In the NOISE-Lab, we are building ultra low-power nanoscale optoelectronic devices by engineering the interaction between light and matter. A fundamental tradeoff in integrated photonics exists between the extent at which one can engineer the amplitude, phase and frequency of light and the energy, speed, active area, and cost needed to do so. In our research, we want to address this tradeoff by exploring new materials (with strong electro-optic and nonlinear optical properties), new photonic devices (nanoscale high quality resonators) and new system architectures (different types of coupled resonator architectures coupled via optoelectronic feedback circuits) to sculpt and tune the properties of light at few photon levels. If you are interested, you can see here the recent talk given by Arka in UW-EE research colloquium in Fall, 2014.

Two main research themes in my group are: integrated low power hybrid silicon compatible photonic platform for optical communication and computing; and miniature optical systems (image sensor, microscope, spatial light modulator and spectrometer) based on nano-photonic devices. Some of the ongoing research projects are:

Hybrid silicon (compatible) photonics(HySiP)

To improve the transceivers in current silicon photonics (SiP), we are looking into new materials, cavities and new modulation techniques. The current SiP devices are limited either by the large size of the devices, and hence large power and low speed (in MZI); or by high Q-resonators (thermal stabilization necessitates large power consumption; and photon lifetime reduces speed). We are exploring nanophotonic innovation to solve this three dimensional optimization problem (speed, power and size). Our approach is to explore a hybrid silicon photonic platform, where the underlying photonic devices are made of silicon, on top of which we will integrate new materials (like electro-optic oxides, polymers etc.). We, however, want to go beyond signal communication, and want to explore the avenues of optical computing. For that we are actively working on new nonlinear optical materials. We want to push the energy of these devices to few photon levels, where we can also study quantum optical effects. These devices can be thought of as precursors to future quantum information processing devices.

Self electro-optic devices for optical computing

Using a photo-absorbing material in a silicon ring resonator, we have proposed a platform, where an optoelectronic feedback could be easily implemented. This device provides a way to have optical bistability, without explicitly relying on any optical nonlinearity. Moreover, this device is shown to satisfy all th criteria, an optical swicth should have to build a scalable digital optical computing system. In our current research, we are looking into new materials, that can be integrated on top of silicon photonics, and can absorb light. Then we will build the optoelectronic feedback.
Funding Sources: AFOSR (YIP-Program); AFOSR (SBIR-CFDRC)

2D-material nanophotonics

We are actively collaborating with leading researchers in the 2D material community to build photonic devices using 2D materials. 2D materials are a newly discovered materials, which are monolayer and single-atom thick. Due to such low volume, the energy required to change this material can be very low. Moreover, these materials can be easily transferred to other materials. In our reseach, we are looking into building new light source, electro-optic modulator as well as strongly nonlinear optical devices using the 2D materials. These materials will be integrated on a large-scale silicon nitride photonic integrated circuits to build active devices. The choice of silicon nitride is motivated by their low loss, and lack of two-photon absorption. Unfortunately, they are essentially dielectric, and hence no active devices can be fabricated. This is where 2D materials will play a very important role.

Single photon nonlinear optics

We are exploring ways to realize single photon nonlinear optics in a scalable fashion. For this we are optimizing various multi-modal cavities to enhance the effective nonlinerity, as well as exploring strongly nonlinear material, including 2D materials, and organic materials. Another research direction is to explore polariton-polariton interaction to reach few photon nonlinear devices.

Tunable photonics

As part of the core HySiP interest, we are exploring various different materials, including complex oxides, polymer and phase change materials to build tunable and reconfigurable optical devices. This work also connects the other research interest of iCOS (tunable dielectric metasurface).
Funding Sources: NSF-EFRI-ACQUIRE; Intel-SRC

Intelligent compact optical sensor (iCOS)

With increase in wearable technology, Internet of things, and in this effort to make everything smart, one needs a lot of sensors, which needs to be compact, low power, and also intelligent to reduce the subsequent data processing. In our research, we are looking into this problem, by using nanophotonics. The compactness of the sensor demands to have integrated photonics to be used. Unfortunately, with small size, the performance of the sensor goes down. Hence we are researching to supplement the sensors with computing, to gain back the performance. We are mainly interetsed in two type of sensors: image sensors and spectrometer.

