Power Amplifier System Research Articles

Compact RGBY light sources with high luminance for laser display applications

Watt-class visible laser light with a high luminance can be created with high-power GaAs-based lasers either directly in the red spectral region or using single-pass second harmonic generation (SHG) for the colors in the blue–yellow spectral region. The concepts and results of red- and near infrared-emitting distributed Bragg reflector tapered lasers and master oscillator power amplifier systems as well as their application for SHG bench-top experiments and miniaturized modules are presented. Examples of these high-luminance light sources aiming at different applications such as flying spot display or holographic 3D cinema are discussed in more detail. The semiconductor material allows an easy adaptation of the wavelength allowing techniques such as six-primary color 3D projection or color space enhancement by adding a fourth yellow color.

Optimization of Portable Electronically Controlled Needle-Free Jet Injection Systems

Jet injection is a process by which a fluid drug is delivered through the skin in the form of a high-velocity jet. Powering jet injection using a controllable actuator, such as a moving-coil permanent magnet motor, offers many advantages, but to date has required large and heavy injection systems to provide the required power and control bandwidth. In order to minimize the size of the injection system, we developed a scaling model for jet injection systems powered by permanent magnet motors, giving the optimal actuator mass as a function of jet velocity, injection volume, motor efficiency, and energy storage density. We combined this model with an existing electromagnetic model to confirm the predicted scaling relationships and find optimal actuator designs. On this basis, we designed an injection system for 50 $\mathrm{\mu {}L}$ volumes, including a compact power amplifier and control system, and verified its performance by performing injections into pig skin. The total mass of the injector system was 578 g, with a 178 g handpiece. This model illustrates fundamental relationships that govern the design of any jet-production device powered by linear electric motors for jet injection or other applications.

High Average Power Second-Harmonic Generation of a CW Erbium Fiber MOPA

We report the generation of 28 W of 780 nm radiation with near diffraction limited beam quality (M2 ≤ 1.15) by frequency-doubling a continuous-wave erbium fiber master oscillator power amplifier system in a periodically poled lithium niobate crystal. The second-harmonic generation conversion efficiency reached 45% with no roll-off observed, suggesting that further power scaling should be possible with higher fundamental pump powers. The generated second-harmonic had a 3 dB spectral bandwidth of 0.10 nm. The presented architecture represents a simple and effective route to generating high-brightness radiation around 780 nm.

Temporally Programmable Hybrid MOPA Laser with Arbitrary Pulse Shape and Frequency Doubling

An arbitrary pulse shape by compensating gain saturation in a solid-state Master oscillator power amplifier (MOPA) system made up of three Neodymium doped yttrium vanadate (Nd:YVO4) amplifiers is demonstrated. By investigating the amplifier dynamics in detail, car-shaped pulse shapes were obtained with compensated pulse distortion. Desired pulse shapes, such as multiple-step, square, parabolic, and Gaussian pulses, were achieved, with a high peak power level of 41.6 kW and a narrow linewidth less than 0.06 nm. In addition, through second harmonic generation (SHG), a green laser with different pulse shapes was obtained, with a maximum conversion efficiency of 42.6%.

A High Slew-Rate Adaptive Biasing Hybrid Envelope Tracking Supply Modulator for LTE Applications

A linear-switch mode hybrid envelope tracking (ET) supply modulator utilizing adaptive biasing and gain enhanced current mirror operational transconductance amplifier (OTA) with class AB output stage in parallel with a switching regulator is presented. In comparison to a conventional OTA design with similar quiescent current consumption, proposed approach improves positive and negative slew rate from 50 to 93.4 V/ $\mu \text{s}$ and −87 to −152.5 V/ $\mu \text{s}$ , respectively, dc gain from 45 to 67 dB while consuming same amount of quiescent current. The proposed hybrid supply modulator achieves 83% peak efficiency, power-added efficiency (PAE) of 42.3% at 26.2 dBm for a 10-MHz 7.24-dB peak-to-average power ratio (PAPR) long-term evolution (LTE) signal and improves PAE by 8% at 6 dB back off from 26.2-dBm power amplifier (PA) output power with respect to fixed supply. With a 10-MHz 7.24-dB PAPR quadrature-phase shift keying LTE signal the ET PA system achieves adjacent channel leakage ratio (ACLR) of −37.7 dBc and error vector magnitude (EVM) of 4.5% at 26.2-dBm PA output power, while with a 10-MHz 8.15-dB PAPR 64QAM LTE signal the ET PA system achieves ACLR of −35.6 dBc and EVM of 6% at 26-dBm PA output power without digital predistortion. The proposed supply modulator core circuit occupies 1.1-mm2 die area, and is fabricated in a 0.18- $\mu \text{m}$ CMOS technology.

