Computer model of an injection laser amplifier

Laser amplifiers can be used in two ways: as preamplifiers to enhance the sensitivity and improve the noise performance of detectors and, in a pulsed mode of operation, as modulators to boost and stabilize the output of an injection laser oscillator. Most mathematical models of injection lasers are based on time-dependent rate equations that ignore the spatial dependence of the electron and photon densities. The model discussed here is based on numerical solutions of traveling-wave equations. The noise output of the laser amplifier is treated by traveling-wave power equations, but the light signal is described by traveling-wave equations for its amplitude. The parameters responsible for spontaneous and stimulated emission are being related to each other by the requirement that the amplifier achieve optimal noise performance in the absence of internal losses and without gain saturation. The most important results obtained from this computer model of a laser amplifier are as follows. 1) The theory contains a heuristic electron injection efficiency parameter. To agree with experimental observations this parameter must be kept small and its value must decrease with increasing current. 2) Cavity amplifiers saturate more readily than amplifiers without feedback. 3) Because of internal loss mechanisms the amplifier supplies more noise than is required by quantum theory, but its noise performance is still surprisingly good. In particular, the optical signal-to-noise ratio prior to detection is insensitive to gain saturation by strong signals. It remains approximately 4 dB below the theoretical maximum value for weak to moderately strong input signals and drops dramatically only when the amplifier is almost completely saturated.     

2-20-GHz GaAs Traveling-Wave Amplifier

Single-stage and two-stage GaAs traveling-wave amplifiers operating with flat gain responses in the 2-20-GHz frequency range are described. The circuits are realized in monolithic form on a 0.1-mm GaAs substrate with 50-Omega input and output lines. Complete gate and drain dc bias circuitry is included on the chip. By cascading these amplifier chips, a 30-dB gain in the 2-20-GHz range is demonstrated, with 9+-1dB noise figure.     

44-GHz monolithic GaAs FET amplifier

Millimeter-wave monolithic GaAs FET amplifiers have been developed. These amplifiers were fabricated using FET's with MBE-grown active layers and electron-beam defined sub-half-micrometer gates. Source groundings are provided through very low inductance via holes. The single-stage amplifier has achieved over a 10-dB gain at 44 GHz. A 300-µm gate-width amplifier has achieved an output power of 60 mW with a power density of 0.2 W per millimeter of gate width.     

Analysis of monolithic integrated master oscillator poweramplifiers

An analysis of a novel, monolithic integrated master oscillator power amplifier (M-MOPA) is presented. The M-MOPA consists of a DBR master oscillator which injects power into a linear chain of amplifiers and detuned second-order grating output couplers. The analysis self-consistently includes amplified spontaneous emission buildup and residual reflections throughout the amplifier stages. It predicts that output powers in excess of 1 W can be expected from a single-lateral-mode waveguide multistage amplifier less than 1 cm in length, injected with less than 15 mW of input power. In addition to the signal gain of >25 dB, the signal-to-noise ratio at 1-W output exceeds 15 dB. Because of the small reflections associated with the grating output couplers, and gain saturation by the injected signal, the amplifier self-oscillation threshold is suppressed to current densities above 15 kA/cm²     

A GaAs monolithic low-noise broad-band amplifier

Describes the design, fabrication, and performance of GaAs monolithic low-noise broad-band amplifiers intended for broadcast receiver antenna amplifier, IF amplifier, and instrumentation applications. The process technology includes the use of Czochralski-grown semiinsulating substrates, localized implantation of ohmic and FET channel regions, and silicon nitride for passivation and MIM capacitors. The amplifiers employ shunt feedback to obtain input matching and flat broad-band response. One amplifier provides a gain of 24 dB, bandwidth of 930 Mhz, and noise figure of 5.0 dB. A second amplifier provides a gain of 17 dB, bandwidth of 1400 MHz, and noise figure of 5.6 dB. Input and output VSWR's are typically less than 2:1 and the third-order intercept points are 28 and 32 dB, respectively. Improved noise figure and intercept point can be achieved by the use of external RF chokes.     

