Mathias Vanwolleghem

Magneto-optical circulator designed for operation in a uniform external magnetic field

We propose an approach for the design of resonant cavities employed in magnetophotonic crystal (MPC) circulators and isolators. Starting from the analysis of a model circularly symmetric cavity, we show how to obtain a significant splitting of the eigenfrequencies of the two counterrotating cavity modes without introducing subdomains magnetized in opposite directions. Using the multiple-scattering method extended to handle uniaxial gyrotropic materials, we demonstrate numerically an MPC circulator working in a uniform external magnetic field.

Transverse magnetic mode nonreciprocal propagation in an amplifying AlGaInAs∕InP optical waveguide isolator

The design, fabrication, and characterization of an amplifying transverse magnetic (TM)-mode optical waveguide isolator operating at a wavelength of 1300nm are presented. The magneto-optical Kerr effect induces nonreciprocal modal absorption in a semiconductor optical amplifier with a laterally magnetized ferromagnetic metal contact. Current injection in the active structure compensates for the loss in the forward propagation direction. Monolithic integration of this optical isolator configuration with active InP-based photonic devices is straightforward. The combination of AlGaInAs∕InP active material and the metal alloy Co50Fe50 results in greatly improved performance. 99dB∕cm TM mode isolation and significantly reduced insertion loss are demonstrated.

Comment on "Nonreciprocal light propagation in a silicon photonic circuit".

We show that the structure demonstrated by Feng et al. (Reports, 5 August 2011, p. 729) cannot enable optical isolation because it possesses a symmetric scattering matrix. Moreover, one cannot construct an optical isolator by incorporating this structure into any system as long as the system is linear and time-independent and is described by materials with a scalar dielectric function.

Experimental demonstration of nonreciprocal amplified spontaneous emission in a CoFe clad semiconductor optical amplifier for use as an integrated optical isolator

Experimental results are presented for an integrated-optical-waveguide-isolator concept. This concept is based on inducing the transverse magneto-optic Kerr effect in a semiconductor InP-based optical amplifier (SOA) by using a transversely magnetized ferromagnetic metal as an electrical contact. As a result, the SOA exhibits nonreciprocal loss/gain for TM polarized light and is easily monolithically integrated with other InP-based active photonic devices. We have designed, fabricated and characterized prototype ferromagnetic metal-clad optical amplifiers for an operation wavelength of 1300nm. In these first generation devices we obtained isolation strengths of up to 2.0dB∕mm.

Calculation of bending losses in dielectric waveguides using eigenmode expansion and perfectly matched layers

In this letter, we present a different approach to accurately calculate the bending losses in curved dielectric waveguides. It is based on the well-known conformal transformation of the index profile and on vectorial eigenmode expansion, but this time with perfectly matched layer (PML) boundary conditions to accurately model radiation losses. The modal spectrum of these waveguides in the presence of PML is discussed and the method is validated by comparing it to previously published results.

Design and optimization of a monolithically integratable InP-based optical waveguide isolator

The optimization design of the layer structure for a novel type of a 1.3 μm monolithically integrated InP-based optical waveguide isolator is presented. The concept of this component is based on introducing a nonreciprocal loss-gain behavior in a standard semiconductor optical amplifier (SOA) structure by contacting the SOA with a transversely magnetized ferromagnetic metal contact, sufficiently close to the guiding and amplifying core of the SOA. The thus induced nonreciprocal complex transverse Kerr shift on the effective index of the guided TM modes, combined with a proper current injection, allows for forward transparency and backward optical extinction. We introduce two different optimization criteria for finding the optimal SOA layer structure, using two different figure-of-merit functions (FoM) for the device performance. The device performance is also compared for three different compositions of the CoxFe1−x(x=0,50,90) ferromagnetic transition metal alloy system. It is found that equiatomic (or quasi-equiatomic) CoFe alloys are the most suitable for this application. Depending on the used FoM, two technologically practical designs are proposed for a truly monolithically integrated optical waveguide isolator. It is also shown that these designs are robust with respect to variations in layer thicknesses and wavelength. Finally, we have derived an analytical expression that gives a better insight in the limit performance of a ferromagnetic metal-clad SOA-isolator in terms of metal parameters.

