Ivan Aldaya

Millimeter-Wave Frequency Radio over Fiber Systems: A Survey

In recent years considerable attention has been devoted to the merging of radio frequency and optical fiber technologies aiming to the distribution of millimeter-wave (mm-wave) signals. This effort has given birth to the field of Radio over Fiber (RoF) technologies and systems. This sort of systems have a great potential to support secure, cost-effective, and high-capacity vehicular/mobile/wireless access for the future provisioning of broadband, interactive, and multimedia wireless services. In this paper we present a comprehensive review of mm-wave frequency RoF systems. In our integral approach, we identified the most important figures of merit of an RoF system, which is divided into three main subsystems: Central Station (CS), Optical Distribution Network (ODN) and Base Station (BS). In each subsystem, the most promising technologies are classified: downlink transmission techniques at the CS, ODN architectures, and optical configurations of the BS. The impact of technology choice on the overall system performance is discussed, and the figures of merit are studied and used to assess the subsystems performance. Finally, we suggest technological opportunities and future developments that should be attracting the attention of researchers and developers.

Artificial Neural Network Nonlinear Equalizer for Coherent Optical OFDM

We propose a novel low-complexity artificial neural network (ANN)-based nonlinear equalizer (NLE) for coherent optical orthogonal frequency-division multiplexing (CO-OFDM) and compare it with the recent inverse Volterra-series transfer function (IVSTF)-based NLE over up to 1000 km of uncompensated links. Demonstration of ANN-NLE at 80-Gb/s CO-OFDM using 16-quadrature amplitude modulation reveals a Q -factor improvement after 1000-km transmission of 3 and 1 dB with respect to the linear equalization and IVSTF-NLE, respectively.

Volterra-Based Reconfigurable Nonlinear Equalizer for Coherent OFDM

A reconfigurable nonlinear equalizer (RNLE) based on inverse Volterra series transfer function is proposed for dual-polarization (DP) and multiband coherent optical orthogonal frequency-division multiplexing (OFDM) signals. It is shown that the RNLE outperforms by 2 dB the linear equalization in a 260-Gb/s DP-OFDM system at 1500 km. The RNLE improves the tolerance to inter/intraband nonlinearities, being independent on polarization tributaries, modulation format, signal bit rate, subcarrier number, and distance.

Nondegenerate Four-Wave Mixing in a Dual-Mode Injection-Locked InAs/InP(100) Nanostructure Laser

The nondegenerate four-wave mixing (NDFWM) characteristics in a quantum-dot Fabry-Perot laser are investigated, employing the dual-mode injection-locking technique. The solitary laser features two lasing peaks, which provides the possibility for efficient FWM generation. Under optical injection, the NDFWM is operated up to a detuning range of 1.7 THz with a low injection ratio of 0.42. The normalized conversion efficiency (NCE) and the side-mode suppression ratio (SMSR) with respect to the converted signal are analyzed. The highest NCE of -17 dB associated with a SMSR of 20.3 dB is achieved at detuning of 110 GHz.

Optical switch emulation in programmable software router testbed

A programmable optical router is a key enabler for dynamic service provisioning in Future Internet scenarios. It is equipped with optical switching hardware to forward information at hundreds of Gigabits/s rates and above, controlled and managed through modular and flexible procedures according to emerging standards. The possibility to test such costly optical architectures in terms of logical and physical performance, without implementing complex and expensive testbeds, is crucial to speed-up the development process of high-performance routers. To this purpose, this paper introduces the software-based emulation testbed of a programmable optical router, which is here developed and applied to test optical switching fabrics. Accurate characterization of the optical devices and physical layer aspects is implemented with the Click software router environment. Power loss and optical signal-to-noise-ratio evaluation are provided through accurate software representation of the physical characteristics of the optical devices employed. The scalability of the proposed emulation testbed is also assessed on standard PC hardware. All the obtained results prove the effectiveness of the proposed tool to emulate an optical router at different levels of granularity.

Novel cost-effective PON-to-RoF photonic bridge for multigigabit access networks.

Telecommunication operators are investing significant resources in developing passive optical networks (PONs) to meet the increasing capacity requirements. Therefore, wireless transmission has become the bottleneck for the wireless broadband internet access due to the spectrum saturation. This issue can be solved taking advantage of the huge portions of unused spectrum at high-microwave / millimeter-wave (mm-wave) bands, but their generation is power consuming. Radio over fiber (RoF) is a cost-efficient solution for the distribution of high-frequency broadband signals to remote base stations. We present a novel photonic PON-to-RoF bridge based on heterodyning a PON signal with an unmodulated tone generated by an independent laser. The proposed scheme is transparent to modulation format and can generate RF signals in the entire microwave band. The feasibility of the bridge is experimentally shown converting a 2-Gbps orthogonal frequency division multiplexing PON signal using inexepensive distributed feedback lasers, whose phase noise is cancelled employing an envelope detection based mobile terminal.

Phase-Insensitive RF Envelope Detection Allows Optical Heterodyning of MHz-Linewidth Signals

We demonstrate the insensitivity of the envelope detection based mobile terminal to phase fluctuations of the RF signal. This property enables the generation of radio over fiber (RoF) signals heterodyning non-narrow linewidth laser signals and using direct modulation. We report the experimental generation of up to 2-Gb/s orthogonal frequency division multiplexing (OFDM) signals and their transmission over a 25-km long fiber span using direct modulation and DFB lasers with a combined linewidth of 2.1 MHz with a resulting BER below 10-3.

Performance of digital modulation formats in radio over fiber systems based on the sideband injection locking technique

Given the technical feasibility of the sideband injection locking technique for optical remote generation and control of RF signals, a performance and channel capacity study of different digital modulations formats is presented. Actual wireless networks, e.g. 3G and WiMax, and future, LTE-4G networks will require optical interconnection of base stations to cope with increasing capacity demands. More interestingly, higher frequency ISM bands, in the 30-70 GHz range, require low-cost base stations that can readily benefit from Radio over Fiber technologies. The flexibility of the technique is established and its performance assessed by simulations performed in the Virtual Photonics platform. Both, Orthogonal Frequency Division Multiplexing and Subcarrier Multiplex show promise in optimizing capacity, performance and flexibility.

Nonlinear carrier dynamics in silicon nano-waveguides

The understanding of free-carrier dynamics in silicon photonic nano-waveguides and micro-cavities is fundamental to several nonlinear optical phenomena. Through time-resolved pump and probe experiments, a complex and nonlinear carrier recombination dynamics is revealed. Our results show that the carrier lifetime varies as the recombination evolves, with faster decay rates at the initial stages (with lifetime of ∼800  ps) and much slower lifetimes at later stages (up to ∼300  ns). The large surface-to-volume ratio in nano-waveguides enables clear observation of the effect of carrier trapping, manifesting as a decay curve that is highly dependent on the initial carrier density. Further, we demonstrate faster recombination rates by operating at high carrier density. Our results, along with a theoretical framework based on trap-assisted recombination statistics applied to nano-waveguides, can impact the dynamics of several nonlinear nanophotonic devices in which free carriers play a critical role, and open further opportunities to enhance the performance of all-optical silicon-based devices.

Experimental comparison of artificial neural network and volterra based nonlinear equalization for CO-OFDM

A novel artificial neural network (ANN)-based nonlinear equalizer (NLE) of low complexity is demonstrated for 40-Gb/s CO-OFDM at 2000 km, revealing ~1.5 dB enhancement in Q-factor compared to inverse Volterra-series transfer function based NLE.