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In this study, we experimentally demonstrated that the nonlinear optical coefficient of the original Si can be enhanced by incorporating a metamaterial structure into an existing silicon waveguide. The two-photon absorption coefficient enhanced by the metamaterial structure was 424 cm/GW, which is 1.2 × 10 3 times higher than that of Si. Using this metamaterial waveguide-based nonlinear optical activation function, we achieved a high inference accuracy of 98.36% in the handwritten character recognition task, comparable to that obtained with the ReLU function as the activation function. Therefore, our approach can contribute to the realization of more power-efficient and compact all-optical neural networks.

The walking sensation is a result of the synthesis of multisensory inputs from various systems. The vestibular system, typically used for detecting acceleration, is a crucial component of the walking sensation. This study investigated the use of galvanic vestibular stimulation(GVS) to enhance the sensation of walking in virtual reality (VR) environments, particularly when users are seated and not engaged in active movements. GVS is a transcutaneous electric stimulation technique to evoke vestibular sensory responses and involves the application of a penetrating current to vestibular afferents. This study revealed that the pseudo-walking sensation can be intensified by applying lateral GVS. However, no difference was observed when it was synchronized with the walking rhythm represented by foot-sole vibration patterns. Furthermore, the study compares the effectiveness of lateral versus anterior-posterior GVS in enhancing walking sensations in VR. The findings provide novel perspectives on enhancing the VR walking experience through vestibular stimulation, even in scenarios in which the user is seated.

Pseudo-haptic techniques are used to modify haptic perception by appropriately changing visual feedback to body movements. Based on the knowledge that tendon vibration can affect our somatosensory perception, this article proposes a method for leveraging tendon vibration to enhance pseudo-haptics during free arm motion. Three experiments were performed to examine the impact of tendon vibration on the range and resolution of pseudo-haptics. The first experiment investigated the effect of tendon vibration on the detection threshold of the discrepancy between visual and physical motion. The results indicated that vibrations applied to the inner tendons of the wrist and elbow increased the threshold, suggesting that tendon vibration can augment the applicable visual motion gain by approximately 13% without users detecting the visual/physical discrepancy. Furthermore, the results demonstrate that tendon vibration acts as noise on haptic motion cues. The second experiment assessed the impact of tendon vibration on the resolution of pseudo-haptics by determining the just noticeable difference in pseudo-weight perception. The results suggested that the tendon vibration does not largely compromise the resolution of pseudo-haptics. The third experiment evaluated the equivalence between the weight perception triggered by tendon vibration and that by visual motion gain, that is, the point of subjective equality. The results revealed that vibration amplifies the weight perception and its effect was equivalent to that obtained using a gain of 0.64 without vibration, implying that the tendon vibration also functions as an additional haptic cue. Our results provide design guidelines and future work for enhancing pseudo-haptics with tendon vibration.

We investigated the enhancement of the perceived force strength in force feedback devices by combining the pulling illusion with kinesthetic illusions. The pulling illusion (i.e., a sensation of being pulled or pushed) is induced by asymmetric vibrations applied to the fingertips, enabling the implementation of small, lightweight, and ungrounded force feedback devices. However, the perceived force intensity is limited. We focused on the kinesthetic illusion, a phenomenon in which the movement of a limb in the direction of muscle extension is illusively perceived by presenting vibrations to tendons or muscles as an illusion that could enhance the perceived strength of the pulling illusion. Moreover, we investigated the perceptual characteristics of force sensation by combining a kinesthetic illusion induced by wrist tendon vibration stimulation with a pulling illusion. The findings demonstrate that the direction of the pulling illusion was accurately perceived, even with simultaneous wrist tendon vibration stimuli. Importantly, the results suggest that tendon vibration on the wrist, rather than cutaneous vibration on the wrist, enhances the perceived force intensity of the pulling illusion at the fingertips. These findings indicate the potential for expanding the expressive capability of the pulling illusion.

