*Article* **Optical Labels Enabled Optical Performance Monitoring in WDM Systems**

**Tao Yang <sup>1</sup> , Kaixuan Li <sup>1</sup> , Zhengyu Liu <sup>1</sup> , Xue Wang <sup>1</sup> , Sheping Shi <sup>2</sup> , Liqian Wang <sup>1</sup> and Xue Chen 1,\***


**Abstract:** Optical performance monitoring (OPM), particularly the optical power and optical signalto-noise ratio (OSNR) of each wavelength channel, are of great importance and significance and need to be implemented to ensure stable and efficient operation/maintenance of wavelength division multiplexing (WDM) networks. However, the critical monitoring module of existing solutions generally are too expensive, operationally inconvenient and/or functionally limited to apply over WDM systems with numerous nodes. In this paper, a low-cost and high-efficiency OPM scheme based on differential phase shift keying (DPSK)-modulated digital optical labels is proposed and demonstrated. Each pilot tone is modulated by digital surveillance information and treated as an identity indicator and performance predictor that ties up to each wavelength channel and thereby can monitor the performance of all wavelength channels simultaneously by only one low-bandwidth photoelectric detector (PD) and by designed digital signal processing (DSP) algorithms. Simulation results showed that the maximum errors of channel power monitoring and OSNR estimation were both less than 1 dB after 20-span WDM transmission. In addition, offline experiments were also carried out and further verified the feasibility of our OPM scheme. This confirms that the optical label based OPM has lower cost and higher efficiency and thereby is of great potential for mass deployment in practical WDM systems.

**Keywords:** optical performance monitoring; wavelength division multiplexing; channel optical power; optical signal-to-noise ratio; optical labels