Analysis and design of high-power and efficient, millimeter-wave power amplifier systems using zero degree combiners

ABSTRACTWe present the analysis and design of high-power millimetre-wave power amplifier (PA) systems using zero-degree combiners (ZDCs). The methodology presented optimises the PA device sizing and the number of combined unit PAs based on device load pull simulations, driver power consumption analysis and loss analysis of the ZDC. Our analysis shows that an optimal number of N-way combined unit PAs leads to the highest power-added efficiency (PAE) for a given output power. To illustrate our design methodology, we designed a 1-W PA system at 45 GHz using a 45 nm silicon-on-insulator process and showed that an 8-way combined PA has the highest PAE that yields simulated output power of 30.6 dBm and 31% peak PAE.

9-kW peak power and 150-fs duration blue-violet optical pulses generated by GaInN master oscillator power amplifier.

Blue-violet optical pulses of 9-kW peak power and 150-fs duration were obtained from a GaInN master oscillator power amplifier system using a nonlinear dispersion compensator. Seed pulses from a dispersion-compensated GaInN mode-locked semiconductor laser diode were stretched to 3-ps duration using a nonlinear dispersion compensator with a spatial light modulator that added second-order phase dispersion to an optimized nonlinear phase dispersion compensating the higher-order dispersion of the optical pulses. The stretched phase-optimized pulses were efficiently amplified to 3.0 nJ by a GaInN semiconductor optical amplifier. The amplified pulses were subsequently compressed using a linear pulse compressor, yielding 1.4-nJ femtosecond pulses. The obtained results show the highest peak-power ever reported for an electrically-pumped semiconductor gain medium.

100 μJ pulse energy in burst-mode-operated hybrid fiber-bulk amplifier system with envelope shaping.

A theoretical method was proposed to compensate the burst envelope distortion in a solid-state master-oscillator power-amplifier (MOPA) system operating in burst mode at an intra-burst repetition rate of 40 MHz. Arbitrary envelope shapes were achieved at inter-burst repetition rate of 100 kHz with 40 pulses in the burst, showing excellent agreement with the calculated ones. This is the first demonstration of arbitrary burst envelope without an adaptive feedback loop in a solid-state laser system. The maximum pulse energy of 100 μJ was achieved at inter-burst repetition rate of 40 kHz, with 10 pulses in the burst.

Radially and azimuthally polarized nanosecond Yb-doped fiber MOPA system incorporating temporal shaping.

We report an Yb-doped fiber master-oscillator power-amplifier (MOPA) system with the capability of selectively generating doughnut-shaped radially and azimuthally polarized beams with user-defined temporal pulse shapes. The desired output polarization was generated with the aid of a nanograting spatially variant half-waveplate (S-waveplate). The latter was used to convert the linearly polarized fundamental (LP01) mode output from the preamplification stages to a doughnut-shaped radially polarized beam prior to the power amplifier stage. A maximum output pulse energy of ∼860 μJ was achieved for ∼100 ns pulses at 25 kHz with user-defined pulse shape for both radial and azimuthal polarization states. The polarization purity and beam propagation factor (M2) were measured to be >12 dB and 2.2, respectively.

The In Vivo Effect of Ytterbium-Doped Fiber Laser on Rat Buccal Mucosa as a Simulation of Its Effect on the Urinary Tract: A Preclinical Histopathological Evaluation.