This study introduced design informatics using deep learning in a topological photonics system and applied it to a topological waveguide with a sharp bending structure to further reduce propagation loss. The sharp bend in the topological waveguide composed of two photonic crystals wherein dielectrics having C 6v symmetry were arranged in triangle lattices of hexagons, and the designing of parameters individually for 6 × 6 unit cells near the bending region using deep learning resulted in an output improvement of 60% compared to the initial structure. The proposed structural design method has high versatility and applicability for various topological photonic structures.

A defect structure is proposed for enhancing the coupling efficiency of vertically incident circularly polarized light in a topological waveguide. In the topological edge-state waveguide based on triangle lattices of hexagons consisting of six nanoholes respecting C 6v symmetry in a silicon optical circuit, the vertical coupling rate is improved by removing the nanoholes from one hexagonal cell near the line. The coupling efficiency was evaluated with and without the defect structure. The introduced defect structure operates suitably for focused beams of left- and right-handed circularly polarized light, enhancing the optical communication wavelength bandwidth by up to 10 dB.

The Metaverse, profoundly and closely related to VR technology, is attracting attention as a space where social activities can be realized online, and among its various applications, its use in education and training is highly anticipated. However, educational and training applications using the Metaverse should not serve as alternatives to the physical world but rather demonstrate their true value in things that can only be realized in VR or are first made possible in the Metaverse. This article discusses the Metaverse's potential and desired state through new educational and training initiatives enabled by it.

Optical waveguide theory is essential to the development of various optical devices. Although there are reports on the theory of optical waveguides with magneto-optical (MO) and magnetoelectric (ME) effects, a comprehensive theoretical analysis of waveguides considering these two effects has not yet been published. In this study, the conventional waveguide theory is extended by considering constitutive relations that account for both MO and ME effects. Using the extended waveguide theory, the propagation properties are also analyzed in a medium where metamaterials and magnetic materials are arranged such that MO and ME effects can be controlled independently. It has been confirmed that the interaction between MO and ME effects occurs depending on the arrangement of certain metamaterials and the direction of magnetization. This suggests a nonreciprocal polarization control that rotates the polarization in only one direction when propagating in plane wave propagation and enhances the nonreciprocal nature of the propagating waves in waveguide propagation.

Illusory self-motion ("vection") has been used to present a sense of movement in virtual reality (VR) and other similar applications. It is crucial in vection research to present a stronger sense of movement. Bone-conducted vibration (BCV) is a small and generally acceptable method for enhancing the sense of movement in VR. However, its effects on vection have not been extensively studied. Here, we conducted two experiments to investigate the effect of BCV on the vection, which generates an upward sensation under the hypothesis that BCV stimulation to the mastoid processes causes noise in the vestibular system and enhances visually-induced self-motion perception. The experiments focused on the effects of BCV stimuli of different frequencies on the vection experience. The results suggested that 500 Hz BCV was more effective as noise to the vestibular system than other frequency BCVs and improved self-motion sensation. This study examines the effects of BCV with different frequencies on the vection experience and designs a theory for using BCV in VR., (© 2023. Springer Nature Limited.)

We analyze a new type of photonic crystal fiber which consists of the core and cladding that distinct in topology by tuning the position of air holes in each hexagonal unit cell where the C 6v symmetry is respected. The p-d band inversion between the core and cladding leads to topological interface modes inside the band gap, which can propagate along the fiber with a nonzero momentum in perpendicular to the corss section of a fiber. The helical topological interface modes possess the pseudospin-momentum locking effect inherited from the corresonding two-dimensional photonic crystal characterized by the Z 2 topology. The wave functions for the topological interface modes are analytically studied and compared successfully to the numerical results, enlighting a novel way to use photonic crystal fiber to transfer information.

In this study, we propose low power consumption, programmable on-chip optical nonlinear units (ONUs) for all-optical neural networks (all-ONNs). The proposed units were constructed using a III-V semiconductor membrane laser, and the nonlinearity of the laser was used as the activation function of a rectified linear unit (ReLU). By measuring the relationship of the output power and input light, we succeeded in obtaining the response as an activation function of the ReLU with low power consumption. With its low-power operation and high compatibility with silicon photonics, we believe that this is a very promising device for realizing the ReLU function in optical circuits.

