Amplitude Modulation Mode Research Articles

Analysis of interchannel crosstalk in a dispersion-managed analog transmission link

A technique for computing the effect of cross-phase modulation (XPM) on two copropagating analog channels in an optical fiber link is presented. In this approach, the interaction between the two channels is linearized by keeping the self-phase modulation (SPM) and XPM interactions in the strong optical carrier components only at lowest order and then at the next order, deriving the effect on the modulation components of both channels when the optical carrier is strong relative to the other components of the channel. In contrast to some previously suggested approaches, it is not assumed that the pump is undistorted, and therefore, this method accurately describes distortions due to SPM, XPM, and dispersion management in both channels. This method is easily applied to systems with multiple spans employing dispersion management with loss and gain. The expressions for the received radio frequency power and crosstalk between the two channels when direct detection is used are then provided. Using this approach, new expressions for the amplitude modulation and phase modulation modes of the two channels are derived, and the way they exchange energy when SPM, XPM, and dispersion are all considered is explained. This method yields excellent agreement between theory and experimental data.

Theory of Q-Controlled dynamic force microscopy in air

The theory of dynamic force microscopy in air is developed with respect to the application of the Q-Control technique, which allows to increase or decrease the effective Q factor of the cantilever via an active external feedback. Analytical as well as numerical approaches are applied to solve the equation of motion describing the cantilever dynamics with and without Q-Control in the presence of a model tip-sample interaction force. Based on this analysis, the characteristics of Q-Controlled dynamic force microscopy are compared to conventional dynamic force microscopy carried out in amplitude modulation mode without active Q-Control (“tapping mode”). In the case of negligible tip-sample interaction (i.e., with the tip “far” from the surface), the theory describes how Q-Control alters the shape of the resonance curves of the cantilever by modifying the effective Q factor and shifting the resonance peak. Explicit consideration of tip-sample forces then permits insight into the imaging properties of Q-Controlled dynamic force microscopy. In particular, it is found that an increased Q factor prevents the oscillating cantilever to jump into a repulsive imaging regime during tip-sample approach, which often occurs during conventional tapping mode imaging in air. The analysis reveals in detail which parts of the tip-sample force curve are contributing to the contrast formation for the different imaging conditions if plotted as a function of the tip-sample distance. Based on these findings, we conclude that the restriction of the maximal tip-sample force to specific parts of the attractive regime, which is triggered by the activation of the Q-Control feedback, is the main reason for the enhanced imaging quality reported in several experimental studies if compared to conventional tapping mode imaging without Q-Control.

Theoretical study of using an amplitude modulation scheme with an electro-optic modulator for generation of the proper power shape function of an optical soliton pulse in a nonlinear waveguide

The main advantage of using soliton pulses in optical communication systems is that the shape of the pulse remains almost unaltered over a long distance. We propose a simple method to achieve the proper power shape function of a pulse for generation of an optical soliton by using an electro-optic modulator in amplitude modulation mode. In this connection some important new characteristics of the pulse are pointed out.

Imaging of biomaterials in liquids: a comparison between conventional andQ-controlled amplitude modulation (‘tapping mode’) atomic force microscopy

Lambda phage DNA and DPPC thin films are imaged in liquids by atomic force microscopyapplying the amplitude modulation mode (‘tapping mode’) with active enhancement of theQ-factorby a ‘Q-control’ electronics. The topography of the resulting images is compared with images obtained withoutactive Q-control. To enable a meaningful comparison, individual scan lines are alternately recorded with andwithout Q-factor enhancement using scan parameters optimized for each mode separately.As the major finding, significant height differences of topographical featuresare observed between the two modes. The heights measured with activeQ-control are reproducibly higher compared to the ones observed withoutQ enhancement. This effect is attributed to the reduction of tip–sample forces byQ-control.

