The traffic carried by core optical networks grows at a steady but remarkable pace of 30-40% year-over-year. Optical transmissions and networking advancements continue to satisfy the traffic requirements by delivering the content over the network infrastructure in a cost and energy efficient manner. Such core optical networks serve the information traffic demands in a dynamic way, in response to requirements for shifting of traffics demands, both temporally (day/night) and spatially (business district/residential). However as we are approaching fundamental spectral efficiency limits of singlemode fibers, the scientific community is pursuing recently the development of an innovative, all-optical network architecture introducing the spatial degree of freedom when designing/operating future transport networks. Spacedivision- multiplexing through the use of bundled single mode fibers, and/or multi-core fibers and/or few-mode fibers can offer up to 100-fold capacity increase in future optical networks. The EU INSPACE project is working on the development of a complete spatial-spectral flexible optical networking solution, offering the network ultra-high capacity, flexibility and energy efficiency required to meet the challenges of delivering exponentially growing traffic demands in the internet over the next twenty years. In this paper we will present the motivation and main research activities of the INSPACE consortium towards the realization of the overall project solution.
This paper will review the current understanding of the so called nonlinear Shannon limit, and will speculate on methods
to approach the limit through new system configurations, and increase the limit using new optical fibres.
In this paper, we report for the first time the detection of a Cy5-labelled DNA probe immobilised within a 3D hydrogel
matrix formed, inside a hollow core Photonic Crystal Fibre (HC-PCF). We show both the sensitivity of fluorescence
detection inside the HC-PCF using a supercontinuum light source and of the variation of the luminescence intensity with
the concentration DNA probe within the hydrogel. The 3D hydrogel matrix is a network of polymer chains, which is
expected to provide highly sensitive detection and selection of bio-molecules, in comparison with 2D coverage. The
biocompatibility of hydrogel in the HC-PCF suggests numerous applications associated with immobilised DNA probe
detection for point-of-care or remote systems.
The ratio (ζ) of surface tension to viscosity of liquids can be determined using hollow core photonic crystal fibres (HCPCF),
and we show here techniques to determine ζ of glucose levels within fluids, of nano-litre quantities. We
demonstrate an optically integrated micro-capillary viscometer, to determine the concentrations of nano-litre solutions
based on properties of their flow within HC-PCF. The filling of the fibres with liquids within a given range of refractive
index will induce a shift in the photonic band gap of the fibre, allowing guidance of light at wavelengths that were
originally outside the bandgap of the HC-PCF.
A regenerative optical grooming switch for interconnecting 100 Gbit/s networks with lower bit-rate networks and
switching functionality in time, space and wavelength domain is demonstrated. Lab and field demonstrations show the
feasibility of the new concept. Q-factors above 20 dB are reported.
We investigate the pattern-dependent decoding failures that occur with electronic dispersion compensation (EDC) when
using full optical-field reconstruction, and find that the performance of such an EDC receiver may be degraded by an
isolated '1' bit surrounded by long strings of consecutive '0's. By reducing the probability of occurrence of this kind of
isolated '1', we experimentally achieved 10Gbit/s on-off keyed signal transmission over 372km field-installed singlemode
fiber without optical dispersion compensation.
Many approaches to achieving high information spectral density (ISD), have been reported recently. The standard non-return-to-zero (NRZ) format, which offers a base line performance around 0.4 bit/s/Hz, may be enhanced using a variety of techniques, including: pre-filtering within the transmitter, multi-level modulation formats and polarisation interleaving or multiplexing. These techniques either increase the information per channel (multi-level formats and polarization multiplexing) or minimise interferometric cross talk (pre-filtering and polarisation interleaving) and result in ISDs around 0.8 bit/s/Hz. Combinations of these techniques have been used to provide ISDs of up to 1.6 bit/s/Hz. In this paper we propose a new technique, which we call Coherent WDM (CoWDM), to increase the ISD of NRZ binary coded signals in a single polarisation from 0.4 to 1 bit/s/Hz whilst simultaneously eliminating the need for pre-filters within the transmitter. Phase control within the transmitter is used to achieve precise control of interferometric cross talk. This allows the use of stronger demultiplexing filters at the receiver, and provides optimum performance when the bit rate equals the channel spacing, giving an ISD of 1 bit/s/Hz. This interference control may be achieved by controlling the phase of each laser individually with optical phase locked loops, or by replacing the typical bank of lasers with one or more coherent comb sources, and encoding data using an array of modulators that preserves this relative optical phase. Since optical filtering is not required in the transmitter, stronger optical filters may be used to demultiplex the individual WDM channels at the receiver, further reducing cross talk.
Multi-wavelength sources are required for wavelength division multiplexed (WDM) optical communication systems, and typically a bank of DFB lasers is used. However, large costs are involved to provide wavelength selected sources and high precision wavelength lockers. Optical comb generation is attractive solution, minimizing the component count and improving wavelength stability. In addition, comb generation offers the potential for new WDM architectures, such as coherent WDM, as it preserves the phase relation between the generated channels. Complex comb generation systems have been introduced in the past, using fibre ring lasers  or non-linear effects within long fibres . More recently, simpler set-ups were proposed, including hybrid amplitude-phase modulation schemes [3-5]. However, the narrow line spacing of these systems, typically 17 GHz, restricts their use to bit rates up to 10 Gbit/s. In this paper, we propose and demonstrate a simple method of comb generation that is suitable for bit rates up to 42.667 Gbit/s. The comb generator was composed of two Mach-Zehnder modulators (MZM) in series, each being driven with a sinusoidal wave at 42.667 GHz with a well-defined phase relationship. As a result, 7 comb lines separated by 42.667 GHz were generated from a single source, when amplitude up to 2.2 Vp was applied to the modulators, giving flatness better than 1 dB. By passively multiplexing 8 source lasers with the comb generator and minimising inter-modulator dispersion, it was possible to achieve a multi-wavelength transmitter with 56 channels, with flatness better than 1.2 dB across 20 nm (2.4 THz).