William S. Fegadolli

Experimental demonstration of a unidirectional reflectionless parity-time metamaterial at optical frequencies

Invisibility by metamaterials is of great interest, where optical properties are manipulated in the real permittivity-permeability plane. However, the most effective approach to achieving invisibility in various military applications is to absorb the electromagnetic waves emitted from radar to minimize the corresponding reflection and scattering, such that no signal gets bounced back. Here, we show the experimental realization of chip-scale unidirectional reflectionless optical metamaterials near the spontaneous parity-time symmetry phase transition point where reflection from one side is significantly suppressed. This is enabled by engineering the corresponding optical properties of the designed parity-time metamaterial in the complex dielectric permittivity plane. Numerical simulations and experimental verification consistently exhibit asymmetric reflection with high contrast ratios around a wavelength of of 1,550 nm. The demonstrated unidirectional phenomenon at the corresponding parity-time exceptional point on-a-chip confirms the feasibility of creating complicated on-chip parity-time metamaterials and optical devices based on their properties.

Reconfigurable silicon thermo-optical ring resonator switch based on Vernier effect control

A proof-of-concept for a new and entirely CMOS compatible thermo-optic reconfigurable switch based on a coupled ring resonator structure is experimentally demonstrated in this paper. Preliminary results show that a single optical device is capable of combining several functionalities, such as tunable filtering, non-blocking switching and reconfigurability, in a single device with compact footprint (~50 μm x 30 μm).

Compact and Low Power Consumption Tunable Photonic Crystal Nanobeam Cavity

A proof-of-concept for a new and entirely CMOS compatible tunable nanobeam cavity is demonstrated in this paper. Preliminary results show that a compact nanobeam cavity (~20 μm(2)) with high Q-factor (~50,000) and integrated with a micro-heater atop, is able of tuning the resonant wavelength up to 15 nm with low power consumption (0.35nm/mW), and of attaining high modulation depth with only ~100 μW. Additionally, a tunable bi-stable behavior is reported.

Ultrasensitive Gas-Phase Chemical Sensing Based on Functionalized Photonic Crystal Nanobeam Cavities

Photonic crystal nanobeam cavities with high-quality factors are very sensitive to the changes of the dielectric properties of their surroundings. Utilizing this high sensitivity and by applying chemical functionalization, an ultrasensitive chemical sensor for gases based on a nanobeam cavity was demonstrated. A limit of detection of 1.5 parts-per-billion (ppb) in ambient conditions, determined from the noise level of the system, was achieved for nerve agent simulant methyl salicylate. The nanobeam cavitys nonlinear thermo-optical bistability is also utilized to realize a threshold detector for cumulative chemical exposure.

Experimental realization of Bloch oscillations in a parity-time synthetic silicon photonic lattice

As an important electron transportation phenomenon, Bloch oscillations have been extensively studied in condensed matter. Due to the similarity in wave properties between electrons and other quantum particles, Bloch oscillations have been observed in atom lattices, photonic lattices, and so on. One of the many distinct advantages for choosing these systems over the regular electronic systems is the versatility in engineering artificial potentials. Here by utilizing dissipative elements in a CMOS-compatible photonic platform to create a periodic complex potential and by exploiting the emerging concept of parity-time synthetic photonics, we experimentally realize spatial Bloch oscillations in a non-Hermitian photonic system on a chip level. Our demonstration may have significant impact in the field of quantum simulation by following the recent trend of moving complicated table-top quantum optics experiments onto the fully integrated CMOS-compatible silicon platform.

Experimental demonstration of a reconfigurable silicon thermo-optical device based on spectral tuning of ring resonators for optical signal processing

We have experimentally demonstrated a reconfigurable silicon thermo-optical device able to tailor its intrinsic spectral optical response by means of the thermo-optical control of individual and uncoupled resonant modes of micro-ring resonators. Preliminarily results show that the devices optical response can be tailored to build up distinct and reconfigurable logic levels for optical signal processing, as well as control of overall figures of merit, such as free-spectral-range, extinction ratio and 3 dB bandwidth. In addition, the micro-heaters on top of the ring resonators are able to tune the resonant wavelength with efficiency of 0.25 nm/mW within a range of up to 10 nm, as well as able to switch the resonant wavelength within fall and rise time of 15 μs.

Hybrid Single Quantum Well InP/Si Nanobeam Lasers for Silicon Photonics

We report on a hybrid InP/Si photonic crystal nanobeam laser emitting at 1578 nm with a low threshold power of ~14.7 μW. Laser gain is provided from a single InAsP quantum well embedded in a 155 nm InP layer bonded on a standard silicon-on-insulator wafer. This miniaturized nanolaser, with an extremely small modal volume of 0.375(λ/n)(3), is a promising and efficient light source for silicon photonics.

Reconfigurable silicon thermo-optical device based on spectral tuning of ring resonators

A novel tunable and reconfigurable thermo-optical device is theoretically proposed and analyzed in this paper. The device is designed to be entirely compatible with CMOS process and to work as a thermo-optical filter or modulator. Numerical results, made by means of analytical and Finite-Difference Time-Domain (FDTD) methods, show that a compact device enables a broad bandwidth operation, of up to 830 GHz, which allows the device to work under a large temperature variation, of up to 96 K.

Nanobeam photonic crystal cavity based multifunctional gas-phase chemical sensor

By applying chemical functionalization to a nanobeam photonic crystal cavity, an ultrasensitive gas-phase chemical sensor was demonstrated. Its nonlinear thermo-optical bi-stability is utilized to realize a novel threshold detector for cumulative chemical exposure.

Athermal Silicon Slot Waveguide With an Ormocomp Polymer Overlayer

We have demonstrated a proof-of-concept for an athermal silicon slot waveguide using Ormocomp as a top cladding. Preliminarily theoretical and experimental results show that the slot waveguide geometry can completely cancel out its thermo-optical coefficient, by tailoring the optical mode overlap with silicon, silicon dioxide, and Ormocomp.