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The integration of quantum well infrared photodetectors with plasmon cavities has allowed for demonstration of sensitive photodetectors in the mid-infrared. These detectors typically use only a single type of plasmon cavity, but previous studies of metasurface absorbers has shown that combining multiple cavities in a single subwavelength period can generate complex photoresponses such as multi-band and broadband absorption. In this report, we use a simple square cavity design as a building block for demonstrating detectors with a broadened photoresponse. Device performance of simple square detectors is comparable to previous highdetectivity designs, and by using a patchwork of square cavities within a single subwavelength period, we can subsequently broaden photoresponse by 1.5 times. Absorption in these patchwork cavity detectors shows good agreement with previous reports for metasurface absorbers, and suggests that this design and fabrication process could serve as a roadmap for integrating detectors and metasurface cavities with more complex photoresponses.

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.

Non-destructive inspection of semiconductor optical waveguides was demonstrated using optical coherence tomography with a visible broadband light source (vis-OCT). Comparisons of measured height and width between the vis-OCT, stylus profiler, and cross-sectional scanning electron microscopy indicated the effectiveness of the vis-OCT as a high-resolution, non-destructive, and non-contact measurement method.

InAs quantum dots (QDs) were grown on GaAs by molecular beam epitaxy using As 2 molecules (As 2 -QDs) and were structurally and optically characterized. Photoluminescence (PL) measurements revealed unique optical properties of the As 2 -QDs, which differ from InAs QDs grown with As 4 (As 4 -QDs). As 2 -QDs exhibited PL emission centered at 1.14–1.21 µm, which is shorter than that of As 4 -QDs (1.21–1.22 µm). In addition, the emission peak wavelength was continuously redshifted with a growth interruption time (Δt), which is an interval between the growth of the As 2 -QDs and capping of the QDs with a GaAs layer. Considering that no apparent difference of structural property was observed among as-grown As 2 -QDs and As 4 -QDs with various Δt, the peak shift can be attributed to the deformation of QDs during the capping process. The continuous peak shift can be applied to control the emission wavelength of InAs QDs, and this enables a broadband light source by combining the As 2 -QDs with different peak wavelengths.

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 Al 2 O 3 /SiO 2 /Si and SiO 2 /Al 2 O 3 /Si. The Al 2 O 3 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 SiO 2 layer.

The electric field in the normal direction was experimentally investigated by using mid-infrared antennas that were formed on a thin Al 2 O 3 layer/Si substrate. The Al 2 O 3 layer could be as thin as a single nm-order employing the atomic layer deposition, and was varied from 2 nm to 50 nm. The field distribution was estimated by observing the reflectivity change. It was found that the electric field decreased rapidly until a 6 nm depth from the antenna plane, and that the degree of attenuation became relaxed in the deeper region.

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.

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 (Vg) 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.

Photonic crystal surface emitting lasers (PCSELs) [1], shown schematically in Fig 1(a), offer the ultimate in control in semiconductor lasers, demonstrating power scaling with area as lasing occurs at the band edge [2], high single-mode powers [3], large scale coherent emission [4], control of the beam shape and polarization with design of the photonic crystal geometry [5], and beam steering [3] Previous PCSELs utilised the high refractive index contrast between semiconductor and voids created in the structure by wafer fusion [1–4] or by epitaxial re-growth [6]. However, the presence of voids presents possible issues in device reliability, and reproducibility, and the low refractive index of the PCSEL layer results in difficulties in the design of the lateral waveguide.

An epitaxial regrowth process is used to realise photonic crystal surface emitting lasers emitting at 980nm. We optimise the growth process for void-free infill and demonstrate laser operation via coupling to photonic crystal bands.

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 waveguides (PC-WGs) composing of the line-defects [1, 2]. The PC-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 in PC-WG of the multimode W3 type (three rows missing line-defect) [3]. In the present study, we observe laser action in InAs-QDs PC-WG of the single-mode W1 type (single row missing line-defect).

To observe optical properties of propagation light through branched coupled-resonator optical waveguides (CROWs), we fabricated ordered chains of transparent microspheres that have 30°- and 60°-branched structures on a lithographically patterned substrate using a self-assembly process. The spectra of propagation light within the chains were directly measured by guide-collection-mode near-field scanning optical microscopy (NSOM) techniques. Moreover, we perform a finite-difference time domain (FDTD) simulation to explain the spectra. The spectrum of light propagating to the 60°-branch shows some sharp peaks, which seem to be associated with whispering gallery modes (WGMs). On the other hand, the spectrum of light propagating to the 30°-branch shows rather broad peaks. The FDTD simulation suggests that the WGM component propagates to both of the 30°- and 60°-branches, and also suggests that almost all of the nanojet-induced mode (NIM) component propagates to the 30°-branch and little propagates to the 60°-branch. Therefore, the most plausible cause of the difference in the NSOM spectra is that the difference in propagation efficiency of the NIM component between the 30°- and 60°-branches. These results suggest that the microspheres' branching chain itself has a splitting function, which is a kind of wavelength-selective filters.

