Hydrogel‐Based Diffractive Optical Elements (hDOEs) Using Rapid Digital Photopatterning

Abstract

Inspired by natural systems, microstructural modification has been exploited as a promising strategy to introduce new optical properties to conventional materials such as manipulation of light based on diffraction or diffraction optical elements (DOEs). [15-18] These DOEs have become increasingly important in biomedical applications ranging from imaging to diagnostics to sensing. [19-22] In the past decades, the DOEs are mostly made of conventional optical materials such as glass, semiconductor, and metals. Nonetheless, the inherent lack of mechanical flexibility and biocompatibility of these materials render their use difficult for in vitro and in vivo biophotonics applications. Hydrogels, due to their unique optical transparency and biocompatibility, provide a good alternative to conventional optical materials. Several natural and synthetic hydrogels, such as, silk, chitin, chitosan, bovine serum albumin, polyacrylamide, polyacrylic acid, and PEGDA have been used to make hydrogel based DOEs or hDOEs with optical performance comparable to conventional materials. [22-28] However, competing challenges such as high resolution, ease/cost of manufacturing, and customization of design based on target applications, prevent its widespread use in the field. At present, hDOEs such as diffraction grating, holographic components, and Fresnel zone plates (FZP) are fabricated using indirect and direct methods. [7,22,26,29-31] Indirect methods, such as mask-based photolithography, inverse opals, soft lithography, and nanoimprinting, require use of expensive physical masks, and time-consuming iterative optimization to fabricate hDOEs. On the other hand, direct methods such as electron beam lithography, direct laser writing, and multibeam interference lithography do not require physical mask to fabricate high-resolution hDOEs, however challenges with scalability and long processing/fabrication times remain. The aforementioned challenges have to be addressed to meet the high demand for hDOEs in the field; this would require an ability to rapidly design and manufacture customized hDOEs based on the needs of target applications. In this work, we report the design and printing of customized DOEs on synthetic PEGDA hydrogel using digital photopatterning technology, which combines digital projection photolithography [32-39] with computer-generated holography. [40-42] In this work, simulated computer-generated holography (SCGH) was used to generate customized digital patterns based on DOE Hydrogels, due to their optical transparency and biocompatibility, have emerged as an excellent alternative to conventional optical materials for biomedical applications. Advances in microfabrication techniques have helped convert conventional hydrogels into optically functional materials such as hydrogel-based diffraction optical elements (hDOEs). However, key challenges related to device customization and ease/speed of fabrication need to be addressed to enable widespread utility and acceptance of hDOEs in the field. Here, rapid printing of customiz...

Equilateral triangle hexagonal array by crossing two one‐dimensional Dammann gratings with 60°

“…As can be seen from Reference 25, although the uniformity is better than our work, the uniformity is not improved excluding the zeroth order energy. In Reference 27, since the scattering light from central zeroth diffraction order affects the intensity profile, only the intensity uniformity in X direction and Y direction are given, which are 0.05 and 0.13 respectively. It can be seen that the uniformity in the X direction is close to our experimental result, but the uniformity in the Y direction is not as good as our result.…”

“…Normally, a two‐dimensional array generator can be constructed by using two crossed one‐dimensional Dammann grating patterns 25,27 . However, in these works, rectangular arrays are generated, which are not dense enough in the diagonal direction.…”

λ/12 Super Resolution Achieved in Maskless Optical Projection Nanolithography for Efficient Cross-Scale Patterning

“…As a promising alternative, the maskless optical projection lithography technique using a digital mirror device (DMD) which consists of hundreds of thousands of individually addressable moving micromirrors to spatially modulate light with a fast, flexible, and highly efficient capability for dynamic pattern generation, − has exhibited the potential for fabricating large-scale microstructures with high throughput. However, the resolution of this technique stops at the submicrometer scale due to the optical diffraction barrier .…”

“…1.45, Nikon). Figure b shows that the light intensity distribution on the focus plane from a line image (one pixel in the x -direction and multiple pixels in the y -direction) generated by DMD has a Gaussian distribution. , …”

“…Figure 1b shows that the light intensity distribution on the focus plane from a line image (one pixel in the x-direction and multiple pixels in the y-direction) generated by DMD has a Gaussian distribution. 17,26 The main components of the non-CA negative photoresist AR-N 7520 are bisazide as cross-linker and novolak as monomer (Figure 1c and Figure S2). There are two absorption peaks, one at 283 and one at 316.5 nm (Figure S3).…”