Abstract
In this work, we systematically analyze the impact of three kinds of Mach-Zehnder modulator (MZM) imbalances, including bias deviation, amplitude mismatch, and differential time skew in intensity-modulation direct-detection (IM-DD) links. It is shown that, for power fading limited transmission, the imbalances can be utilized as advantages rather than impairments. Specifically, the bias deviation with single-arm driven mode and amplitude mismatch with differential driven mode can increase the available bandwidth by shifting the frequency of fading notches. Meanwhile, time skew provides another way to avoid fading by shaping the double sideband (DSB) signal into a vestigial sideband (VSB) with an asymmetrical transfer function. In the transmission experiment, 34 Gbaud Nyquist 6/8-ary pulse amplitude modulation (PAM-6/8) signals are used for investigation in a 20 km dispersion-uncompensated standard single-mode fiber (SSMF) link. With the help of a Volterra nonlinear equalizer, all three kinds of imbalances can achieve bit-error rates (BERs) below the 7% and 20% hard-decision forward error correction (HD-FEC) thresholds for PAM-6 and PAM-8 signals, respectively. The received power sensitivity is also compared at the back-to-back (BTB) case and after fiber transmission. Both numerical simulation and experimental demonstration confirm that the dispersion-induced power fading can be effectively suppressed with bias, amplitude, or skew imbalance, providing a feasible solution for transmission distance extension of C-band DD links.
Highlights
Driven by the emerging broadband services, such as cloud computing, augmented/virtual reality (AR/VR), and high-definition videos, in 5 G Era, the capacity of data center interconnects (DCI), and other short-reach applications are looking for evolutions to accommodate the Internet traffic
By extending our recent work in Reference [31], we provide a comprehensive investigation of the influence of three kinds of Mach-Zehnder modulator (MZM) imbalances, including bias deviation, amplitude mismatch, and differential time skew in short-reach DD systems at C-band
We systematically investigated the impact of bias deviation, amplitude mismatch, and time skew for MZM-based short-reach DD links
Summary
Driven by the emerging broadband services, such as cloud computing, augmented/virtual reality (AR/VR), and high-definition videos, in 5 G Era, the capacity of data center interconnects (DCI), and other short-reach applications are looking for evolutions to accommodate the Internet traffic. The complex optical field can be linearly obtained with dispersion compensated by digital equalizers [6,7]. Since the optical-to-electrical conversion in photodiode (PD) follows square-law detection, the power fading effect would limit the bandwidth-distance product of DD systems by introducing notches in the signal spectrum [8]. It is worth studying the methods of suppressing the power fading and extending the reach of DD optical links
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