Current Modulation Frequency Research Articles

Numerical analysis of slow and fast light effect in semiconductor optical amplifier with certain facet reflection

In this paper, the slow and fast light (SFL) effects of the semiconductor optical amplifier (SOA) having certain facet reflections are theoretically investigated. The theoretical model is used to account for the SFL phenomenon causing the coherent population oscillation. The influence of the current modulation frequency, the value of the current, the linewidth enhancement factor, facet reflectivity as well as the relative phase of the modulated current on the phase delay in the SOA are studied. It is demonstrated that the SFL effect could be controlled by the modulation frequency, the value and relative phase of the current. Finally, it is shown that the magnitude of the SFL delay could be tuned by a change in the linewidth enhancement factor as well as the facet reflectivity of the SOA.

A method for calculating the parameters of the sine filter of the frequency converter, taking into account the criterion of starting current limitation and pulse-width modulation frequency

An analysis of the method for ensuring the sinusoidality of the output voltage in power generation systems with self-commutated voltage inverters under the requirements of the international standard IEEE-519 is presented. In a number of programs, especially low-power generation systems, a low-cost solution is needed to provide the sinusoidal waveform of the output voltage with the total harmonic distortion of 5 %. This solution is to use two-level voltage inverters with an output sine LC filter. However, the feature of the sine filter with the frequency converter is that the PWM frequency affects the spectrum of higher harmonics of the output voltage. In addition, there is the starting current of the filter capacitor, which can disable the power switches of the voltage inverter. The developed method for calculating the values of the LC filter with the two-level voltage inverter in the PWM mode is presented meeting the requirements of the international standard IEEE-519, taking into account the modulation frequency and limitation of the starting current of the filter capacitor. To confirm the required quality of the output voltage of the two-level voltage inverter with the sine filter, an appropriate simulation model was created in the Matlab/Simulink computer simulation environment. The oscillograms and harmonic analysis of the input and output voltages of the sine filter, which showed the total harmonic distortion of 1.88 %, are presented. A physical prototype of the investigated system was created on the basis of a 5.5 kW OVEN PChV203-5K5-V frequency converter (Ukraine). Using the SIGLENT SDS1104X-E oscilloscope (China), the real waveform and the results of the harmonic analysis of the sine filter output voltage, confirming the implementation of the necessary sinusoidality criteria, were obtained

Structure and hardness of wear-resistant coatings with low-frequency current modulation deposited on low carbon steel

Influence of the modes of manual electric arc surfacing of coatings with T-590 electrodes on low-alloy steel 09G2S on their structure and hardness was investigated. It is shown that the pulsed arc surfacing of coatings by electrodes forms a fine-dendritic structure of the deposited metal. Microstructure of the heat-affected zone after surfacing consists of several sections: the overheating zone with a widmanstett structure and the normalization zone with a characteristic fine-grained ferrite-perlite structure. In the initial state, the base metal (steel 09G2S) has a hardness of ~2500 MPa. The hardness of the deposited coating material due to strong mixing with the steel metal is ~ 2700 – 3000 MPa, and of thermal impact zone: 2100 – 2300 MPa. When applying the coating on DC mode, heating temperature of the surfacing bath is higher; this, as a consequence, causes grain growth. When coating on pulse modes, a structure with smaller component sizes is formed by directed low-frequency high-energy impact of the electric arc on the formed metal and due to the constant reciprocating motion of the melt with the frequency of current modulation. It was established that the application of the pulse-arc surfacing method allows preserving the previously formed hardening phases in the deposited coatings.

Structure and Hardness of Wear-Resistant Coatings Deposited on Low-Carbon Steel upon Low-Frequency Current Modulation

The effect of manual electric arc surfacing modes of low-alloy 09G2S steel by T-590 electrodes on their structure and hardness has been investigated. It is shown that pulse-arc surfacing of coatings by electrodes forms a fine-dendritic structure of the deposited metal. The microstructure of the heat-affected zone after surfacing consists of several regions: the overheating zone with a Widmanstatten structure and the normalization zone with a characteristic fine-grained ferrite-perlite structure. In the initial state, the base metal (09G2S steel) has a hardness of ~2500 MPa. The hardness of the deposited coating material due to strong mixing with steel is ~2700–3000 MPa and 2100–2300 MPa for the thermal impact zone. When coating in a DC mode, the heating temperature of the surfacing bath is higher, causing grain growth. When coating in pulse modes, a structure with smaller sizes of components is formed by directed low-frequency high-energy impact of the electric arc on the formed metal and due to the constant reciprocating motion of the melt with the frequency of current modulation. It is established that the application of the pulse-arc surfacing method enables preserving the previously formed hardening phases in deposited coatings.

