Three-dimensional (3D) printing, pioneered in the 1980s, has revolutionized manufacturing by enabling the layer-by-layer additive construction of complex stereoscopic structures. Unlike traditional subtractive methods, 3D printing allows for intricate geometries and the binding of multiple materials, leading to innovations across various fields. Applications range from aerospace manufacturing (e.g., enhancing material properties in aircraft turbines) to personalized medicine (e.g., creating customized drug delivery systems). The resolution of 3D printing, defined by the voxel size (the smallest printable element), varies greatly depending on the technique employed. While macro-scale 3D printers with millimeter-scale voxels are common, achieving micro/nanoscale resolution remains a challenge. Stereolithography (STL), a photopolymerization-based technique, shows promise for high-resolution 3D printing. In STL, a liquid photopolymer is cured into a solid structure by exposure to light of a specific wavelength. The laser's energy distribution directly influences the cured voxel size, with smaller focal spots leading to higher resolution. However, conventional STL systems are limited to resolutions of approximately 5 µm due to limitations in focal spot size. Femtosecond laser-based systems can achieve nanoscale resolution, but their high cost, complex optics, limited printing area, and the need for intricate stitching processes hinder widespread adoption. Therefore, there is a need for a cost-effective and high-resolution 3D printing method that overcomes these limitations. This paper introduces a novel approach that utilizes a readily available and inexpensive component: the optical pickup unit (OPU) from a gaming console.

Existing research on cost-effective nanoscale photopolymerization has explored using low-cost ultraviolet light-emitting diodes (UV LEDs) for large-area nanoscale lithography. However, these systems require two-stage optical setups, limiting their ability to create multi-layer 3D structures. Other approaches have used less expensive diode lasers, but these often rely on expensive 3D printers and high-numerical-aperture objective lenses, maintaining the high cost and complexity. Furthermore, these systems often require a stitching process to achieve larger printing areas, adding complexity. The use of optical pickup units (OPUs) from optical storage devices (like Blu-ray, DVD, and CD drives) has been explored for applications such as atomic force microscopy and photolithography, showcasing their potential for high-precision applications. These OPUs offer a compact, integrated light source and optics at a significantly lower cost than traditional solutions for nanoscale lithography. However, their adaptation to 3D micro/nanoscale printing was not fully explored before this paper.

This study proposes the use of an HD-DVD OPU extracted from an Xbox 360 gaming console as a cost-effective solution for high-resolution 3D printing. The HD-DVD OPU offers a longer working distance (1.25 mm) compared to Blu-ray OPUs, enhancing flexibility for STL 3D printing. It also includes multiple-wavelength (405/650/780 nm) continuous wave semiconductor laser diodes, expanding compatibility with various photopolymers and curing wavelengths. The OPU's integrated astigmatic optical path and photodiode integrated circuit (PDIC) provide a focus error signal (FES) for closed-loop laser focusing, enhancing precision. The voice coil motor in the OPU is used for substrate parallelism correction and real-time fine-tuning of the printing level. The researchers designed an inverted STL system, where the laser spot is directed upwards. The 3D printer consists of XYZ linear stages (with resolutions of 312.5 nm and 62.5 nm for XY and Z axes, respectively), a tilt stage, a substrate holder, a photopolymer vat, and a control system with an embedded controller, OPU driver, and motor driver. The system uses the OPU's embedded sensors to measure the distance between the focal spot and the substrate surface with nanoscale resolution via the FES. The substrate surface and OPU focal plane are precisely aligned using the XY linear stage and tilt stage. A non-curing laser wavelength (e.g., 650 nm, 780 nm) is utilized for substrate levelling when a 405 nm photopolymer is in the vat. Once levelled, the Z-axis linear stage raises the substrate for layer-by-layer printing, controlled via G-code commands. The optical design software Zemax OpticStudio 20.1 was used to simulate the laser spot size at different photopolymer thicknesses. Experiments were conducted to evaluate the influence of photopolymer thickness and laser exposure dose (by adjusting printing speed and laser intensity) on cured line width. Finally, various 3D microstructures were fabricated to demonstrate the system's capabilities. The cured structures were analysed using scanning electron microscopy (SEM).

The researchers successfully demonstrated that a modified HD-DVD OPU from a gaming console could be used for high-resolution 3D printing. Through optical simulations and experiments, they determined the impact of photopolymer thickness and laser exposure dose on printing resolution. Reducing the photopolymer thickness resulted in a smaller and more concentrated focal spot, leading to higher resolution. The experiments showed that the cured line width was significantly influenced by photopolymer thickness, with thinner layers resulting in narrower lines. By optimizing these parameters, they achieved a nanoscale printing resolution of 385 nm along the lateral direction, which is significantly better than commercially available STL printers. The use of the OPU's built-in FES and voice coil motor enabled closed-loop control, significantly improving the accuracy and precision of the printing process. This allowed them to fabricate various 3D microstructures, including pyramids, towers, cylinders, and structures with overhanging features, without the need for stitching. The achieved printing volume was up to 50 × 50 × 25 mm³. The use of a silicon substrate enhanced the adhesion of the printed structures. The analysis of a cross-section contour of a 385 nm wide line revealed a non-Gaussian laser energy distribution, potentially due to optical aberrations. While the system demonstrated high lateral resolution, limitations in vertical resolution and potential issues due to inconsistent photopolymer thickness were observed. The study also noted that the use of G-code commands for creating curved surfaces resulted in some surface discontinuity. Enlarged corners were also observed in the printed structures, likely due to motor speed variations and laser energy accumulation near corners.

This research demonstrates a significant advancement in affordable high-resolution 3D printing. The utilization of a readily available, low-cost OPU from a gaming console provides a compelling alternative to expensive femtosecond laser-based systems. The system's closed-loop control mechanism, leveraging the OPU's built-in sensors and actuators, significantly enhances printing accuracy and reduces reliance on external sensors. The ability to achieve nanoscale lateral resolution (385 nm) opens up new possibilities for fabricating complex microdevices for various applications, including drug delivery, microactuators, and micro-optical components. The significant reduction in cost and complexity compared to existing high-resolution 3D printing techniques makes this technology more accessible to a wider range of researchers and industries. Further improvements could focus on enhancing vertical resolution, addressing the issue of inconsistent photopolymer thickness, and implementing more sophisticated G-code commands for creating smoother curved surfaces.

This study successfully demonstrated a novel, cost-effective, and high-resolution 3D printing system using an off-the-shelf optical pickup unit. The system achieved a lateral resolution of 385 nm, surpassing commercially available systems. The use of the OPU's integrated features simplifies the system's design and enhances control. Future research could focus on improving vertical resolution, optimizing photopolymer handling, and exploring parallel printing using arrays of OPUs to increase throughput. The system holds significant promise for various applications requiring intricate micro/nanoscale structures.

The current system exhibits some limitations, particularly regarding vertical resolution and the consistency of photopolymer thickness. Inconsistent thickness could potentially lead to variations in laser energy distribution and affect the quality of the printed structures. The use of G-code for defining curved surfaces resulted in some degree of surface discontinuity, suggesting improvements are needed in the path planning algorithms. The enlarged corners observed in some printed structures indicate a need for further optimization of laser intensity control, particularly around corners. Further investigation is warranted to fully address these limitations.