Input Signal Intensity Research Articles

Hydroacoustic communication channel capacity

Objectives . Capacity, describing the maximum rate of information transmission, is an important characteristic of any communication channel. The main purpose of this work isto determine the capacity of a hydroacoustic communication channel with constrained average intensity of the transmitted signal. An additional aim consists in finding the optimal spectrum of a transmitted signal and calculate its boundary frequencies. A model of a single-path channel was considered, which is characteristic of the deep sea with the receiver or transmitter placed at a sufficient depth. Methods . Concepts of applied hydroacoustics, the theory of random processes, and information theory were used. Results . An expression for gain in a hydroacoustic communication channel has been obtained. A novel expression derived for the spectral level of sea noise caused by sea surface waves is based on piecewise linear approximation of the curves of the spectral levels of noise obtained from four sources: turbulence, shipping, sea waves, and the thermal noise of the sea. Dependencies of the hydroacoustic channel capacity on communication distance, intensity of the transmitted signal, and sea state, are characterized. The definition of the optimal spectrum itself is determined along with the lower and upper boundary frequencies of the optimal spectrum of the transmitted signal. The dependence of the bandwidth usage on the intensity of the input signal at various communication distances has been investigated. Conclusions . On the basis of the Francois–Garrison attenuation coefficient, channel capacity was correlated with the parameters of the marine environment: temperature, salinity, and pH in the study area. At a given intensity of the input signal, channel capacity was shown to decrease significantly with increasing distance and sea wave intensity. It is also shown that the width of the optimal spectrum decreases with increasing distance. Sea wave noise was noted to affect significantly the shape of the optimal spectrum and its boundary frequencies. The possibility of cases where bandwidth usage increases with increasing distance at a given input signal intensity cannot be ruled out.

Modeling the method for determining the stimulated brillouin scattering threshold in a single-mode optical fiber

Nonlinear optical effects in optical waveguides play an important role in the development of fiber and integrated optics systems for optical communication and information processing. On the one hand, nonlinear effects impose restrictions on the radiation power that can be transmitted through an optical fiber or light guide. In this paper, the problem of the occurrence of the phenomenon from the stimulated Brillouin scattering (SBS) effect is investigated using two optical sources of rays in a single-mode optical fiber at joint waves of 1310 nm and 1550 nm. Due to the fact that in all trunk fiber-optic lines, the intensity and energy of input signals is limited due to the influence of SBS, methods are currently being sought to reduce the influence of this phenomenon. It was found that the energy of the input beam in the combined propagation of the compound did not reach the value of the threshold of SBS in the values of 25 dBm and 27 dBm due to the discrepancy between the experimental results and the results of the model. The SBS effect was not observed when the threshold threshold of 15 dBm and 27 dBm – SBS was reached when combining a dual beam along a single optical fiber in one direction. As a result, by double integration, the value of the SBS threshold was raised, and the direction for future scientific research was determined. If the possibility of increasing the threshold of SBS is proved, then increasing the distance of amplifiers in the main networks, respectively, its economic effect increases. In addition, it can be noted that there are no scientific papers devoted to the study of the effects of optical nonlinear effects by combining and distributing these two compounds along a single optical fiber. This article discusses the issues of improving the capacity and determination of the threshold for stimulated Brillouin scattering. To increase the power threshold is invited to consider the dependence of the phase modulation frequency of the spectral width of the laser radiation. In addition, the fact that the SBS threshold did not reach the value at an energy of 27 DB in the case of the double-beam distribution can be proved by discrepancies in comparison with the results of experimental studies and the results of the model that determines the SBS effect

Constrained plasticity reserve as a natural way to control frequency and weights in spiking neural networks

Biological neurons have adaptive nature and perform complex computations involving the filtering of redundant information. However, most common neural cell models, including biologically plausible, such as Hodgkin–Huxley or Izhikevich, do not possess predictive dynamics on a single-cell level. Moreover, the modern rules of synaptic plasticity or interconnections weights adaptation also do not provide grounding for the ability of neurons to adapt to the ever-changing input signal intensity. While natural neuron synaptic growth is precisely controlled and restricted by protein supply and recycling, weight correction rules such as widely used STDP are efficiently unlimited in change rate and scale. The present article introduces new mechanics of interconnection between neuron firing rate homeostasis and weight change through STDP growth bounded by abstract protein reserve, controlled by the intracellular optimization algorithm. We show how these cellular dynamics help neurons filter out the intense noise signals to help neurons keep a stable firing rate. We also examine that such filtering does not affect the ability of neurons to recognize the correlated inputs in unsupervised mode. Such an approach might be used in the machine learning domain to improve the robustness of AI systems.

