Josep Prat

Optical network unit based on a bidirectional reflective semiconductor optical amplifier for fiber-to-the-home networks

An optical access network transceiver based on a reflective semiconductor optical amplifier operating as modulator and photodetector is demonstrated. Device characterization and modulation/detection tests show the system proper operation at 1.25 Gb/s to 30-km reach. This optical network unit design is a simple and capable solution for future fiber-to-the-home networks.

Hybrid WDM/TDM PON using the AWG FSR and featuring centralized light generation and dynamic bandwidth allocation

A novel time/space/wavelength division multiplexing (TDM/WDM) architecture using the free spectral range (FSR) periodicity of the arrayed waveguide grating (AWG) is presented. A shared tunable laser and a photoreceiver stack featuring dynamic bandwidth allocation (DBA) and remote modulation are used for transmission and reception. Transmission tests show correct operation at 2.5 Gb/s to a 30-km reach, and network performance calculations using queue modeling demonstrate that a high-bandwidth-demanding application could be deployed on this network.

Integrated IP/WDM routing in GMPLS-based optical networks

Future transport networks will have to cope with the continuous growth of IP traffic. Furthermore, transport networks need to evolve so as to drastically reduce both deployment costs and operating expenses. A reasonable strategy to achieve this goal consists of simplifying the network architecture by reducing the number of layers. Assuming a peer model IP over optical network, we propose an integrated routing strategy that takes into account constraints and dynamic occupancy of both the IP and optical layers. The collaboration of both layers in the routing process leads to optimization of network performance. The main emphasis is on the implementation requirements of this grooming functionality using GMPLS-TE mechanisms. Simulation results show the benefits obtained by applying this strategy.

Roadmap of optical communications

Quantum physics allows one to produce truly random bits. Moreover, it allows one to distribute them in such a way that one can certify their privacy before eventually using them for cryptography applications. Quantum Random Number generators (QRNG) and Quantum Key Distribution (QKD) have found a few niche markets. Today, some commercial clients use QKD continuously 24×7 a week. In this workshop world specialists will talk about reliability tests in quantum networks; about quantum hacking, its importance and limitations, and its role in classical and quantum cryptography; about high rate and about low cost QKD systems; about free space quantum communication; and about future quantum repeaters for continental scale quantum communication.Lightwave communications is a necessity for the information age. Optical links provide enormous bandwidth, and the optical fiber is the only medium that can meet the modern societys needs for transporting massive amounts of data over long distances. Applications range from global high-capacity networks, which constitute the backbone of the internet, to the massively parallel interconnects that provide data connectivity inside datacenters and supercomputers. Optical communications is a diverse and rapidly changing field, where experts in photonics, communications, electronics, and signal processing work side by side to meet the ever-increasing demands for higher capacity, lower cost, and lower energy consumption, while adapting the system design to novel services and technologies. Due to the interdisciplinary nature of this rich research field, Journal of Optics has invited 16 researchers, each a world-leading expert in their respective subfields, to contribute a section to this invited review article, summarizing their views on state-of-the-art and future developments in optical communications.

Investigation of 10-Gb/s RSOA-Based Upstream Transmission in WDM-PONs Utilizing Optical Filtering and Electronic Equalization

Enhanced upstream transmission at 10 Gb/s using a low-bandwidth reflective semiconductor optical amplifier is demonstrated and discussed for extended wavelength- division-multiplexing passive-optical-network applications. Significant improvement in terms of transmission performance is achieved with the use of electronic equalization and optimum filter offset placed at the receiver (optical line terminal) end only. According to filtering detuning, an analytical discussion is presented, explaining the bandwidth enhancement achieved with the proposed technique. The experimental studies consider the benefits of the electronic feed-forward and decision-feedback equalization as well as the required optimum offset optical filtering characteristics.

Scalable Extended Reach PON

Extended reach highly-scalable, fully passive WDM/TDM-PON allows reaching >1000 users along protected 100 km by colorless ONUs, centralized light-generation and control, single-fiber access and remote amplification. ONUs are based on 1.25/2.5/5Gbps-capable RSOA and downstream at 10 Gbps.

Full-duplex single fiber transmission using FSK downstream and IM remote upstream Modulations for fiber-to-the-home

Full-duplex single fiber bidirectional transmission, using frequency-shift-keying modulation for downstream, by direct modulation of a tunable laser, and intensity modulation for upstream, in a wavelength-division-multiplexing passive optical access network is demonstrated. The optical network unit, located at the end user premises, reflects and orthogonally remodulates the received light. Rayleigh scattering effects are reported and analyzed. The system shows proper operation up to 1 Gb/s at 30-km reach.

Reflections and Multiple Rayleigh Backscattering in WDM Single-Fiber Loopback Access Networks

The optical gain of reflective optical network units (ONUs) may produce a critical amplifying feedback on the single-fiber transmission impairments. In this paper, its influence on the passive optical networks transmission with reflective-ONU is theoretically analyzed and experimentally confirmed. Analytical expressions for the optical crosstalk-to-signal ratio and the Q-parameter in presence of Rayleigh backscattering, reflection interferences and ASE noise are given. As a resulting design guideline, the ONU gain should be adjusted to about 3 dB below the total link loss; in addition, component return loss at the drop section must be higher than 30 dB. Experimental results with two basic types of reflective-ONUs, namely a loop structure formed by a Mach-Zehnder modulator and an optical amplifier, and another one employing a reflective-SOA, are in agreement with the theoretical approach.

10 Gb/s full-duplex bidirectional transmission with RSOA-based ONU using detuned optical filtering and decision feedback equalization

Full-duplex bidirectional transmission at 10 Gb/s is demonstrated for extended wavelength division multiplexed passive optical network (WDM-PON) applications, achieving transmission distances up to 25 km of standard single mode fiber (SSMF) when using a low-bandwidth (approximately 1.2 GHz) reflective semiconductor optical amplifier (RSOA) for signal re-modulation at the optical network unit (ONU). The system is assisted by optimum offset filtering at the optical line terminal (OLT)-receiver and the performance is further improved with the use of decision-feedback equalization (DFE). Chromatic dispersion (CD) and Rayleigh Backscattering (RB) effects are considered and analyzed.

Reach Extension Strategies for Passive Optical Networks [Invited]

We present here the main results for reach extension in passive optical network (PON) technologies. Both passive and active architectures integrating several multiplexing techniques are studied, and they provide promising results for the future generation of optical access networks. Extender boxes based on optical amplification and optical-electrical-optical (OEO) repeaters are evaluated over a standardized gigabit PON (GPON) system. With this architecture, the optical budget of a class B+ access network can be increased so as to achieve a total budget of 65 dB. Furthermore, using the technique of remotely pumped optical amplification on a wavelength division multiplexing/time division multiplexing (WDM/TDM) topology, the optical budget of a class C+ PON tree could be increased by an additional 22 dB amounting to a total budget of 55 dB. These results are promising since they should enable high flexibility on the optical budget to achieve more reach and splitting ratio, which are prerequisites needed for the migration to the next-generation access networks.