Analgesia Induced by Microwave Irradiation of an Acupuncture Point under Conditions of Visceral Pain in Mice: Role of the Serotonergic Cerebral System

We studied behavioral manifestations of analgesic effects induced in mice by irradiation of the E36 acupuncture point (AcP) by low-intensity microwaves under conditions of visceral pain evoked by i.p. injections of 0.08 ml of a 2% solution of acetic acid. We also examined changes in these analgesic effects resulting from a drop in the level of serotonin after i.p. injection of 300 mg/kg of a blocker of synthesis of serotonin, DL-parachlorophenylalanine (PChPhA). Two modes of irradiation were tested, with a wide frequency range (30 to 300 GHz) and amplitude modulation (mode 1) and with a stable frequency (61 ± ± 4 GHz, mode 2). Irradiation in mode 1 provided a higher level of analgesia than that in mode 2 (decreases in the duration of manifestations of the pain reaction were, on average, 35.7 and 20.4%, respectively). The level of analgesia dropped after injections of PChPhA; the durations of behavioral pain manifestations 24 h after such injections were greater than those in the group with no injections of the blocker by 41.3 and 12.1% in irradiation modes 1 and 2, respectively. The respective figures 48 h after PChPhA injections were 52.0 and 16.1%. Thus, under conditions of visceral pain, irradiation of the AcP by low-intensity microwaves provides noticeable analgesia, and the serotonergic brain system mediates the development of analgesia under the above-mentioned conditions.

Delta Wing Stall and Roll Control Using Segmented Piezoelectric Fluidic Actuators

The separated flow around a balance-mounted, 60-deg sweptback, semispan delta wing with a sharp leading edge was controlled using zero-mass-flux periodic excitation from a segmented leading-edge slot. Excitation was generated by cavity-installed piezoelectric actuators operating at resonance with amplitude modulation (AM) and burst mode (BM) signals being used to achieve reduced frequencies (scaled with the freestream velocity and the root chord) in the range from O(1) to O(10). Results of a parametric investigation, studying the effects of AM frequency, BM duty cycle and frequency, excitation amplitude, location of the actuation along the leading edge, and optimal phase difference between the actuators, as well as the Reynolds number, are reported and discussed

Experimental determination of conservative and dissipative parts in the tapping mode on agrafted layer: comparison with frequency modulation data

The aim of the present work is to extract the conservative and dissipative parts of thetip–sample interaction from the atomic force microscope amplitude modulation mode (AM,often called tapping). To do so, analytical expressions are used to transform theexperimental amplitudes and phase variations with tip–sample distance to frequencyshift and damping coefficient. The experimental procedure for the separation isdetailed. The separated conservative and dissipative parts from the AM mode arecompared for two driving frequencies, and then they are compared to the frequencymodulation mode (FM, often called resonant non-contact) measurements for twodifferent amplitudes. The conservative parts from the AM measurements aresimilar to the frequency shifts measured in the FM mode and also the dissipativeparts from the AM measurements are very close to the dissipation measuredin the FM mode. Experimentally, this good agreement is related to the smallamplitude variation in the AM data on a chemically controlled grafted layer.Those results show experimentally that the AM and FM modes are just twodifferent ways to probe the same tip–sample interaction. They also validate the AMdata treatment to separate the conservative and dissipative parts as the onlyhypothesis needed is that only the fundamental harmonic contributes to the signal.

Robust OFDM Receivers for Dispersive Time-Varying Channels: Equalization and Channel Acquisition

In orthogonal frequency-division multiplexing, time variations of a multipath channel lead to a loss of orthogonality between the subcarriers, and thereby limit the achievable throughput. This paper proposes a general framework for a controlled removal of intercarrier interference (ICI) and channel acquisition. The core idea behind our method is to use a finite power series expansion for the time-varying frequency response, along with the known statistical properties of mobile radio channels. Channel acquisition and ICI removal are accomplished in the frequency domain and allow for any desired tradeoff between the residual ICI level, the required training for channel acquisition, and processing complexity. The proposed approach enables a high spectral efficiency (64-quadrature amplitude modulation mode) of digital video broadcasting-terrestrial in highly mobile environments.

Experimental investigation of resonance curves in dynamic force microscopy

A precise experimental investigation of the amplitude and phase resonance curvesof a driven dynamic force microscope (DFM) cantilever interacting with an Al2O3(0001)surface in ultra-high vacuum is reported. The large amplitude (a few tens ofnanometres), high cantilever stiffness (25 N m−1) and high qualityfactor (a few 104)characterizing these experiments are typical of the frequency modulation(FM) mode of DFM. The whole range of tip–substrate distances where astationary oscillation of the cantilever can be maintained is explored.It covers two different regimes: a large distance regime where only longrange conservative van der Waals interactions contribute and a smalldistance regime where short range interactions play a significant role. Acomparison is made with frequency shift and excitation amplitude curves as afunction of the distance acquired in the FM mode. It is also shown thatapproach–retract amplitude and phase curves usually obtained in the amplitudemodulation mode can be extracted from these data. These experimentalresults are compared with analytical predictions reported in the literature.An excellent agreement is found in the van der Waals domain, allowingus to evaluate the Hamaker constant for the alumina–vacuum–siliconsystem.

