Circular slot antennas were formed in an array on the surface of SiC. Surface-phonon polariton and surface-plasmon polariton signals were observed to appear at the same time in the spectra. The resonance spectrum of the surface-phonon polariton varied with the wavelength shift of the surface-plasmon polariton in association with the period of an array. This suggested a possibility that surface-plasmon polariton, in which electrons had a role, produced an effect on the spectral transformation of surface-phonon polariton.

It has been believed that the energy transfer of one exciton arising in an organic layer creates one SPP on a proximally-positioned metal surface. However, because excitons in the organic layer are close to one another, there is the possibility that multiple SPPs are generated in phase, entering an appearance of constructive interference among the scattered electromagnetic waves. This should lead to an increase in SPP scattering probability effectively. To investigate the possibility and light enhancement associated with this, we prepared a device consisting of Alq3 on a quarter-wavelength dielectric multilayer film/glass as a reference instead of the usual Alq3/glass substrate. This reference device eliminated the influence of complicated optical interference, and made it possible to calculate SPP-mediated light enhancement accurately. The contributions of SPPs and non-radiative components to light emission were adjusted in the calculation as the results corresponded with the measured enhancement dependence on Alq3 thickness. As a result, it was found that the SPP scattering rate was larger than the ordinary calculation based on the assumption that excitons create SPPs randomly. In-phase energy transfer from excitons to SPPs is supported by evidences obtained from this study.

The development of small sized laser operating above room temperature is important in the realization of optical integrated circuits. Recently, micro-lasers consisting of photonic crystals (PhCs) and whispering gallery mode cavities have been demonstrated. Optically pumped laser devices could be easily designed using photonic crystal-slab waveguides (PhC-WGs) with an air-bridge type structure. In this study, we observe lasing at 1.3μm from two-photon pumped InAs-quantum-dots embedded GaAs PhC-WGs above room temperature. This type of compact laser shows promise as a new light source in ultra-compact photonics integrated circuits.

Extremely-compact SiO2-based waveguide-type mirrors composed of deeply-etched trenches are fabricated. The newly-developed deep and small trench enables us to fabricate extremely-compact integrated optical devices including red-green-blue multiplexers for laser projectors.

We developed a spectral-domain optical coherence tomography (SD-OCT) with a white light source for high-resolution, non-destructive profile imaging. By using a 625-nm-centered white light (260 nm bandwidth), 0.69 /nm of axial resolution was achieved. This resolution is suitable for the inspection of thin photoresists (e.g., 1-2 μm) coated semiconductor wafers, which are used for optical device fabrication.

Distribution of electric fields normal to the antenna plane in the depth direction was experimentally investigated by using mid-infrared circular antennas that were formed on Al2O3/SiO2/Si and SiO2/Al2O3/Si. The Al2O3 layer was deposited using an atomic layer deposition technique which allowed for layer thickness control with an accuracy of nanometers. The field distribution in the depth direction was estimated by observing the surface phonon polariton signals originating from the SiO2 layer.

Optical electric field enhancement in the normal direction was experimentally investigated using mid-infrared slot antennas that were formed on a thin Al2O3 layer/Si substrate. The Al2O3 layer thicknesses could be controlled to an accuracy of a given atomic layer through the use of atomic layer deposition, and varied from 0nm to 60nm. An in-depth probe of the electric field was performed by observing the change in the reflection signal arising from the Restrahlen band of the natural oxide of Si formed on the surface of a Si substrate. In contrast to dipole nanoantennas, we could clearly observe Restrahlen bands of Al2O3 as well as the native Si oxide film. This was because the direction of the enhanced electric field was primarily parallel to the substrate surface in the slot antennas, which was different from the dipole nanoantenna having strong normal electric fields at the antenna ends. The atomic layer deposition technique provides versatile information on the electric field distribution within the depth direction, being considered complementary to the electromagnetic simulation of nanoantennas.

Amorphous Si wire waveguides with stacked gratings are successfully fabricated by carefully controlling the SOG coating thickness. The peak energy of the light from the waveguide is controlled to be just 1.55 μm as designed.

