Ultra-Fast Wavelength-Hopping Optical CDMA Principal Investigator: Eli Yablonovitch;

Co-PI’s: Prof. Rick Wesel, Prof. Bahram Jalali, Prof. Ming WuElectrical Engineering Department, University of California, Los Angeles CA 90095

ObjectivesApproach

Accomplishments

To create an Optical Code Division Multiplexing system that:•That is more secure than a WDM optical communications system using conventional time domain codes.•That suffers little or no capacity degradation compared to a WDM system.•That is ultimately scalable to 100 simultaneous users running at 10Gbits/sec each.•That is usable for both free-space optical as well as fibers•That will be reasonably close in hardware cost compared to a WDM system.

We will encode individual bits in a wavelength-time matrix, that is programmed by provably secure algorithms, and that hops with every bit period.

OCDMATime

Wav

elen

gth 2

222222222

TDMTime

Wav

elen

gth

WDM

1 2 1

2 1

1 2

2 1 1

1

2

1 2

2 2

Time

Wav

elen

gth

111111111111

1 1 1 1 1 1 1 1

2 2 2 2 2 2 2 2

•Have distinguished the advantages and dis-advantages between direct sequence spread spectrum and frequency hopping.

•Designed a system for secure wavelength hopping OCDMA.

t

tm

tm

t

tmt

)cos(2

)cos(2

cos

)cos(1cos

carrier

+-

Amplitude Modulation

freq

Coherent Communication(homodyne detection)

signal(t)

carrier wave local oscillator

signal(t)cos t2signal(t)cos t

Transmitter Receiver

)(2

1tsignal

Direct Sequence Spread Spectrum:

carrier wavecos t code(t) signal(t)

Transmittersignal(t)

code(t)

“noisy” carrier

1

-1time

chip

local oscillatorcos t

code(t)local codegenerator

Receivercos t2 code(t)2 signal(t)

)(2

1tsignal

1

t

1

1

direct sequence PN code

data

PN data

Tc

0

0

0

Tb

c(t)

t

t

d(t)

sds(t)

d(t)

c(t)

sds(t) direct sequence encoding

Figure 2a

Figure 2b

Frequency Hopping Spread Spectrum

1. Time Division - TDMA2. Wavelength Division - WDMA3. Code Division - CDMA

OCDMATime

Wav

elen

gth 2

222222222

TDMTime

Wav

elen

gth

WDM

1 2 1

2 1

1 2

2 1 1

1

2

1 2

2 2

Time

Wav

elen

gth

111111111111

1 1 1 1 1 1 1 1

2 2 2 2 2 2 2 2

CDMA or Spread-Spectrum

• Seemingly wasteful of bandwidth

channels

nmmn ttcodetcode d)()(

Codes are orthogonal, N channels N codesChannel capacity is unchanged!

• Secret• Covert• Jamming resistant

• Multi-path or speckle resistant• Self-managed network - users pick codes at random

Orthogonality Condition:

• Direct Sequence (homogeneous broadening)• Frequency Hopping (inhomogeneous) first patented by Hedy Lamarr (actress) in 1941• Used by Secret Service (U.S.)• Military radios• Cellular telephones: Subtle optimization competition between TDMA and CDMA•About 50% of US cellphones use CDMA, including particularly the Sprint PCS network.•World-Wide Generation 3.0 Cellphone standard will be CDMA.

