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Optical bias selector based on
a multilayer a-SiC:H optical
filter
1 Lisbon
•We demonstrate an integrated VIS-NIR optical
filter based on SiC technology.
•The concept is extended to implement a 1 x 5
WDM in the VIS-NIR range.
• FCT – ref. UID/EEA/00066/2013
ACKNOWLEDGEMENTS
p-i’-n p-i-n
• Light-to-dark sensitivity
depends on the carbon
concentration
• Color recognition
depends on the applied
bias
400 450 500 550 600 650 700 750 8000,00
0,02
0,04
0,06
0,08
0,10
0,12
0,14
0,16
0,18
0,20
#M007192 (2mWcm-2)
#M007192(L=0)
#M006301(L=0)
#M006291(2mWcm-2)
#M006301(2mWcm-2)
#M006291(L=0)
Sen
siti
vit
y (
A/W
)
Wavelength (nm)-6 -5 -4 -3 -2 -1 0 1 2
-8x10-8
-6x10-8
-4x10-8
-2x10-8
0
a)
S=650 nm
NC#5 (pin/pin)
whithout
optical bias
L=550 nm
L=650 nm
L=450 nm
Photo
curr
ent (A
)
Voltage (V)
a-S
i/S
iC P
ho
tod
iod
es
• Light filtering depends on
the bias wavelength and
side
• WDM device
RGB channels; 6000bps
• Coder/decoder device
IR/RGBV/UV channels;
30kbps
1
0
1
1
1
0
1
1
0
0
0
1
1
0
1
1
1
0
1
1
1
1
0
1
1
0
1
1
1
0
1
1
0
0
0
1
0
0
1
1
1
0
1
1
0
0
0
1
0
1
1
0
Devic
e c
on
fig
ura
tio
n
an
d o
pe
rati
on
c
•Produced by PECVD
•The thickness of the front
photodiode are optimized for blue
collection and red transmittance
•The thickness of the back
photodiode was adjusted to
achieve high collection in the red
spectral range
Op
tic
al
bia
s O
ptic
al
bia
s
GL
AS
S
200 nm
((a-SiC:H)
V=-8V
Input
channels
B TC
O
i
1000 nm
(a-Si:H)
p p n n TC
O
Front diode Back diode
G
i’
R, IR
B
Both front and back diodes act as optical filters confining,
respectively, the blue and the red optical carriers, while the green
ones are absorbed across both.
400 450 500 550 600 650 7000
20
40
60
80
100
120
140
No
rma
lize
d P
ho
tocu
rre
nt
No background
Red background
Green background
Blue background
Violet background
V=-8V
500 Hz
Ph
oto
cu
rre
nt (n
A)
Wavelength (nm)
N3500
R3500
G3500
B3500
Violtet 3500
0
1
p-i'-n diode
p-i-n diode
B
C
400 450 500 550 600 650 7000
5
10
15
20
25
30
35
40
45
50Back optical bias
Norm
aliz
ed P
hoto
curr
ent
V=-8V
500 Hz
Photo
curr
ent (n
A)
Wavelength (nm)
no bias 500 Hz
R10mA
G10mA
B10mA
V10mA
0
1
2
p-i'-n diodep-i-n diode
B
C
I
ITO
Gla
ss p
i’(a-S
iC:H
)
i (a
-Si:H
)
n p nIT
O
ITO
Gla
ss p
i’(a-S
iC:H
)
i (a
-Si:H
)
n p nIT
O
400 450 500 550 600 650 7000
1
2
3
4
5
6
7
8
9
10
11
12
Back Front
2300 Wcm-2
360 Wcm-2
16Wcm-2
Violet background
Gain
(
V)
Wavelength (nm)
R3500Hz
V3500
D
E
G
H
The device acts as an active long-pass filter under front
irradiation and a low-pass filter under back irradiation.
Back Front
Optical bia
s filt
eri
ng
effects
•By switching the irradiation side the short-, and long- spectral
region can be sequentially tuned.
•The medium region (475 nm-530 nm) can only be tuned by using
both active filters.
