Performance of optical and hybrid joint transform correlators for tasks of optical security
Performance of optical and hybrid joint transform correlators (JTCs) for security verification of optical marks containing transformed phase masks (PMs) is studied. The peak-to-noise ratio (PNR) and relative intensity of correlation peaks are selected as basic criteria for comparative analysis of su...
Saved in:
| Date: | 2002 |
|---|---|
| Main Authors: | , , , , , , , |
| Format: | Article |
| Language: | English |
| Published: |
Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2002
|
| Series: | Semiconductor Physics Quantum Electronics & Optoelectronics |
| Online Access: | https://nasplib.isofts.kiev.ua/handle/123456789/121189 |
| Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
| Journal Title: | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| Cite this: | Performance of optical and hybrid joint transform correlators for tasks of optical security / L.I. Muravsky, Ya.P. Kulynych, O.P. Maksymenko, T.I. Voronyak, I.Y. Pogan, F.L. Vladimirov, S.A. Kostyukevych, V.M. Fitio // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2002. — Т. 5, № 2. — С. 222-230. — Бібліогр.: 11 назв. — англ. |
Institution
Digital Library of Periodicals of National Academy of Sciences of Ukraine| id |
nasplib_isofts_kiev_ua-123456789-121189 |
|---|---|
| record_format |
dspace |
| spelling |
nasplib_isofts_kiev_ua-123456789-1211892025-02-09T20:29:59Z Performance of optical and hybrid joint transform correlators for tasks of optical security Muravsky, L.I. Kulynych, Ya.P. Maksymenko, O.P. Voronyak, T.I. Pogan, L.Y. Vladimirov, F.L. Kostyukevych, S.A. Fitio, V.M. Performance of optical and hybrid joint transform correlators (JTCs) for security verification of optical marks containing transformed phase masks (PMs) is studied. The peak-to-noise ratio (PNR) and relative intensity of correlation peaks are selected as basic criteria for comparative analysis of such two types of JTCs. The theoretical model of an interference noise produced as a result of an input and reference binary PMs cross-correlation on a conventional JTC output is developed. The optically addressed spatial light modulator (OASLM) based on the chalcogenide glass photoconductor - nematic liquid crystal structure is considered. The experimental setup of an OASLM JTC is designed on the basis of this SLM. The relations a PNR and relative intensity versus an effective focal length of an optical Fourier processor are studied and the basic reasons limiting efficiency of the setup are analyzed. The optoelectronic device for identification of credit cards based on a hybrid optical-digital JTC architecture is built. The conditions of a joint power spectrum recording by a CCD-camera in this device are investigated. The concluding about expediency of OASLM JTC and optoelectronic device usage for different security applications is made. The authors are grateful to M.V. Shovgenyuk, T.V. Fityo and Р.А. Hlushak for fruitful discussions and technical support. 2002 Article Performance of optical and hybrid joint transform correlators for tasks of optical security / L.I. Muravsky, Ya.P. Kulynych, O.P. Maksymenko, T.I. Voronyak, I.Y. Pogan, F.L. Vladimirov, S.A. Kostyukevych, V.M. Fitio // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2002. — Т. 5, № 2. — С. 222-230. — Бібліогр.: 11 назв. — англ. 1560-8034 PACS: 42.30.Va https://nasplib.isofts.kiev.ua/handle/123456789/121189 en Semiconductor Physics Quantum Electronics & Optoelectronics application/pdf Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| collection |
DSpace DC |
| language |
English |
| description |
Performance of optical and hybrid joint transform correlators (JTCs) for security verification of optical marks containing transformed phase masks (PMs) is studied. The peak-to-noise ratio (PNR) and relative intensity of correlation peaks are selected as basic criteria for comparative analysis of such two types of JTCs. The theoretical model of an interference noise produced as a result of an input and reference binary PMs cross-correlation on a conventional JTC output is developed. The optically addressed spatial light modulator (OASLM) based on the chalcogenide glass photoconductor - nematic liquid crystal structure is considered. The experimental setup of an OASLM JTC is designed on the basis of this SLM. The relations a PNR and relative intensity versus an effective focal length of an optical Fourier processor are studied and the basic reasons limiting efficiency of the setup are analyzed. The optoelectronic device for identification of credit cards based on a hybrid optical-digital JTC architecture is built. The conditions of a joint power spectrum recording by a CCD-camera in this device are investigated. The concluding about expediency of OASLM JTC and optoelectronic device usage for different security applications is made. |
| format |
Article |
| author |
Muravsky, L.I. Kulynych, Ya.P. Maksymenko, O.P. Voronyak, T.I. Pogan, L.Y. Vladimirov, F.L. Kostyukevych, S.A. Fitio, V.M. |
| spellingShingle |
Muravsky, L.I. Kulynych, Ya.P. Maksymenko, O.P. Voronyak, T.I. Pogan, L.Y. Vladimirov, F.L. Kostyukevych, S.A. Fitio, V.M. Performance of optical and hybrid joint transform correlators for tasks of optical security Semiconductor Physics Quantum Electronics & Optoelectronics |
| author_facet |
Muravsky, L.I. Kulynych, Ya.P. Maksymenko, O.P. Voronyak, T.I. Pogan, L.Y. Vladimirov, F.L. Kostyukevych, S.A. Fitio, V.M. |
| author_sort |
Muravsky, L.I. |
| title |
Performance of optical and hybrid joint transform correlators for tasks of optical security |
| title_short |
Performance of optical and hybrid joint transform correlators for tasks of optical security |
| title_full |
Performance of optical and hybrid joint transform correlators for tasks of optical security |
| title_fullStr |
Performance of optical and hybrid joint transform correlators for tasks of optical security |
| title_full_unstemmed |
Performance of optical and hybrid joint transform correlators for tasks of optical security |
| title_sort |