Dispersion-Limited Signal Propagation Distance

TDM2)rate data total(

1

L

2

2

)rate data total(

M

L

2)rate data total(

M

LCDM

WDM

= dispersion coefficientM = # of channels (length of code)

The basic idea: wavelength-time matrix

OCDMATime

Wav

elen

gth 2

222222222

TDMTime

Wav

elen

gth

WDM

1 2 1

2 1

1 2

2 1 1

1

2

1 2

2 2

Time

Wav

elen

gth

111111111111

1 1 1 1 1 1 1 1

2 2 2 2 2 2 2 2

Legend:

1 2 user1, user2

Generate hopping patterns1. Bob chooses secret primes p and q and computes n = pq.2. Bob chooses integer e which is prime to (p-1)(q-1).3. Bob computes d with de mod (p-1)(q-1) 1.4. Bob makes n and e public, and keeps p, q, d secret.5. Alice encrypts m as c me mod n, and sends c to Bob over a public channel.6. Bob decrypts by computing m cd mod n.7. Both Bob and Alice use m as a seed and feed it in to Advanced Encryption Standard (AES) encoder to generate a string of random numbers.8. That string is fed back into to AES encoder to generate a 2nd string, etc., etc. 9. Both Bob and Alice use the string of random numbers to fill the wavelength-time matrix, using modular arithmetic.10. Bob and Alice generate the hopping patterns according to the wavelength-time matrix, using a different modular arithmetic

RSApublickeyalgorithm

AESencoder

Seed

Sk-1

Sk

}

Fill the wavelength-time matrixRandom numbers: 232 192 108 173 182 69 178 228 185 156 141 96 186 37 157 168 55 106 148 201 181 35 143 8 164 228 220 134 221 104 27 137 192 23 235 110 36 16 192 4 50 56 201 107 181 6 128 249 146 241 104 136 58 183 208 42 99 60 193 30 101 111 252 128

7 32 4 1 59 44 6 40

24 20 43 14 5 16 28 31

23 18 39 17 42 49 8 46

36 48 58 38 15 22 61 45

19 41 56 60 12 37 57 10

0 50 27 51 55 47 13 33

2 35 30 26 11 53 3 9

21 34 25 62 54 52 63 29

TimeW

avel

engt

h

Wav

elen

gth

232 mod 64 = 40

192 mod 63 = 3

108 mod 62 = 46

173 mod 61 = 51Time

1

0

2 3

yk= N mod (64-k), k = 0, 1, … 63

“The pattern never repeats”

Then randomly fill the next matrix using a continuation of the random string.

Define users from wavelength-time matrix

1

17 49

41 57

33

9

25

Time

Wav

elen

gth

32 40

24 16

8

48

56

0

Time

Wav

elen

gth

User1 User2

User k: numbers with N mod 8 = k-1, k = 1, 2, …, 8

High level of security in the case with only one user

Non-vulnerable

1 1

1

1

1 1

1

1

Time

Wav

elen

gth

Vulnerable

1 1

1

1

1

1

1

1

Time

Wav

elen

gth

Legend:

1 user1

Overall system design using electronic switches

Pattern generator

Data 1

Data 2

Data 3

Data 4

Hopping

pattern

4:1

FiberSpace

DivisionSwitch +

small buffer

Modulator

Modulator

Modulator

Modulator

1:4

Data 1

Data 2

Data 3

Data 4

Detector

Detector

Detector

Detector

Space

DivisionSwitch +

small buffer

Transm

itter

Receiver

The first milepost demo of 4x2.5Gbps: transmitter

Pattern generator

16X16Switch

155MHzData 2.5Gbps

Data

Data

Data

User 1

User 2

User 3

User 4

Hopping

pattern

4:1

Modulator

Modulator

Modulator

Modulator

Fiber

1:16

1:16

1:16

1:16

16:1

16:1

16:1

16:1

2.5Gbps

16X16Switch

16X16Switch

16X16Switch

de-Serializer Serializer

1:16 16:1

Hopping

pattern

1:4

Detector

Fiber

Detector

Detector

Detector

Data

User 116X16Switch

155MHz

1:16

1:16

1:16

1:16

16:1

16:1

16:1

16X16Switch

16X16Switch

16X16Switch

16:1

Data

User 2

Data

User 3

Data

User 4

Pattern generator

de-Serializer Serializer

1:16 16:1

The first milepost demo of 4x2.5Gbps: receiver

Switching FabricsIn general, the implementation of an NXN switch need NlogN 2X2 switches. For an NXN rearrangeable permutation switch, the number of 2X2 swithes is at least log(N!), which is approximately equal to NlogNN+log(2N)/2. For N=16, log(N!) = 44.2.

