Amplitude Tuning Research Articles

Restoring Color Perception to the Blind: An Electrical Stimulation Strategy of Retina in Patients with End-stage Retinitis Pigmentosa

Bioelectronic retinal prostheses that stimulate the remaining inner retinal neurons, bypassing degenerated photoreceptors, have been demonstrated to restore some vision in patients blinded by retinitis pigmentosa (RP). These implants encode luminance of the visual scene into electrical stimulation, however, leaving out chromatic information. Yet color plays an important role in visual processing when it comes to recognizing objects and orienting to the environment, especially at low spatial resolution as generated by current retinal prostheses. In this study, we tested the feasibility of partially restoring color perception in blind RP patients, with the aim to provide chromatic information as an extra visual cue. Case series. Seven subjects blinded by advanced RP and monocularly fitted with an epiretinal prosthesis. Frequency-modulated electrical stimulation of retina was tested. Phosphene brightness was controlled by amplitude tuning, and color perception was acquired using the Red, Yellow, Green, and Blue (RYGB) hue and saturation scaling model. Brightness and color of the electrically elicited visual perception reported by the subjects. Within the tested parameter space, 5 of 7 subjects perceived chromatic colors along or nearby the blue-yellow axis in color space. Aggregate data obtained from 20 electrodes of the 5 subjects show that an increase of the stimulation frequency from 6 to 120 Hz shifted color perception toward blue/purple despite a significant inter-subject variation in the transition frequency. The correlation between frequency and blue-yellow perception exhibited a good level of consistency over time and spatially matched multi-color perception was possible with simultaneous stimulation of paired electrodes. No obvious correlation was found between blue sensations and array placement or status of visual impairment. These findings present a strategy for the generation and control of color perception along the blue-yellow axis in blind patients with RP by electrically stimulating the retina. It could transform the current prosthetic vision landscape by leading in a new direction beyond the efforts to improve the visual acuity. This study also offers new insights into the response of our visual system to electrical stimuli in the photoreceptor-less retina that warrant further mechanistic investigation.

Optical Multipath RF Self-Interference Cancellation Based on Phase Modulation for Full-Duplex Communication

Optical multipath RF self-interference cancellation (SIC) based on phase modulation for full-duplex communication is proposed and demonstrated experimentally. Phase modulation is utilized to convert the RF signal into optical domain, in which the time delay tuning, amplitude tuning and phase inversion for multipath RF SIC are completed. The comprehensive theoretical model of the optical multipath RF SIC system is established, and the factors affecting SIC performance including the time delay, amplitude and phase deviations are analyzed. The experimental results verify the feasibility of the proposed scheme for full-duplex communication with the cancellation depth of 26 dB and 28 dB over 100 MHz at central frequency of 6 GHz and 10 GHz, respectively. A figure of merit of the maximum interference to signal of interest ratio is defined to characterize the SOI recovery capability of optical RF SIC system.

Tunable dual-band amplitude modulation with a double epsilon-near-zero metasurface

In this paper, we demonstrate an electrically tunable double epsilon-near-zero (D-ENZ) metasurface by incorporating an ultra-thin indium-tin-oxide layer (≈ 5 nm) into an array of moderately-doped silicon (Si) nanobars. The D-ENZ phenomenon is achieved by accumulation and depletion of carrier densities in ITO and Si active layers under applying the external bias voltages. An active dual-band amplitude modulator is proposed which can realize the modulation depths of 0.86 and 0.71 at operating channels of λ1 = 1547 nm and λ2 = 1564.2 nm, leveraging the D-ENZ mechanism. The reasonably low intrinsic loss in such an optical device gives us the opportunity to have continuous amplitude modulation at both operating wavelengths without the necessity of a complicated multi-resonator unit-cell.

