Growing capacity demands motivate the network evolution from conventional fixed optical networks to future agile optical networks. Recently, hitless flexible transceiver has gained worldwide attentions owing to its ability to adapt transceiver configurations such as bit-rate and modulation format according to the instantaneous link margin without interrupting network traffic. Such hitless flexible transceivers further exploit potential network capacity in a dynamic environment. A key building block of hitless flexible transceiver is modulation format identification (MFI), which is used to reconfigure the digital signal processing (DSP) flow at the receiver-side (Rx) when the format of received signals is changed.
Prof. Songnian Fu and Ph.D student Meng Xiang, with the Wuhan National Lab for Optoelectronics, Huazhong University of Science and Technology, propose a modulation format identification technique for the hitless flexible transceiver. It’s well known that the RF-pilot has been proposed for compensation of both laser phase noise and fiber nonlinearities by extracting the pilot phase information at Rx. However, the amplitude information of the RF-pilot is not utilized in those systems. Here, we propose to encode arbitrary modulation format information onto the amplitude of the RF-pilot. In our experiment, we use a two-level amplitude modulation on the RF-pilot, as shown in the Fig. 1. The proposed MFI covers a wider range of modulation formats and is more reliable especially at low optical-to-signal noise ratio (OSNR). Furthermore, the hitless transceiver with our proposed MFI can support fast modulation format switching on a block by block basis.
Fig. 1. Extracted phase and amplitude of the received RF-pilot.
Fig. 2: Experimental setup and DSP flow.
Fig. 3. (a) BER and SNR versus block index for interleaved DP-8QAM, DP-16QAM and SP-128-QAM blocks. BER and SNR are shown in black squares and blue circles, respectively. (b) Corresponding amplitude symbols of the received RF-pilot.
Fig. 4. (a) Probability of false identification versus OSNR for back-to-back DP-16QAM transmissions. (b) Probability of correct MFI versus SSMF transmission distance for DP-16QAM signals with 1000 times identification.
This paper was published at Optics Express (Vol. 25, No. 1, pp. 463-471, 2017) and partially supported by the 863 High Technology Plan (2015AA015502), and National Natural Science Foundation of China (61275069, 61331010).
