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High-Speed Optical Network Subsystems Print
The application notes listed below are the result of the Joint Experimental Activities performed by the 17 members of EURO-FOS consortium and Network, during the 4 years of the duration of the project. They formulate an extremely useful source of on-hands information and consolidated laboratory know-how to the researchers in the domain of photonics communications.

Contributing Institutions: ICCS/NTUA
Summary: The basic theory of Bragg-gratings is described through mathematical relations and indicative transmission/reflection spectra. Instructions for preparing an efficient testbed (probe-station) for the characterization of integrated Bragg-grating structures are provided. Further instructions for characterizing and monitoring the wavelength-tunability of the (polymer) Bragg-gratings are also given.
Contributing Institutions: IT, ICCS/NTUA, TU/e
Summary: This is an Application Note resulting from the JEA2.16 Mobility Action: Applications of All-Optical Flip-Flops. The objective was to study and to implement an all?optical clocked D flip?flop based on a hybrid integrated S-R latch and two additional Mach-Zehnder interferometer structures with Semiconductor Optical Amplifiers (MZI-SOA) acting as AND logic gates. We also needed to realize a NOT gate using a semiconductor optical amplifier (SOA). This technology allows reduced rise and fall times (hundreds of ps), high output extinction ratios and enables further photonic integration capability In this application note the following topics are addressed:

I.   Introduction to all-optical flip-flops

II.  All-Optical Clocked D Flip-Flop  

Contributing Institutions: IT, NTUA, TU/e, INSTITUT TELECOM, SSSUP
Summary: This activity aims to design an all-optical router since, with the ever-increasing demand of data communication, is desirable that switching and routing can be carried out in the physical layer to keep the efficiency of the network and to allow high data bit rates. In an optical packet switching (OPS) network, traffic is sent to the optical network without any coordination among transmitter edge switches. Then, when multiple packets arrive for the same output link of an OPS core switch, at the same time, they may contend. In general, collision is the major problem for an OPS network. In this JEA, all optical flip?flops will be also investigated, continuing the work started in JEA 2.16: Applications of all?optical flip?flops. All?optical flip-flops have become a very important issue of optical processing of digital information and can be used in threshold functions, 2R and 3R regeneration, demultiplexing and rate conversion of telecommunication data, and temporary storage of decisions made on telecommunication data packets.
Contributing Institutions: IT
Summary: The objective of this application note is to describe an experimental methodology to implement all-optical clocked D and S-R flip-flops, with a higher priority input (clock), responsible for making the device sensitive or not to the values present at its inputs. The presented optical clocked flip- flops are based on hybrid-integrated Mach-Zehnder interferometers with nonlinear SOAs and phase shifters assembled in each interferometer arm (MZI-SOA). 
Contributing Institutions: ICCS/NTUA
Summary: The current application note describes the standard procedure for estimating the losses of Silicon-on-Insulator (SOI) grating couplers. A SOI chip equipped with a cutback section as well as several straight waveguides is employed for the characterization process. The accurate estimation of the grating coupler loss is based on a step-wise methodology that includes the definition of the optimum incident beam angle, the estimation of the waveguide propagation losses and the measurement of the gratings’ spectral response. Finally, a table with the characterization results is presented together with a useful conclusion about unexpected propagation losses that are imposed by the cutback section.
Contributing Institutions: ICCS/NTUA, ParisTech
Summary: The main principles of the Direct-sequence optical code-division multiple-access (DS-OCDMA) encoder/decoder based on Superstructured Fiber Bragg Gratings (SS-FBGs) are presented. The well?matching of the SS-FBG correlators is explored taking account all the practical issues that are exhibited at the real experimental studies. The steps that are followed in order to obtain the desirable auto- and cross­-correlation functions are described. The experimental characterization results are demonstrated giving a sufficient point of view to the aforementioned processes. Finally, some practical system­?level approaches that are relied on the well-matching process are discussed in order to extend the view and the targets of this procedure.  
Contributing Institutions: ICCS/NTUA
Summary: The current application note describes briefly the theory behind the SOA-based wavelength conversion and the recovery time acceleration of the SOA with the chirp filtering teching. It also focuses on the clarification of some practical issues and common practices which are useful for relevant experiments.
Contributing Institutions: Scuola Sant'Anna (SSSUP), Universidad Politecnica de Valencia (UPVLC).
Summary: This Application Note describes how a sample of Single-­Walled Carbon Nanotubes (CNT) on a tapered standard single mode fibre (SMF) can be tested to assess its insertion loss, transmittance, absorptance, Kerr nonlinearity and saturable absorption (SA).
Contributing Institutions: Tyndall National Institute, University College Cork
Summary: This application note presents a technique to achieve real-time sampling of amplitude, phase and  alpha factor in nonlinear optical devices such as semiconductor optical amplifiers, electroabsorption  modulators (EAMs), silicon waveguides, etc. The nonlinear device-under-test (DUT) is placed inside a TOAD interferometric loop, both pump and probe pulses are injected into the loop and the output  from the loop at the probe wavelength is detected using photodiodes. The pump and probe sources  are mode-locked lasers (MLLs) that emit pulse trains with pulse-widths of 3ps at a repetition rate of  10.65GHz. The probe pulse train is temporally scanned through the pump pulse train to enable  observation of the DUT’s response to optical excitation [1, 2].
Contributing Institutions: UEssex
Summary: We propose and experimentally demonstrate simultaneous format and wavelength conversion of multiple fragmented signals suitable for gridless and multi-granular networks. Conversion of NRZ and large-RZ to short-RZ-OOK by means of a single commercial Quad SOA-MZI is demonstrated for grooming 85.4 Gb/s frame. The output RZ?OOK signal is suitable for further tributary multiplexing onto a 170.8 Gb/s OTDM stream. The resultant OTDM channel is transmitted over a 110 km dark fiber link.
Contributing Institutions: IT
Summary: The characteristics of MZI-SOAs with hybrid integration are affected by their internal design yields and asymmetries. This application note describes an experimental methodology to characterize active and passive internal components, such as phase shifters, SOAs and couplers. Real measurement results are presented so as to provide an example or reference: operational parameters are extracted from output powers only, using static operational conditions. Moreover, we explain a simple process to find the optimum SOAs bias point in order to maximize the power extinction ration between output ports.
Contributing Institutions: IT
Summary: The objective of this application note is to describe how to balance a Mach-Zehnder Interferometer with Semiconductor Optical Amplifiers (MZI-SOA) in each MZI arm. When we are using MZI-SOA structures it is very important to balance the interferometer before implementing the desired setup. The MZI-SOA is balanced when a maximum extinction ratio (ER) between the interferometer output ports is achieved.
Contributing Institutions: IT, TU/e, NTUA, Institut Telecom, SSSUP, UPVLC
Summary: This is an Application Note resulting from the JEA4.10 Mobility Action: All-optical packet routing. The objective is to demonstrate how an all-optical packet routing scheme works, with a contention resolution circuit. 
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