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Related Concept Videos

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

Time and frequency -Domain Interpretation of Phase-lead Control

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...
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,...
Small-Signal Analysis of MOSFET Amplifiers01:23

Small-Signal Analysis of MOSFET Amplifiers

In small-signal analysis, a MOSFET transistor amplifier acts as a linear amplifier when operating in its saturation region. The gate-to-source voltage (VGS) of the MOSFET is the sum of the DC biasing voltage and the small time-varying input signal. This combination sets up the operating point and modulates the drain current (ID) that flows from the drain to the source. When a small AC signal is superimposed on the DC bias voltage at the gate, the instantaneous drain current comprises three...
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...
Linear Approximation in Frequency Domain01:26

Linear Approximation in Frequency Domain

Linear systems are characterized by two main properties: superposition and homogeneity. Superposition allows the response to multiple inputs to be the sum of the responses to each individual input. Homogeneity ensures that scaling an input by a scalar results in the response being scaled by the same scalar.
In contrast, nonlinear systems do not inherently possess these properties. However, for small deviations around an operating point, a nonlinear system can often be approximated as linear.
Node Analysis for AC Circuits01:14

Node Analysis for AC Circuits

Consider an angioplasty system featuring a catheter equipped with a turbine, a critical tool for removing plaque deposits from coronary arteries. This intricate medical device operates using a circuit model reminiscent of a dual-node RLC circuit powered by a current-controlled voltage source.
To unravel the complexities of this system, nodal analysis is employed, a powerful technique founded on Kirchhoff's current law (KCL), which remains valid for phasors. AC circuits can effectively be...

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Related Experiment Video

Updated: Jun 19, 2026

Shaping the Amplitude and Phase of Laser Beams by Using a Phase-only Spatial Light Modulator
08:39

Shaping the Amplitude and Phase of Laser Beams by Using a Phase-only Spatial Light Modulator

Published on: January 28, 2019

Semiconductor laser phase-noise cancellation using an electrical feed-forward scheme.

Mahmood Bagheri1, Firooz Aflatouni, Alireza Imani

  • 1Department of Electrical Engineering-Electrophysics, University of Southern California, Los Angeles, California 90089-0271, USA.

Optics Letters
|October 2, 2009
PubMed
Summary
This summary is machine-generated.

This study reduces semiconductor laser phase noise using an electrical feed-forward scheme. This method offers significant noise reduction and potential linewidth narrowing for lasers.

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Last Updated: Jun 19, 2026

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Published on: January 28, 2019

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Area of Science:

  • Photonics
  • Semiconductor device physics
  • Optical communications

Background:

  • Semiconductor lasers are crucial for optical communications but suffer from phase noise.
  • Existing phase noise reduction techniques often have limitations in bandwidth, stability, and speed.
  • Minimizing phase noise is essential for improving laser performance and enabling advanced applications.

Purpose of the Study:

  • To demonstrate an electrical feed-forward scheme for reducing phase noise in semiconductor lasers.
  • To investigate the effectiveness of this scheme on a commercial distributed-feedback (DFB) laser.
  • To assess the potential for significant linewidth reduction using this approach.

Main Methods:

  • Implementation of an electrical feed-forward control system.
  • Experimental validation using a 1550 nm distributed-feedback (DFB) semiconductor laser.
  • Characterization of phase noise power spectrum before and after applying the feed-forward scheme.

Main Results:

  • Achieved over a 20-fold reduction in the phase noise power spectrum.
  • Demonstrated that the feed-forward scheme avoids bandwidth, stability, and speed limitations of feedback systems.
  • Showcased the potential for complete phase noise cancellation in the absence of electronic noise.

Conclusions:

  • The electrical feed-forward scheme effectively reduces phase noise in semiconductor lasers.
  • This method offers advantages over traditional feedback systems, including higher speed and stability.
  • The approach holds promise for reducing laser linewidth by 3-4 orders of magnitude using advanced transistors.