Ultra-Fast Wavelength-Hopping Optical CDMA
Principal Investigator: Eli Yablonovitch;
Co-PI’s: Prof. Rick Wesel, Prof. Bahram Jalali, Prof. Ming Wu
Electrical Engineering Department, University of California, Los Angeles CA 90095
Objectives
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.
Approach
We will encode individual bits in a wavelength-time
matrix, that is programmed by provably secure
algorithms, and that hops with every bit period.
•Designed a system for secure wavelength hopping
OCDMA.
2
2
2
2
2
2
2
2
2
2
T im e
TDM
1
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
W avelength
1
1
1
1
1
1
1
1
1
1
1
1
W avelength
•Have distinguished the advantages and dis-advantages
between direct sequence spread spectrum
and frequency hopping.
W avelength
Accomplishments
2
2
1
2
2
1
1
1
2
1
2
2
T im e
W DM
1
1
2
T im e
OCDM A
Amplitude Modulation
t
cos  t  1  m cos(   t )
 cos  t 
m
cos(     ) t 
2
m
cos(     ) t
2
carrier
-

+
freq
Coherent Communication
(homodyne detection)
signal(t)
signal(t)cos t
signal(t)cos t2

1
2
carrier wave
local oscillator
Transmitter
Receiver
signal ( t )
Direct Sequence Spread Spectrum:
Transmitter
signal(t)
carrier wave
“noisy” carrier
cos t  code(t)  signal(t)
code(t)
1
-1
time
chip
Receiver
|cos t|2  |code(t)|2  signal(t)

1
signal ( t )
2
local oscillator
cos t
code(t)
local code
generator
d(t)
sds(t)
direct sequence encoding
c(t)
Figure 2a
c(t)
1
Tc
direct sequence PN code
0
t
d(t)
1
0
Tb
data
t
sds(t)
1
PN  data
0
t
Figure 2b
Frequency Hopping Spread Spectrum
1. Time Division - TDMA
2. Wavelength Division - WDMA
3. Code Division - CDMA
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
Time
TDM
1
2
2
1
1
1
1
1
1
1
1
1
1
1
2
2
1
1
1
2
2
2
2
2
2
2
2
2
1
2
2
Time
WDM
2
Time
OCDMA
CDMA or Spread-Spectrum
• Seemingly wasteful of bandwidth
Orthogonality Condition:
channels