Photonic crystal surface emitting lasers (PCSELs) [1] offer the ultimate in control in semiconductor lasers. PCSELs have been shown to have high power scaling with area, high single-mode powers [2], large scale coherent emission, control of the beam shape and polarization with design of the photonic crystal geometry [3,4], as well as beam steering [5]. The photonic crystal, a two-dimensional variation in refractive index, provides feedback in multiple orthogonal directions. Wave propagating in various directions couple with one another and a 2D standing wave (cavity mode) is constructed over a broad area. These devices have previously been fabricated through wafer fusion or the formation of voids during the re-growth process. The manufacturability of such devices prompted the move towards epitaxially regrown structures that do not contain voids.

Summary form only given. Photonic crystals are very suitable for controlling radiation field and propagation characterization of light. As an important application, it is ultra compact and ultrafast optical integrated circuits (OIC) based on photonic crystals slab waveguide (PhC-WG) composing of the line-defects [1, 2]. The PhC-WG is also attractive for laser lasing, because very small group velocity of near the Brillouin zone (BZ) edge should enhance interactions between the radiation field and matter. Indeed, the lasing spectrum has been observed from optically pumped InAs-quantum dots (InAs-QDs) embedded PhC-WG [3]. And a small group velocity (V g ) in the PhC-WG gives rise to enhancement intensity and, therefore, is advantageous to nonlinear optical effect. In this work, we present the 1.55 μm to 1.3 μm upconversion luminescence (UL) based on two-photon absorption in InAs-QDs GaAs PhC-WG.

After growing a thin Al2O3 layer by atomic layer deposition on a Si substrate, slot antenna arrays were formed on it. Reflectivity spectra measured in the mid-infrared range showed characteristic aspects, presumably caused by the surface phonon polariton of a SiO2 layer naturally formed on the Si substrate. When the Al2O3 layer thickness was 6 nm, such spectral features disappeared. In this way, we could estimate experimentally the electric field distribution normal to the surface of the substrate.

We have grown bi-layer InAs quantum dots (QDs) on GaAs substrates for extending the emission wavelength of InAs/GaAs QDs beyond 1.3 mu m. The QD bi-layer, which comprises two QDs layers (seed- and active-QDs) separated with a GaAs spacer layer of 10 nm in thickness, exhibits light emission from active-QDs with longer wavelength. An enlargement of the active-QDs occurred by optimizing several growth parameters: growth temperature of seed-QDs, amount of InAs supplied for seed- and active-QDs layers. These optimized parameters lowered the density of the seed-QDs strain spreading upward, which resulted in an enlargement of the active-QDs. We achieved a control of the extension of emission wavelength up to approximately 1.4 mu m from 1.2 mu m. These results indicate that the QD bi-layer can be applied to a broadband light source exhibiting an emission spectrum centered at 1.3 mu m with a bandwidth of 200 nm. (c) 2013 Elsevier B.V. All rights reserved.

Alternating stacks of metal and dielectric films with nano-hole arrays, called fishnet structures, control the propagation of electromagnetic waves. In such a structure, changing a dimension or a shape, especially the change in shape of nanoholes, affect propagation constants. In this study, we report the dispersivity of fishnet structures is controllable with different hole shapes, by measuring the interferometric fringe in various wavelengths. Two structures were fabricated, which consist of five alternating stacks of aluminum and silicon dioxide with nano-hole arrays. The holes in one of the structures are circular with diameters of 500nm, and the other are square with 500nm sides. The lattice constant in each case is 1,000nm. Since fishnet structures are wavelength-dependent structures, the variable-wavelength interferometric microscope was set up. The phase shift of the circular hole and the square hole fishnet were about 110 degrees and 85 degrees, respectively, within a tunable wavelength from 1,470nm to 1,545nm. These values were equivalent to a refractive-index-change of 0.8 and 0.6, respectively. From these results, fishnet structures indicate high dispersivity within target wavelengths. The dispersion of fishnet structure can be controlled by the shape of the hole.

Regular arrays of InP nano pillars have been fabricated by low energy Electron Cyclotron Resonance (ECR) Ar+ ion irradiation on InP(111) surface. Several scanning electron microscopy (SEM) images have been utilized to invetsigate the width, height, and orientation of these nano pillars on InP(111) surfaces. The average width and length of these nano-pillars are about 50 nm and 500 nm, respectively. The standing angle with respect to the surface of the nano-pillars depend on the incidence angle of the Ar ion irradiation during the fabrication process. Interestingly, the growth direction of the nano pillars are along the reflection direction of the ion beam and the standing angles are nearly same as the ion incidence angle with the surface normal. This nano-pillas are easily transferred from the InP surface to double sided carbon tape without any damage. High Resolution Transmission Electron Microscopy (HRTEM) study of single nano-pillar reveals that this nano-pillar are almost crystalline in nature except 2-4 nm amorphous layer on the outer surface. The transmission electron microscopy combined with energy-dispersive x-ray spectroscopy (TEM-EDS) analysis of these nano pillars exhibit that the ratio of In and P is little higher compared to the bulk InP.

