The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

http://ieeexplore.ieee.org/iel5/6354/16969/00781867.pdf

Photonic crystals

Linearly and circularly polarized conformal strip-fed dielectric resonator antennas (DRAs) are studied in this article. In the latter case, a parasitic patch is used to excite a nearly degenerate mode. The hemispherical DRA, excited in its fundamental broadside TE111 mode, is used for the demonstration. In the analysis, the mode-matching method is used to obtain the Green's functions, whereas the method of moments is used to solve for the unknown strip currents. In order to solve the singularity problem of the Green's functions, a recurrence technique is used to evaluate the impedance integrals. This greatly increases the numerical efficiency. Measurements were carried out to verify the calculations, with good results.


Keywords:

circularly polarized antenna;
dielectric antennas;
mode-matching methods;
moment methods;
parasitic antennas;
resonance

Dielectric Resonator Antennas

Recent advances in photonic integration have propelled microwave photonic technologies to new heights. The ability to interface hybrid material platforms to enhance light–matter interactions has led to the development of ultra-small and high-bandwidth electro-optic modulators, low-noise frequency synthesizers and chip signal processors with orders-of-magnitude enhanced spectral resolution. On the other hand, the maturity of high-volume semiconductor processing has finally enabled the complete integration of light sources, modulators and detectors in a single microwave photonic processor chip and has ushered the creation of a complex signal processor with multifunctionality and reconfigurability similar to electronic devices. Here, we review these recent advances and discuss the impact of these new frontiers for short- and long-term applications in communications and information processing. We also take a look at the future perspectives at the intersection of integrated microwave photonics and other fields including quantum and neuromorphic photonics. This Review discusses recent advances of microwave photonic technologies and their applications in communications and information processing, as well as their potential implementations in quantum and neuromorphic photonics.

Integrated microwave photonics

Optics offers unique opportunities for reducing energy in information processing and communications while simultaneously resolving the problem of interconnect bandwidth density inside machines. Such energy dissipation overall is now at environmentally significant levels; the source of that dissipation is progressively shifting from logic operations to interconnect energies. Without the prospect of substantial reduction in energy per bit communicated, we cannot continue the exponential growth of our use of information. The physics of optics and optoelectronics fundamentally addresses both interconnect energy and bandwidth density, and optics may be the only scalable solution to such problems. Here we summarize the corresponding background, status, opportunities, and research directions for optoelectronic technology and novel optics, including subfemtojoule devices in waveguide and novel two-dimensional (2-D) array optical systems. We compare different approaches to low-energy optoelectronic output devices and their scaling, including lasers, modulators and LEDs, optical confinement approaches (such as resonators) to enhance effects, and the benefits of different material choices, including 2-D materials and other quantum-confined structures. With such optoelectronic energy reductions, and the elimination of line charging dissipation by the use optical connections, the next major interconnect dissipations are in the electronic circuits for receiver amplifiers, timing recovery, and multiplexing. We show we can address these through the integration of photodetectors to reduce or eliminate receiver circuit energies, free-space optics to eliminate the need for timing and multiplexing circuits (while also solving bandwidth density problems), and using optics generally to save power by running large synchronous systems. One target concept is interconnects from ∼1 cm to ∼10 m that have the same energy (∼10 fJ/bit) and simplicity as local electrical wires on chip.

Attojoule Optoelectronics for Low-Energy Information Processing and Communications

An overview is given over some of the most widely used numerical techniques for solving the electromagnetic scattering problem that start from rigorous electromagnetic theory. In particular, the theoretical foundations of the separation of variables method, the finite-difference time-domain method, the finite-element method, the method of lines, the point matching method, the method of moments, the discrete dipole approximation, and the null-field method (or extended boundary condition method) are reviewed, and the advantages and disadvantages of the different methods are discussed. Aspects concerning the T matrix formulation and the surface Green's function formulation of the electromagnetic scattering problem are addressed.

Numerical methods in electromagnetic scattering theory

The combination of atomic force microscopy and Kelvin probe technology is a powerful tool to obtain high-resolution maps of the surface potential distribution on conducting and nonconducting samples. However, resolution and contrast transfer of this method have not been fully understood, so far. To obtain a better quantitative understanding, we introduce a model which correlates the measured potential with the actual surface potential distribution, and we compare numerical simulations of the three-dimensional tip–specimen model with experimental data from test structures. The observed potential is a locally weighted average over all potentials present on the sample surface. The model allows us to calculate these weighting factors and, furthermore, leads to the conclusion that good resolution in potential maps is obtained by long and slender but slightly blunt tips on cantilevers of minimal width and surface area.

