Optical Circuit Devices Research Articles

Boosting optical nonreciprocity: surface reconstruction in iron garnets

Bi-substituted iron garnet films are extensively used in the fabrication of nonreciprocal devices in optical telecommunications. The miniaturization of these devices for on-chip integration requires the development of more efficient magneto-optic materials than presently available. Recent evidence has emerged of large near-surface enhancements in the magneto-optic response in these materials. However, their operative mechanisms at the atomic and electronic levels are not as yet understood. We report significant differences in the ionic structure between surface and bulk in bismuth-substituted iron garnet materials. It is found that the unit cell is elongated normal to the surface, thus enlarging the separation between F e 3 + ions. These ions play a central role in the magneto-optic response of this material. A marked displacement of Fe ions creates gaps at the surface that are populated in the bulk. Concomitantly, surface- and bulk-sensitive measurements of spin-polarized 3d F e 3 + states show significant differences in the magnitude of L 2 edge x-ray magnetic circular dichroism, as well as differences in L 3 edge dichroism, which, in the presence of spin-orbit coupling in 3d states, can be assigned to high-energy states. An increase in magnetic circular dichroism correlates with larger Faraday rotation. These findings provide a deeper understanding of the role of the surface in the electronic transitions to excited F e 3 + 3d states, responsible for these nonreciprocal phenomena. Together with the surface reconstruction underlying these effects reported here, they provide a useful tool for the further development of improved materials technologies to advance the integration of nonreciprocal devices in optical circuits.

Engineering Donor–Acceptor Heterostructure Metal–Organic Framework Crystals for Photonic Logic Computation

AbstractPhotonic materials use photons as information carriers and offer the potential for unprecedented applications in optical and optoelectronic devices. In this study, we introduce a new strategy for photonic materials using metal–organic frameworks (MOFs) as the host for the rational construction of donor–acceptor (D–A) heterostructure crystals. We have engineered a rich library of heterostructure crystals using the MOF NKU‐111 as a host. NKU‐111 is based upon an electron‐deficient tridentate ligand (acceptor) that can bind to various electron‐rich guests (donors). The resulting heterocrystals exhibit spatially segregated multi‐color emission resulting from the guest‐dependent charge‐transfer (CT) emission. Spatially effective mono‐directional energy transfer results from tuning the energy gradient between adjacent domains through the selection of donor guest molecules, which suggests potential applications in integrated optical circuit devices, for example, photonic diodes, on‐chip signal processing, optical logic gates.

Engineering Donor-Acceptor Heterostructure Metal-Organic Framework Crystals for Photonic Logic Computation.

Photonic materials use photons as information carriers and offer the potential for unprecedented applications in optical and optoelectronic devices. In this study, we introduce a new strategy for photonic materials using metal-organic frameworks (MOFs) as the host for the rational construction of donor-acceptor (D-A) heterostructure crystals. We have engineered a rich library of heterostructure crystals using the MOF NKU-111 as a host. NKU-111 is based upon an electron-deficient tridentate ligand (acceptor) that can bind to various electron-rich guests (donors). The resulting heterocrystals exhibit spatially segregated multi-color emission resulting from the guest-dependent charge-transfer (CT) emission. Spatially effective mono-directional energy transfer results from tuning the energy gradient between adjacent domains through the selection of donor guest molecules, which suggests potential applications in integrated optical circuit devices, for example, photonic diodes, on-chip signal processing, optical logic gates.

Composite one-way transmission waveguide based on the curved metal slit and 1D photonic crystal

The one-way devices in optical circuits are the key components just as the diodes in electric circuits, which allow the light going in only one direction. A novel one-way transmission structure is proposed which is a curved waveguide containing a confined photonic crystal. When the waveguide is made of perfect electric conductor, the exact calculation results demonstrate that the device shows excellent one-way properties. The forward transmissivity approaches 100% and the largest transmission ratio exceeds 100.92N, where N is the cell number of the photonic crystal in the structure. When the waveguide is made of real metal, the device also presents excellent one-way transmission properties, which can be confirmed by an approximate calculation as well as by the simulation. In working region, the lowest forward tranmissivity is about 30% and the largest one exceeds 70%. The highest transmission ratio exceeds 104.

