Emerging Digital Micromirror Device Based Systems and Applications XVII

The formation of three-dimensional objects through the tomographic reconstruction of a patterned light dose, also known as computed axial lithography (CAL), is enabled by careful co-optimization of the reactive material’s composition, the algorithm that computes the delivered light patterns, and the opto-mechanical system that delivers the light. To approach industrially relevant component sizes, spatial resolution, and dimensional accuracy, work is needed on all three of these technological pillars. Firstly, I will describe recent progress in formulating ceramic-photopolymer nanocomposites where careful selection of particle geometry, mixing protocol, and illumination wavelength offer a path towards CAL printing. Secondly, I will describe a first-principles approach to modeling the aggregate scattering behavior of such materials, based on Mie scattering theory, to aid in the computation of projected light patterns. Thirdly, I will explore some physical considerations for scaling up the printing volume of CAL systems. Finally, I will describe some ongoing work to expand the range of CAL-printable materials to those shaped by ring-opening metathesis polymerization.

In tomographic volumetric additive manufacturing (VAM), 3D objects are printed by irradiating a rotating body of photocurable resin with time-varying near-UV light patterns. Operating a VAM printer requires significant user skill and familiarity. In particular, the correct UV exposure time is estimated before or manually during printing. This results in poor repeatability and wasted resin, resulting from variation in printing rates due to resin history, object geometry, and temperature variability. In this talk we will present a robust approach to automatic print exposure setting by quantifying the side-scattered light signal, allowing the user to walk away from the printer during printing. The print is terminated automatically when print completion is detected. To demonstrate the accuracy of this technique, we will present objects built with multiple VAM-printed parts, VAM-printed mechanical metamaterials, and x-ray computed tomography scans of test objects to quantify print fidelity.

This presentation about Tomographic Volumetric Additive Manufacturing (TVAM) shows that advances in the computer graphics literature can be leveraged to build a more general optimization framework for TVAM pattern generation. We show that obtaining suitable projection patterns can be formulated as an inverse light transport problem. We present Dr.TVAM, a new open-source framework that implements a physically-based differentiable renderer suited to TVAM, producing high-quality patterns. This approach can account for various printing process effects like refraction and scattering, and outperforms prior methods.

In this talk we present improvements and novel printing results obtained with our differentiable ray optical framework (called Dr. TVAM) for Tomographic Volumetric Additive Manufacturing (TVAM). In TVAM different 2D patterns are illuminated on a rotating vial containing a photosensitive resin. Dr. TVAM produces patterns which outperform printing results in scattering media by simulating the ray optical propagation physically. Also, for the first time we print in a square vial without index matching bath. And for striation mitigation we print in a tilted TVAM geometry where the light illumination is not perpendicular to the rotation axis.

The use of additive manufacturing to produce Graded Index (GRIN) lenses has taken the forefront in the search for new design techniques. While multiphoton direct laser writing and inkjet technologies are the leading technologies into this venture, digital light processing (DLP) printers have scarcely been investigated. Using the principles of partial polymerization and a conversion prediction model designed to restrict polymerization exposure, DLP printers can be utilized to generate spatial conversion gradients which further enables the tuning of refractive index profiles. Following the production of a GRIN lens, both optical and chemical characterization must be performed to verify proper performance has been achieved. Recent advances in model development and characterization techniques have displayed more accurate results and produced parts on par with equivalent AM techniques. This work aims to utilize the grayscale capabilities of DLP 3D printers alongside an in-house developed model to produce GRIN lenes with performance approaching the diffraction limit.

To meet future demands for microelectronic devices – dimensional, environmental, functional – new fabrication technologies are sought after. Manufacturing technologies that minimise the footprint of such devices while concurrently integrating electronics with microfluidics and other functionalities. This is made possible by printing electronics at high resolution and incorporating and interconnecting bare die chips. At Holst Centre, we have been developing a new multi-material additive manufacturing technology to meet the demands stated before. “3D Additive Lithography for Electronics” combines high-resolution direct imaging lithography with groove filling of conductive metal pastes to build structural electronics with down to 10 µm feature sizes. The structural material, a photopolymerisable resin, is patterned using a DMD-based light engine that scans over the build area. A custom-built foil recoating solution provides fresh resin to the build area as the printing progresses, and industry-standard metal pastes are used to interconnect incorporated functional components in the 100 µm to 1 mm size range.

