Multi-material heterogeneous integration on a 3-D Photonic-CMOS platform

Photonics has been one of the primary beneficiaries of advanced silicon manufacturing. By leveraging on mature complementary metal-oxide-semiconductor (CMOS) process nodes, unprecedented device uniformities and scalability have been achieved at low costs. However, some functionalities, such as optical memory, Pockels modulation, and magnetooptical activity, are challenging or impossible to acquire on group-IV materials alone. Heterogeneous integration promises to expand the range of capabilities within silicon photonics. Existing heterogeneous integration protocols are nonetheless not compatible with active silicon processes offered at most photonic foundries. In this work, we propose a novel heterogeneous integration platform that will enable wafer-scale, multi-material integration with active silicon-based photonics, requiring zero-change to existing foundry process. Furthermore, the platform will also pave the way to a class of high-performance devices. We propose a grating coupler design with peak coupling efficiency reaching 93%, an antenna with peak diffraction efficiency in excess of 97%, and a broadband adiabatic polarization rotator with conversion efficiency exceeding 99%

Monolithic on-chip nonreciprocal photonics based on magneto-optical thin films

Monolithic integration of nonreciprocal optical devices on semiconductor substrates has been a long-sought goal of the photonics community. One promising route to achieve this goal is to deposit high quality magneto-optical (MO) oxide thin films directly on a semiconductor substrate. In this article, we will review our ongoing progress in material development and device engineering towards enabling a monolithically integrated, high-performance magneto-optical nonreciprocal photonics platform. In particular, we will discuss our recent work which has led to a new pulsed laser deposition (PLD) technique of Ce or Bi substituted yttrium iron garnet (YIG) thin films with reduced thermal budget, simplified growth protocols and improved magneto-optical characteristics. These materials were incorporated in monolithic resonator and interferometer based isolator devices to demonstrate on-chip optical isolation with improved device figure of merit. Challenges and opportunities for monolithic magneto-optical devices will be discussed in the context of our latest material and device performance metrics

Topology Optimization of Surface-enhanced Raman Scattering Substrates

Surface-enhanced Raman spectroscopy is a powerful and versatile sensing method with a detection limit down to the single molecule level. In this article, we demonstrate how topology optimization (TopOpt) can be used for designing surface enhanced Raman scattering (SERS) substrates adhering to realistic fabrication constraints. As an example, we experimentally demonstrated a SERS enhancement factor of 5*10e4 for the 604 cm-1 Raman line of rhodamine 6G using metal nanostructures with a critical dimension of 20 nm. We then show that, by relaxing the fabrication constraints, TopOpt may be used to design SERS substrates with orders of magnitude larger enhancement factor. The results validate topology optimization as an effective method for engineering nanostructures with optimal performance and fabrication tolerance.Comment: 12 page

Mid-IR high-index dielectric Huygens metasurfaces

In this paper, we proposed highly efficient all-dielectric Huygens' metasurfaces working at mid-IR frequencies. The meta-Atom of the designed Huygens' metasurface is a cubic dielectric resonator or its variety, which is made from PbTe that possesses a high refractive index of around 5 at mid-IR frequencies. By overlapping spectrally both the magnetic and electric dipole modes of the high-index dielectric resonators, a full phase coverage of 2π and an equal-magnitude transmission could be achieved, which are essential conditions for realizing a metasurface. Two Huygens' metasurfaces for beam bending are designed with a phase change between two consecutive meta-Atoms of π/4 and π/3, respectively. The simulation results agree well with the design theory.National Science Foundation (U.S.) (Grant CMMI-1266251