The Optical Networks and Systems Laboratory is equipped with appropriate facilities for the experimental activities mainly conducted within the common framework provided by ADRENALINE testbed ®. Thereby, it is possible to evaluate the service levels seen by the client layers of an optical infrastructure of a dynamic wavelength switched optical network (WSON), in order to obtain meaningful performance data (e.g., packet loss, delay, BER). To this end, dedicated broadband testing equipment can be configured to generate and correlate a wide range of optical client interfaces. In the ONS laboratory, there is dedicated optical network test and measurement equipment, with features such as IP traffic generation and analysis over 10/100 Ethernet, Gigabit Ethernet (GigE) and STM-16 interfaces, or GigE plus 10GBit interfaces, with GMPLS/MPLS network emulation and protocol testing.
Physical layer degradations can be modelled, measured and quantified with optical communication test and measurement equipment also available in the laboratory (Fig. 1), such as a communications signal analyzer (up to 20 GSa/s, with 4 GHz bandwidth, provided with optical and electrical inputs), a digital sampling oscilloscope (up to 13.5 Gb/s with 9 GHz optical/20 GHz electrical sampling module), an optical spectrum analyzer (with dense wavelength division multiplexing analysis, DWDM, for a wavelength range between 600 and 1750 nm), various tunable laser sources (covering S+C+L bands, some of them with low linewidth <100 KHz, providing up to 13 dBm output power), a dual wavelength laser light source (of 1310 and/or 1550 nm), a portable optical time-domain reflectometer (OTDR, with two wavelengths of 1310 nm and 1550 nm), a high-performance optical multimeter (with variable optical attenuator and high power sensor modules), some optical power meters (for 850, 1300, 1310, 1490, and 1550 nm), a polarization scrambler, polarization mode dispersion (PMD, using the interferometric method) and chromatic dispersion (CD, using phase-shift method) analyzers, a broadband source (C and L bands, useful as a PMD/CD analyzer source), and a fixed PMD emulator (1, 5 and 10 ps). Belonging to this category, there is additional equipment in the laboratory intended for the development of an Experimental platform for Optical OFDM Systems (EOS), within the ADRENALINE testbed®: on one hand, an arbitrary waveform generator (up to 24 GSa/s, 9.6 GHz effective RF frequency output, and 7.5 GHz analog bandwidth) provides an analog signal (from a digital one) to be modulated and transmitted on an optical link; on the other hand, the received signal is photo-detected and amplified by 18+ GHz InGaAs PIN photo-receivers (lab-Buddy bench-tops, with 0.55 A/W responsivity at 1550 nm). Finally, the signal is electrically captured, sampled and post-processed by a real-time digital phosphor oscilloscope (up to 100 GSa/s, 20 GHz bandwidth). Off-line DSP at transmitter/receiver is performed by software codes (e.g. Matlab or Python) running on 2xIntel Xeon E5-2603 Quad-64GB platform, which is connected to the instruments through TCP/IP sockets. Two bench-top Erbium-doped fiber amplifiers (EDFAs) for DWDM multichannel (covering C-band, with output power up to +23 dBm and nominal Gain of 30 dB) are available for amplification at transmitter/receiver sides, and two programmable optical filters based on high resolution liquid crystal on Silicon technology (LCoS, with arbitrary filter shape, control of filter dispersion, and filter bandwidth variable from 10 GHz to 5 THz, covering C+L bands) can be placed in the transmitter/receiver for the configuration of flexi-grid links. One of those filters is provided with 1×4 ports, being usable as a wavelength selective switch (WSS) in order to aggregate/distribute multiple flows.
Figure 1. Optical communication test and measurement equipment
In addition, EOS platform also integrates several optical, electro-optical and electrical devices necessary to implement different schemes of both transmitter and receiver subsystems, including proof-of-concept on sliceability (i.e, multiple flows): a LiNbO3 Mach-Zehnder modulator (MZM) with RF driver (both up to 40 GHz) to generate the optical signal for intensity modulation (IM) schemes with direct detection (DD), another LiNbO3 MZM usable up to 40 GHz with low Vpi and ultra linear RF driver (50 GHz), a LiNbO3 phase modulator (up to 12 GHz bandwidth for constant envelope, CE, schemes), a nested I/Q MZM (based on GaAs, for advanced 40 Gb/s DQPSK transmission) with ultra linear RF drivers (up to 40 GHz) as depicted in Fig. 2 (left), an ultrafast InGaAs PIN photo-detector (50 GHz bandwidth, loaded with 50 ?, and 0.6 A/W of responsivity), some RF amplifiers (24 dB of Gain, up to 20 GHz) to adapt the power of the RF signal wherein they are needed, four pairs of waveguide-integrated photo-detectors on a single chip connected as balanced detectors (with 42 GHz bandwidth and 0.6 A/W at 1550 nm) for coherent (CO) receivers, a 90º optical hybrid with two single polarization (enabling to extract phase, amplitude and polarization from a signal with any polarization) also for CO receivers, and two athermal arrayed waveguide gratings (AWGs, with 40 Gaussian channels of 100GHz) for the transmission of multiple flows aggregated in sliceable bandwidth variable transponders (S-BVTs) and noise filtering at reception side. A four-channel digital-to-analog converter (DAC) with up to 65 GSa/s and >13 GHz bandwidth (Figure 2, right) was achieved for EOS platform, in order to implement (S)-BVT with much higher performance. By using additional devices also available, such as, double-balanced mixers (IF up to 10 GHz, LO/RF from 9 to 20 GHz), a 2 way-0º power splitter (up to 18 GHz) and a voltage controlled oscillator (VCO, up to 20 GHz), it is possible to implement RF up-conversion/down-conversion stages within the transmitter/receiver respectively. Recently, a single-stage EDFA Gain Block (Fig. 3, left) was acquired to provide a flattened gain spectrum at the output/input of the sliceable transmitter/receiver prototype with low Noise Figure (NF) for C-Band. It can be programmed with two different configurations, with a Gain range between 15 and 30 dB (PreAmp) or 25 dB (Booster), and 20 dBm of saturation power at least.
