Automatic differentiation approach for acoustic holograms: Performance and potential applications

Designs of optical lenses based on metallic nanoslits are carried out based on the phase and amplitude modulation by tuning the slit widths. The slits are perforated on thin metallic film, and the width of each slit is achieved by simulated annealing algorithms, which is connected with both the amplitude and phase modulation. Two kinds of focal lenses, which can realize one or two focus points, have been designed. The finite-difference time-domain method is employed to check the performance of the designed lenses. Simulation results show that the designed lenses can perform the preset functions well. Using this method, multiple optical elements with different functions can be conveniently achieved in subwavelength scale.

In this paper we report the results of extensive research on phase modulation (PM) and amplitude modulation (AM) noise in linear bipolar junction transistor (BJT) amplifiers. BJT amplifiers exhibit 1/f PM and AM noise about a carrier signal that is much larger than the amplifier's thermal noise at those frequencies in the absence of the carrier signal. Our work shows that the 1/f PM noise of a BJT based amplifier is accompanied by 1/f AM noise which can be higher, lower, or nearly equal depending on the circuit implementation. The 1/f AM and PM noise in BJTs is primarily the result of 1/f fluctuations in transistor current, transistor capacitance, circuit supply voltages, circuit impedances, and circuit configuration. We discuss the theory and present experimental data in reference to common emitter amplifiers, but the analysis can be applied to other configurations as well. This study provides the functional dependence of 1/f AM and PM noise on transistor parameters, circuit parameters, and signal frequency, thereby laying the groundwork for a comprehensive theory of 1/f AM and PM noise in BJT amplifiers. We show that in many cases the 1/f PM and AM noise can be reduced below the thermal noise of the amplifier.

This paper deals with mechanical fault monitoring in induction machines from stator current measurements. The considered faults lead to amplitude and/or phase modulations of the measured stator current. The different faults can be characterized by their time-frequency signatures via the Wigner distribution. The time-frequency representations apply to complex signals that may be obtained through the Hubert transform of the real measured signal. In case of high frequency modulations, it can not be taken advantage of the time frequency signatures. This study proposes an alternative complex signal representation for modulated stator currents. The so-called space vector is obtained through the Concordia transform. From three stator current measurements, the Concordia transform builds a complex vector which conveniently carries the information about phase and amplitude modulations. This paper applies and compares the Wigner distribution computed with the Hilbert and Concordia transforms in case of simulated and experimental signals with various modulation frequency ranges.

A nonlinear circuit with periodic operation, such as a mixer and oscillator, can be modeled as a linear periodic time‐varying circuit by assuming a small‐signal input and output. This paper presents a method by which the transfer function of such a periodic time‐varying circuit can be decomposed into phase and amplitude modulation components. Assuming a small input, the phase modulation component can be interpreted as a result of narrow‐band phase modulation with a small modulation index. Thus, it suffices to consider only the first sideband. As regards the spectrum of the amplitude modulated signal, it suffices to consider only the first sideband, regardless of the modulation index. Thus, the two spectra corresponding to the upper and lower sidebands around the carrier are decomposed into narrow‐band phase and amplitude modulation components, and the transfer function can be decomposed into phase and amplitude modulation components. By this method, it becomes possible to decompose the noise of the mixer and the oscillator into the amplitude noise and the phase, or to simulate AM‐PM conversion. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 85(7): 29–37, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.1105

A series of experiments investigated the interaction of phase and amplitude modulation in the auditory perception of movement of a fused, lateralized sound image. A technique was developed whereby the perception of periodic motion in the coronal plane of the head could be produced either by sinusoidal modulation of the amplitude or phase relation of a pure tone carrier presented to each ear. At a given modulation frequency the observer set the amplitude of either the phase shift or the differential amplitude change in order to just detect motion in the sound image. The threshold amount of each measure was defined as unity and the observer was then presented with various ratios of the two mixed in two ways: (1) Phase lead to one ear with amplitude increase to the same ear or (2) phase lead to one ear with amplitude increase to the other ear. Evidence for super additivity of amplitude and phase modulation was found for condition I while evidence for subadditivity for am and pm was found in condition number 2. Both these results suggest that, although both time and intensity differences are used by the human auditory mechanisms involved in the perception of movement, they have at least some different neural substrates.