Theory of Q control in atomic force microscopy

We discuss the performance of an atomic force microscope (AFM) operated in the amplitude modulation mode under a self-excitation signal, known as quality factor control (Q control). By using the point-mass description of the AFM, we provide a complete description of Q control in tapping mode AFM. The theoretical simulations show three major results: (i) the steady-state motion of the system contains contributions from homogeneous and particular components, (ii) the active response of the microcantilever can be increased or decreased depending on the phase shift of the self-excitation with respect to the instantaneous deflexion, and (iii) in general, Q enhancement reduces the maximum force exerted for the tip on the sample surface.

Amplitude, phase, and hybrid ternary modulation modes of a twisted-nematic liquid-crystal display at approximately 400 nm.

Applicability of a commercial twisted-nematic liquid-crystal display is examined at approximately 400 nm. Different modulation modes predicted by Jones-matrix calculus are experimentally tested. High contrast amplitude modulation with negligible loss, high contrast and low loss hybrid ternary modulation, and 1.5pi continuous phase delay without intensity modulation and with low loss are presented. Simulation results of a 4f holographic system prove the usefulness of the high contrast for amplitude modulation, and the importance of pi phase difference between high transmission white levels in a hybrid ternary modulation.

Amplitude or frequency modulation-detection in Kelvin probe force microscopy

Kelvin probe force microscopy in ultrahigh vacuum is a sensitive tool to determine the absolute work function of sample surfaces. For the detection of the electrostatic force, an a.c.-voltage with a frequency ω is applied between tip and sample. Two different methods can be employed for the measurement: the frequency modulation (FM) mode or amplitude modulation (AM) mode detection. In FM-mode the oscillation of the frequency shift at ω is measured, which is proportional to the gradient of the electrostatic force. In AM-mode the amplitude of the cantilever oscillation at ω is measured which is proportional to the electrostatic force itself. A detailed comparison between AM and FM detection modes is presented, using measurements of gold islands on highly oriented pyrolytic graphite. The effect of tip geometry was studied for both detection modes. In the FM-mode mainly the tip apex contributes to the measured signal due to the detection of the force gradient, however, a.c.-voltages of around 2 V are necessary to perform stable measurements. A much stronger influence of the tip shape was determined for AM detection, reducing the contrast in the measured contact potential difference images. Nevertheless, the main advantage of the AM-mode is the possibility to use a.c.-voltages as low as 100 mV, which allows absolute work function measurements also on semiconductor surfaces.

OFDM-based turbo-coded hierarchical and non-hierarchical terrestrial mobile digital video broadcasting

The feasibility of terrestrial digital video broadcast (DVB) to mobile receivers is studied and turbo coded performance enhancements are proposed. Initially, the MPEG-2 codec is subjected to a rigorous bit error sensitivity investigation, in order to assist in designing various error protection schemes for wireless DVB transmission. The turbo codec is shown to provide signal-to-noise ratio (SNR) performance advantages in excess of 5-6 dB over conventional convolutional coding both in terms of bit error rate and video quality. Our experiments suggested that-despite our expectations-multi-class data partitioning did not result in error resilience improvements, since a high proportion of relatively sensitive video bits had to be relegated to the lower integrity subchannel, when invoking a powerful low-rate channel codec in the high-integrity protection class. Nonetheless, DVB transmission to mobile receivers is feasible, when using turbo-coded OFDM transceivers at realistic power-budget requirements under the investigated highly dispersive fading channel conditions. It is interesting to note furthermore that the 5-6 dB SNR improvement due to turbo coding allows us to invoke for example the double-throughput 16-level quadrature amplitude modulation (16-QAM) mode instead of the standard convolutional-coded 4-QAM mode. This facilitates doubling the bit rate and hence improving the video quality.

