In their quest to create miniaturized and lightweight optics, researchers at the University of Illinois Urbana-Champaign have successfully developed compact, visible wavelength achromats using 3D printing and porous silicon. This breakthrough in materials science and engineering has enormous potential for various applications in imaging technology. The innovative hybrid micro-optics developed by the team offer high focusing efficiencies while significantly reducing volume and thickness. This article explores the research conducted by professors Paul Braun, David Cahill, Lynford Goddard, and former graduate student Corey Richards, as published in Nature Communications.
In many imaging applications, especially those involving white light, multiple wavelengths are present. When a single lens is used to focus this light, different wavelengths focus at different points, resulting in a color-blurred image. To solve this problem, traditional achromatic lenses stack multiple lens elements together to achieve a unified focus across all colors. However, the thickness of a classical achromatic lens proves impractical for modern technological platforms requiring miniaturization. The development of achromatic lenses suitable for ultracompact visible wavelength cameras, portable microscopes, and wearable devices becomes a necessity.
To address the limitations of traditional achromatic lenses, the researchers fused a refractive lens with a flat diffractive lens to create a much thinner hybrid achromatic imaging system. The functionality of this lens is achieved by canceling out the different focal points of various wavelengths, ensuring a unified focus. The bottom lens, a diffractive lens, focuses red light closer, while the top lens, a refractive lens, focuses red light further. Through the combination of these two lenses, the researchers achieved achromatic focusing in a substantially thinner lens.
The research team introduced a novel fabrication process called Subsurface Controllable Refractive Index via Beam Exposure (SCRIBE) to create the hybrid achromatic lens. Using 3D printing, the researchers printed polymeric structures within a porous silicon host medium that mechanically supports the optical components. This approach eliminates the need for external support structures when stacking lenses. The liquid polymer filled into the porous silicon is converted into solid polymer using an ultrafast laser, resulting in the integration of refractive and diffractive elements. Not only does this process enhance ease of fabrication, but it also minimizes volume and improves efficiency in achromatic focusing.
By utilizing porous silicon as a host medium for the 3D printed lenses, the researchers achieved seamless integration of the lens components. Unlike traditional methods where support structures are required for each lens, the unique properties of porous silicon allow for the suspension of two lenses over each other. The integration becomes much more streamlined, demonstrating the benefits of using porous silicon in the fabrication process.
The compact hybrid achromatic imaging system opens up exciting possibilities in various fields. Notably, the ability to construct arrays of these hybrid achromatic microlenses allows for the capturing of light-field information. Traditional polymer microlenses are generally not achromatic, making the achievement of light-field information a significant challenge. However, with the development of these hybrid microlenses, applications such as light-field cameras and light-field displays become a reality.
The innovative combination of 3D printing and porous silicon has revolutionized the field of optics. The creation of compact, visible wavelength achromats using these techniques allows for miniaturization, lightweight design, and high-performance focusing efficiencies. The researchers at the University of Illinois Urbana-Champaign have overcome the limitations of traditional achromatic lenses, paving the way for the next generation of ultracompact imaging devices and wearable technology. The SCRIIBE fabrication process showcases the potential of integrating refractive and diffractive lens elements, improving ease of fabrication and overall efficiency. As technology continues to advance, the applications of these hybrid achromatic microlenses will undoubtedly expand, providing infinite possibilities in the world of optics.
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