Arash Joushaghani

Sub-volt broadband hybrid plasmonic-vanadium dioxide switches

The insulator-metal phase transition of a correlated-electron material, vanadium dioxide, is used to demonstrate electrically controlled, compact, broadband, and low voltage plasmonic switches. The devices are micron-scale in length and operate near a wavelength of 1550 nm. The switching bandwidths exceed 100 nm and 400 mV is sufficient to attain extinction ratios in excess of 20 dB. The results illustrate the promise of using phase transition materials for efficient and ultra-compact plasmonic switches and modulators.

A Palladium-Catalyzed Alkylation/Direct Arylation Synthesis of Nitrogen-Containing Heterocycles

A norbornene-mediated palladium-catalyzed sequence is described in which an alkyl-aryl bond and an aryl-heteroaryl bond are formed in one reaction vessel. The aryl-heteroaryl bond-forming step occurs via a direct arylation reaction. A number of six-, seven-, and eight-membered ring-annulated indoles, pyrroles, pyrazoles, and azaindoles were synthesized from the corresponding bromoalkyl azole and an aryl iodide.

Design of electrically driven hybrid vanadium dioxide (VO 2 ) plasmonic switches

We present two types of designs for plasmonic switches based on hybridization between single interface surface plasmon polaritons and modes of a thin film of transition metal oxide material, vanadium dioxide (VO(2)). The design includes integrated, localized heaters that activate the VO(2) transition. The device operation is investigated and optimized by electromagnetic, electrical, and thermal simulations. The large change in the VO(2) refractive index in the infrared wavelength range enables highly compact and efficient plasmonic switches. The proposed designs achieve extinction ratios of 23-32 dB using only a 5 μm active region, a switching voltage of about 60 mV, and a switching power of about 9 mW.

Wavelength-size hybrid Si-VO(2) waveguide electroabsorption optical switches and photodetectors.

Ultra-compact waveguide electroabsorption optical switches and photodetectors with micron- and sub-micron lengths and compatible with silicon (Si) waveguides are demonstrated using the insulator-metal phase transition of vanadium dioxide (VO(2)). A 1 μm long hybrid Si-VO(2) device is shown to achieve a high extinction ratio of 12 dB and a competitive insertion loss of 5 dB over a broad bandwidth of 100 nm near λ = 1550 nm. The device, operated as a photodetector, can measure optical powers less than 1 μW with a responsivity in excess of 10 A/W. With volumes that are about 100 to 1000 times smaller than todays active Si photonic components, the hybrid Si-VO(2) devices show the feasibility of integrating transition metal oxides on Si photonic platforms for nanoscale electro-optic elements.

Voltage-controlled switching and thermal effects in VO2 nano-gap junctions

Voltage-controlled switching in lateral VO2 nano-gap junctions with different gap lengths and thermal properties was investigated. The effect of Joule heating on the phase transition was found to be strongly influenced by the device geometry, the contact material, and the current. Our results indicate that the VO2 phase transition was likely initiated electronically, which was sometimes followed by a secondary thermally induced transition.

Electronic and Thermal Effects in the Insulator-Metal Phase Transition in VO2 Nano-Gap Junctions

By controlling the thermal transport of VO2 nano-gap junctions using device geometry, contact material, and applied voltage waveforms, the electronically induced insulator-metal phase transition is investigated in the adiabatic heating and transient carrier injection regimes. With a gradual ramping of an applied voltage on a microsecond time scale, the transition electric field threshold can be directly reduced by the Joule heating. With an abrupt applied voltage, the transition threshold is initiated by carriers injected within the first tens of nanoseconds, but the complete insulator-metal phase transition is limited by thermal redistribution times to hundreds of nanoseconds.

Electrically controllable extraordinary optical transmission in gold gratings on vanadium dioxide

Highly tunable optical transmission through one-dimensional gold gratings patterned on top of a film of the phase transition material, vanadium dioxide (VO2), is demonstrated. Dense electrical integration is enabled by grating features that also function as electrical contacts to the VO2. Extraordinary optical transmission is observed in the VO2 insulator phase, and the optical transmission is extinguished by up to about 6 dB in a 170 nm thick VO2 film. Measurements of gratings with varying duty cycles demonstrate the dependence of the optical transmission and tuning on the device geometry.

Harmonic Oscillation in Coupled Waveguide Arrays

Following the idea of optical analogy to electronic systems, harmonic oscillations are spatially mimicked in waveguide arrays. We study and demonstrate the oscillations of light in AlGaAs waveguide arrays.

Electrically controllable extraordinary optical transmission in metallic surface gratings on VO 2

We present metallic gratings on a VO2 film with electrical control of the transmission spectrum. The extraordinary optical transmission was tunable by up to a factor of 2.75X to achieve an extinction ratio of 26 dB/μm.

Integrated photonic devices and circuits in hybrid silicon platforms

Si3N4-on-SOI and VO2-on-SOI integrated photonic devices and circuits, including an ultra-broadband and efficient grating coupler, adiabatic polarization rotator splitters, and wavelength-scale modulators, are described. Hybrid integration enables functionalities not attainable in each material separately.