Garching Bei Munchen, Germany
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News Article | April 18, 2017
Site: www.spie.org

Multicarrier modulation is a technique for increasing the amount of information that can be transported by a communication system (i.e., the capacity). The approach is based on splitting a high-bit-rate signal into hundreds of orthogonal sub-carriers, each with a very low symbol rate. The exploitation of this technique in short-range data networks can hugely increase the throughput of a single optical link, thereby removing the need for high-complexity and high-performance components.1 Future low-cost, energy-efficient datacenters and access networks that employ this modulation technique could therefore operate at very high bit rates by using cost-effective and bandwidth-limited optical sources. For short-range data network scenarios, as well as for long- and medium-range networks, optical communications represent the most promising solution for both professional and consumer applications. Compared with optical transport networks, however, short-reach networks are much more sensitive to cost, footprint, and power consumption. For these reasons, such networks require the use of cost-effective and energy-efficient optical sources—such as vertical-cavity surface-emitting lasers (VCSELs)—combined with direct intensity modulation (IM) and direct detection (DD).2 In the near future, however, these requirements could be met by using standard and low-cost devices with limited electro-optical (E/O) bandwidths. Key to achieving this is a drastic increase in the spectral efficiency of the transmitted signal from the current standard (i.e., 0.5bit/s/Hz, achieved with on-off-keying transmission). Two different modulation methods—i.e., orthogonal frequency division multiplexing and discrete multitone modulation—have recently been proposed as a way to enhance the transported capacity. Both approaches enable modulated data to be carried on several parallel channels.3 However, the complexity of the transmission systems, the need for massive digital-signal processing, and the non-idealities that arise during operation could limit the realistic exploitation of these methods in short-reach networks.4, 5 In our work,6,7 we propose a different multicarrier approach, based on frequency division multiplexing (FDM). Our technique retains the advantages of multicarrier modulation, but reduces non-idealities and transmission-system complexity by limiting the number of sub-carriers. We used a long-wavelength VCSEL, characterized by a very limited bandwidth (of around 5GHz), to highlight the huge enhancement to the capacity of transported information that our technique enables. Of all channel distortion types, we hoped particularly to mitigate chromatic dispersion. This type of distortion causes each spectral component of the modulated signal to accumulate a different phase modulation after propagation through fiber, thereby causing significant deterioration of the transmitted signal (i.e., via destructive interference). Direct modulation gives rise to a double-sideband optical spectrum, as we are only modulating the intensity of the optical field. Because of this, the electrical spectrum of the modulation signal is real (i.e., it shows an even parity with respect to the continuous-wave component). After modulation, the optical spectrum could therefore be considered a replica of the electrical spectrum, shifted at the frequency of the optical carrier (i.e., it shows an even parity with respect to the optical carrier). Since the phase modulation that is induced by chromatic dispersion has no even parity with respect to the optical carrier, destructive interference occurs. This results in a frequency-selective channel that induces significant distortions to the signal spectrum and imposes a limit on the maximum transported capacity.8 We observed that the frequency of the fading dips (i.e., the minimums in signal strength) depends on the cumulated chromatic dispersion. Higher dispersion causes a move toward lower frequencies, thereby reducing the undistorted region of the electrical spectrum (see Figure 1). To overcome the channel distortion and limited E/O bandwidth of the VCSEL source, we performed a tailored allocation of the sub-bands. We modulated every sub-band at a rate of 1Gbaud. Because we employed Nyquist shaping of the modulating symbol pattern for every sub-band (i.e., with a roll-off factor of 0), all sub-bands acquire a rectangular-shaped spectrum and can therefore fill 1GHz of the electrical spectrum, removing the need for an inter-subcarrier guard-band. Hence, the FDM signal consists of 10 subcarriers filling a frequency range of 10GHz. We also achieve a trade-off between the modulation order, subcarrier power, and bit error rate (BER) that are associated with the single subcarrier. At lower frequencies, we exploit a higher-order modulation format, such as 16-QAM (16 quadrature amplitude modulation), to maximize the transported capacity. The spectral dips, on the other hand, are filled by robust FDM sub-bands with lower spectral efficiency—such as BPSK (binary phase-shift keying)—to limit the impact of frequency fading. To test our approach, we performed the same procedure for different propagation lengths, with transmission distances ranging from 100m (a distance typical for intra-datacenter communications) to 20km, through standard single-mode fiber (SSMF). The received electrical spectra and relative BERs are shown in Figure 2. As a result of the equalization and tailored modulation assignment that we implemented, no significant difference is visible among the sub-bands, and all 10 FDM subcarriers satisfy the BER target that is required for the exploitation of an advanced FEC (forward-error-correction) code (with a 7% overhead). Depending on the propagation distance, the transmitted capacity ranges from 34Gb/s over 100m to 25Gb/s for 20km propagation. In summary, we have demonstrated short-range transmission based on the employment of a bandwidth-limited VCSEL combined with direct IM and DD. Our technique exploits a novel multicarrier approach to achieve very high transported throughput. VCSEL band limitation can be overcome, and the non-uniform frequency response of the system can be matched by tailoring the FDM subcarrier allocation. Our technique therefore increases the spectral efficiency by a factor of 3.4, 2.8, and 2.5 over 0.1, 10, and 20km of uncompensated SSMF, respectively, compared with the standard optical transmission system (i.e., an on-off keying transmission system with an efficiency of 0.5bit/s/Hz). In our future research, we will focus on the comparison between FDM and other multicarrier techniques, and on achieving further capacity increases by using different optical sources. This work was supported by MIUR through the ROAD-NGN project (PRIN2010-2011). The authors would like to thank VERTILAS for support with experimentation.