CONTROL OF CO2 LASER POWER BY ACOUSTIC FIELDS

The present study investigates the optimization of the operation of the CO2 laser in the acoustoplasma mode (i.e., dependence of the laser radiation power on the composition of the working mixture, pressure, value of the direct component of the discharge current, frequency, and modulation depth). A three-dimensional dependence on the frequency and modulation depth of the discharge current is experimentally obtained for the normalized efficiency of the conversion of the electric power supplied to the discharge tube into laser power. The maximum gain when transition to the acoustoplasma mode exceeds 2.5 times. The optimum depth of the discharge current modulation is 0.5–0.7. The laser radiation power modulation caused by the discharge current modulation is measured. Laser power is not modulated at modulation frequencies of current >1 kHz. Meanwhile, at current modulation frequencies <0.5 kHz, the modulation depth of the laser radiation power nonlinearly depends on the modulation depth of the discharge current and has a threshold character. The modulation depth of the laser radiation power is associated with the creation of an acoustoplasma and not simply with the discharge current modulation.

CONTROL OF CO2 LASER POWER BY ACOUSTIC FIELDS

The present study investigates the optimization of the operation of the CO2 laser in the acoustoplasma mode (i.e., dependence of the laser radiation power on the composition of the working mixture, pressure, value of the direct component of the discharge current, frequency, and modulation depth). A three-dimensional dependence on the frequency and modulation depth of the discharge current is experimentally obtained for the normalized efficiency of the conversion of the electric power supplied to the discharge tube into laser power. The maximum gain when transition to the acoustoplasma mode exceeds 2.5 times. The optimum depth of the discharge current modulation is 0.5–0.7. The laser radiation power modulation caused by the discharge current modulation is measured. Laser power is not modulated at modulation frequencies of current >1 kHz. Meanwhile, at current modulation frequencies <0.5 kHz, the modulation depth of the laser radiation power nonlinearly depends on the modulation depth of the discharge current and has a threshold character. The modulation depth of the laser radiation power is associated with the creation of an acoustoplasma and not simply with the discharge current modulation.

Frequency-Modulated Optical Feedback Interferometry for Nanometric Scale Vibrometry

We demonstrate a novel method that makes an efficient use of laser nonlinear dynamics when subject to optical self-injection for subwavelength displacement sensing purposes. The proposed methodology combines two different phenomena taking place inside the laser cavity: optical self-injection, which results in optical feedback interference, and laser continuous wave frequency modulation, giving rise to a wavelength sweeping effect in the laser’s emission. We present a combination of these phenomena to measure vibration amplitudes below $\lambda /2$ with the resolutions of a few nanometers, bandwidth dependent upon the distance of external target, amplitude, and frequency of current modulation. The basic theoretical details and a mathematical model are presented for the developed measurement principle. Experimental results with the system working as a vibrometer to measure a target vibration of amplitude ${\lambda }/{5}$ (137.5 nm) with a mean peak-to-peak error of 2.4 nm just by pointing the laser diode onto the target and applying some signal processing are also demonstrated.

A Study on CO Detection System of Vehicle Emissions based on QEPAS

In this paper, the technology of QEPAS was used to detect the concentration of carbon monoxide gas. The regulation of DBF laser’s input current frequency and temperature was made first, current modulation frequency being 0 / 2 16420 f f HZ  (frequency modulation is half of the resonance frequency of the QTF) and operating temperature being T=23 degrees Celsius. Then enable the output wavelength to be near 1.567 µm and measure CO gas of different concentrations. Through the analysis of the relationship between the second harmonic signals of different concentration CO gas, it is found that between CO concentration and the second harmonic intensity exists good linear relationship and that the system has no independence on the incident light wavelength and has high sensitivity and large dynamic measurement range. The study provides a new way of thinking for other types of trace gas detection and can be applied to the detection of automobile exhaust emissions.

Enhancement of the modulation bandwidth for GaN-based light-emitting diode by surface plasmons.