We demonstrate a membrane photonic integrated circuit (MPIC) that includes a membrane distributed feedback (DFB) laser and a p-i-n photodiode with a buried-ridge-waveguide (BRW) on a Si substrate, using a-Si nanofilm-assisted room-temperature surface activated bonding (SAB) for on-chip optical interconnection. The BRW structure enhanced the lateral optical confinement compared with that of the conventional flat structure. The directly bonded membrane DFB laser using SAB had a lower thermal resistance and higher output power than the previous structure using a benzocyclobutene (BCB) bonding layer. The DFB laser had a low threshold current of 0.27 mA at 25 °C. The maximum detected photocurrent and slope efficiency were 0.95 mA and 0.203 mA/mA, respectively, at 25 °C. The MPIC was successfully operated at temperatures up to 120 °C. The 3-dB bandwidths of 16.8 GHz and 10.1 GHz were achieved at 25 °C and 80 °C, respectively, and 25 Gbps and 15 Gbps non-return-to-zero (NRZ) 2 15 -1 pseudo-random bit sequence signals were recorded at 25 °C and 80 °C, respectively.

In this study, we developed a photonic band microscope based on hyperspectral Fourier image spectroscopy. The developed device constructs an infrared photonic band structure from Fourier images for various wavelength obtained by hyperspectral imaging, which make it possible to speedily measure the dispersion characteristics of photonic nanostructures. By applying the developed device to typical photonic crystals and topological photonic crystals, we succeeded in obtaining band structures in good agreement with the theoretical prediction calculated by the finite element method. This device facilitates the evaluation of physical properties in various photonic nanostructures, and is expected to further promote related fields.

We propose a method for selectively propagating optical vortex modes with specific charge numbers in a photonic integrated circuit (PIC) by using a topological photonic system. Specifically, by performing appropriate band tuning in two photonic structures that comprise a topological waveguide, one specific electromagnetic mode at the Γ point of a band diagram can be excited. Based on theoretical analysis, we successfully propagated optical vortex modes with specific charge numbers over a wide range in the C band in the proposed topological waveguide. The proposed method could be useful in controlling optical vortex signals at the chip level in future orbital angular momentum multiplexing technologies.

Sensory information from movements of body parts can alter their position when exposed to external physical stimuli. Visual information monitors the position and movement of body parts from an exterior perspective, whereas somatosensory information monitors them from an internal viewpoint. However, how such sensory data are integrated is unclear. In this study, a virtual reality (VR) system was used to evaluate the influence of the temporal difference between visual and somatosensory information from hand movements on the directional perception of a torque while modifying the visual appearance (human hand vs. non-human object) and visuohaptic congruency (congruent vs. incongruent) of self-avatars. Visual information was provided by the movement of the self-avatars in a VR environment, while somatosensory information was provided by vibrations with asymmetrical amplitudes that gave the participants the sensation of being continuously pushed or pulled without actually moving any body part. Delaying the movement of the avatar by 50 ms resulted in the sensitivity of the force direction perception to be lower with human hands than with non-human avatars, whereas a delay of 200 ms resulted in a higher sensitivity. This study can contribute to applications requiring multisensory integration in a VR environment., (© 2022. The Author(s).)

In this study, we propose a defect structure that enhances the vertical coupling efficiency of circularly polarized light incident on topological waveguides consisting of triangle nanoholes with C 6v symmetry arranged in honeycomb lattice. The defect structure was formed by removing triangle nanoholes from a certain hexagonal unit cell around the topological waveguide. As a result of comparing the coupling efficiency with and without the defect structure through three-dimensional finite-difference time-domain analysis, significant improvement in the vertical coupling efficiency was observed over the entire telecom C band (4460%@1530 nm). In addition, it was also found that the wavelength showing maximum coupling efficiency can be controlled over the entire C band by changing the arrangement of the dielectric around the defect structure.