Tunable dielectric metasurface

Metasurfaces are two-dimensional quasi-periodic array of subwavelength features. Dielectric metasurfaces allow wavefront shaping of the incident light. However, the true potential of such metasurface can be realized, if one can tune them. We are looking into new materials with tunable refractive index to achieve this goal, or using flexible substrates to mechanically tune the metasurfaces. The goal is to build fast (~10's of MHz) sub-wavelength spatial light modulators.
Funding Sources: UW-RRF; Samsung-GRO

Cell-size Optical Microscope

Using the metasurface technology, we plan to build untra-compact, implantable optical microscopes. Using such microscopes,we can implant several of them inside a mouse brain, and image several parts of the brain simultaneously, thus truly enabling large scale brain imaging. Details of the project can be found here (PDF).

Freeform optics

Using metasurfaces, we are designing and building freeform optics, where we realize higher order polynominal surfaces, such as cubic surfaces. Details of the project can be found here. These freeform metasurfaces can be useful for various applications, including tunable eyewears, augmented reality visors, laser beam shaper and retroreflectors. Going beyond a single metasurface, we are exploring stacked meteasurfaces to create a simple volume optics.
Funding Sources: Tunoptix Inc.

Monolithic photonics for nonlinear image processing and optical neural network

Photons can pass each other without interacting with each other. That provides an attractive way to create large-scale optical network exploiting free-space geometry. For example a simple display with a million pixels can be placed in front of a CMOS camera with a million detectors, and just by introducing a lens in between them we can create few billion channels. This inherent parallellism of light, which made optics an attractive candidate at the first place for optical information processing, is lost when we go for integrated photonics, which relies on waveguides, or photonic wires. Using metasurface as lenses, and DBR as mirrors, we can create a monolithic geomtery, where we can take advantage of both free space (inherent parallellism) and integrated photonics (small size, robustness to misalignment). Using these devices, along with emerging nonlinear and tunable materials, we can create an optical resonator, which can process images, and can also potentially implement a monolithic optical neuron.

Our Collaborators

  • Alejandro Rodriguez, Princeton University
  • Eric Pop, Stanford
  • Xiaodong Xu,UW-Seattle
  • Dario Gerace, Univ. of Pavia, Italy
  • Jayakanth Ravichandran, USC, CA
  • Rehan Kapadia, USC, CA
  • Volker Sorger, GWU, DC

  • We also have active collaboration with DoD labs: NRL and AFRL.

    Research Facilities

  • Optics: We have optical characterization facilities in the wavelength range 400-1600nm, by using Fianium supercontinuum source, Priceton Instruments spectrometers (visible+IR), Santec CW laser (1425-1565nm) and spatial light modulators. We also have the capability to characterize photonic devices using grating-coupler in a fiber-in fiber-out setup. Addtionally, we have numeorus light sources in the visible frequency range to characterize metasurfaces and imaging optics.
  • Fabrication: We have access to state-of-the-art electron beam lithography, etching and deposition tools. We also have a 2D materials and cavity trasnfer station in our lab.
  • Computation: We have access to many electromagnetic solvers including, Lumerical FDTD, and have a high-end server for faster computation.

  • Past projects

    Low contrast metasurface

    Previous realizations of metasurfaces are base on metal or silicon. The rationale behind using these materials is their high refractive index. However, this is problematic as both the materials significantly absorb light at visible and near IR wavelength (<1 micron). In our research we are exploring ways to build such metasurface based optical elements using low-contrast materials.
    Funding Sources: Intel Early Career Award; Amazon Catalyst