Compensation of excess noise in a fiber-optic gyroscope with a 3×3 directional coupler

It is shown theoretically that the excess noise of the radiation source can be compensated in a fiber-optic gyroscope with a 3×3 ring directional coupler and a differential amplifier at the exit. This noise is one of the main factors limiting the precision of a fiber-optic gyroscope. Pis’ma Zh. Tekh. Fiz. 23, 36–38 (August 12, 1997)     

利用源强分布声辐射模态识别噪声源

为了解决噪声源识别中存在的识别精度不高、分辨率受限、对测量条件要求高等问题,提出了基于源强声辐射模态的噪声源识别方法。该方法首先计算结构的源强声辐射模态矩阵和声场分布模态矩阵,然后利用声场中测得的声压数据向量与结构声场分布模态矩阵的关系求出声辐射模态展开系数向量,最后通过声辐射模态矩阵和声辐射模态展开系数向量的积就可得到结构的源强分布,从而达到对噪声源识别的目的。该方法利用较少的测量点可以获得较高分辨率和识别精度。通过平板振动仿真和音箱实验验证了该方法对平面结构噪声源识别的有效性。     

Excess noise of an Er/Yb fiber superfluorescent radiation source

A study is made of the noise in the output intensity of a high-power superfluorescent fiber radiation source generating 20 mW in the 1.55 μm region of the spectrum. The source is constructed in an all-fiber technology from a quartz fiber activated with ytterbium and erbium. It is found that the spectral density of the noise in the frequency range 100–500 kHz is uniform and corresponds to the excess noise of “thermal” sources. It is shown that the noise in the output intensity of the source can be compensated (decreased by an order of magnitude) in a two-channel scheme of photodetection, where it approaches a level close to the photon shot noise. Pis’ma Zh. Tekh. Fiz. 23, 1–6 (December 12, 1997)     

水中目标辐射噪声特性仿真

文章中讨论了水中目标一船体辐射噪声的特性。运用冲激响应不变法来设计IIR数字一阶低通滤波器，并用此滤波器对高斯白噪声进行滤波，滤波器的输出能很好地模拟船体辐射宽带连续噪声，此输出信号的功率谱在高频端以6dB／oct的斜率下降。运用直接数字信号合成技术产生多个低频线谱信号，并将它与宽带连续噪声相加，从而来模拟船体辐射的低频线谱。     

Study of the excess noise associated with demodulation of ultra-short infrared pulses

The demodulation of ultra-short light pulses with photodetectors is accompanied by excess phase noise at the pulse repetition rate and harmonics in the spectrum of the photocurrent. The major contribution to this noise is power fluctuations of the detected pulse train that, if not compensated for, can seriously limit the stability of frequency transfer from optical to microwave domain. By making use of an infrared femtosecond laser, we measured the spectral density of the excess phase noise, as well as power-to-phase conversion for different types of InGaAs photodetectors. Noise measurements were performed with a novel type of dual-channel readout system using a fiber coupled beam splitter. Strong suppression of the excess phase noise was observed in both channels of the measurement system when the average power of the femtosecond pulse train was stabilized. The results of this study are important for the development of low-noise microwave sources derived from optical "clocks" and optical frequency synthesis.     

抑制噪声的宽带碲基掺铒光纤放大器性能分析

设计了一个带光隔离器的复合型宽带碲基掺铒光纤放大器（EDTFA）,通过对该结构模型下的速率方程和光功率传输方程组的数值模拟,理论研究了EDTFA在插入光隔离器后的性能变化。研究表明,通过插入光隔离器抑制反向传输的放大自发辐射（ASE）噪声,可以有效地改善宽带EDTFA的信号增益和噪声特性。在光纤激活长度240cm、铒掺杂浓度2000ppm和前向泵浦功率200mW下,光隔离器插入在最佳位置处时,1540nm～1600nm波段内16路信道小信号增益分别提高了0.8dB～5．9dB,噪声系数降低了0.2dB～2．2dB。研究结果对于新型宽带EDTFA应用于WDM通信系统中具有理论指导意义。     

Wide-band suppression of laser intensity noise

A simple and efficient laser intensity stabilization system was constructed based on an electro-optical modulator (EOM) and a photodetector. It is capable of reducing the laser intensity fluctuations to the shot noise limit within the range of Fourier frequencies from a few tens of hertz to a few megahertz. The achieved bandwidth of the laser control system is limited by the light handling capacity of the photodetector and spurious resonances of the EOM. We discuss the general approach to the design of the laser intensity stabilization system and its noise properties.     

Optimal suppression of quantization noise with pseudoperiodic multilevel phase gratings

A comprehensive two-step approach to design staircase-type multilevel diffractive phase elements (DPEs) that generate arbitrary desired diffraction patterns with the highest possible accuracy is presented. First a preliminary periodic grating with an unconstrained phase delay and an optimized nonuniform amplitude profile is designed by means of a customized iterative Fourier-transform algorithm. Then this preliminary grating is subjected to a phase quantization in which strict periodicity is forgone in favour of the best possible preservation of the shape of the power spectrum yielding a final phase only DPE with only rudimentary periodicity. An arbitrarily high similarity between the diffraction patterns of the final DPE and the preliminary grating can be achieved independently of the number D of discrete phase delay levels as long as D > or = 3. The signal-to-noise ratio of the final DPE is close to the theoretical upper limit. These properties are confirmed in computer simulations and demonstrated in optical experiments. Pseudoperiodic DPEs may have applications in optical computing, optical communication and networking, optical authentication, or coherent laser coupling.     

