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Micro-scale to Nano-scale photonic structures for optical communications
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Acronym: NAMIC
Submission from the University of Glasgow (Prof. Richard M. De La Rue)
List of partners: see annexes
Call Identifier : EOI.FP6.2002
Date of submission : 6th June 2002
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| 1. |
Need and Relevance
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The main objectives of the proposed Network of Excellence are to exploit the potential of components that are micro-structured on a wavelength scale in photonics - and to promote their use primarily for optical communications by enabling a rapid transition from concept to research prototypes and commercial devices in systems based on advanced and co-ordinated enabling technologies. The co-ordinated effort will enable much enhanced system performance because of its objective of achieving a higher level of hardware integration (the devices involved being compact and having low power consumption) - and greater device functionality, due to a more effective interaction between photonic structures and material properties.
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Researchers in established industry, research institutes and universities around the world are investigating the properties of nano- and micro-structured materials, in particular photonic crystals, in an effort to fully harness the potential of wavelength-scale photonic components. In Europe, several national and international projects are investigating various aspects of the field. These include the IST supported TUNVIC, PICCO and PCIC projects and the COST 268 Action now coming to an end. COST 268 has investigated the potential of wavelength scale photonics from telecommunications and promoted a faster transition from research prototypes to commercial devices in systems. The unified efforts under the COST umbrella resulted in highly efficient interactions and yielded notable results that have helped place Europe at the forefront of world research in the field. An integrated and co-ordinated European approach is needed because of the difficulty of covering and fully resourcing the broad spectrum of research topics and emerging underpinning technologies in isolation. With this expression of interest, we propose the establishment of a Network of Excellence to enlarge and enhance these scientific and technical collaborations, thus enabling Europe to maintain and exploit its leading role and to lead the world in bringing new products to market. Despite the strong scientific results already obtained, the field is clearly one still in its infancy and one that is in need of a strong pan-European approach to exploitation.
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The planned Network of Excellence proposes to co-ordinate, on a Europe-wide scale, research activities in the development and application of micro-structured materials in photonics. The scientific programme will be based on a pragmatic synthesis of technology-driven and applications-driven approaches to build on existing expertise. The Network will provide a broad forum to catalyse the development and deployment of wavelength-scale photonic components, in order to strengthen European competitiveness in exploiting advanced photonics. Key aspects of the organisation of the network will be to provide (i) efficient access to training and (ii) the infrastructure for the implementation and realisation of creative ideas generated by European scientists and technologists, whether or not they are formal network partners.
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Current state of the art
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The potential impact of technological developments which may be described as photonic microstructures or photonic nanostructures is now widely recognised and of increasing importance for information society technology applications and other applications of photonics, including the life sciences.
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Examples of concepts already identified include first stage-commercialised devices such as vertical cavity light emitters and micro-opto-electro-mechanical (MOEM) devices - and rapidly emerging technologies such as photonic crystal or photonic bandgap structures, sub-wavelength structured optical elements and photonic wires. Entirely new concepts/paradigms with much the same technology base could well emerge within a four year time-scale and then undergo rapid evolution towards making a major impact. Among the more obvious materials bases are silicon, in various technological forms such as CMOS and silicon-on-insulator (SOI) - and epitaxial III-V semiconductor structures grown on a variety of substrates, but most typically gallium arsenide and indium phosphide. In the present expression of interest, the prefixes 'micro-' and 'nano-' are both applicable since features which are defined and resolved to a well sub-micrometre (i.e. nanometre) scale may be involved in photonic objects which have overall dimensions that may be defined on a several micrometre scale and then into complex aggregates to much larger sizes.
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Advanced photonic structures on a (sub-) wavelength scale provide the novel technology base needed for truly high-density optical integrated circuits. Perhaps the most familiar technology is that of photonic crystals, which offer the possibility of next-generation multifunctional integrated components with footprints significantly smaller than conventionally achievable. Becasuse of their unique electromagnetic properties, photonic crystal structures can be expected to increase systems performance significantly and it is particularly noteworthy that several SMEs (eg Mesophotonics and Blaze Photonics) have already been established to develop and commercialise photonic crystal technology in the fields of micro-photonics, telecommunications and computing.