PurposeThe aim of this study was to perform a histological analysis of the effect of a ytterbium-doped fiber (YDF) laser on oral buccal mucosa tissue in vivo to simulate its effect on the mucosa of the lower urinary tract.MethodsA total of 90 8-week-old Sprague-Dawley rats were anesthetized with urethrane (1.2 g/kg intraperitoneally). A prespecified inner buccal mucosal site was irradiated with a YDF master-oscillator power amplifier (MOPA) system for 60 seconds, with output power settings of 0.5, 1, and 2 W, respectively, in 3 treatment groups. Specimens of irradiated tissue were harvested at 2 hours, 24 hours, 2 weeks, and 4 weeks after irradiation. The tissue specimens were stained with hematoxylin and eosin for histological analysis. ResultsIn the group treated with 0.5 W, basal cell elongation and vacuolization were observed at 2 hours and 24 hours after treatment, respectively. No evident injury was observed after 2 or 4 weeks. The group treated with 1 W presented partial basal layer separation, and even complete epidermal ablation, within 2 hours. At 24 hours after laser treatment, new capillaries on an edematous background of fibroblasts and myofibroblasts, as well as profuse infiltration of the neutrophils to the basal layer, were observed. Collagen deposition and reepithelization were observed in specimens taken 2 weeks and 4 weeks after treatment. The group treated with 2 W presented bigger and deeper injuries at 2 hours after irradiation. Meanwhile, subepidermal bullae with full-thickness epidermal necrosis and underlying inflammatory infiltrate were observed 24 hours after treatment. The presence of fibrous connective tissue and collagen deposition were observed 2 weeks and 4 weeks after the treatment.ConclusionsTo our knowledge, this is the first report regarding the effect of a YDF laser on living tissue. Our study demonstrated that the typical histological findings of the tissue reaction to the YDF MOPA apparatus were very similar to those associated with thermal injuries. The extent and degree of tissue damage increased proportionally to the output power.

Longitudinally excited N2 laser with large-diameter discharge tube.

To realize an ultraviolet laser with high beam quality and high output power, we are developing a master oscillator power amplifier system for a longitudinally excited gas laser. In this system, high beam quality is produced by an oscillator stage, and high output power is produced by an amplifier stage. Here, the beam profile of the longitudinally excited gas N2 laser had a quasi-Gaussian shape when using a large-diameter discharge tube, which enabled the use of the amplifier stage. The discharge tube consisted of a dielectric pipe with an inner diameter of 14 mm and a length of 30 cm. The discharge tube was covered with a metallic tube for pre-ionization. The strength and spatial distribution of pre-ionization were optimized by adjusting the gap between the metallic tube and the discharge tube. The uniform discharge achieved by controlling the pre-ionization produced a quasi-Gaussian laser beam profile with a correlation factor of 0.99513, a laser pulse energy of 343 μJ, and an input energy of 2.95 J.

High-repetition-rate all-fiber femtosecond laser with an optical integrated component.

We demonstrate a high-repetition-rate all-fiber soliton pulse laser mode-locked by the nonlinear polarization rotation technique. The laser cavity is effectively shortened by incorporating an optical integrated component possessing the hybrid functions of a polarization-dependent isolator, a wavelength-division multiplexer, and an output coupler. Resultant output soliton pulses have a fundamental repetition rate of 384MHz, a 3-dB spectral bandwidth of 25.2nm, and a dechirped pulse duration of 115fs. By using an external power amplification and pulse recompression system, the average output power of the laser is boosted to 207mW. The amplified pulses have a 2.33-ps duration, which is recompressed to 340fs. Numerical simulations reproduce the generation of high-repetition-rate soliton pulses in the fiber laser. Such a simple and low-cost high-repetition-rate fiber laser is a potential laser source for various practical applications.

2.36 J, 50 Hz nanosecond pulses from a diode side-pumped Nd:YAG MOPA system

We report on a high-energy high-repetition-rate nanosecond Nd:YAG main oscillator power amplifier (MOPA) system. Maximum output pulse energy of 2.36J with duration of 9.4ns at 50Hz has been achieved. The master oscillator was a LD side-pumped electro-optical Q-switched Nd:YAG rod laser adopting unstable cavity with variable reflectivity mirror (VRM). It delivered a pulse train with energy up to 180mJ and pulse duration of 10.7ns. The near-field pattern demonstrated a nearly super Gaussian flat top profile. In the amplification stage, the pulse was boosted via double-pass two Nd:YAG rod amplifiers. Maximum pulse energy was obtained at the peak pump power of 37.5kW, corresponding to an optical-optical conversion efficiency of 25.2%. The correlative peak power was deduced to be 251MW. We also presented the result of 100Hz nanosecond laser with average output power of >100W.