Broadband Light Amplitude Tuning Characteristics of SnSe2 Coated Microfiber

Broadband light amplitude tuning characteristics are demonstrated in a 2-D tin diselenide (SnSe2) nanosheets coated microfiber (MF) structure (SnSe2CMF). Due to the strong absorption characteristics of SnSe2 in broadband wavelengths, the transmitted optical power (TOP) of SnSe2CMF can be tuned by external pump lights with different wavelengths (405, 532, and 660 nm) over a broadband spectrum (1520–1620 nm). Five wavelengths are extracted in order to investigate the tuning performance. The TOP of SnSe2CMF increases with the pump light power and a maximum tuning efficiency of ∼0.3074 dB/mW is achieved. In terms of tuning speed, the minimum response time is ∼3.7/3.9 ms. The experimental results have qualitatively good agreement with the simulations predicted by FEM models. The demonstrated structure has the advantages of broad tuning bandwidth and high tuning efficiency. Therefore, it might be a promising candidate for building high performance broadband fiber-optic sensors and modulators.

Feedforward attractor targeting for non-linear oscillators using a dual-frequency driving technique.

A feedforward control technique is presented to steer a harmonically driven, non-linear system between attractors in the frequency-amplitude parameter plane of the excitation. The basis of the technique is the temporary addition of a second harmonic component to the driving. To illustrate this approach, it is applied to the Keller-Miksis equation describing the radial dynamics of a single spherical gas bubble placed in an infinite domain of liquid. This model is a second-order, non-linear ordinary differential equation, a non-linear oscillator. With a proper selection of the frequency ratio of the temporary dual-frequency driving and with the appropriate tuning of the excitation amplitudes, the trajectory of the system can be smoothly transformed between specific attractors; for instance, between period-3 and period-5 orbits. The transformation possibilities are discussed and summarized for attractors originating from the subharmonic resonances and the equilibrium state (absence of external driving) of the system.

Direct routing of intensity-editable multi-beams by dual geometric phase interference in metasurface

Abstract Controlling spin electromagnetic waves by ultra-thin Pancharatnam-Berry (PB) metasurfaces show promising prospects in the optical and wireless communications. One of the major challenge is to precisely control over the complex wavefronts and spatial power intensity characteristics without relying on massive algorithm optimizations, which requires independent amplitude and phase tuning. However, traditional PB phase can only provide phase control. Here, by introducing the interference of dual geometric phases, we propose a metasurface that can provide arbitrary amplitude and phase manipulations on meta-atom level for spin waves, achieving direct routing of multi-beams with desired intensity distribution. As the experimental demonstration, we design two microwave metasurfaces for respectively controlling the far-field and near-field multi-beam generations with desired spatial scatterings and power allocations, achieving full control of both sophisticated wavefronts and their energy distribution. This approach to directly generate editable spatial beam intensity with tailored wavefront may pave a way to design advanced meta-devices that can be potentially used in many real-world applications, such as multifunctional, multiple-input multiple-output and high-quality imaging devices.

Optical rectification coefficient of GaAs/AlxGa1−xAs Thue–Morse multiple quantum wells

In the present work, we numerically investigate the optical properties of GaAs/AlxGa1−xAs Thue–Morse multiple-quantum-well systems (TM-MQWs) in the presence of an external electric field. We study the effects of the layers arrangements, total system length, number of layers and composition parameter x on the optical rectification coefficient of the TM-MQWs. We also consider three structural cases within which the system can be fabricated by repeating two, three or four composition parameters x1, x2, x3 and x4 in the adjacent layers. The most tunable ORC amplitude is due to the systems containing four different composition parameters and least tunable one is the systems which contain two different composition parameters. By increasing the number of layers, the ORC peak position periodically redshifts and blueshifts. We also show that by using the number of layers, total system length and composition parameter x, the ORC peak amplitudes are greatly tunable in a considerably large interval. This fact shows that the Thue–Morse MQWs are suitable candidates for optoelectronic device applications.

