Sabarni Palit

Dynamic tuning of an infrared hybrid-metamaterial resonance using vanadium dioxide

We demonstrate a metamaterial device whose far-infrared resonance frequency can be dynamically tuned. Dynamic tuning should alleviate many bandwidth-related roadblocks to metamaterial application by granting a wide matrix of selectable electromagnetic properties. This tuning effect is achieved via a hybrid-metamaterial architecture; intertwining split ring resonator metamaterial elements with vanadium dioxide (VO2)-a material whose optical properties can be strongly and quickly changed via external stimulus. This hybrid structure concept opens a fresh dimension in both exploring and exploiting the intriguing electromagnetic behavior of metamaterials.

Hybrid metamaterials enable fast electrical modulation of freely propagating terahertz waves

We demonstrate fast electrical modulation of freely propagating terahertz waves at room temperature using hybrid metamaterial devices. The devices are planar metamaterials fabricated on doped semiconductor epitaxial layers, which form hybrid metamaterial—Schottky diode structures. With an applied ac voltage bias, we show modulation of terahertz radiation at inferred frequencies over 2MHz. The modulation speed is limited by the device depletion capacitance which may be reduced for even faster operation.

Dual-band planar electric metamaterial in the terahertz regime

We present the design, fabrication, and measurement of a dual-band planar metamaterial with two distinct electric resonances at 1.0 and 1.2 THz, as a step towards the development of frequency agile or broadband THz materials and devices. A method of defining the effective thickness of the metamaterial layer is introduced to simplify the material design and characterization. Good agreement between the simulated and measured transmission is obtained for the fabricated sample by treating the sample as multi-layer system, i. e. the effective metamaterial layer plus the rest of the substrate, as well as properly modeling the loss of the substrate. The methods introduced in this paper can be extended to planar metamaterial structures operating in infrared and optical frequency ranges.

A dual-resonant terahertz metamaterial based on single-particle electric-field-coupled resonators

We report the design, fabrication, and measurement of a terahertz metamaterial composed of single geometry electric field coupled resonators that has two closely spaced electric resonances near 1.0 and 1.5THz. Due to the mutual coupling between the different resonances in the particle, the lower frequency resonance of this metamaterial is stronger than that in a metamaterial composed of identically sized single-resonant particles, leading to a larger insertion loss and broader bandwidth. This feature provides more flexibility in metamaterial design and application in the terahertz regime.

Reconfigurable gradient index using VO2 memory metamaterials

We demonstrate tuning of a metamaterial device that incorporates a form of spatial gradient control. Electrical tuning of the metamaterial is achieved through a vanadium dioxide layer which interacts with an array of split ring resonators. We achieved a spatial gradient in the magnitude of permittivity, writeable using a single transient electrical pulse. This induced gradient in our device is observed on spatial scales on the order of one wavelength at 1 THz. Thus, we show the viability of elements for use in future devices with potential applications in beamforming and communications.

Chip scale integrated microresonator sensing systems.

Medicine, environmental monitoring, and security are application areas for miniaturized, portable sensing systems. The emerging integration of sensors with other components (electronic, photonic, fluidic) is moving sensing toward higher levels of portability through the realization of self-contained chip scale sensing systems. Planar optical sensors, and in particular, microresonator sensors, are attractive components for chip scale integrated sensing systems because they are small, have high sensitivity, can be surface customized, and can be integrated singly or in arrays in a planar format with other components using conventional semiconductor fabrication technologies. This paper will focus on the progress and prospects for the integration of microresonator sensors at the chip scale with photonic input/output components and with sample preparation microfluidics, toward self-contained, portable sensing systems.

Progress in Chip-Scale Photonic Sensing

Chip-scale integrated planar photonic sensing systems for portable diagnostics and monitoring are emerging, as photonic components are integrated into systems with silicon (Si), Si complementary metal-oxide semiconductor, and fluidics. This paper reviews progress in these areas. Medical and environmental applications, candidate photonic sensors, integration methodologies, integrated subsystem demonstrations, and challenges facing this emerging field are discussed in this paper.

Quantitative investigation of a terahertz artificial magnetic resonance using oblique angle spectroscopy

The authors present a spectroscopic analysis of a planar split-ring-resonator (SRR) medium at terahertz frequencies, quantitatively characterizing the associated magnetic resonance. Experimental quantification at terahertz and infrared frequencies of metamaterial optical constants has been primarily absent, largely due to the difficulty of collecting phase information at these frequencies. In this letter, the authors circumvent the need for phase information in the characterization by acquiring the power transmitted through the metamaterial at a series of oblique angles, and relating the multiangle data set to the effective permittivity and permeability through the Fresnel expressions. The resulting measurements reveal the expected resonant permeability of the SRR which exhibits a range of negative values, the minimum value being μ=−0.8 at 1.1THz.

Low-threshold thin-film III-V lasers bonded to silicon with front and back side defined features.

A III-V thin-film single-quantum-well edge-emitting laser is patterned on both sides of the epitaxial layer and bonded to silicon. Injected threshold current densities of 420 A/cm(2) for gain-guided lasers with bottom p-stripes and top n-stripes and 244 A/cm(2) for index-guided bottom p-ridge and top n-stripe lasers are measured with a lasing wavelength of approximately 995 nm. These threshold current densities, among the lowest for thin-film edge-emitting lasers on silicon reported to date (to our knowledge), enable the implementation of integrated applications such as power-efficient portable chip-scale photonic sensing systems.

Top-Bottom Stripe Thin Film InGaAs/GaAsP Laser integrated on Silicon

Integration of photonic active and passive components - and ultimately, full systems - directly onto Si and Si CMOS are a critical step toward chip scale photonic system integration. Thin film compound semiconductor lasers heterogeneously integrated onto silicon open up a wide range of applications, including portable sensing systems, optical interconnects, and chip scale ultrafast optical signal processing. Thin film lasers on silicon are a critical component for these applications, and a low threshold current density is especially desirable for low power, portable applications. In this paper, a thin film InGaAs/GaAsP single quantum well (SQW) laser with strain compensation and a unique top/bottom stripe contact structure for efficient current distribution is presented. The thin film (3.8 mum thick), and the ability to perform fabrication processes on both sides of this thin film laser, enable this new contact structure.