Measurement of bound states in the continuum by a detector embedded in a photonic crystal

We directly measure optical bound states in the continuum(BICs)by embedding a photodetector into a photonic crystal slab.The BICs observed in our experiment are the result of accidental phase matching between incident,reflected and in-plane waves at seemingly random wave vectors in the photonic band structure.Our measurements were confirmed through a rigorously coupled-wave analysis simulation in conjunction with temporal coupled mode theory.Polarization mixing between photonic crystal slab modes was observed and described using a plane wave expansion simulation.The ability to probe the field intensity inside the photonic crystal and thereby to directly measure BICs represents a milestone in the development of integrated opto-electronic devices based on BICs.

Advanced mid-infrared plasmonic waveguides for on-chip integrated photonics

Long-wave infrared(LWIR, 8–14 μm) photonics is a rapidly growing research field within the mid-IR with applications in molecular spectroscopy and optical free-space communication. LWIR applications are often addressed using rather bulky tabletop-sized free-space optical systems, preventing advanced photonic applications,such as rapid-time-scale experiments. Here, device miniaturization into photonic integrated circuits(PICs) with maintained optical capabilities is key to revolutionize mid-IR photonics. Subwavelength mode confinement in plasmonic structures enabled such miniaturization approaches in the visible-to-near-IR spectral range. However,adopting plasmonics for the LWIR needs suitable low-loss and-dispersion materials with compatible integration strategies to existing mid-IR technology. In this paper, we further unlock the field of LWIR/mid-IR PICs by combining photolithographic patterning of organic polymers with dielectric-loaded surface plasmon polariton(DLSPP) waveguides. In particular, polyethylene shows favorable optical properties, including low refractive index and broad transparency between ~2 μm and 200 μm. We investigate the whole value chain, including design, fabrication, and characterization of polyethylene-based DLSPP waveguides and demonstrate their first-time plasmonic operation and mode guiding capabilities along S-bend structures. Low bending losses of ~1.3 d B and straight-section propagation lengths of ~1 mm, pave the way for unprecedented complex on-chip mid-IR photonic devices. Moreover, DLSPPs allow full control of the mode parameters(propagation length and guiding capabilities) for precisely addressing advanced sensing and telecommunication applications with chip-scale devices.