Search

Internet-generated traffic growth is forcing the development of new low-cost solutions in metropolitan area networks (MANs), in particular in the transceiver and network node architectures. Semiconductor optical amplifier (SOA)-based wavelength blockers can be used as fundamental building blocks to add and drop optical channels in the node architecture of several network hierarchical levels. Even if its employment is advantageous in terms of costs and amplification bandwidth, the SOA can operate in a nonlinear regime. This work analyzes the impact of SOA-based node crossing on high-capacity discrete multitone (DMT) signals. In order to properly evaluate the interplay between optical channels and SOA self-gain modulation, both external and direct modulations are considered. Dual-sideband (DSB) and single-sideband (SSB) DMT variants are taken into account, showing no significant difference in the impact of SOA crossing for external modulation of a DFB laser. On the other hand, an important effect of subcarrier suppression arises on DSB DMT direct modulation of a vertical cavity surface emitting laser (VCSEL), less consistent for SSB DMT direct modulation. The analysis allowed to properly choose the bias current for the SOA employed in an experimental setup used to evaluate the transmission performance in a MAN scenario including add-drop lossless switch nodes. The experimental results demonstrate that a target capacity of more than 50 Gb/s per channel can be achieved in a 116-km MAN network composed of an SOA-based metro-access node and two metro-core aggregators, considering the transmission of three 25-GHzspaced DMT channels. [ABSTRACT FROM AUTHOR]

Spatial division multiplexing (SDM) can support the capacity demand increase in short-range optical link, but the communication is affected by the intermodal crosstalk. In order to target a low-cost energy-efficient solution, we propose to exploit direct modulation and direct detection without MIMO post-processing in a mode division multiplexed (MDM) system. We theoretically analyze the frequency distribution of the crosstalk contributions taking into account that directly modulated sources at the same nominal wavelength are actually characterized by a certain frequency shift. Our model demonstrates that this shift originates a non-uniform beating noise in the frequency domain due to the intermodal crosstalk. We propose to exploit discrete multitone modulation and a guard band in the multicarrier spectrum to cope with the non-uniform crosstalk issue for typical crosstalk values due to present commercial multi-plane light conversion MUX/DEMUX devices and propagation in few few-mode fiber (FMF) kilometers. The model is validated by comparing simulations and experimental results in the case of a 2-mode MDM system. We demonstrate in a pure SDM scenario that, with respect to single mode transmission, the capacity can be increased of 2.3 times in a 10-km FMF link with 4-modes exploiting direct detection, limited-bandwidth directly modulated lasers and commercial mode MUX/DEMUXs. [ABSTRACT FROM AUTHOR]

Pulse width modulation (PWM) can support centralized radio access networks in analog optical fronthaul, avoiding the bandwidth expansion of the digital fronthaul. The PWM encodes the analog samples at the transmitter onto the duration of the on-off-keyed optical signal, splitting the sampling and quantization of the radio signal between remote radio units (RRUs) and baseband units (BBU). In-between the PWM encoded signal is transmitted over a novel wavelength-division-multiplexed passive optical network (WDM PON) architecture, exploiting broadband-seeded reflective semiconductor optical amplifiers in a polarization retracing circuit, which is resilient to Rayleigh scattering impairments. Multiple RRU-to-BBU links are supported through virtual point-to-point connections based on the wavelength resource. We demonstrate the performance of the proposed PWM-based colorless self-tuning WDM PON supporting the fronthaul of 100-MHz RF signals up to 20-km transmission over standard single mode fiber for 30 WDM channels. [ABSTRACT FROM PUBLISHER]

The self-seeded cavity appeared in the last few years as a colorless and low cost solution for wavelength division multiplexing access. Although the self-seeded source presents a simple architecture, its behavior has been misunderstood for a long time. In this paper, we explain its operating principles and why we can define such a source as a laser. We evidence a laser threshold and show cavity modes for various lengths. We describe the conditions required by the reflective semiconductor optical amplifier to sustain the self-seeded cavity, by evaluating the choice of its epitaxial structure and the influence of its optical confinement factor. An analysis of the cavity behavior is given, pointing out that the relative intensity noise results from the beating noise between the cavity modes. An overview over the last performances in the C- as well as in the O-band is then presented. Some practical applications are reported. In particular, we detail the mobile front-haul as a possible employment for the self-seeded cavity to achieve a self-organized wavelength network. [ABSTRACT FROM PUBLISHER]