performance of optical and hybrid joint transform correlators for tasks of optical security |
| publisher |
Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| publishDate |
2002 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/121189 |
| citation_txt |
Performance of optical and hybrid joint transform correlators for tasks of optical security / L.I. Muravsky, Ya.P. Kulynych, O.P. Maksymenko, T.I. Voronyak, I.Y. Pogan, F.L. Vladimirov, S.A. Kostyukevych, V.M. Fitio // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2002. — Т. 5, № 2. — С. 222-230. — Бібліогр.: 11 назв. — англ. |
| series |
Semiconductor Physics Quantum Electronics & Optoelectronics |
| work_keys_str_mv |
AT muravskyli performanceofopticalandhybridjointtransformcorrelatorsfortasksofopticalsecurity AT kulynychyap performanceofopticalandhybridjointtransformcorrelatorsfortasksofopticalsecurity AT maksymenkoop performanceofopticalandhybridjointtransformcorrelatorsfortasksofopticalsecurity AT voronyakti performanceofopticalandhybridjointtransformcorrelatorsfortasksofopticalsecurity AT poganly performanceofopticalandhybridjointtransformcorrelatorsfortasksofopticalsecurity AT vladimirovfl performanceofopticalandhybridjointtransformcorrelatorsfortasksofopticalsecurity AT kostyukevychsa performanceofopticalandhybridjointtransformcorrelatorsfortasksofopticalsecurity AT fitiovm performanceofopticalandhybridjointtransformcorrelatorsfortasksofopticalsecurity |
| first_indexed |
2025-11-30T12:13:01Z |
| last_indexed |
2025-11-30T12:13:01Z |
| _version_ |
1850217368568987648 |
| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics. 2002. V. 5, N 2. P. 222-230.
© 2002, Institute of Semiconductor Physics, National Academy of Sciences of Ukraine222
PACS: 42.30.Va
Performance of optical and hybrid joint transform
correlators for tasks of optical security
L.I. Muravsky1), Ya.P. Kulynych1), O.P. Maksymenko1), T.I. Voronyak1),
I.Y. Pogan1), F.L. Vladimirov2), S.A. Kostyukevych3), V.M. Fitio4)
1)Karpenko Physico-Mechanical Institute, NAS of Ukraine, 5 Naukova Str., 79601 Lviv, Ukraine;
Phone: +380 (322) 63 3388; e-mail: dep24@ah.ipm.lviv.ua
2)S.I.Vavilov State Optical Institute, 12 Birjevaya liniya, 199034 St. Petersburg, Russia;
Phone: +88(12)151 0852; e-mail: vlv@fl.spb.ru
3)Institute of Semiconductor Physics, NAS of Ukraine, 45 prospect Nauky, 03028 Kiev, Ukraine;
Phone: +390 (44) 265 6205; e-mail: sergeyk@isp.kiev.ua
4)National University �Lvivska Polytechnika�, 12 Bandera Str., 79013 Lviv, Ukraine;
Phone: +380 (322) 72 7747
Abstract. Performance of optical and hybrid joint transform correlators (JTCs) for security
verification of optical marks containing transformed phase masks (PMs) is studied. The peak-
to-noise ratio (PNR) and relative intensity of correlation peaks are selected as basic criteria
for comparative analysis of such two types of JTCs. The theoretical model of an interference
noise produced as a result of an input and reference binary PMs cross-correlation on a con-
ventional JTC output is developed. The optically addressed spatial light modulator (OASLM)
based on the chalcogenide glass photoconductor � nematic liquid crystal structure is consid-
ered. The experimental setup of an OASLM JTC is designed on the basis of this SLM. The
relations a PNR and relative intensity versus an effective focal length of an optical Fourier
processor are studied and the basic reasons limiting efficiency of the setup are analyzed. The
optoelectronic device for identification of credit cards based on a hybrid optical-digital JTC
architecture is built. The conditions of a joint power spectrum recording by a CCD-camera in
this device are investigated. The concluding about expediency of OASLM JTC and optoelectronic
device usage for different security applications is made.
Keywords: optical security, transformed phase mask, joint transform correlator, peak-to-
noise ratio, spatial light modulator, optoelectronic device, interference noise.
Paper received 05.06.01; revised manuscript received 03.06.02; accepted for publication 25.06.02.
1. Introduction
Usage of optical security systems and devices based on a
joint transform correlator (JTC) architecture for identifi-
cation of credit cards, documents and other products is
very promising. The experimental demonstrations of the
random phase encoding technique for security verifica-
tion show that both optical and hybrid JTCs can be suc-
cessfully applied [1-4]. The comparative analysis of these
JTCs types is useful for improvement the well-known
methods and development the new methods for optical
security. Besides such comparative analysis is useful for
designing and creation of new high-performance secu-
rity systems constructed on the basis of the JTC
architectures. For this purpose, we have engineered the
experimental setup of a JTC with an optically addressed
SLM in a frequency domain (OASLM JTC) and the
optoelectronic device for identification of credit cards
based on a hybrid optical-digital JTC (HOD JTC) archi-
tecture. In these correlators we used a random phase mask
(PM) [1,2] as a reference image and a transformed PM
[3-6] as an input image or as an optical mark. To com-
pare the performance of these correlators, we used the
same optical marks for both JTC. Thus, a peak-to-noise
ratio (PNR) as the main yardstick, with which the
correlators were compared, was selected. At first, we car-
ried out the theoretical estimation of an interference noise
surrounding the correlation peak and found the PNR on
the JTC output, if two binary random PMs are entered
into its input. Further we studied the OASLM JTC and
analysed the characteristics of the OASLM. To study the
performance of the OASLM JTC, we found the PNRs
and relative intensities of correlation peaks. We also ex-
amined the performance of the optoelectronic device based
on a HOD JTC architecture. For this purpose, we have
found the PNRs and relative intensities of peaks for dif-
ferent conditions of a joint power spectra recording by a
CCD-camera. The performed researches have shown the
L.I. Muravsky et al.: Performance of optical and hybrid joint transform...
