Evolution of the statistical properties of photons passed through atraveling-wave laser amplifier

The authors determine the evolution of the photon statistics of a light beam as it passes through a traveling-wave laser amplifier, modeled as a birth-death immigration (BDI) medium. The relationship between the input and output probability distributions and probability generating functions with given (but possibly varying) birth, death, and immigration rates for arbitrary input statistics is obtained. The case of constant birth, death, and immigration rates is considered in particular detail. The photon statistics at the output of a general BDI traveling-wave amplifier are always broader than those at the input, and they can take many forms. The most general solution can be applied when the input distribution to the amplifier takes the form of a negative-binomial transform     

Quantum-statistical properties of pulse amplification in opticalfibers with gain saturation

We studied the quantum-statistical properties of pulse amplification in erbium-doped fiber amplifiers (OFAs), including saturation of the atomic population inversion and pump depletion. We use a fully quantum theory to describe the atom-field interaction as wed as the light propagation. The generating function of the output photon number distribution (PND) is determined as a function of time during the course of the pulse, with an arbitrary input PND assumed. For input light with Poisson PND, the output PND is shown to be the Laguerre distribution with parameter 1 at all times smaller than the coherence time τ_c, even in the presence of nonlinear effects. An expression for the photon count moment generating function is found for counting times T≫τ_c. The mean pulse shape is shown to be altered by the nonlinear amplification. The variance is similarly altered, and the excess amplifier noise is greater at the leading side of the pulse     

Minimization of intermodulation distortion in GaAs MESFETsmall-signal amplifiers

It is shown how the intermodulation (IM) distortion performance of a small-signal amplifier can be optimized when the amplifier is designed according to available-gain criteria. In this process the MESFET's output is conjugate-matched and its input is mismatched to obtain a specified gain. This method generally results in a better dynamic range than obtained with other options such as matching the input and mismatching the output or simultaneously matching both the input and output (which, in many cases, is impossible). In available-gain design the value of source impedance that provides the desired gain is not unique and can be selected to optimize IM levels. A numerical formulation of the Volterra series allows a complete equivalent circuit of the FET to be used, and the intermodulation calculations include all feedback effects. The sensitivity of the IM intercept point (IP₃ ) to the source-reflection coefficient, Γ_s, is shown to decrease with increasing frequency and is related to the MESFET's stability     

对卡塞格林式多程放大器中环形光束传输的数值模拟

利用光线追迹法以及分步傅里叶-贝塞耳变换法,考虑了光阑对光束的拦截和通光作用以及激光放大过程中的增益饱和效应,对环形腔调Q钕玻璃激光系统振荡器输出的光束经卡塞格林式放大器多程放大后的光场演化过程进行了数值模拟,并进行了实验验证。分析得出现有系统中输入输出镜的阶跃反射率分布是导致输出环形光束质量不好的主要原因,并重点对放大器的腔镜部分进行了优化设计,提出了反超高斯反射率分布的输入镜与超高斯反射率分布的输出镜相组合的腔镜对结构。数值模拟结果表明,该腔镜对的使用可大大改善输出环形光束的质量。     

Information transmission with photon-number-squeezed light

Several methods have been proposed for the generation of photon-number-squeezed (sub-Poisson) light by imparting to the photon stream and anticorrelation that regularizes the times of arrival of the photons. This is accomplished by means of control of the excitation or emission process or by feedback, using a copy of the photon point processes when the emissions occur in parts. Possible advantages of communication by photon-number-squeezed light are discussed. For receivers in which the photon arrival times are observed, the channel capacity cannot be improved by modifying an initially Poisson photon stream and making it sub-Poisson. For photon-counting receivers, however, improvement of the channel capacity is possible. The bit-error-rate of an on-off keying communication system using sub-Poisson photons created by introducing anticorrelation into an initially Poisson beam may or may not be smaller than the error rates of the Poisson channel, depending on where the maximum power constraint is placed     

一种输出匹配可调的、高线性度宽带功率放大器

采用自适应偏置技术和有源电感实现了一款输出匹配可调的、高线性度宽带功率放大器(PA)。自适应偏置技术抑制了功放管直流工作点的漂移,提高了PA的线性度。有源电感参与输出匹配,实现了输出匹配可调谐,该策略可调整因工艺偏差、封装寄生造成的输出匹配退化。利用软件ADS对电路进行验证,结果表明,在4 GHz频率下,输入1dB压缩点(Pin 1dB)为-7dBm,输出1dB压缩点(Pout 1dB)为11dBm,功率附加效率(PAE)为8.7%。在3.1GHz~4.8 GHz频段内,增益为(20.3±1.1)d B,输入、输出的回波损耗均小于-10dB。     

2.4GHz CMOS高线性功率放大器

采用A类与B类并联的结构,设计了一种2.4GHz高线性功率放大器.输入信号较小时,A类放大器起主要作用;随着输入信号的增大,B类放大器起的作用越来越明显,来补偿A类的压缩,由此显著提高了放大器的线性度.电路主体为共栅管采用自偏置方法的共源共栅结构,提升了功放大信号工作时的可靠性.电路采用中芯国际0.13 μmCMOS工...     

