U.S. patent application number 17/832729 was filed with the patent office on 2022-09-29 for labelling scheme and apparatus.
The applicant listed for this patent is Oxford University Innovation Limited. Invention is credited to Konstantin BORISENKO, Paul EWART, Rohanah HUSSAIN, Angus Ian KIRKLAND, Andrew LUERS, Giuliano SILIGARDI, Ben WILLIAMS.
Application Number | 20220309265 17/832729 |
Document ID | / |
Family ID | 1000006394828 |
Filed Date | 2022-09-29 |
United States Patent
Application |
20220309265 |
Kind Code |
A1 |
KIRKLAND; Angus Ian ; et
al. |
September 29, 2022 |
LABELLING SCHEME AND APPARATUS
Abstract
A method and system for writing a label (defined within a
predetermined region of the sample 110), the label displaying a
visible layout of light-modified regions in a predetermined spatial
arrangement. The method comprises: modifying regions of a material
within the label using light, wherein the modifying comprises using
light of a first polarisation state to provide photo-induced
optically active regions of a first type having a first optical
activity state which is characteristic of having been formed by
light of the first polarisation state, in order to encode covert
information in the label using the locations of the first type of
light-modified regions within the spatial arrangement of the
label.
Inventors: |
KIRKLAND; Angus Ian; (Oxford
(Oxfordshire), GB) ; EWART; Paul; (Oxford
(Oxfordshire), GB) ; BORISENKO; Konstantin; (Oxford
(Oxfordshire), GB) ; WILLIAMS; Ben; (Oxford
(Oxfordshire), GB) ; LUERS; Andrew; (Oxford
(Oxfordshire), GB) ; SILIGARDI; Giuliano; (Oxford
(Oxfordshire), GB) ; HUSSAIN; Rohanah; (Oxford
(Oxfordshire), GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Oxford University Innovation Limited |
Oxford |
|
GB |
|
|
Family ID: |
1000006394828 |
Appl. No.: |
17/832729 |
Filed: |
June 6, 2022 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16970043 |
Aug 14, 2020 |
11354527 |
|
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PCT/GB2019/050452 |
Feb 19, 2019 |
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17832729 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B42D 25/41 20141001;
G06K 7/10732 20130101; B42D 25/305 20141001; G06K 7/1447 20130101;
B41J 3/01 20130101; B41J 3/4075 20130101 |
International
Class: |
G06K 7/14 20060101
G06K007/14; B42D 25/305 20060101 B42D025/305; B42D 25/41 20060101
B42D025/41; B41J 3/01 20060101 B41J003/01; B41J 3/407 20060101
B41J003/407; G06K 7/10 20060101 G06K007/10 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 19, 2018 |
GB |
1802661.7 |
Claims
1-43. (canceled)
44. A method of reading a label within a sample, the label
comprising a plurality of light-modified regions having a
predetermined spatial arrangement therebetween, the modified
regions comprising light-modified regions which can be of at least
a first type having a first optical activity state characteristic
of having been formed by light of a first polarisation state, the
method comprising: illuminating the label with light of a
predetermined polarisation state to reveal the locations of the
first type of light-modified regions to read covert information
encoded by their locations.
45. The method as claimed in claim 44, wherein the light-modified
regions can comprise light-modified regions of at least a second
type having a second optical activity state characteristic of
having been formed by light of a second polarisation state, the
method comprising: illuminating the label with light of the
predetermined polarisation state to reveal the locations the second
type of light-modified regions to read covert information encoded
by their locations.
46. The method as claimed in claim 45, wherein the light-modified
regions can comprise a third type of light-modified region having a
third optical activity state characteristic of having been formed
by light of a third polarisation state, the method comprising:
illuminating the label with light of the predetermined polarisation
state to reveal the locations the third type of laser modified
regions to read covert information encoded by their locations.
47. The method as claimed in claim 46, comprising: illuminating the
label with light of a second polarisation state to reveal the
locations of the second type of light-modified regions to read
covert information encoded by their locations; and/or illuminating
the label with light of a third polarisation state to reveal the
locations of the third type of light-modified regions to read
covert information encoded by their locations.
