RESUMEN
We experimentally demonstrate a digital-to-analog-converter-less (DAC-less) vestigial sideband (VSB) 4-level pulse amplitude modulation (PAM4) transmission system for data center interconnects (DCIs) using a silicon photonic (SiP) multi-electrode Mach-Zehnder modulator (ME-MZM) based DAC-less transmitter and a VSB self-coherent receiver. The impacts of linear and nonlinear impairments on the proposed system and their mitigation methods are comprehensively studied. By using Kramer-Kronig (KK) detection, frequency domain chromatic dispersion compensation, and short-memory time domain Volterra equalization at the receiver, we report a 112 Gb/s PAM4 transmission over 40 km standard single mode fiber (SSMF) with a bit error rate (BER) below the 7% overhead (OH) hard-decision forward error correction threshold of 3.8 × 10-3, and a 120 Gb/s PAM4 transmission over 80 km SSMF with a BER below the 20% OH soft-decision forward error correction threshold of 2 × 10-2, without any transmitter side digital signal processing such as pre-emphasis and pulse shaping.
RESUMEN
In this work, we experimentally investigate the performance improvement in IM/DD systems using constellation switching (CS), which is simple to implement with a reasonably low complexity. By encoding extra bits on the selection of a PAM constellation pattern from a set of constellations, a lower symbol rate can be used to achieve the same system bit rate compared with standard PAM systems based on a single constellation pattern. In our experiments with bandwidth limited components, including a 14 GHz bandwidth digital-to-analog converter (DAC), we demonstrate that the CS signals can improve the receiver sensitivity. In particular, in the 112 Gbit/s PAM4 case, the required receiver power was reduced by 0.8 dB and 1.1 dB using the CS at the HD FEC threshold of BER = 4 × 10-3 in the back-to-back (B2B) and 3 km fiber transmission, respectively. Similarly, in the 84 Gbit/s two-dimension (2D) PAM4 case, the required receiver power was reduced by 1.05 dB and 3.5 dB at the HD FEC threshold of BER = 4 × 10-3 in the back-to-back (B2B) and 5 km fiber transmission, respectively. Moreover, we show by simulations that the improved performance of using the CS signals is also observed over a wide range of transmitter bandwidth, further indicating the merits of using the CS in IM/DD PAM transmissions.
RESUMEN
We propose a self-homodyne system for next generation intra-datacenter networking. The proposed system has a higher spectral efficiency for the modulated signal compared to the intensity-modulation/direct-detection (IM/DD) systems and uses digital signal processing of reduced complexity compared to a conventional coherent system. The concept of the proposed system is to send the modulated signal and a tone originating from the same laser over the full-duplex fiber with the aid of circulators to be used remotely at the receiver for coherent detection. The overall system physical complexity approaches the equivalent IM/DD system giving the same target data rate for 400G systems and beyond. We experimentally demonstrate emulation of the proposed system and report data rates of 530 Gb/s, 448 Gb/s and 320 Gb/s on a single wavelength below the KP4 forward error correcting threshold over 500 m, 2 km and 10 km of single mode fiber, respectively.
RESUMEN
We demonstrate experimentally the transmission of single carrier 56 Gbaud 16-QAM, 8-QAM and QPSK optically modulated signals over 320, 960 and 2,880 km, respectively, using a fully packaged InP IQ modulator and a Stokes vector direct detection (SV-DD) receiver realized using discrete optics. Results show that by optimizing the carrier-to-signal-power ratio, the total throughput-times-distance product for 16 QAM and QPSK are 71,680 Gbps.km and 322,560 Gbps.km, respectively, at bit error rate (BER) below the hard decision forward error correcting threshold (HD-FEC) of 4.5 × 10-3.
RESUMEN
We comment on the recent letter by Wang et al. [Opt. Lett. 34, 1955 (2009)], in which the authors presented a high-speed digital image correlation (DIC) method. We consider that the so-called high-speed DIC method has considerable deficiencies and that the Letter is misleading in terms of applicability and measurement accuracy as well as processing speed.