Strong Skyrmion Oscillations Driven by Spatially Dependent Spin Current

Nanoscale spintronic oscillators have attracted research interest in recent years because of their potential application in neuromorphic computing. Sustainable magnetization precession or gyrotropic motion of a skyrmion triggered by spin-polarized current or spin current gives rise to spintronic oscillation. However, the amplitude of skyrmion oscillation is exceedingly small. In this work, we report a skyrmion oscillation with a much larger amplitude based on periodical deformation of the skyrmion in a region with geometric confinement. This periodical deformation is induced by spatial-dependent spin current and is relevant to the skyrmion Hall effect. The amplitude and period of the oscillation can be well manipulated by modifying the damping coefficient, the slope of spin-current density, and the dimension of medium. The characteristic frequency of skyrmion oscillation determined by fast Fourier transformation is split under an external magnetic field that breaks the symmetry for the oscillation in the left and right parts of the skyrmion. This work paves the way to develop nanoscale skyrmion oscillators with tunable frequency and amplitude for neuromorphic computing.

Stable and metastable kinetic ferromagnetism on a ring

Performing an exact diagonalization of the effective spin problem, a ferromagnetic ground state of kinetic origin is shown to emerge in a system of $N$ strongly correlated electrons on a $L$-site ring ($L > N$). This phenomenon is brought about by the quantum necklace statistics originated from the no double occupancy constraint leading to a fractional shifted electron momentum quantization. As a consequence of such special energy level distribution, the kinetic ferromagnetism is stable only for $N=3$. For odd $N>3$ the fully polarized FM state energy is only a local minimum but it is protected by a finite energy barrier that inhibits one spin-flip processes. The metastable ferromagnetic state survives perturbations of small magnitude opening up a possibility of being experimentally observed by an appropriate tuning of the interdot tunneling amplitudes in currently available quantum dot arrays.

Amplitude and Phase Tuning of Microwave Signals in Magnetically Biased Permalloy Structures

In this paper, a permalloy layer has been employed in the fabrication of a coupled line electromagnetic bandgap (EMBG) device to tune both amplitude and phase. A magnetically biased microwave coplanar configuration manufactured with evaporated permalloy has been measured, and a circuit modelling has been studied to evaluate the measured effects in terms of variable attenuation and phase shift. Starting from a permalloy made by the mixture 80% nickel and 20% iron content, we fabricated an electromagnetic bandgap (EMBG) structure based on a periodic arrangement of single sections of a transmission line with variable impedance, also including a central region with coupled lines. The bandpass characteristics of the EMBG device can be tuned by changing permalloy’s permeability through the application of a DC magnetic field $H_{0}$ (parallel to the plane of the structure). In particular, using a magnetic field up to 3000 Oe, it was possible to change the phase by ca. 45° and the amplitude by ca. 7 dB in the X band.

A Low-Power Tunable Square-Wave Generator for Instrumentation Applications

In this article, a low-power fully on-chip tunable amplitude and frequency waveform generator (WFG) is proposed. In the proposed architecture, frequency and amplitude are tuned by varying the currents in the respective branches. The waveform generator is designed and fabricated in the United Microelectronics Corporation (UMC) 180-nm CMOS process technology with a 1.8-V supply. It generates a square wave of 50% duty cycle, and the output is symmetric with respect to the common-mode voltage. The measured results show tuning of amplitude from 500 mVpp to 1.15 Vpp and frequency from 50 to 650 kHz approximately. It consumes $620~\mu \text {W}$ of power while occupying 0.03-mm2 silicon area only, making it suitable for low-power integrated system applications.

Electro-optical Amplitude and Phase Modulators Based on Tunable Guided-Mode Resonance Effect

Here, electrically tunable amplitude and phase modulators are designed by the hybridization of indium tin oxide (ITO) into a guided-mode resonance mirror (so-called GMRM), which consists of a high-...

Tunable VO2 relaxation oscillators for analog applications

The reversible insulator-to-metal phase transition of vanadium dioxide (VO2) makes this material an ideal candidate to realize electrical oscillators with both tunable frequency and amplitude characteristics. Here we report results for VO2 oscillators operating under voltage actuation. Large amplitude electrical oscillation waveforms with stable frequency were observed for the investigated devices. The frequency and amplitude of the waveforms were controlled by changing the values of the capacitor in the oscillator circuit, the supply voltage and by varying the temperature of the devices. An equivalent circuit model was developed to simulate the waveforms. A good agreement between simulations and experiments was verified for different oscillator circuit conditions. We also present a graphical phase portrait analysis of the differential equations governing the time-dependent external capacitor voltage in the oscillator circuit. A simple technique to analyze the operating conditions of these devices was developed based on this approach using the oscillator circuit parameters and the resistances of the VO2 device in the insulating and metallic states.