48. The method as claimed in claim 45, comprising: illuminating the
label with light of a second polarisation state to reveal the
locations of the second type of light-modified regions to read
covert information encoded by their locations.
49. The method as claimed in claim 44, comprising: alternately
illuminating a light-modified region of the label with a pulse of
light of a first polarisation state and a pulse of light of a
second polarisation state; timing detection of the illuminating
light, for a first predetermined period, so as to detect only light
of the first polarisation state; timing detection of the
illuminating light, for a second predetermined period, so as to
detect only light of the second polarisation state; and comparing
signals detected in the first predetermined period and the second
predetermined period to determine the type of the laser modified
region.
50. The method as claimed in claim 45, comprising: alternately
illuminating a light-modified region of the label with a pulse of
light of a first polarisation state and a pulse of light of a
second polarisation state; timing detection of the illuminating
light, for a first predetermined period, so as to detect only light
of the first polarisation state; timing detection of the
illuminating light, for a second predetermined period, so as to
detect only light of the second polarisation state; and comparing
signals detected in the first predetermined period and the second
predetermined period to determine the type of the laser modified
region.
51. The method as claimed in claim 46, comprising: alternately
illuminating a light-modified region of the label with a pulse of
light of a first polarisation state and a pulse of light of a
second polarisation state; timing detection of the illuminating
light, for a first predetermined period, so as to detect only light
of the first polarisation state; timing detection of the
illuminating light, for a second predetermined period, so as to
detect only light of the second polarisation state; and comparing
signals detected in the first predetermined period and the second
predetermined period to determine the type of the laser modified
region.
52. The method as claimed in claim 47, comprising: alternately
illuminating a light-modified region of the label with a pulse of
light of a first polarisation state and a pulse of light of a
second polarisation state; timing detection of the illuminating
light, for a first predetermined period, so as to detect only light
of the first polarisation state; timing detection of the
illuminating light, for a second predetermined period, so as to
detect only light of the second polarisation state; and comparing
signals detected in the first predetermined period and the second
predetermined period to determine the type of the laser modified
region.
53. A label reader apparatus for reading a label in a sample, the
label displaying a visible layout of light-modified regions in a
predetermined spatial arrangement, and comprising light-modified
regions of a first type having a first optical activity state
characteristic of having been formed by light of a first
polarisation state, the apparatus comprising: an illumination
device for illuminating the label in the sample; a polarisation
device for imparting one of a plurality of polarisation states to
the illuminating light; a detection device arranged to detect light
from the illumination device; and a processor configured to
determine from the detected light locations of the first type of
modified regions and read covert information encoded by their
locations.
54. The label reader apparatus as claimed in claim 53, wherein the
illumination device is arranged to illuminate only part of the
label at a time.
55. The label reader apparatus as claimed in claim 53, wherein the
illumination device is arranged to illuminate the whole label all
at once.
56. A system for writing a label and reading a label, comprising: a
labelling system for writing a label within a sample of a material,
the label comprising a visible layout of light-modified regions in
a predetermined spatial arrangement, the labelling system
comprising: a light source for modifying regions of the sample
using light; and a polarisation apparatus for imparting any one of
a plurality of polarisation states to the light for modifying the
regions of the sample; and the label reader apparatus of claim
53.
57. The system for writing a label and reading a label as claimed
in claim 56, wherein the illumination device is arranged to
illuminate only part of the label at a time.
58. The system for writing a label and reading a label as claimed
in claim 56, wherein the illumination device is arranged to
illuminate the whole label all at once.
59. A non-transitory computer-readable storage medium comprising
instructions which, when executed by a computer, cause the computer
to perform the method of claim 44.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method and apparatus for
writing a label, a method and apparatus for reading a label, and a
sample with a label written therein. Particularly the invention
relates to a method for writing a label having a plurality of
light-modified regions with characteristic optical properties.