Improving hearing-aid gains based on automatic speech recognition.

This study provides proof of concept that automatic speech recognition (ASR) can be used to improve hearing aid (HA) fitting. A signal-processing chain consisting of a HA simulator, a hearing-loss simulator, and an ASR system normalizing the intensity of input signals was used to find HA-gain functions yielding the highest ASR intelligibility scores for individual audiometric profiles of 24 listeners with age-related hearing loss. Significantly higher aided speech intelligibility scores and subjective ratings of speech pleasantness were observed when the participants were fitted with ASR-established gains than when fitted with the gains recommended by the CAM2 fitting rule.

Theoretical analysis of ultra-fast multi-wavelength switch containing Kerr nonlinear material and its application as simultaneous AND and NOR logic gates.

In this paper, an all-optical plasmonic multi-wavelength switch based on Kerr nonlinear material is proposed. It consists of circular waveguides wrapped around three side-coupled nano-ring resonators. Fundamentally, introducing the circular waveguide increases the coupling coefficient and switching modulation depth. The transmission response of the proposed multi-switching structure is studied theoretically based on coupled mode and transfer matrix theories. The validity of the derived transmission formula is confirmed by the numerical result obtained by the finite element method. Also, based on the self-phase modulation and cross-phase modulation (XPM) nonlinear effects, the resonance wavelengths are effortlessly tuned by changing the intensity of the incident lightwave without changing the dimensions of the structure. As a result, by utilizing the XPM effect, the required input signal intensity is significantly decreased to 6.5MW/cm2. The obtained modulation depths are 18.08, 31.83, and 28.40 dB at wavelengths of 850, 1310, and 1550 nm, respectively. Finally, to show the application of the proposed switch, the simultaneous AND and NOR logic gates are designed with intensity contrast ratios of 78.81 and 85.49 dB, respectively. The proposed plasmonic switch has many advantages such as being multi-wavelength and having low required switching intensity, ultra-fast switching time of 23 fs, and optical bistability. These features are promising for future integrated plasmonic devices for applications such as communications, signal processing, and sensing.

Inlet Effect Caused by Multichannel Structure for Molecular Electronic Transducer Based on a Turbulent-Laminar Flow Model

The actual fluid form of an electrolyte in a molecular electronic converter is an important factor that causes a decrease in the accuracy of a molecular electronic transducer (MET) liquid motion sensor. To study the actual fluid morphology of an inertial electrolyte in molecular electron transducers, an inlet effect is defined according to the fluid morphology of turbulent-laminar flow, and a numerical simulation model of turbulent-laminar flow is proposed. Based on the turbulent-laminar flow model, this paper studies the variation of the inlet effect intensity when the thickness of the outermost insulating layer is 50 µm and 100 µm, respectively. Meanwhile, the changes of the inlet effect intensity and the error rate of central axial velocity field are also analyzed when the input signal intensity is different. Through the numerical experiment, it verifies that the thickness of the outermost insulating layer and the amplitude of the input signal are two important factors which can affect the inlet effect intensity and also the accuracy of the MET. Therefore, this study can provide a theoretical basis for the quantitative study on the performance optimization of a MET liquid sensor.

Mechanisms of Invariant Anti-Noise Encoding in Pulse Neural Networks

Nonlinear dynamics, physical processes, and information processing in selective pulse neurons are studied. A way of encoding input information, in which a piece of information is the entire pulse sequence and the intensity of input signals is coded according to the asynchronous change in the mean frequency of pulse sequences, is considered. The proposed means of encoding pulse sequences is tested. The invariance of positional recognition is demonstrated with respect to changes in the input signal intensity, which, according to the Weber–Fechner law, results in a synchronous change in the frequency of pulse sequences.