Recent developments in Volumetric Additive Manufacturing (VAM) have demonstrated the potential to print intricate objects using a more efficient light engine based on coherent light patterns encoded in Lee holograms displayed on a digital micromirror device (DMD) within a holographic configuration. Here we present an implementation of a Phase-only Spatial Light Modulator (PLM), a piston-mode design of a DMD for Holographic Volumetric Additive Manufacturing (HOLOVAM) based on reverse tomography. In this work, we characterize the PLM at 405nm and measure the diffraction efficiency. By synchronizing the laser, the rotation stage, and the PLM, we experimentally demonstrate the printing of centimeter-scale objects with diffraction-limited resolution in less than one minute. The PLM opens new avenues for Tomographic VAM with low-cost single mode UV laser diodes.

As DLP® Products at Texas Instruments, Inc. approaches mass production for its phase-only spatial light modulator (PLM), it builds on its decades of experience in manufacturing and testing digital micro-mirror devices (DMD) to launch a high-quality new product. Demonstrating a new test flow on a prototype tester, DLP has been developing new methodologies and parametrics to evaluate PLMs for high volume production. This paper discusses key device parametrics and how they are used to grade device operation, performance, and quality. The relevance of the metrics will be grounded in how the device operates and how the test hologram is affected by variance in the metric. As part of this discussion, the phase hologram used to extract the parametrics will be covered and why specific holograms were chosen.

Adaptive optics (AO) systems are widely used in astronomy, microscopy, and vision science for removing optical aberrations. One critical component of each AO system is the corrector, which commonly utilizes deformable mirrors, liquid crystal spatial light modulators, and deformable phase plates. The key properties to consider when choosing a corrector include spatial resolution, speed, and dynamic range. For highly dynamic and turbulent applications, such as terrestrial Free Space Optical Communications (FSOC), the existing correctors have key tradeoffs in speed and resolution which limit their performance. A fast and high-actuator count corrector with sufficient dynamic range is needed. In this paper, we introduce a Texas Instruments Phase Light Modulators (TI-PLM) based AO system. Our work demonstrates the first steps towards a fast and high-resolution AO system using a 0.67” TI-PLM and considerations for integrating the device into a FSOC system.

Infrared (IR) beam steering using the Texas Instruments Phase Light Modulator (TI-PLM) as a quasi-solid-state beam steering device to replace fast steering mirror (FSM) components in systems that need to be mechanically robust. Simulation and experimental results are presented to discuss capabilities and limitations.

Phase Light Modulators (PLMs) are a recently developed type of micro-electromechanical system (MEMS)-based Spatial Light Modulator (SLM). PLMs consist of 2D mega-pixel arrays of micromirrors, each of which can be raised or lowered with 4-bit precision at switching speeds of <50 µs. These features mean PLMs have the potential to outperform existing SLM technology in high-dimensional adaptive optics applications. In this work, we demonstrate in-situ aberration correction using a PLM. We characterize and correct the phase curvature of the PLM chip, and demonstrate high-fidelity, high-efficiency, and fast-switched diffractive beam shaping.

Digital micromirror devices (DMDs) allow for complex wavefront shaping with their unique advantage of modulation speeds reaching up to a few tens of kilohertz. Here, we have developed a method called the fast line-scanning amplitude-encoded scattering-assisted holography (FLASH) technique to further increase the speed of complex wavefront shaping by three orders of magnitude using a DMD. By converting spatial degrees of freedom into temporal degrees of freedom, the FLASH technique achieves three-dimensional control of micron-sized foci at a speed of 30 MHz, though at the cost of focal contrast. Potential applications include 3D laser-scanning microscopy, laser micromachining, and high-speed beam scanning.

Structuring the fundamental degrees of freedom of optical beams has exploded as a research area in recent years. DMDs have become a common method to generate these fields. In this work, we address some remaining hurdles to reducing the size, complexity and ease of use of systems able to generate vector beams (beams with inhomogeneous polarization). We analyse some of the design considerations for higher efficiency and remove crosstalk to increase the possible complexity of the beams produced. An increase in the azimuthal index of Laguerre-Gaussian modes from 4 to 15 has been observed. Finally, we built a feedback system to get the resolution of alignment and realignment to sub-300 microns. These improvements and techniques aid in improved dissemination in application areas outside of physics and optics such as chemistry, microscopy, communication and optical characterisation.

