We quantify, through simulations and experiments at 21.4 GBaud, the effect of in-band crosstalk on several advanced optical modulation formats, showing a 1-dB penalty at a bit-error ratio of 1×10 -3 from a crosstalk of -18 dB, -24 dB, and -32 dB for QPSK, 16-QAM, and 64-QAM, respectively. OCIS codes: (060.2360) Fiber optics links and subsystems; (060.4080) Modulation IntroductionCommercial 100-Gb/s transmission systems available and in development today are largely based on single-carrier 28-Gbaud polarization-division-multiplexed (PDM) quadrature phase-shift keying (QPSK). Such signals can be operated on a 50-GHz frequency grid in wavelength-division-multiplexed (WDM) systems (i.e., at a spectral efficiency, SE, of 2 b/s/Hz), while still providing spectral margin for several optical add/drop nodes. In order to further increase transport capacities, greater SEs can be achieved using higher-level quadrature amplitude modulation (QAM), such as 16-QAM and 64-QAM. The more severe impact of in-band crosstalk on these higherorder formats can represent an important limitation arising, e.g., from imperfect optical add/drop nodes or doubleRayleigh backscatter in Raman amplified systems [1,2]. In addition, in-band crosstalk represents a key limitation in the upcoming class of spatially multiplexed systems, where low-crosstalk multi-core fiber [3,4] is being designed to avoid complicated multiple-input multiple-output (MIMO) processing to counteract crosstalk [5,6]. In all of the above scenarios, it is important to know the crosstalk levels at which higher-order modulation formats start to suffer penalties. In this paper we quantify the increasing crosstalk penalties when increasing the constellation size in single-polarization QAM systems, using simulations and 21.4-GBaud QPSK, 16-QAM, and 64-QAM experiments.

We demonstrate a 222 GBd on-off-keying transmitter in a short-reach intra-datacenter scenario with direct detection after 120 m of standard single mode fiber. The system operates at net-data rates of >200 Gb/s OOK for transmission distances of a few meters, and >177 Gb/s over 120 m, limited by chromatic dispersion in the standard single mode fiber. The high symbol rate transmitter is enabled by a high-bandwidth plasmonic-organic hybrid Mach-Zehnder modulator on the silicon photonic platform that is ribbon-bonded to an InP DHBT 2:1 digital multiplexing selector. Requiring no driving RF amplifiers, the selector directly drives the modulator with a differential output voltage of 622 mV pp measured across a 50 Ω resistor. The transmitter assembly occupies a footprint of less than 1.5 mm × 2.1 mm.

The paper presents a new method for signal flowgraph analysis of large electronic networks. A hierarchical decomposition approach is realized using the so-called upward analysis of the decomposed network. This approach allows fully symbolic network formulas to be obtained in time linearly proportional to the size of the network. A multiconnection characterization, suitable for upward analysis, has been defined and used in topological formulas. Examples of large scale networks analysis are discussed. The approach can be used to obtain symbolic solutions of linear systems of equations.