GL
AS
S
200 nm
(a-SiC:H)
Applied Voltage
Channels
B
TC
O
i
1000 nm
(a-Si:H)
p p n
n
TC
O
Front diode Back diode
G
i’
G
Wavelength
Division
Multiplexing
Wavelength
Division
Demultiplexing
MU
X/D
EM
UX
Devic
e
Op
tica
l
bia
s
V
R
G
B
V
0,0 0,5 1,0 1,5 2,0 2,50,0
0,5
1,0
1,5
2,0
2,5
Dark
Red Channel
Photo
curr
ent (
A)
Time (ms)
RdarkFront
Rfron
Back
Rback
0,0 0,5 1,0 1,5 2,0 2,50,0
0,5
1,0
Dark
Violet Channel
Photo
curr
ent (
A)
Time (ms)
VdarkBack
Vback
Front
Vfront
Op
tic
al
bia
s
The input signals exhibits a nonlinear dependence on the wavelength.
Gains (αV R,G.B,V) at the input red, green, blue and violet channels.
0,0 0,5 1,0 1,5 2,0 2,5 3,00,0
0,5
1,0
1,5BGR
MU
X s
ignal (
A)
Time (ms)
V
I
•The output presents 23 ordered
levels each one related with RGB
bit sequences
•The output presents 24
ordered levels each one
related with RGBV bit
sequences
•The output presents 25 ordered
levels each one related with
RGBVI bit sequences
0,0 0,5 1,0 1,5 2,0 2,5 3,00,0
0,5
1,0
1,5BGR
MU
X s
ignal (
A)
Time (ms)
V
I
Lo
ok-u
p T
able
Co
der/
deco
der
devic
e
0,0 0,5 1,0 1,5 2,0 2,5
0,0
0,5
1,0
1,5
2,0
2,5
3,0
3,5
4,0
4,5
Back
Front
RGBV
V=1 V=0V=0 V=1
Violet backgroundViolet
0001
0
0011
0
0101
0
0111
0
1001
0
1011
0
1101
0
Red
Green
Blue
1111
0
Photo
curr
ent (
A)
Time (ms)
Red
Green
Blue
Violet
VFront
Vback
•The output presents 24 ordered levels each one related with RGBV bit
sequences •The signal magnitude under irradiation is balanced by the amplification
factors
V
αVR >>1 αVG >1 αVB ~ 1 αVV <<1
αVV >>1
ER
RO
R C
ON
TR
OL
BA
SE
D O
N A
-SIC
TE
CH
NO
LO
GY
( D
EC
OD
ING
AL
GO
RIT
HM
S)
0.0 0.5 1.0 1.5
0.0
0.5
1.0
1.5
d0
d3
d5
d7
d9
d11
d13
d15
400 nm
470 nm
RGBV
V
=390 nm
0001
0
0011
0
0101
0
0111
0
1001
0
1011
0
1101
0
626 nm
524 nm
1111
0
MU
X s
ignal
Time (ms)
0,0 0,5 1,0 1,5 2,0 2,5 3,00,0
0,5
1,0
1,5
2,0
00000
11110
11111
RGBVI
=390 nm
d31
d15
d0
Front
700 nm400 nm470 nm524 nm626 nm
MU
X s
igna
l (
A)
Time (ms)
Four channels transmission.
• The background acts as selector that chooses one or more of the 2n
sublevels, with n the number of transmitted channels, and their n-bit
binary code .
Five channels transmission
• 2n ordered levels pondered by their optical gains are
detected and correspond to all the possible combinations of
the on/off states
• By assigning each output level to a n digit binary code the signal can
be decoded. A maximum transmission rate capability of 60 Kbps
was achieved in a five channel transmission
PA
RIT
Y C
HE
CK
BIT
S
Transmitted data[RGBV PRPGPB ]
p
Glass
i’
200 nm
a-SiC:H
p
i
1000 nm
a-Si:H
n nTCO
TCO
V
Op
ticalBias
B
G
R
Inputchannels
Front diodes Back diodes
V=-8VTCO
p n p n
TCO
G
R
i’
B
i
V=-8V
Op
ticalBias
MU
X C
OD
E M
UX
PAR
ITY
• The proximity of consecutive levels causes occasional errors in the
decoded information that should be corrected.
• For parity check, and in a four or five channel transmission, three or
four synchronous channels, red, green, blue and violet were read in
simultaneous with the data code.
As an application, data was sent through one detector while error detection
and correction bits were sent through the other.