223SQO, 5(2), 2002
two reviewed types of correlators can be used for con-
struction of security devices.
2. Random phase masks
The correlation methods of optical security are based on
usage of optical marks containing PMs. To study the
performance of phase and transformed phase masks in a
JTC, we have used analytical equations that describe be-
forehand known spacing of pixels in a mask.3-5 However
these equations are unacceptable for random binary PMs.
In this connection, we have considered a binary PM as
set of spatially ordered pixels of the identical shape, the
phase of which is equal to 0 or π . We considered two
masks entered into the conventional JTC as input and
reference images. To find expressions for variance of an
interference noise and autocorrelation function on an
output of a conventional JTC, we have used the formula
[7] for mean square deviation of a cross-correlation func-
tion for two arbitrary unidimensional binary PMs with
equal lengths. This formula is fair for a binomial distri-
bution law of pixels in a mask. For pixels of length a and
with a step between adjacent pixels, equal a, this formula
can be expressed as [7]
( ) mMaSR mm
~~~ −=−σ , (1)
where mR~ is a quantity of a cross-correlation function
terms in a point am~ , equal +1; mS~ is a quantity of a
cross-correlation function terms in a point am~ , equal -1;
M is a quantity of pixels in each of masks, thus
Mm ,...,2,1= is a number of a pixel;
( )1,...,1,0~
0 −±±= Mm , MM ≤0 .
Using the formula (1), we can find expression for vari-
ance of a spatial interference noise, which one is pro-
duced along a coordinate axis x′r as a result of a cross-
correlation of two unidimensional masks of identical
length. Because the complex amplitude of each pixel with
a center in an origin of the axis x′r can be defined as
( )[ ]xj
a
x
rectxt θexp)(
= , (2)
where ( )xθ is equal 0 or π , the autocorrelation of a
function (2) is
( ) ( ) =′∗′ xtxt
′
Λ
a
x
a
′
=
a
xγ , (3)
where ∗ stands for correlation, ( )...Λ is the triangle func-
tion. If the step between adjacent pixels is equal c, the
variance of a spatial interference noise in an arbitrary
point on the interval ( ) ( )[ ]cmcm 1~,1~ +− , arranged on the
axis x′r , can be expressed using Eqs (1)-(3) as
( ) ( )[ ] ( )
−′
−=+−
a
cmx
mMcmcm
~
~1~,1~ 22 γσ , (4)
where =
−′
a
cmx ~
γ
−′
Λ
a
cmx
a
~
.
If the center of a spatial interference noise is coin-
cided with the origin of the axis x′r , Eq. (4) can be written
as a variance of this noise in an arbitrary point of this
axis, i.e.,
( ) ( )∑
−=
+−=
−′
−
−
=′
1~
1~
22
~
~
12
1 Mm
Mm
a
cmx
mM
M
x γσ . (5)
In a case, when two phase masks are identical, the
interference noise is not change for all m~ except for
0=m~ , and Eq. (5) can be written as
( )
( )
×
−−
=′
112
12
M
xσ
( )
′
−
−′
−× ∑
−=
+−= a
x
M
a
cmx
mM
Mm
Mm
1~
1~
22
~
~ γγ (6)
The autocorrelation peak is produced within the lim-
its of the interval [ ]c,c− . The amplitude distribution of
this peak can be represented as
( )
′
=′
a
x
MxP γ . (7)
If two different two-dimensional binary random phase
masks with equal dimensions NM × are placed apart
02y one from another in an input of a conventional JTC,
the variance of the interference noise in a diffraction
center (DC) of a JTC output plane ( )y,x ′′ allowing to (5)
is given by
( ) =′′ yx ,2σ ( )( )
×
−− 1212
1
NM
( )( )
−−× ∑ ∑
−=
+−=
−=
+−=
1~
1~
1~
1~
~~
Mm
Mm
Nn
Nn
nNmM −
−′−′
b
dny
a
cmx ~
,
~
2γ
′′
−
b
y
a
x
MN ,2 2γ ,
where M and N are the quantities of columns and rows in
these masks; Mm ,...,2,1= is a number of a column;
Nn ,...,2,1= is a number of a row;
( )1,...,1,0~
0 −±±= Mm ; MM ≤0 ; ( )1,...,1,0~
0 −±±= Nn ;
NN ≤0 ; a is a size of a pixel along the axis xr ; b is a
size of a pixel along the axis yr ; c and d are a width
and high of a rectangular cell dc× of a phase mask, in
which the pixel is arranged (see Fig.1).
The expression for the noise variance in a ±1-st dif-
fraction order of a JTC output becomes
( ) =′±′± yx ,2σ ( )( )
×
−− 1212
1
NM
( )( )×−−× ∑ ∑
−=
+−=
−=
+−=
1~
1~
1~
1~
~~
Mm
Mm
Nn
Nn
nNmM
′−−′±−′±×
b
ydny
a
cmx 02 2~
,
~
γ
where
00 yy =′ .