Resolution and contrast in Kelvin probe force microscopy

A 1-18-GHz broadband double-ridged horn antenna with coaxial input feed section is investigated. For the ridged horn antenna it is found that the radiation pattern, contrary to common belief, does not maintain a single main lobe in the direction of the horn axis over the full frequency range. Instead, at frequencies above 12 GHz, the main lobe in the radiation pattern starts to split into four large side lobes pointing in off-axis directions with a dip of up to 6 dB between them along the main axis. Although this type of horn is the preferred test antenna, which is in common use for over four decades, no explanation for this unwanted behavior was found in the open literature. To investigate this phenomenon in detail, a method of moments approach has been adopted to simulate the complete antenna system. The simulations are in good agreement with the measurements over the 1-18-GHz operational bandwidth and indicate that the use of this type of horn antenna in EMC applications remains questionable.

Analysis and Simulation of a 1-18-GHz broadband double-ridged horn antenna

A scheme for the direct conversion of millimeter and THz waves to optical signals is introduced. The compact device consists of a plasmonic phase modulator that is seamlessly cointegrated with an antenna. Neither high-speed electronics nor electronic amplification is required to drive the modulator. A built-in enhancement of the electric field by a factor of 35 000 enables the direct conversion of millimeter-wave signals to the optical domain. This high enhancement is obtained via a resonant antenna that is directly coupled to an optical field by means of a plasmonic modulator. The suggested concept provides a simple and cost-efficient alternative solution to conventional schemes where millimeter-wave signals are first converted to the electrical domain before being up-converted to the optical domain.

/pdf/direct-conversion-of-free-space-millimeter-waves-to-optical-41p2gbgs0s.pdf

Direct Conversion of Free Space Millimeter Waves to Optical Domain by Plasmonic Modulator Antenna

A new generalized local time-step scheme is introduced to improve the computational efficiency of the finite-volume time-domain (FVTD) method. The flexibility of unstructured FVTD meshes is fully exploited by avoiding the disadvantage of a single short time step in the entire mesh. The great potential of this scheme is fully revealed in the FVTD simulation of electromagnetic (EM) problems with both large and fine structures in close proximity. The scheme is based on an automatic partition of the computational domain in subdomains where local time steps of the type 2/sup /spl lscr/-1//spl Delta/t(/spl lscr/=1,2,3,...) can be applied without violating the stability condition. Interfaces between subdomains are reduced to a generic two-level system which requires a very limited number of time interpolations during the FVTD iteration, therefore resulting in a very simple and robust technique. The application of local time stepping to three-dimensional EM problems demonstrates a significant speed-up of the computation without compromising the accuracy of the results.

/pdf/a-generalized-local-time-step-scheme-for-efficient-fvtd-ro2foiwjee.pdf

A generalized local time-step scheme for efficient FVTD simulations in strongly inhomogeneous meshes

Complementing plasmonic slot waveguides with highly nonlinear organic materials has rendered a new generation of ultracompact active nanophotonic components that are redefining the state of the art. In this paper, we review the fundamentals of this so-called plasmonic–organic–hybrid (POH) platform. Starting from simple phase shifters to the most compact $IQ$ modulators, we introduce key devices of high-speed data communications. For instance, all-plasmonic Mach–Zehnder modulators (MZMs) are reviewed and long-term prospects are discussed. This kind of modulator already features unique properties such as a small footprint ( $ 20 $\mu$ m $^{2}$ ), a large electro–optic bandwidth ( $>$ 110 GHz), a small energy consumption ( $\sim$ 25 fJ/b), a large extinction ratio ( $>$ 25 dB) in combination with a record small voltage-length product of 40 V $\mu$ m. Finally, as an example for seamless integration we introduce novel plasmonic $IQ$ modulators. With such modulators we show the generation of advanced modulation formats (QPSK, 16-QAM) on footprints as small as 10 $\mu{\hbox {m}}\times {\hbox {75}}\ \mu{\hbox {m}}$ . This demonstration ultimately shows how plasmonics can be used to control both phase and amplitude of an optical carrier on the microscale with reasonably low losses.

Pascal Leuchtmann

Papers

Resolution and contrast in Kelvin probe force microscopy

Analysis and Simulation of a 1-18-GHz broadband double-ridged horn antenna

Direct Conversion of Free Space Millimeter Waves to Optical Domain by Plasmonic Modulator Antenna

A generalized local time-step scheme for efficient FVTD simulations in strongly inhomogeneous meshes

Plasmonic Organic Hybrid Modulators—Scaling Highest Speed Photonics to the Microscale