An experimental study of the effects of harmonic loading onmicrowave MESFET oscillators and amplifiers

This paper reports an extensive experimental investigation of the effects of second harmonic loading on the performance of microwave GaAs MESFET oscillators; and strongly driven amplifiers. The measurement system used is an active load system based on six-port techniques. Harmonic load pull measurements were obtained for the NE72084 MESFET; the measurements show how the second harmonic load can influence the power gain and the power added efficiency in strongly driven amplifiers. The device line characterization technique was combined with the harmonic load pull technique; the measurement results illustrate how the output power and the DC to RF conversion efficiency of an oscillator depend on the choice of the second harmonic load. Amplifier and oscillator circuits have been designed using these measurements; the circuits have been constructed and measured. The results validate the experimental approach used and clearly illustrate the importance of properly selecting the second harmonic load in amplifier and oscillator circuits. Significant improvements in gain, output power and efficiency have been achieved by properly selecting the second harmonic load     

A 25-W 5-GHz GaAs FET Amplifier for a Microwave Landing System

A 25-W 29-dB gain 5-GHz GaAs FET amplifier has been developed which can be used for a transmitter in the Microwave Landing System. By using 10-W class practical internally matched GaAs FET's hermetically sealed in ceramic packages, the four-stage amplifier has been constructed simply. The amplifier provides 30-W power output with 18.5 percent power efficiency at 17-dBm power input level. It also exhibited an exceffent AM/PM conversion of approximately 1°/dB, compared to 6°/dB for TWT amplifiers.     

毫米波大动态宽带单片低噪声放大器

利用0.25μmGaAsPHEMT低噪声工艺,设计并制造了2种毫米波大动态宽带单片低噪声放大器。第1种为低增益大动态低噪声放大器,单电源+5V工作,测得在26～40GHz范围内,增益G=10±0.5dB,噪声系数NF≤2.2dB,1分贝压缩点输出功率P1dB≥15dBm;第2种为低压大动态低噪声放大器,工作电压为3.6V,静态电流0.6A(输出功率饱和时,动态直流电流约为0.9A),在28～35GHz范围内,测得增益G=14～17dB,噪声系数约4.0dB,1分贝压缩点输出功率P1dB≥24.5dBm,最大饱和输出功率≥26.8dBm,附加效率约10%～13.6%。结果中还给出了2种放大器直接级联的情况。     

32-GHz cryogenically cooled HEMT low-noise amplifiers

The cryogenic noise temperature performances of a two-stage and a three-stage 32-GHz HEMT (high-electron-mobility transistor) amplifier were evaluated. The amplifiers utilize quarter-micrometer conventional AlGaAs/GaAs HEMT devices, hybrid matching input and output microstrip circuits, and a cryogenically stable DC biasing network. The noise temperature measurements were performed in the frequency range of 31 to 33 GHz over a physical temperature range of 300 to 12 K. Across the measurement band, the amplifiers displayed a broadband response, and the noise temperature was observed to decrease by a factor of ten in cooling from 300 to 15 K. The lowest noise temperature measured for the two-stage amplifier at 32 GHz was 35 K with an associated gain of 16.5 dB, while for the three-stage amplifier it was 39 K with an associated gain of 26 dB. It was further observed that both amplifiers were insensitive to light     

Pulsed laser sampling photon amplifier

The performance of semiconductor laser amplifiers can be significantly improved by injecting carriers with pulsed electric currents of subnanosecond duration. Pulsed operation is illustrated in a Fabry-Perot amplifier and in a traveling-wave amplifier. The resonant amplifier is most sensitive to an input light wave at the instant the carrier density is crossing over the critical region, giving a sharply pulsed sampling effect on the input light wave signal. Compared to a resonant amplifier operating at subcritical electron density, the pulsed amplifier gives much higher gain and peak power. In fact, pulsed operation of a resonant amplifier is also expected to give significantly higher gain than and about the same peak output power as a traveling-wave amplifier. Pulsed operation also improves the performance of a traveling-wave amplifier by attenuating its internally reflected waves.<>     

