A recent study published in Light | Science & Applications introduces a novel method for fabricating optical Fresnel zone plate (FZP) flat lenses. By using colored photoresists and an i-line stepper, researchers have streamlined the production process, enhancing both precision and cost-effectiveness. This approach has the potential to support a wide range of light manipulation and imaging applications, addressing the growing demand for miniaturized optical components in modern technology.
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Advancements in Optical Technology
Modern optical technologies, including telecommunications, imaging systems, and consumer electronics, rely heavily on controlling and manipulating light. However, traditional refractive lenses often struggle with miniaturization because they depend on physical thickness to function effectively.
This limitation has sparked interest in planar lens technologies, such as diffractive optical elements and metasurfaces. These advanced designs use sub-wavelength structures to reduce lens size and thickness. However, producing these advanced lenses, especially those designed for visible wavelengths, often requires complex and expensive methods, including precise lithography and specialized etching techniques, which limit their scalability.
FZPs offer an alternative. These diffractive optical elements use concentric rings to focus light through constructive interference. Unlike metasurfaces, they don’t require high-aspect-ratio structures, making them easier and more cost-effective to produce using standard photolithography methods.
A New Fabrication Process
The researchers developed a simple method to fabricate visible FZP planar lenses suitable for mass production. Using an i-line stepper and colored photoresists, they eliminated the need for etching and other complex post-processing steps.
The process involved three colored photoresists—red, green, and blue—selected for their specific absorption properties in the visible spectrum. These were spin-coated onto 8-inch silica glass wafers, exposed to ultraviolet light through a photomask, and then developed. This created amplitude-type diffractive optical elements with precise microscopic patterns.
Using corresponding color resists, the researchers designed FZP lenses to operate at 450 nm, 550 nm, and 650 nm wavelengths. These lenses were constructed based on the principle of diffraction, featuring alternating opaque and transparent regions that focus light through constructive interference.
Key Findings
The fabricated lenses achieved a focusing efficiency of 7.2 % at 550 nm, with a minimum focal spot diameter of 1.1 μm. Under optimal conditions with monochromatic light, the efficiency increased to 10.9 %. Numerical simulations closely matched experimental results, underscoring the reliability of this fabrication process.
The lenses also demonstrated high-resolution imaging capabilities, resolving features as small as 1.1 μm when tested with a USAF resolution chart. The streamlined process, which involves only coating, exposure, and development, offers a scalable solution for producing large-scale optical components. Its compatibility with existing semiconductor fabrication techniques makes it particularly relevant for applications like smartphone cameras and imaging systems.
Potential Applications in the Optical Industry
This research offers valuable advancements in optics and photonics. The fabrication process for FZP lenses provides a cost-effective and scalable method to produce high-performance optical components. These lenses can improve imaging resolution in microscopy applications, aiding biological and material science research, and enhance medical imaging technologies such as endoscopes and optical coherence tomography.
In optical sensors, the lenses enable precise monitoring in environmental and industrial contexts. They also have potential applications in telecommunications, where they could contribute to more efficient optical systems for faster data transmission. Additional uses include improvements in smartphone cameras, lightweight optics for augmented and virtual reality devices, beam shaping in medical and industrial laser systems, and the development of optical components for quantum computing and information processing.
The incorporation of colored photoresists simplifies the manufacturing process while allowing optical properties to be adjusted for specific applications. This adaptability supports the creation of tailored optical solutions for various contemporary technologies.
Future Directions in FZP Lens Development
This approach marks a notable advancement in the fabrication of FZP lenses, particularly for visible light applications.
Ongoing research will focus on refining these methods, investigating advanced materials to improve lens performance, and incorporating the lenses into existing technologies. Real-world testing will be crucial for evaluating their functionality and scalability to meet industry requirements.
Journal Reference
Yamada, R., et al. (2025) Optical Fresnel zone plate flat lenses made entirely of colored photoresist through an i-line stepper. Light Sci Appl. DOI: 10.1038/s41377-024-01725-6, https://www.nature.com/articles/s41377-024-01725-6
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