BACKGROUND
[0002] It is often necessary to mark or label an item for the sake
of identification, validation, accreditation and so on. For
example, trade marks are displayed on products to indicate their
origins to a consumer. Barcodes are commonly fixed to the packaging
of products to identify them for sale. Quick response (QR) codes
encode information that e.g. may be scanned to direct a consumer to
a website. Security holograms are used to indicate the authenticity
of consumer electronics because they are difficult to forge.
[0003] There are a great many applications for labels, and the
specific characteristics required of a particular label will be
dependent upon how the label is to be used. In some cases it is
desirable to label an item with a covert feature, so that the item
cannot be easily copied or can only be verified by an authorised
party. For example, modern coinage and banknotes in the UK display
some labels only under illumination by particular frequencies of
ultraviolet light.
[0004] While many such methods for covert labelling exist, there
remains a need for continuing improvement in the field. Such labels
often need to be durable to mechanical wear and changes in
temperature, easily made, and reliably read.
SUMMARY OF THE INVENTION
[0005] According to a first aspect of the present invention there
is provided a method of writing a label, the label displaying a
visible layout of light-modified regions in a predetermined spatial
arrangement, the method comprising: modifying regions of a material
within the label using light, wherein the modifying comprises using
light of a first polarisation state to provide photo-induced
optically active regions of a first type having a first optical
activity state which is characteristic of having been formed by
light of the first polarisation state, in order to encode covert
information in the label using the locations of the first type of
light-modified regions within the spatial arrangement of the
label.
[0006] The optically active regions of the first type are formed by
exposure of the material to light of a first polarisation state
(for example, left circular polarisation, right circular
polarisation, left elliptical polarisation, right elliptical
polarisation, linear horizontal polarisation, linear vertical
polarisation etc.). The light exposure must be above an energy
threshold required for modification of the material. During
formation, molecules and/or crystallites of the material are
aligned by the electromagnetic field of the modifying light into an
arrangement characteristic of the electromagnetic field, i.e.
characteristic of the light's polarisation. For example, the
molecules and/or crystallites of material exposed to left
circularly polarised (LCP) light will align so as to create a
left-chiral formation between them. Similarly a right chiral
formation will be created by exposure to right circularly polarised
(RCP) light. Molecules and/or crystallites exposed to linearly
polarised light will align linearly with the electromagnetic field
of the modifying light.
[0007] As a consequence of the their molecular and/or crystallite
configuration, the light-modified regions of the first type will
exhibit optical activity when exposed again to light of a first
polarisation state--i.e. a polarisation state which is the same as
that of the light which originally created the modified region. For
example, light-modified regions formed by right circularly
polarised (RCP) light will transmit right circularly polarised
(RCP) light more efficiently than other polarisations. Hence, they
will appear brighter when illuminated from behind with RCP light.
These regions will also reflect LCP light more efficiently and
hence will appear brighter when illuminated from the front with LCP
light.
[0008] A similar phenomenon happens for laser modification by light
of a linear polarisation. The molecules and/or crystallites within
the modified region are aligned by the electromagnetic field of the
modifying light into an arrangement characteristic of the
electromagnetic field, i.e. characteristic of the light's linear
polarisation. Then, these modified regions exhibit optical activity
characteristic of their arrangement, and hence interact with
linearly polarised light more strongly than other
polarisations.
[0009] It is therefore possible to create a label comprising
spatially arranged light-modified regions of different types of
optical activity. Since, ambient light is a mixture of random
polarisations, light-modified regions of all types will appear
substantially the same under ambient illumination and hence will
display a visible layout. As such, the label may comprise a spatial
arrangement of modified regions encoding information which is
generally visible under ambient light or the like--for example, in
the same way a typical barcode, QR code, number, word or the like
encodes and displays information. Moreover, a covert (i.e. not
openly displayed) spatial arrangement of light-modified regions may
be revealed by illuminating the label with light of a particular
polarisation of light (or by light comprising a substantial
proportion of light of a particular polarisation). Thus a subset of
the light-modified regions may be revealed as exhibiting an optical
activity and hence may themselves encode covert information. The
covert arrangement of these modified regions thus hides additional
information within the label. Thus, the label may encode both overt
and covert information within an overt label which can be
recognised as a label by the naked eye. The label may appear
differently under illumination by different polarisations of light
and ambient light.
