, the bottleneck effect, in a ZnSe based microcavity. Finally, lasing at room
temperature in the blue spectral region is presented for a metal/dielectric hybrid microcavity
- …