The Pleasure Of Finding Things Out

The Pleasure of Finding Things Out Optical Society of America Deborah Berebichez, Ph.D.

July, 2009

Feynman, Photonics and Communications The ideal physics professor. Utterly brilliant and engaging, he was an inspiration.

"An honest man, the outstanding intuitionist of our age, and a prime example of what may lie in store for anyone who dares to follow the beat of a different drum" - Dr. Julian Schwinger

Problem with science is that a lot of people don’t find it interesting or relevant “I find it odd when an introduction mentions that I play the bongo drums it rarely finds it necessary to mention that I also do theoretical physics. It shows that we have more respect for the arts than for science.” Richard Feynman

“Don't blindly accept the word of authority. Test it for yourself! And this is what science does. It tests and it tests again, and it doubts and it doubts—always.” Feynman

Feynman’s Open Questions

“There is Plenty of Room at the Bottom” 1959 Feynman challenged physicists to write the entire Encyclopedia Brittanica on the head of a pin He was predicting nanotechnology

Feynman examines Bill McLellan’s motor, 1960

We actually did it! Charles Dickens’ A Tale of Two Cities:12 characters per micron. (Stanford University)

And the Story Continues…

The S U Hologram

Fabricating these tiny objects is not easy

What are Photonic Crystals? •Photonic crystals are periodic optical nanostructures that are designed to affect the motion of photons •They work by affecting the propagation of electromagnetic waves (EM)

•Photons (waves) propagate through the structure - or not - depending on their wavelength. Wavelengths of light that are allowed to travel are known as models

Trapping Light in Photonic •ByCrystals making point defects in a photonic crystal, light can be localized, trapped in the defect.

•The repeating regions of high and low dielectric constants have to be of ~200 nm (blue) to 350 nm (red) . This makes the fabrication of optical photonic crystals cumbersome and complex.

Let me tell you why it matters… Recent research shows promise in trapping light in crystals to build waveguides, or to replace electron storage for computer logic

Quantum computers will harness the power of atoms and molecules to perform memory and processing tasks 10X faster than silicon based ones

Let me tell you how we helped… Modeling the trapping of light in crystals Courant Institute, NYU and Department of Applied Physics and Applied Mathematics, Columbia University

Optimization of Scattering Resonances Journal of Mathematical Optimization P. Heider D. Berebichez R.V. Kohn M.I. Weinstein

Physics is the act of modeling the world Simulating Physics with Computers

Waves are everywhere!

More Waves: Communications Wireless communications with desired users Stanford University

Time-Reversal for Focusing Waves

WHAT IS TIME-REVERSAL? It is reversing the order in which a series of waves arrive at a defined position

WHY IS IT IMPORTANT? It can compress signals and focus them on a desired target, ex: lithotripsy, targeted ads, secure communications

Conventional waves disperse when traveling through a medium Communicating with time reversal

Focusing waves has applications in several areas such as secure wireless communications

IMAGINE THE FOLLOWING SCENARIO…

Using time-reversal, when sending a secret message, the sender could ensure that only one location would receive the message. Interceptors at other locations would only pick up noise due to unfocused waves.

t0

Time Reversal explained

source

T – t0

detecto r 2.59m

2.8m

2.4m

T

A picture of what happens in space FWD phas e 1

2

3

4

BWD phas e

The Two Main Results of TR From Long Time-Dispersion…

Temporal Compression of the Acoustic Wave to the Initial Pulse

From a State of Multiple Scattering…

Spatial Focusing to within λ/2 From original λ=2.6 cm

λ=1.29 red: original blue: after TR

cm

With TR The Bit Stream is Recovered Recompressed signal after TR obtained at Rx

-1

+1 We Recover the Bit Stream: { 0, 1, 1+1 }

Computational Model Wave Equation where r0 = source location and r = any position in the enclosure

Initial Pulse

Dirichlet Reflecting Neumann

Boundary Conditions Initial Conditions

Absorbing

,

23 Solve, We Use a FDTD Numerical Schem

Waves in Empty Room with Reflecting Walls

Close-up near source

Side Lobes = 35% of the Main Peak

Image Sources due to Reflecting Boundaries Actual Detector

Actual Domain

Actual Source

Image Sources due to Reflecting Boundaries Acoustic Field after TR in Enclosure with reflecting walls

Room with Multiple Detector κ=1

Close-up near source

ZOOM +

Enclosure with Multiple Detectors and Randomly-Placed κ = 1Close-up near source Scatterers

ZOOM +

Room with Absorbing Boundaries Field in the room at the Refocusing Time Close-up near source

ZOOM +

Enclosure with Randomly-Placed Scatterers and a Single Detector Close-up near source

ZOOM +

Spatial Focusing after TR a.

b. Ballisti c Sectio n

Diffus e Sectio Normalized n Field in Enclosure after TR

Wave Field Around the Source

Conclusions on TR Communications • Spatial Focusing ⇒ Only the Intended Receiver Gets the Message

• Temporal Compression ⇒ Bit Streams can be Recovered with Fidelity and Relatively Low Interference

TR works without line of sight

Tx

Message focuses at desired location

Rx

Experimental TR: Measurement locations LOCATION A

29 floors (5, 19, 28) 1.2km

Balconies SW & NE

LOCATION C

7 floors (roof)

2km LOCATION B

28 floors (19, 29)

2.6km

COMMUNICATIONS IN INDOOR BUILDINGS (UWB)

SECURE WIRELESS COMMUNICATIONS THAT REACH ONLY THE INTENDED RECEIVER AND CANNOT BE INTERCEPTED

UNDERWATER ACOUSTIC COMMUNICATIONS Antisubmarine warfare and underwater communications that benefit from targeted signaling

IN THE BATTLEFIELD: LOCATING SOLDIERS AND FINDING TANKS IN COMPLICATED FOLIAGE SCENARIOS

•Since spatial focusing can deliver focused energy at the intended receiver it can have applications also in homeland security and military communications. SPONSORS: NSF, ONR, DOE, DARPA, Intel UWB

Science is fun! But: People get discouraged at a young age to be analytical, scientific or technologically oriented

We can change that!

Why Now? • We’re not growing enough scientists, especially compared to India and China • The Problems that need solving need science: Energy, Climate, Genetics, Medicine, IT • Good Citizens need to understand scientific issues to be informed, good voters

The Science of Everyday Life

It’s good to see a

cool Woman

doing science

science and biology

I want to study

-Ana, age 14

I enjoy being in

the

lab thank you for showing me that

A

Woman Can do Science

Ximena, age 16

Thank You for your Attention

To engage people, we need to make science easy to relate to, fun, relevant and personal

E+Sc+Ee=C

2

To engage people, we need to make science easy to relate to, fun, relevant and personal

E+Sc+Ee=C

2

Entertainment + Scientific Content + Everyday Experiences = Cool Comprehension “The physics of high heels," "chemistry in the kitchen," "new hi-tech gadgets for women," “going fashionably green”