 code
n
( t )  code
m
( t ) d t   nm
Codes are orthogonal, N channels  N codes
Channel capacity is unchanged!
• Secret
• Covert
• Jamming resistant
• Multi-path or speckle resistant
• Self-managed network - users
pick codes at random
• 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
TDM
CDM
WDM
L 
L 
L 
1
  ( total data rate )
2
M
  ( total data rate )
M
2
2
  ( total data rate )
 = dispersion coefficient
M = # of channels (length of code)
2
The basic idea: wavelength-time matrix
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
2
1
 user1,
1
1
1
1
1
1
1
2
1
1
1
2
2
2
2
2
2
2
2
2
1
2
2
Time
TDM
1
1
1
1
2
Time
Legend:
2
WDM
2
 user2
2
Time
OCDMA
Generate hopping patterns
1. 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.
Seed
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
}
RSA
public
key
algorithm
AES
encoder
Sk-1
Sk
Fill the wavelength-time matrix
Random 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
192 mod 63 = 3
yk= N mod (64-k), k = 0, 1, … 63
1
0
2
3
232 mod 64 = 40
Time
108 mod 62 = 46
173 mod 61 = 51
7
24
23
36
19
0
2
21
32
20
18
48
41
50
35
34
4
43
39
58
56
27
30
25
1
14
17
38
60
51
26
62
59
5
42
15
12
55
11
54
44
16
49
22
37
47
53
52
6
28
8
61
57
13
3
63
40
31
46
45
10
33
9
29
Time
“The pattern never repeats”
Then randomly fill the next matrix using a continuation of the random string.
Define users from wavelength-time matrix
User k: numbers with N mod 8 = k-1, k = 1, 2, …, 8
User1
User2
32
40
24
1
16
8
17
49
48
56
41
57
0
33
9
25
Time
Time
High level of security in the case with only one user
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
Time
Time
Vulnerable
Legend:
Non-vulnerable
1
 user1
Overall system design using electronic switches
Data 1
Transmitter
Data 2
Data 3
Data 4
l1
l2
1:4
l3
l4
Hopping
pattern
Space
Division
Switch +
small buffer
Detector
Detector
Detector
Detector
Pattern
generator
l1
Modulator
l2
Modulator
4:1
l3
Modulator
l4
Modulator
Data 1
Space
Division
Switch +
small buffer
Data 2
Data 3
Data 4
Fiber
The first milepost demo of 4x2.5Gbps: transmitter
155MHz
Data 2.5Gbps
User 1
Data
16X16
Switch
User 2
Data
16X16
Switch
User 3
Data
16X16
Switch
User 4
Hopping
pattern
16X16
Switch
2.5Gbps
l1 Modulator
l2
Modulator
4:1
l3
Modulator
l4 Modulator
Pattern
generator
de-Serializer
Serializer
Fiber
The first milepost demo of 4x2.5Gbps: receiver
l1
155MHz
16X16
Switch
Detector
16X16
Switch
Detector
Fiber
l2
1:4
Data
User 1
Data
User 2
l3
16X16
Switch
Detector
l4
Detector
Hopping
Pattern
pattern
generator
Data
User 3
Data
16X16
Switch
User 4
de-Serializer
Serializer
Switching Fabrics
In 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 NlogNN+log(2N)/2. For
N=16, log(N!) = 44.2.
Network implementing 16X16 using 56 2X2 switches.
Overall system design using LiNbO3 optical switches
l0
Data 1
l0
Data 2
l0
Data 3
l0
Data 4
Modulator
16X16
LiNbO3
Space
Division
Switch
Modulator
Modulator
Modulator
l1
l2
1:4
l3
l4
Hopping
pattern
OE
EO
OE
EO
OE
EO
EO
OE
EO
OE
EO
OE
EO
l1
l2
l3
Fiber
4:1
l4
OE Data 1
EO
OE
OE
16X16
LiNbO3
Space
Division
Switch
OE
Data 2
OE Data 3
OE
Data 4
Pattern
generator
Bit time division
demultiplexer
Bit interleaving time
division multiplexer
Availability of components:
2X2 switch
VSC830
2.5Gbits/sec Dual 2x2
Crosspoint 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
VSC8164 1:16 de-Serializer
Features:
2.5Gb/s Operation
+3.3V Single Supply Operation
VSC8163 16:1 Serializer
Features:
2.5Gb/s Operation
+3.3V Single Supply Operation
Intensity
S u p erco n tin u u m
P u lse
AWG
W a velen gth
In ten sity
T im e g a te
C hirped
S uperC ontinuum
pulse
(a)
T im e / W avelen gth
• 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:
Electronics
Code
Control
Matched
Fast Wavelength
Hopping Code
Data
EAM
t
EAM
2t
EAM
3t
EAM
Time-toWavelength
Converter
To Star
Coupler
From Star
Coupler
1xN
Wavelengthto-Time
Converter
Electronic
Gating
Optical Decoder
Nx1 Combiner
Chip-Scale
Supercontinuum
Source
1xN Splitter
Monolithic Optical Encoder
Time-Division
Demultiplxer
Fast Wavelength
Hopping Code
l  time
FG-PD
l  time
FG-PD
l  time
FG-PD
l  time
FG-PD
l  time
=
Wavelengthto-Time
Converter
FG-PD
=
Fast-Gated
Photodetector
l
l
t
Time
Time
Detector Output
Time
Time
Time
Time
Time
Time
Receiver
Transmitter
Time
E le c tro n ic s
Code
C o n tro l
F a s t W a ve le n g th
H o p p in g C o d e
D a ta
W a ve le n g th to -T im e
C o n ve rte r
EAM
t
EAM
2t
EAM
3t
EAM
N x 1 C o m b in e r
C h ip -S c a le
S u p e rc o n tin u u m
S o u rc e
1 x N S p litte r
M o n o lith ic O p tic a l E n c o d e r
T im e -to W a ve le n g th
C o n ve rte r
T o S ta r
C o u p le r
l
T im e
t
T im e
T im e
T im e
T im e
M a tc h e d
F a s t W a ve le n g th
H o p p in g C o d e
E le c tro n ic
G a tin g
T im e -D ivis io n
D e m u ltip lx e r
F ro m S ta r
C o u p le r
1 x N
O p tic a l D e c o d e r
l  tim e
F G -P D
l  tim e
F G -P D
l  tim e
F G -P D
l  tim e
F G -P D
l  tim e
=
W a ve le n g th to -T im e
C o n ve rte r
F G -P D
=
F a s t-G a te d
P h o to d e te c to r
l
D e te c to r O u tp u t
T im e
T im e
T im e
T im e
E le c tro n ic s
Code
C o n tro l
F a s t W a ve le n g th
H o p p in g C o d e
D a ta
W a ve le n g th to -T im e
C o n ve rte r
EAM
t
EAM
2t
EAM
3t
EAM
N x 1 C o m b in e r
C h ip -S c a le
S u p e rc o n tin u u m
S o u rc e
1 x N S p litte r
M o n o lith ic O p tic a l E n c o d e r
T im e -to W a ve le n g th
C o n ve rte r
T o S ta r
C o u p le r
l
T im e
t
T im e
T im e
T im e
T im e
tim e sy n c
sig n al
tim e sy n c
sig n al
T ra n sm itter 1
T ra n sm itter K
R eceiv er 1
R eceiv er K
T ra n sm itter 2
T ra n sm itter i
S ta r C o u p ler
R eceiv er 2
tim e sy n c
sig n al
R eceiv er i
T ra n sm itter 3
T ra n sm itter 4
R eceiv er 3
R eceiv er 4
User
#6
User
#5
User
#7
1 0 -d B
C o u p le r
User
#4
User
#i
-1 0 d B
User
#3
User
#j
OCDMA
T ra n s m itte r
2x2
P ro te c tio n
S w itc h
-1 0 d B
User
#N
User
#2
User
#1
tim e sy n c
sig n al
1 0 -d B
C o u p le r
OCDMA
Node
OCDMA
R e c e iv e r
tim e sy n c
sig n al
tim e sy n c
sig n al
Fast wavelength-hopping OCDMA
is compatible with conventional WDM components,
allowing early technology demonstrations.
Rapid Summary of Mile-Posts:
•demonstration of the wavelengthtime 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 interchannel 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.
hop pattern
generator
c(t)
lN
...
Multi-wavelength
source
l2
Figure 6
WDM MUX
l1 … lN
WDM DEMUX
l1
wavelength
select
...
sds(t)
d(t)
transmitted
signal
wavelength
select
c(t)
...
DEMUX
...
MUX
3-dB
splitter
hop pattern
generator
li0 or li1
(A)

Tb
...
MUX
DEMUX
0
li1 or li0
...
c(t)
wavelength
select
hop pattern
generator
Figure 7
output data
threshold
device
T ( )
2
balanced
receiver
1.0
balanced
transmitter
0.5

0
T
or 1  T
2
1  T ( )
2
star
coupler
2
1.0
0.5
0

complementary
spectral decoder
input
data
complementary
spectral encoder
T
2
received
data
1 T
2