0.0 0.5 1.0 1.50.0
0.2
0.4
0.6
0.8
1.0
1.1
1.3
pR p
G p
B
0 0 0
0 0 1
0 1 00 1 1
1 0 0
1 0 1
1 1 01 1 1p
7
p6
p5
p4
p3
p2
p1
p0
Code w
ord
d15
d0
d3
d4
d7
d8
d11
d12
PB
PG
PR
VB
GR
MU
X s
ignals
Time (ms)
0.0 0.5 1.0 1.5 2.0 2.5 3.00.0
0.3
0.5
0.8
1.0
1.3
1.5
1.8
1 1 0 0
1 1 1 1
pR p
G p
B p
V
d27
d4
d8
PVPBPG
PRI
VBGR
d17
p0
p15
Code w
ord
d0
d15
d31
MU
X s
ignals
Time (ms)
B
C
D
E
F
H
J
K
L
M
O
G
PR-(VRB) = V + R +B
PG-(VRG) = V + R +G
PB-(VGB) = V + G +B
PV-(I) = I
Five channels transmission
The parity bits are SUM bits of the three-
bit additions of violet pulsed signal with
two additional bits of RGB
Four channels transmission
one-bit extra
Th
e p
arity
bits
• The parity of the word is checked after reading the word.
• The word is accepted if the parity of the bits read out is correct. If the parity
of the bits is incorrect, an error is detected and should be corrected.
0.0 0.3 0.5 0.8 1.0 1.3
0.0
0.3
0.6
0.9
1.2
1.5
1.8
R G
B V
P
RP
GP
B
d13
d9
d7
d3
d14
d4
d10
d12
d1
d6
d8
d2
d15
d0
p0
p1
p2
p3
p5
p6
p7
d5
p4
d11
MU
X s
ignal
Time (ms)
0.0 0.5 1.0 1.5 2.0 2.5 3.0
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
Parity levels
Word levels
PV
PBPGPRI
VBGR
Photo
curr
ent [
A]
Time [ms]
B
C
D
E
F
H
J
K
L
M
O
The decoding algorithm is based
on a proximity search after each
time slot is translated to a vector
in multidimensional space.
The vector components are
determined by I1 and I2, where
I1 (d levels) and I2 (p levels) are
the currents measured.
We have tested the algorithm with different random sequences of the
channels and we have recovered the original color bits Cod
e a
nd p
arity
MU
X/D
EM
UX
sig
nals
The result is then compared with
all vectors obtained from a
calibration sequence where to
each code level, d(0-31), is
assigned the correspondent
parity level, p(0-15).
0.0 0.5 1.0 1.5 2.0 2.5 3.00.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
Back
Front
Back=390 nm
R=626nm
G=524nm
B=470nm
I=700nm
v=400nm
Photo
curr
ent (
A)
Time (ms)
B
C
D
E
F
W
X
1 x
5
WD
M in
th
e
VIS
-NIR
range
400 500 600 700 800
0
2
4
6
8
10
12
Back Front
Back
=390 nm
F
,B
Wavelenght (nm)
B
C
0.0 0.5 1.0 1.5 2.0 2.5 3.00.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
Back
R=626nm
G=524nm
B=470nm
I=700nm
v=400nm
Front
MU
X s
ign
al (
A)
Time (ms)
B
C
D
E
F
W
X
0.0 0.5 1.0 1.5 2.0 2.5 3.00.0
0.5
1.0
1.5
2.0
Front
V=626 nm
G=524 nm
B=470 nm
I=700 nm
V=400 nm
Back
Ph
oto
cu
rre
nt
(A
)
Time (ms)
B
C
D
E
F
W
X
•The output presents 25 ordered
levels each one related with
RGBVI bit sequences
Op
toele
ctr
on
ic m
od
el
V 1/C1
2/C2
i1(t)
i2(t)
-1/R1C1
1/R1C2
1/R1C1
dt
dt
-1/R1C2 -1/R2C2
1/R2
i (t)B
G
R
v1
+
+ +
++
+
v2
v1
v2
.
.