Network implementing 16X16 using 56 2X2 switches.

Overall system design using LiNbO3 optical switches

Pattern generator

Hopping

pattern

1:4

Data 1

4:1

Fiber16X16LiNbO3

SpaceDivisionSwitch

ModulatorData 1

1:4

ModulatorData 2

1:4

ModulatorData 3

1:4

ModulatorData 4

1:4

4:1

4:1

4:1

4:1

OE

OE

OE

OE

EO

EO

EO

EO

OE

OE

OE

OE

EO

EO

EO

EO

16X16LiNbO3

SpaceDivisionSwitch

1:4

1:4

1:4

1:4

4:1

4:1

4:1

4:1

OE

OE

OE

OE

Data 2

Data 3

Data 4

1:4Bit time division demultiplexer 4:1

Bit interleaving time division multiplexer

Availability of components:2X2 switch

VSC8302.5Gbits/sec Dual 2x2Crosspoint Switch

Features

•Up to 2.5GHz Clock, 2.5Gb/s NRZ Data Bandwidth

•Output Jitter <40ps Peak-to-Peak

•Output Skew <50ps

•Single 3.3V Power Supply

•Industry Standard 44 Pin PQFP Packaging

•Switch configuration time < 1ns

Availability of components: de-Serializer and Serializer

VSC8163 16:1 Serializer

Features:2.5Gb/s Operation

+3.3V Single Supply Operation

VSC8164 1:16 de-Serializer

Features:2.5Gb/s Operation

+3.3V Single Supply Operation

Time / Wavelength

Inte

nsi

ty

Time gate Chirped SuperContinuumpulse

Time / Wavelength

Inte

nsi

ty

Time gate Chirped SuperContinuumpulse

(a)

SupercontinuumPulse

AWG

Wavelength

Inte

nsit

y

SupercontinuumPulse

AWG

Wavelength

Inte

nsit

y

Chip-ScaleSupercontinuum

Source

Wavelength-to-Time

Converter

Fast WavelengthHopping Code

Time

EAM

EAM

EAM

EAM

2

3

Time

1xN

Sp

litt

er

Nx

1 C

om

bin

er

To StarCoupler

ElectronicsCode

Control

Time-to-WavelengthConverter

Time Time

Monolithic Optical Encoder

Time

Data

Wavelength-to-Time

Converter

Matched Fast WavelengthHopping Code

FG-PD

FG-PD

FG-PD

FG-PD

1 x

N

Tim

e-D

ivis

ion

De

mu

ltip

lxe

r

From StarCoupler

ElectronicGating

Time

Optical Decoder

Time

time

time

time

time

time =

Time Time

De

tec

tor

Ou

tpu

t

FG-PD =Fast-Gated

Photodetector

• Since the wavelength-hopping occurs in the time domain, the initial implementation requires only time-encoded WDM hardware.

• Four OCDMA channels at 10 Gbit/sec requires only 4 WDM channels, that can be implemented in Coarse WDM hardware, time encoded by a Silicon chip.

•100 simultaneous OCDMA users (out of 1000 subscribers) can be implemented at the expense of more WDM hardware, and would require Dense WDM.