We have fabricated the surface plasmon (SP) coupled GaN-based nanorod LEDs with Ag nanoparticles (Nps), and demonstrate the enhancement of the optical modulation bandwidth by SPs. Compared with the LED without Ag Nps, the optical modulation bandwidth of the LED with Ag Nps increases by a factor of ~2 at 57 A/cm2. The photoluminescence (PL) and electroluminescence (EL) experimental results are consistent with each other, and both suggest the effective coupling between quantum wells (QWs) and SPs. Furthermore, the current dependent modulation frequency characteristics show that the QW-SP coupling can increase the modulation bandwidth, especially for LEDs with high intrinsic internal quantum efficiency (IQE). These findings will help to open a new solution to design the ultrafast LED light source for the application of the visible light communication.

Generation of mode-locked optical pulses at 1035 nm from a fiber Bragg grating stabilized semiconductor laser diode

We report the generation of transform-limited, ~18 ps optical pulses from a fiber Bragg grating (FBG) stabilized semiconductor laser diode. Up to 7.2 pJ of pulse energy and a peak power of 400mW were achieved when operating at a repetition frequency of 832.6 MHz, a multiple of the cavity (diode + FBG) free spectral range (FSR). A small detuning in the repetition frequency resulted in broader optical pulses. We have shown experimentally the transition from a gain-switched regime of operation to mode-locked operation once the injection current modulation frequency is set to match a harmonic of the cavity FSR. The transition also results in a reduction in the timing jitter of the optical pulses.

Ultrafast polarization modulation in vertical cavity surface emitting lasers with frequency dependent current injection

We report on a polarization modulation in vertical cavity surface emitting lasers (VCSEL), based on RF electrical injection. Complex polarization dynamics in the single mode regime is studied as a function of RF frequency and power at different bias currents. It has been observed that the polarization state of the VCSEL can be altered by changing the frequency of RF current modulation. Time resolved measurements show that by injecting periodic bursts of RF modulation in the VCSEL, it is possible to change the dominant polarization between the two orthogonal modes at gigahertz rates.

Stabilization of Joule Heating in the Electropyroelectric Method

Recently the so-called electropyroelectric technique for thermal characterization of liquids has been proposed (Ivanov et al., J. Phys. D: Appl. Phys. 43, 225501 (2010)). In this method a pyroelectric sensor, in good thermal contact with the investigated sample, is heated by passing an amplitude-modulated electrical current through the electrical contacts. As a result of the heat dissipated to the sample, the pyroelectric signal measured as a voltage drop across the electrical contacts changes in a periodical way. The amplitude and phase of this signal can be measured by lock-in detection as a function of the electrical current modulation frequency. Because the signal amplitude and phase depend on the thermal properties of the sample, these can be determined straightforwardly by fitting the experimental data to a theoretical model based on the solution of the heat diffusion equation with proper boundary conditions. In general, the experimental conditions are selected so that the thermal effusivity becomes the measured magnitude. The technique has the following handicap. As the result of heating and wear of the metal coating layers (previously etched to achieve a serpentine form) with time, their electrical resistance changes with time, so that the heat power dissipated by the Joule effect can vary, and thermal effusivity measurement can become inaccurate. To avoid this problem in this study, a method is proposed that allows maintaining stable the Joule dissipated power. An electronic circuit is designed whose stability and characteristics are investigated and discussed.

Simulation of convection-stabilized modulated discharges in atmospheric-pressure air

A model describing modulated regimes of convection-stabilized discharges in atmospheric-pressure air is developed that accounts for deviation of the plasma state from the local thermodynamic equilibrium. The model is based on an approximate approach relating the variation of plasma parameters with time and their variation along the discharge axis. The validity of this approach is supported by agreement, for steady-state regimes, of calculated plasma parameters with those obtained on the basis of a more rigorous model. Results of calculation of modulated discharge parameters over a wide current range are presented for various current modulation frequencies and depths.

Resonant Excitation of Boundary Layer Instability of DC Arc Plasma Jet by Current Modulation

Instabilities of thermal plasma jets were studied on the basis of analysis of plasma radiation fluctuations recorded by an array of high frequency photodiodes. Characteristic frequencies of jet oscillations were found and spatial distribution of amplitude of plasma fluctuations was determined. The influence of arc current ripple on plasma instabilities was investigated for two types of power supply—classical thyristor controlled unit with the frequency of the current ripple 300 Hz and the rectifier with the high frequency converter and frequency of the current modulation 30 kHz. Generation of boundary layer instability with the current modulation frequency and its harmonics was proved using fast Fourier transform, contour plots and phase portraits. It was found that the character of fluctuations of plasma jet was substantially influenced by current ripple with the frequency or its harmonics close to the frequency of oscillations generated by boundary layer instability.

