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With electrical stimulation, retinal prostheses bypass dysfunctional photoreceptors and activate the surviving bipolar or retinal ganglion cells (RGCs). Therefore, the effective modulation of RGCs is crucial for developing retinal prostheses. Substantial research has been performed on the ability of an electrical stimulus to generate a reliable RGC response. However, different experimental conditions show varying levels of how well the electrical stimulation evokes RGC spikes. Therefore, in this study, we attempted to extract an indicator to understand how the electrical stimulation effectively evokes RGC spikes. Six cynomolgus monkeys were used: three as controls and three as an N-methyl-N-nitrosourea (MNU)-induced retinal degeneration model. The retinal recordings were performed using 8 x 8 multi-electrode arrays (MEAs). Electrical stimulation consisted of symmetrical biphasic pulses of varying amplitudes and durations. The number of stimulation conditions that resulted in significantly higher post-stimulation firing rates than pre-stimulus firing rates was defined as the modulation efficiency ratio (MER). The MER was significantly lower in degenerated retinas than in normal retinas. We investigated the relationship between the variables and the MER in normal and degenerated primate RGCs. External variables, such as duration and inter-electrode distance, and internal variables, such as average firing rates and statistics (mean, standard deviation, and coefficient of variation [CV]) of inter-spike intervals (ISIs) of spontaneous spikes, were used. External variables had similar effects on MER in normal and degenerated RGCs. In contrast, internal variables affected MER differently in normal and degenerated RGCs. While in normal RGCs, they were not related to MER, in degenerated RGCs, the mean ISIs were positively correlated with MER, and the CV of ISIs was negatively correlated with MER. The most important variable affecting MER was the mean ISI. A shorter ISI indicates hyperactive firing in the degenerated retina, which prevents electrical stimulation from evoking more RGCs. We believe that this hyperactivity in degenerated retinas results in a lower MER than that in the normal retina. Our findings can be used to optimize the selection of stimulation channels for in vitro MEA experiments and practical calibration methods to achieve higher efficiency when testing retinal prostheses. [ABSTRACT FROM AUTHOR]

On-chip optical modulators, which are capable of converting electrical signals into optical signals, constitute the foundational components of photonic devices. Photonics modulators exhibiting high modulation efficiency and low insertion loss are highly sought after in numerous critical applications, such as optical phase steering, optical coherent imaging, and optical computing. This paper introduces a novel accumulation-type vertical modulator structure based on a silicon photonics platform. By incorporating a high-K dielectric layer of ZrO2, we have observed an increase in modulation efficiency while maintaining relatively low levels of modulation loss. Through meticulous study and optimization, the simulation results of the final device structure demonstrate a modulation efficiency of 0.16 V·cm, with a mere efficiency–loss product of 8.24 dB·V. [ABSTRACT FROM AUTHOR]

In silicon modulator design, implantation is always a key factor, significantly influencing the doping profile and carrier distribution. As waveguide doping is limited by the compact footprint of the modulator rib, three-dimensional complex optimization is a viable option to improve performance. This work proposes an X-intersected modulator based on two inversely slanted junctions using the effective 3D Monte Carlo method for junction generation. The optimized results show that the modulation efficiency of the design is 1.09 V·cm, while the loss is 18 dB/cm, and the 3 dB bandwidth reaches over 35 GHz owing to the decreased resistance and capacitance of the 3D junction. This work demonstrates the benefits of 3D doping design in silicon modulators, contributing to higher efficiency and avoiding additional PN overlap to introduce lower capacitance. The design of 3D doping profiles well balances the DC and AC performance, and provides novel modulator solutions for high-speed datacom. [ABSTRACT FROM AUTHOR]

Interleaved doped Mach-Zehnder Modulators (MZMs) are one solution to attaining higher modulation efficiencies compared with lateral junction structures, due to greater modal overlap with the depletion regions of the PN junctions. In this work, we present an interleaved Si modulator device design and process simulation based on a three-step ion implantation process that aims to obtain a realistic PN junction doping profile using a Monte Carlo simulation method. A high doping concentration on the order of 5×1018 cm−3 for the P and N regions is explored. Device simulations to track the carrier motion under different voltage biases are performed. Using equivalent medium theory, we calculated the modulation efficiency Vπ·Lπ of the interleaved Si modulator to be 0.19 V·cm under 1V reverse bias. This work is among the highest reported modulation efficiencies thus far in MZMs without photonic resonance structures.