Design of Three-Dimensional Optical Circuit Devices by Using Topology Optimization Method With Function-Expansion-Based Refractive Index Distribution

We extend topology optimization method with function-expansion-based refractive index distribution to optimization for three-dimensional optical circuits, in which a refractive index distribution in a design region is expressed by an expansion with some analytical functions. Three-branch optical waveguides have been optimized as numerical examples. Equally branching three-branch waveguides are achieved using our method. A limitation of topology optimization in two dimensions and dependency of initial structure are also shown.

Polarization-dependent optical switch and its application for integrated optical circuit devices

An optical switching mechanism that uses chiral photonic band-gap structures is proposed. The switching is carried out by shifting the band-gap of the configuration. The component employs selective reflection in cholesteric layers and phase-shifting variance in retardation plates. The prototype has been designed and its parameters have been investigated. The spectral response of the component is calculated with respect to the input of orthogonal linear polarizations which are shown to be either efficiently transported to the forward and the backward directions within different photonic band-gaps. Two designs for stop-band tuning can be considered in the modulation functionalities, and thus a tunable dual-state polarization switching for mutually orthogonal polarized lights could be realized. Related applications of this component as a variable in-line polarization router and combiner for optical communication systems are emphasized.

Design of optical circuit devices based on topology optimization

We apply a design method based on topology optimization technique to optical waveguide devices. In our approach, after a refractive index profile in a design region is automatically generated using a topology optimization method, the obtained structure is redefined using primitive geometries with some design parameters and those parameters are optimized by a sequential linear programming. As numerical examples, we demonstrate how the method can be used for 90/spl deg/ bends and T-branching waveguides with arbitrary splitting ratio.

Design of Photonic Crystal Directional Coupler with High Extinction Ratio and Small Coupling Length

As one of the key component of photonic crystal optical circuit devices, the directional coupler is investigated. We explain the reason the directional coupler consisting of an ordinary symmetric parallel waveguide cannot have a high extinction ratio and a small coupling length simultaneously. To realize both characteristics simultaneously, we propose a novel directional coupler structure. By numerical calculation, we show the possibility of a directional coupler with a high extinction ratio (-24 dB) and a small coupling length (18a).

Tunable Photonic Crystal Waveguide Coupler With Nematic Liquid Crystals

Photonic crystals (PCs) have great potential in applications for their ability to control lightwave propagation and the possibilities of implementing PC-based optical waveguide into waveguide coupler systems. In this letter, the novel tunable PC waveguide coupler based on nematic liquid crystals is proposed, and its coupling properties are numerically investigated by using the finite-difference time-domain method. The coupling length of PC waveguide couplers with liquid crystals is shorter than the coupling length of coupler without liquid crystals at the same input wavelength. The refractive indexes of liquid crystals can be changed by rotating the directors of liquid crystals. Then, we can control the direction of light propagation in PC waveguide coupler. These results may provide novel application of switching devices in optical circuits.

Optical circuit devices

Optical circuit devices

Tunable light propagation in Y-shaped waveguides in two-dimensional photonic crystals utilizing liquid crystals as linear defects

We theoretically investigate the tunability of light propagation in Y-shaped waveguides in two-dimensional photonic crystals with triangular lattices composed of air holes utilizing liquid crystals as linear defects. Waveguides can be obtained by the infiltration of liquid crystals into air regions in two-dimensional photonic crystals composed of air holes with triangular lattices. The refractive indices of liquid crystals can be changed by rotating the directors of liquid crystals. Then, we can control the direction of light propagation in Y-shaped waveguides in two-dimensional photonic crystals with triangular lattices, which would provide novel applications of switching devices in optical circuits.

Analysis of fundamental property of 2D photonic crystal optical waveguide with various medium conditions by condensed node spatial network

AbstractPhotonic crystals have a stopband characteristic (photonic bandgap: PBG) in which the light in a specific wavelength band is strongly attenuated. This structure is expected to exhibit the possibility of fine‐structure devices with sharp bends on the order of a wavelength that cannot be realized by weakly guided waves such as those in an optical fiber and a slab waveguide. However, significant difficulties are expected for their design and fabrication. Therefore, understanding and prediction by simulation are indispensable. To date, many analyses have been carried out by the FDTD method and the BPM method. In particular, for the fabrication of functional optical‐circuit devices, it is necessary to carry out a global analysis of the photonic crystal optical waveguide, including dielectric materials with dispersion and nonlinear effects. In this paper, the fundamental properties of photonic crystal optical waveguides containing various media are analyzed by means of the special feature of treating the medium condition in the condensed node spatial network method. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 85(5): 10–20, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.10018