Spectral and angular characteristics of the radiation from a cylindrical radionuclide source

Translated from Izmeritel'naya Tekhnika, No. 2, pp. 13–16, February, 1993.     

一种低噪声开关电源在光纤陀螺系统中的应用

在高精度光纤陀螺系统中,开关电源中的spike毛刺噪声会串扰光纤陀螺的信号处理电路,造成系统采样误差。本文分析了开关电源spike噪声的成因及其对光纤陀螺性能的影响机理,并在此基础上提出摆率控制是一种适用于光纤陀螺系统电源的低噪声电源技术。利用摆率控制技术,一种低噪声特性的开关电源模块被开发出来,并应用于光纤陀螺系统。该开关电源模块由DC-DC电路和LDO电路两部分组成,并在DC-DC电路中通过摆率控制电路实现其低噪声性能。完成后的低噪声电源模块能够在200 MHz的测试带宽下实现1 mV量级的峰峰值噪声水平。经过对比测试,采用低噪声电源的两支被测光纤陀螺分别表现出了3.1%和4.4%的噪声优化特性。

     

舰艇辐射噪声特性仿真

本文讨论了舰艇辐射噪声的特性.运用冲激响应不变法来设计了一个IIR数字一阶低通滤波器,并用此滤波器对高斯白噪声进行滤波,滤波器的输出能很好地模拟舰艇辐射宽带连续噪声,此输出信号的功率谱在高频端以每倍频程6分贝的斜率下降.运用直接数字信号合成技术产生多个低频线谱信号,并将它与宽带连续噪声相加,从而来模拟舰艇辐射的低频线谱.     

Interrelation of the energetic noise equivalent with the other parameters of silicon radiation detectors

Translated from Izmeritel'naya Tekhnika, No. 1, pp. 49–50, January, 1990.     

卫星控制力矩陀螺微振动抑制装置的动力学建模与实验研究

为了隔离卫星主要振源控制力矩陀螺的微振动,给航天器有效载荷提供超静工作环境,基于松弛型阻尼器,设计了控制力矩陀螺六自由度微振动抑制装置,完成了隔振平台的动力学建模和实验研究.使用牛顿-欧拉法建立了微振动抑制装置的动力学模型,分析了微振动抑制装置在基础激励下的频域特性和隔振系统的耦合特性;搭建了微振动抑制装置实验平台,并...     

多线谱干扰下的盔内语音通信降噪算法研究

航天服头盔内语音通信系统工作时,受到来自航天服自身的风机、泵、通风气流所产生的噪声影响,通话质量下降严重。传统降噪方法能有效抑制宽带噪声,但对线谱干扰的抑制较弱。文章以此为出发点,开展了多线谱干扰下的语音降噪算法研究,设计了一种自适应线谱检测方法,可有效识别线谱,定位其所处频带,在抑制宽带噪声的同时,进一步抑制线谱干扰。文章结合盔内实录噪声数据对算法进行了验证,结果显示,相对于传统降噪方式,文中方法对多线谱干扰的抑制能力更强,语音客观语音质量评估得分提高约6%。     

Zero-order noise suppression with various space-shifting manipulations of reconstructed images in digital holography

In this paper, we describe various numerical space-shifting manipulations of the reconstructed images to remove the dc noise in the reconstruction, in terms of the periodicity characteristics of images in digital holography. The theoretical interpretation on different reconstruction periods of the image and the dc noise is described in detail for the first time, to the best of our knowledge. It is related to CCD sampling periods or frequencies for the fringes and the dc term of a hologram. With the calculations of Hadamard product of two different spatially shifted images and subsequent extraction of the root of it, the dc noise can be suppressed effectively and a clear image with the original intensity contrast can be obtained at the center in the hologram reconstruction, particularly when the image and the dc noise are completely or partially superposed with each other. The experiments for both in-line and off-axis imaging cases show that all results are completely consistent with theoretical predictions.     

Strong suppression of electrical noise in bilayer graphene nanodevices

Low-frequency 1/f noise is ubiquitous and dominates the signal-to-noise performance in nanodevices. Here we investigate the noise characteristics of single-layer and bilayer graphene nanodevices and uncover an unexpected 1/f noise behavior for bilayer devices. Graphene is a single layer of graphite, where carbon atoms form a two-dimensional (2D) honeycomb lattice. Despite the similar composition, bilayer graphene (two graphene monolayers stacked in the natural graphite order) is a distinct 2D system with a different band structure and electrical properties. 1,2In graphene monolayers, the 1/f noise is found to follow Hooge's empirical relation with a noise parameter comparable to that of bulk semiconductors. However, this 1/f noise is strongly suppressed in bilayer graphene devices and exhibits an unusual dependence on the carrier density, different from most other materials. The unexpected noise behavior in graphene bilayers is associated with its unique band structure that varies with the charge distribution among the two layers, resulting in an effective screening of potential fluctuations due to external impurity charges. The findings here point to exciting opportunities for graphene bilayers in low-noise applications.