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.

Silicon microcavity arrays with open access and a finesse of half a million

Optical resonators are essential for fundamental science,applications in sensing and metrology,particle cooling,and quantum information processing.Cavities can significantly enhance interactions between light and matter.For many applications they perform this task best if the mode confinement is tight and the photon lifetime is long.Free access to the mode center is important in the design to admit atoms,molecules,nanoparticles,or solids into the light field.Here,we demonstrate how to machine microcavity arrays of extremely high quality in pristine silicon.Etched to an almost perfect parabolic shape with a surface roughness on the level of 2A and coated to a finesse exceeding F=500,000,these new devices can have lengths below 17μm,confining the photons to 5μm waists in a mode volume of 88λ^(3).Extending the cavity length to 150μm,on the order of the radius of curvature,in a symmetric mirror configuration yields a waist smaller than 7μm,with photon lifetimes exceeding 64 ns.Parallelized cleanroom fabrication delivers an entire microcavity array in a single process.Photolithographic precision furthermore yields alignment structures that result in mechanically robust,pre-aligned,symmetric microcavity arrays,representing a lightmatter interface with unprecedented performance.