Grant
Agency: European Commission | Branch: FP7 | Program: CP | Phase: ICT-2011.3.5 | Award Amount: 4.96M | Year: 2011

The objective of FIREFLY is the introduction of novel polymer waveguide and photonic crystal structures based on highly structured 3D nano-hybrids into industrial applications by using a new cost effective production process for larger scale manufacturing. The target applications are optical waveguides and photonic structures for the manipulation of light in, for example, optical interconnects. The optical interconnects technology will initially be applied for data communication in high performance supercomputers, and eventually these optics will also find their way into high-end server systems, mid-range servers and in consumer-like applications such as high-end multimedia devices.\nWaveguides and photonic crystals based on polymers have been proven in a laboratory environment to be interesting technologies for light management. In most cases these structures are manufactured on small scale. We propose the use of a relatively new technology to manufacture these structures on a larger scale.\nThe nano-hybrids will be manufactured using a combined approach of nano-imprint process in a polymer resins and self assembly of material in the polymer nano-structures. The nano-structures will be filled with new modified polymer compositions having a high refractive index and optical clarity at relevant wavelengths, necessary for waveguides, and with inorganic nanoparticles to prepare photonic crystals, for the manipulation of light for guiding the light in waveguides through sharp horizontal and vertical bends. Some material developments are needed: new silicone polymers that will be modified for improved optical properties such as low optical loss and tuneable refractive index, and new inorganic particles that will combine a high refractive index with a very high level of monodispersity.\nThe manufacturing process will be suitable for up-scaling to an industrial process. This new bottom-up approach will enable the development of hybrid materials with new optical properties.


Grant
Agency: European Commission | Branch: FP7 | Program: CP | Phase: ICT-2007.3.5 | Award Amount: 3.73M | Year: 2008

Wavelength-tunable lasers are key components for future reconfigurable optical networks and for cost-effective and compact telecommunication infrastructures. Moreover, a broadband and continuously tunable laser with high purity emission spectrum is a versatile tool for many sensing applications, e.g. for greenhouse gases (laser absorption spectroscopy) or deformations of buildings (fiber Bragg grating sensors).\nA novel concept for widely and continuously wavelength-tunable single-mode laser diodes in the 750-2100 nm wavelength range will be developed. The underlying VCSEL structure is completed by a micro-machined moveable Bragg-mirror with a sub-wavelength grating (SWG). The single-mode property of the VCSEL structure is thus ideally combined with the polarization stability of the SWG and the wide and continuous tunability of the electro-thermally or electro-statically actuated mirror. For the fabrication of the nano-scale SWGs an electron-beam writing process will be developed.\nThe curvature of the micro-mirror will be matched to the phase front of the fundamental mode to achieve its maximum support while suppressing undesired polarization modes by means of a SWG. This technology can select the single fundamental mode from relatively large apertures. The optical output power will be high and a very good sidemode suppression will be achieved during tuning. The project will develop both long wavelength InP-based VCSELs (1.3m to 2.1m) and short wavelength GaAs VCSELs (down to 800nm), and thus introduces widely tunable VCSELs in a broad range of the optical spectrum. Additionally, a technology for integrated tunable VCSELs with dielectric Bragg mirrors will be developed for efficient manufacturing of the laser modules.\nThe devices will be optimized in close cooperation between the university and industrial partners. Devices for gas detection, fiber Bragg grating sensing and optical communications will be investigated.


