Tunable Tamm plasmon cavity as a scalable biosensing platform for surface enhanced resonance Raman spectroscopy.

Surface enhanced Resonance Raman spectroscopy (SERRS) is a powerful technique for enhancing Raman spectra by matching the laser excitation wavelength with the plasmonic resonance and the absorption peak of biomolecules. Here, we propose a tunable Tamm plasmon polariton (TPP) cavity based on a metal on distributed Bragg reflector (DBR) as a scalable sensing platform for SERRS. We develop a gold film-coated ultralow-loss phase change material (Sb2S3) based DBR, which exhibits continuously tunable TPP resonances in the optical wavelengths. We demonstrate SERRS by matching the TPP resonance with the absorption peak of the chromophore molecule at 785 nm wavelength. We use this platform to detect cardiac Troponin I protein (cTnI), a biomarker for early diagnosis of cardiovascular disease, achieving a detection limit of 380 fM. This scalable substrate shows great promise as a next-generation tunable biosensing platform for detecting disease biomarkers in body fluids for routine real-time clinical diagnosis.

Erratum: Roadmap for phase change materials in photonics and beyond.

[This corrects the article DOI: 10.1016/j.isci.2023.107946.].

Roadmap for phase change materials in photonics and beyond.

Phase Change Materials (PCMs) have demonstrated tremendous potential as a platform for achieving diverse functionalities in active and reconfigurable micro-nanophotonic devices across the electromagnetic spectrum, ranging from terahertz to visible frequencies. This comprehensive roadmap reviews the material and device aspects of PCMs, and their diverse applications in active and reconfigurable micro-nanophotonic devices across the electromagnetic spectrum. It discusses various device configurations and optimization techniques, including deep learning-based metasurface design. The integration of PCMs with Photonic Integrated Circuits and advanced electric-driven PCMs are explored. PCMs hold great promise for multifunctional device development, including applications in non-volatile memory, optical data storage, photonics, energy harvesting, biomedical technology, neuromorphic computing, thermal management, and flexible electronics.

Electrically Tunable Steganographic Nano-Optical Coatings.

Thin film coatings with tunable colors have a broad range of applications, from solid-state reflective displays to steganography. Here, we propose a novel approach to chalcogenide phase change material (PCM)-incorporated steganographic nano-optical coatings (SNOC) as thin film color reflectors for optical steganography. The proposed SNOC design combines a broad-band and a narrow-band absorber made up of PCMs to achieve tunable optical Fano resonance in the visible wavelength, which is a scalable platform for accessing the full-color range. We demonstrate that the line width of the Fano resonance can be dynamically tuned by switching the structural phase of PCM from amorphous to crystalline, which is crucial for obtaining high-purity colors. For steganography applications, the cavity layer of SNOC is divided into an ultralow loss PCM and a high index dielectric material with identical optical thickness. We show that electrically tunable color pixels can be fabricated using the SNOC on a microheater device.

Wide-Angle Tunable Critical Coupling in Nanophotonic Optical Coatings with Low-Loss Phase Change Material.

Realizing perfect light absorption in stacked thin films of dielectrics and metals through critical light coupling has recently received intensive research attention. In addition, realizing ultra-thin perfect absorber and tunable perfect absorber in the visible spectrum is essential for novel optoelectronics applications. However, the existing thin film stacks cannot show tunable perfect absorption in a wide-angle range. Here, a tunable perfect absorption from normal incidence to a wide-angle range (0° to 70°) by utilizing a two-layer stack consisting of a high refractive index low-loss dielectric on a high reflecting metal is proposed. This is experimentally demonstrated by depositing a thin layer of low-loss phase change material such as stibnite (Sb2 S3 ) on a thin layer of silver. This structure shows tunable perfect absorption with large spectral tunability in the visible wavelength. Furthermore, the absorption enhancement in 2D materials by transferring monolayer molybdenum disulfide on the stack, which shows 96% light absorption with enhanced photoluminescence, is demonstrated. In addition, the thin film stack can work as a scalable phase modulator offering a maximum phase tunability of ≈140° by changing the structural state of Sb2 S3 from amorphous to crystalline.

Plasmon Resonant Silica-Coated Silver Nanoplates as Contrast agents for Optical Coherence Tomography.

Silica-coated silver nanostructures are identified as potential contrast agents for visible and near-infrared bio-imaging applications due to their high optical extinction caused by localized surface plasmon resonance (LSPR), improved chemical stability, and lower toxicity. We demonstrate the potential of plasmon resonant silica-coated silver nanoplates as a contrast agent for optical coherence tomography (OCT). It is shown that, triangular-shaped silica-coated silver nanoplates (SSNPs) with a side length of 170 ± 5 nm, base silver thickness of 10 ± 1 nm, and silica shell thickness of 40 ± 2 nm, exhibit higher optical extinction at a 1300 nm wavelength range, thus making them an excellent contrast agent for OCT imaging. Optical extinction characterization using OCT is found to be reasonably consistent with ultraviolet (UV)-Vis-near infrared (NIR) spectroscopy and finite difference time-domain (FDTD)-based analysis. Ex vivo studies on pig adipose tissue demonstrate that LSPR-induced enhanced scattering in SSNPs contributes to the OCT signal, leading to images with better contrast. Moreover, average A-scan profiles acquired at different time delays show the downward propagation of SSNPs and the extension of signal enhancement at the deeper regions. Speckle variance OCT images show that SSNPs are efficiently distributed over the targeted tissue region, demonstrating their applicability in a large lesion area.

Design and characterization of low loss 50 picoseconds delay line on SOI platform.

We design and experimentally demonstrate 50 picoseconds (ps) low loss delay line on 300 nm SOI platform. The delay line unit consists of straight rib waveguide and strip bend section linked by a transition taper waveguide. Low propagation loss of ~0.1 dB/cm is achieved on the straight rib waveguide. With taking into account both low loss and desirable delay, a complete design and characterization process for passive delay line is presented. Our measurement results show that about 0.7 dB excess loss is achievable for 50 ps delay. The loss can be further reduced by adjusting the layout parameters.

Ultra-compact low loss polarization insensitive silicon waveguide splitter.

We observe that the cascaded typical Y junctions will introduce unwanted periodic fringes over the spectrum in practical systems when they link with multimode waveguides. To solve the problem, we design and experimentally demonstrate a wavelength insensitive multimode interferometer (MMI) based 3-dB splitter which has all the merits of Y-splitters such as polarization insensitivity and ultra-compactness. The splitter has a footprint of 1.5 × 1.8 µm(2), nearly one order smaller than the previously reported MMI splitters. The measured excess losses for TE and TM modes at telecom wavelength are as low as -0.11 dB and -0.18 dB respectively.