)(111
11
)( 2,1
222121
11112,1
2
,2
1
,,1
2,1tv
CRCRCR
CRCRti
C
C
dt
dv
GR
GBV
tvR
ti 2,1
2
10
;
tvR
ti 2,1
2
10
n n
i p i´ p
n p
IV ,IB,IG
IR,IG
Q2
Q1
R1 ( V)
αG IGb αR IR R2 C2
Q1
C1
αG IGf
αV IV
αB IB
Q2
MATLAB as a
programming
environment and the
four order Runge-
Kutta method to
solve the state
equations
Op
tical
bia
s (α
1 )
Op
tical
bia
s (α
2)
0,0 0,3 0,5 0,8 1,0 1,3 1,50,0
0,5
1,0
1,5
2,0
2,5
3,0
3,5
V
R =7.3
V
G =3.2
V
B =1.5
V
V =0.6
ExperimentalPhoto
curr
ent (
A)
Time (ms)
G
Simulated
C
0.0 0.5 1.0 1.5 2.0 2.5 3.0
0.0
0.3
0.6
0.9
1.2
1.5
1.8
Experimental
400 nm
700 nm
470 nm
524 nm
626 nmFront
MU
X s
ign
al
Time (ms)
B2
B3
C
D
E
F
G Simulation
Back C
D
Pre
dic
tio
n o
ver
rela
tional
multip
lexed s
igna
ls
14
0,0 0,5 1,0 1,5 2,0 2,50
1
2
3
4
5
6
7 697 nm
470 nm
850 nm
400 nm Back Experimental
Front
MU
X s
ign
al (
A)
Time (ms)
B
C1
C2
C3
C9
C14 Simulation
F
I
0.0 0.5 1.0 1.5 2.0 2.50.0
0.2
0.4
0.6
0.8
1.0
1.2 697nm
524nm
850nm
400nm
Back
Experimental Front
MU
X s
ign
al (A
)
Time (ms)
400
850
524
697
back
front
Simulation
F
I
0,0 0,5 1,0 1,5 2,0 2,5 3,0-0,2
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
1,8
Experimental
400 nm
700 nm
470 nm
524 nm
626 nmFront
MU
X s
ign
al
Time (ms)
B2
B3
C
D
E
F
G Simulation
Back
C
D
CO
NC
LU
SIO
NS
• A a-SiC 1x5 WDM device, with channel separation in the visible range, was presented and its operation as wavelength selector explained.
• Encoding and decoding data was analyzed and the codewords generated using the MUX signals due to the data transmitted together with the check parity bits tested.
• An algorithm to decode the transmitted information was presented. A transmitter capability of 60 kbps using the generated codeword was achieved.
A a-SiC 1x5 WDM device, with channel
separation in the visible range, was
presented and its operation as
wavelength selector explained.
Encoding and decoding data was
analyzed and the codewords generated
using the MUX signals due to the data
transmitted together with the check
parity bits tested.
An algorithm to decode the transmitted
information was presented. A transmitter
capability of 60 kbps using the
generated codeword was achieved.
Transmitted data[RGBV PRPGPB ]
p
Glass
i’
200 nm
a-SiC:H
p
i
1000 nm
a-Si:H
n nTCO
TCO
V
Op
ticalBias
B
G
R
Inputchannels
Front diodes Back diodes
V=-8VTCO
p n p n
TCO
G
R
i’
B
i
V=-8V
Op
ticalBias
MU
X C
OD
E M
UX
PAR
ITY
0.0 0.3 0.5 0.8 1.0 1.3
0.0
0.3
0.6
0.9
1.2
1.5
1.8
R G
B V
P
RP
GP
B
d13
d9
d7
d3
d14
d4
d10
d12
d1
d6
d8
d2
d15
d0
p0
p1
p2
p3
p5
p6
p7
d5
p4
d11
MU
X s
ignal
Time (ms)
Indoor positioning system using a-
SiC:H a WDM device
16
• The nonlinear property of SiC multilayer devices under UV irradiation is
used to design an optical processor for indoor positioning.
Lisbon
MO
TIV
AT
ION
VLC – Visible Light Communication
Indoor use:
• atmospheric absorption
• shadows
• light dispersion
• influence of other light sources
• Internet service distribution
• Navigation techniques
3 Gbps
WH
ITE
LE
Ds
Red, Green and Blue LED
Blue LED with phosphor layer
350 450 550 650 750 (nm)
LE
Ds E
MIS
SIO
N S
PE
CT
RU
M
400 500 600 700 8000,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
Optical in
tensity (
a. u.)
Wavelength (nm)
400 500 600 700 8000,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
Op
tica
l in
ten
sity (
a.
u.)
Wavelength (nm)
Phospor LED
RGB LED
635 nm
532 nm
463 nm
452 nm
• The magnitude and width of each
RGB peaks are optimized for the
white.
• The green component is lowest
because the human eye has a
maximum sensitivity at 530 nm.
0 5 10 15 200,0
0,2
0,4
0,6
Inte
nsity (
a.u
.)
Driving current (mA)
470 nm
626 nm
SY
ST
EM
DE
SIG
N
• The system is a self-positioning system in which the
measuring unit is mobile.