Replacing part of a conventional optical circuit with a topological photonic system allows for various controls of optical vortices in the optical circuit. As an underlying technology for this, in this study, we have realized a topological converter that provides high coupling efficiency between a normal silicon wire waveguide and a topological edge waveguide. After expanding the waveguide width while maintaining single-mode transmission from the Si wire waveguide, the waveguides are gradually narrowed from both sides by using a structure in which nanoholes with C 6 symmetry are arranged in a honeycomb lattice. On the basis of the analysis using the three-dimensional finite-difference time-domain method, we actually fabricated a device in which a Si wire waveguide and a topological edge waveguide were connected via the proposed topological converter and evaluated its transmission characteristics. The resulting coupling efficiency between the Si wire waveguide and the topological edge waveguide through the converter was -4.49 dB/taper, and the coupling efficiency was improved by 5.12 dB/taper compared to the case where the Si wire waveguide and the topological edge waveguide were connected directly.

A metamaterial is an artificial material designed to control the electric permittivity and magnetic permeability freely beyond naturally existing values. A promising application is a slow-light device realized using a combination of optical waveguides and metamaterials. This paper proposes a method to dynamically control the slow-light effect in a metamaterial-loaded Si waveguide. In this method, the slow-light effect (i.e., group index) is controlled by changing the phase of the control light incident on the device from a direction opposite to that of the signal light. The group index of the device could be continuously controlled from 63.6 to 4.2 at a wavelength of 1.55 µm.

Walking is an innate human behavior that propels the body forward. Recent studies have investigated the creation of a walking sensation wherein, the body neither moves nor is forced to move. However, it is unclear which whole-body motions effectively induce the sensation of walking. Here, we show that passive whole-body motions, such as heave and/or yaw motions, produced by a motorized chair induced a sensation of walking for seated participants in virtual environments as if the participant were walking while viewing a virtual reality scene through a head-mounted display. Our findings suggest that the passive whole-body motions in the gravitational axis-and to a lesser extent in the yaw axis-provide a clear perception of pseudo-walking, but only with limited motion amplitudes, namely one-fourth or less than those of actual walking. In addition, we found a negative correlation between the scores of walking sensation and motion sickness.

This article reports the first psychological evidence that the combination of oscillating optic flow and synchronous foot vibration evokes a walking sensation. In this study, we first captured a walker's first-person-view scenes with footstep timings. Participants observed the naturally oscillating scenes on a head-mounted display with vibrations on their feet and rated walking-related sensations using a Visual Analogue Scale. They perceived stronger sensations of self-motion, walking, leg action, and telepresence from the oscillating visual flow with foot vibrations than with randomized-timing vibrations or without vibrations. The artificial delay of foot vibrations with respect to the scenes diminished the walking-related sensations. These results suggest that the oscillating visual scenes and synchronous foot vibrations are effective for creating virtual walking sensations., (© The Author(s) 2019.)

The limited space immediately surrounding our body, known as peripersonal space (PPS), has been investigated by focusing on changes in the multisensory processing of audio-tactile stimuli occurring within or outside the PPS. Some studies have reported that the PPS representation is extended by body actions such as walking. However, it is unclear whether the PPS changes when a walking-like sensation is induced but the body neither moves nor is forced to move. Here, we show that a rhythmic pattern consisting of walking-sound vibrations applied to the soles of the feet, but not the forearms, boosted tactile processing when looming sounds were located near the body. The findings suggest that an extension of the PPS representation can be triggered by stimulating the soles in the absence of body action, which may automatically drive a motor program for walking, leading to a change in spatial cognition around the body.

Infrared refractive index is an indispensable parameter for various fields including infrared photonics. To date, critical-angle refractometers, V-block refractometers, and spectroscopic ellipsometry have been commonly used to measure the refractive index. Although every method has an accuracy of four decimal places for the refractive index, a measurable wavelength region is limited up to about 2 µm. In this study, we demonstrated a metamaterial infrared refractometer for determining broadband complex refractive index. Using the device, a broadband (40-120 THz; wavelength 2.5-7.5 µm) and high-precision(< 5 ×10 -3 ) complex refractive index of polymethyl methacrylate was measured for the first time.

We demonstrated a novel slow-light Si-wire waveguide combined with metamaterials, which can be easily integrated with other Si photonics devices. The slow-light effect can be produced simply by placing metamaterials at an appropriate position on a Si-wire waveguide. It was confirmed that the large group index of more than 40 could be obtained because of a steep and discontinuous change of dispersion relation near the resonance frequency of metamaterials.