First experimental demonstration of a monolithically integrated InP-based waveguide isolator

Abstract The architect should be equipped with knowledge of many branches of study and varied kinds of learning. This knowledge is mainly constructed by means of practice and theory (Vitrivius, 1914). Architectural education is considered to be a complex process. Its creative demands must be supported by an understanding of art, science, psychology, mathematics, engineering and etc. The design studio has long been the major component of architectural education. Traditionally it has involved a relatively small group of students under the direction of a studio master, and an instructor. This paper analyzes the characteristics of traditional studio environments, compares it with the constructivist studio in general and recommends a transformation in the design studio.

Modeling of a novel InP-based monolithically integrated magneto-optical waveguide isolator

A method based on Yehs rigorous 4×4 matrix algebra and a fast perturbation-theory-based method are proposed for modeling and optimization of an integrated magneto-optical (MO) waveguide isolator. The transverse MO Kerr effect in ferromagnetic Co90Fe10 is used to design the integrated isolator. Waveguide losses introduced by absorption in the MO metallic film are compensated for by optical gain in an InP-based semiconductor optical amplifier with a tensile strained multiple-quantum-well (MQW) active region. The desired device isolation, which originates from the nonreciprocity of the transverse MO effect, is obtained by operation of the device under appropriate current injection, leading to zero modal net gain in the forward direction while the device remains lossy in the backward direction. In the approach based on Yehs matrix formalism, phenomena such as the MO effects described by anisotropic permittivity tensors, waveguide losses in absorbing layers, and optical gain in the active layer are explicitly included. Numerical aspects of the resonant condition solution for waveguide modes are discussed. In the perturbation theory method, the MO nonreciprocal waveguide effects are calculated in a first-order scheme. The general models are applied in an example of a realistic InP-based MQW isolator with a Co90Fe10 MO layer, indicating that practical isolation ratios are achievable within reasonable levels of necessary material gain. Rigorous and perturbation models are compared, and good agreement is obtained. This result indicates that first-order perturbation theory modeling of integrated magneto-optics is accurate enough, even for devices that employ MO materials with relatively strong Voigt parameters.

Broadband ultra-low-loss mesh filters on flexible cyclic olefin copolymer films for terahertz applications

The cyclic olefin copolymer (COC) has recently demonstrated promising properties for THz applications due to its extremely high transparency in the THz region. Here, we prove that COC can be efficiently used as substrate material for free-space THz devices through the design, fabrication, and characterization of high-pass metal mesh filters. Measurements are in good agreement with calculations, and a transmittance higher than 75% has been measured between 1.5 THz and 2.5 THz for a single-layer filter. In addition, we prove that stacked meshes can be easily embedded to improve their rejection ratio in the stop-band, while preserving a high transparency in the pass-band. The broadband behavior of these filters should extend up to their diffraction limit estimated at around 6.3 THz for the single-layer filter.

Magnetic properties of the magnetophotonic crystal based on bismuth iron garnet

This article reports on the magnetism of continuous and patterned bismuth iron garnet (Bi3Fe5O12 or BIG) thin films for magnetophotonic crystal (MPC) applications. The exact knowledge of the magnetic properties is crucial for the design of fully functional MPC. BIG thin films were grown on several types of isostructural substrates by pulsed laser deposition. The growth conditions and bismuth transfer were optimized to obtain good quality magneto-optically active films compatible with nanostructuring process. MPC were successfully fabricated from BIG/GGG(001) films with low roughness and high Faraday rotation. Magnetic characteristics (magnetization, anisotropy, magnetic domains, magnetization reversal) of the continuous BIG films and MPC were extensively studied and compared to the results of the micromagnetic simulations performed for MPC with different anisotropy. The present study shows that the fabrication of the MPC structure lowers the magnetocrystalline and uniaxial in-plane anisotropies and induce...