Impact of Chirp in High-Capacity Optical Metro Networks Employing Directly-Modulated VCSELs

Abstract

Directly modulated long-wavelength vertical cavity surface emitting lasers (VCSELs) are considered for the implementation of sliceable bandwidth/bitrate variable transceivers for very high capacity transmission (higher than 50 Gb/s per wavelength) in metropolitan area systems characterized by reduced cost, power consumption, and footprint. The impact of the frequency chirp measured for InP VCSELs with different kinds of design (high-bandwidth very short cavity and widely-tunable with micro electro-mechanical systems (MEMS) top mirror) is analyzed in case of discrete multitone (DMT) direct modulation in combination with 25-GHz wavelength selective switch (WSS) filtering. The maximum transmitted capacity for both dual side- and single side-band DMT modulation is evaluated as a function of the number of crossed nodes in a mesh metro network, comparing VCSEL based transmitters performance also with the case of external electro-absorption modulator use. Finally, the maximum reach achieved based on the received optical signal to noise ratio (OSNR) and the fiber span length is discussed. The results confirm the possibility to use directly-modulated long-wavelength VCSELs for the realization of sliceable bandwidth/bitrate variable transmitters targeting 50-Gb/s capacity per polarization, also in the presence of 5 crossed WSSs for reaches of hundreds of kilometers in multi-span Erbium-doped fiber amplified (EDFA) metro links supported by coherent detection.

Spectrum/Space Switching and Multi-Terabit Transmission in Agile Optical Metro Networks

“…Larger paths (up to 735 km) can be reached if the connection is characterized by shorter hop distances (35 km), assuming the same number of filtering stages. These results have been achieved, considering a measured chirp factor α of 3.7 [3]. Then, we have assessed the cascading effect of a single channel DMT signal passing through multiple AWG and WSS filters over an established MAN connection, taking into account node and transceiver architectures.…”

Programmable VCSEL-based Transceivers for Multi-terabit Capacity Networking

“…Therefore, the flow is adapted to the required bandwidth, traffic demand and quality of transmission required by the established connection. Recent results have numerically demonstrated that 50 Gb/s capacity per 25 GHz bandwidth flow can be transmitted over hundreds of km, using discrete multitone (DMT) with single sideband (SSB) modulation and CO detection [5,6]. Therefore, a submodule would provide up to 500 Gb/s.…”

“…7-core fiber or a bundle of 7 fibers) more than 100 Tb/s can be supported (see bottom insets of Fig.1). The peculiarities of the adopted technologies, such as the combination of DM with CO-Rx and the effect of chirp [6], or the limited tunability/flexibility of the laser sources, should be taken into account for the transceiver design. This is also particularly relevant for the S-BVT modeling and its programmability handled by the SDN controller [7].…”

“…By integrating multiple photonic modules and exploiting the spectral and spatial dimensions, aggregated flows supporting multi-terabit capacity can be provided. In order to extend the achievable reach, direct modulation can be combined with coherent (CO) detection [5,6]. In the framework of the EU H2020 PASSION project, programmable modular S-BVT architectures based on these concepts are proposed to address the challenges posed by future metro networks [7].…”

VCSEL Technologies for High-Capacity Dense WDM Networks

“…At first, we performed chirp measurements on a short-cavity 20-GHz long-wavelength VCSEL emitting at 1533.4 nm, and on an 8-GHz MEMS-based VCSEL tuneable over about 70 nm in the C band [2], see Fig.1 a).…”