Nano-photonic structures/materials such as surface plasmon and negative-index material as well as quantum dots (QD) and photonic crystals (PCs) are discussed from potentials for new photonic devices and technologies. PC slab waveguides and QDs were developed for key photonic devices such as ultra-small and ultrafast symmetrical Mach-Zehnder (SMZ)-type all-optical switch (PC-SMZ) and an optical flip-flop device (PC-FF). We have studied energy-saving light/matter interaction in a PC waveguide with emphasis on virtual-excitation-based nonlinear effects such as optical Kerr effect. We have also demonstrated a new RGB color filter on Al film with sub-wavelength holes in a large area with a high precision and optical beam-steering device with a wide steering angle.

A color filter comprising an aluminum film with arrays of sub-wavelength holes has been fabricated. In addition to processability, the aluminum film enables the excitation of visible-range SP due to its high plasma frequency.

A photonic crystal- and quantum dot-based all-optical flip-flop switch (PC-FF) capable of synchronizing with high frequency clock was fabricated for a future optical digital signal processing device with high-speed capability of 40 Gb/s and beyond. Nanostructures constructing the PC-FF exhibit excellent characteristics and suggest successful optical FF demonstration.

A sixfold acceleration of the phase shift recovery time in photonic crystal/quantum dot waveguides having a Purcell enhanced spontaneous emission peak resonant to the excited state of the quantum dots is experimentally demonstrated.

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.

We have developed a technique for selective-area-growth (SAG) of InAs quantum dots (QDs) having different absorption wavelengths, with the goal of using them in all-optical integrated devices. This technique, using the metal-mask method and the insertion of a strain-reducing-layer, provides successful SAG of QDs absorbing at different wavelengths in different areas. This SAG technique is promising for various QD applications as well as our proposed photonic-crystal-based all optical switch (PC-SMZ) and digital flip-flop device (PC-FF).

The phase shift of signal pulse due to carrier excitation in quantum dots (QDs) induced by repetition control pulses is measured by two-color pump/probe measurements to investigate the effects of repetition frequency on the switch operation.The result suggests the possibility of beyond 40 GHz repetitive switch operations in photonic-crystal-based Mach-Zehnder (PC-SMZ) by using QDs with faster decay time constant, e. g., 100 ps.

Photonic crystal structures allow an unprecedented control of light on length scales equivalent to the wavelength. The intricate interaction of light and the periodic lattice can lead to phenomena like localization, negative refraction and slow light. In order to understand the optical behaviour of such novel structures, an investigation of the underlying photonic eigenstates is crucial, since the propagation of light through them is governed by their photonic eigenstates and the coupling between these states. Here we investigate the propagation of light pulses through a complex photonic crystal device in real-time. Analysis of the photonic eigenstates in k-space allows different states to be identified. By tracking the evolution of the eigenstates in both k-space and time, we uncover the dynamics of the eigenstates and their mutual coupling directly on femtosecond time-scales.

We report design, fabrication, and characterization of a high refractive index micro planar lens for coupling of light to 2D photonic crystal waveguides (PhC WG) on an AlGaAs membrane. The lens reduced coupling loss by 4dB and the depth of fine Fabry-Perot fringes in a transmission spectrum by 1/10, relative to a PhC waveguide terminated by a cleaved facet. The lens not only stabilizes a coupling performance over different waveguides formed on different chips but also considerably tolerates the degree of precision required in aligning external optical components.

A metal-mask (MM) method for selective-area-growth (SAG) of self-assembled InAs quantum dots (QDs) on a GaAs substrate was developed for applications of ultra-small and ultra-fast all optical devices based on a combination of QD and photonic crystal waveguides (PC-WGs). Successful SAG of QDs with high density and high optical quality comparable to conventional InAs-QDs grown without the MM was confirmed by atomic force microscopy and photoluminescence (PL) measurements. The QD density was 4times1010 cm-2 and FWHM of the PL emission was around 30 meV at room temperature. By insertion of a strain-reducing layer on the QD, the PL peak wavelength was controlled from 1240 nm to 1320 nm. The MM method is promising for realizing the PC-based all optical devices, which require SAG of QDs and a QD ensemble with a different absorption-peak wavelength in a different area.

We have demonstrated the selective area growth of high density InAs quantum dots (QDs) in the square regions by using site-controlled InAs dots that were formed in the desired regions as templates. These fabricated InAs dots for the templates were enabled by the use of a specially designed atomic-force-microscope (AFM) cantilever, referred to as the Nano-Jet Probe (NJP). Using the NJP, two-dimensional (2D) arrays of ordered In nano-dots were fabricated in the desired square regions on a GaAs substrate. These In nano-dots were directly converted to InAs QD arrays by subsequent annealing with irradiation of arsenic flux. By using the converted QD arrays as strain templates, self-organized InAs QDs with high density were formed in the selected square regions.

Topology optimization has been used to design intersections and bends in two-dimensional photonic crystal slab waveguides. We have experimentally confirmed that the optimized intersection displays high transmittance with low crosstalk for the straightforward beam line.

