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Related Concept Videos

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

Time and frequency -Domain Interpretation of Phase-lag Control

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 finite,...
Time and frequency -Domain Interpretation of Phase-lead Control01:24

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Phase-lead controllers are commonly used in various control systems to enhance response speed and stability. Adjusting the brightness on a television screen offers a practical example of phase-lead control. When contrast is enhanced, a phase-lead controller is employed. Mathematically, phase-lead control is identified when the first parameter is smaller than the second.
The design of phase-lead control involves the strategic placement of poles and zeros to balance steady-state error and system...
Phase-lead and Phase-lag Controllers01:22

Phase-lead and Phase-lag Controllers

Understanding the working function of different types of controllers can be illustrated with practical analogies, such as adjusting a stereo's volume equalizer. Cranking up the bass involves a phase-lead controller, which functions as a high-pass filter, while increasing the treble uses a phase-lag controller, which acts as a low-pass filter. PD controllers, similar to high-pass filters, enhance the system's response to high-frequency components. PI controllers, akin to low-pass filters, manage...

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Updated: Jun 19, 2026

Automation of Mode Locking in a Nonlinear Polarization Rotation Fiber Laser through Output Polarization Measurements
14:18

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Published on: February 28, 2016

Mode locking in semiconductor lasers by phase-conjugate optical feedback.

G R Gray, D H Detienne, G P Agrawal

    Optics Letters
    |October 28, 2009
    PubMed
    Summary
    This summary is machine-generated.

    Phase-conjugate feedback using four-wave mixing can achieve mode locking in semiconductor lasers. This method directly couples laser modes, enabling ultrashort pulse generation under continuous pumping.

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    Area of Science:

    • Optics and Photonics
    • Semiconductor Physics
    • Laser Technology

    Background:

    • Multilongitudinal-mode semiconductor lasers are crucial for various applications.
    • Achieving stable mode locking in these lasers, especially under continuous pumping, remains a challenge.
    • Traditional optical feedback methods have limitations in controlling longitudinal mode interactions.

    Purpose of the Study:

    • To theoretically investigate the potential of phase-conjugate optical feedback for mode locking semiconductor lasers.
    • To explore the mechanism by which phase-conjugate feedback influences longitudinal modes.
    • To demonstrate the feasibility of generating ultrashort mode-locked pulses using this technique.

    Main Methods:

    • Theoretical analysis using computer simulations.
    • Modeling of phase-conjugate optical feedback realized through four-wave mixing.
    • Investigation of the coupling between longitudinal modes under phase-conjugate feedback.

    Main Results:

    • Phase-conjugate feedback directly couples pairs of longitudinal modes.
    • Specific strengths of phase-conjugate reflectivity lead to the locking of mode phases and beat frequencies.
    • Continuous-wave pumping combined with phase-conjugate feedback results in mode-locked ultrashort pulse generation.

    Conclusions:

    • Phase-conjugate feedback is a viable method for achieving mode locking in semiconductor lasers.
    • This technique offers a novel approach to generating ultrashort pulses from lasers under continuous pumping.
    • The direct coupling of longitudinal modes by phase-conjugate feedback is key to the observed mode-locking phenomenon.