Analysis of gain and saturation characteristics of a semiconductorlaser optical amplifier using transfer matrices

The transfer matrix method (TMM) has been applied to analyze the gain and saturation characteristics of semiconductor laser optical amplifiers. This method approximates the amplifier cavity by dividing it into M discrete subsections, and TMM has been applied to analyze the stepwise longitudinal field distribution at each subsection along the amplifier cavity. By incorporating also the carrier rate equations into the analysis, it has been shown that the approximation can accurately describe the carrier density and longitudinal field distribution along the amplifier cavity if M is sufficiently large (i.e., the size of each subsection is about an order of magnitude of one wavelength of the input signal). By assuming that the amplifier is biased below oscillation threshold such that the contribution of spontaneous emissions to the gain characteristics can be neglected, we have shown that our proposed method yields a fast and efficient algorithm in analyzing the gain and saturation characteristics of laser amplifiers. We have compared the results produced by our method to those analyzed using the average photon density (AVPD) approximation technique, as well as to experimental results on a 1.5-μm buried heterostructure semiconductor laser amplifier     

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.     

基于GaN 的3. 4~ 3. 6 GHz 高增益Doherty 功率放大器

基于两级功率放大器架构,设计了一款平均输出功率为37 dBm(5 W)的高增益Doherty 功率放大器。 该器件通过增加前级驱动功率放大器提高Doherty 功率放大器的增益,采用反向Doherty 功率放大器架构,将λ/4 波 长传输线放置在辅助功放后端,相位补偿线放置在主功放前端,并使主功放输出匹配网络采用双阻抗匹配技术实现 阻抗变换,如此可扩宽功率放大器的工作带宽。连续波测试结果显示:3. 4~3. 6 GHz 工作频段内,饱和输出功率在 44. 5 dBm 以上,功率饱和工作点PAE 在43. 9%以上;在平均输出功率(37 dBm,5 W)工作点,回退量大于7. 5 dB,功 率附加效率PAE 为36. 8%以上,功率增益在31 dB 以上。     

基于光子数可分辨探测器的单脉冲光子数检测

为了对未知脉冲所含的光子数进行标定,针对不同光子数的光脉冲在超导环境下,微波动态电感探测器(MKID)作用时,测量系统输出的信号差异性,采用平均区间取值法和迭代法分别进行标定,并进行了理论分析和实验验证。结果表明,MKID能够在低温测量系统中对未知1550nm单脉冲光的光子数进行识别; 经过数据处理后得到平均光子数分别为1.98和1.81;其中平均区间取值法标定光子数过程较为简单,迭代法有待继续探索。这一结果对单脉冲光子数检测是有帮助的。     

一种带功率检测和自适应偏置的CDMA功率放大器

设计了一款包含功率检测和自适应线性化偏置电路的CDMA功率放大器,功率检测器能根据输入信号的大小来调整功率管的偏置点,大幅提升低功率输出时的效率,从而提升系统整体效率;自适应线性化偏置能有效抑制功率放大器的增益压缩和相位失真,改善其线性度.采用2 μm InGaP/GaAs HBT晶体管工艺成功流片,测试结果表明,与普...     

Rate-equation analysis of output efficiency and modulation rate ofphotonic-crystal light-emitting diodes

The performance characteristics of photonic-crystal light-emitting diodes (LEDs) are analyzed, taking into account the effects of both nonradiative recombination and photon reabsorption processes using multimode rate equations. It is shown that, in the presence of strong photon reabsorption, the optimum output efficiency and modulation rates are achieved when the width of the photon density-of-state distribution function is comparable to the width of the spontaneous emission lineshape of the active material. On the other hand, when photon reabsorption is weak, it becomes beneficial to construct high-Q cavities. Based on this analysis, the characteristics of different photonic crystal LED configurations are discussed     

低抖动准分子激光放大器光源的研究

为了获得低抖动的准分子激光放大器光源,设计了一种以氢闸流管作为高压开关的低抖动准分子激光放大器系统。利用抖动小于4 ns的闸流管触发电路来触发导通氢闸流管,从外部触发信号到准分子光信号之间有一定的延时时间。研究了以氢闸流管作为高压开关的准分子激光放电回路,外部控制信号发生电路产生外部充电信号和出光信号,转换电路将外部充电信号和出光信号转换成固定脉宽的光信号,在实现低抖动出光前,准分子激光放大器系统热平衡过程中会有一定的出光延时漂移现象。讨论了激光运行重复率、激光运行电压和气体状态在热平衡过程中对稳定延迟时间大小的影响。实验表明,在相同运行电压下,稳定延迟时间随着激光运行重复频率的提高而增大;运行电压越高,稳定延迟时间上升的幅度越大。气体恶化后,光脉冲稳定延迟时间变小。激光运行电压和重复频率越高,延时漂移时间越大。在温漂一定时间后,准分子激光放大器内部系统达到热平衡,以外部触发信号为基准,准分子光脉冲信号实现在5、10、15 Hz重复频率下的5 ns内低抖动出光。     