In silicon modulator design, implantation is always a key factor, significantly influencing the doping profile and carrier distribution. As waveguide doping is limited by the compact footprint of the modulator rib, three-dimensional complex optimization is a viable option to improve performance. This work proposes an X-intersected modulator based on two inversely slanted junctions using the effective 3D Monte Carlo method for junction generation. The optimized results show that the modulation efficiency of the design is 1.09 V·cm, while the loss is 18 dB/cm, and the 3 dB bandwidth reaches over 35 GHz owing to the decreased resistance and capacitance of the 3D junction. This work demonstrates the benefits of 3D doping design in silicon modulators, contributing to higher efficiency and avoiding additional PN overlap to introduce lower capacitance. The design of 3D doping profiles well balances the DC and AC performance, and provides novel modulator solutions for high-speed datacom.

Interleaved doped Mach-Zehnder Modulators (MZMs) are one solution to attaining higher modulation efficiencies compared with lateral junction structures, due to greater modal overlap with the depletion regions of the PN junctions. In this work, we present an interleaved Si modulator device design and process simulation based on a three-step ion implantation process that aims to obtain a realistic PN junction doping profile using a Monte Carlo simulation method. A high doping concentration on the order of 5×1018 cm−3 for the P and N regions is explored. Device simulations to track the carrier motion under different voltage biases are performed. Using equivalent medium theory, we calculated the modulation efficiency Vπ·Lπ of the interleaved Si modulator to be 0.19 V·cm under 1V reverse bias. This work is among the highest reported modulation efficiencies thus far in MZMs without photonic resonance structures. [ABSTRACT FROM AUTHOR]

MEMS-based magnetoresistive (MR) sensors have attracted considerable attention for years due to their small weight, low power consumption, and high sensitivity, whereas the 1/ $f$ noise is larger in the low-frequency region and degrades the low-frequency magnetic field detection limit. To reduce the impact of 1/ $f$ noise, MEMS resonators are utilized to modulate the low-frequency field to a high-frequency region where the 1/ $f$ noise vanishes. This article proposes a novel modulation method called synchronous motion modulation (SMM) using a comb-driven resonator and a piezoelectric cantilever resonator; meanwhile, it analyzes the relationship of modulation efficiency of SMM, vertical motion modulation (VMM), and gap change modulation (GCM) theoretically and with finite element method (FEM) simulation. It is found that the theoretical analysis is coincident with numerical simulation, and the SMM is the optimal modulation method for improving the low-frequency magnetic field detection limit due to its modulation efficiency is the sum of that of VMM and GCM. [ABSTRACT FROM AUTHOR]

A field-induced modulation efficiency enhancement method was developed in this paper. Based on the proposed modulation contrast model, when DC electric field increases, the increased DC field intensity generates a gradually declining positively contribution due to the quadratic electro-optic effect. Simultaneously, the increased polar-nano regions concentration generates a gradually increasing negatively contribution due to the light wave depolarization. Therefore, the modulation contrast can be enhanced by properly increasing the electric field to accumulate the maximum contribution. In the experimental research, the DC bias electric field is increased from 15.9 kV/m set by traditional method to 106.3 kV/m, the modulation efficiency can be increased by 2.8-fold. The modulation efficiency enhancement method of potassium tantalate niobate (KTN) electro-optic modulator could play an important significance to the commercial application in laser 3D imaging. [ABSTRACT FROM AUTHOR]

The optical single sideband (OSSB) modulation with tunable optical carrier to sideband ratio (OCSR) is a promising and popular technique in wideband analog signal transmission and microwave signal processing, which can improve modulation efficiency and combat the fiber chromatic dispersion. However, in all reported schemes for achieving OSSB modulation with tunable OCSR, the spurious free dynamic ranges (SFDR) of the systems are all limited by the third-order intermodulation distortion (IMD3). In this paper, our object is to improve the SFDR and suppress the IMD3 in a novel OSSB modulation with tunable OCSR. The proposed system consists of a primary channel and a secondary channel. In primary channel, an OSSB modulation with tunable OCSR is implemented. In secondary channel, the optical carrier and first-order sidebands are perfectly cancelled out, which can suppress the IMD3 without gain penalty at the same received optical power. In this way, a large-SFDR OSSB modulation with tunable OCSR is realized. Experimental results exhibit that the IMD3 gets effective cancellations without gain penalty under unchanged total received power, and the output microwave signal power obtains about 11-dB improvement by optimizing the OCSR. A greatly increased SFDR of over 128 dB·Hz4/5 is achieved in the proposed system. [ABSTRACT FROM AUTHOR]

