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Overview: The optical performance monitoring (OPM) refers to monitoring various performance parameters of optical signals at intermediate nodes or receiver terminal nodes of the optical fiber communication system in order to reduce network operating costs, ensure full utilization of resources, and guarantee reliable operation and flexible management of the system. The amplified spontaneous emission (ASE) noise introduced by optical amplifiers is the main noise source in the optical fiber communication system. Thus, the optical signal-to-noise ratio (OSNR) parameter used to measure the ASE noise accumulation can accurately reflect the quality of the optical signal, which is one of the most important parameters in OPM. Therefore, accurate monitoring of OSNR is an essential part of optical fiber communication systems. However, with the improvement of the channel capacity and transmission rate of the optical fiber communication system and the evolution of the optical network to the dynamiclly reconfigurable direction, the traditional out-of-band OSNR monitoring technique based on linear interpolation is facing the problem of failure. Thereupon, the in-band OSNR monitoring technique has received more and more attention. We propose a novel GPR-based in-band OSNR monitoring technique suitable for intermediate nodes. Firstly, the technology changes the center wavelength of the broadband tunable optical bandpass filter (OBPF) in a constant step size, so as to realize the sweep filtering of the whole C-band. Then, the optical power sequence collected from the center wavelength of the broadband tunable OBPF in the midpoint range of the channel to be monitored, and the adjacent channel is taken as the input features of the GPR model. Finally, the in-band OSNR monitoring is realized by utilizing the trained GPR model. By constructing a 9×32 Gbaud PDM-16QAM coherent optical communication system, a comprehensive experiment was conducted to verify the effectiveness and feasibility of our proposed technique. The experimental results show that in a 9×32 Gbaud PDM-16QAM system with 50 GHz channel spacing, the root means squared error and the mean absolute error are below 0.43 dB and 0.3 dB in the OSNR range of -1 dB to 30 dB, respectively. Even better, our proposed technique has the following advantages: higher monitoring accuracy; wider monitoring range; strong robustness to chromatic dispersion, polarization mode dispersion, nonlinear effect, and cascade filtering effect; no prior knowledge of link configuration required; low cost; distributed monitoring. Therefore, our proposed technique can realize OSNR monitoring at any node which is suitable for dynamically reconfigurable high-speed dense wavelength division multiplexing (DWDM) optical fiber communication systems and has huge development prospects and wide practical application potential.
Schematic diagram of the proposed OSNR monitor
The signal optical spectrum after scanning the center wavelength of the tunable OBPF.The solid black lines represent the signal optical spectrum; the dashed green lines represent the filter shape of the tunable OBPF
Block diagram of the signal processing unit architecture
Experimental setup.MUX: multiplexer; AWG: arbitrary waveform generator; VOA: variable optical attenuator; OSA: optical spectrum analyzer
OSNR monitoring error for PDM-16QAM signals during the testing phase in the first category.(a) With the transmission distance and launch power among the input features; (b) Without the transmission distance or launch power among the input features
OSNR monitoring error for PDM-16QAM signals during the testing phase in the second category.(a) With the transmission distance and launch power among the input features; (b) Without the transmission distance or launch power among the input features
OSNR monitoring error for PDM-16QAM signals during the testing phase in the third category.(a) With the number of cascaded WSSs among the input features; (b) Without the number of cascaded WSSs among the input features
OSNR monitoring error for PDM-16QAM signals during the testing phase including the above three categories.(a) With the transmission distance, the launch power and the number of cascaded WSSs among the input features; (b) Without the transmission distance, the launch power or the number of cascaded WSSs among the input features
OSNR deviation from true OSNR for PDM-16QAM signals during the testing phase including the above three categories.(a) With the transmission distance, the launch power and the number of cascaded WSSs among the input features; (b) Without the transmission distance, the launch power or the number of cascaded WSSs among the input features