In a groundbreaking study, researchers at the University of Illinois Urbana-Champaign have made significant strides in the development of compact, visible wavelength achromats. By utilizing 3D printing and porous silicon, these high-performance hybrid micro-optics offer exceptional focusing efficiencies while minimizing volume and thickness. The potential applications of these microlenses are vast, ranging from achromatic light-field imagers to wearable devices. The study, led by materials science and engineering professors Paul Braun and David Cahill, electrical and computer engineering professor Lynford Goddard, and former graduate student Corey Richards, was published in Nature Communications.
The Problem of Color-Blurred Images
In many imaging applications, such as white light imaging, multiple wavelengths of light are present. When a single lens is used to focus this light, different wavelengths focus at different points, resulting in color-blurred images. Traditionally, multiple lenses are stacked together to form an achromatic lens, where all the colors focus at the same point. However, the challenge lies in the thickness of the lens stack, making it unsuitable for compact technological platforms like ultracompact visible wavelength cameras and portable microscopes.
An Innovative Solution
To address this issue, the research team combined a refractive lens with a flat diffractive lens to create a much thinner lens. The bottom lens, known as the diffractive lens, focuses red light closer, while the top lens, called the refractive lens, focuses red light further away. These two lenses cancel each other out and focus to the same spot, resulting in an achromatic lens. The integration of these elements provides the necessary functionality of a classical compound optic in a highly miniaturized form.
In order to fabricate the compact hybrid achromatic imaging system, the researchers developed a fabrication process called Subsurface Controllable Refractive Index via Beam Exposure (SCRIBE). This process involves 3D printing polymeric structures in a porous silicon host medium, which serves as mechanical support for the optical components. By filling the porous silicon with liquid polymer and using an ultrafast laser to convert it into a solid polymer, the team was able to integrate the diffractive and refractive elements of the lens without the need for external supports. This method not only minimized volume and increased ease of fabrication but also provided high-efficiency achromatic focusing.
One of the key advantages of utilizing porous silicon is the seamless integration of multiple lenses. Unlike traditional methods that require building support structures, the researchers found that by suspending the lenses over each other in porous silicon, the integration became much more seamless. This unique feature allows for the stacking of lenses without the need for external support structures, streamlining the fabrication process.
The development of compact hybrid achromatic microlenses opens up new possibilities in capturing larger area images. By constructing arrays of these microlenses, light-field information can be captured, overcoming a significant challenge faced by conventional polymer microlenses, which are generally not achromatic. This breakthrough paves the way for applications such as light-field cameras and light-field displays, revolutionizing the field of optics.
The research conducted by the University of Illinois Urbana-Champaign represents a significant advancement in the field of compact, visible wavelength achromats. By combining 3D printing and porous silicon, the research team has achieved high-performance hybrid micro-optics that offer high focusing efficiencies while minimizing volume and thickness. The innovative fabrication process, Subsurface Controllable Refractive Index via Beam Exposure (SCRIBE), allows for the integration of diffractive and refractive elements without the need for external support structures. With the potential to construct arrays of these achromatic microlenses, the possibilities for achromatic light-field imagers and displays are vast. This research sets the stage for a new era of compact, lightweight optics that will revolutionize various industries and technological platforms.
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