Planar focusing lens gratings are investigated in order to realize an efficient coupling from an optical fiber to a two-dimensional photonic crystal slab waveguide. The optimal gratings exhibit the calculated coupling efficiency of 34%.

We fabricated a microcavity on AlGaAs-based photonic crystal slab. Bistable responses of the resonant peak were achieved with input power less than 1 mW in optical communication band for future optical switch and memory applications.

Numerical and experimental studies on the photonic crystal waveguide intersection based on the topology optimization design method are reported and the effectiveness is shown by achieving high transmission spectra with low crosstalk for the straightforward beam-propagation line.

A two-dimensional photonic crystal (2DPC) slab waveguide-based symmetric Mach-Zehnder type all-optical switch (PC-SMZ) is promising for a future ultra-fast photonic network system. An ultra-fast (~ ps) and ultra-low energy (~ 100 fJ) switching has already been demonstrated as the 1st phase. The 2nd phase is to create a PC SMZ-based ultra-fast photonic logical switch with a latch function for an ultra-fast photonic digital processor. One of the steps towards the goal is to develop a new design method of waveguides with wide/flat bandwidth, high transmittance and low reflectivity for improving switching performances. Another one is to develop a selective area growth of quantum dots. This paper dominantly reviews these two recent topics as well as briefing the PC-SMZ performances.

We demonstrated a novel two-dimensional photonic-crystal based Symmetric Mach Zehnder type all-optical switch (PC-SMZ) with InAs quantum dots acting as a nonlinear phase-shift source. The 600-mum-long PC-SMZ exhibited a 15-ps-wide switching-window at sufficiently low optical-energy of ~100 fJ.

Optical microcavity was fabricated in an AlGaAs-based photonic crystal slab. The optical resonance was within the communication wavelengths and had a quality factor of 1900. Optical bistability due to thermo-optic origin was observed.

We have studied the dispersion of femtosecond pulses in a photonic crystal waveguide. We found that slow propagating pulses were asymmetrically broadened, due to higher order dispersion. With decreasing group velocity, the asymmetry increased.

We have successfully fabricated several ultra-small photonic-crystal (PC)-waveguide-based components utilizing single-line-defect in the air-bridge type GaAs PC involving InAs quantum dots. By controlling the Al content of a sacrificial AlGaAs clad layer and the wet etching duration, a PC core layer with a very smooth surface was obtained. An extremely low propagation loss of 0.76 dB/mm was achieved for a GaAs core PC waveguide.

We have developed a two color pump-probe ellipsometry for the measurement of the optical nonlinear phase shift in a waveguide with quantum dot (QD) core layers. The key point of the method is to utilize the large polarization-dependent property in the optical nonlinearity arising from a flat-dome-like shape of the QDs. In this paper we report the time resolved behavior of the nonlinear response in the QD waveguides obtained by this method. Optical phase shift of more than /spl pi//2 rad was obtained by a pumping of 30 pJ//spl mu/m/sup 2/. Delay time dependence of the phase shift is discussed in connection with the carrier dynamics.

Numerical and experimental studies on photonic crystal waveguide directional couplers (DCs) with coupling-strength-control defects are reported here. The basic structure consists of two parallel-coupled single-defect waveguides separated by a triple-line air-hole array, with some air holes in the middle of the triple-line eliminated. Fundamental operation as the DC at a wavelength of /spl sim/1.3 /spl mu/m is observed with a short coupling length.

An ultrafast semiconductor all-optical switch using a third-order optical nonlinearity is attractive for a future OTDM system. This type of switch essentially requires both ultrafast and low optical-power operations. However, the tradeoff between them, based on the optical nonlinearity in general, often makes it difficult to achieve such a switch in practical use. This paper proposes a novel enhancement method of the third order nonlinearity by using quantum dots (QDs) embedded in a photonic crystal (PC), thus reducing the optical consumption power.

A InGaAs QW vertical cavity surface-emitting laser with a broad-gain bandwidth was fabricated by using multiple-quantum-well active layers with different bandgap energies, increasing the temperature range by more than 20/spl deg/C.

Research and development of vertical-cavity surface-emitting lasers (VCSELs) has made rapid progress in recent years. VCSEL array link modules have been developed with increasing speed by American consortiums such as OETC and POLO. On the other hand, high-performance VCSELs, such as low-threshold or high wall-plug efficiency ones, are being developed using AlAs selective oxidation. With this background, we describe the future prospects of VCSELs from an industrial viewpoint. The topics discussed include: reliability; low-voltage and low-power operations; and module assembly techniques. The authors conclude that the VCSEL is a promising device for achieving optical interconnections.

An AlGaAs-based two-dimensional (2D) photonic crystal (PC) air-bridge structure with defect waveguides has been fabricated for an application to miniaturized planar lightwave circuits. Measured optical transmission characteristics showed a good agreement with theoretical band structure calculation for the sample without waveguides, while optical beam transmission through the waveguide was observed in the wavelength ranging around 1 /spl mu/m for the sample with waveguides.