A practical implementation of a portable secondary standard for phase modulation (PM) and amplitude modulation (AM) noise at 5, 10, and 100 MHz is described. The accuracy of the standard for both PM and AM noise is +or-0.14 dB, and the temperature coefficient is less than 0.02 dB/K. The noise floor of the standard for PM noise measurements is less than -190 dBC rel to 1 rad/sup 2//Hz at 5, 10, and 100 MHz. The noise floor for AM measurements depends on the configuration. A calibrated level of PM and AM noise of approximately-130+or-0.2 dB rel to 1 rad/sup 2//Hz is used to evaluate the accuracy versus Fourier frequency. This standard can also be used as an alternative to the normal method of the PM/AM detector for PM/AM measurements. >

An experimental investigation into the role of simultaneous amplitude and phase modulation of velocity fluctuations characterizing the near-field transition of an initially laminar planar jet at moderate Reynolds number is presented. Very low level periodic acoustic excitation at selected frequencies is applied upstream of the nozzle exit in order to introduce an organized carrier wave into the flow. Instantaneous amplitude and phase modulates are computed directly from hot-wire velocity fluctuation data which allows their respective role in the jet transition process to be quantified. It is found that amplitude modulation serves to provide energy to amplifying sideband fluctuations which multitone phase modulation effectively redistributes to neighboring spectral modes in the nonlinear stages of transition. The phase modulation is found to result from an experimentally verified amplitude dependence in the dispersion relation. The phase angle between amplitude and phase modulation is found to be an important parameter in governing the spectral development of the shear layer by its effect on sideband asymmetry. While the essential physics associated with the modulation phenomenon is found to be quite similar to that previously reported in plane wakes, the presence of the subharmonic resonant interaction in the planar jet shear layer adds an additional dimension to the modulation phenomenon.

We present a subsampling polar transmitter (SSPTX) in 28-nm CMOS that consists of a low-noise phase modulating (PM) digital subsampling phase-locked loop (PLL) and a harmonic rejection mixed (HRM) inverse-class-D ( $\mathrm {D}^{-1}$ ) digital power amplifier (DPA) for amplitude modulation (AM). The DPA is, unlike in a typical polar transmitter (TX), placed within the PLL and the phase-error detection happens directly at the DPA output. The subsampling polar TX thus becomes sensitive not only to phase errors but also to modulation amplitude. That feature enables AM–AM and PM–PM distortion to be detected and cancelled digitally in the background, while the transmitter operates normally. Moreover, the AM–PM cross distortion is filtered by the loop itself. The chip operates from a 0.9-V supply at 5.5 GHz with 2.5 MHz BW (1024 QAM) with average 1.1-dBm output power and total power consumption of 50 mW.

Electrical control of amplitude and phase of terahertz radiation (THz) is the key technological challenge for high resolution and noninvasive THz imaging. The lack of active materials and devices hinders the realization of these imaging systems. Here, we demonstrate an efficient terahertz phase and amplitude modulation using electrically tunable graphene devices. Our device structure consists of electrolyte-gated graphene placed at quarter wavelength distance from a reflecting metallic surface. In this geometry, graphene operates as a tunable impedance surface which yields electrically controlled reflection phase. Terahertz time domain reflection spectroscopy reveals the voltage controlled phase modulation of π and the reflection modulation of 50 dB. To show the promises of our approach, we demonstrate a multipixel phase modulator array which operates as a gradient impedance surface.

When an RF carrier is amplified by a GaAs MESFET, amplitude modulation (AM) and phase modulation (PM) noises are imposed on the carrier. This is generally believed to be caused by transposition to the carrier frequency of the low-frequency flicker noise generated by the FET. The cross correlation between the AM and PM noises and the low-frequency noise observed on the drain of the FET is measured. While the AM noise and the low-frequency noise on the drain of the FET exhibit a high degree of correlation, the PM noise and the low-frequency drain noise are not highly correlated. The latter result may explain the limited success of oscillator phase noise reduction methods which rely on the existence of a large cross correlation between the PM and low-frequency noises. >

For the amplitude modulation (AM) radio broadcast band, there are several standards being considered for digital audio broadcast (DAB), all using orthogonal frequency-division multiplexing (OFDM). One of the main challenges to implementing digital audio broadcasting is that existing broadcast equipment was not designed for it. Unlike analog AM, which is a low bandwidth amplitude modulated signal, OFDM is a noise-like signal with significant amplitude and phase modulation. Most AM transmitters use an envelope elimination and restoration (EER) amplifier architecture, where the amplitude and phase components of the signal are amplified separately then recombined at the high power stage. The magnitude and phase component bandwidths are several times that of the input signal, and any filtering in the amplifier will result in spectral regrowth due to poor cancellation of this high frequency content. This paper develops the concept of using time-domain preprocessing on the signal to reduce the bandwidth expansion in EER amplifiers. The processing exploits the localization of the bandwidth expansion and its correlation with spectral regrowth at the output. The proposed algorithm identifies distortion- causing signal sections and replaces each one with an alternative signal trajectory. Using the processing, out of band emissions are reduced at the expense of increased computational complexity and error vector magnitude. Promising results are shown for the DRM 10 kHz digital signal, with reductions in spectral regrowth of up to 10 dB.