Tunable band (pass and stop) filters based on plasmonic structures using Kerr-type nonlinear rectangular nanocavity

We have proposed and numerically investigated two plasmonic structures for bandpass and band-stop filters. The bandpass filter is composed of two metal–insulator–metal (MIM) waveguides coupled to each other by a nonlinear rectangular nanocavity. The band-stop filter consists of an MIM waveguide side coupled to a Kerr-type nonlinear rectangular nanocavity. The optical filtering effect is verified by two-dimensional (2-D) finite-difference time-domain (FDTD) simulations. It is demonstrated that based on optical nonlinearity we can easily make the proposed filters tunable by properly adjusting the intensity of incident light without changing the dimensions of the structures. The simulation results revealed that within the transmission spectrum, the selected central wavelength and the bandwidth of the filter can be tuned by the input signal intensity. The proposed structures are suitable to be used as highly dense integrated optical circuits, where limitations on the dimensions of the filter structure are vital.

Surgical Grasping Forceps With Enhanced Sensorimotor Capability via the Stochastic Resonance Effect

Haptic information is crucial in the execution of precise dexterous manipulations. Laparoscopic surgery, a type of minimally invasive surgery, requires that the surgeon senses force information about tissue through forceps, because he or she cannot touch the organs directly. We propose the concept of surgical grasping forceps with enhanced sensorimotor capability based on attaching a vibrator to the forceps’ grip by evoking a stochastic resonance (SR) effect. To apply appropriate vibrations, a summing network of FitzHugh–Nagumo neurons was built to investigate the system's response when white noise was applied to each of the four types of tactile receptor. The relation among the tactile sensitivity, noise intensity, and amplitude of input signal is discussed by the simulation with the neural network composed of different tactile receptors. The simulation results revealed that the working range of the SR effect is extended by taking advantage of having multiple receptors with different characteristics in skins. It was also found that improved tactile sensitivity could be obtained even without a strict set of vibration intensity values. Based on the findings from the simulation, we developed surgical forceps with sensorimotor-enhancing capability taking advantage of the SR effect. The forceps are equipped with a lead zirconate titanate actuator at the grip as a vibration source. We conducted touch testing, texture discrimination testing, and tumor detection testing to verify their improved tactile sensitivity. The experiments conducted with the proposed forceps showed that maintaining the noise intensity within the optimal range could improve tactile sensitivity, and confirmed the usefulness of the SR application for medical devices.

Impact of signal filling factor for switching in reflective vertical cavity-based fast semiconductor saturable absorbers

ABSTRACTA numerical model on reflective vertical cavity-based fast semiconductor (carrier recombination time in ps regime) saturable absorbers (VC-FSSA) is investigated for all-optical high-speed future applications, where the fluctuation of cavity optical length due to thermo-optic effects and cavity heating, and optically induced carrier density change are considered simultaneously with the increase of input signal intensity. The phase-shift due to thermal-optic effects and cavity heating is very important for high-speed device performances. At first, intensity and wavelength bi-stabilities are modelled with the different intensity time filling factor of RZ modulated pump signals and also, with the different input intensities, where the intensity tuning time is considered at few μs. Then the inverse saturation characteristics of reflectivity for the universal logic operations are shown for probe signal with the proper wavelength, which can control the negative effects of optically induced heating effects. These characteristics can be used for the high-speed thermally stable bi-stable optical switch and all-optical logic applications.

All-optical transistors and logic gates using a parity-time-symmetric Y-junction: Design and simulation

Classical nonlinear or quantum all-optical transistors are dependent on the value of input signal intensity or need extra co-propagating beams. In this paper, we present a kind of all-optical transistors constructed with parity-time (PT)-symmetric Y-junctions, which perform independently on the value of signal intensity in an unsaturated gain case and can also work after introducing saturated gain. Further, we show that control signal can switch the device from amplification of peaks in time to transformation of peaks to amplified troughs. By using these PT-symmetric Y-junctions with currently available materials and technologies, we can implement interesting logic functions such as NOT and XOR (exclusive OR) gates, implying potential applications of such structures in designing optical logic gates, optical switches, and signal transformations or amplifications.

Nanoscale plasmonic filter based on coupled metal-insulator-metal waveguides using nonlinear nanoslot resonator

A nanoscale optical filter based on metal-insulator-metal waveguides and a Kerr-type nonlinear nanoslot resonator is introduced and numerically investigated by finite-difference time-domain simulations. It is demonstrated that the resonant wavelengths of the nanoslot resonator experience a red shift due to the intensity dependence of the Kerr nonlinear effect. The simulation results reveal that the resonant modes of the proposed filter can be tuned by properly adjusting the input signal intensity without changing the dimensions of the filter structure. The findings of this study are useful for highly integrated optical circuits, for which we have limitations on the dimensions of the filter structure. In addition, the results are suitable for design of integrated optical waveguides and resonators based on the plasmonic effect. A significant advantage of the proposed tunable filter is its ease of fabrication.

