Sang-Yeon Cho

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.

The heterogeneous integration of optical interconnections into integrated microsystems

Emerging techniques for integrating optoelectronic (OE) devices, analog interface circuitry, RF circuitry, and digital logic into ultra-mixed signal systems offers approaches toward and demonstrations of integrated optical interconnections in electrical microsystems. As rising data rates dictate the use of optical interconnections and interfaces at increasingly smaller distances, optical interconnections stand at a threshold of opportunity for pervasive implementation if cost-effective integration process technology and performance can be implemented. Heterogeneous integration is one approach toward the integration of compound semiconductor OE devices, Si CMOS circuits, and organic materials. Heterogeneous integration approaches, which utilize dissimilar materials which can be independently grown and optimized, and are subsequently bonded together into an integrated system, are particularly attractive methods for creating high-performance microsystems. This paper describes a variety of optical interconnections integrated into microsystems using thin film heterogeneous integration. Thin film heterogeneous integration is attractive from the standpoint that the topography of the integrated microsystem can remain flat to within a few microns, substrates which are often optically absorbing are removed, both sides of the thin film devices can be processed (e.g., contacted, optically coated), and three-dimensionally stacked structures can be implemented. Demonstrations of interconnections using thin film heterogeneous integration technology include an integrated InGaAs/Si CMOS receiver circuit operating at 1 Gbps, an InGaAs thin film photodetector bonded onto a foundry Si CMOS microprocessor to demonstrate a single chip optically interconnected microprocessor, smart pixel emitter and detector arrays using resonant cavity enhanced P-i-N photodetectors bonded on top of per-pixel current controlled oscillators and resonant cavity enhanced light emitting diodes integrated onto digital to analog converter gray-scale per-pixel driver circuitry, and photodetectors embedded in waveguides on electrical interconnection substrates to demonstrate chip-to-chip embedded waveguide interconnections.

A Polymer Microdisk Photonic Sensor Integrated Onto Silicon

Optical sensors are attractive for integrated chip-scale sensor systems. In this letter, integrated microdisk sensors have been fabricated and characterized for five different D-glucose concentrations in deionized water. The microdisk sensor reported is in an orthogonal configuration, reducing the sensor size toward chip-scale sensor applications. The measured wavelength shift in the resonant peak of the microdisk sensors has a linear response as a function of D-glucose concentration. The estimated sensitivity (defined by Deltalambdaresonant/wt%D-glucose) of the fabricated microdisk sensor for the D-glucose solution was 0.12[nm/wt%] based on the slope of the linear regression line from the measured results

Integrated detectors for embedded optical interconnections on electrical boards, modules, and integrated circuits

Significant opportunities exist for optical interconnections at the board, module, and chip level if compact, low-loss, high-data-rate optical interconnections can be integrated into these electrical interconnection systems. To create such an integrated optoelectronic/electronic microsystem, mask-based alignment of the optical interconnection waveguide, optoelectronic active devices, and interface circuits is attractive from a packaging alignment standpoint. This paper describes an integration process for creating optical interconnections which can be integrated in a postprocessing format onto standard boards, modules, and integrated circuits. These optical interconnections utilize active thin-film optoelectronic components embedded in the waveguide/interconnection substrate, thus eliminating the need for optical beam turning elements and their alignment, and providing an electrical output on the substrate from an optical interconnection. These embedded optical interconnections are reported herein using BCB polymer optical waveguides with embedded InGaAs-based thin-film inverted metal-semiconductor-metal (I-MSM) photodetectors on an Si substrate. These interconnections have been fabricated and tested, and the coupled optical signal from the waveguide to the embedded photodetector was theoretically modeled at 56.4%, which was supported by an experimental estimate of 47.8%. The measured full-width at half maximum of the electrical pulse from the MSM photodetector embedded in the waveguide was 16.73 ps for an input 500-fs optical laser pulse.

Directional coupling between dielectric and long-range plasmon waveguides

We have designed, fabricated and characterized integrated directional couplers capable of converting the mode of an optical dielectric waveguide into a long-range plasmon propagating along a thin metal stripe. We demonstrate that the coupling between the two types of waveguides is generally very weak unless specific conditions are met. This sensitivity could be potentially exploited in sensing applications or for developing novel active photonic components.

