Shiyang Zhu

Metalenses based on dielectric nanostructures operating in the transmission mode are of great practical significances. As large-area, multifunctional metalenses are increasingly demanded at higher volumes nowadays, the quality and efficiency of the nanofabrication processes for these lenses are made even more important. Yet, no fabrication is without defects or errors. Using numerical calculation by finite-difference time-domain (FDTD) method, we study, in simulation, a set of common fabrication-induced errors such as inclined sidewall, critical dimension (CD) bias and process defects, and analyze their influences on the optical performances of two types of metalenses - one made of amorphous silicon and the other of silicon nitride. The study concludes that the lens behavior generally relies on the resonant nature of the nanostructure array. While most types of defects discussed in this work linearly decrease the focusing efficiency, a few would also influence the quality of the focal spot. Potential solutions to mitigate the effect of the process-induced defects are also investigated. The study provides the particular knowledge to understand the actual metalens performance when fabricated.

ScAlN has been applied in piezoelectric micro-electro-mechanical systems, while application in photonics remains unexplored. Here, ScAlN photonic circuits on silicon are presented, demonstrating waveguide propagation loss of 9±2 dB/cm and microring quality factor of 1.4×10⁴.

We present integrated optical phased arrays with cascaded phase shifting architectures for easy and effective electronic control. The input light is distributed to N emitters equally through a cascaded 1×2 splitter network with log₂N stages and with identical phase shifters on each stage, which enables continuous beam steering using log₂N voltages or one voltage. A 32-element SiN OPA with one input voltage was measured to exhibit 16° continuous steering at 13-V bias with 0.7° beam width. The same design can be easily adjusted for large element OPAs with easy and effective electronic control.

We demonstrate ultralow loss AlN single-mode channel waveguide and AlN electro-optic (EO) modulators in CMOS compatible AlN-on-insulator photonic circuits. Propagation loss was measured to be ~0.42 dB/cm at 1550 nm and ~2.36 dB/cm at 905 nm. A push-pull MZI modulator with arm length of 2.8 cm exhibits V_π of ~21 V at 1550 nm and ~12.9 V at 1064 nm, and modulation speed of ~140 MHz, limited by the resistive-capacitive delay. A dual-ring modulator exhibits extension ratio of ~12 dB and high modulation speed of ~4 GHz because of its small footprint as compared with the MZI modulator.

We propose and demonstrate an efficient and fast thermo-optic phase shifter for integrated silicon photonics. By inserting a small AlN block between the TiN heater and Si waveguide, both the phase-shifting efficiency and the modulation speed are improved from ~9.4 to ~8.2 mW/π and from ~26 to ~32 kHz, respectively, as compared to the counterpart without the AlN block. The improvement can be attributed to the very large thermal conductivity of AlN (~285 W/m-K), which makes the waveguide has almost similar temperature as the heater upon it is heated. Numerical simulation shows that the proposed method is also applicable for the Si₃N₄ waveguide.

An AlN electro-optic phase shifter with a parallel plate capacitor structure is fabricated on Si using the back-end complementary metal-oxide-semiconductor technology, which is feasible for multilayer photonics integration. The modulation efficiency (V_π⋅L_π product) measured from the fabricated waveguide-ring resonators and Mach-Zehnder Interferometer (MZI) modulators near the 1550-nm wavelength is ∼240 V⋅cm for the transverse electric (TE) mode and ∼320 V⋅cm for the transverse magnetic (TM) mode, from which the Pockels coefficient of the deposited AlN is deduced to be ∼1.0 pm/V for both TE and TM modes. The methods for further modulation efficiency improvement are addressed.

Optics InfoBase is the Optical Society's online library for flagship journals, partnered and copublished journals, and recent proceedings from OSA conferences.

Optics InfoBase is the Optical Society's online library for flagship journals, partnered and copublished journals, and recent proceedings from OSA conferences.

Optics InfoBase is the Optical Society's online library for flagship journals, partnered and copublished journals, and recent proceedings from OSA conferences.

An ultracompact silicon electro-optic modulator operating at 1550-nm telecom wavelengths is proposed and analyzed theoretically, which consists of a Cu-TiO₂-Si hybrid plasmonic donut resonator evanescently coupled with a conventional Si channel waveguide. Owing to a negative thermo-optic coefficient of TiO₂ (~-1.8 × 10⁻⁴ K⁻¹), the real part of effective modal index of the curved Cu-TiO₂-Si hybrid waveguide can be temperature-independent (i.e., athermal) if the TiO₂ interlayer and the beneath Si core have a certain thickness ratio. A voltage applied between the ring-shaped Cu cap and a cylinder metal electrode positioned at the center of the donut, − which makes Ohmic contact to Si, induces a ~1-nm-thick free-electron accumulation layer at the TiO₂/Si interface. The optical field intensity in this thin accumulation layer is significantly enhanced if the accumulation concentration is sufficiently large (i.e., > ~6 × 10²⁰ cm⁻³), which in turn modulates both the resonance wavelengths and the extinction ratio of the donut resonator simultaneously. For a modulator with the total footprint inclusive electrodes of ~8.6 μm², 50-nm-thick TiO₂, and 160-nm-thick Si core, FDTD simulation predicts that it has an insertion loss of ~2 dB, a modulation depth of ~8 dB at a voltage swing of ~6 V, a speed-of-response of ~35 GHz, and a switching energy of ~0.45 pJ/bit, and it is athermal around room temperature. The modulator’s performances can be further improved by optimization of the coupling strength between the bus waveguide and the donut resonator.