Dr. Ragip Pala Profile

Dr. Ragip Pala

R&D Manager at Meta Materials Inc.

SPIE Involvement:

Author

Publications (2)

This will count as one of your downloads.

You will have access to both the presentation and article (if available).

DOWNLOAD NOW

This content is available for download via your institution's subscription. To access this item, please sign in to your personal account.

Email or Username Forgot your username?

Password Forgot your password?

Show

Keep me signed in

No SPIE account? Create an account

Proceedings Article | 14 March 2018 Presentation

>270-degree phase shift in aluminum gate tunable conducting oxide metasurfaces for continuous optical beam steering at 1550 nm (Conference Presentation)

Ghazaleh Kafaie Shirmanesh, Ruzan Sokhoyan, Ragip Pala, Harry Atwater

Proceedings Volume 10541, 105410B (2018) https://doi.org/10.1117/12.2286384

KEYWORDS: Aluminum, Oxides, Antennas, Phase shifts, Phased array optics, Beam steering, Phase shift keying, Optical components, Prisms, Lenses

Read Abstract +

In the last several years, metasurfaces have demonstrated promise as both flat optical elements to replace conventional three-dimensional components (prisms or lenses) as well as to access functions that are unachievable in conventional optics. To date, the functional performance of metasurfaces have typically been encoded at the time of fabrication, which fixes the achievable phase and amplitude for each elements in an array. However if actively controlled metasurface elements can be designed to dynamically control the phase shift and amplitude change imposed by each metasurface element, we could realize phased arrays to enable complex spatio-temporal wavefront engineering. We report here design and experimental demonstration of a tunable conducting oxide metasurface that achieves such active control by incorporating materials with voltage-tunable optical permivitties, such as indium tin oxide (ITO), into a metasurface [1]. We design a metasurface that consists of an aluminum back plane, HfO2 gate dielectric followed by a 14 nm thick ITO active layer, and a periodic array of aluminum patch antennas. We choose the dimensions of the Al antennas so that the antenna magnetic dipole resonance occurs at 1550 nm. By applying a gate bias between the Al antenna and ITO active layer, charge accumulation or depletion occurs at the ITO/HfO2 interface. This results in modulation of the ITO complex permittivity, thus altering the metasurface reflection phase and amplitude. The designed metasurface is capable of >270° phase shift. Our design enables independent control of each metasurface element enabling electrical control of the metasurface phase profile, which is an essential requirement for demonstration of continious beam steering. [1] Y.-W. Huang et al., “Gate-Tunable Conducting Oxide Metasurfaces”, Nano Letters 16, 5319-5325 (2016).

Proceedings Article | 3 November 2016 Presentation

Angle- and polarization-insensitive, small area, subtractive color filters via a-Si nanopillar arrays (Conference Presentation)

Katherine Fountaine, Mikinori Ito, Ragip Pala, Harry Atwater

Proceedings Volume 9927, 992705 (2016) https://doi.org/10.1117/12.2238433

KEYWORDS: Optical filters, Amorphous silicon, Waveguides, Nanophotonics, Plasmonics, Thermography, UV optics, Nanolithography, Imaging devices, Ultraviolet radiation

Read Abstract +

Spectrally-selective nanophotonic and plasmonic structures enjoy widespread interest for application as color filters in imaging devices, due to their potential advantages over traditional organic dyes and pigments. Organic dyes are straightforward to implement with predictable optical performance at large pixel size, but suffer from inherent optical cross-talk and stability (UV, thermal, humidity) issues and also exhibit increasingly unpredictable performance as pixel size approaches dye molecule size. Nanophotonic and plasmonic color filters are more robust, but often have polarization- and angle-dependent optical response and/or require large-range periodicity. Herein, we report on design and fabrication of polarization- and angle-insensitive CYM color filters based on a-Si nanopillar arrays as small as 1um2, supported by experiment, simulation, and analytic theory. Analytic waveguide and Mie theories explain the color filtering mechanism-- efficient coupling into and interband transition-mediated attenuation of waveguide-like modes—and also guided the FDTD simulation-based optimization of nanopillar array dimensions. The designed a-Si nanopillar arrays were fabricated using e-beam lithography and reactive ion etching; and were subsequently optically characterized, revealing the predicted polarization- and angle-insensitive (±40°) subtractive filter responses. Cyan, yellow, and magenta color filters have each been demonstrated. The effects of nanopillar array size and inter-array spacing were investigated both experimentally and theoretically to probe the issues of ever-shrinking pixel sizes and cross-talk, respectively. Results demonstrate that these nanopillar arrays maintain their performance down to 1um2 pixel sizes with no inter-array spacing. These concepts and results along with color-processed images taken with a fabricated color filter array will be presented and discussed.

My Library

You currently do not have any folders to save your paper to! Create a new folder below.

Folder Name

Folder Description

View contact details

UPDATE YOUR PROFILE

Is this your profile? Update it now.

Sign into your SPIE.org account

Don’t have a profile and want one?

Create an account on SPIE.org

Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks. You are receiving this notice because your organization may not have SPIE eBooks access.*

*Shibboleth/Open Athens users─please sign in to access your institution's subscriptions.

To obtain this item, you may purchase the complete book in print or electronic format on SPIE.org.

ORGANIZATIONAL
Sign in with credentials provided by your organization.

Organizational Username

Organizational Password

Show/Hide Password

INSTITUTIONAL
Select your institution to access the SPIE Digital Library.

SELECT YOUR INSTITUTION

PERSONAL
Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.

PERSONAL SIGN IN

No SPIE Account? Create one

;

PURCHASE THIS CONTENT

SUBSCRIBE TO DIGITAL LIBRARY

50 downloads per 1-year subscription

Members: $195

Non-members: $335 ADD TO CART

25 downloads per 1 - year subscription

Members: $145

Non-members: $250 ADD TO CART

PURCHASE SINGLE ARTICLE

Includes PDF, HTML & Video, when available

Members:

Non-members: ADD TO CART

Keywords/Phrases

Search In:

Publication Years