• This unit receives the signals from several transmitters
in known locations, and has the capability to compute
its location based on the measured signals.
• p-i'(a-SiC:H)-n/p-i(a-
Si:H)-n heterostructure
produced by PECVD.
Receiver
p
Glass
i’
200 nm
a-SiC:H
p
i
1000 nm
a-Si:H
n nTCO
TCO
V
Op
ticalBiasO
pti
calB
ias
B
G
R
Inputchannels
Front diode Back diode
V=-8V
• Red, Green and Blue
white LED
Transmitter
• The grid size was chosen to avoid data
overlap in the receiver from adjacent
grid points.
• The LEDs can be switched on and off
individually for a desired bit sequence.
Tra
ns
mit
ter
400 500 600 700 8000.0
0.2
0.4
0.6
0.8
1.0
B
G
R
Inte
nsity (
a.u
.)
Wavelength (nm)
Nearest regions 1 2 3 4 5 6 7 8 9
Overlap RGBV RGB GB GBV BV RBV RV RGV RG
• The magnitude and width of
each RGB peaks are
optimized for the white.
• The green component is
lowest because the human
eye has a maximum
sensitivity at 530 nm.
RGB WHITE LED
PO
SIT
ION
ING
MU
X/D
EM
UX
SIG
NA
LS
Four channels transmission
0.0 0.5 1.0 1.50.0
0.5
1.0
1.5
0000
0111
1111RGBV
Position 1
d15
d0
Back
Front
V
R
B
G
MU
X s
ignal (
A)
Time (ms)
• Looking to the different levels, we have ascribed a binary
code of 4 bits (RGBV) to each position, where 1 means that
the channel is received and 0 that is absent .
• 24 ordered levels
pondered by their
optical gains are
detected and
correspond to all
the possible
combinations of
the on/off states.
0.0 0.5 1.0 1.50.0
0.4
0.8
1.2Position 2
d7
d0
Back
Front
R
B
G
MU
X s
ignal (
A)
Time (ms)
0.0 0.5 1.0 1.50.0
0.5
1.0
1.5
Position 3
d4
d0
Back
Front
B
G
MU
X s
ignal (
A)
Time (ms)
Nearest regions 1 2 3 4 5 6 7 8 9
Code position 1111 1110 0110 0111 0011 1011 1001 1101 1100
Parity position 111 000 110 001 010 100 001 010 101
PO
SIT
ION
ING
MU
X/D
EM
UX
SIG
NA
LS
• A node requires only information about
the locations of its neighbors, but not the
other nodes in the network to make an
initial estimate of its own location.
NA
VIG
AT
ION
DA
TA
BIT
S
0.0 0.5 1.0 1.50.0
0.5
1.0
1.5
d7
1 RGBV
3 GB
4 GBV
5 BV
d15
d0
Front
V
R
B
G
MU
X s
ignal (
A)
Time (ms)
• For each transition between an initial location and a final one,
two code words are generated, the initial (i) and the final (f). If
the receiver stays under the same region they should be the
same, if it moves away they are different.
North
South
EastWest
NE
SE
NW
SW
1
2
3
4
CompassNeedle
5
6
North
South
EastWest
NE
SE
NW
SW
1
2
3
4
CompassNeedle
5
7
8
9
0.0 0.5 1.0 1.50.0
0.5
1.0
1.5
2.0
Position ID
t1 RGBV
t3 GB
t4 GBV
t5 BV
R
G
B
V
RGBV
GB
GBV
BV
d15
d0
Front
V
R
B
G
Photo
curr
ent (
A)
Time (ms)
0.0 0.5 1.0 1.5 2.00.0
0.5
1.0
1.5
2.0 V
R
B
G
Position ID
Front lighting t1 RGBV
t3 GB
t4 GBV
t5 BV
Photo
curr
ent (
A)
Time (ms)
G
G
G
G
B
C
D
E
• The device’s position (ID position) during the
receiving process will be given by the
highest detected level (vertical dot line in the
figures), i. e, the level where all the n (n=1,
2, 3, 4) channels are simultaneously on.
• At each regions the MUX signals present
different pattern that after decoding give
information about the mobile navigation and
received information along the time.
North
South
EastWest
NE
SE
NW
SW
1
2
3
4
CompassNeedle
5
6
North
South
EastWest
NE
SE
NW
SW
1
2
3
4
CompassNeedle
5
7
8
9T
RA
NS
MIS
SIO
N D
ATA
BIT
S
CO
NC
LU
SIO
NS
• A a-SiC 1x5 WDM device, with channel separation in the visible range, was presented and its operation as wavelength selector explained.
