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The evolution of future Data Centers requires novel means of information transmission due in part to the energy dissipated in the transport of information. Photonics in the form of active optical cables is used for both inter-rack as well as intra-rack connections. However, due to the superior bandwidth-density properties of photonics over copper based transmission, photonics is now being considered for inter-chip and even intra-chip interconnects. This requires novel approaches to create smaller (nanoscale), lower power dissipation functional devices in the transmission fabric, a development that could also be useful for a range of other applications. The current status as well as the prospects to achieve these ends and to take the next quantum leap in integrated nanophotonics are discussed.

Nanophotonics has received much attention in recent years, fuelled by general interest and progress in nanotechnology but also by rapid advances in photonics technology. The tutorial will cover basics and applications of nanophotonics.

Integrated nanophotonics has shown a remarkable development in recent years and can find applications in virtually all fields of photonics, though its predominant focus has so far been in telecom and lately computer interconnects. This progress has primarily been based on nano- and III–V technology development, the introduction of silicon technology, with larger refractive index contrast than previously available, as well as subwavelength plasmonics structures. For the latter, a main problem, especially for ICT applications, has been the large optical loss associated with deep subwavelength confinement, as discussed below.

Integrated photonics has largely been based on silicon/silica and III–Vs in recent times. Both have their advantages and disadvantages, but neither seem capable of supporting a further significant reduction of device footprint to sustain the exponential decrease of this important parameter that we have witnessed since decades. The talk will analyze different aspects of plasmonics from this and a functionality point of view and further discuss some possible alternative materials.

Nanophotonics in general and plasmonics in particular have received much attention in recent years, fuelled by a general interest in nanotechnology but also by rapid advances in integrated photonics over the years, primarily brought about by using silicon/air or quartz interfaces, giving larger refractive index contrast than previously employed [1,2]. The minimum lateral spatial field width for a planar silicon waveguide in air is ∼300 nm, with a wavelength in the medium of ∼500 nm, at a vacuum wavelength of 1550 nm. Photonics integration density has thus shown a steady exponential growth since the 80s, but to pursue this state of affairs, it is necessary to find a successor/complement to the silicon technology. Such new (meta) materials seem to have to rely on a negative e (such as in metals) somewhere in the system [3,4] since this offers a possibility for increasing the integration density in photonic lightwave circuits in two ways: (i) By using principles other than total internal reflection, i.e. surface polaritons and (ii) Employing e.g. metamaterials to generate artificially very large effective media refractive indices. Both methods could allow denser lateral packing of waveguides as well as shorter resonators and filters. In general, operating the metal/dielectric structures close to resonance [4] gives the highest confinement but also the highest spatial losses, since in essence (i) the field is forced into the lossy metal and (ii) in general the group velocity is significantly reduced. Thus, a main problem for many (albeit not all) applications is the optical loss associated with these high confinement metal-based metamaterials. In anticipation of a possible future breakthrough in developing metamaterials with at least a factor of 10 lower losses [5, 6] we analyze in this paper different resonant and nonresonant structures and the achievable performance. One example is waveguides made from arrays of near resonantly operated near-field coupled metal nanoparticles in the shape of e.g. spheres, which have attracted some attention [3,7,8]. Nanoarray waveguides, based on silver nanoparticles are, however, very lossy, see e.g. [9].

Electroabsorption modulators (EAM) based on quantum-confined Stark effect (QCSE) in multiple-quantum wells (MQW) have been demonstrated to provide high-speed, low drive voltage, and high extinction ratio. They are compact in size and can be monolithically integrated with source lasers. In order to achieve both high speed and low drive-voltage operation, travelling-wave (TW) electrode structures can be used for EAMs. Modulation bandwidths of 100 GHz (-3 dBe) have been accomplished and transmission at 80 Gbit/s with non-return-to-zero (NRZ) code has been demonstrated for InP-based TWEAMs, indicating the possibility of reaching speeds of 100Gbit/s and beyond. In order to further increase the efficiency and reduce the drive voltage, MQW structures using intersubband (IS) instead of interband (QCSE) absorption are being investigated. Materials systems with large conduction band offset, such as GaN/Al(Ga) N or InGaAs/AlAsSb, are required for IS modulators. Critical for the performance of IS modulators is the linewidth of the absorption peak, hence IS modulators have the potential to outperform interband modulators given that a sufficiently high material quality can be achieved.