Parity-Time-Symmetric Optoelectronic Oscillator Based on Stimulated Brillouin Scattering

Parity-time (PT) symmetry has been intensively exploited in optoelectronic oscillators (OEOs), enabling mode selection in mutually coupled feedback loops. However, two mutually coupled feedback loops are usually established to achieve a spatial PT-symmetric architecture, which increases system complexity and instability. Here, we propose and experimentally prove a PT-symmetric OEO based on stimulated Brillouin scattering (SBS). The PT symmetry is implemented in an overlapping spatial loop in which the gain and loss are realized based on SBS gain and SBS loss, respectively. By adjusting the pump power and the polarization states of the probe and pump lights, the gain and loss can be balanced, thus achieving stable single-mode oscillation. In experiment, a 9.66 GHz microwave signal with a side-mode suppression ratio of 41 dB is generated. At 10 kHz offset frequency, the single-sideband phase noise reaches as low as -120.1 dBc/Hz. This demonstration opens new avenues to enhance mode selectivity in an OEO and can potentially be integrated on a chip.

Automated summary

In this study, a parity-time (PT) symmetric optoelectronic oscillator (OEO) based on stimulated Brillouin scattering (SBS) is proposed and experimentally demonstrated. Instead of using two mutually coupled feedback loops, the PT symmetry is achieved in a single overlapping spatial loop by utilizing SBS gain and SBS loss. Stable single-mode oscillation is achieved by balancing the gain and loss through adjusting the pump power and the polarization states of the probe and pump lights. Experimental results show the generation of a 9.66 GHz microwave signal with a side-mode suppression ratio of 41 dB, and a single-sideband phase noise as low as -120.1 dBc/Hz at a 10 kHz offset frequency. This research opens up new possibilities for enhancing mode selectivity in OEOs and potential integration on a chip.