A theoretical study of pulsed laser sampling photon amplifiers

Theoretical studies point to significant improvements in the performance of semiconductor laser amplifiers by injecting carriers with pulsed electric currents of sub-nanosecond duration. A pulsed Fabry-Perot amplifier (FPA) is most sensitive to input lightwave at the instant the carrier density is crossing the critical region, and gives a sharply pulsed sampling effect on the input lightwave signal. Compared with a FPA operating at subcritical electron density, the pulsed amplifier gives much higher gain, peak power, and bandwidth. In fact, pulsed operation of a FPA is also expected to give significantly higher gain and about the same peak output power as a traveling wave amplifier. Pulsed operation also improves the performance of a traveling wave amplifier by attenuating its internally reflected waves     

Amplified spontaneous emission effects in semiconductor laseramplifiers

The analysis presented provides a quantitative method for predicting semiconductor laser amplifier performance in the presence of ASE (amplified spontaneous emission). It indicates that in order to increase the fraction of pump power that contributes to the amplification of the input laser field relative to that spent in overcoming internal losses, an amplifier should operate at as high an excitation level as possible. This may mean operating an amplifier above its free-running oscillation threshold. A limitation to the maximum pump power is the increase in ASE. With too high an excitation, ASE dominates over the amplified input laser field, resulting in a quenching of the amplifier gain, efficiency and coherence. ASE effects may be mitigated by increasing the input laser intensity, decreasing the amplifier facet reflectivities, or, in some cases, tuning the master oscillator so that it is resonant with the amplifier. The analysis indicates that minimizing the facet reflectivity is the most effective way to circumvent ASE limitations to power scaling semiconductor laser amplifiers     

Compact Vertically Stacked Master Oscillator Power Amplifier Based on Grating Coupled Laser Diodes

A new design of hybrid master oscillator power amplifier (MOPA) has been proposed and realized by vertically stacking laser diodes with optical coupling provided by identical in-plane integrated gratings. Low beam divergence, large emitting and input areas of the grating coupled devices simplify the assembling technique over the fabrication of MOPA devices based on edge-emitting laser diodes. The master oscillator also incorporates a dual-grating reflector providing a wavelength-selective feedback resulting in a narrow emission spectrum of 0.2 nm at a wavelength of 975.4 nm. The power amplifier is a tapered chip with two integrated grating couplers. The operational characteristics of the MOPA were evaluated in the pulse regime demonstrating an output peak power of 32 W with a total amplification factor of 9.3dB.     

Crosstalk between intensity-modulated wavelength-divisionmultiplexed signals in a semiconductor laser amplifier

The performance of a 1.5-μm Fabry-Perot type laser amplifier having two input signals at different wavelengths is experimentally studied. Crosstalk between the two signals at the output of the amplifier is measured. The crosstalk is strongly dependent on the input powers and on the signal gain, and is found to be very sensitive to the relative wavelengths of the input signals. The crosstalk can be either positive or negative, depending on the wavelength offsets. A theoretical model taking gain saturation and wavelength shift of the amplifier spectrum into account is shown to explain the experimental results well. Using this model, some general aspects on crosstalk in semiconductor laser amplifiers are discussed     

GaAs HBT wideband matrix distributed and Darlington feedbackamplifiers to 24 GHz

The designs and performances of a 2-24 GHz distributed matrix amplifier and 1-20 GHz 2-stage Darlington coupled amplifier based on an advanced HBT MBE profile that increases the bandwidth response of the distributed and Darlington amplifiers by providing lower base-emitter and collector-base capacitances are presented. The matrix amplifier has a 9.5 dB nominal gain and a 3-dB bandwidth to 24 GHz. This result benchmarks the highest bandwidth reported for an HBT distributed amplifier. The input and output VSWRs are less than 1.5:1 and 2.0:1, respectively. The total power consumed is less than 60 mW. The chip size measures 2.5×2.6 mm². The 2-stage Darlington amplifier has 7 dB gain and 3-dB bandwidth beyond 20 GHz. The input and output VSWRs are less than 1.5:1 and 2.3:1, respectively. This amplifier consumes 380 mW of power and has a chip size of 1.66×1.05 mm²      

