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Updated: Oct 22, 2026

Shaping the Amplitude and Phase of Laser Beams by Using a Phase-only Spatial Light Modulator
Published on: January 28, 2019
Beam control method of a liquid crystal spatial light modulator based on fractional-order active disturbance
Chunyang Wang1, Wenliang Feng2, Xuelian Liu1
1Xi'an Key Laboratory of Active Optoelectronic Imaging Detection Technology, Xi'an Technological University, Xi'an 710021, Shaanxi, China.
Abstract:
The viscoelasticity and relaxation of liquid crystal molecules make the beam deflection dynamics of the liquid crystal spatial light modulator present a memory effect depending on historical states, which integer-order control cannot characterize, causing sluggish response and poor accuracy. FOPID lacks disturbance observation and compensation capability and can only suppress disturbances passively through error feedback. A fractional-order active disturbance rejection control method is proposed: a fractional-order extended state observer estimates the internal and external disturbances as a total disturbance and compensates them by feed-forward; a Smith predictor cancels the time delay; FOPSO-GWO tunes the controller parameters. It reduces settling time and steady-state error while improving deflection accuracy and robustness.
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