The Tabanidae has a unique eye structure that structural color filter in cornea display advantages for color vision system. The combination of color filter layers and ommatidia can provide the advantages of miniaturization, and multispectral imaging. We report an ultrathin multi-spectral camera inspired by the structure of Tabanidae vision system. The ultrathin multi-spectral camera consists of Fabry-Perot color filter arrays, microlens arrays with chrome aperture, and a CMOS image sensor. The fully packaged camera shows a FWHM under 31nm, a total track length of 1mm. This provides new opportunity for point-of-care testing (POCT) and medical applications.
Focused light field cameras utilize microlens arrays (MLAs) as an imaging system to obtain spatial and angular information. MLAs are efficiently fabricated by thermal reflow whereas MLAs formed by thermal reflow have relatively small f-numbers, resulting in small depth-of-field. Here we report a focused light field camera with large f-number by incorporation solid immersion MLAs. Solid immersion using PDMS spin coating over conventional MLAs facilitates large-area fabrication of large f-number MLAs using refractive index differences. Solid immersion MLAs extend depth-of-field several times. This method can broaden focused light field camera application range.
High-speed imaging provides an opportunity to access detailed information in various biomedical fields. However, conventional high-speed cameras still suffer from slow framerates or difficulty to resolve dense information. This study presents a compact ultrafast camera by combining a compound eye camera inspired by the nature insect with an offset array. OFAC is packaged within 10.4 × 8.3 × 1.5 mm3 excluding image sensor boards, and successfully resolves high-temporal image sequences up to 91,200 framerate. The proposed ultrafast compound eye camera will provide new methods to approach miniaturized high-speed biomedical imaging.
We report a fiber-optic plasmonic probe with nanogap-rich gold nanoislands for on-site surface-enhanced Raman spectroscopy (SERS). The plasmonic probe features nanogap-rich Au nanoislands on the top surface of a single multimode fiber. Au nanoislands were monolithically fabricated using repeated solid-state dewetting of thermally evaporated Au thin film. The plasmonic probe shows 7.8 × 106 in SERS enhancement factor and 100 nM in limit-of-detection for crystal violet under both the excitation of laser light and the collection of SERS signals through the optical fiber. The fiber-through measurement also demonstrates the label-free SERS detection of folic acid at micromolar level. The plasmonic probe can provide a tool for on-site and in vivo SERS applications.
Eyes of insects in the nature have been evolved in assorted structures according to the place of residence, hours of living, or the way of perception. The structure of the insect eye not only has different composition that dissolve the incoming light according to its direction of origin, i.e., an apposition and a superposition eyes, but also has a wide field-of-view (FOV), a high spatial resolution, and a sensitivity. Conventional artificial compound eye cameras have limited features that only focus on one of the characteristics of the insect eye, such as lens diameter and lens barrel length. We report an optically adjustable ultrathin arrayed camera, which adjusts the FOV, lens diameter and focal length independently. The ultrathin arrayed camera consists of UV-curable resin based microlens array on CMOS image sensor and each lens is surrounded by a liquid-filled blocking layer to reduce optical cross-talks between neighboring lenses. Fabrication of the arrayed lens includes photolithography process of Au/Cr metal pattern on frontside and Cr pattern on backside of borosilicate glass. Each of the lenses are replicated from microhole arrays fabricated by isotropic wet etching of the borosilicate glass with HF (49%) etchant. The arrayed camera has adjustable lens diameter and curvature by etching time control and SU-8 post thickness control during photolithography. Fingerprint image was successfully obtained by an image processing from individual optical channels. This ultrathin arrayed camera will suggest a new approach to the development of light-filled camera and compact ultrathin camera in the medical, industrial, or military fields.
Perforated periodic nanostructures (i.e. nanohole arrays) have become of great alternatives for transmissive structural coloration due to high transmission efficiency and high sensitivity upon incident angles. However, structural colors of conventional periodic nanostructures inevitably exhibit a substantial color-crosstalk due to the multiple resonances. Our previous work (M.-S. Ahn et al., nanoscale) had already reported that the complementary plasmonic structures (CPS) effectively attenuate the high-order resonances, and thus improve color-purity in the range from VIS (red) to NIR.
In this work, we successfully demonstrated transmissive structural coloration with high color-purity in fully visible ranges by using inverted CPS (iCPS) of aluminum (Al) nanoholes and nanodisks. Unlike previous Ag CPS, the Al iCPS features inverted configuration of suspended nanoholes and buried nanodisks by high refractive index (polyurethane acrylate; PUA) substrate, which blue-shifts the resonances of Al nanoholes and redshifts the extinction dip of Al nanodisks. As a result, carefully engineered extinction dip effectively suppresses the first-order resonance of Al nanoholes, and thus iCPS exhibit a pure visible-coloration with a single resonance, depending on the incident angles.
iCPS were nanofabricated by UV nanoimprinting lithography (UV-NIL) and thermal evaporation of aluminum, which enables uniform nanopattering with inch scale. Polyurethane acrylate (PUA) was used for a substrate due to its high refractive index and UV-curable property. After the replication of nanohole patterns into PUA, aluminum was evaporated on PUA nanohole substrate. Then the Al nanoholes are formed on top surface of PUA and Al nanodisks are buried in PUA nanohole. Structural coloration of iCPS provides a new direction for a tunable optical filter that highly requires tunability and selectivity.
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