Toward the realization of ultralow-power-consumption on-chip optical interconnection, two types of membrane-based GaInAs/InP p-i-n photodiodes were fabricated on Si host substrates by using benzocyclobutene bonding. A responsivity of 0.95 A/W was estimated with a conventional waveguide-type photodiode with an ∼30-μm-long absorption region. The fitting curves based on the experimental data indicated that an absorption efficiency above 90% could be achieved with a length of 10 μm. In addition, increased absorption per length of a photonic crystal waveguide-type photodiode was obtained because of the enhanced lateral optical confinement or the slow-light effect, enabling a further reduction in the device length.

We show the feasibility of controlling the magnetic permeability of optical semiconductor devices on InP-based photonic integration platforms. We have achieved the permeability control of GaInAsP/InP semiconductor waveguides by combining the waveguide with a metamaterial consisting of gate-controlled split ring resonators. The split-ring resonators interact magnetically with light travelling in the waveguide and move the effective relative permeability of the waveguide away from 1 at optical frequencies. The variation in permeability can be controlled with the gate voltage. Using this variable-permeability waveguide, we have built an optical modulator consisting of a GaInAsP/InP Mach-Zehnder interferometer for use at an optical communication wavelength of 1.55 μm. The device changes the permeability of its waveguide arm with controlling gate voltage, thereby varying the refractive index of the arm to modulate the intensity of light. For the study of variable-permeability waveguide devices, we also propose a method of extracting separately the permittivity and permeability values of devices from the experimental data of light transmission. Adjusting the permeability of optical semiconductors to the needs of device designers will open the promising field of 'permeability engineering'. Permeability engineering will facilitate the manipulation of light and the management of photons, thereby contributing to the development of novel devices with sophisticated functions for photonic integration., Competing Interests: The authors declare no conflict of interest.

We propose the concept of organic membrane photonic integrated circuits (OMPICs), which incorporate various functions needed for optical signal processing into a flexible organic membrane. We describe the structure of several devices used within the proposed OMPICs (e.g., transmission lines, I/O couplers, phase shifters, photodetectors, modulators), and theoretically investigate their characteristics. We then present a method of fabricating the photonic devices monolithically in an organic membrane and demonstrate the operation of transmission lines and I/O couplers, the most basic elements of OMPICs.

We analyzed two types of Mach-Zehnder plasmonic modulators on a silicon-on-insulator platform with a different furan-thiophene chromophore electro-optic polymer to compare to other reports. The metal-taper coupling structure and the metal-insulator-metal cross section in our design have been optimized based on the new material parameters. According to the simulation result, a modulator with a slot width of 50 nm and an on-off voltage of Vπ=20  V can be 21 μm long, leading to a total modulator loss of 15 dB, which is comparable to previously reported devices.

Human imaging studies have reported activations associated with tactile motion perception in visual motion area V5/hMT+, primary somatosensory cortex (SI) and posterior parietal cortex (PPC; Brodmann areas 7/40). However, such studies cannot establish whether these areas are causally involved in tactile motion perception. We delivered double-pulse transcranial magnetic stimulation (TMS) while moving a single tactile point across the fingertip, and used signal detection theory to quantify perceptual sensitivity to motion direction. TMS over both SI and V5/hMT+, but not the PPC site, significantly reduced tactile direction discrimination. Our results show that V5/hMT+ plays a causal role in tactile direction processing, and strengthen the case for V5/hMT+ serving multimodal motion perception. Further, our findings are consistent with a serial model of cortical tactile processing, in which higher-order perceptual processing depends upon information received from SI. By contrast, our results do not provide clear evidence that the PPC site we targeted (Brodmann areas 7/40) contributes to tactile direction perception.

The present study investigated whether a tactile flow created by a matrix of vibrators in a seat pan simultaneously presented with an optical flow in peripheral vision enhances the perceived forward velocity of self-motion. A brief tactile motion stimulus consisted of four successive rows of vibration, and the interstimulus onset between the tactile rows was varied to change the velocity of the tactile motion. The results show that the forward velocity of self-motion is significantly overestimated for rapid tactile flows and underestimated for slow ones, compared with optical flow alone or non-motion vibrotactile stimulation conditions. In addition, the effect with a temporal tactile rhythm without changing the stimulus location was smaller than that with spatiotemporal tactile motion, with the interstimulus onset interval to elicit a clear sensation of tactile apparent motion. These findings suggest that spatiotemporal tactile motion is effective in inducing a change in the perceived forward velocity of self-motion.