224 SQO, 5(2), 2002
L.I. Muravsky et al.: Performance of optical and hybrid joint transform...
If two identical phase masks are entered to a conven-
tional JTC, the noise variance in a the ±1-st order can be
defined as (see Eq. (6))
( ) =′±′± yx ,2σ ( )( )
×
−− 1212
1
NM
( )( )×−−× ∑ ∑
−=
+−=
−=
+−=
1~
1~
1~
1~
~~
Mm
Mm
Nn
Nn
nNmM
′−−′±−′±×
b
ydny
a
cmx 02 2~
,
~
γ , (8)
where 00 yy =′ . Using Eq. (7), the correlation peak am-
plitude in the point ( )02,0 y± is given by
( ) =′±± 02,0 yP MN ( )0,0γ . (9)
Let both identical reference and input PMs are dis-
played simultaneously in the input plane of a conven-
tional JTC. We can estimate influencing dimension of
such masks on the PNR on the output of a correlator.
Using Eqs (8) and (9), the PNR can be expressed as
=µ
( )
( )
( )
( )
=
′±±±
′±
=
′±±±
′±±
0
2
0
0
2
0
2
2~,~
2,0
2~,~
2,0
ydncm
yI
ydncm
yP
σσ
( ) ( ) ( )( ) ×
−++
=
11
~
21
~
2
1
0,022
NM
MN γ
( )( )
−−−× ∑ ∑
=
−=
=
−=
MNnNmM
Mm
Mm
Nn
Nn
~~
1
~~
~~
~~
~~
, (10)
where Mm
~
,...,1,0~ = ; Nn
~
,...,1,0~ =
The dependencies PNR versus dimension of a win-
dow ( ) ( )1
~
21
~
2 +×+ NM limiting readouts of a noise are
obtained from Eq. (10) and represented in Fig. 2 for dif-
ferent M (if NM
~~ = and NM = ). These dependencies
show that the PNR increases, if M increases. They also
demonstrate, that the larger is a window
( ) ( )1
~
21
~
2 +×+ NM , the more precise is the estimation of
the PNR. On the other hand, the correlation peak inten-
sity sharply decreases with increase of masks dimension,
if rotation angles of one mask relatively to another are
equal [5]. If transformed phase masks are used in a JTC
as optical marks, the dependencies PNR versus dimen-
sion of a window ( ) ( )1
~
21
~
2 +×+ NM remain approxi-
mately the same (see Fig. 2). However, in this case the
PNR can essentially decrease because of mutual overlap
of an interference noise producing as a result of a cross-
correlation between a transformed mask fragments and a
reference mask.
3. Optically addressed SLM JTC
To study the performance of transformed PMs as optical
marks in an optical JTC containing an OASLM in a fre-
quency domain, we have developed the OASLM JTC ex-
perimental setup. In this setup, we used the OASLM based
on the chalcogenide glass photoconductor � nematic liq-
uid crystal (CGP-NLC) structure [8]. The reference and
transformed PMs were entered to the JTC input plane.
The distance between two masks was =02y 8 mm. The
reference PM consists of 256×256 square pixels. The pixel
size is 20×20 µm. The transformed mask consists of sev-
eral fragments of the reference mask shifted relatively to
the initial position by given distance and given direction.
3.1. Optically adressed SLM
The OASLM based on the chalcogenide glass photocon-
ductor � nematic liquid crystal (CGP-NLC) structure has
high sensitivity and good resolution. High sensitivity (up
to 0.01 µW/cm2) makes it possible to input images in co-
herent optical processor directly, without an intermedi-
Fig. 1. Fragment of a phase mask containing a rectangular grat-
ing of pixels.
Fig. 2. Dependencies of µ versus
~
M for M = 12 (1); M = 16
(2); M = 24 (3); M = 32 (4); M = 64 (5); M = 128 (6);
M = 256 (7); M = 512 (8).
n=N-2
n=N-1
n=N
m=1
m=2 m=3 m=4
8
7
6
5
4
3
2
1
µ
M
2x10
10
10
10
10
10
1010
1 20
L.I. Muravsky et al.: Performance of optical and hybrid joint transform...
225SQO, 5(2), 2002
ate TV channel. These type of the SLMs have quite good
optical quality and low level of spatial noises owing to
alignment technique for nematics was recently perfected
very well. Response speed of the NLC-SLM is defined by
decay time of the NLC that is typically 40-100 ms at LC
layer thickness 5-10 µm and time constant of redistribu-
tion of the charges in the photoconductor - liquid crystal
structure: LCPCCR≈τ , where PCR is the resistance of
the photoconductor layer, LCC is the capacity of the LC
layer. This time constant under typical conditions for the
chalcogenide glass semiconductor - nematic liquid crys-
tal structure is about 100 ms. So, usually response speed
of the NLC-SLM does not exceed 10-30 Hz.
The SLM based on the CGP-NLC structure consists
of number of thin films sandwiched between two glass
substrates: a photoconductor, a liquid crystal layer and
transparent ITO electrodes. Voltage applied to the ITO
electrodes is divided between the photoconductor and the
liquid crystal layers according to writing light intensity.
Thin films (1 µm) of semiconductor As20Se80 (sensitive in
the wide spectral range from 400 to 650 nm) were used as
a photoconductor. Twisted nematic effect was used for
light modulation. Used LC-materials (ZKS-1630B,
NIOPIK, Moscow) has the following parameters: n∆ =
0.13, =ε∆ +4.4, t∆ = -20 - +90 oC, d = 3 µm. The
main characteristics of the transmission mode SLM have
been measured in the holographic coherent optical test
bench. An interference pattern was written to the SLM
and was read by semiconductor laser beam simultane-
ously. We used a He-Ne laser ( λ =633 nm) for writing
and a semiconductor laser ( λ = 814 nm) for reading. We
studied the behavior of diffraction efficiency in the first
diffraction order as a function of operating conditions.