Reflective semiconductor optical amplifier fiber cavity lasers (RSOA-FCLs) are appealing, colorless, self-seeded, self-tuning and cost-efficient upstream transmitters. They are of interest for wavelength division multiplexed passive optical networks (WDM-PONs) based links. In this paper, we compare RSOA-FCLs with alternative colorless sources, namely the amplified spontaneous emission (ASE) spectrum-sliced and the externally seeded RSOAs. We compare the differences in output power, signal-to-noise ratio (SNR), relative intensity noise (RIN), frequency response and transmission characteristics of these three sources. It is shown that an RSOA-FCL offers a higher output power over an ASE spectrum-sliced source with SNR, RIN and frequency response characteristics halfway between an ASE spectrum-sliced and a more expensive externally seeded RSOA. The results show that the RSOA-FCL is a cost-efficient WDM-PON upstream source, borrowing simplicity and cost-efficiency from ASE spectrum slicing with characteristics that are, in many instances, good enough to perform short-haul transmission. To substantiate our statement and to quantitatively compare the potential of the three schemes, we perform data transmission experiments at 5 and 10 Gbit/s. [ABSTRACT FROM AUTHOR]

We propose a network-embedded colorless self-tuning transmitter for wavelength division multiplexed (WDM) networks based on self-seeding in reflective semiconductor optical amplifiers (RSOAs). We compare up to a 10-Gb/s data rate in either O-band or C-band operation. In particular, the transmitter exploits a two-Faraday rotator configuration to ensure polarization-insensitive operation and allowing for the exploitation of high-gain C- and O-band RSOAs, which present a very high polarization- dependent gain. Two different multiplexers and various lengths of drop fibers constituted the networkembedded transmitters in order to evaluate various dispersion load influence on cavity buildup. Moreover, transmission over standard single-mode feeder fiber has been evaluated both at 2.5 and 10 Gb/s to compare the performance in both bands, confirming the absence of chromatic dispersion penalties for the O-band operation. [ABSTRACT FROM PUBLISHER]

Operation of a network-embedded colorless self-tuning transmitter for wavelength division multiplexing (WDM) networks is experimentally demonstrated at 10-Gb/s data rate. Colorless operation is achieved by self-seeding an O-band reflective semiconductor optical amplifier (RSOA) with the feedback signal reflected at the remote node WDM multiplexer filter. In particular, the transmitter exploits a 2-Faraday rotators configuration to ensure polarization insensitive operation and allowing for the exploitation of high gain O-band RSOAs, which present a very high polarization dependent gain. Two different multiplexers and various lengths of drop fibers constituted the network-embedded transmitters. Transmission up to 72 km of standard single mode fiber has been demonstrated at 10 Gb/s, confirming the absence of chromatic dispersion penalties as expected from the choice of the O-band operation. [ABSTRACT FROM PUBLISHER]

The operation of a network-embedded colorless self-tuning transmitter for WDM networks is experimentally demonstrated from 2.5- up to 10.7-Gb/s data rates. Colorless operation is achieved by self-seeding an ultra-fast reflective semiconductor optical amplifier (RSOA) with the feedback signal reflected at the WDM multiplexer filter. In particular, the transmitter exploits a 2-Faraday rotators configuration to ensure polarization insensitive operation and allowing for the exploitation of high gain RSOAs, which can be designed to operate on a single polarization. The impact on the transmission of the fiber chromatic dispersion at different bit-rates and with different channel bandwidths of the WDM multiplexer filter is experimentally investigated up to 10.7 Gb/s. The tolerance to positive and negative dispersive loads is also assessed. [ABSTRACT FROM PUBLISHER]

The evolution of radio access networks is towards a centralized architecture (C-RAN), with massive antenna deployments and large radio-frequency bandwidths. In the next future, traditional optical transport technologies based on digital radio over fiber will no longer be able to support the mobile fronthaul traffic connecting antennas hosted at remote radio units and centralized baseband units. Analog radio over fiber can be selected to support the mobile fronthaul (MFH) network and, in particular, pulse width modulation (PWM) is a viable alternative for analog signal transport. In order to increase the MFH spectral efficiency, we propose to exploit multilevel PWM (M-PWM) in a wavelength division multiplexing-passive optical network (WDM-PON) network, comparing its performance with a conventional 2-level PWM solution. Experimental results show successful transmission over 7.5-km standard single mode fiber (SSMF) of up to 16 aggregated LTE-like 20-MHz signals with 64-QAM on each subcarrier, while up to eight aggregated LTE-like 20-MHz signals with 256-QAM could be supported. M-PWM thus allows either using higher order modulation formats or aggregating a higher number of LTE channels. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We present a 20 Gb/s return-to-zero differential quadrature phase-shift keying transmission over a 2000 km in a 33 GHz spaced 64-channel dense-WDM system. Successful transmission is demonstrated in a laboratory straight line, designed for standard intensity-modulated submarine systems. [Copyright &y& Elsevier]