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Recognising the complexity involved in harnessing fully the potential of photonic micro- and nanostructures, the need for an NoE has been identified by a number of key players in the European arena. Only an NoE at the European level will be capable of attacking the problems with a sufficient level of multi-disciplinarity in terms of material-generation. The involvement of industrial members in the NoE provides an efficient means for an early transfer and pick-up of results.
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Innovations/challenges in the approach to be adopted
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In the present context it is natural to work with technological approaches, which are normally describable as planar. But we believe that a major aspect of the work to be carried out should be the extension of planar technology through exploitation of the third ('vertical') dimension by using a multilayer approach. This multilayer or multi-level approach could follow quite closely the modern VLSI approach in which wafer-scale polishing is carried out repeatedly (as many as 10 times) to re-planarise the surface after combinations of multiple layer deposition and patterning. But this VLSI-technology related approach is certainly not the only possible one - and techniques such as wafer-fusion and molecular adhesion, in which entire layered structures are transferred from one substrate to another could also likely be used extensively. A further example is the surface micro-machining technology used for MOEMS (especially III-V) devices, which can produce multilayer stacks of suspended membranes.
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One possible example of the requirement of a multi-level approach is the use of optical interconnects in the form of embedded or surface waveguide channels incorporated directly into a multilayer system that also provides electrical interconnection and other standard silicon VLSI functions. But in the proposed programme the third ('vertical') dimension is to be exploited in more innovative ways, i.e. for more complex combinations of functionality. For example photonic functionality requirements could define situations in which light passes through a multilayer structure made up of combinations of dielectric mirror stacks, bi-refringent layers, high contrast holographic layers, photorefractive layers, magneto-optically active layers and so on. Individual layers or combinations of layers may be structured across and within the layer with microscopic and nanometric-scale features.
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Alternatively, photonic functionality can involve the propagation of light along the layers of a complex structure, with additional possibilities for controlled (active or passive) transfer of light from one level to another. Photonic functionality could also involve interactions, in either direction, between light propagating in-plane and light propagating through the planes of a multi-layer structure - and coupled interactions with light propagating out of the photonic structure. Exploitation of silicon IC-compatible sources integrated onto silicon (either Si sources or bonded III-V sources), fast photodetectors (either IV-IV type or bonded III-V), non-linear mechanisms for coupling of light beams and various forms of electro-optically controlled coupling within photonic structures - or on exterior surfaces - will become more important.
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The celebrated objective of obtaining full photonic band-gap behaviour from three-dimensionally periodic photonic crystals is, of course, interesting. But it is certainly not dominant in our thinking in relation to multiply-structured, multi-layer optics. It is perhaps more appropriate to think in terms of '2.5-dimensional' photonic structures' in which an interplay occurs between waveguide-confined photons and photons propagating through the planar layer structure. It will nevertheless be necessary to define what functionalities could be produced by a particular form of multiply structured photonic object or might be required to meet a specified functionality.
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In summary, we propose in this network not only to investigate widely the possibilities offered by planar integrated photonic technologies that are based on sub-wavelength 2D lateral structuring of planar optical components (e.g. in 2D Photonic Crystal structures), but also to deliberately open up the third space dimension, while remaining on a planar technology base. This objective will be achieved by further structuring, on a sub-wavelength scale, the third dimension via a multilayer approach. Our motivation is twofold: from the point of view of innovation this '2.5-dimensional' approach should broaden considerably the combinations of functionalities beyond those presently contemplated with 2D photonic integration. But motivation comes also from the fact that, from a technological point of view, the approach to be followed is substantially compatible with and will rely on the technologies which have already become available, in particular in the world of silicon microelectronics. The network will be also concerned with important issues such as the coupling of photonic devices and circuits to the external world (fibres, for instance), as well as the vitally important issue of "packaging'.
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| 2. |
Excellence
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Within the Network of Excellence we envisage an integrated research capability involving co-operation between established centres that will provide, in the first instance, a rapid route from concept to realisation and optimised behaviour. To enable this line of action, the proposed Network brings together groups with expertise in the four general enabling areas of photonics technology; (i) materials and their characterisation, (ii) lithography and fabrication, (iii) device assessment, characterisation and exploitation and (iv) computational analysis, design and synthesis. A fifth enabling group (v) will provide specialist input on applications and systems requirements. The partners within each group will provide scientific excellence coupled with experience of successful cross-European co-operation via COST and IST funded projects etc. Each group will provide a core of established techniques and shared know-how in these essential enabling technologies. As an example, a key to cost-effective deployment will be the ability to mass-produce devices. Conventional direct-write electron-beam lithography does not lend itself to mass production but recent work at IMEC under the IST PICCO project indicates that, with an understanding of proximity effects, excimer-laser based photolithography offers a route to mass-manufacture of highly complex, yet low-cost, optoelectronic/photonic components. As another example, shared know-how within the Network of Excellence among the partners of the IST supported TUNVIC, PICCO and PCIC projects could result in new classes of MOEMS devices, where use is made of mechanically tunable membranes that are suspended and laterally micro-structured.