Grant
Agency: European Commission | Branch: FP7 | Program: CP | Phase: ICT-2013.3.2 | Award Amount: 4.38M | Year: 2014

Our goal is to develop technology for fast optical communication using revolutionary concepts that challenge the mainstream approaches for photonics integration and packaging. The primary application is optical communication inside high performance computing systems, such as supercomputers and datacenters, but the technologies will also find use in many other applications.Power-efficient InP VCSEL arrays will be directly modulated to provide up to 50 Gb/s signals at 1.3 m wavelength where optical fibers have no chromatic dispersion. Fast InP photodiode arrays will receive the signals. Our semiconductor optical amplifiers and electroabsorption modulators will be based on novel dilute nitride materials that enable low-cost fabrication on large GaAs wafers and uncooled operation. Passive components will be realised with 3 m SOI waveguides that are integrated with polymer waveguides for athermal operation and highly efficient, polarisation independent and ultra-broadband I/O coupling. Innovative concepts will radically shrink the footprint of the SOI and GaAs chips, and avoid chip-level processing steps. The hybrid integration of active chips on SOI and the wafer-level packaging of the optoelectronic modules will be based on novel concepts that significantly improve the alignment accuracy, yield, throughput and passive cooling, and also lead to dramatic reduction in the cost and size of the modules. To increase the datarate and to enable flexible communication between processors we apply advanced modulation formats, wavelength multiplexing and optical packet switching. We demonstrate up to 80 Gb/s per wavelength without offline signal processing, and up to 8 wavelength channels. The concept is directly scalable to Pb/s systems by combining spatial and wavelength multiplexing. For intra-rack communication we also integrate single-mode polymer waveguides into line cards and backplanes and develop optical connectors between those and the optoelectronic modules.


PhoxTrot is a large-scale research effort focusing on high-performance, low-energy and cost and small-size optical interconnects across the different hierarchy levels in Data Center and High-Performance Computing Systems: on-board, board-to-board and rack-to-rack. PhoxTrot will tackle optical interconnects in a holistic way, synergizing the different fabrication platforms (CMOS electronics, Si-photonics, polymers, glass, III-Vs, plasmonics) in order to deploy the optimal mix&match technology and tailor this to each interconnect layer. PhoxTrot will follow a layered approach from near-term exploitable to more forward looking but of high expected gain activities. The main objectives of PhoxTrot include the deployment of:\n. generic building block technologies (transmitters, modulators, receivers, switches, optochips, multi- and single-mode optical PCBs, chip- and board-to-board connectors) that can be used for a broad range of applications, extending performance beyond Tb/s and reducing energy by more than 50%.\n. a unified integration/packaging methodology as a cost/energy-reduction factor for board-adaptable 3D SiP transceiver and router optochip fabrication.\n. the whole food-chain of low-cost and low-energy interconnect technologies concluding to 3 fully functional prototype systems: an >1Tb/s throughput optical PCB and >50% reduced energy requirements, a high-end >2Tb/s throughput optical backplane for board-to-board interconnection, and a 1.28Tb/s 16QAM Active Optical Cable that reduces power requirements by >70%.\nTo ensure high commercial impact after the end of PhoxTrot, all activities have been designed around current market roadmaps that will be updated during the course of the project and are led by industrial partners. PhoxTrot brings together the major European industrial and research players in the field. In so doing it will create a highly timely thrust and of unprecedented momentum in optical interconnects in Europe with worldwide impact.