[0010] It is well understood that positioning and/or sizing of
defining marks within a specified region may be used to convey
information. For example, a barcode achieves such an encoding of
information by relative locations and sizes of vertical lines
within a finite region. A quick response code (`QR` code) achieves
a similar encoding of information. Indeed, a photograph or even a
written word also encodes information therein. It will be
appreciated that a wide variety of ways of encoding information is
possible and the invention is not limited to any particular scheme
or type of information encoding.
[0011] The material in which the label is written may be any
suitable material in which optically active regions may be formed
by modification by light. For example, the material
Ge.sub.2Sb.sub.2Te.sub.5 (GST) may be particularly suitable by
virtue of its being relatively easy to modify and being robust
enough to hold a written modification for a sufficient period of
time. Other types of chalcogenide material may be used, and other
types of phase change material may be used.
[0012] The chalcogenide material may comprise one or more chalcogen
elements, e.g. selected from O, S, Se, Te and Po, and one or more
electropositive elements, e.g. selected from N, Si, Ni, Ga, Ge, As,
Ag, In, Sn, Sb, Au, Pb and Bi. The chalcogenide material may be in
the form of a binary, ternary, or quaternary alloy.
[0013] The material may comprise a chiral fragment which can exist
in the material in a plurality of non-superimposable forms. For
example, a nitrogen-doped chalcogenide material containing Ge may
contain a cluster of nitrogen and germanium atoms which can exist
in at least two non-superimposable forms.
[0014] Thus, the material may comprise any material that can be
transformed from a non-chiral (achiral) amorphous state to a state
with retained or sculpted chirality (or optical activity caused by
circular or linear birefringence) induced by one or more light
pulses having a particular polarisation state.
[0015] The step of modifying a region with light may comprise using
any suitable light source. For example, the light source may be a
lamp such a xenon lamp or a tungsten lamp, or may be suitable
laser. Therefore, modifying a region may comprise laser modifying a
region, and light-modified regions may be laser modified
regions.
[0016] The modifying may comprise using light or laser pulses of a
second polarisation state to provide photo-induced optically active
regions of a second type having a second optical activity state
which is characteristic of having been formed by light of the
second polarisation state, in order to encode covert information in
the label using the locations of the second type of laser modified
regions within the spatial arrangement of the label. As such, laser
modified regions may be either the first type or the second type.
Each type of region will respond differently under different
polarised illumination and hence another degree of freedom exists
in which to encode information. The second polarisation state may
be different to the first, and where the first polarisation state
has a chirality (i.e. a handedness, for example right-handed), the
second polarisation may have the opposite chirality (for example,
left-handed).
[0017] The laser modifying may comprise using laser pulses of a
third polarisation state to provide photo-induced optically active
regions of a third type having a third optical activity state which
is characteristic of having been formed by light of the third
polarisation state, in order to encode covert information in the
label using the locations of the third type of laser modified
regions within the spatial arrangement of the label. The third
polarisation state may be different to the first and second
polarisation states. For example, the third polarisation state may
be linear polarisation (LP). As such, the optical activity of the
third type of laser modified regions may be different to that of
the first and second types, and another degree of freedom may be
available for encoding information within the label.
[0018] Then, each laser modified region may have one of three types
of optical activity, discoverable by suitable illumination or a
suitable reading method. Moreover, a region of the label may be
left unmodified, which is another type of optical activity (i.e.
optical property) in which the region behaves the same under all
types of illumination. Each region of the label, modified or not,
can therefore comprise one of four types of optical activity to
encode information. The information storage density of the label
may therefore be increased as compared to a standard binary label
(such as 0 and 1 bit), in which a region may be modified or not,
providing two degrees of freedom.
[0019] The method may comprise predetermining locations and types
of each of the laser modified regions. It may comprise encoding a
number or any other information into a spatial arrangement of marks
for writing into the label. The method may comprise converting the
information into a base-4 system for representation by units of 4
degrees of freedom (analogous to the use of bits in a binary
system).
