Theoretical and experimental studies of mid-infrared (mid-IR) suspended membrane waveguide (SMW) and suspended membrane ring (SMR) resonator are presented. An array of periodical holes beside the rib waveguide facilitates the local removal of buried oxide to form suspended membrane devices on silicon-on-insulator (SOI). The waveguide design is optimized in terms of hole size, etch depth, and bend radius to minimize device strain and optical loss. We calculate waveguide dimension to attain the wide low-dispersion ($\pm$ 100 ps/nm/km) bandwidth for the wavelength range from 2.0 to 8.0 $\mu \hbox{m}$, and optical nonlinearity is also studied. The SMWs are fabricated on a commercial SOI wafer and characterized by an $\hbox{Er}^{3+} - \hbox{Pr}^{3+}$ codoped fiber laser at 2.75 $\mu\hbox{m}$. Negligible bending losses are measured for a 40-$\mu\hbox{m}$ radius bend. The minimum waveguide loss of 3.0 $\pm$ 0.7 dB/cm is measured experimentally. The SMR resonator has a quality factor ($Q$) of $\sim$10 000 and an extinction ratio of $\sim$13 dB in near-IR. In mid-IR, the resonator has a $Q$ of $\sim$ 8100.

Surface-enhanced Raman spectroscopy (SERS) is a powerful tool for vibrational spectroscopy as it provides several orders of magnitude higher sensitivity than inherently weak spontaneous Raman scattering by exciting localized surface plasmon resonance (LSPR) on metal substrates. However, SERS can be unreliable for biomedical use since it sacrifices reproducibility, uniformity, biocompatibility, and durability due to its strong dependence on “hot spots”, large photothermal heat generation, and easy oxidization. Here, we demonstrate the design, fabrication, and use of a metal-free (i.e., LSPR-free), topologically tailored nanostructure composed of porous carbon nanowires in an array as a SERS substrate to overcome all these problems. Specifically, it offers not only high signal enhancement (~10⁶) due to its strong broadband charge-transfer resonance, but also extraordinarily high reproducibility due to the absence of hot spots, high durability due to no oxidization, and high compatibility to biomolecules due to its fluorescence quenching capability.

Breathtaking innovations in optical imaging have opened new exciting avenues for science, industry, and medicine over the last few decades. One of such innovations is optical time-stretch imaging—an emerging method for ultrafast optical imaging that builds on temporally stretching broadband pulses by using dispersive properties of light in both spatial and temporal domains. It achieves continuous image acquisition at an ultrahigh frame rate of 10–1000 million frames per second by overcoming technical and fundamental limitations that exist in traditional imaging methods. By virtue of its inherent affinity with optical signal processing, optical time-stretch imaging can be combined with various optical techniques such as amplification, nonlinear processing, compressive sensing, and pattern correlation to realize unique capabilities that are not possible with the traditional imaging methods. Applications enabled by such capabilities are versatile and include surface inspection, surface vibrometry, particle analysis, and cell screening. In this paper, we review the principles and limitations of conventional optical imaging, the principles and applications of optical time-stretch imaging, and discuss our future perspective.

Silicon photonic devices used in the photonics industry over the past three decades have helped in realizing large-scale photonic integrated circuits. Silicon nitride (Si ₃ N ₄ ) is another CMOS-compatible platform that provides several advantages such as low loss, high optical power tolerance, and broad spectral operation band from visible to infrared wavelengths. Recently, the combination of Si ₃ N ₄ waveguide technology with silicon photonics and III-V materials has opened up new areas in on-chip applications. Researchers in the field are primarily focusing on its applications such as on-chip gas sensing, nonlinear optical signal processing, and label-free biosensors based on photonic integrated circuits. In this review paper, we discuss Si ₃ N ₄ material-based platforms for a variety of applications with devices ranging from passive to active and hybrid photonic devices.