• Encoding and decoding data was analyzed and the codewords generated using the MUX signals due to the data transmitted together with the check parity bits tested.
• An algorithm to decode the transmitted information was presented. A transmitter capability of 60 kbps using the generated codeword was achieved.
VLC system characteristics for positioning on its
different components such as the transmitter and the
receiver, the multiplexing techniques, the visible light
sensing and lastly, indoor localization and motion
recognition were analized.
The results showed that by using a pinpin double
photodiode based on a a-SiC:H heterostucture as
receiver and RBG-LED as transmitters it is possible
not only to determine the position of a mobile target
but also to infer the travel direction along the time.
Future work will consider to improve the transmission
rate through parallelizing communication by using
multiple emitters and receivers.
Coupled Data Transmission and
Indoor Positioning by Using
Transmitting Trichromatic White
LEDs and a SiC Optical MUX/DEMUX
Mobile Receiver
27 Lisbon
SY
ST
EM
DE
SIG
N
• The system is a self-positioning system in which the measuring
unit is mobile.
• This unit receives the signals from several transmitters in known
locations, and has the capability to compute its location based on
the measured signals.
• p-i'(a-SiC:H)-n/p-i(a-
Si:H)-n heterostructure
produced by PECVD.
Receiver
p
Glass
i’
200 nm
a-SiC:H
p
i
1000 nm
a-Si:H
n nTCO
TCO
V
Op
ticalBiasO
pti
calB
ias
B
G
R
Inputchannels
Front diode Back diode
V=-8V
• Red, Green and Blue
white LED
Transmitter
0.0 0.5 1.0 1.5 2.0
[0101 0011]
V
B
G
R
Code w
ord
(R
GB
V)
Time (ms)
400 500 600 700 8000.0
0.2
0.4
0.6
0.8
1.0
B
G
R
Inte
nsity (
a.u
.)
Wavelength (nm)
TO
PO
LO
GY
Region 1 2 3 4 5 6 7 8 9 10 11 12 13
Overlap RGBV RGB GB GBV BV RBV RV RGV RG G B V R
Region 1 2 3 4 5 6 7 8 9 10
Overlap RGBV RGV GBV RBV RV GV RB R G B
R G
B V
1
2
3
4
5
6
7
8
9 10
11 12
13 Square
R
G B
V
Triangular
1 2
3
4
5
6 7
8
9 10
• Four modulated LEDs
(RGBV), three of them
(RGB-LED) are located at
the vertices of an equilateral
triangle and a fourth one (V)
is located at its centroid.
• Four modulated LEDs
(RGBV) located at the
corners of a square grid.
1,1 1,3
2,1
1,2
2,32,2
3,23,1 3,3
Rece
iver
co
nfi
gu
rati
on
an
d o
pe
rati
on
c
•Produced by PECVD
•The thickness of the front
photodiode are optimized for
blue collection and red
transmittance
•The thickness of the back
photodiode was adjusted to
achieve high collection in the
red spectral range
Op
tic
al
bia
s O
ptic
al
bia
s
GL
AS
S
200 nm
((a-SiC:H)
V=-8V
Input
channels
B TC
O
i
1000 nm
(a-Si:H)
p p n n TC
O
Front diode Back diode
G
i’
R, IR
B
Both front and back diodes act as optical filters confining, respectively, the
blue and the red optical carriers, while the green ones are absorbed across
both.
I
0.0 0.5 1.0 1.5 2.00.00
0.05
0.10
0.15
Dark Back
Front
Ph
oto
cu
rre
nt
(A
)
Time (ms)
0.0 0.5 1.0 1.5 2.00.00
0.02
0.04
0.06
0.08
0.10
V=400 nm
Dark
Back
Front
Ph
oto
cu
rre
nt
(A
)
Time (ms)
GL
AS
S
200 nm
(a-SiC:H)
Applied Voltage
Channels
B
TC
O
i
1000 nm
(a-Si:H)
p p n
n
TC
O
Front diode Back diode
G
i’
G
Wavelength
Division
Multiplexing
Wavelength
Division
Demultiplexing
SY
ST
EM
OP
ER
AT
ION
Op
tica
l
bia
s
V
R
G
B
V
Op
tic
al
bia
s
The input signals exhibits a nonlinear dependence on the wavelength.