Generation of Transform-Limited Pulse Train in New Scheme of Harmonically Mode-Locked Er-Doped Fiber Ring Lasers

A new scheme of an amplitude modulated harmonically mode-locked Er-doped fiber ring laser is proposed, and the lasing characteristics are experimentally investigated. The transform-limited sech2 pulses at the repetition frequency of 1.64 GHz are stably generated. The pulse width and spectral bandwidth are independent of both the amplitude modulated (AM) modulation signal frequency and the AM modulation depth.

Modern optical signal processing experiments demonstrating intensity and pulse-width modulation using an acousto-optic modulator

Two experiments are presented to introduce undergraduate students in electrical engineering or physics to modern optical signal processing. Both experiments use an acousto-optic (AO) Bragg cell together with additional electronics to modify the intensity of a laser beam. Specifically, we show how an AO feedback system operating in the Bragg regime can be configured to produce amplitude modulated (AM) and pulse-width modulated optical signals. The basic components of the AO feedback system include a laser, an AO Bragg cell, an electronic AM modulator, a photodetector, an amplifier, and an electronic adder. Except for the laser, the AM modulator, and the Bragg cell, each of these components can be constructed with low cost electronics. A tutorial outlining the principles of acousto-optics is included to provide sufficient understanding of the Bragg cell. The project described in the paper has been used as a demonstration for junior- and senior-level undergraduate students in electrical engineering communications and optics classes.

Climatic switches

Previous studies have established that air/surface temperature variations at any location along the Earth take place in three different amplitude modulation modes (or states). In this paper we show that two of these amplitude modulation modes can be switched from one to the other by simple meteorological processes which are herein termed “climatic switches”. The two climatic switches (for a given location) specifically established and discussed here are a (sufficiently rapid) heating/warming episode and a (sufficiently rapid) cooling episode. Existence and influences of these two climatic switches are further ascertained and illustrated using climatic records from the U.K., Africa and U.S.A. It is inferred that a rapid man-created greenhouse-warming which is sufficiently large and spread along a given location may act as a climatic switch and hence a cause for climatic change in that particular location. A climatic change caused by climatic switches may involve an increase or a decrease in the average of some naturally existing temperature oscillations. This implies that climatic switches may be mechanisms built into the climatic system in order to make it wriggle temporarily out of a steadily rising (or falling) temperature trend caused by a sizeable heating (or cooling) process.

A comparison of the frequency modulation transfer function with the modulation transfer function in a Room

Room transmission properties for the frequency modulated (FM) band of noise have been investigated and compared with the calculated amplitude modulation (AM) transfer function. Room modulation attenuation for both kinds of modulation is taken into account. The comparison of the calculated average values of the modulation transfer shows that the mean modulation attenuation is comparable for the AM and FM modulation and in a similar way depends on the reverberation time and the modulation frequency. Selected experimental results are also presented to explain room transmission properties for FM signals.

A digital receiver design for AM stereo signals using a general purpose digital signal processor

Digital signal processing (DSP) techniques are becoming the standard for high quality digital sound on compact disks and digital audio tapes in consumer audio entertainment systems. Incorporating DSP technology to improve the quality of AM (amplitude modulation) and FM (frequency modulation) stereo radio reception assures high fidelity performance for all radio functions. The paper only deals with the AM stereo problem. It discusses the compatible quadrature amplitude modulation AM stereo decoding and how it can be digitally implemented on a general purpose digital signal processor (GPDSP).< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Amplitude modulation mode locking of lasers by regenerative feedback

We analyze the performance of regenerative feedback mode locking using intracavity amplitude modulation (AM). Regenerative feedback is predicted to improve the stability of AM mode locking especially at low and moderate repetition rates and short pulse durations. We report on AM regenerative-feedback mode locking of a continuous wave Nd:glass laser. The generated train of 8 ps pulses has an excellent long-term stability and is completely free of relaxation oscillation instabilities inherent in conventional AM mode locking.

Measurement of AM to PM conversion in medium wave AM transmitter

A method for measuring AM (amplitude modulation) signal distortion caused by AM to PM (phase modulation) conversion at the output of an AM radio transmitter is presented. A novel type of measuring instrument is also presented for testing the phase distortion which may occur in an AM radio transmitter when an AM modulation signal is applied. The down-converted AM signal is first divided into the inphase and orthogonal-phase components, and these signals are processed by an operational circuit to obtain phase distortion, which is the angle between the orthogonal-phase and inphase components. A phase angle of 10 degrees or more is detected in the prototype version.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>