Transmission of single lane 128 Gbit/s PAM-4 signals over an 80 km SSMF link, enabled by DDMZM aided dispersion pre-compensation

Abstract

Direct detection systems with advanced modulation schemes are of great importance in metropolitan networks, because of their low cost and low power requirements. In particular, PAM-4 has attracted considerable attention, but has significant transmission distance limitations in the C-band. To extend its reach, we used a dual drive Mach-Zehnder modulator to generate a chromatic dispersion (CD) pre-compensated signal with an extra (j-1) multiplication to align the optical carrier and the modulated optical signal; by doing so, we achieved successful 128 Gbit/s transmission over an 80 km SSMF link, the longest reported reach of single lane 100 Gbit/s PAM-4 signals over DCF-free links. Synchronized bandwidth pre-compensation was also used, to reduce the influence of bandwidth-limitations.

Recent Advances in Equalization Technologies for Short-Reach Optical Links Based on PAM4 Modulation: A Review

“…The last term k v is the additive Gaussian noise variable at the k-th sampling instant. To investigate the performance impact of bandwidth limitation, a typical measured system frequency response is shown in Figure 2a [60]. The 3 dB bandwidth of the total transmission system is approximately 7.5 GHz, which is far below the required bandwidth for 64 Gbaud PAM4 signal.…”

“…The obtained BER performance is degraded as the bandwidth reduces, which confirms that the narrow bandwidth is one of the factors that deteriorate the performance of PAM4 optical links. (a) Frequency response in band-limited system and eye diagrams (I) before and (II) after bandwidth compensation (redrawn after [60]). (b) Effect of bandwidth to system performance (redrawn after [19,61]).…”

“…When PAM4 is used in the C-band, the CD tolerance is considered as one key drawback, which critically impairs the high-frequency components of the signal. The typical tolerance to residual CD [60]). (b) Effect of bandwidth to system performance (redrawn after [19,61]).…”

“…Therefore, the best choice for practical implementation is a combination of an FFE and a DFE, which can be seen from Figure 8b. The FFE and DFE can be placed in the transmitter for pre-compensation or in the receiver for post-compensation [60]. To solve the problem of error propagation, a transmitter-side DFE called Tomlinson-Harashima pre-coding has recently been proposed and investigated in various PAM4 short-reach optical links [70][71][72][73].…”

Inter-data center 28 Gbaud 4-PAM transmission over 240 km standard single mode fiber

“…In cases where 4-PAM modulation have been used for longer transmission distances (100-400 km) the symbol rates have been lowered, for example to 20 Gbaud as in [5]. In between these two cases we find demonstrations of 128 Gbit/s 4-PAM with transmission distances up to 80 km [6]. The speed and distance is enabled by the use of an external dual drive Mach-Zehnder modulator and dispersion pre-compensation.…”