Grant
Agency: European Commission | Branch: FP7 | Program: CP | Phase: ICT-2013.3.3 | Award Amount: 4.32M | Year: 2013

The ACTION project builds on the recent discovery that relatively low levels of pulsed infrared laser light are capable of triggering activity in hair cells of the partially hearing (hearing impaired) cochlea and vestibule. So far the excessively large volume of optical fibre systems and external light sources used for animal studies prevented the practical use of this discovery for long term animal research devices or for human grade implants. ACTION aims to develop a self-contained, smart, highly miniaturised system to provide optoacoustic stimuli directly from the electrode array of a cochlear implant system. The resultant neural cell response will be electrically recorded and direct feedback to the light source will be provided to enable automated, objective hearing threshold assessment and optimization of sound feature coding enhancements for improved quality of the acoustic sound. The new implant is aimed to lead to more effective non-contact treatment, as a device with intra-cochlear sound sources offers many potential advantages over a traditional in the ear hearing aid/speech processor combination. This approach will at the same time avoid damage of neural tissue by high electrical current, and introduction of high-frequency artifacts to the recording signal. Biocompatible, long-term implantable materials for micropackage and integration principles for the light sources (specific pulsed vertical cavity surface emitting lasers optimized for optical neurostimulation) will be selected. The project includes neural response measurements and communication between discrete elements to achieve robust and reliable miniature standalone devices with high acceptance within the medical sector. Pre-clinical tests for optoacoustic cochlear implants will be an integral part of the project.


Grant
Agency: European Commission | Branch: FP7 | Program: CP | Phase: ICT-2007.3.5 | Award Amount: 9.12M | Year: 2008

The need for higher speed is a never ceasing requirement for broadband access and requirement of 1 Gbps is expected around 2016. The copper lines are expected to reach their maximum capacity at about 10Mbps while the capacity required only for watching one channel of HDTV is 20Mbps. Tithe total number of homes connected to fibres will grow from about 11 million at the end of 2006 to about 86 million at the end of 2011, dominated by Asia with 59 million household connected. Our idea is to develop and implement WDM-PON as the new future proof FTTH technology to satisfy the coming BW requirements with a point to point architecture. The aim is to develop application specific optical components of a WDM-PON broadband access network targeting a system cost per subscriber below todays implementation of GPON by develop innovative new low cost components with high level of integration in addition to new manufacturing processes. Even the cheapes WDM-PON solution cost 2 -3 times as much as GPON. Up to 95% of the cost of optical components is due to packaging. The project aims to develop a system with a integration scale that is around 100 times higher than SOA that can be implemented as an upgrade of xPON systems, that are currently being installed, and will not require changes or re-routing of optical fibres. The European citizens and society will benefit from GigaWAM through: Easier access to a broad range of services; online maintaining communication links, avoiding discrimination and exclusion, benefit regarding telemedicine and eHealth, e-learning, and bridge the gap between urban and rural areas and Eastern and Western Europe. Overall, the market opportunity in year 5 post market launches is 230 Mn annually with market launch in Europe, Asia and US assuming a conservative market penetration the first years followed by a steeper growth to 5% market penetration in Europe in year 5.


Patent
Vertilas | Date: 2012-09-18

A luminous unit for an optical gas detector, an optical gas detector including the luminous unit, and a method of recording an absorption spectrum in an optical gas detector include a light source for linearly polarised light radiation and a housing with an exit window. A wavelength of the light radiation radiated from the light source is tunable. The light source is arranged in the housing such that the main emission direction (OA) of the light source encloses an inclination angle () of between 10 and 50 with a normal (N) to the main extension plane (HE) of the exit window. The direction of polarisation (P) of the light radiation encloses a rotation angle () of between 22.5 and 67.5 with the plane of incidence on the exit window.


Patent
Vertilas | Date: 2011-10-28

The present invention relates to a surface-emitting laser diode with an active amplifying region (2) which is bounded by two laser mirrors (1, 3), while one or more polarization-selective layers (4) are provided for stabilising the polarization in a region that is located on that side of at least one of the laser mirrors (1, 3) that is opposite the active amplifying region (2), these layers (4) extending parallel to the respective mirror (1; 3) and having a polarization-dependent refractive index and/or absorption.


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