The diffraction efficiency was determined as a ratio of
the light intensity in the first order to the reference beam
intensity.
The special feature of the SLM operating under DC
voltage and slowly changed writing light intensity is the
high sensitivity to writing light. It is explained by ab-
sence of any capacitive current in the PC-LC structure
under these conditions. In this case photocurrent is used
with maximum efficiency and causes maximum voltage
across the LC layer that is defined by conductivity of PC
and LC layers. The dependence of diffraction efficiency
η from writing light intensity under DC voltage (U = 22
V) and constant illumination is shown in Fig. 3. The sen-
sitivity of the SLM at η=0.1% is E =3.3 µW/cm2. The
sensitivity at η= 10% is E =11 µW/cm2. The maximum
diffraction efficiency η= 14.7% is achieved at E = 43
µW/cm2. The SLM under these conditions has large dy-
namic range of both writing light intensity and diffrac-
tion efficiency that is extremely important when the de-
vice is used in optical correlators. The optimal power
supply voltage for realization of maximum dynamic
range is defined by maximum input light decreasing of
intensity. Increasing of writing light intensity from 42 to
430 mW/cm2 causes the decrease of optimal voltage from
30 to 7.5 V. This decrease of the operating DC voltage
results in improvement of dynamic range and decreasing
threshold sensitivity of the SLM.
The response speed and real-time recording possibil-
ity of the SLM is characterized by dependence of modu-
lation depth of diffraction efficiency
minmax
minmax
ηη
ηη
η +
−
=m
as a function of writing pulse frequency wf , where maxη
is the maximum diffraction efficiency (when writing light
is turned on), minη is the minimum diffraction efficiency
(when writing light is turned off or dark period). This
parameter characterizes decay of recorded grating after
turning out writing radiation. Simultaneously with in-
creasing maximum diffraction efficiency, the SLM un-
Fig. 3. Diffraction efficiency as a function of writing light inten-
sity at different modulation frequency of writing light (DC volt-
age, n=28 lp/mm).
Fig. 4. Modulation depth of diffraction efficiency as a function of
writing pulse frequency (DC voltage). The ratio hmax/hmin is shown
on the right axis.
10
1
0.1
0.01
1
10
100
W r it in g lig h t in tens it y, W /cmµ
η, %
f = 0 H z
f = 1 H z
f = 2 .5 H z
f = 1 0 H z
w
w
w
w
W r it in g pu lse freq uen cy, H z
m η
1.0
0.8
0.6
0.4
0.2
0
0 10 20 30 40 50
2:1
5:1
10:1
100:1
226 SQO, 5(2), 2002
L.I. Muravsky et al.: Performance of optical and hybrid joint transform...
der modulated writing light displays reduced modula-
tion depth of diffraction efficiency (see Fig. 4). The modu-
lation depth is decreased up to 0.16 at wf = 10 Hz. This
means that potential relief on the LC layer does not relax
completely during time period between writing light
pulses. This process results in a decreasing modulation
depth of diffraction efficiency.
3.2. OASLM JTC experimental setup
The OASLM JTC experimental setup is shown in Fig. 5.
To simplify the scheme of this setup and to provide here-
after creation of the compact security device based on it
basis, we used only one laser diode LD ( λ = 635 nm) that
formed both writing and reading beams. In this setup, the
reference PM was built in a special bracket, in which the
regulation of a mask position is foreseen. Energizing on
the OASLM and recording correlation peaks at the
correlator output were provided simultaneously with in-
put of a transformed PM (TPM) in an optical writing
beam through the device S1. The writing beam was formed
by the LD and the collimator lens (CL). The TPM and
reference PM were illuminated by the writing beam, and
a joint Fourier spectrum is produced by a Fourier lens
FL1 in a frequency domain of the JTC setup. The
OASLM was recorded the produced interference pattern
in the JTC frequency domain. The output correlation sig-
nal was formed as a result of reading out the recorded
interference pattern and its Fourier transform by a
Fourier lens FL2. The bright and sharp correlation peaks
were formed in the ±1-st diffraction order of the JTC.
Thus, the quantity of peaks was equal to quantity of sepa-
rate fragments in the transformed mask. Each peak was
produced as a result of the autocorrelation between the
corresponding fragment and the same fragment arranged
within the reference PM. The +1-st diffraction order was
recorded by a CCD-camera and entered to a PC using a
frame grabber (FG).
Different transformed PMs were studied in this setup.
The scheme of the three-fragment transformed mask fab-
rication procedure that also used in the OASLM JTC, is
shown in Fig. 6.
3.3. Peak-to-noise ratio and relative intensity
To investigate the performance of this setup and its possi-
bility to identify the optical marks containing the trans-
formed PMs, we studied the PNR as a function of an
effective focal length ef of the JTC setup first stage.
