Spectrometers with ever-smaller footprints are sought after for a wide range of applications in which minimized size and weight are paramount, including emerging in situ characterization techniques. We report on an ultracompact microspectrometer design based on a single compositionally engineered nanowire. This platform is independent of the complex optical components or cavities that tend to constrain further miniaturization of current systems. We show that incident spectra can be computationally reconstructed from the different spectral response functions and measured photocurrents along the length of the nanowire. Our devices are capable of accurate, visible-range monochromatic and broadband light reconstruction, as well as spectral imaging from centimeter-scale focal planes down to lensless, single-cell–scale in situ mapping.

This work presents an original approach to create holograms based on the optical scattering of plasmonic nanoparticles. By analogy to the diffraction produced by the scattering of atoms in X-ray crystallography, we show that plasmonic nanoparticles can produce a wave-front reconstruction when they are sampled on a diffractive plane. By applying this method, all of the scattering characteristics of the nanoparticles are transferred to the reconstructed field. Hence, we demonstrate that a narrow-band reconstruction can be achieved for direct white light illumination on an array of plasmonic nanoparticles. Furthermore, multicolor capabilities are shown with minimal cross-talk by multiplexing different plasmonic nanoparticles at subwavelength distances. The holograms were fabricated from a single subwavelength thin film of silver and demonstrate that the total amount of binary information stored in the plane can exceed the limits of diffraction and that this wavelength modulation can be detected optically in the far field.holography | nanotechnology | optics M etallic nanoparticles have been used for centuries to create vibrant colors in works of art. The Lycurgus cup (fourth century), for example, uses metallic nanoparticles to produce a dichroic effect. The nanoparticles are positioned randomly, and the optical characteristics can be approximated using its effective refractive index. Their spectra response depends on the size, shape, and material of the nanoparticles (1). This phenomenon is analogous to the electronic resonance of an antenna in the visible region of the electromagnetic spectrum. In photonics, behavior of this kind is attributed to the interaction of the electric component of light and free electron oscillations in the materials, commonly referred to as surface plasmon resonance (SPR). Although this phenomenon has always fascinated scientists, only over recent years has it been possible to accurately manipulate these structures on the nanoscale due to improved fabrication techniques. In this work, we show a novel approach to produce narrow-band diffraction and holography based on plasmonic enhanced optical scattering of nanostructures. The diffraction produced by the scattering of atoms has been widely studied in X-ray crystallography. We apply a similar concept with 2D arrays of scattering nanoparticles to produce diffraction for visible light. Furthermore, we designed and fabricated a directbeam hologram that produces a narrow-band image when directly observed in reflection. We also achieved colorful holography by placing two independent plasmonic nanostructures in a subwavelength distance to diffract two colors simultaneously. In contrast with dielectric multiplexing of nansutructures, we show that metallic nanoparticles can be uncoupled because of their plasmonic properties. This feature allows them to carry independent wavelength information without cross-talk.In the traditional concept of holography, the fringes that produce diffraction are larger than half the wavelength. For instance, accor...

Tunable narrowband spectral filtering across arbitrary optical wavebands is highly desirable in a plethora of applications, from chemical sensing and hyperspectral imaging to infrared astronomy. Yet, the ability to reconfigure the optical properties, with full reversibility, of a solid-state large-area narrowband filter remains elusive. Existing solutions require either moving parts, have slow response times, or provide limited spectral coverage. Here, we demonstrate a 1-inch diameter continuously tunable, fully reversible, all-solid-state, narrowband phase-change metasurface filter based on a GeSbTe-225 (GST)-embedded plasmonic nanohole array. The passband of the presented device is ∼ 74 n m with ∼ 70 % transmittance and operates across the 3–5 µm thermal imaging waveband. Continuous, reconfigurable tuning is achieved by exploiting intermediate GST phases via optical switching with a single nanosecond laser pulse, and material stability is verified through multiple switching cycles. We further demonstrate multispectral thermal imaging in the mid-wave infrared using our active phase-change metasurfaces. Our results pave the way for highly functional, reduced power, compact hyperspectral imaging systems and customizable optical filters for real-world system integration.

Snapshot multispectral image (MSI) sensors have been proposed as a key enabler for a plethora of multispectral imaging applications, from diagnostic medical imaging to remote sensing. With each application requiring a different set, and number, of spectral bands, the absence of a scalable, cost-effective manufacturing solution for custom multispectral filter arrays (MSFAs) has prevented widespread MSI adoption. Despite recent nanophotonic-based efforts, such as plasmonic or high-index metasurface arrays, large-area MSFA manufacturing still consists of many-layer dielectric (Fabry–Perot) stacks, requiring separate complex lithography steps for each spectral band and multiple material compositions for each. It is an expensive, cumbersome, and inflexible undertaking, but yields optimal optical performance. Here, we demonstrate a manufacturing process that enables cost-effective wafer-level fabrication of custom MSFAs in a single lithographic step, maintaining high efficiencies (∼75%) and narrow line widths (∼25 nm) across the visible to near-infrared. By merging grayscale (analog) lithography with metal–insulator–metal (MIM) Fabry–Perot cavities, whereby exposure dose controls cavity thickness, we demonstrate simplified fabrication of MSFAs up to N-wavelength bands. The concept is first proven using low-volume electron beam lithography, followed by the demonstration of large-volume UV mask-based photolithography with MSFAs produced at the wafer level. Our framework provides an attractive alternative to conventional MSFA manufacture and metasurface-based spectral filters by reducing both fabrication complexity and cost of these intricate optical devices, while increasing customizability.

We demonstrate spectrally-tunable Fabry-Perot bandpass filters operating across the MWIR by utilizing the phasechange material GeSbTe (GST) as a tunable cavity medium between two (Ge:Si) distributed Bragg reflectors. The induced refractive index modulation of GST increases the cavity's optical path length, red-shifting the passband. Our filters have spectral-tunability of ~300 nm, transmission efficiencies of 60-75% and narrowband FWHMs of 50-65 nm (Q-factor ~70-90). We further show multispectral thermal imaging and gas sensing. By matching the filter's initial passband to a CO2 vibrational-absorption mode (~4.25 µm), tunable atmospheric CO2 sensing and dynamic plume visualization of added CO2 is realized.