Design of a broadband polarization controller based on silicon nitride-loaded thin-film lithium niobate.

A novel design of a polarization controller based on "etch-less" Si3N4-loaded thin film LiNbO3 is described. Broadband operation in the spectral range between 1.45 and 1.65 µm is achieved by using a mode evolution TM/TE splitter/converter, two mode evolution 3-dB couplers, and two electro-optic phase shifters. Numerical simulations show that the on-chip insertion loss should not exceed 1 dB. A single TE-mode output can be adjusted by applying control voltages lower than 10 V for an arbitrary input polarization state.

Bound modes in the continuum in integrated photonic LiNbO3 waveguides: are they always beneficial?

We discuss several types of integrated photonic LiNbO3 waveguides supporting propagation of modes which can be classified as bound states in the continuum (BICs). The key properties leading to the existence of BICs (or quasi-BICs) considered here are the material anisotropy, the waveguide birefringence, or the combination of both. Typical examples are titanium diffused and proton exchanged waveguides in bulk LiNbO3 crystals and recently proposed dielectric-loaded waveguides on LiNbO3 thin films. Proton exchanged waveguides in thin film LiNbO3 are considered, too. These waveguide structures are discussed from the point of view of their benefit for applications, especially in electro-optic devices.

Guiding light through quasi-TE modes embedded in the radiation continuum.

We introduce a new, to the best of our knowledge, type of a bound state in the continuum (BIC) which appears in the photonic structure consisting of two coupled waveguides where one of them supports a discrete eigenmode spectrum embedded in the continuum of the other one. A BIC appears when the coupling is suppressed by suitable tuning of structural parameters. In contrast to the previously described configurations, our scheme facilitates genuine guiding of quasi-TE modes in the core with the lower refractive index.

Simulations of high-Q optical nanocavities with a gradual 1D bandgap.

High-quality cavities in hybrid material systems have various interesting applications. We perform a comprehensive modeling comparison on such a design, where confinement in the III-V material is provided by gradual photonic crystal tuning, a recently proposed method offering strong resonances. The III-V cavity couples to an underlying silicon waveguide. We report on the device properties using four simulation methods: finite-difference time-domain (FDTD), finite-element method (FEM), bidirectional eigenmode propagation (BEP) and aperiodic rigorous coupled wave analysis (aRCWA). We explain the major confinement and coupling effects, consistent with the simulation results. E.g. for strong waveguide coupling, we find quantitative discrepancies between the methods, which establishes the proposed high-index-contrast, lossy, 3D structure as a challenging modeling benchmark.

Measurements of light scattering in an integrated microfluidic waveguide cytometer.

An integrated microfluidic planar optical waveguide system for measuring light scattered from a single scatterer is described. This system is used to obtain 2D side-scatter patterns from single polystyrene microbeads in a fluidic flow. Vertical fringes in the 2D scatter patterns are used to infer the location of the 90-deg scatter (polar angle). The 2D scatter patterns are shown to be symmetrical about the azimuth angle at 90 deg. Wide-angle comparisons between the experimental scatter patterns and Mie theory simulations are shown to be in good agreement. A method based on the Fourier transform analysis of the experimental and Mie simulation scatter patterns is developed for size differentiation.