michal tutorial 1 - fep.if.usp.brfep.if.usp.br/~mmartine/transparencias/18_2_lipson.pdf · cornell...

Cornell Nanophotonics Group Cornell Nanophotonics Group �� http://http://nanophotonics.ece.cornell.edunanophotonics.ece.cornell.edu

Photonics on-chip Michal Lipson

School of Electrical and Computer Engineering

Cornell University

nanophotonics.ece.cornell.edu


Outline

• Motivation and wave guiding theory

(quantum optics on chip)

• Resonators and applications of waveguides

on-chip

• Changing properties of light using

resonators (analogous to quantum optics on-

chip)


Photonics Drives Telecom

10-2

100

102

104

106

108

1010

1012

1014

1880 1900 1920 1940 1960 1980 2000 2020 2040

Rel

ativ

e In

form

atio

n C

apac

ity (

bit/s

)

Year

Telephone lines first constructed

Carrier Telephony first used 12 voicechannels on one wire pair

Early coaxial cable links

Advanced coaxial and

microwave systems

CommunicationSatellites

Single channel (ETDM)

Multi-channel(WDM)

OPTICAL FIBER SYSTEMS

~10Mbps.Km

We are experiencing this drive on-chip!


Luxtera CMOS Photonics Technology


Kimerling, 1997

Silicon photonics on-chip


Silicon photonics for multi-core

interconnect

Photonic Network Interconnect Plane (includes optical devices, electronic drivers & amplifiers and electronic control network)

Optical Off-chipInterconnects

Memory Plane

Memory Plane

Memory Plane

BEOL verticalelectrical interconnects

Processor Plane w/ local memory cache

Photonic Network Interconnect Plane (includes optical devices, electronic drivers & amplifiers and electronic control network)

Optical Off-chipInterconnects

Memory Plane

Memory Plane

Memory Plane

BEOL verticalelectrical interconnects

Processor Plane w/ local memory cache

Bergman-Columbia, J. Kash, IBM

Opt

ical

I/O

Opt

ical

I/O


Why light is guided?How light is guided?

Total internal reflection!

θθθθ> θθθθcrit=sin-1(nL/nH)

The larger is the index-the easier it is to guide

θθθθ


Is it a ray or is it a wave?

Ray picture

Wave picture

E~e-γx


Wavector of propagation

• Light propagating in a medium with index

n:

• vp=c/n

• λ=λo/n

kon kf

β

β2 =(kon+ kf)2

β ≡koneff


Different modes in a waveguide

kon

β

β2 =(ko2n2- kf

2)

E ~ cos kfx e-γx

γ =sqrt(β2-ko2nclad

2)

kf

Lower order

Higher order

β= koneff> koncladd and < konslab


Bending light on-chip

Work only with high confinement,

single mode waveguides!


“Slot-Waveguide” for High Confinement in sub-

wavelength regions!

nH nH

ws wh

h nS

wh

nC

x

y z

nH = 3.48

nC = nS = 1.46

wS = 50 nm

wh = 180 nm wh = 180 nm

nH = 3.48

0

1.0

Col

or s

cale

nH = 3.48

nC = nS = 1.46

wS = 50 nm

wh = 180 nm wh = 180 nm

nH = 3.48

0

1.0

Col

or s

cale

� True eigenmode

TE-like mode


Si Si

E-Field Distribution

BBAA

rr

BA

EnEn

nED

DDSdD

,

2

,

2

2

0

,,

,

0

⊥⊥

⊥⊥

=⇒

==

=⇒=⋅∫εεε

rr

rr

(nA > nB) � E⊥,B > E⊥,A

x

Si Si

x

nH = 3.48

nC = nS = 1.46

wS = 50 nm

wh = 180 nm wh = 180 nm

nH = 3.48

0

1.0

Col

or s

cale

nH = 3.48

nC = nS = 1.46

wS = 50 nm

wh = 180 nm wh = 180 nm

nH = 3.48

0

1.0

Col

or s

cale

V.Almeida, and M. Lipson et al,, Optics Letters 29, 2387(2004).


Fabrication of Slot-Waveguide and

Measurement of Effective Index

slot

nH nH

ws wh

h nS

wh

nC

x

y z

2

0

22

knn xCeff

γ+≅


1 .5 0 1 .5 2 1 .5 4 1 .5 6 1 .5 8 1 .6 0 1 .6 2 1 .6 40 .0

0 .2

0 .4

0 .6

0 .8

1 .0

Qua

si-T

M T

rans

mis

sion

(a.u

.)

W a v e le n g th ( µµµµ m )

1 .5 0 1 .5 2 1 .5 4 1 .5 6 1 .5 8 1 .6 0 1 .6 2 1 .6 40 .0

0 .2

0 .4

0 .6

0 .8

1 .0

Qua

si-T

E T

rans

mis

sio

n (a

.u.)

W a ve le n g th (µµµµ m )

TE

1.54 1.56 1.58 1.60

2.2

2.4

2.6

2.8

Wavelength (µµµµm)

Gro

up

Ind

ex

TE (calculated)TM (calculated)TM (experimental)TE (experimental)

Slot-Waveguides for

Highly Integrated Photonics

TM

20 µµ µµ

m

A. Scherer, SPIE, Denver, Aug 2004


Slots for sensing

optical input

optical output

gas input gas output

slot


High index contrast leads to high

confinement kon

kf

β

γ =sqrt(β2-ko2ncladd

2)

High confienmentLow confienment


High confinement waveguides for functional

devices

Light

� Intensity in the waveguides can be orders of magnitude higher than the

intensity in the core of single mode optical fiber.

� Nonlinear optical effect can be excited with moderate optical power in

short distances.

Si

SiO2

450 nm ×××× 250 nm

Silicon waveguides:

•High index contrast (very small waveguides: 3 orders of magnitude light

enhancement when compared to fibers)

•Compatible with CMOS microelectronics.

•Ability of large-scale integration.


BOx: 3µm

Si: 250nm

Si Substrate

BOx: 3µm

Si Substrate

BOx: 3µm

Width = 450nm

Ebeam Lithography EBeam Resist

Oxide Deposition

Etching using RIE

Fabrication


Orientation of the waveguides

Highly polarization dependent


Why not every angle (wavector) can

propagate?

k on

2konhcos θθθθ+Ødown+ Øup=q2ππππ q=1,2,3…..

or cos θθθθ~q ππππ/nkoh

θθθθ


A Very small waveguide

cos θθθθ~q ππππ/nkoh

If q=1 and h small

cos θθθθ~ ππππ/nkoh is large (small angle)

k onθθθθ

Small angle means very large evanescent field!


Silicon waveguide

Fiber

Light

~3% transmission


Naive Solution

0.5 µ µ µ µm

10 µ µ µ µm

cm


Inverse Taper

0.5 µ µ µ µm

10 µ µ µ µm20µm

NTT, IBM


0.5 µ µ µ µm

10 µ µ µ µm20µm

Inverse Taper


Substrate

x

z

y

Substrate (Si)

Optical Fiber

MFD = 4.9 µm ws = 120 nm

h = 250 nm

Cladding (SiO2)

Simulations

95% efficiency


Fabrication

<1dB losses

200 nm

CouplerWaveguide

Almeida, V. R., Panepucci, R. R., and M. Lipson, Optics Letters, 28, 1302 (2003).


Summary

Motivation

Wave guiding theory

Slot waveguide

Fiber to waveguide coupler

High confinement waveguides/fabrication

michal tutorial 1 - fep.if.usp.brfep.if.usp.br/~mmartine/transparencias/18_2_lipson.pdf · cornell...

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