After decades of development, low modulation efficiency is still the bottleneck of magnetic flux modulation technology for 1/f noise reduction of magnetoresistance sensors. To address this difficulty, a simulation on modulation efficiency improvement was conducted. It was interpreted that the major factors affecting the modulation efficiency were the initial position of the modulation film and its minimum distance to the magnetic sensitive element during the vibrating process. Moreover, size optimization and permeability increment of the modulation film also contribute to the increase in modulation efficiency. Given these simulation results, a piezoelectric actuated magnetic flux modulation structure with amplitude feedback function was proposed and then fabricated using micro-electromechanical system technology, primarily considering the initial height control, the expected amplitude control as well as the material properties of the modulation film. Test results of the sensor prototype suggested that the modulation efficiency is up to 68.7%, much higher than the currently reported value of 18.8%. [ABSTRACT FROM AUTHOR]

Doping profiles are always a key factor in the design of silicon modulators. As the doping in the waveguide cross-section is limited by the compact footprint, three-dimensional complex optimization presents itself as a viable option for improved performance. This work proposes two different types of unequal-proportioned omni-junction modulators obtained by the linear-decline weight particle swarm optimization algorithm with appropriate figure of merits (FOM). With FOM targeting at overall performance, the obtained modulator composed of unequal-proportioned vertical and lateral junctions has high bandwidth of 40 GHz with the V π L of 1.07 V cm. With FOM for higher modulation efficiency, the modulator composed of unequal-proportioned U-shaped and L-shaped junctions demonstrates low V π L of 0.72 V cm and bandwidth maintaining over 36 GHz. The algorithm together with the 3D design method provides greater flexibility in improving the device performance. • Unequal-proportioned omni-junction modulator improves modulation performance. • LDWPSO algorithm is utilized for efficient and extensive search of solutions. • Segmented transmission line is adopted for broad bandwidth. [ABSTRACT FROM AUTHOR]

A silicon (Si) and lanthanum-doped lead zirconium titanate (PLZT) hybrid microring modulator based on silicon-on-insulator (SOI) platform is designed theoretically and investigated numerically in this paper. The heterogeneous integration of PLZT film with Si material enables the waveguide to acquire both excellent electro-optical property and strong mode confinement capacity. Such hybrid microring modulator (100 μm in radius) has a PLZT rib-loaded cladding and is integrated with optimized tuning electrodes. The simulation results demonstrated that the Si/PLZT hybrid microring modulator could operate at 14 GHz with a relative high modulation efficiency (<0.8 V cm), which is much better than the other proposed Si/ferroelectric modulators. Meanwhile, under a driving voltage of 20 V, our modulator exhibits an extinction ratio of 32 dB at 1550.22 nm wavelength and a resonant wavelength tunability of 25 pm/V for TE mode. With these outstanding performances, the Si/PLZT hybrid microring modulator holds a great potential as a reliable on-chip device for optical communications and links. [ABSTRACT FROM AUTHOR]

• A universal modulation theory is established for magnetoresistance (MR). • A design principle is put forward to achieve a modulation efficiency of 100 %. • A novel tunnel magnetoresistance (TMR) accelerometer is proposed. • The established theory can be applicable to various MR and resonant sensors. A universal modulation theory is established to clarify the main parameters affecting the modulation efficiency, making a breakthrough progress on the 1/f noise problem in magnetoresistance (MR) that has not been effectively solved with trial and error for a long time. For achieving a modulation efficiency of 100 %, the theory indicates that the magnetic field strength along the sensitive direction of MR should be designed to be proportional to the displacement of the modulation structure. The established theory is thereafter experimentally demonstrated by proposing a new tunnel magnetoresistance (TMR) accelerometer with the highest modulation efficiency of 87 % than ever. The established theory is not only applicable to various kinds of MR sensors such as magnetometers, displacement meters, accelerometers, resonant galvanometer (Wang galvanometer), as well as other resonant sensors for improving sensing properties, but also a complementary solution to materials research in MR and its relevant field. [ABSTRACT FROM AUTHOR]