Figure 2. Nested I/Q MZM with RF Drivers (left). DAC with 65 GSa/s and >13 GHz (right)
Design, development and assembly of hardware for new opto-electronic subsystems (Fig. 3, right) is possible thanks to several facilities, such as, printed circuit board (PCB) designer software (for schematics and layouts, including integration with manufacturing output tools), FPGA simulation and synthesis software, dual (up to 20V) and triple (up to 30V, with tracking function) DC Power supplies, a DC+AC RMS multimeter (able to perform frequency, capacitance, duty cycle and pulse width measurements), and other devices that are accessible: soldering irons, microscopes, a circuit board plotter suitable for producing PCB prototypes (0.1 mm of minimum conductor width and interval), a natural convection oven for drying and sterilizing (up to 250 ºC), and a CeNeCe milling machine suitable for making front and rear panels of prototypes (with resolution of 0.01 mm). Moreover, the floor of the ONS laboratory is certified with an electrostatic behavior of Conductive, so it drains electrostatic charges deposited on it to ground, in order to avoid electrostatic discharge when handling hardware components. In the laboratory, there are different types of components for grounding, providing ESD protection: grounding mats, adjustable wriststrap sets, heel grounders and Earth bonding plugs.
Figure 3. PreAmp/Booster EDFA module (left). Developed and assembled prototype for ADRENALINE Testbed® (right)
Optical passive components and fiber-optic inspection devices are suitable for making measurements and experiments that involve the use of test and measurement equipment or hardware design and development facilities, and for the EOS platform development: a mini video microscope with camera and TFT display can be found, also a precision fiber cleaver (for fibers between 80 and 200 µm), or several fiber-optic adapters (simplex and duplex, for different kinds of connectors), attenuators (different kinds, from 1 to 15 dB), several fiber-optic patch cords (1,2, 3, 5 or 10 m, also terminated with different kinds of connectors), different 1×2 SM optical couplers (ratio equal to 50/50, 10/90 or 5/95), two 45º Faraday rotators (in-line, from PMF to PMF), four Polarization Controllers (PC), and two Polarization Beam Splitters/Combiners (PBS/PBC). Furthermore, three standard G652 SM fiber-optic spools are available (10, 25 and 50 Km, all with 0.19 dB/Km of attenuation), in order to evaluate the transmission over different distances. In the same way, several RF Components are also available: 50? cable assemblies with different lengths (up to 1.5 m), material characteristics (hand-formable, semi-rigid or flexible), frequency range (from DC to 12.4, 13, 18, 26.5, 40 and 65 GHz), and with different terminations (SMA, SMP, V, GPPO, etc.). There are also several RF adapters (SMA, V or K interfaces) up to 40 GHz, RF attenuators (from 3 to 20 dB, with frequency range either up to 18 GHz or up to 26 GHz), loads (50 ?), DC-blocks and different low-pass filters (from DC to either 5 GHz or 7.2 GHz). Additionally, test and measurement cables (red and black with different terminations) can be used for providing electrical connections throughout the experiments.
The following simulation software facilities are also available: VPI photonics provides design and analysis of optical transmission systems, by means of electrical and optical basic modules (e.g. transmitters, modulators, receivers, amplifiers, filters or fibers). This software also includes network elements, signal processing and math functions. OPNET tools are usable for the design and analysis of different communication networks, devices, protocols and applications. There are hundreds of protocols and vendor device models with source code included.
Software applications are designed and developed on the requirements of researchers. The ONS department has strong knowledge of C/C++ (C99 / c++11), including standard, Boost and Qt libraries, proved by the expertise in developing GNU/Linux system and applications. Software development team also uses Perl, Python and Java. The servers include all necessary services for software development: bugtracking, version control (subversion), Fully Automated Linux, drupal and phpBB for web-based services. Several development methodologies have been successfully applied, such as Waterfall, V-Model or Agile.
At the beginning of 2015, the room 0.02 of CTTC B4 building was refurbished and integrated with the former installations (i.e., rooms 0.03-0.04) of the ONS laboratory. The new room provides much more space for the storage and operation of sensitive components and equipment, and it includes the appropriate facilities for the development, implementation and experimental evaluation of different optical transmission subsystems, ensuring reliability and security. The floor carpet is also conductive and grounded, and some elements provide ESD protection along the different work benches. Furthermore, in the middle of the new room a 2.5m x 1.5m all-steel optical table (Fig. 4, left) was acquired and installed; its surface is mechanized with M6 x 1.0 mounting holes; and the four legs feature closed pneumatic isolation system and passive vertical vibration isolating supports, with 22 dB of vertical transmissibility at resonance, and 74% of isolation efficiency at 10 Hz. Besides the vibration isolation, the optical table provides secure-fixing of devices/components and a good thermal conductivity. Finally, the new room is connected, from two different locations, to the ADRENALINE testbed ® racks (i.e., rooms 0.03-0.04) by means of two underground technical optical links, each consisting of several single-mode patch cords connected between a pair of fiber-optic patch panels (Fig. 4, right). This makes possible the experimental validation and performance evaluation of the implemented transmission subsystems over the WSON of ADRENALINE.
Figure 4. New room with optical table (left). Fiber-optic patch panel on the optical table shelf (right)