With this purpose we used two modifications of the JTC
first stage, namely: 1) a Fourier lens FL1 before input
images, 2) a Fourier lens behind input images. Applica-
tion of these schemes allowed rather easily to change the
effective focal length. In these schemes we have used a
divergent lens, due to which we reduced the sizes of the
JTC first stage. We calculated the PNR by using the next
metrics [4-6]:
PNR = ( )[ ] 21
,
,
var ji
jik
u
uI −
, (11)
where kI is the k -th peak intensity, j,iu is the intensity
of the surrounded response outside the 50% peak inten-
sity, k is a number of a peak or number of a transformed
PM fragment. We measured the PNR for 21×21-pixel
window centered relatively to each of peaks. The high
resolution of the used OASLM allowed to make the PNR
measurements in a broad band of effective focal lengths
down to ef = 200 mm. The results of the PNR versus ef
measurements, when the 256×256 pixel reference PM and
transformed PM (represented in Fig. 6) were used, are
listed in Table 1 for the mentioned above two modifica-
tions of the JTC first stage. In this Table, the relative
intensities dckk, III =0 of correlation peaks, as atti-
tudes of a k -th peak intensity kI to a dc intensity dcI ,
also are represented. The relative intensity can be esti-
Fig. 5. The OASLM JTC experimental setup: LD - laser diode; C - collimator lens; M1, M4 - beam splitters; M2, M3 - mirrors; PM
- phase mask; TPM - transformed phase mask; S1 - switch; FL1, FL2 - Fourier lenses; OASLM - optically addressed SLM based on
the CGP-NLC structure; DC - DC voltage; P1 - polarizer; CCD - CCD-camera; FG - frame grabber.
L D
M 1
C
M 2
S 1
T P M
P M
F L 1 M 4
M 3
O A S L M
F L 2
D C
C C D
F G
P C
L.I. Muravsky et al.: Performance of optical and hybrid joint transform...
227SQO, 5(2), 2002
mated as one of possible characteristics of a correlator
efficiency. This characteristic is not so obvious, as for
example, the Horner efficiency [9], but it is quite reason-
able, if an optical and a hybrid optical-digital correlators
are compared. Really, the estimation of a hybrid
correlator efficiency through the metrics suitable for an
estimation of optical correlators is inconvenient, because
the intensity of a correlation peak produced in a hybrid
correlator digital part and the intensity of a reading beam
in an optical correlator are measured in different metrics.
On the other hand, the intensity of a DC can be exactly
measured both in optical and digital correlator. Moreo-
ver, the relative intensity can be easily connected to known
estimations of correlator efficiency.
The data represented in Table 1 demonstrate that the
downward tendency of PNR is watched with reduction
of ef . Such tendency is quite natural, as the OASLM
resolution is monotonously decreased, if spatial frequency
is increased. More difficult is to explain lets for the PNR
(for example, in the string #3, if =ef 430 mm and in the
string #8 for 3-d peak, if =ef 200 mm). We suppose that
such lets are connected first of all to phase distortions of
correlation signals called rather by poor quality of manu-
facturing of phase masks and availability of local defects
in the OASLM. The correlation response as outcome of a
cross-correlation between the three-fragment transformed
and reference masks in the output plane ( )y,x ′′ of the
OASLM JTC, if =ef 400 mm, is adduced in Fig. 7.
4. Optoelectronic device
The optoelectronic device for identification of credit cards
is intended for security verification of credit cards and
other similar products. This device is built up on the ba-
sis of a HOD JTC architecture. It consists of an optical
Fourier processor (OFP), a CCD-camera, a frame grab-
ber and a PC with developed software for realization of
the 512×512-pixel Fast Fourier transform (FFT). A trans-
Fig. 6. Scheme of the three-fragment transformed mask fabrica-
tion procedure: the reference phase mask (a); separation of the
reference PM on fragments (b); the transformed PM (optical
mark) (c).
Modification Scheme 1 (before) Scheme 2 (behind)
PNR I0 PNR I0
# Focal length (mm) Peak 1 Peak 2 Peak 3 Peak 1 Peak 2 Peak 3 Peak 1 Peak 2 Peak 3 Peak 1 Peak 2 Peak 3
(×10-4) (×10-4) (×10-4) (×10-4) (×10-4) (×10-4)
1 530 10.7 11.2 14.4 12 8.1 6.3
2 450 8.8 8.8 10.2 12 8.3 6.2
3 430 10.1 10.8 18.0 12 8.4 6.2
4 400 10.2 8.3 11.2 12 8.5 6.2 11.3 10.1 14.8 13 8.7 7.2
5 350 9.5 10.6 14.7 13 9.1 6.7
6 300 12.4 12.0 10.1 12 9.6 7.1 8.0 10.5 12.6 12 9.8 7.5
7 250 8.0 9.3 10.7 12 9.2 3.3
8 200 9.1 9.1 15.9 6.1 5.3 5.1 10.1 11.8 4.5 11 9.2 1.5
Table 1. Results of the PNR and 0I versus ef measurements for the OASLM experimental setup, if the three-fragment
transformed PM (see Fig. 6) is used
Fig. 7. Correlation response as outcome of a cross-correlation
between the three-fragment transformed and reference masks in
the output plane ( )′ ′x y, of the OASLM JTC for f e =400 mm
(dc is truncated).
a ) b ) c )
228 SQO, 5(2), 2002
L.I. Muravsky et al.: Performance of optical and hybrid joint transform...
formed PM is used in this device as an optical mark bonded
to a credit card to be identified.
The scheme of the device is shown in Fig. 8. The laser
beam is generated by a laser diode 1 ( λ =635 nm) and is
collimated by a collimator 2. The collimated laser beam
illuminats the transformed PM 3 and the reference PM 4
placed in the input plane of the OFP. The reference mask
is strongly attached to the special holder in the OFP in-
put plane. The transformed mask is entered into the OFP
input plane as the optical mark bonded to the credit card.
