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相关概念视频

Time and frequency -Domain Interpretation of Phase-lag Control01:21

Time and frequency -Domain Interpretation of Phase-lag Control

381
Phase-lag controllers are widely used in control systems to improve stability and reduce steady-state errors. A dimmer switch controlling the brightness of a light bulb serves as a practical example of phase-lag control, gradually adjusting the bulb's brightness. Mathematically, phase-lag control or low-pass filtering is represented when the factor 'a' is less than 1.
Phase-lag controllers do not place a pole at zero, but instead influence the steady-state error by amplifying any...
381
Load-frequency control01:28

Load-frequency control

603
Load-frequency control (LFC) is vital for maintaining power system stability, ensuring that frequency and power flows remain within acceptable limits during load changes. Turbine-governor control eliminates rotor accelerations and decelerations following load changes. However, a steady-state frequency error persists when the change in the turbine-governor reference setting is zero. In an interconnected power system, each area agrees to export or import a scheduled amount of power through...
603
Carrier Generation and Recombination01:22

Carrier Generation and Recombination

1.2K
Carrier generation is the process by which electron-hole pairs (EHPs) are created within the semiconductor. In direct-bandgap semiconductors, such as gallium arsenide (GaAs), this occurs efficiently when energy absorption prompts valence electrons to leap into the conduction band, leaving behind holes.
This process is given by the generation rate G and is efficient due to the conservation of momentum between the valence band maximum and conduction band minimum.
Indirect generation involves an...
1.2K
IR Frequency Region: X–H Stretching01:24

IR Frequency Region: X–H Stretching

1.4K
In IR spectroscopy, signals produced by the X−H bonds (such as C−H, O−H, or N−H) can be observed in the frequency range of  2700–4000 cm–1. The C−H stretching vibration forms sharp bands in the region 2850–3000 cm–1. The presence of the O−H stretching vibration leads to the forming of an absorption band in the frequency range 3650–3200 cm−1. At the same time, N−H stretching can be confirmed by absorption bands in...
1.4K
Atomic Nuclei: Larmor Precession Frequency01:11

Atomic Nuclei: Larmor Precession Frequency

2.7K
The earth's gravitational field produces a 'twisting force' perpendicular to the angular momentum of a spinning mass (such as a spinning top) that causes the mass to 'wobble' around the gravitational field axis in a phenomenon called precession. Similarly, the magnetic moment (μ) of a spinning nucleus precesses due to an external magnetic field directed along the z-axis. The precession of the magnetic moment vector about the magnetic field is called Larmor precession,...
2.7K
IR Frequency Region: Fingerprint Region01:03

IR Frequency Region: Fingerprint Region

1.8K
IR spectra are divided into two main regions: the diagnostic region and the fingerprint region. The diagnostic region of the spectrum lies above 1500 cm−1. The absorptions resulting from single-bond vibrations of the N–H, C–H, and O–H stretch at higher wavenumbers and appear on the left side of the spectrum. The stretching absorptions of the C≡C and C≡N occur between 2100–2300 cm−1. In contrast, those arising from stretching absorptions of the...
1.8K

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相关实验视频

Updated: Jan 11, 2026

Construction and Characterization of External Cavity Diode Lasers for Atomic Physics
09:10

Construction and Characterization of External Cavity Diode Lasers for Atomic Physics

Published on: April 24, 2014

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对于卫星间连贯激光通信中载波的任意频差锁定方法.

Weijie Ren, Yuhao Zhang, Peipei Hou

    Optics express
    |November 11, 2025
    PubMed
    概括

    一种新的载波频率锁定方法解决了卫星间激光通信中的漂移,减少了位误差率 (BER). 这种技术通过精确跟踪激光频率来确保稳定的通信,这对于可靠的数据传输至关重要.

    科学领域:

    • 光学通信是指光学通信.
    • 卫星技术 卫星技术 卫星技术
    • 信号处理 信号处理

    背景情况:

    • 卫星间连贯激光通信中的载波频率漂移,由多普勒转移和激光不稳定引起,增加了位误差率 (BER).
    • 这种漂移可能导致星座旋转和通信性能下降.
    • 现有的方法很难弥补显著的频率变化.

    研究的目的:

    • 设计和验证载波任意频差锁定方法,用于卫星间连贯激光通信.
    • 克服载波频率漂移在维持稳定的通信链路方面的局限性.
    • 提高激光通信系统的可靠性和降低激光通信系统的BER.

    主要方法:

    • 使用了激光内部调制和相位和正方位 (IQ) 直角调制的原理.
    • 开发了一种用于任意频差锁定的方法,适用于二进制相位移开关键 (BPSK) 和正方位相位移开关键 (QPSK) 信号.
    • 在不同的条件下,量化频率锁定错误,包括多普勒频率转移的缺失和存在.

    主要成果:

    • 该方法成功地锁定了BPSK的±240 MHz和QPSK的±120 MHz内的载波频率差异.
    • 频率锁定错误的标准偏差为26.1kHz (BPSK) 和29.2kHz (QPSK),没有多普勒转移.

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  • 在QPSK信号的±5.2 MHz/s多普勒转移下,频率锁定错误的标准偏差为149.4 kHz.
  • 结论:

    • 拟议的方法有效地将局部振荡器载波频率跟踪到光信号载波频率.
    • 允许随后的解调算法利用更多的带宽来减轻激光相位噪声.
    • 确保低位误差率 (BER) 提供强大的卫星间连贯激光通信.