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Domains of application
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The excellence and ambition of the network is demonstrated by the many potential domains of application for the technological approaches to be developed. Within telecommunications, areas of end-application include fibre-optical telecommunications over the range from long-haul down to on-chip optical interconnection for microelectronics. But free-space optical communications where, for instance, beam-shaping and steering of light from vertical emitters is a requirement, could also benefit from much the same technology base. The multi-layer planar approach could help to meet the challenge of producing devices for efficient and cheap conversion between mobile communications tools and the fibre-optical backbone, particularly when it becomes necessary to go beyond the presently exploited radio-frequency spectrum.
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But the scope of the potential applications is obviously much wider than optical telecommunications and could include items from a well-known catalogue, i.e. displays, optical switching, optical memory, optical sensors, adaptive optics and holographic optical elements and quantum-optical devices such as single-photon emitters. Optical versions of 'lab-on-a-chip' approaches are already an important topic of photonics research activity under the heading of bio-photonics, but further advances in this area are likely to emerge from more complex and finer micro-structuring. Photonic crystal membranes are of interest, in part, because of their potential role as sensor interaction 'substrates', which may be used in both chemical and biological applications.
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All these areas of optoelectronics and photonics activity could be strongly affected by the creation of the genuinely complex optoelectronic and photonic integrated circuits that we envisage emerging from this network.
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Summary of benefits
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The partners in the NoE indicate expertise covering the full technology spectrum of wavelength-scale photonic components. The network will promote an open collaboration between groups already world leaders in the field and groups entering the field. This approach will lead to faster identification of possibilities and solution to problems, thus increasing the competitiveness of the European telecommunications industry. Furthermore, the fabrication technology is generic and there will be mutual benefit in terms of the know-how generated and distributed. Hence, the benefits of the network can be summarised as follows:
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- The consolidation of resources to enable integrated research and rapid progress from concept to realisation captured via project and technical area steering groups and workshop activities.
- The ability for a larger research community to identify and produce a rapid response to industrial needs.
- The development of applications, e.g. in optical interconnects, data communication, optical data storage, sensors, displays, optical information processing and medically related science and technology.
- The provision of a broad engineering forum beyond that already provided by existing projects, bringing together scientists, manufacturers and potential users.
- Facilitation of human resource exchange and discussions. In particular, the ability for researchers to gain access to a wide range of training and education facilities and to test novel ideas.
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| 3. |
Integration and structuring effects
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Each group will identify and work together strategically to enhance the available base technology, taking inputs from partners at all levels, from materials to systems.
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In technology area (i), initial work will concentrate on further extensions of the silicon and III?V semiconductor bases, as well as ambitious high-risk high pay-back technologies (such as self-organising nanostructures). Further calls for partners will then be used to identify and add expertise in additional technologies that may be required, such as magnetic metal oxides, ferroelectric thin films and 'photon sieve' metallisation. In technology area (ii), participating groups will provide leading-edge expertise in 'conventional' lithography, emerging techniques such as nano-imprint lithography that potentially offer cheaper and faster production - and direct methods such as focussed ion beam etching. Holographic lithography based on one- and two-dimensionally periodic phase masks could also be valuable. Various versions of dry-etch processing technology, such as RIE, CAIBE, RIBE, ICP etching and ECR etching, will be used extensively and will obviously require further development. But within technology areas (i) and (ii), scope remains for innovative approaches to producing base materials, and self-organisation could also be a key technology.
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Device assessment and characterisation (area (iii)) will invoke spatially and spectrally resolved imaging methods, including high-resolution scanning microscopy. There is a need to assess base materials and aspects related to the physics of wavelength-scale structured materials - and then go on to evaluate fully the devices produced, with potential applications and exploitation in mind. Groups with expertise in electromagnetic modelling and simulation (area (iv)) will provide and develop tools for the initial evaluation of new device concepts, strategies for efficient implementation and synthesis tools for new device concepts - and will identify allowable tolerances. Synthesis tools to be developed will differ from conventional simulation tools in that they will make it possible to investigate many possible designs, thus meeting performance-specific criteria.