1/ $f$ noise is one of the main noise sources of magnetoresistance (MR) field sensors, which can cause intrinsic detection limit at low frequency. To suppress this noise, a novel magnetic flux vertical motion modulation (MFVMM) design using micro-electromechanical system flux concentrator (FC) and actuator is proposed in this paper, which can mitigate the 1/ $f$ noise by shifting the measurement frequency to kilohertz range. The proposed MFVMM has high efficiency and simple structure. The magnetic FC and the modulation film of MFVMM were analyzed with a numerical simulation. The simulation results show that the modulation efficiency of MFVMM exceeds 21%. A preliminary prototype sensor based on the multilayered giant MR AA002 and MFVMM was fabricated, and its modulation efficiency achieves 18.8% at a frequency of 7.01 kHz, which exceeds the efficiency of most existing sensors with the other modulation schemes. In addition, the magnetostatic detection ability is improved to 0.44 nT/ $\surd $ Hz. [ABSTRACT FROM AUTHOR]

The authors have developed a new heterogeneous‐integration method for fabricating semiconductor lasers with high modulation efficiency on Si substrates. The method employs the direct bonding of an InP‐based active layer to the SiO2 layer of a thermally oxidised Si substrate (SiO2 /Si substrate), followed by the epitaxial growth of InP to form a buried heterostructure (BH). By using the InP membrane, the authors realise epitaxial growth of an InP on the InP membrane directly bonded to Si without crystal quality degradation. Both a theoretical estimation and photoluminescence measurements revealed that the total laser thickness must be less than the critical thickness determined by the applied thermal strain. The authors confirmed that the crystal quality of the BH is comparable to that fabricated on an InP substrate when using a 250‐nm‐thick InP‐based membrane. A distributed feedback laser fabricated on a SiO2 /Si substrate exhibited continuous‐wave operation up to 100°C and was directly modulated by a 40 Gbit/s non‐return‐to‐zero signal with a bias current of 15 mA. These results indicate that epitaxial growth using a directly bonded InP‐based active layer on a SiO2 /Si substrate allows us to achieve lasers with high modulation efficiency and to use a large‐scale Si wafer as a fabrication platform, resulting in low‐cost fabrication. [ABSTRACT FROM AUTHOR]

This letter presents a novel graphene-embedded optical ring modulator that significantly enhances the modulation efficiency and tunability. Due to the enhanced light-matter interaction of graphene-embedded design, the shift rate of the resonance peak has been improved to 1.08 nm per applied voltage, which is two orders of the magnitude higher than previous ring modulators. The narrow bandwidth of the resonant modulator has been ameliorated to 149 GHz. In addition, our proposed modulator exhibits the advantages of high extinction ratio (22.13 dB) and smaller power consumption. Furthermore, a good tolerance of temperature drift (27 K) has been demonstrated in the proposed modulator. [ABSTRACT FROM PUBLISHER]

We propose a graphene-based modulator integrated into currently used communication fibers. The graphene is directly built into the core of the fiber to ensure the coupling efficiency. The fiber is deliberately side-polished to enhance the light-graphene interaction. The two-dimensional model analysis method and three-dimensional finite difference time domain method are used to rigorously disclose the light modulation mechanism under the anisotropic graphene modeling, which is merely conducted in previous studies. Based on such a structure, a phase modulator with an arm length of 127 μm is numerically demonstrated with enhanced modulation efficiency. A quasi-linear relation between the phase change and chemical potential of graphene is found theoretically for the first time, providing a large linear dynamic range to control the phase of optical modulation. [ABSTRACT FROM PUBLISHER]

A novel calibration-free electrical spectrum analysis method for microwave characterization of electrooptic phase modulators is proposed and experimentally demonstrated based on frequency-shifted optical heterodyning. The method achieves the electrical domain measurement of the modulation efficiency of phase modulators without the need for correcting the responsivity fluctuation in the photodetection. Moreover, it extends double the measuring frequency range through setting a specific frequency relationship between the driving microwave signals. Modulation depth and half-wave voltage of phase modulators are experimentally extracted from the heterodyning spectrum of two phase-modulated signals with and without frequency shifting, and the measured results are compared to those obtained with the traditional optical spectrum analysis method to check the consistency. The proposed method provides calibration-free and accurate measurement for high-speed optical phase modulators with the high-resolution electrical spectrum analysis. [ABSTRACT FROM PUBLISHER]

he standard for high efficiency digital coding was agreed by the International Telecommunication Union in January 2013. This article reviews the technology issues that are associated with delivery of television services using spectrum. It then examines the consumer implications of the new standard - the likely requirement for replacement equipment. The impacts on broadcasters and content providers are also considered in an environment where advertising share is diminishing and where consumers increasingly expect subscription video on demand (SVoD) models. The article suggests that newer coding techniques are likely to result in ultra-high-definition television (UHDTV) services being available to consumers. However, there is a strong likelihood that these services will not be delivered using terrestrial or satellite broadcasting services and instead will be delivered over broadband. [ABSTRACT FROM AUTHOR]

