Topic
Pulse-frequency modulation
About: Pulse-frequency modulation is a research topic. Over the lifetime, 4151 publications have been published within this topic receiving 53039 citations. The topic is also known as: PFM.
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TL;DR: In this article, the authors developed a theory of injection modulation and calculated the waveforms in amplitude and frequency for a dual-mode He-Ne laser and showed that injection modulation effects are appreciable even at very weak levels of injected amplitudes.
Abstract: Injection modulation is the effect observed when laser oscillation is perturbed by an injected signal below the threshold of locking. In this regime the oscillation becomes a wave modulated in frequency as well as in amplitude. The modulation envelope has a characteristic waveform which depends on the amplitude and phase of the injected signal. Starting from the Lamb's equations for a dual-mode oscillator, we develop a theory of the injection modulation and calculate the waveforms in amplitude and frequency. The treatment applies both to the external injection into a laser and to the case of mutual coupling between two modes. Experimental results for a dual mode He-Ne laser are found to be in good agreement with the theory. It is pointed out how the injection modulation effects are appreciable even at very weak levels of injected amplitudes, e.g., down to 10-5with respect to the oscillation field amplitude.
19 citations
IBM1
TL;DR: The digital echo modulation eliminates the need for precise analog filters and minimizes the effects of component instability; in addition, it gives a great flexibility to the design, allowing special features such as efficient half-speed operation.
Abstract: A new technique for the transmission of binary data over band-limited channels is described. The signaling method is a generalization of Nyquist's telegraph theory, it allows pulse modulation without intersymbol interference within a frequency spectrum centered at any multiple of one quarter of the signaling rate. The signals are derived from pulse trains generated by a combination of logic circuits and weighting resistors. The number of pulses constituting a signal element varies typically from 5 to 9 in function of the desired total bandwidth. Signaling at 80 percent of the Nyquist rate has been easily achieved with 40-dB out-of-band attenuation. The digital echo modulation eliminates the need for precise analog filters and minimizes the effects of component instability; in addition, it gives a great flexibility to the design, allowing special features such as efficient half-speed operation.
19 citations
TL;DR: AdaptAdaptive Ratio as discussed by the authors is a modulation scheme which combines the beneficial features of several available techniques and makes the necessary compromises to optimize the operating characteristics of a modulated six-step inverter.
Abstract: Pulsewidth modulation of a six-step inverter can be accomplished in different ways. Comparisons between different modulation techniques are based primarily on harmonic content in the output waveform and circuit constraints imposed by semiconductor characteristics. Adaptive ratio is a modulation scheme which combines the beneficial features of several available techniques and makes the necessary compromises to optimize the operating characteristics of a modulated six-step inverter.
19 citations
TL;DR: In this article, the power spectral densities of the envelopes of measured Doppler signals were investigated by studying the power spectrum densities and showed that the amplitude modulation effect is much more significant with water-droplet seeding than it is with smoke-particle seeding.
Abstract: Laser-Doppler-anemometry measurements of instantaneous acoustic particle velocity are presented. The Doppler signals, from measurements in air, display quasi-periodic amplitude modulation with a fundamental frequency equal to the frequency of the acoustic field. This effect can cause signal-processing problems. Periodic amplitude modulation is investigated by studying the power spectral densities of the envelopes of measured Doppler signals. Various seeding and acoustic conditions are considered. It is shown that the periodic amplitude modulation is much more significant with water-droplet seeding than it is with smoke-particle seeding. Random amplitude modulation replaces periodic amplitude modulation when a significant steady flow is superimposed on the acoustic field. The harmonic content of the Doppler-signal envelope increases with the intensity of the acoustic field. A simple computational model is used to simulate Doppler-signal envelopes. The simulation is in good qualitative agreement with many experimental observations. However, there is is some discrepancy with experimental measurements, notably a 90° phase difference between the positions of measured and simulated envelope maxima. The paper briefly considers the possibility of exploiting the periodic amplitude modulation effect in a new type of anemometer for acoustic velocity measurement in sound fields with low acoustic frequency and high acoustic particle velocity amplitude.
19 citations
TL;DR: In this article, optical modulation is used to determine the intrinsic frequency response of a laser diode and the shape of the measured frequency response agrees very well with the predicted intrinsic response of semiconductor lasers.
Abstract: For the first time, optical modulation is used to determine the intrinsic frequency response of a laser diode. It is shown that the shape of the measured frequency response agrees very well with the predicted intrinsic response of semiconductor lasers. As anticipated, the measured frequency response lacks the frequency rolloff that occurs with direct RF current modulation. The resonant frequencies measured are shown to be proportional to the square root of the probe laser bias power and the damping rates are found to be linear in power, in agreement with expectations.
19 citations