Direct Observation of Polariton Waveguide in ZnO nanowire at Room Temperature

motivation

abstractWe report the direct experimental evidence of polariton waveguide, a well confinement of the propagation of polariton at room temperature. By using the angle resolve measurement, we obtained the dispersion of strong coupling in ZnO whispering gallery microcavity. While with the separation between the excitation laser and collection lens, we observed the propagation of polariton along the ZnO nano wire. This implies that the ZnO nano wire can be served as good candidate for one dimensional waveguide of polariton and provides the opportunity for polariton waveguide-based device.

Yanjing Ling, Zhanghai Chen, Hongxing Dong, Wei Xie, Liaoxin Sun Surface Physics Laboratory, Department of Physics, Fudan University, China

Recently, much research has been devoted to the question of whether optical digital processing could offer higher performance than electronic digital processing. Indeed, the mixture of both is an alternative route.

Polariton is a quansiparticale that arises from the strong coupling between an exciton and a photon mode confined in a optical cavity. Polaritons are good bosons, might leading to Bose-Einstein condensation at room temperature.

So far, the toolbox of polariton device elements already includes light-emitting diodes, polariton laser. An important step toward polaritronics is to develop a polariton waveguide that can link these elements to carry out complex tasks such as optical circuits on chip.

Method

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High quanlity of ZnO nanowire is attained. The binding energy of ZnO is more than 60 meV. Taking advantage of hexagonal cross section perpendicular to the longitudinal crystal axis (c-axis) of ZnO, fabrication of hexagonally shaped whispering gallary (WG ) resonator is easily achieved.

To detect the waveguide effect, there are two lenses in the set up, one is used to excitation, the other is to collect the PL signal. And the degree of nonalignment between the detection and excitation can be change easily.

resultsStrong coupling regime

By performing a scanning excitation along the ZnO nanowire, a transition from the pure WG optical modes in the weak interaction regime to the polariton in the nearly resonant regime is observed. Since the energy of the interband transition luminescence is closed to the photon energies of the WG modes in the microcavity, therefore the observed bending and strong off-linearity luminescence is dominated by excitonic polariton. we choose a nanowire with uniform size to study the polariton waveguide.

To get detail information about polariton we perform the angular resolve measurement. Also, experimental results can be reproduced by theory very well. The group velocity is creasing when k in plane becomes larger. So, with the separation of the two lenses, only those polariton states with group velocity large enough can be detected.

ConclusionsGuided polariton propagation was observed in spatially resolved k space.

Polariton waveguided will open the possibility of its application.

references(1) Hopfield, J.J. Phys. Rev.(1958) 112 1555.

(2) Sun. L. X, Chen. Z. H, Ren. Q. J, and Yu. K, Phys. Rev. Lett. 100, 156403.

(3) Kasprazk, J. Richard. M, and Kundermann, S. nature 443, 409.