[Paper Review] Holographic Volumetric Additive Manufacturing

Maria Isabel Álvarez-Castaño, Andreas Gejl Madsen+4 more|arXiv (Cornell University)|Jan 24, 2024

Advanced Optical Imaging Technologies7 citations

TL;DR

The paper demonstrates holographic phase modulation for volumetric additive manufacturing, achieving at least 10x projection efficiency improvement, diffraction-limited resolution, and rapid fabrication of millimetric 3D objects using a DMD-based holographic setup with Lee encoding and tiling to reduce speckle.

ABSTRACT

3D printing has revolutionized the manufacturing of volumetric components and structures in many areas. Different technologies have been developed including light-induced techniques based on the photopolymerization of liquid resins. In particular, a recently introduced method, so-called Tomographic Volumetric AM (VAM), allows the fabrication of mesoscale objects within tens of seconds without the need for support structures. This method works by projecting thousands of amplitude patterns, computed via a reverse tomography algorithm, into a resin from different angles to produce the desired three-dimensional shape when the resin reaches the polymerization threshold. To date, only amplitude modulation of the patterns has been reported. Here, we show that holographic phase modulation unlocks new capabilities for VAM printing. Specifically, the effective light projection efficiency is improved by at least a factor of 10 over amplitude coding; the resolution can reach the light diffraction limit; and phase encoding allows to control ballistic photons in scattering media, which potentially increases the volume of 3D objects that can be printed in opaque and non-absorbing resins. The approach uses CGH to convert phase, encoded on a 2D modulator to the desired intensity projections by light propagation in a photosensitive resin container. We demonstrate the potential of holographic phase coding using simulations and experiments, the latter by implementing a volumetric printer using a DMD, as the 2D phase modulator in a Fourier configuration. Specifically, we use Lee holograms to encode phase onto a binary DMD. Combining tiled holograms with PSF shaping mitigates the speckle noise typically associated with computer-generated holograms and speed-up their computation. We use these holographic projections to fabricate millimetric 3D objects in less than a minute with a resolution down to 164 um.

Motivation & Objective

• Motivate holographic phase coding to enhance volumetric additive manufacturing.
• Show that phase modulation enables higher light efficiency and finer resolution than amplitude-only methods.
• Demonstrate practical implementation using spatial light modulators and holographic encoding techniques.
• Assess ability to print millimetric 3D objects in under a minute with improved image quality.

Proposed method

• Use computer-generated holography (CGH) to convert phase encoded on a 2D modulator into the desired intensity projections within a photosensitive resin.
• Employ Lee holograms to encode phase onto a binary DMD in a Fourier configuration.
• Combine tiled holograms with point-spread function (PSF) shaping to mitigate speckle noise and accelerate computation.
• Project thousands of holographic projections from multiple angles to create the target 3D shape via tomographic volumetric AM principles.
• Demonstrate simulations and experiments, including a DMD-based volumetric printer, achieving resolution down to 164 μm and printing millimetric objects in under a minute.

Experimental results

Research questions

• RQ1 Can holographic phase modulation improve light projection efficiency in volumetric additive manufacturing compared to amplitude-only methods?
• RQ2 What resolution and printing speed can be achieved with phase-encoded holographic VAM in scattering or opaque resins?
• RQ3 How do tiled holograms and PSF shaping affect speckle noise and computational throughput in holographic VAM?
• RQ4 Is it feasible to realize a practical holographic VAM printer using a DMD in a Fourier configuration with Lee encoding?

Key findings

• Phase modulation increases effective light projection efficiency by at least a factor of 10 versus amplitude coding.
• Resolution can reach the light diffraction limit in the demonstrated system.
• Phase encoding allows potential control of ballistic photons in scattering media, expanding printable volume.
• A DMD-based holographic VAM printer in Fourier configuration with Lee holograms can fabricate millimetric 3D objects in under one minute.
• Tiled holograms combined with PSF shaping mitigate speckle noise and speed up hologram computation.