A joint Fourier transform spectrum is formed by the
Fourier lens 5 and is produced on the OFP output as a
result of a joint Fourier transform of both masks. The
CCD-camera 7 records the joint power spectrum. The
interference pattern is captured by the frame grabber 8
and is converted into a digital massif with a 512×512-
pixels dimension. The modified FFT algorithm is used
to perform the inverse Fourier transform in the PC 15. If
the optical mark is authentic, the several narrow and
bright correlation peaks are produced in the first diffrac-
tion order of the JTC output, and quantity of peaks is
equal to quantity of fragments of the transformed PM.
Calculated distances between peaks form an identifica-
tion feature vector (FV) which is compared with a refer-
ence FV [6]. If the distance D between the identification
and reference FVs is less than the given distance 0D , the
credit card is considered authentic. Then the identifica-
tion signal is emerged on the display 16. A divergent lens
6 is used to change the effective focal length ef of the
OFP.
To define minimum permissible focal length k,Nf of
the Fourier transform lens in the OFP, at which the re-
covery of the k -th correlation peak without a loss of in-
formation still agrees with the sampling theorem [10],
we have used the following equation:
( ) ( )
λ
ββ kkkxy
kN
ltgpp
f
r
cos2
,
+
= , (12)
where xp and yp are the pitches between pixels in the
CCD matrix in horizontal and vertical directions accord-
ingly; kl
r
is the vector arranged in an input plane of a
correlator, this vector connects center of a k -th frag-
ment in a reference mask to center of the same k -th frag-
ment in the transformed mask (see Fig. 9); kβ is the an-
gle between vector kl
r
and axis yr of the JTC input plane
( )y,x . Note, that kβ is equal to the angle between vec-
tor kl ′
r
from a point about the origin of the JTC output
plane ( )y,x ′′ up to the point of the k -th correlation
peak maximum and axis yr′ of the output plane (see Fig.
10). If the scales of direct and inverse Fourier transforms
in the JTC are identical, then =kl
r
kl ′
r
.
Different transformed PMs were tested in the
optoelectronic device. One of these masks is represented
Fig. 8. Scheme of the optoelectronic device: OFP - optical Fourier processor, 1 - laser diode (l=635 nm), 2 - collimator lens, 3 -
transformed PM (optical mark), 4 - reference PM, 5 - Fourier lens, 6 - divergent lens, 7 - CCD-camera, 8 - frame-grabber, 9 - video
amplifier, 10 - ADC, 11 - RAM, 12 - data bus, 13 - address bus, 14 - signal synchronizer, 15 - PC, 16 - display.
Fig. 9. Arrangement of the vector in a JTC input plane ( )x y, .
1
2 3
4
5
6
7
8
9
10 11 12
1314
15
16Credit
card
OFP
2y
0
'
2=kl
'
3=kl
y
x
1
2
3
1
1 2
3
1
0
L.I. Muravsky et al.: Performance of optical and hybrid joint transform...
229SQO, 5(2), 2002
in Fig. 6. The calculated quantities of minimum allow-
able focal length k,Nf for all three correlation peaks
produced at the optoelectronic device output as a result
of a cross-correlation between this mask and the refer-
ence PM are represented in Table 2. In this Table, kx
and ky are projections of the vector kl
r
(see Fig. 9). This
Table shows that minimum focal length of the Fourier
transform lens for this mask corresponds to
==3k,Nf 299.3 mm.
To compare performances of the OASLM JTC and
optoelectronic device based on a HOD JTC, we used the
same masks in the optoelectronic device. We calculated
the PNR at the output of the optoelectronic device by
using the same Eq. (11), as for calculation of the PNR in
the OASLM JTC. The results of the PNR calculations
for =ef 400 mm are represented in Table 3. This Table
also represents the relative intensities k,I 0 of the correla-
tion peaks.
The results of the PNR and relative intensity 0I meas-
urements are represented in Table 3 for the next condi-
tions of the interference pattern recording: string #1 - the
CCD-camera records the center of the interference pat-
tern (1 - 4-th quadrants of a frequency domain ( )yx ,νν );
string #2 - the bottom of the interference pattern (3-d and
4-th quadrants); string #3 - the top of the interference
pattern (1-st and 2-nd quadrants), string #4 - the upper
right hand part of an interference pattern (1-st quadrant).
So, the PNR and 0I are different, if the different parts of
k kx , mm 02yyk − , mm kβ , deg kl
r
, mm k,Nf , mm
1 0 0 0 8.000 202.2
2 2.560 -2.560 25.20 6.012 169.9
3 -2.560 2.560 13.63 10.867 299.3
Table 2. Calculation of the minimum focal length k,Nf of the Fourier transform lens in the OFP for the three-fragment trans-
formed PM.
Fig. 10. Arrangement of the vectors in a JTC output plane
( )′ ′x y, .
Fig. 11. Correlation response as outcome of a cross-correlation.
2
1
3
Table 3. Results of the PNR and relative intensity 0I measurements for the optoelectronic device based on a HOD JTC
architecture, if the three-fragment transformed PM (see Fig. 6) is used.