Single-Chip 3072-Element-Channel Transceiver/128-Subarray-Channel 2-D Array IC With Analog RX and All-Digital TX Beamformer for Echocardiography

This paper presents a single-chip 3072-element-channel (ECh) transceiver/128-subarray-channel (SCh) 2-D array IC with analog receiver (RX) and all-digital transmitter (TX) beamformer for echocardiography. The proposed IC integrates 3072-ECh transceivers that are composed of a low-power tunable amplitude three-level pulser (TA3LP), zero-power-TX-and-RX- isolation switch (ZTRSW), programmable gain-and-input-impedance low-noise amplifier (PGZLNA), bidirectional dynamically reconfigurable switched-capacitor delayer (BDR- SCD), and 24-ECh-to-1-SCh charge-domain adder (CDADD). It also has 128-SCh low-noise cable buffers (LNCBUFs) and all the related peripheral circuits, including control and interface circuits. It has an all-digital TX architecture with a digital beamformer (TX-DBF) that is free from the waveform distortion and timing error caused by long cable propagation between the main instrument unit and the IC. The TA3LP launches the three-level bipolar signals that are necessary for tissue harmonic imaging (THI). The BDR-SCD can delay 2-bit TX digital signals or an RX analog signal; 24 RX signals in an SCh are coherently delayed using BDR-SCDs, summed in the charge domain with a CDADD without signal headroom concerns, and converted into an SCh signal. The proposed IC is fabricated with a $0.18-\mu \text{m}$ high-voltage silicon-on-insulator (HV SOI) CMOS process. Each ECh transceiver occupies only a $300 ~\mu \text{m}\,\,\times 300 ~\mu \text{m}$ silicon area while having a greater than 85-dB dynamic range, 25-ns resolution, 750-ns maximum time delay, and $138-{V}_{\textrm {pp}}$ output capabilities. The total die size is 417 mm2. An ultrasound system was also made to visualize 2-D/3-D phantom images with 0.74-mW/ECh power consumption in the B-mode.

Metamaterial absorber with independently tunable amplitude and frequency in the terahertz regime.

A tunable metamaterial absorber is proposed in the terahertz regime. The amplitude and center frequency of the absorber can be tuned independently. Owing to the effective combination of graphene and strontium titanate (STO) in one metamaterial structure, the tunable properties of the amplitude and center frequency are implemented. The amplitude can be tuned by adjusting the chemical potential of graphene sheet, and center frequency can get a shift through temperature changes in the STO material. In a full-wave numerical simulation, the amplitude of the absorber can be tuned from approximately 100% to 35% with a fixed center frequency when chemical potential varies from 0.7 eV to 0.0 eV. The center frequency of the absorber can shift from 0.43 THz to 0.3 THz when temperature changes from 400 K to 200 K. The complex surface impedance of the graphene and permittivity of STO material in this research range are thoroughly examined, and the independently tunable mechanism of the absorber is explored by elucidating the electric field distribution. The influence of the oblique incidence of electromagnetic wave to the absorber is studied. The absorber can be scalable to the infrared and visible frequencies and demonstrates promising application on tunable sensors, filters, and photovoltaic devices.

Mechanically tunable opacity effect in transparent bilayer film: Accurate interpretation and rational applications

Transparent bilayer films, consisting of a stiff layer and a compliant layer, may gradually be tuned into an opaque state under mechanical stretching, which is interesting and is useful in intelligent window. However, an accurate interpretation of this effect is still absent, and there is no rational guidance for well realizing its applications at present. Here, we demonstrate that this effect is mainly induced by the diffractive behaviors of the wrinkles emerging and evolving in stiff film under stretching. Changes in the 0th order diffracted beam efficiency, which depend on mechanically tunable wrinkle amplitude, are the primary reason for the tunable property of this effect. The tunable rate of wrinkles amplitude change is proportional to the stiff layer thickness. Therefore, a guided approach to the application of this kind of bilayer film involves rationally combining stiff layer thickness and stretching percentage. We show the practical applications of this kind of bilayer films in window display. The films with different stiff layer thicknesses need different minimum stretching percentages to tune into completely opaque, while the wrinkle patterns induced by these stretching with the similar amplitude (1100nm). This work accurately interprets the opacity effect in bilayer films and further proposes theoretical guidance for its application, which may efficiently promote the fabrication of new bilayer films and their rational use in light tuning field.