Active touch sensing is known to facilitate the discrimination or recognition of the spatial properties of an object from the movement of tactile sensors on the skin and by integrating proprioceptive feedback about hand positions or motor commands related to ongoing hand movements. On the other hand, several studies have reported that tactile processing is suppressed by hand movement. Thus, it is unclear whether or not the active exploration of force direction by using hand or arm movement improves the perception of the force direction. Here, we show that active manual movement in both the rotational and translational directions enhances the precise perception of the force direction. To make it possible to move a hand in space without any physical constraints, we have adopted a method of inducing the sensation of illusory force by asymmetric vibration. We found that the precision of the perceived force direction was significantly better when the shoulder is rotated medially and laterally. We also found that directional errors supplied by the motor response of the perceived force were smaller than those resulting from perceptual judgments between visual and haptic directional stimuli. These results demonstrate that active manual movement boosts the precision of the perceived direction of an illusory force.

Low-power consumption directly-modulated lasers are a key device for on-chip optical interconnection. We fabricated a GaInAsP/InP membrane DFB laser that exhibited a low-threshold current of 0.21 mA and single-mode operation with a sub-mode suppression ratio of 47 dB at a bias current of 2 mA. A high modulation efficiency of 11 GHz/mA 1/2 was obtained. A 10 Gbit/s direct modulation using a non-return-to-zero 2 31 -1 pseudo-random bit sequence signal was performed with a bias current of 1 mA, which is the lowest bias current ever reported for direct modulation of a DFB laser. A bit-error rate of 10 -9 was successfully achieved.

HfS2 is the novel transition metal dichalcogenide, which has not been experimentally investigated as the material for electron devices. As per the theoretical calculations, HfS2 has the potential for well-balanced mobility (1,800 cm(2)/V·s) and bandgap (1.2 eV) and hence it can be a good candidate for realizing low-power devices. In this paper, the fundamental properties of few-layer HfS2 flakes were experimentally evaluated. Micromechanical exfoliation using scotch tape extracted atomically thin HfS2 flakes with varying colour contrasts associated with the number of layers and resonant Raman peaks. We demonstrated the I-V characteristics of the back-gated few-layer (3.8 nm) HfS2 transistor with the robust current saturation. The on/off ratio was more than 10(4) and the maximum drain current of 0.2 μA/μm was observed. Moreover, using the electric double-layer gate structure with LiClO4:PEO electrolyte, the drain current of the HfS2 transistor significantly increased to 0.75 mA/μm and the mobility was estimated to be 45 cm(2)/V·s at least. This improved current seemed to indicate superior intrinsic properties of HfS2. These results provides the basic information for the experimental researches of electron devices based on HfS2.

The direct modulation characteristics of a membrane distributed feedback (DFB) laser on a silicon substrate were investigated. Enhancement of the optical confinement factor in the membrane structure facilitates the fabrication of a strongly index-coupled (κ(I) = 1500 cm(-1)) DFB laser with the cavity length of 80 µm and a threshold current of 270 µA. Small-signal modulation measurements yielded a -3dB bandwidth of 9.5 GHz at 1.03-mA bias current, with modulation efficiency of 9.9 GHz/mA(1/2), which is, to the best of our knowledge, the highest value among those reported for DFB lasers.

Photonic wire bonding (PWB) was used to achieve flexible chip-scale optical interconnection as a kind of 3D-freeform polymer waveguide based on the two-photon polymerization of SU-8. First, the fabrication conditions of PWB were determined for the two-photon absorption process, and the coupling structure between PWB and III-V optical components was numerically simulated in order to obtain high coupling efficiency. Then, using PWB, chip-to-chip optical transmission was realized between laser and detector chips located on a common Si substrate. We fabricated a 2.5-μm-wide PWB with 1:3 aspect ratio between two optical chips of 140-μm gap and achieved a connection loss of approximately 10 dB.

