Researchers at Tsinghua University have developed a volumetric 3D printing method that produced millimetre-scale polymer structures in as little as 0.6 seconds. Called digital incoherent synthesis of holographic light fields (DISH), the method uses holographically optimized light projections delivered through a high-speed rotating periscope, removing the need to rotate the resin container during printing.
Published in Nature, the research addresses the trade-off between resolution and volumetric build rate in additive manufacturing. Using a 0.055-NA objective, the team reports a stable printing resolution of around 19 μm across a 1 cm range, with the finest independent positive features measuring approximately 12 μm. The method was demonstrated using several acrylate-based and hydrogel materials, including PEGDA, DPHA, BPAGDA, GelMA, SilMA, and UDMA.
Volumetric additive manufacturing forms complete 3D objects by controlling light dose throughout a volume of photosensitive material. Existing methods such as computed axial lithography can produce complex parts without the layer-by-layer process used in stereolithography or digital light processing. However, many systems rely on rotating the sample to deliver projections from multiple angles. This can limit speed, introduce alignment issues, and make in situ printing harder to implement.
DISH avoids this by keeping the container fixed and rotating the projection path instead. A digital micromirror device (DMD) generates light patterns at high speed, while a periscope placed in front of the objective lens changes the projection angle. The DMD patterns are synchronized with the rotation angle, allowing multiple light fields to combine inside the resin and form the target 3D dose distribution.
The researchers used a coherent 405 nm laser source and a wave-optics-based algorithm to calculate the projected light fields. This was necessary because, at higher resolution, diffraction and defocus effects become significant. According to the paper, this enabled high-resolution modulation across a depth range of up to 1 cm using the 0.055-NA objective, more than 20 times larger than its native depth of field.
Holographic optimization enables high-resolution volumetric printing
To produce the required 3D light distributions, the team developed a coarse-to-fine iterative algorithm. The first stage calculates coarse 3D dose distributions for different projection angles. The second stage refines groups of binary DMD patterns using a holographic propagation model that accounts for wave optics and refraction at the air-material interface.
The authors compared their method with previous penalty minimization approaches used in computed axial lithography and with a global Gerchberg–Saxton algorithm. In simulations, DISH produced more accurate 3D dose distributions, measured using the Jaccard index and signed distance errors. The researchers selected 1,800 binary projections per rotation cycle for practical experiments, corresponding to 180 coarse 3D dose distributions.
Because high-speed, high-resolution volumetric printing is sensitive to optical errors, the researchers also developed an adaptive-optics-based calibration method. Fluorescent images captured by two orthogonal cameras were used to detect beam misalignment, allowing the DMD patterns for each projection angle to be shifted and corrected. The paper states that this calibration process can be completed within a few minutes and does not require hardware modification once the system is fixed.
Experimental tests showed that DISH maintained high-resolution optical features at positions away from the focal plane. Triple-dot patterns with 10.8 μm features and 10.8 μm gaps were projected at different axial positions. Conventional backprojection degraded away from the printing centre, while the holographically optimized method preserved the features at positions 4.8 mm from the centre.
To evaluate printing resolution, the team fabricated several test structures, including relief stripes, dense stripe patterns, a fishbone model, a star, a triangular pyramid, and a conch model. Relief structures printed across a 1 cm axial length showed linewidths of 11.0 ± 1.2 μm. Independent positive features in a fishbone model measured 11.9 ± 2.1 μm, while lines on the conch model measured 19.3 ± 3.4 μm across different directions and axial positions.
Negative features were also tested using an inner conical model, where the diameters of inscribed circles were measured at around 50 μm. The team further printed a Theodoric statue and compared the printed part with X-ray computed tomography data to evaluate fidelity.
Flow-based setup supports successive production
The researchers integrated DISH with a fluidic channel to demonstrate successive production of 3D structures. In this setup, a pump moves printed products away from the exposure area and replenishes the material, while a strainer collects printed parts and separates uncured material for reuse. In the demonstrated flow-based setup, each sample was exposed for 0.6 seconds.
Unlike mould-based mass production, the system can fabricate different objects in succession. Demonstrated geometries included cube frames, tetrahedron frames, flowers, squids, spinal cord slice-like structures, bifurcated tubes, a Benchy model, and a Theodoric statue. Helical and bifurcated tubes were also printed to show possible relevance for biological applications.
Material compatibility was tested using multiple photocurable materials. Rigid structures were printed with DPHA and BPAGDA, hydrogel tubes were printed with GelMA and SilMA, and elastic parts were printed with UDMA. The tested inks ranged from low-viscosity PEGDA hydrogel at 4.734 cP to higher-viscosity acrylate resins above 500 cP.
In the discussion, the authors calculate a maximum volume printing rate of approximately 333 mm³/s, based on an effective printable volume of about 200 mm³ and an exposure time of 0.6 seconds. They report a voxel printing rate of 1.25 × 10⁸ voxels/s using a voxel size of 11 μm × 11 μm × 22 μm.
The researchers note that several factors still affect print quality, including material response, dose contrast, diffusion, speckle noise, and the missing-cone problem introduced by single-side illumination, which can reduce axial resolution relative to lateral resolution. Future improvements could come from better dose-control algorithms, DMDs with smaller pixels or larger pixel counts, GPU acceleration, neural-network-based hologram generation, and modified periscope designs.
Volumetric 3D printing targets projection and light-control limits
Recent volumetric additive manufacturing research has focused on how light is delivered, controlled, and computed inside photosensitive materials. Last June, researchers from École Polytechnique Fédérale de Lausanne (EPFL) introduced a holographic tomographic VAM system using a MEMS-based phase-only light modulator. The system was developed to improve light efficiency and reduce speckle noise, two factors that can affect print quality in coherent-light volumetric printing.
Researchers from Beihang University and The Hong Kong Polytechnic University have also targeted the projection bottleneck in VAM. Their sparse-view irradiation processing method reduced the number of required projections from more than 1,000 to as few as 15 for complex objects, while cutting light-pattern computation time from over an hour to about seven minutes. DISH addresses a related constraint from a different direction, replacing sample rotation with a rotating projection path while using holographic optimization to preserve resolution across a larger depth range.
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Featured image shows a diagram showing the DISH volumetric 3D printing method, which uses a rotating periscope to project holographically optimized light fields into a fixed resin container. Image via Wang et al.