Optical parametric amplification in one-dimensional photonic bandgap structures

In this paper, optical parametric amplification based on the degenerate four-wave mixing principle in a one-dimensional photonic bandgap (PBG) structure has been numerically studied. First, the multiple scale method was introduced to derive a complete set of nonlinear coupled-mode equations for a finite structure with different inhomogeneous nonlinear coefficients than those used in previous works. This finite structure is composed of 680 dielectric layers, which are alternating half-wave/eight-wave films. The wavelengths of the pump, signal, and idler pulses have been determined from the transmission spectrum, which was illustrated by using the transfer matrix method. The parametric interaction of the pump, signal, and idler pulses inside PBG structure has been numerically simulated by using the split-step Fourier transform method. The results of the simulation have shown that the intensities of the signal and idler have exponential growth with respect to the number of layers in the medium. Meanwhile, pump wavevector detuning directly affects the intensities of both pulses due to a band-edge phase-matching condition that might be achieved from only one optimal detuning parameter. Moreover, both the amplification gain and the conversion efficiency of the idler pulse have been shown to be dependent on the bandwidth of the pump pulse spectrum. A very narrow pulse, with a bandwidth much less than the relevant transmission peak, enables the highest amplification and conversion efficiency in this medium because the most efficient phase-matched condition occurs in this situation. Finally, the conversion efficiency grows exponentially with input pump intensity for several input signal intensities. Furthermore, the maximum conversion efficiencies directly vary with input signal intensity.

Development of a DNA sensor using a molecular logic gate

This communication reports the increase in fluorescence resonance energy transfer (FRET) efficiency between two laser dyes in the presence of deoxyribonucleic acid (DNA). Two types of molecular logic gates have been designed where DNA acts as input signal and fluorescence intensity of different bands are taken as output signal. Use of these logic gates as a DNA sensor has been demonstrated.

Growth of stochastic resonance in neuronal ensembles with the input signal intensity

The presence of noise can improve the response of certain nonlinear systems to input signals through the effects of stochastic resonance (SR). The optimal noise intensity for SR is proportional to the signal frequency if the signal is periodic, but proportional to the signal intensity if the signal is aperiodic. Here, we demonstrate using linear response theory that the optimal noise intensity for SR is necessarily dependent on the signal intensity even if the signal is periodic. We also demonstrate that the SR curves grow according to the signal intensity from a bell-shaped curve to a plateau, resulting in the emergence of SR without tuning. In particular, we present a theoretical analysis indicating that the SR peak shifts with the signal intensity due to the scaling of the stationary neuronal firings. The growth of SR may serve as a useful design principle for many noise-exploiting applications.

Conversion of Electrical and Synaptic Actions into Impulse Discharge Patterns in Purkinje Neurons with Active Dendrites: A Simulation Study

