某些商品激光器的低频激光噪声

近来，对于测定激光器中的低频噪声产 生了很大兴趣，这是光传感技术(诸如，光声传感器，和光纤陀螺)广泛流行的直接结果。在这些装置中，对于检测极低压力或速率的能力取决于激光器能否工作于接近散粒噪声范围的有效性。最终，这种装置将采用小型化的固体红外激光二极管。可是，这种技术目前在实验研究中通常都是使用可见光气体激光器。因此，这里报导了各种商用激光器噪声谱的测定情况。     

同步POL转换器降低差拍噪声

采用DPA(分布式电源架构)的电源子系统通常在系统中有多个独立的电源模块,提供不同的电压和电流,甚至可能是不同的开关频率.这些不同的频率可以在系统中产生明显的噪声问题.     

同步POL转换器降低差拍噪声

ARM公司与深圳英蓓特信息技术有限公司(简称英蓓特)联合推出中国市场版本RealView微处理器开发工具包(MDK).这一新产品是特别为满足中国软件和系统开发厂商的需求而推出的,起价低于5000元人民币,易于纳入设计工具的整体预算中.     

折射率波导半导体激光器低频跳模噪声

在一定温度范围内,横模稳定的激光器出现低频激光噪声会严重影响光盘系统的性能,尤其对视频唱片系统的影响更大。在折射率波导激光器中经常观察到激光噪声。如图1所示,出现激光噪声处的温度与纵模跳跃到下一个模式处的温度正好相对应。跟所谓模式竞争噪声的情况不同,即使不用选模光学元件,也观察到这种跳模噪声。这种噪声功率谱跟频率f的联系为1/f(α=1～2),并在频率低于几十MHz时可清楚看见。当噪声出现时,示波器的输出功率图形中可观察到几个功率水平之间的随机转换。功率水平之间的差异通常低于dc功率水平的2%。功率水平的数值与含有跳模的纵     

半导体激光器低频噪声测试及参数提取

半导体激光器低频电噪声的大小受器件潜在缺陷的影响,与器件可靠性具有相关性。介绍了半导体激光器噪声测试及参数提取的原理,设计了基于超低噪声前置放大器和低频频谱分析仪的低频电噪声测试系统,可测量半导体激光器的低频电噪声并提取相关噪声参数,进而通过低频电噪声的研究对半导体激光器进行可靠性评价,具有灵敏度高、非破坏性等优点。     

内腔He-Ne激光的磁致差拍噪声

本文报导了内腔He-Ne激光器的一种特殊噪声,它是由空间磁场(主要是地磁)引起的。根据Zeeman激光理论和激光介质的色散特性,解释了这种噪声产生的机制和变化规律。最后给出了消除此类噪声的方法。     

NTSC彩电信号取样、量化的差拍噪声

为了推动电视数码化,本刊特向读者推荐一组译文。这四篇文章虽然都是NTSC彩电信号复合编码,但从理论设计到实验有较全面的介绍,可作为我国设计试制PAL彩电信号的复合编码数字传输终端设备的技术借鉴。     

光电反馈抑制掺铒光纤激光器的低频强度噪声

通过光电反馈电路对掺铒光纤激光器的中低频噪声进行了抑制。根据速率方程理论,分析了影响掺铒光纤激光器强度噪声的因素,通过电路仿真分析优化反馈电路参数,重点讨论反馈信号的相位对噪声抑制的影响。实验表明：激光器的低频(小于20KHz)强度噪声平均降低了10dB,中频弛豫振荡峰处（30KHz附近）抑制达35dB,并且克服了光电反馈抑制强度噪声使弛豫振荡峰向高频移动,导致高频噪声增大的问题。优异的噪声特性使光纤激光器在光传感领域具有很高的实用价值。     

气体激光器

评述了气体放电激光器的现状,特别注意到1965年和1966年初的进展。在介绍简史之后,把气休激光器分为三类,即中性原子、离子及分子激光器,比较了各种类型激光器的特性。简短地讨论了噪声和相干性质。对现在特别重要的三方面发展,即CO2激光器、氩离子激光器和脉沖式自终止激光器作了较详细的描述最后简单介绍了目前气体激、光器几种最重要的应用。     

气体激光器

在紫外波段的高功率连续振荡的离子激光器中，有使用氧化铍等高耐热放电管，由数十安培的强电流进行激励的氩III激光器(波长364，351毫微米，输出为数瓦）和由数十毫安的空心阴极放电进行激励的氦-镉激光器(波长325毫微米，输出功率为十毫瓦)，都能作为紫外区域的相干光源。近来，使用多层介质膜反射镜(波长在160毫微米处反射率为96%)，采用500毫微秒的脉宽，10千安/厘米2的强电流进行脉冲激励的氖、氩、氪、氦等1价到4价的离子，获得了从紫外区域到真空紫外区域的许多条新的激光振荡谱线。其最短波长为氪IV的176毫微米，峰值输出为0.1~1千瓦。此外，在稀有气体-金属离子激光器中，由于空心阴极放电时的电极溅射作用，放电管内蒸气压较低的金属铜II(270~249毫微米)、银(383~224毫微米)、金II(296~253毫微米）以及铝II(359毫微米)可得到连续及准连续振荡，并将可能具有较高的效率。     

Low-frequency intensity noise in semiconductor lasers

The observed 1/f noise in the light-output power S _p of four different types of heterostructure lasers is explained in terms of spatially uncorrelated gain fluctuations and spontaneous emission fluctuations. Two possible noise sources are suggested: fluctuations in the absorption coefficient and fluctuations in the number of free carriers. Both models are in agreement with the experimental results obtained from index-guided and gain-guided diodes at wavelengths of 1.3 and 0.8 μm. The dependence S_p ∝P^m has been observed with P the average light-output power and m=3/2 under spontaneous emission, a small transition region with m=5/2, m=4 in the superradiation region, and 0⩽m⩽1 in the laser region     