Active polarization control of a 1.43 kW narrow linewidth fiber amplifier based on SPGD algorithm

Active polarization control of a high power fiber amplifier has been demonstrated. The master oscillator power amplifier system consisted of a narrow linewidth laser seed and a three-stage Yb-fiber amplifier. The narrow linewidth laser seed was generated by phase modulating a single frequency fiber laser using a white noise source. Maximum power of 1437 W was obtained from the main amplifier, which was limited by the available pump power. When the polarization state of the narrow linewidth (∼0.17 nm) laser was actively controlled by using a polarization controller based on stochastic parallel gradient descent algorithm, the polarization extinction ratio of the laser beam was more than 11.1 dB at the maximum output power.

A stable gain-switched Ho:CYA laser resonantly pumped at 1922 nm

We report on a gain-switched Ho:CaYAlO4 laser resonantly pumped by a home-constructed high power Tm:fiber laser at ~1922 nm. Stable nanosecond single-pulse operation could be maintained when the continuous-wave pump signal was modulated at repetition rates of 60–100 kHz with an acousto-optic modulator. A pulse duration of 311 ns has been obtained at a 60 kHz repetition rate under a pump power level of 11 W. The temporal stability and simplicity of operation make this laser suitable for a variety of applications, such as spectroscopy, gas sensing, and as the seed source of a master oscillation power amplifier system.

High power generation of adaptive laser beams in a Nd:YVO4 MOPA system

We report efficient power scaling of the laser output with an adaptive beam profile from an Nd:YAG dual-cavity master oscillator using a three-stage end-pumped Nd:YVO4 amplifier. We succeed in the fast switching of an excited laser mode by modulating an acousto-optic modulator loss in a dual-cavity master oscillator, thereby achieving temporal modulation of the output beam profile. The outputs from the master oscillator are amplified via a three-stage power amplifier yielding 36.6, 40.5, and 45.4 W of the maximum output at 116.8 W of incident pump power for the transverse electromagnetic, Laguerre–Gaussian, and quasi-top-hat beam, respectively. The prospects for further power scaling and applications via the dual-cavity master-oscillator power-amplifier (MOPA) system are considered.

Design of High-efficiency Power Amplifier System for High-directional Speaker

Design of High-efficiency Power Amplifier System for High-directional Speaker

Picosecond high-power 355-nm UV generation in CsLiB6O10 crystal.

We report third-harmonic generation (THG) at 355 nm in CsLiB6O10 (CLBO) by using sum-frequency mixing process. As a fundamental laser source, we employ a hybrid master oscillator power amplifier (MOPA) system seeded by a gain-switched laser diode (GS-LD) at 1064 nm to produce narrow spectral picosecond pulses. Both CLBO and walk-off compensated prism-coupled CLBO device generate over 30-W output of 355-nm UV lights, which means walk-off effect in CLBO is negligible in the picosecond laser system. The maximum THG conversion efficiency from the fundamental reaches about 48%, which is 1.2 times higher than that of LiB3O5 (LBO). Theoretical THG outputs with CLBO and LBO are numerically calculated in order to verify the validity of these experimental results in detail.

General analysis of SRS-limited high-power fiber lasers and design strategy.

In this paper, a spectral model by incorporating SRS effect is proposed and established, which is feasible for analyzing the SRS effect both in high-power fiber oscillator and master oscillator power amplifier (MOPA) system. The theoretical results show that the SRS effect is tightly related to the bandwidths of the fiber Bragg gratings (FBGs) and it can be efficiently suppressed by optimizing the bandwidth of the FBGs. Besides, the established theoretical model is also feasible for analyzing the influence of seed power on the SRS effect. The theoretical predictions agree well with the previous experimental results.

Design and Simulation of a Microcontroller Based Loudspeaker Protection System Against Amplifier Direct Current (D.C) Offsets

A number of failure mechanisms can result in the damage of loudspeakers that are directly connected to an audio power amplifier system. One of such failure modes occurs when the amplifier circuit develops an output d.c voltage, in which case, the loudspeaker coil will be damaged by overheating. D.c offset detection circuits, usually based on simple transistor circuits are normally used to protect the loudspeaker against this failure mode. However, as effective as they are, these circuits can fail in ways that can result in loudspeaker damage. In this work, a microcontroller based circuit that monitors the critical components of a loudspeaker d.c detection circuit, namely the switching transistor and the isolating relay circuit was developed. The hardware of the developed circuit was modelled with Proteus® software and its firmware was written using MikroC® software. The modelled circuit successfully detects the presence of d.c signals and also reports the states of the isolating relay and the switching transistors when these components fail.