We studied relations between the cell output spiking patterns (neuronal codes) and the intensity of input signals on a model of cerebellar Purkinje neuron with reconstructed dendritic arborization and nonlinear membrane properties. The input influences were either a depolarizing current, I s, applied at the soma or tonic synaptic excitation resulting in a synaptic conductivity, G s homogeneously distributed over the dendrites. The spiking patterns were distinguished based on periodical or nonperiodical (stochastic) sequences of spikes and/or their groups (bursts). The role of dendrites in pattern forming was revealed from time-varying spatial distributions of the dendritic membrane potential and the corresponding voltages in the soma and distal axon. As integrative indicators, interspike intervals, ISIs, and mean firing rates, f, characterized the output spiking, while mean voltage differences, ΔĒ, between the remotest equidistant sites in all pairs of the sister dendrite branches characterized the electrical heterogeneity of the arborization. To explore a wide range of conditions, I st and G s were varied, respectively, from 0.55 to 1.4 nA and from 50 μS/cm2 to 7 mS/cm2 On average, the output firing rate f increased with increased intensities of either input signal. The f-I st and f-G s relations, however, differed from each other. The former was an approximately logarithmic function with small deviations at mid-range currents, while the latter was a nonmonotonically increasing function with remarkable slope breaks within an intermediate Gs range. Within the intensity ranges, the electrical heterogeneity of the arborization ΔĒ increased with greater I st, but it first increased and then decreased with increasing G s. The leading pattern-forming factor of dendritic origin consists of transitions of the dendritic domains between states of spatially homogeneous near-resting depolarization (down-state) and spatially heterogeneous high depolarization (up-state) manifested as the appearance of slow plateau-like depolarization potentials. The latter were generated with phase shifts between dendritic subtrees in response to the applied current I st > 1.5 nA (about threefold greater than the threshold current) or in response to synaptic activation of low (G s ≤ 66 μS/cm2) and high (G s > 75 μS/cm2), but not intermediate intensities. Under these conditions, the output patterns were either continuous firing with nearly constant ISIs or simple periodical sequences of identical bursts accompanied by moderate elevations of ΔĒ. At intermediate synaptic intensities, the synchronous transitions were periodically perturbed by nonsynchronous ones, leading to generation of several dissimilar bursts or “single spike-burst” complexes. These events were associated with the largest ΔĒ elevations indicating the greatest electrical heterogeneity of the arborization. Such desynchronized transitions are explained by the existence of an asymmetry-induced difference in the transfer properties of the dendrite subtrees, leading to increased differences in the electrical states. We conclude that the dendritic arborization of Purkinje neurons behaves like a complex of high-threshold low-frequency spatial electrical oscillators, while the axo-somatic trigger zone has a low threshold and is capable of providing a high firing frequency. These properties determine the conversion of the input signal intensity into output firing patterns depending on which of these coupled oscillators is at present the predominant receiver of the input signal and also on the input intensity.

Investigation on competition between the input signal and noise in a Brillouin amplifier

We theoretically and experimentally investigate the competition mechanism between the input signal and noise in a Brillouin amplifier, and the influence of the delay time of the pump pulse relative to the signal pulse on this competition. Results show that as the input signal intensity increases, the amplified Brillouin scattering (ABS) noise gradually weakens, while the signal amplification predominates. When the ratio of the input signal to the pump intensity is greater than 10−4, the ABS noise will be almost completely suppressed. The delay time should be controlled as the pump pulse half-width to achieve high signal-noise-ratio and high amplification.

Efficiency and phase of optical parametric amplification in chirped quasi-phase-matched gratings

Three-wave nonlinear interactions in chirped quasi-phase-matched (QPM) gratings are shown to exhibit conversion efficiency approaching 100% with increasing input pump and signal intensities, evading backconversion, as long as the idler vanishes at the input and the QPM grating is sufficiently chirped. The signal phase is described in terms of Kerr-like self- and cross-phase modulations, in the cascade χ((3)) approximation. Achieving high gain and efficiency simultaneously can lead to a large nonlinear phase, and the resulting trade-off is discussed.

Non-collinear optical parametric chirped-pulse amplifier for few-cycle pulses

Modified parametric coupled equations for three-wave interaction in non-collinear optical parametric chirped-pulse amplification (OPCPA) are presented, in which the effects from the non-collinear configuration have been taken into account. By utilizing this new model, a two-stage OPCPA system based on a BBO crystal is numerically calculated with a split-step Fourier transform algorithm. Tracing the dynamics of the signal wave in the crystal reveals that in the first stage spectral gain narrowing occurs due to the weak input signal intensity and the non-uniform temporal distribution of the pump light. However, in the saturation regime the spectrum of the signal will be broadened as a consequence of back conversion. The simulation shows that it is crucial to correctly control the experimental parameters to balance both processes. For maximizing the energy-bandwidth product (EBP), an optimized configuration is sought by examining several parameters such as pump intensity, seed energy and crystal length. With a pump intensity of 7.75 GW/cm2 and a crystal length between 3.75 and 4.25 mm pulses with a sub-10 fs duration can be amplified with a total gain of up to 1.7×106.

Inverse problem of optical parametric chirped pulse amplification

A method for solving the inverse problem of optical parametric chirped pulse amplification, i.e., for a given shape of the output signal pulse, how to calculate the shape of the input signal pulse, is proposed. Based on numerical techniques such as split-step Fourier transform and fourth-order Runge-Kutta, the quantitative relation between the input signal intensity and the output signal intensity was obtained by numerical fitting. Taking the chirped Gaussian pulse and the shaping pulse with a certain shape as the required output signal pulse, the input signal pulse shape can be worked out by the inverse calculation. The results indicate that the inverse problem can be solved quickly and precisely with the method proposed in this paper, and this method is useful for pulse shaping.