Gains (αV R,G.B,V) at the input red, green, blue and violet channels.
10011001 11011101 10001001
Bit decode LED ID data transmit with fast
blinking
Coder/decoder device
Transmitter / Receiver of VLC
0.0 0.5 1.0 1.5 2.00.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
R=626 nm
B=470 nm
G=530 nm
V=400 nm V
B
G
R
Front
Back
Dark
Photo
curr
ent (
A)
Time (ms)
0,0 0,5 1,0 1,5 2,0 2,5 3,00,0
0,5
1,0
1,5BGR
MU
X s
ignal (
A)
Time (ms)
V
I
•The output presents 23 ordered
levels each one related with RGB
bit sequences
•The output presents 24
ordered levels each one
related with RGBV bit
sequences
•The output presents 25 ordered
levels each one related with
RGBVI bit sequences
0,0 0,5 1,0 1,5 2,0 2,5 3,00,0
0,5
1,0
1,5BGR
MU
X s
ignal (
A)
Time (ms)
V
I
Lo
ok-u
p T
able
0.0 0.5 1.0 1.5 2.00.0
0.1
0.2
0.3
0.4
0.5
0.6
d11
(1011)
d0 (0000)
d4 (0100)
d8 (1000)
d15
(1111)
d (RGBV)
Back
Front
V
B
G
R
MU
X s
ign
al (a
.u.)
Time (ms)
0.0 0.5 1.0 1.5 2.00.0
0.1
0.2
0.3
d0 (0000)
d4 (0100)
d8 (1000)
d12
(1100)
d15
(1111)
d (RGBV)
V
B
G
R
Back
Front
MU
X s
ign
al (a
.u.)
Time (ms)
Square topology Triangular topology.
• The background acts as selector that chooses one or more of the 2n
sublevels, with n the number of transmitted channels, and their n-bit
binary code .
• 2n ordered levels pondered by their optical gains are
detected and correspond to all the possible combinations of
the on/off states.
• By assigning each output level to a n digit binary code the signal can
be decoded. A maximum transmission rate capability of 30 Kbps
was achieved. De
codin
g a
lgori
thm
PO
SIT
ION
ING
MU
X/D
EM
UX
SIG
NA
LS
0.0 0.5 1.0 1.50.0
0.5
1.0
1.5
0000
0111
1111RGBV
Position 1
d15
d0
Back
Front
V
R
B
G
MU
X s
ignal (
A)
Time (ms)
• Looking to the different levels, we have ascribed a binary code of 4 bits
(RGBV) to each position, where 1 means that the channel is received and
0 that is absent .
0.0 0.5 1.0 1.50.0
0.4
0.8
1.2Position 2
d7
d0
Back
Front
R
B
G
MU
X s
ignal (
A)
Time (ms)
0.0 0.5 1.0 1.50.0
0.5
1.0
1.5
Position 3
d4
d0
Back
Front
B
G
MU
X s
ignal (
A)
Time (ms)
[1110]
[1111]
[0110]
PO
SIT
ION
ING
0.0 0.5 1.0 1.5 2.00.0
0.5
1.0
1.5
2.0
2.5
0000
0010
01000110
1000
1010
11001110RGBV
Position 3
Position 2
B
G
R
MU
X s
ignal (a
.u.)
Time (ms)
0.0 0.5 1.0 1.5 2.00.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
00000001
0100010110001001
11001101RGBV
Position 6
Position 2
V
G
R
MU
X s
ign
al (a
.u.)
Time (ms)
Nearest regions 1 2 3 4 5 6 7 8 9 10 11 12 13
Code position
(Square topology)
1111 1110 0110 0111 0011 1011 1001 1101 1100 0100 0010 0001 1000
Code position
(Triangular topology)
1111 1101 0111 1011 1001 0101 1010 1000 0100 0010 - - -
Square topology
Triangular topology
[1110]
[0110]
[1101]
[0101]
NA
VIG
AT
ION
DA
TA
BIT
S
0.0 0.5 1.0 1.50.0
0.5
1.0
1.5
d7
1 RGBV
3 GB
4 GBV
5 BV
d15
d0
Front
V
R
B
G
MU
X s
ignal (
A)
Time (ms)
• For each transition between an initial location and a final one,
two code words are generated, the initial (i) and the final (f). If
the receiver stays under the same region they should be the
same, if it moves away they are different.
