phaseonly

Phase-only refers to modulation schemes in which only the phase component of an optical or electromagnetic field is altered, while the amplitude remains fixed or is not independently controllable. In optics, the complex light field can be written as E(x,y) = A(x,y) exp[iφ(x,y)]. Phase-only devices aim to realize a target phase φ(x,y) without changing A. This is typically achieved with phase-only spatial light modulators based on liquid crystal on silicon (LCOS) or related technologies, which impart a spatially varying phase shift over 0 to 2π with a finite number of discrete levels.

In practice, phase-only modulation is used to shape wavefronts for imaging, holography, and beam control. Phase-only spatial light modulators (SLMs) are common tools, sometimes combined with Fourier optics in 4f configurations to realize complex field distributions. The devices are sensitive to wavelength, polarization, and viewing angle, and they introduce quantization of phase that can affect fidelity.

Applications of phase-only systems include beam shaping for laser machining, optical trapping, and adaptive optics in astronomy, as well as holographic displays and pupil-plane phase masks for improved imaging performance. Phase-only encoding techniques attempt to encode a desired intensity pattern or complex field using only phase manipulation, often employing iterative algorithms such as the Gerchberg–Saxton method or related phase retrieval methods to approximate targets.

Limitations and performance trade-offs include limited diffraction efficiency, speckle noise, polarization dependence, and quantization error from finite phase levels. Despite these, phase-only approaches remain widely used for their relative simplicity, robustness, and ability to control wavefronts without amplitude modulators.