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In technological area (v) (applications and systems), photonic-electronic hybrid integration will be a major concern: the integration, in monolithic and hybrid forms, of photonic microstructures and nanostructures with 'conventional' electronics is an obvious but vital task. For example, the development of monolithically integrated silicon-based electronics to drive on-chip micro-opto-electro-mechanical structures (MOEMS) is clearly a task that will be important for some time to come. But future possibilities are more powerful and diverse, with photonic and electronic functionality becoming more closely integrated on a scale extending down to well below the micrometre level.
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The proposed Network of Excellence will have a four year duration, with the intention of developing a sustainable continuation. In particular it will provide a forum for future, more targeted, 'Integrated Project' proposals originating from sub-sets of the groups and laboratories involved in the Network. Tentative examples of such 'Integrated projects' are given below :
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- Basic building blocks of planar photonic integrated circuits based on 2D Photonic Crystals (especially devices and structures utilising the distinctive features of 2D PC structures, eg very "flat" dispersion curves, providing strong lateral optical confinement and large velocity variation. These characteristics lead to very efficient miniaturised devices: for example devices for wavelength selective routing, for non-linear optics and for the control of the dispersion will be at the leading edge of this project.)
- Free space micro-optic devices based on multilayer 2D photonic crystal structures (including: surface emitting micro-sources, wave-length selective photodetectors, non-linear optical devices for all-optical and wavelength convertion functionalities, new versions of MOEMS switching devices that combine spatial and spectral resolution).
- IC-compatible, optical interconnects for microelectronics, with silicon channel waveguides embedded in a silica matrix providing the required interconnection. Silicon-on-insulator wafers would provide an obvious base - and strongly confined, single-mode, photonic wire type guides could play a central role.
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In the course of preparing this submission, we have become aware of a number of other expressions of interest in subject areas more-or-less closely related to the present submission, e.g. 'Emerging Nanophotonic Technologies' (from Wuppertal) and 'DIverse NAnophotonic Multifunctional Integrated Circuits' (from St. Andrews). This is, of course, to be expected - and our view is that combinations of Networks of Excellence and Integrated Projects are likely to be an appropriate mode of action within FP6, enabling new research topics to be identified and rapid responsive action to be taken.
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Networking activities management
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Management of the network will require a full time Scientific Co-ordinator with responsibility for co-ordination of the network and communication within it, including regular reporting and progress meetings. The leader will also be responsible for communication with the Commission services and supervisory bodies - and for reporting, dissemination and launching of initiatives leading to integrated projects. Dedicated administrative support will be provided for financial management, management of knowledge generated by the network including protection of Intellectual Property. The Scientific Co-ordinator and support team will maintain a web page that will provide up-to-date information on the activities of the Network for general public dissemination and including the provision of access to training for researchers from outside the network. Web-site provision will include a bulletin board and discussion forums.
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A Network Development Manager (NDM) will help co-ordinate network activities, organise meetings and exchanges of personnel, liaise with professional bodies (e.g. IEEE, IOP, EPS, MRS, OSA, IEE), organise external workshops - and seek external funding for the network. The NDM will also be responsible for development of collaborative formal training, including PhD programmes and Masters level teaching, taking advantage, where appropriate, of existing funding routes (e.g. Marie Curie Fellowships, national funding).
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Scientific Management will be through technical area and project management teams reporting to an overall network management committee chaired by the Scientific Co-ordinator. The Network Management Committee will have one representative from each partner.
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Following a kick-off meeting, the programme of activities will include six-monthly scientific review meetings (typically lasting three days) with presentation of recent results, new technological developments and exploitation opportunities. The state of the art will be reviewed and new directions will be identified. Where possible these review meetings will be co-located with international conferences and workshops since this offers an effective route to dissemination. Additional workshops (open to people outside of the Network) will enable broader representation of the Network's present state-of-the-art and receive advice and ideas on new technologies and applications. These workshops will provide a key mechanism for evaluating direction and identifying new partners and so particular encouragement will be given to international invited speakers, young scientists and emerging groups
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