Previous methods for the generation of accelerating beams are mostly based on bulky phase-only spatial light modulator. Here we propose an experimental scheme for the generation of accelerating beams by fabricating a quartz plate capable of realizing both phase and amplitude modulation. The phase modulation is implemented by aligned 16-level etching into the quartz plate, while the amplitude modulation is realized by controlling the duty ratio of the partial metal coverage locally. Based on this approach, a sinusoidal accelerating beam with multiple bending is generated for demonstration and propagates along a sinusoidal trajectory as expected.

This paper describes the development of numerical simulation models of soliton systems using a newly developed Fourier Series Analysis Technique (FSAT) to analyze the non-linear Schrodinger equation of soliton propagation. Generation of sub-picosecond solitons in an active mode-locked fiber ring laser with amplitude and phase modulators and soliton pulse compression mechanisms using dispersion decreasing fiber are investigated. Soliton propagation in optical fiber has been studied extensively for high data rate and ultra-long distance applications in recent years. Numerical methods to study the non-linear Schrodinger equation (NLSE) include inverse scattering method, pertubation method, and split-step Fourier method. The proposed FSAT [1] method has several advantages over the others including reduced sampling points, better computation efficiency, and ease in handling high order dispersion and nonlinear terms. In this paper, FSAT is applied to model soliton pulse generation and compression. The first numerical simulation model is to investigate the generation of sub-picosecond solitons in active mode-locked fiber ring laser. The laser model consists of a polarization preserving Er-doped single mode fiber, an amplitude modulator and a phase modulator. The model has taken into account of dispersive spreading, self-phase modulation, finite amplification bandwidth, pump depletion, and Raman self-frequency shift. The propagation of soliton pulses in the gain section of the fiber laser can be described by a simplified nonlinear equation [1]: ∂u/∂z= j ∂ 2 u/∂T 2 + j|u| 2 u + Gu + γ a G∂u/∂T - jγ R u ∂|u| 2 /∂T (1) where u is the normalized amplitude, T is the normalized time and z is the normalized distance. In (1), the first term in the right hand side describes the pulse dispersion spreading, the second term describes the Kerr effect, the third and forth terms represent the finite gain bandwidth and pump depletion of Er 3+ fiber, respectively. The last term describes the Raman self-frequency shift of the laser. Equation (1) can be solved via the FSAT method to analyze the formation of soliton pulses [2] by first expressing u(z,T) in terms of the Fourier series as shown below: N Σ n=-N ∂u n (z)/∂z exp(jneT)=- jΣ N n =-N n 2 e 2 u n (z)exp(jneT)+jΣ N n=-N Ψ n (z)exp(jneT) (2) + GΣ N n=-N u n (z)exp(jneT) + jγ a G Σ N n=-N neu n (z)exp(jneT) - jγ R Σ N n=-N Φ n (z)exp(jneT).

We have built an optical VanderLugt-type correlator that uses two Epson liquid crystal televisions (LCTVs) separately generating the amplitude and phase modulation properties. The input scene is displayed in amplitudemostly regime on the first LCTV. Thereafter a phase-only filter with a different level of phase quantization is addressed in phase-mostly regime on the second LCTV. To characterize this device, the phase and amplitude modulations were experimentally measured and investigated in pattern recognition application where the grey-level input scenes and multilevel kinoforms are displayed on the LCTVs.

We show that a high-resolution software package can be adapted to calculate the amplitude modulation (AM) and phase modulation (PM) noise performance of Si Bipolar Junction Transistor (BJT) amplifiers. Our simulations predict that the PM noise induced by bias current noise can be greatly suppressed by operating at special bias conditions. Furthermore, a dc balance amplifier circuit is introduced to stabilize the base-to-collector voltage. The total sensitivity of PM noise to power supply noise using dc balance architecture can be reduced by 40 dB compared to basic amplifier architecture. This is experimentally verified.