With rapid development of cloud services, real-time video, and online social networks, there occurs an urgent requirement of transmission capacity for interconnection among data-centers. The interconnection operating at 100 Gb/s or 400 Gb/s has drawn significant research efforts as well as standardization activities, such as the IEEE 802.3bs 400G Ethernet Task Force.Since the data-center interconnection is particularly sensitive to cost, power consumption, and footprint, intensity modulation and direct detection (IM-DD), advanced modulation formats and digital signal processing (DSP) are always attractive.
Prof. Songnian Fu, MS student Fan Gao and Shiwei Zhou, with theWuhan National Lab for Optoelectronics, Huazhong University of Science and Technology, propose a Sparse Volterra filter (SVF) equalizer for compensating the transmission impairments in data-center interconnection. It’s well known that digital signal processing is highly preferred for achieving low-cost and good performance IM-DD system. However, all the equalization techniques that can compensate the fiber nonlinearities have high computation complexity (CC) at present. In order to reduce the CC of traditional VF equalizer expressed as Eq. (1), modified Gram-Schmidt orthogonal with re-orthogonalization is applied to transform the signal into orthogonal domain as Eq. (2). With the orthogonal search approaching, the normalized square error (NMSE) can be represented as Eq. (3), so the less important kernels which contribute less to NMSE can be reasonably removed. We find that the redundancy kernels can be reasonably removed by SVF equalizer. By applying SVF equalizer to compensate the transmission impairments, we can achieve similar system performance but with half computational complexity (CC), in comparison with traditional VF equalizer.
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Fig. 1. Experimental setup of O-band 2×64 Gb/s PAM-4 transmission with DSP flow. Insert: (i) optical spectral at the transmitter side; eye-diagram of the PAM-4 signal (ii) before and (iii) after SVF equalizer.
Fig. 2. BER of 28 GBaud PAM-4 signal versus the received power after 70 km SSMF transmission (a) for two channels and (b) with various equalization techniques
Fig. 6. Number of SVF kernels in various terms versus IF for (a) second order kernels, and (b) third order kernels
Thispaper was published at Optics Express (Vol.25,No.7, pp.7230-7237, 2017) andpartiallysupported by the 863High Technology Plan (2015AA015502), and National Natural Science Foundation of China (61711530043, 61575071).
