TimeTime--Reversal Optical Phase Reversal Optical Phase Conjugation for Tissue Conjugation for Tissue Turbidity SuppressionTurbidity Suppression

Zahid Yaqoob1, Emily McDowell1, GuoanZheng1, Snow Tseng2, Michael S. Feld3,

Demetri Psaltis1,4, Changhuei Yang1

1California Institute of Technology2Taiwan National University

3MIT4EPFL

Caltech Biophotonics Laboratory

Caltech Biophotonics Laboratory

References:References:

Snow Tseng, Changhuei Yang, “2-D PSTD simulation of optical phase conjugation for turbidity suppression”, OE 15, 16005 (2007)

Guoan Zheng, Lixin Ran, and Changhuei Yang, “Electromagnetic equivalent model for phase conjugate mirror based on the utilization of left handed material”, OE 15, 13877 (2007)

Zahid Yaqoob, Demetri Psaltis, Michael S. Feld, Changhuei Yang, “Turbidity Suppression by Optical Phase Conjugation”, Nature Photonics 2, 110 (2008).

A Key Difference between A Jellyfish And Me A Key Difference between A Jellyfish And Me

Caltech Biophotonics Laboratory

http://www.glaucus.org.uk/Moonjell.htm

Transparent Not Transparent!

- being transparent will really help with disease detection!

Phase Conjugation And ScatteringPhase Conjugation And Scattering

Caltech Biophotonics Laboratory

Scattering is a deterministic process. Scattering is at least 10x stronger than absorption in tissue.

At λ = 633nm,a photon’s average scattering length is 40 μm.

average absorption length is 100 mm!average travel length to lose orientation is 1.2 mm

Caltech Biophotonics Laboratory

OPCWavefront

PCM

IncidentWavefront

PCM

Recording Ref Beam

Readout Ref Beam

scatterers scatterers

What is Phase Conjugation?What is Phase Conjugation?

What is Phase Conjugation?What is Phase Conjugation?

Caltech Biophotonics Laboratory

Reproduce the incident wavefront and propagate it back towards sourceEquivalently, reverses the phase wavefront.

mirrorphase conjugate mirror

http://www.futureworld.dk/tech/ether/phasecon/phasecon.htmhttp://en.wikipedia.org/wiki/Image:PhaseConjugationPrinciple.en.png

Phase Conjugation And ScatteringPhase Conjugation And Scattering

100 μm

100 μm

100 μm

USAF target

photo-refractive crystal

USAF target 0.5 mm chicken tissue

photo-refractive crystal

USAF target clear agarose

Recording

Phase Conjugation And ScatteringPhase Conjugation And Scattering

100 μm

100 μm

100 μm

100 μm

photo-refractive crystal

photo-refractive crystal

USAF target 0.5 mm chicken tissue

USAF target clear agarose

With Chicken Breast Tissue (~ 250 With Chicken Breast Tissue (~ 250 μμm thick)m thick)

Caltech Biophotonics Laboratory

photo-refractive crystal

photo-refractive crystal

Some Surprising ResultsSome Surprising Results

Caltech Biophotonics Laboratory

TS-OPC reconstruction quality does not appear to deteriorate with increased scattering initially.

TS-OPC can be observed through tissues as thick as 5 mm at 532 nm wavelength

Potential ChallengesPotential Challenges

Caltech Biophotonics Laboratory

1. Living tissues will likely have micro-motions originating from cell agitations.

2. Blood flowDoes indeed impact on TSOPC, but deterioration rate is measured to be ~ 10’s seconds.

We lose light trajectories that pass through blood, but TSOPC does not require complete wavefrontreplication.

Both are non-issues if we employ real-time optical phase conjugation approaches.

Examples: 4-wave mixing, 2D phase modulator + wavefront sensor

What is this phenomenon good for?What is this phenomenon good for?

Caltech Biophotonics Laboratory

photorefractive crystal

Probably not a good idea….

1. A means for targeting strong 1. A means for targeting strong scatterersscatterers in in tissuetissue

Caltech Biophotonics Laboratory

photorefractive crystal

photorefractive crystal

Step 1: Send in weak illumination

photorefractive crystal

Step 2: Record the backscattering

Step 3: Play back the PC wavefront

Good for:

1. Photodynamic Therapy2. Neuron Activation3. Port-wine Stain Removal4. Basically any situation where you

want to concentrate light on strong scatterers in tissue.

absorbing dyemolecules

strongscatterer

Caltech Biophotonics Laboratory

forward illumination

transmission

side scatter

back scatter

forward illumination

transmission

side scatter

back scatter

A

B

2. A means for measuring scattering site 2. A means for measuring scattering site heterogeneityheterogeneity

3. Deep tissue imaging (separation of 3. Deep tissue imaging (separation of absorption and scattering contributions)absorption and scattering contributions)

Caltech Biophotonics Laboratory

BiologicalSample

PCM1

(a)

BiologicalSample

PCM1

(b)

BiologicalSample

PCM1

(c)

PCM2 PCM2

brown = absorptive objects

Caltech Biophotonics Laboratory

References:References:

Snow Tseng, Changhuei Yang, “2-D PSTD simulation of optical phase conjugation for turbidity suppression”, OE 15, 16005 (2007)

Guoan Zheng, Lixin Ran, and Changhuei Yang, “Electromagnetic equivalent model for phase conjugate mirror based on the utilization of left handed material”, OE 15, 13877 (2007)

Zahid Yaqoob, Demetri Psaltis, Michael S. Feld, Changhuei Yang, “Turbidity Suppression by Optical Phase Conjugation”, Nature Photonics 2, 110 (2008).