• Component count can be reduced, and spectral efficiency increased, by using chirped sources and time gating in Silicon to fill-in the spectral guard bands:

Receiver Transmitter

Chip-ScaleSupercontinuum

Source

Wavelength-to-Time

Converter

Fast WavelengthHopping Code

Time

EAM

EAM

EAM

EAM

23

Time1x

N Splitter

Nx1

Com

bin

er

To StarCoupler

ElectronicsCode

Control

Time-to-WavelengthConverter

Time Time

Monolithic Optical Encoder

Time

Data

Wavelength-to-Time

Converter

Matched Fast Wavelength

Hopping Code

FG-PD

FG-PD

FG-PD

FG-PD

1 x

N

Tim

e-D

ivis

ion

Dem

ult

iplx

er

From StarCoupler

ElectronicGating

Time

Optical Decoder

Time

time

time

time

time

time =

Time Time

Det

ecto

r O

utp

ut

FG-PD =Fast-Gated

Photodetector

Chip-ScaleSupercontinuum

Source

Wavelength-to-Time

Converter

Fast WavelengthHopping Code

Time

EAM

EAM

EAM

EAM

23

Time

1xN Splitter

Nx1

Com

bin

er

To StarCoupler

ElectronicsCode

Control

Time-to-WavelengthConverter

Time Time

Monolithic Optical Encoder

Time

Data

Transmitter 1

Receiver 1

time syncsignal

Transmitter K

Receiver K

Star CouplerTransmitter i

Receiver i

Transmitter 3

Receiver 3

Transmitter 4

Receiver 4

time syncsignal

Transmitter 2

Receiver 2

time syncsignal

time syncsignal

time syncsignal

time syncsignal

User#1

User#2

User#3

User#4

User#6

User#7

User#i

User#j

User#N

User#5

-10 dB

-10 dB

OCDMAReceiver

OCDMATransmitter

OCDMANode

2x2Protection

Switch

10-dBCoupler

10-dBCoupler

Fast wavelength-hopping OCDMA is compatible with conventional WDM components,

allowing early technology demonstrations.

Rapid Summary of Mile-Posts:•demonstration of the wavelengthtime concept using discrete conventional off-the-shelf WDM components.

• 2 users @ 2.5Gbit/sec is expected to lead rapidly to 4 users @ 10Gbit/sec, using conventional components.

• 100 simultaneous users, out of 1000 subscribers should be feasible, but would require a large number of Dense WDM components.

• Time chirped hardware would lead to more efficient use of components, and more efficient spectral packing of the optical channels, and the inter-channel spaces.

Critical Milestones, (Go/No Go decision) at 15 months:

1. Deliver Fiber System of Two OCDMA users @ 2.5Gbit/sec.

2. Validate Si-Ge time gating chip design for >4 users at higher speed.

Progression of FWH-OCDMA capabilities as a function of hardware progress:

Initial Demonstrations Using Conventional WDM components:1. Four OCDMA users @ 2.5Gbit/sec. (15 month deliverable)2. Ultimately Ten OCDMA users @ 10Gbit/sec.

All components are off-the-shelf, except for fast time-gating logic that implements the hopping code in Si-Ge logic technology.

Later Demonstrations Using Chirped WDM hardware:

1. In this later phase, we will demonstrate an Optical-CDMA transmitter with four wavelengths and four parallel electro-absorption modulators, duplicating the coarse WDM result; four OCDMA users @ 10Gbit/sec.

2. Increase the number of parallel optical channels, that will require large numbers of modulators and photo-detectors on-chip.

...

WD

M D

EM

UX

1 …N

2

transmittedsignal

WD

M M

UX

d(t)

c(t)

wavelengthselect

sds(t)

hop patterngenerator

Figure 6

Multi-wavelengthsource

...

output data

MU

X

DE

MU

X

...

...

MU

X

DE

MU

X

...

...

i0 or i1

bT

0

thresholddevice

3-dBsplitter

(A)

wavelengthselect

hop patterngenerator

c(t)

i1 or i0

wavelengthselect

hop patterngenerator

c(t)

Figure 7

1.0

0.50

2)(1 T

2)(T

1.0

0.50

receiveddata

com

plem

enta

rysp

ectral

dec

oder

balancedreceiver

2T

21 T

starcoupler

2T

21 Tor

com

plem

enta

rysp

ectral

enc

oder

inputdata

balancedtransmitter