We propose an energy-efficient dispersion compensation method, based on a dispersive prism, for DMD. This method first simulates the diffraction of the optical field reflected from the DMD with an angular spectrum model. According to the simulation, a prism and a set of optical components are introduced to compensate for the angular dispersion of DMD-modulated optical fields. In the experiment, our method reduced the angular dispersion, between the 532 nm and 660 nm light beams, by a factor of ∼8.5.

A novel approach for a ghost imaging measurement method is presented, combining the single-detector measurement technique with a coded aperture approach to detect and quantify the surface fluorescence effect as two-dimensional information and to determine the fluorescence lifetime. A lock-in approach and estimation of the phase information of harmonically modulated illumination light up to 10MHz are used to improve the signal sensitivity and make the measurement method suitable for multiple applications, especially in highly light-polluted environments. The combination of these methods enables an amplitude and phase measurement of the samples to be evaluated to determine an amplitude and phase reconstruction numerically depending on the modulation frequency to characterize the surface fluorescence effect and to determine the fluorescence lifetime down to 100ns. With this new measurement method, different samples, e.g. solar cells, polymers or other composite materials, can be examined, realizing the scalability of the measurement system for various applications.

Hadamard Transform Spectral Imaging (HTSI) is a technique used to recover spectra via encoding with multi-slit masks, and is particularly useful in low photon flux applications where non-signal dependent noise is the dominant source of noise. This work focuses on the procedure that is used to recover spectra encoded with multi-slit masks generated from a Hadamard matrix; the decoding process involves multiplying the output encoded spectral images by the inverse of the Hadamard matrix, which separates any spectra that were overlapping in the target object.

In this paper, we present a novel calibration method for the FPP system that enables the adoption of arbitrary patterns where patterns are not eligible to be known before the projection. The calibration process include solving PnP problem and adopts pixel-wise calibration method. During the calibration process, a novel phase artifacts removal method has been developed. Circular and hyperbolic patterns were successfully tested in the experiment, and the results demonstrate the effectiveness of the proposed method. We expect this research to broaden the spectrum of patterns and the variety of projector devices for the FPP system.

Whispering gallery mode (WGM) microtoroid resonators are ultra-sensitive biochemical sensors. Traditional coupling using tapered optical fibers is fragile and requires precise alignment. Here we demonstrate free-space coupling using a digital micromirror device and an objective lens. Using this approach, we are able to achieve ultra-high Q-factors in excess of 100 million. This innovation paves the way for the creation of a robust, portable, ultra-sensitive biological and chemical sensing platform.

The urgent need for sustainable, cost-effective long-term data storage remains unmet due to the finite lifespans of current storage media. Cerabyte addresses this with an innovative optical storage solution, ablating matrices of bits onto a ceramic film on ultra-thin glass sheets for virtually indefinite data preservation without degradation. Using fs-laser pulses, special beam shaping and a DMD, it achieves high data throughput rates. Cerabyte’s low power usage and recyclable media significantly reduce total ownership costs and environmental impact, making it a superior alternative for data centres and archives.

SlitLED introduces a telemedicine examination system enhancing access to eye care. This system allows patients to receive comprehensive eye examinations at convenient point-of-care locations, conducted remotely by an eye physician. The century-old, primary tool of eye physicians, the 'Slit Lamp', is unsuitable for telemedicine. Additionally, camera-equipped devices do not provide an adequate alternative, as the quality heavily depends on the skills of the non-clinician local operator. The presented approach incorporates a DLP projector and stereo imaging, replacing the traditional bulb with mechanical slit illumination and binocular microscope. Image acquisition is automated and completes in less than a second, with a series of slits projected onto the eye, and corresponding images captured synchronously. This method eliminates the need for time-consuming mechanical movements and thus minimizes the impact of the patient's eye movements. Equipped with advanced capabilities, the system ensures that acquisition quality and consistency are independent of the operator’s clinical skills, providing a robust solution for remote ophthalmic examinations and enhancing in-person setups.

Optical diffraction tomography (ODT) maps 3D refractive index (RI) distributions. RI maps provide valuable biophysical information, which aiding precise assessment of physiological states. Current ODT systems using visible light limit depth to few cell layers due to multi-scattering. We propose the use 1.3 µm illumination in ODT that avoids high water absorption and reduces the scattering, while maintaining ~ 1 µm resolution. We tested the imaging depth using homemade turbid solution that has similar attenuation length as brain tissues. We are now exploring the capabilities of the system for in vivo imaging applications.