Small-signal modulation characteristics of a polariton laser

Md Zunaid Baten,Saniya Deshpande,Ivan Iorsh,Alexey Kavokin,Pallab Bhattacharya,Thomas Frost

doi:10.1038/srep11915

Abstract

Use of large bandgap materials together with electrical injection makes the polariton laser an attractive low-power coherent light source for medical and biomedical applications or short distance plastic fiber communication at short wavelengths (violet and ultra-violet), where a conventional laser is difficult to realize. The dynamic properties of a polariton laser have not been investigated experimentally. We have measured, for the first time, the small signal modulation characteristics of a GaN-based electrically pumped polariton laser operating at room temperature. A maximum −3 dB modulation bandwidth of 1.18 GHz is measured. The experimental results have been analyzed with a theoretical model based on the Boltzmann kinetic equations and the agreement is very good. We have also investigated frequency chirping during such modulation. Gain compression phenomenon in a polariton laser is interpreted and a value is obtained for the gain compression factor.

Highlights

Use of large bandgap materials together with electrical injection makes the polariton laser an attractive low-power coherent light source for medical and biomedical applications or short distance plastic fiber communication at short wavelengths, where a conventional laser is difficult to realize
The proposal for generating coherent light by spontaneous emission from a coherent, macroscopic and degenerate exciton-polariton condensate in a microcavity[1] was followed by experimental demonstration of such emission at cryogenic[2,3,4,5,6,7,8,9] and higher temperatures, including room temperature[10,11,12,13,14,15,16,17,18], in a variety of material systems
The characterization of optically or electrically pumped polariton lasers made with a variety of material systems has enabled a detailed study of the underlying physical processes such as polariton scattering and Bose-Einstein condensation[20,21,22,23], spontaneous symmetry breaking[24] and superfluidity[25] in the condensate

Summary

Methods

The polariton dispersion characteristics were determined from angle-resolved electroluminescence measurements (see Supplementary information). The polariton occupation in k-space at different injection levels was measured by angle-resolved electroluminescence, using a digital readout angular mount having a precision of 0.1°. The number of polaritons per k-state is estimated from the LP electroluminescence integrated intensity by taking into account the radiative lifetime. The occupation is calculated from the output power measured with a power meter. The transient response was measured by superimposing a small-signal periodic switching pulse (1–3 mV) on different DC bias voltages set above the polariton lasing threshold. In measuring chirp of the polariton laser, we recorded the average broadening of the coherent emission spectra under small signal (2 mV) pulsed bias condition above threshold (1.15 Jth) for different modulation frequencies.

Author Contributions

Additional Information