Interferometric microring-resonant 2 x 2 optical switches.

We present modeling and simulation results on a new family of waveguided interferometric 2 x 2 optical routing switches actuated by electro-optic or thermo-optic or all-optical control. Two pairs of coupled microring resonators provide two 3dB coupling regions within a compact Mach-Zehnder geometry. An index perturbation (delta)n of 2 x 10(-3) is sufficient to produce 100% 2 x 2 switching. This perturbation can be applied to one arm of the MZI or to the four rings in the device or to an additional ring that is coupled to one arm. We find that push-pull control is effective for switching: for example, when carriers are injected in one region and depleted in a corresponding second region. An optical transfer-matrix technique is employed to determine the electromagnetic response (the 1550-nm switching characteristics) of the three device-types. Microdisks can be employed instead of microrings, if desired.

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.

High-speed large-area inverted InGaAs thin-film metal-semiconductor-metal photodetectors

Inverted metal-semiconductor-metal (I-MSM) photodetectors, which are thin-film MSMs with the growth substrate removed and fingers on the bottom of the device (to eliminate finger shadowing to enhance responsivity), are reported herein for high-speed high-efficiency large-area photodetectors. Reported herein are the highest speed vertically addressed large-area (40-/spl mu/m diameter) photodetectors reported to date, which operate with a responsivity of 0.16 A/W and a full-width half-maximum of less than 5 ps. Materials, fabrication processes, heterogeneous integration, and characterization of I-MSM photodetectors are presented in this paper, as measured using a fiber-based electrooptic sampling system. These large-area photodetectors are ideal for vertically addressed high-speed optical links which need alignment-tolerant packaging for cost sensitive applications.

Optical interconnections on electrical boards using embedded active optoelectronic components

Significant opportunities are emerging for optical interconnections at the board, module, and chip level if compact, low loss, high data rate optical interconnections can be integrated into these electrical interconnection systems. This paper describes an integration process for creating optical interconnections which can be integrated in a postprocessing format onto standard boards, modules, and integrated circuits. These optical interconnections utilize active thin-film optoelectronic components embedded in waveguides, which are integrated onto or into the interconnection substrate, thus providing an electrical output on the substrate from an optical interconnection. These embedded optical interconnections are reported herein using BCB (Benzocyclobutene ) polymer optical waveguides in two different formats, as well as a third waveguide structure using a BCB cladding with an Ultem core. All of these waveguides were fabricated with InGaAs-based thin-film inverted metal-semiconductor-metal (I-MSM) photodetectors embedded in the waveguide layer, thus eliminating the need for beam turning elements at the output of the waveguide. These embedded interconnections have been fabricated and tested, and the coupling efficiency of the optical signals from the waveguides to the embedded photodetectors was estimated from these measurements. These measurement-based estimates are then compared to theoretical models of the coupling efficiency. Using the theoretical coupling efficiency model, variable coupling can be engineered into the interconnect design, thus enabling partial coupling for arrays of photodetectors embedded in waveguide interconnections.

Board-level optical interconnection and signal distribution using embedded thin-film optoelectronic devices

Optical interconnection and signal distribution at the backplane, board, and substrate level can be implemented using thin-film active optoelectronic devices embedded in polymer waveguide structures. These active embedded devices eliminate the need for optical beam turning to and from photodetectors and emitters, respectively, for inputs and outputs to the substrate waveguides. In this paper, optical interconnections using fully embedded thin-film metal-semiconductor-metal (MSM) photodetectors in polymer optical waveguides are demonstrated, and the experimental characterization of these thin-film MSMs embedded in polymer waveguides is reported. To illustrate the potential for high-level signal distribution at the backplane, board, and substrate levels, a 1/spl times/4 balanced multimode interference (MMI) coupler has also been demonstrated in a photoimageable polymer for the first time. Finally, a 1/spl times/4 thin-film MSM photodetector array has been embedded in the output arms of the a photoimageable polymer MMI for the first time, and the MSM array photocurrent outputs from the 4 arms show that highly balanced optical signal distribution has been achieved.