Integrated Amplifier Circuits for 60 GHz Broadband Telecommunication

Wide frequency bandwidth has been internationally allocated for unlicensed operation around the oxygen absorption frequency at 60 GHz. A power amplifier and a low noise amplifier are presented as building blocks for a T/R-unit at this frequency. The fabrication technology was a commercially available 0.15 m gallium arsenide (GaAs) process featuring pseudomorphic high electron mobility transistors (PHEMT). Using on-wafer tests, we measured a gain of 13.4 dB and a +17 dBm output compression point for the power amplifier at 60 GHz centre frequency when the MMIC was biased to 3 volts V_dd. At the same frequency, the low noise amplifier exhibited 24 dB of gain with a 3.5 dB noise figure. The AM/AM and AM/PM characteristics of the power amplifier chip were obtained from the large-signal S-parameter measurement data. Furthermore, the power amplifier was assembled in a split block package, which had a WR-15 waveguide interface in input and output. The measured results show a 12.5 dB small-signal gain and better than 8 dB return losses in input and output for the packaged power amplifier.     

超短强激光作用下的CsLiB6O10晶体的光参量放大理论分析

对超短强激光抽运波长为355nm，脉冲宽度为10ps的CsLiB6O10。光参量放大器(OPA)的最佳晶体长度、能量转换效率和输出信号光脉宽进行了理论分析和数值模拟。得到了在IP(0)=300MW／cm^2，Is(0)=5MW／cm^2，Ii(0)=0的情况下，最佳晶体长度为27．0mm。随着抽运功率和信号光功率增大时，CsLiB6O10晶体作为光参量放大器的非线性晶体时，其作用的晶体长度变得更短。高转换效率的信号光输出取决于抽运光和初始信号光的强度及晶体长度的最佳优化值。     

Computer simulation of laser photon fluctuations: Coupled-cavity lasers

This third paper of the series deals with photon fluctuations in the light output of coupled-cavity lasers. As before, statistics on laser photon fluctuations are collected from numerical solutions of noise driven rate equations. Compared to the single-cavity injection laser, the coupled-cavity laser is found to have the following advantages. 1) The coupled-cavity laser can be made to operate in a single mode by driving one of its sections above and the other below threshold. For a given amount of output power from the high-current end, fewer photon fluctuations occur if it is the longer laser section that is driven above threshold. 2) The order of magnitude of the photon fluctuations of the single lasing mode of a coupled-cavity laser is comparable to the fluctuations of the total power output of a single-cavity laser. 3) Contrary to single-cavity lasers, which cannot be made to operate in a single mode if they are driven by short current pulses, coupled-cavity lasers will readily deliver a single, pulsed mode. Thus, if thermal effects and backreflection of scattered light (for example, from an attached fiber) can be ignored, mode jumping need not occur.     

Influence of reflected light on erbium-doped fiber amplifiers foroptical AM video signal transmission systems

Investigates experimentally the influence of reflected light on an erbium-doped fiber amplifier for use in optical AM frequency-division multiplexing (FDM) video distribution systems when reflection points exist before and after the amplifier. It is found that amplifier distortion is not affected by reflected light but that the signal gain and the noise figure of the fiber amplifier degrade with increased reflectivity. Gain was decreased by 3 dB when reflectivity after the amplifier was -12 dB. It was theoretically and experimentally clarified that the noise figure degradation was related to the internal reflection of the erbium-doped fiber, in addition to the reflection before and after the fiber amplifier. This internal reflection is caused by input signal light scattered within the erbium-doped fiber     

An Inductorless 300 MHz Wideband CMOS Power Amplifier

The power amplifier tends to be one of the most demanding parts to fully integrate when building an entire radio on a CMOS chip. In this paper the design of a fully integrated RF power amplifier without inductors is described. As inductors in CMOS technology are associated with various problems, it is interesting to examine what performance can be achieved without them. An amplifier with an operating band from 60 MHz to 300 MHz (–3 dB) is built in 0.8 m CMOS. A 3 V supply is used. The measured midband power gain is 30 dB with 50 resistive source and load impedance. As linearity is important for many modern modulation schemes, the amplifier is designed to be as linear as possible. The measured third order intercept point is 23 dBm and the 1 dB compression point is 10 dBm, both referred to the output. The output is single ended to avoid an off-chip differential to single ended transformer.     

重复频率3Hz、100mJ高光束质量钕玻璃放大器的研制

研制了具有放大纳秒方形激光脉冲的高光束质量、高稳定的激光二极管(LD)抽运的钕玻璃激光放大器。为了获得较高的输出能量,采用LD泵浦的"串联式双程放大"高增益组件进行能量放大。为了获得高光束质量的光斑,利用液晶空间光调制器(LCSLM)对光束近场分布进行空间整形,使之产生特定的空间分布,进而对后级放大器增益不均匀性进行光学预补偿。放大器工作波长为1 053nm,工作频率为3 Hz,输入1nJ的3ns方形激光脉冲,输出激光脉冲能量为100mJ、光束口径为10mm×10mm的方光斑,能量不稳定度小于2%(均方根),净增益大于109。光束的近场调制度小于1.3∶1,远场焦斑衍射极限小于2DL,远场角漂移小于9.5μrad。