What is Phase Light Modulation?

Phase Light Modulation (PLM) is a way to shape monochromatic light by controlling the phase of the wavefront pixel-by-pixel. Instead of turning pixels “on or off,” a PLM chip slightly delays or advances the reflected light at each pixel. Those tiny delays create a programmable phase pattern. When the phase-shaped light travels, the waves interfere with each other and form the desired intensity pattern at the image plane.

Texas Instruments’ PLM is a MEMS micromirror array derived from DLP technology, but operated in piston mode: each micromirror moves up and down in multiple discrete height levels to impose a controllable phase shift on the reflected beam.

In short:
PLM doesn’t directly “direct brightness.” It “directs phase,” and brightness appears through interference downstream.

What is different to Digital Light Processing?

DLP uses a tilting micromirror array. Each mirror flips between two angles to send light either into the optics (“on”) or away from them (“off”). That is amplitude modulation, controlling brightness by blocking/redirecting light.

PLM uses a similar MEMS mirror array, but with a crucial difference:

• DLP: mirrors tilt - binary on/off intensity pixels.
• PLM: mirrors move up or down – interference pattern is defined by the grating.

This changes what the device is good at:

• DLP is ideal for projecting images by intensity with a classical optic path.
• PLM is ideal for wavefront shaping: beam steering, holography, multi-spot patterns, and arbitrary illumination profiles created by diffraction / computer-generated holograms.

In short:
DLP tilts mirrors to switch light on/off (amplitude control), while PLM moves mirrors up/down to set phase delays (phase-only control).

Why use PLM?

PLM is used when you want to not just control intensity distribution but also phase.

Key highlights are:

1. No OFF-light
   Because PLM redistributes light via phase instead of blocking it, far less power is wasted compared to amplitude modulators.
2. High speed
   TI uses its efficient design for high-speed DMD manipulation, meaning that the PLM-chip can move with up to 5 kHz.
3. High power handling & robustness
   The reflective MEMS architecture tolerates higher laser power densities.
4. Phase-only control enables “programmable optics”
   With the right phase map, one PLM chip can generate single spots, multi-spots, lines, top-hat profiles, grayscale dose distributions, or complex structured illumination including holographics - purely by software.

In short:
PLM enables efficient, high-speed, high-power software-defined beam shaping by redistributing light instead of wasting it.

Where to use PLM?

PLM is best wherever a system needs laser-based, programmable light distributions rather than simple on/off pixels, including in more than one image plane.

• Computer-generated holography (CGH) & holographic projection
  Producing complex images or intensity patterns from phase maps.
• Beam steering / scanning without moving parts
  Real-time steering of a laser into one or multiple directions using blazed gratings and CGHs.
• Industrial lithography & direct imaging
  Writing lines, vias, or arbitrary dose profiles with high efficiency and fast reconfiguration.
• Additive manufacturing / resin curing / volumetric exposure
  Creating multi-spot or grayscale exposure patterns to optimize throughput and feature control.
• Infrared/defense photonics applications
  Where polarization independence, power handling, and rugged MEMS operation matter

In short:
Use PLM for programmable laser patterns like holography/CGH, beam steering, LiDAR/3D sensing, volumetric additive manufacturing and adaptive optics.

All about IN-VISION's PLM Development Kit