We fabricated GaInAsP/InP waveguide-integrated lateral-current-injection (LCI) membrane distributed feedback (DFB) lasers on a Si substrate by using benzocyclobutene (BCB) adhesive bonding for on-chip optical interconnection. The integration ofa butt-jointed built-in (BJB) GaInAsP passive waveguide was performed by organometallic vapor-phase epitaxy (OMVPE).By introducing a strongly index-coupled DFB structure with a 50-µm-long cavity, a threshold current of 230 µA was achieved for a stripe width of 0.8 µm under room-temperature continuous-wave (RT-CW) conditions. The maximum output power of 32 µW was obtained. The lasing wavelength and submode suppression ratio (SMSR) were 1534 nm and 28 dB, respectively, at a bias current of 1.2 mA.

Metamaterials are artificially structured materials that can produce innovative optical functionalities such as negative refractive index, invisibility cloaking, and super-resolution imaging. Combining metamaterials with semiconductors enables us to develop novel optoelectronic devices based on the new concept of operation. Here we report the first experimental demonstration of a permeability-controlled waveguide optical modulator consisting of an InGaAsP/InP Mach-Zehnder interferometer with 'tri-gate' metamaterial attached on its arms. The tri-gate metamaterial consists of metal resonator arrays and triple-gate field effect elements. It changes its permeability with a change in the controlling gate voltage, thereby changing the refractive index of the interferometer arm to switch the modulator with an extinction ratio of 6.9 dB at a wavelength of 1.55 μm. The result shows the feasibility of InP-based photonic integrated devices that can produce new functions by controlling their permeability as well as their permittivity.

With the goal of creating magneto-optical devices, we demonstrated forming nanostructures inside a substrate of cerium-substituted yttrium iron garnet (Ce:YIG) by means of direct laser writing. Laser irradiation changed both the optical and magnetic properties of Ce:YIG. The measurements showed that the refractive index was increased by 0.015 (about 0.7% change) and the magnetization property was changed from hard to soft to decrease the coercivity. This technology enables the formation of 3-dimensional optical and magnetic nanostructures in YIG and will contribute to the development of novel devices for optical communication and photonic integration.

This paper proposes a directional torque feedback technique for mobile devices that creates brief unbalanced torque by suddenly starting to rotate a stationary flywheel and then stopping it soon after. The experimental results show that a twisting sensation was induced effectively with angular velocity profiles that include sudden starts.

An InP-based Mach-Zehnder interferometer combined with a metamaterial layer consisting of a split-ring resonator array was constructed to measure the complex permeability of the metamaterial. At a wavelength of 1.5 μm, the metamaterial showed non-unity relative permeability induced by magnetic interaction with propagating light in the device. This method of measurement would be useful to determine constitutive parameters in such waveguide-based photonic devices, allowing us to design photonic integrated circuits that make use of metamaterials.

We fabricated a novel lateral-current-injection-type distributed feedback (DFB) laser with amorphous-Si (a-Si) surface grating as a step to realize membrane lasers. This laser consists of a thin GaInAsP core layer grown on a semi-insulating InP substrate and a 30-nm-thick a-Si surface layer for DFB grating. Under a room-temperature continuous-wave condition, a low threshold current of 7.0 mA and high efficiency of 43% from the front facet were obtained for a 2.0-μm stripe width and 300-μm cavity length. A small-signal modulation bandwidth of 4.8 GHz was obtained at a bias current of 30 mA.

In the visual modality adaptation to high temporal frequency can result in spatially localized apparent duration compression. The principal point of adaptation is thought to be early in the visual system, at which point temporal information is encoded within sustained (parvocellular) and transient (magnocellular) channels. Here, we investigate whether the adaptation-based time compression could also be found in the tactile modality, which also has sustained (slowly adapting) and transient (rapidly adapting) neural channels. Our results showed that periods of vibration seem compressed when presented to a region of the skin surface adapted earlier to higher frequencies. This finding indicates that human duration perception can be altered by adaptation of temporal sensory channels in similar ways in vision and touch.