[0020] The first polarisation state may be one of linear
polarisation, left circular polarisation, and right circular
polarisation. The second and/or third polarisations may be the
others of the linear, left circular and right circular
polarisation, so that the first, second, and third polarisation
states are any permutation of linear polarisation, left circular
polarisation, and right circular polarisation. Such polarisation
states may be used in combination with un-modified regions (e.g. of
an amorphous achiral material) to encode the covert
information.
[0021] Where linear polarisation is used, the method may also
permit differentiation between modified regions formed by vertical
polarisation and modified regions formed by horizontal
polarisation. The method may also permit differentiation between
modified regions formed by linear polarisation aligned at a tilted
angle in between the horizontal and vertical. Thus, but modifying
regions of a sample using different orientations of linear
polarisation, the method may further increasing the density of
information storage available in the label. Similarly, left and/or
right elliptical polarisation may also be used, as another degree
of freedom so that the information in the label may comprise a base
system which is greater than base 4. For example, by using left
circularly polarised light, right circularly polarised light,
horizontal linearly polarised light and vertical linearly polarised
light, each region of the sample may have one of five predetermined
properties (including un-modified).
[0022] The method may comprise defining the label as a portion of
the material, and leaving unmodified at least a portion of the
label. In this way, part of the label may have an optical activity
that is the same under all types of polarisation. This can serve as
a reference point within a label against which other optical
activity types may be compared.
[0023] The method may comprise defining the label as an array of
addressable locations within a portion of the material and
predetermining for each location an optical property. The optical
property may be the optical property of the unmodified sample (so
that that point need not be modified) or may be that of any of the
types of laser modified regions.
[0024] The array may be a multi-dimensional, regular array of
modified regions, or may be a multi-dimensional, irregular array of
modified regions. For example, the array may be a two-dimensional
square or rectangular array, and each location within the array may
be assigned a type of optical property. The modified regions may
form pixels of the covert information in their own right, or they
may be arranged as groups which collectively make up a pixel. The
method may comprise writing an array in which the laser modified
regions are coplanar (i.e. all on a flat plane within the sample).
The plane of the array may be at a uniform depth beneath a surface
of the sample, or may be at the surface of the sample. The array
may be a three-dimensional array so that laser modified regions are
disposed at varying depths within the sample. The method may
comprise modifying the sample in accordance with predetermined
characteristics of the label.
[0025] The laser modifying may comprise simultaneously modifying a
plurality of regions of the material to provide laser modified
regions of the first type. Thus, multiple spatially separated laser
modified regions of the first type may be created at once. The
method may comprise laser modifying a plurality of regions
simultaneously, each region being any one of the above described
types. Laser modification of a second type of region may be
simultaneous with that of a first type. Laser modification of a
third type may be simultaneous with that of the first type and/or
the second type. The method may comprise laser modifying a
plurality of regions and may comprise simultaneously laser
modifying the plurality of regions using the first, second and/or
third polarisations of light, or may include simultaneously laser
modifying a subset of the plurality of regions.
[0026] The method may therefore comprise simultaneously creating
all laser modified regions of the label having optical activity
characteristic of having been formed by light of the first
polarisation, and may subsequently or simultaneously comprise
creating all regions having optical activity characteristic of
having been formed by light of the second polarisation, and may
subsequently or simultaneously comprise creating all regions having
optical activity characteristic of having been formed by light of
the third polarisation. The method may comprise simultaneously
modifying (i) a first plurality of regions using light of the first
polarisation and (ii) a second plurality of regions using light of
the second polarisation. The method may further comprise modifying,
simultaneously with the first and second pluralities of regions, a
third plurality of regions using light of the third
polarisation.
[0027] The laser modifying may comprise creating chiral structures
within the material. The chiral structures may be formed of
molecular and/or crystallite fragments and/or chiral fragments of
the material, and their chirality may arise because of the spatial
arrangement between the constituent fragments of the structure. The
method may comprise creating left-handed chiral structures within
the material using left circularly polarised light, and/or may
comprise creating right-handed chiral structures within the
material using right circularly polarised light.
[0028] The method may comprise providing a plurality of laser
modified regions proximate one another to create a visible pixel.