# Quadrant PNR I0
Peak 1 Peak 2 Peak 3 Peak 1 Peak 2 Peak 3
Direct recording 1 1-4 27.7 19.5 23.8 0.25 0.09 0.15
of an interference 2 3,4 24.9 14.1 44.8 0.22 0.07 0.25
pattern 3 1,2 34.1 16.1 41.8 0.26 0.06 0.18
4 1 34.4 16.1 31.1 0.52 0.12 0.31
Fourier plane 5 3,4 8.1 16.4 14.3 0.13 0.09 0.16
image subtraction 6 1,2 7.9 13.7 18.3 0.06 0.07 0.18
technique 7 1 33.6 7.1 7.1 0.25 0.07 0.07
Power spectrum 8 1,2 25.5 23.1 23.1 0.19 0.31 0.31
subtraction 9 1 15.1 22.4 14.1 0.31 0.25 0.23
technique
x =2
k
'
y =2
k
2y
0
1
2
3
0'
y
x
'
2=kl
'
1=kl
'
3=kl
230 SQO, 5(2), 2002
L.I. Muravsky et al.: Performance of optical and hybrid joint transform...
the same interference pattern are recorded by the CCD-
camera. Such different values of the PNR and 0I , first of
all, should be explained by a high level of an optical
noise in the optoelectronic device. The correlation re-
sponse as outcome of a cross-correlation between the
three-fragment transformed and reference masks in the
output plane ( )yx ′′, of the optoelectronic device
( =ef 400 mm) is adduced in Fig. 11. This responce was
obtained by recording of the third and fourth quadrants
of a frequency domain ( )yx νν , .
We also investigated the effectiveness of a Fourier
plane image subtraction technique [11] in the
optoelectronic device (see to graph «Fourier plane im-
age subtraction technique» in the Table 3). The made
attempts of its application were not crowned with suc-
cess, to what the outcomes induced in strings #5-7 as
Table 3 testifies. The unexpected and interesting outcomes
were obtained in that case, when we subtracted the power
spectrum ( )yxS νν ,2 of the transformed mask complex
amplitude transmittance ( )yxs , from the power spectrum
( )yxR νν ,2 of the reference mask�s transmittance ( )yxr ,
(see to graph «Power spectrum subtraction technique»).
Now we spend more in-depth studies of this effect.
5. Conclusions
The comparative analysis of Table 1 and Table 3
shows that the PNR and relative intensity 0I in the
optoelectronic device are much above, than in the
OASLM JTC. The low PNR and 0I in the OASLM JTC
are explained to that we have used the recording and
reading beam from the same laser diode. The prelimi-
nary researches have shown that usage in a JTC of a
reading beam on a wavelength λ = 814 nm results in ap-
proximately three-fold increase of a PNR. Let�s also note,
that the rather low-level values of the PNR for both JTC
types in comparison with theoretically calculated PNR
values (see Fig. 2) are explained by poor quality of a
substrate, on which the phase masks were produced, as
well as by a high level of optical noise in both correlators.
Thus, it is possible to assert that security devices for
identification of phase masks can be created on the basis
of architectures of both hybrid and optical correlators.
However, it is necessary to allow for features of creation
of such devices. So, for example, if we design the optical
security devices on the basis architectures of an optical
correlator, the main attention should be given to research
of operating characteristics of the SLM and selection of
its optimum regimes in the device. Thus, the main design
problem for creation of such devices will be reduction
their overall dimensions. If we design the hybrid security
devices, the main attention should be paid on mining of
the interface and operating FFT-processor. The overall
dimensions of such devices will be determined in the main
scale of the optical scheme. Therefore, basic requirement
to the optical scheme in OFP consists in achievement of
the largest possible effective focal distance at minimum
allowable overall OFP dimensions.
Acknowledgments
The authors are grateful to M.V. Shovgenyuk, T.V.
Fityo and P.A. Hlushak for fruitful discussions and tech-
nical support.
References
1. B. Javidi and J.L. Horner, Optical pattern recognition for
validation and security verification // Opt. Eng. 33(6),
pp.1752-1756 (1994).
2. B. Javidi, G. Chang, and J. Li, Experimental demonstration
of the random phase encoding technique for image encryption
and security verification // Opt. Eng. 35(9), pp.2506-2512
(1996).
3. L.I. Muravsky, V.M. Fitio, M.V. Shovgenyuk, and P.A.
Hlushak, Separation of random phase mask in optical
correlator for security verification // SPIE Proc. 3466, pp.267-
277 (1998).
4. L.I. Muravsky, T.I. Voronyak, V.M. Fitio, and M.V.
Shovgenyuk, Transformed phase mask and photoanisotropic
material in optical correlators applied for security verifica-
tion // Opt. Eng. 38(1), pp.25-32 (1999).
5. L.I. Muravsky, Binary phase image processing in optical and
optical-digital correlation systems, Serpen�, Ternopil�, 1999
(in Ukrainian).
6. L.I. Muravsky, Ya. P. Kulynych, T. I. Voronyak, V. M. Fityo,
and S. A. Kostyukevych, Transformed phase mask in a hy-
brid joint transform correlator for security verification // SPIE
Proc. 3804, pp.233-240 (1999).
7. V.M. Fitio, L.I. Muravsky, and A.I. Stefansky, Using of ran-
dom phase masks for image recognition in optical correlators
// SPIE Proc. 2647, pp.224-234 (1995).
8. F.L. Vladimirov, A.N. Chaika, N.I. Pletneva, I.E. Morichev,
and N. Collings, Spatial light modulators based on
chalcogenide glass photoconductor - liquid crystal structure
operating in pulse regime // SPIE Proc. 3490, pp.432 - 435
(1998).
9. J.L. Horner, Metrics for assessing pattern-recognition per-
formance // Appl. Opt. 31(2), pp.165-166 (1992).
10. R.N. Bracewell, The Fourier Transform and Its Applications,
Mc Graw-Hill Book Company, New York, 1965.
11. M.A. Alam, and M.A. Karim, Multiple target detection us-
ing a modified fringe-adjusted joint transform correlator //
Opt. Eng. 33(5), pp.1610-1617 (1994).
|