Low-frequency relative intensity noise in self-pulsatingridge-waveguide quantum-well lasers

Self-pulsating diode lasers are used in optical systems in which optical coherence is undesirable. The relative intensity noise behavior of self-pulsating lasers at frequencies below the self-pulsating frequency is investigated both theoretically and experimentally, and is compared to the relative intensity noise behavior of conventional non-self-pulsating lasers. It is shown that the predictions of the relative intensity noise of self-pulsating lasers can be made based on a simple conjecture for a dynamically unstable system and yield good empirical agreement with experimental results     

Low-frequency mode-hopping optical noise in AlGaAs channeled substrate lasers induced by optical feedback

Experiments on mode-hopping noise induced by optical feedback are presented for AlGaAs CSP lasers. The influence of the amount of feedback and of the output power have been investigated. It turns out that the amount of excess noise associated with mode hopping strongly depends on the occurrence of hysteresis associated with the mode-hopping transition. The results indicate that the gain suppression near the lasing mode is asymmetric.     

Low-frequency noise in n-GaN

Low-frequency noise has been investigated in the hexagonal polytype of n-type gallium nitride (GaN) with equilibrium electron concentration at 300 K n ₀⋍7×10¹⁷ cm⁻³. The frequency and temperature dependence of the noise spectral density S _I/I² was studied in the range of analysis frequencies f from 20 Hz to 20 kHz in the temperature range from 80 to 400 K. Over the entire temperature range the frequency dependence of the dark noise is close to S _I/I²∼1/f (flicker noise). The rather weak temperature dependence of the noise level is characterized by very high values of the Hooge constant α⋍5–7. These large α values indicate a rather low level of structural quality of the material. The effects of infrared and band-to-band illumination on low-frequency noise in GaN are studied here for the first time. The noise level is unaffected by illumination with photon energy E _ph<E _g (E _g is the band gap) even for a relatively high value of the photoconductivity Δσ⋍50%. Band-to-band illumination (E _ph⩾E _g) influences the low-frequency noise level over the entire investigated temperature range. At relatively high temperatures the influence of illumination is qualitatively similar to that of band-to-band illumination on low-frequency noise in Si and GaAs. At relatively low temperatures the influence of illumination on the noise in GaN is qualitatively different from the results obtained earlier for Si and GaAs. Fiz. Tekh. Poluprovodn. 32, 285–289 (March 1998)     

Low-frequency noise considerations for MOS amplifiers design

Equivalent input noise voltages of MOS amplifiers working in a low-frequency range have been calculated in the three basic technologies, i.e., single-channel enhancement-load, single-channel depletion-load and CMOS. Means of reducing that noise are discussed and practical results given for CMOS technology.     

Low-frequency noise in near-fully-depleted TFSOI MOSFETs

Low-frequency (1/f) noise in near-fully-depleted Thin-Film Silicon-On-Insulator (TFSOI) CMOS transistors designed for sub-l-V applications is investigated in the subthreshold region, linear region, and saturation region of operation for the first time. The noise in these surface-channel devices is composed of a bias invariant 1/f component and a bias dependent generation-recombination (G/R) component that becomes enhanced in the subthreshold region of operation for both n- and p-channel MOSFETs. Results presented in this letter are consistent with the noise being dominated by a number fluctuation model. These results demonstrate that the bias independent 1/f noise spectrum of the n-channel TFSOI MOSFET is comparable to the 1/f noise level found in conventional bulk silicon submicron CMOS fabrication processes     

Low-frequency noise in Gallium Arsenide MESFETs

We observed the noise spectrum of GaAs MESFETs from $\text{1/?}$ noise through diffusion noise ($\text{1/?}{}^{1.5}$ spectrum) to thermal noise in the frequency range from 20 Hz to 2 MHz. At negative gate bias and floating drain the drain shows thermal noise, but when the gate is biased positively so that it draws gate current it will contribute excess noise to the floating drain. The current noise spectrum $\text{S}{}_{\mathrm{I}}\text{(?)}$ at both the gate and the floating drain shows an relationship, which is common for the Schottky barrier diodes.     

Low-frequency noise in GaAs current limiters

The theory of the one-dimensional diffusion noise is modified and applied to explain the low frequency noise in GaAs current limiters. The devices show noise spectra with $\text{f}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}$ and $\text{f}{}^{\mathrm{<mtext>?</mtext><mtext>3</mtext><mtext>2</mtext>}}$ branches. The turn-over frequency increases with the applied voltage and temperature increase. The diffusion constant depends exponentially on temperature and the activation energy varies with electric field because of Poole-Frenkel effect. The experimental data confirms the temperature and voltage dependence of noise. The calculated activation energy is very close to the value reported in connection with leakage current in GaAs MESFET. Since the diffusion constant differs by many orders of magnitude from diffusion constant of electrons or ions one-dimensional diffusion of ions along dislocation lines is proposed. However, the mechanism of diffusion is not fully understood yet.     

Low-frequency noise in hot-carrier degraded nMOSFETs

This paper discusses the low-frequency (LF) noise in submicron nMOSFETs under controlled transistor aging by hot-carrier stress. Both traditional, steady-state LF noise as well as the LF noise under periodic large-signal excitation were found to increase upon device degradation, for both hydrogen passivated and deuterium passivated Si–SiO₂ interfaces. As hot-carrier degradation is slower in deuterium-annealed MOSFETs, so is the increase of the noise in these devices. The noise-suppressing effect of periodic OFF switching is gradually lost during hot-carrier degradation, as the LF noise under periodic large-signal excitation increases more rapidly than the LF noise in steady-state.