Bound states in the continuum (BIC) to achieve highly efficient frequency conversion using high quality-factor (high-Q) metasurfaces have been demonstrated using symmetry-broken structures with high robustness; however, the breaking-symmetry tactics are typically limited to one of the dimensions of the structures, which restricts the nonlinearity with BIC. In this work, we present a new metasurface structure in the form of an array of unit cells composed of two identical nano-bars with two mirror-symmetric corners cut into each nano-bar to break this limit. By using the high refractive index and large third-order nonlinearity of amorphous silicon (a-Si), we demonstrate ultra-high theoretical Qs up to ~ 2×10^5. Owing to the large nearfield enhancement in the meta-atoms, we observe optical Kerr effect in efficient third harmonic generation from the a-Si BIC metasurfaces via different levels of pump power, which paves the way for variational quasi-BIC for switchable nonlinear generation.
An on-package optical interconnect design is proposed for the first time, with silicon photonics in conjunction with the polymer-on-glass interposer technology to enable heterogeneous integration. Glass substrates are used for low-cost, high reliability packaging while silicon photonics allows for high-speed modulation and wavelength division multiplexing within a small footprint. By combining silicon-photonic and benzo-cyclobutene-on-glass interposer technologies, we propose a scalable on-package photonic interconnect that can provide data rates >224 Gb / s for medium-reach links. Our proposed interconnect considers microring modulators and high-speed detectors available in photonic-foundry processes. We present the power-budget analysis to identify the key limiting parameters toward achieving an energy consumption of < 1 pJ / bit.
Subwavelength nonlinear optical sources with high efficiency have received extensive attention although
strong dynamic tunability of these sources is still elusive. Germanium antimony telluride (GST) as a well-established phase-change chalcogenide is a promising candidate for the reconfiguration of subwavelength
nanostructures. Here, we design an electromagnetically induced transparency (EIT)-based high-quality-factor (high-Q) silicon metasurface that is actively controlled with a quarter-wave asymmetric Fabry-Perot cavity incorporating GST to modulate the relative phase of incident and reflected pump waves. We demonstrate a multi-level third-harmonic generation (THG) switch with a theoretical modulation depth as high as ~ 70 dB for the fundamental C-band crossing through multiple intermediate states of GST. This study shows the high potential of GST-based dynamic nonlinear photonic switches for a wide range of applications ranging from communications to optical computing.
We demonstrate a polarization rotator-splitter (PRS) design on standard 220 nm silicon-on-insulator (SOI) wafers with all rib waveguides and 2 μm silicon dioxide (SiO2) claddings. The design is fully compatible with the imec iSiPP50G silicon photonics platform. We show TM0-TE0 converting loss < 0.5 dB and all polarization crosstalk < -10 dB in the wavelength range of 1500- 1600 nm.
3C-SiC is a large bandgap material with a wide range of applications both in electronics and photonics. Here we demonstrate a low-loss 3C-SiC-on-Oxide (SiCOI) platform over an octave frequency range from visible to near-infrared. A 3C-SiC film is transferred onto an oxide-on-silicon substrate through wafer bonding to form a reliable SiCOI platform suitable for device integration, and the defect-rich transition layer in SiC is removed by chemical mechanical polishing (CMP). With low density of defects and a small root-mean-square (RMS) surface roughness (Rq) of about 1.4 Å in our SiC thin film, we are able to demonstrate record-high intrinsic quality factors of ~250,000 at 1550 nm wavelength and ~85,000 at 770 nm wavelength. Our low-loss SiCOI platform is promising for wideband nonlinear optical applications including second harmonic generation (SHG), four wave mixing (FWM), and Kerr frequency comb.
We leverage a dimensionality reduction approach to develop a novel inverse design platform applicable to a wide class of optical nanoantennas. The proposed dimensionality reduction technique uses a high level of correlation (in frequency and space domains) in the propagation of electromagnetic waves to considerably reduce the dimensionality of the response space of the problem. In addition, the correlation that often exists among the effects of design parameters on the response of the structure (i.e., selecting more design parameters than needed for uniquely identifying a structure for a given input-output relation) is used to reduce the dimensionality of the design space. In addition to the considerable mitigation of computation time and complexity, the two key features of dimensionality reduction, i.e., : 1) the ability to train a NN and later use it for a large class of problems, and 2) the possibility of analytically relating the reduced design space to the original design space to obtain valuable intuitive information about the roles of each design parameter in the overall performance of the nanostructure, highlight the superiority of the proposed approach. This is in contrast to existing analysis and optimization techniques, which require an intensive repetition of the simulations for each design problem without providing an intuitive understanding of the roles of design parameters. As a proof of concept, we apply this approach to a nanoscale structural color recently emerged as a promising candidate to organic colors in the printing technology. To circumvent the high absorption loss and efficiency of plasmonic color generators, we harness the fundamental dipolar Mie resonances of an array of asymmetric titanium dioxide elliptical nanopillars. We will further experimentally demonstrate such an optimized polarization-sensitive all-dielectric significantly enhance the resolution, saturation, and hue of color palettes. Such a novel inverse design approach highlights the performance of machine learning based approaches in developing highly-efficient metastructures.
We demonstrate a hybrid material platform for high-speed integrated optical modulation through integration of graphene with silicon-on-insulator (SOI) substrates after adding a thin layer of an oxide material. The modulation is performed by charge accumulation in the graphene and Si layers of the resulting capacitor to change the index of refraction of both layers (through free-carrier plasma dispersion effect). The advantages of graphene layer include stronger free-carrier plasma dispersion effect, and larger carrier mobility (to achieve smaller device resistance and thus, higher operation speed). We also report solving some of the major challenges in achieving high-quality hybrid platform, especially avoiding the tearing of the graphene layer during the mechanical transfer through adding a layer of hexagonal boron nitride (h-BN) on the two sides of the graphene layer. The h-BN layer also works as an isolation layer to maintain the intrinsic carrier mobility of graphene. We demonstrate reduced graphene resistance by a factor of 3 through h-BN encapsulation. The potential performance measures of the resulting structure along with its extension to double-layer graphene modulators will be discussed. The hybrid graphene modulator has the potential for applications including optical interconnection, optical signal processing, and optical computing.
Two-dimensional transition metal dichalcogenide (TMDC) heterostructures provide a unique platform for strong light-matter interaction in a wide wavelength range. Here, we report the formation of high-quality TMDC heterostructures through a dry transfer method along with the study of the detailed physical properties of heterostructures formed between MoS2 and MoSe2 (especially, simultaneous quenching of photoluminescence of both materials in the overlapping region, red shift and broadening of the MoSe2 photoluminescence) will be reported. We also report the formation of a thin tunable diode by depositing metal contacts on TMDCs and the back-gate.
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