Thermal effects and dynamical hysteresis in the turn-on and turn-off of vertical-cavity surface-emitting lasers

Thermal effects and dynamical hysteresis in VCSELs under dc modulation have been experimentally studied. The results show that the VCSEL turn-on and turn-off currents can display both positive hysteresis and negative hysteresis, depending on the current modulation frequency and on the substrate temperature. Numerical simulations of semiconductor laser rate equations, extended to take into account thermal effects, show a good agreement with the observations.

Influence of changing the forbidden-band gap on radiation frequency sweeping of quantum-well heterolasers

The principal features of changing (sweeping) the "instantaneous" emission frequency of quantum-well heterolasers as functions of the modulation frequency and depth and the constant component of the pump current when tuning the lasing frequency within the gain band are established using numerical modeling. The active medium is described in the framework of a two-band model with similar distributions of levels in subbands of electrons and holes assuming transitions between ground subbands with no k-selection rule. Emission frequency sweeping occurs because of changes in both the index of refraction of the active medium due to a variation in the concentration of non-equilibrium charge carriers and the forbidden-band gap. Emission frequency sweeping does not occur at low frequencies of current modulation that correspond with quasi-stationary lasing regimes. The modulation depth of the output radiation and, therefore, the emission frequency sweeping, also approach zero for the other limiting case of relatively high current modulation frequencies. The sweeping is greatest at intermediate current modulation frequencies. The sweeping value is approximately halved in certain instances by taking into account the change of forbidden-band gap of the semiconductor. In general, the sweeping value is determined by the combined effect of the modulation frequency and depth, the constant component of the pump current, and the spectral position of the laser emission frequency within the gain band.

Influence of Low-Frequency Modulation on Polarization Switching of VCSELs Subject to Optical Feedback

The influence of low-frequency modulation on the polarization switching (PS) properties of vertical-cavity surface-emitting lasers (VCSELs) under optical feedback has been investigated experimentally. The current modulation frequency has a large impact on the PS of VCSELs even in the low-frequency range between 1 and 100 kHz. Thermal effects play an important role in this phenomenon.

Major features of frequency sweeping of emission from heterojunction quantum lasers

We have used numerical modeling to establish the major features of the variation (sweeping) of the “ instantaneous” laser frequency of heterojunction quantum lasers as a function of the pump current modulation frequency and tuning of the lasing frequency within the gain band. The active medium is described within a two-band model with identical distribution of levels for the electron and hole subbands, assuming transitions with no selection rule between the ground-state subbands. Sweeping of the laser frequency occurs due to variation of the refractive index of the active medium, as a result of the variation in the concentration of nonequilibrium charge carriers. Laser frequency sweeping does not occur for low current modulation frequencies, corresponding to realization of the quasisteady-state lasing regime. In the other limiting case of relatively high current modulation frequencies, the modulation depth of the laser output also tends toward zero. The magnitude of the sweep is greatest in the intermediate current modulation frequency region. For a specified current modulation frequency, the dynamic shift of the laser mode depends on the position of the lasing frequency within the gain band.

Nondegenerate Phase-Locking of a Semiconductor Laser by Sideband Injection

A semiconductor laser rate equation theory is presented that describes sideband injection locking under both weak optical injection and current modulation. By simultaneous optical injection and current modulation, control of both the phase and the frequency of a semiconductor laser is demonstrated. The phase-locked semiconductor laser operates at a different frequency to the optical injection source, with a frequency-difference given by the current modulation frequency. This method can be used to produce broadband sources, such as those producing ultrashort pulses and those required for coherent control, or to create high-frequency electronic oscillator sources with phase control by interference beating

Frequency sweeping of emission from heterojunction quantum lasers with pump current modulation

We have used numerical modeling to study the dynamic shift of the “instantaneous” laser frequency (sweeping) as a function of the pump current modulation frequency for heterojunction quantum lasers when the lasing frequency is tuned within the gain band. As the model for the active medium, we used a two-band model with identical distribution of levels for the electron and hole subbands, in which we take into account direct transitions between the ground-state subbands. We have established that the variation in the sweep qualitatively corresponds to the behavior of the amplitude detuning characteristics of the laser. Depending on the parameters of the system during emission of pulses, the variation in the laser frequency can be monotonic or nonmonotonic. By selecting the pump current modulation frequency and setting the laser frequency within the gain band, we can realize the cases of maximum or minimum dynamic shift of the lasing frequency.