Search

In a seminal paper, Humblet decomposed the angular momentum of a classical electromagnetic field as a sum of three terms: the orbital angular momentum (OAM), the spin, and the more unfamiliar surface angular momentum. In this paper, we present the result of such decomposition for various metallic waveguides. We investigate two hollow metal waveguides with circular and rectangular cross sections, respectively. The waveguides are excited with two TE eigenmodes driven in phase quadrature. As references, two better known modes are also analyzed: a plane, a circularly polarized wave (a TEM mode), and a TE-Bessel beam, both of infinite transverse extent and with no metallic boundaries. Our analysis shows that modes carrying OAM and spin can also propagate in the metallic waveguides, even when the cross section of the waveguide is distinctly non-circular. However, the mode density of orthogonal modes carrying OAM is at most equal to that of the waveguides' eigenmodes.

A permittivity function suggested in the literature describing a material that exhibits negative permittivity and no loss at a specific frequency (and losses at other frequencies) is analyzed using electrical network theory. An equivalent circuit of the polarization admittance consisting of RLC components is derived. Further, a proof is given showing that if the admittance is lossless at a specific frequency, then all components with losses (resistances) in the circuit have to be short circuited or blocked or virtually disconnected at this frequency by the use of ideal lossless resonant LC circuits. However, in the literature, inductors in metamaterials are associated with inherently lossy metal nanoparticles, hence invalidating the suggested permittivity function unless a lossless inductor at optical frequencies is found or proved possible.

The feasibility of using metal optics or negative ɛ materials, with the aim of reducing the transversal extent of waveguided photonic fields to values much less than the vacuum wavelength, in order to achieve significantly higher densities of integration in integrated photonics circuits that is possible today is discussed. Relevant figures of merit are formulated to this end and used to achieve good performance of devices with today’s materials and to define required improvements in materials characteristics in terms of decreased scattering rates in the Drude model. The general conclusion is that some metal based circuits are feasible with today’s matals. Frequency selective metal devices will have Q values on the order of only 10∼100, and significant improvements of scattering rates or lowering of the imaginary part of ɛ have to be achieved to implement narrowband devices. A photonic “Moore’s law” of integration densities is proposed and exemplified.

A reshaping optoelectronic repeater is investigated in a loop experiment. If such a device is used in an optical network, the jitter accumulation and its influence on the cascadability are important issues. Whereas the RMS jitter was fairly independent for PRBS patterns, the bit-error rate showed a large pattern dependence. In order to explain these results, a simplified model of the repeater is used, where the device is modelled as a filter followed by an ideal limiter.

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.

The development of Si-based photonics has been far behind the development of electronics for long time. There are two reasons for that. As silicon is an indirect band gap semiconductor, achieving light emission and gain is quite difficult. On the other hand, for using silicon as a light guiding material for passive devices, the main constrains until recently were relatively high propagation losses and high fiber-to-waveguide incoupling losses. The general trend towards more compact photonic devices together with progress in fabrication techniques resulted in the development of two nano-photonic technologies for next generation optical devices: photonic crystals and nanowire waveguides-based devices. To drastically increase the integration density and achieve subwavelength confinement of light along the propagation direction, plasmonic waveguides have been proposed. Surface plasmons are electromagnetic modes constituted on the interface between a metal and a dielectric. The tradeoff between the light confinement and propagation loss has here a vital importance.

The orbital momentum of optical or radio waves can be used as a degree of freedom to transmit information. However, mainly for technical reasons, this degree of freedom has not been widely used in ...

A three-dimensional metal-coated semiconductor-quantum-dot (QD) nanoscale lattice structure is designed for optical waveguiding. It is based on three notions: (i) Excitons are first photogenerated in the QDs by the incident electromagnetic field which is the optical wave to be guided: (ii) The exciton-polariton effect in the QD structure induces an extra optical dispersion in the QDs: (iii) The high contrast ratio between the optical dispersions of the QDs and the background material creates clear photonic bandgaps. By carefully designing the QD size and the QD lattice structure, perfect electromagnetic field reflection can be obtained for the incident wave in the lossless case, thus providing the fundamental basis of QDs for optical waveguide applications. Metal coating at the QD surface generates a surface plasmon spatially confined in the QD so that the exciton generation becomes enhanced for a better dielectric modulation.

We discuss the status of some promising emerging photonics technologies: Plasmonics, coherent light matter interactions and photonic crystals, which could have a significant long-term impact.

―A vertical grating assisted codirectional coupler laser with a super structure grating distributed Bragg reflector is demonstrated. A record stepwise tuning range of 114 nm was measured with good side-mode suppression. The tuning behavior of the device is investigated showing a potential of a tuning range exceeding 100 nm with complete wavelength coverage.

To investigate the potential for dense integration of photonic components, we analyse passive plasmonic/metallic waveguides and waveguide components at optical frequencies by using mostly microwave engineering approaches. Four figures of performance are formulated that are utilised to compare the characteristics of four different slab waveguides with zero frequency cut-off modes. Three of these are metallic based whereas the fourth one, which also serves as a reference, is dielectric based with high index-contrast. It is found that all figures of performance cannot be optimised independently; in particular there is a trade-off between the waveguide Q-value and the transversal field confinement. Microwave methods are used to design several photonic transmission line components. The small Q-value of the metallic waveguides is the main disadvantage when using materials and telecom frequencies of today. Hence plasmonic waveguides do not offer full functionality for some important integrated components, being severe for frequency-selective applications. To achieve a dense integration, it is concluded that new materials are needed that offer Q-values several orders of magnitude higher than metals.