North
South
EastWest
NE
SE
NW
SW
1
2
3
4
CompassNeedle
5
6
North
South
EastWest
NE
SE
NW
SW
1
2
3
4
CompassNeedle
5
7
8
9
0.0 0.5 1.0 1.50.0
0.5
1.0
1.5
2.0
Position ID
t1 RGBV
t3 GB
t4 GBV
t5 BV
R
G
B
V
RGBV
GB
GBV
BV
d15
d0
Front
V
R
B
G
Photo
curr
ent (
A)
Time (ms)
0.0 0.5 1.0 1.5 2.00.0
0.5
1.0
1.5
2.0 V
R
B
G
Position ID
Front lighting t1 RGBV
t3 GB
t4 GBV
t5 BV
Photo
curr
ent (
A)
Time (ms)
G
G
G
G
B
C
D
E
• The device’s position (ID position) during the
receiving process will be given by the
highest detected level (vertical dot line in the
figures), i. e, the level where all the n (n=1,
2, 3, 4) channels are simultaneously on.
• At each regions the MUX signals present
different pattern that after decoding give
information about the mobile navigation and
received information along the time.
North
South
EastWest
NE
SE
NW
SW
1
2
3
4
CompassNeedle
5
6
North
South
EastWest
NE
SE
NW
SW
1
2
3
4
CompassNeedle
5
7
8
9N
AV
IGA
TIO
N D
ATA
BIT
S
0.0 0.5 1.0 1.5 2.00.0
0.3
0.5
0.8
1.0
1.3
1.5
Position ID
t3
t4
t2
t1
d3
d7
d9
d11
0111
0011
1001
R
G
B
V
VR
BVR
BV
GBV
1011
RGBV
V
B
G
R
MU
X s
ignal (a
.u.)
Time (ms)
0.0 0.5 1.0 1.5 2.00.0
0.1
0.3
0.4
0.5
0.7
0.8
0.9
1.1
1.2 Position IDV
B
G
R
5- t1
RV
4- t2
RBV
7- t3
BV
3- t4
GBVd
11 1011
d7 0111
d9 1001
d3 0011
RGBV
MU
X s
ignal (a
.u.)
Time (ms)
B
C
D
E
VR
BVR
BV
GBV
[1001]
[1011]
[0111]
[0011]
NA
VIG
AT
ION
DA
TA
BIT
S
0.0 0.5 1.0 1.5 2.00.0
0.2
0.4
0.6
0.8
1.0 R
G
V
VRG
GV
[0010 0110]
00000001
0100
0101
11001101
RGBV
Position 6
Position 2
V
G
R
MU
X s
ign
al (a
.u.)
Time (ms)
0.0 0.5 1.0 1.5 2.00.0
0.2
0.4
0.6
0.8
1.0
[0101 0101]
00000001
01000101
10001001
11001101RGBV
Position 6
Position 2
V
G
R
MU
X s
ignal (a
.u.)
Time (ms)
the 8-bit positioning ID decoded from the
violet channel is: [0010 0110], which
corresponds to line 2, column 6 of the
network.
The 8-bit positioning ID decoded from the
violet channel is: [0101 0101], which
corresponds to line 5, column 5 of the
network.
• The 4-bit code that corresponds to the ID position inside the unit cell is the
same: Position 2 [1101] and Position 6 [0101] but the unit cell is different.
Fin
e-g
rain
ed
in
do
or
lo
ca
liza
tion
• The eight first bits of the violet packet give the 8-bit address of the unit cell
CO
NC
LU
SIO
NS
• A a-SiC 1x5 WDM device, with channel separation in the visible range, was presented and its operation as wavelength selector explained.
• Encoding and decoding data was analyzed and the codewords generated using the MUX signals due to the data transmitted together with the check parity bits tested.
• An algorithm to decode the transmitted information was presented. A transmitter capability of 60 kbps using the generated codeword was achieved.
A coupled data transmission and indoor positioning was
presented. To transmit the data, an On-Off Keying code was
used. A square and a triangular topology were considered for the
unit cell.
Fine-grained indoor localization was tested. A 2D localization
design, demonstrated by a prototype implementation was
developed.
A detailed analysis of the characteristics of various components
within the VLC system were discussed.
Results showed t is possible not only to determine the position of
a mobile target inside the unit cell but also in the network and
concomitantly to infer the travel direction along the time.
For future work, by using multiple emitters and receivers, the
transmission data rate through parallelized spatial multiplexing
can be improved.
