Demis D. John

Ultra-low-loss high-aspect-ratio Si3N4 waveguides

We characterize an approach to make ultra-low-loss waveguides using stable and reproducible stoichiometric Si3N4 deposited with low-pressure chemical vapor deposition. Using a high-aspect-ratio core geometry, record low losses of 8-9 dB/m for a 0.5 mm bend radius down to 3 dB/m for a 2 mm bend radius are measured with ring resonator and optical frequency domain reflectometry techniques. From a waveguide loss model that agrees well with experimental results, we project that 0.1 dB/m total propagation loss is achievable at a 7 mm bend radius with this approach.

Planar waveguides with less than 0.1 dB/m propagation loss fabricated with wafer bonding

We demonstrate a wafer-bonded silica-on-silicon planar waveguide platform with record low total propagation loss of (0.045 ± 0.04) dB/m near the free space wavelength of 1580 nm. Using coherent optical frequency domain reflectometry, we characterize the group index, fiber-to-chip coupling loss, critical bend radius, and propagation loss of these waveguides.

Multilayer Platform for Ultra-Low-Loss Waveguide Applications

We investigate a multilayer vertical stacking scheme for use in the Silicon Nitride-based low-loss waveguide platform. In this letter, we use common fabrication techniques to produce test structures for probing the interactions between vertically separated parallel waveguide planes and the characteristics of vertical directional couplers. Single-mode and multimode waveguide geometries are investigated, with designs similar to our previously demonstrated ultra-low-loss technologies. Group index measurements via narrowband OFDR reveal an index mismatch between the vertically separated waveguides of 8.6e-3, generated by the stress of the deposited upper cladding. Vertical directional couplers with a 3-μm vertical coupling gap and a 50 nm × 4 μm geometry exhibited an excess coupling loss of 0.19±0.20 dB and cross-coupled power of 54%, limited by the aforementioned velocity mismatch. The 1.23-m spiral structures with perpendicular crossings on adjacent layers show a transmission loss of the crossings below 0.25 dB for a multimode geometry, while the single-mode design showed a minimum crossing loss of 1.0 dB.

Ultra-low loss silica-based waveguides with millimeter bend radius

We characterize an approach to make compact low loss silica on silicon waveguides and achieve good agreement with theory. Record low losses of 8 dB/m for 0.5-mm bend radius down to 3 dB/m for 2-mm bend radius were achieved.

Fabrication and demonstration of a pure silica-core waveguide utilizing a density-based index contrast

We report a novel approach for creating a dopant-free pure silica-core waveguide (PSCW) for chip-scale waveguides with the goal of reaching fiber-like losses on-chip. Stoichiometric silica films were used as both the cladding and core material for buried channel waveguides, with the required index contrast generated by a difference in physical density. The bulk densities of the thin-films were measured with X-Ray Reflectometry, and these density values were compared with the expected change in refractive index using the Lorentz-Lorenz (Clausius-Mosotti) relation. We found the difference in density of 5.29% to correspond with the difference in refractive index of 1.17%, and measured propagation losses of 2.119 to 2.660 dB/cm.

Ultra-low-loss (< 0.1 dB/m) Planar Silica Waveguide Technology

We demonstrate record low (0.045 dB/m) total propagation loss in silica-on-silicon planar waveguides fabricated with wafer-bonded thermal oxide upper claddings.