This paper has been investigated the best candidate selected acousto optic materials based AOM for upgrading speed response and transmission performance characteristics. These materials are common materials for acousto-optic devices such as silica glass (SiO2), tellurium dioxide (TeO2), gallium phosphide (GAP), and gallium arsenide (GaAs). As well as we have deeply investigated the important transmission characteristics of acousto optic modulators such as transmission performance efficiency, transmission bit rate, diffraction angle and efficiency, transient speed response, signal transmission quality, bit error rate (BER) and modulation bandwidth under wide range of the affecting parameters for different selected acousto optic materials to be the major of interest. [ABSTRACT FROM AUTHOR]

Abstract: Magnetic tunnel junctions (MTJs) have larger magnetoresistance ratio and higher magnetic sensitivity than other magnetoresistive structures, whereas their 1/f noise is also larger. To reduce the 1/f noise and improve the low frequency detection capability of MTJ sensors, some magnetic flux modulation schemes based on MEMS flux concentrators have been put forward, and several prototypes with gap-changed modulation (GCM) were fabricated by Army Research Laboratory (ARL). Presently, the problem of low magnetic modulation efficiency in GCM is still an obstacle for MTJ sensors with a resolution of pico-Tesla. In this paper, a novel magnetic flux modulation called vertical motion modulation (VMM) is proposed. In VMM, a modulation film driven by a MEMS actuator vibrates vertically above the air gap of the flux concentrator and the MTJs in the air gap detect an AC magnetic field with a DC bias. Theoretically the modulation efficiency of VMM can exceed 30% when the air gap varies from 30μm to 70μm. A preliminary prototype sensor with VMM was fabricated and its modulation efficiency achieves 17.4%. It is expected that the modulation efficiency of MTJ magnetic sensors with VMM can surpass 30% through modifying the sizes and improving the magnetic permeability of modulation films. [Copyright &y& Elsevier]

Testing of active photonic devices is totally different from testing of pure electronics; in particular, reduction of testing time in silicon photonics has been a significant issue. In this study, a compact behavioral model of optical phase shifters is constructed for carrier-depletion Mach–Zehnder (MZ) silicon modulators in the push–pull regime. The target characteristics, i.e., the dynamic extinction ratio (ER), absorption loss, and chirp parameter, are expressed in simple forms in terms of parameters representing the voltages-dependent modulation efficiency (ME) and the imaginary part of the effective index. The parameters reflecting manufacturing variability can be quickly extracted from fast DC measurements, which shortens the testing time. The theoretical concept relies on the proposal of a generalized form of the large-signal ME and an effective approximation for model construction that avoids the problem of the conventional small-signal definition being not applicable and large-signal definition leading to a cumbersome and non-intuitive formulation. It is shown that the constructed model suitably explains the physics and the reported experimental results for the slightly positive chirp characteristics of balanced phase shifters. Moreover, a parametric extraction applying the model is demonstrated in the C-band wavelength on a 300-mm SOI wafer. [ABSTRACT FROM AUTHOR]

In this paper, we propose the dynamic P-V curve for modulator and P-I curve for laser diode, and present a simple approach to deriving the curves from the small-signal frequency responses measured using a microwave network analyzer. The linear response range, modulation efficiency, optimal driving conditions at different frequency can, therefore, be determined. It is demonstrated that the large-signal performance of electro-absorption (EA) modulator and the directly modulated semiconductor lasers can be predicted from the dynamic curved surface. Experiments show a good agreement between the evaluated characteristics and the measured large-signal performance. [ABSTRACT FROM PUBLISHER]

A high-speed optical modulator with cascaded resonant-type electrodes is presented. To reduce the drive power and switch voltage Vπ and to maintain high-modulation efficiencies, resonant reduced-length electrode structures were cascaded and integrated on LiNbO3. Electrical power coupling into the resonators was realized by a single-input source distributed with electrical power dividers and delay lines. As a result, an optical modulator with four resonant-type cascaded electrodes was fabricated and characterized. This device, with a total active-electrode length as short as 3.4 (4 × 0.85) mm, achieved a switch efficiency Vπ· L of 68 V · mm at 25 GHz at 1.55-μm wavelength, resulting in a drive power 8.7 dB less than that required for a traveling wave modulator with the same active length. [ABSTRACT FROM PUBLISHER]