Development of frequency-tunable multiple-band terahertz absorber based on control of polarization angles.

Controlling and tuning the spectral absorption response of metamaterial absorbers fabricated by arranging a set of resonators in a regular array is challenging. Polarization tunable multi-band terahertz resonant absorbers were developed using anisotropic microstructure arrays. The unit cell consisted of four pairs of H-shaped resonators of different sizes and a metallic ground plane separated by a dielectric layer. Discrete operating frequency shifts and dynamic amplitude tuning were observed by changing the polarization angle. The effect of the polarization angle on the absorption amplitude was evaluated. This work provides a concise approach to realize tunable absorption characteristics, which can be applied in sensors, detectors, and switches.

Broadband all-light-control with WS2 coated microfibers.

All-optical light amplitude tuning functionality is demonstrated in a layered tungsten disulfide (WS2) nanosheets coated microfiber (MF) structure. Due to the strong light-matter interactions between WS2 nanosheets and the evanescent field around the MF, a large variation in the transmitted power can be observed under both external and internal pump light excitations over a broadband spectrum (~100 nm). A power variation rate of ~0.3744 dB/mW is obtained under external violet pump light excitation, whereas the power variation rate of similar devices in the state of the art are usually less than 0.3 dB/mW. In terms of the response time, a moderate rise/fall time of ∼20.5/19.6 ms is achieved, which is mainly limited by the employed structure fabrication methods. These results indicate that the optical transmitted power of the WS2 coated MF can be modulated by different pump light with the power in the order of mW, thus the proposed device might have potential applications in all optical controllable devices and sensors, etc.

EM lens design using thin planar metasurfaces for high antenna gain and low SLL applications

A novel electromagnetic (EM) lens with high gain, suppressed side-lobe level (SLL) and low profile is designed using thin planar metasurfaces. The proposed design consists of a source patch antenna and an EM lens based on two thin planar metasurfaces. The two thin metasurfaces with an air gap are placed at the focal distance H of about λ /2.25 above the source patch antenna. This configuration forms a thin planar lens in which the source patch antenna emitted quasi-spherical wave in order to transform into plane wave. The total size of source antenna and an EM lens is same. The miniaturised EM lens antenna faces high SLL, which can be reduced by maintaining the uniform transmission phase coefficient and tunable transmission amplitude coefficient of metasurface unit cells. By implementing this topology on metasurfaces, the SLL of the proposed EM lens can be reduced without affecting the boresight gain of source patch antenna. The measured results of the proposed EM lens achieve 7 dB gain enhancement at designed frequency (5.8 GHz) with the SLL suppression of -24 dB. The total volume of planar lens antenna is 1.17 λ × 1.17 λ × λ /2.25 mm 3 , which is very compact compared with other reported planar lens designs.

Active multifunctional terahertz modulator based on plasmonic metasurface.

An active multifunctional terahertz modulator based on plasmon-induced transparency (PIT) metasurface under the effect of external infrared light was investigated theoretically and experimentally. A distinct transparency window, which resulted from the near-field coupling between two resonators, could be observed in the transmission spectra. Experimental results showed a phenomenon infrared light induced blue shift on the both resonator with increasing optical powers. When the optical power was tuned from 0 mW to 400 mW, the amplitude tunability of transmission at transparency window reached to 34.01%, much larger than that at the two resonance frequencies. Moreover, the phase tunability of the transmission at 0.98 THz reached to 31.35%. Meanwhile, the amplitude variation was limited to 10%. Furthermore, a coupled Lorentz oscillator model was adopted to analyze the near-field interaction of the resonances. Experimental results were in good agreement with the analytical fitting results.