Design, fabrication, and characterization of monolithic microwave GaAs power FET amplifiers

The design, fabrication, and characterization of three- and four-stage monolithic GaAs power FET amplifiers are described. Each of the amplifier chips measures 1 mm × 4 mm. Procedures for characterizing these monolithic amplifiers are outlined. Output powers of up to 1 W with 27-dB gain were achieved with a four-stage design near 9 GHz. The circuit topologies used were flexible enough to allow external bondwires to be used as shunt inductors for amplifier operation at C- or S-bands. An output power of 2 W with 28-dB gain and 36.6-percent power-added efficiency was achieved at 3.5 GHz, using a modified four-stage amplifier.     

DC-40 GHz光通信系统用GaAs PHEMT驱动放大器。

利用0.2μmGaAsPHEMT工艺研制了40Gb/s光通信系统中的光调制器驱动放大器。该放大器芯片采用有源偏置的七级分布放大器结构,工作带宽达到40GHz,输入输出反射损耗约-10dB,功率增益14dB,功耗700mW,最大电压输出幅度达到7V。两级芯片级连后,功率增益约27dB,在40Gbit/s速率下得到清晰的眼图。     

人眼安全高重频窄脉宽单模全光纤激光器特性研究

介绍了基于主振荡功率放大结构的人眼安全全光纤激光器.首先对比了电光调制及直接调制产生的种子激光在百kHz重复频率、纳秒级脉冲宽度的激光放大器中优缺点,综合系统需求选择直接调制方式;之后对窄脉冲单模放大中出现的脉冲分裂现象进行了研究,选用10 m纤芯的双包层铒镱共掺光纤,仅通过两级放大即获得了1 550 nm,重复频率为200 kHz,脉冲宽度为4.07 ns,峰值功率为1.02 kW的单模激光输出.具有结构紧凑、稳定可靠的特点,可用于三维视频激光雷达.     

On Theory and Performance of Solid-State Microwave Distributed Amplifiers

The performance characteristics of n-link distributed amplifiers employing GaAs MESFET'S are studied. At first, formulas of tie symmetrical amplifier using lumped circuit elements are developed for the case of an idealized FET model. The theoretical analysis is then extended to distributed line elements and later to an S-parameter derived transistor model. In efforts to optimize amplifier performance, the restriction of circuit symmetry is subsequently removed and the performance characteristics of two concepts, that of equal characteristic impedances and that of equal line lengths, are proposed and compared. Based on this analysis and practical considerations, several three-link hybrid amplifiers utilizing the equal line lengths approach have been assembled and test results are reported. A gain of G = 5.5+-0.6 dB was measured over the bandwidth of 2-20 GHz. Across this frequency band a maximum VSWR of 2.2:1 for the input and 2.5:1 for the output terminaf have been reafized, while a minimum output power at the l-dB compression points of 19.3 dBm was achieved from 2-18 GHz. Agreement between measured and computed small-signal gain as well as reverse isolation is excellent.     

K-Band High-Power GaAs FET Amplifiers

Lumped-element internal matching techniques were successfully adopted for K-band power GaAs FET amplifiers. The developed 18-GHz band two-stage amplifier provides 1.05-W power output at 1-dB gain compression and 1.26-W saturated power output with 8.1-dB small-signal gain. The 20-GHz band single-stage amplifier has 1.04-W power output with 3-dB associated gain. Lumped-element internal matching circuit design as well as amplifier fabrication are described. Intermodulation distortion and AM-to-PM conversion characteristics are also presented.