Multi-color quantum dot (QD) ensembles were grown by selective-area growth method to realize a shape-controlled broadband light source. By using a metal-mask, QD ensembles and strain reducing layer (SRL) were formed in selective areas on a wafer. The SRL thickness was varied to achieve appropriate shifts in the peak wavelength of the QD emission spectrum up to 90nm. A summation of PL spectra obtained from the multi-color QD ensembles shows a broadband emission spectrum with a width of approximately 120nm, even though this spectrum is attributed to the ground state emissions of these QD ensembles. A current-induced broadband light source such as a superluminescent diode (SLD) based on the multi-color QD ensembles is expected to have an emission spectrum with a width of more than 120nm owing to the combination of excited state emissions. Furthermore, a desired shape of the SLD spectrum can be obtained by controlling the injection current applied to each QD ensemble. This approach is promising for a shape-controlled broadband SLD, and it is particularly applicable to optical coherence tomography (OCT).

Ultra-small, ultra-low energy and ultra-fast SMZ-type all-optical analog switch, PC-SMZ and digital optical flip-flop, PC-FF, have been investigated by using GaAs-based photonic crystal (PC) waveguides and InAs-based quantum dots (QDs). For this purpose, a topology optimization design method for wide/flat-band PC waveguides and selective-area-growth of QDs using a metal-mask MBE method have been developed. This chapter reviews successful operation of an ultra-low energy (similar to 100 fJ) PC-SMZ at an ultra-fast (similar to ps) speed with a high repetition-rate up to 40 Gb/s. It also reviews successful computational verification of optical bi-stability in the PC-FF with a high repetition-rate up to 40 Gb/s.

Two types of nanophotonic technologies—two-dimensional photonic crystal (2D PC) slab waveguides (WGs) and quantum dots (QDs)—were developed for key photonic device structures in the future. For an ultrafast digital photonic network, an ultrasmall and ultrafast symmetrical Mach–Zehnder (SMZ)-type all-optical switch (PC-SMZ) and an optical flip–flop device (PC-FF) have been developed. To realize these devices, one method is to develop a selective-area molecular beam epitaxial growth QD technique by employing a metal mask method. Another method is to establish a new design method, i.e., topology optimization of the 2DPC WG with a wide and flat bandwidth, high transmittance, and low reflectivity. We also fabricated an optical microcavity in a photonic crystal slab embedded with GaAs QDs by droplet epitaxy. The Purcell effect on the exciton emission of GaAs QDs was confirmed by microphotoluminescence and lifetime measurements.

GaAs-based two-dimensional photonic crystal (2DPC) slab waveguides (WGs) and InAs quantum dots (QDs) were developed for key photonic device structures in the future. An ultrasmall and ultrafast symmetrical Mach-Zehnder (SMZ)-type all-optical switch (PC-SMZ) and an optical flip-flop device (PC-FF) have been developed based on these nanophotonic structures for an ultrafast digital photonic network. To realize these devices, two important techniques were developed. One is a new simulation method, i.e., topology optimization method of 2DPC WGs with wide/flat bandwidth, high transmittance and low reflectivity. Another is a new selective-area-growth method, i.e., metal-mask molecular beam epitaxy method of InAs QDs. This technique contributes to achieving high-density and highly uniform InAs QDs in a desired area such as an optical nonlinearity-induced phase shift arm in the PC-FF. Furthermore, as a unique site-controlled QD technique, a nano-jet probe method is also developed for positioning QDs at the centre of the optical nonlinearity-induced phase shift arm.

The configuration of coupled ultra-small Mach-Zehnder all-optical switches is quite attractive for high-speed optical flip-flops. Its bistability is experimentally demonstrated with an emulated setup. High-speed capability corresponding to 10 and 40 Gb/s is confirmed with simulation based on rate equation analysis.