The method may therefore be used to create a visible mark or pixel
within the material which is larger than the constituent laser
modified regions by grouping the modified regions sufficiently
closely. Each laser modified region may therefore contribute to a
portion of a pixel, and groups of laser modified regions may form a
single pixel. The pixels may be more easily identified for reading
the label and the covert information.
[0029] The method may comprise modifying regions of the material
within the label using light of a first polarisation state and a
first wavelength, and modifying regions of the material within the
label using light of a first polarisation state and a second
wavelength. Then, modified regions of the first type and first
wavelength may be distinguished from modified regions of the first
type and second wavelength, by their having different peaks in
their respective response signals when read using the different
wavelengths. Each of the first, second, and third type of modified
regions may be formed using light of the respective polarisation
state and a plurality of wavelengths, so as to allow types of
modified regions to be distinguished from those of the same
(polarisation) type but different wavelength.
[0030] The laser pulse may have a duration of between 1 femtosecond
and 20 nanoseconds, between 5 and 15 nanoseconds, and may be about
10 nanoseconds. The pulse may have a duration of less than 10
nanoseconds. The pulse duration may be measured by its full width
at half maximum (FWHM). Laser modification may comprise a single
laser pulse exposure, or may comprise multiple pulse exposures of a
single region. Laser modification may comprise any suitable number
of exposures, for example between 1 and 100,000 exposures,
preferably between 1 and 1000 exposures, and more preferably
between 10 and 100 exposures.
[0031] The method may comprise writing a barcode, and may comprise
writing a covert barcode. The method may comprise writing a QR
code, and may comprise writing a covert QR code. The method may
comprise writing a unique identifier.
[0032] The label may be below an outer surface of the sample and
hence may be within the sample. The sample may have any suitable
thickness, and may preferably be less than 100 micrometres in
thickness, and more preferably may be between 20 and 60 micrometres
in thickness.
[0033] The laser modified regions may be written with spacing of
more than 10 micrometres therebetween. The laser modified regions
may be greater than 20 micrometres apart, 50 micrometres apart, 100
micrometres apart, 250 micrometres apart, 500 micrometres apart,
and/or 1000 micrometres apart.
[0034] The steps of the method may be carried out in any suitable
order, and may be carried out in the order recited in the claim, or
may be carried out in another order.
[0035] According to a second aspect of the present invention there
is provided a labelling system for writing a label within a sample
of a material, the label comprising a visible layout of
light-modified regions in a predetermined spatial arrangement, the
system comprising: a light source for modifying regions of the
sample using light; and a polarisation apparatus for imparting any
one of a plurality of polarisation states to the light for
modifying the regions of the sample.
[0036] The light source may be any suitable light source, for
example a lamp such as a xenon lamp or a tungsten lamp. The light
source may preferably be a laser for modifying regions of the
sample using laser pulses.
[0037] The method may comprise using light of any suitable
wavelength to modify the sample. The light may have a wavelength
between ultraviolet and infrared.
[0038] The polarisation apparatus may be operable to impart any one
of all of the polarisation states at different times, and may be
controlled to impart a predetermined one polarisation state to the
laser pulses.
[0039] The labelling system may further comprise: a beam splitting
device for dividing the laser into a plurality of laser beams, each
laser beam for simultaneously laser modifying a respective region
of the sample; and the polarisation apparatus may comprise a
plurality of polarisers each arranged for simultaneously polarising
a respective one of each of the plurality of laser beams.
[0040] The polarisation apparatus may impart the same polarisation
for all of the plurality of laser beams simultaneously, or may
impart different polarisations to each beam respectively. The
polarisations may be any of the polarisations described above with
respect to the first aspect of the invention. The labelling system
may generate LCP beams, RCP beams, and LP beams for writing as
needed. It may further be configured to generate different
orientations of LP beam such as vertical, and/or horizontal, and/or
any angle therebetween.
[0041] Each of the plurality of polarisers may comprise a linearly
polarising element for imparting linear polarisation to a laser
beam and a circularly polarising element for imparting circular
polarisation to a laser beam. The circular polarising element may
be a quarter wave plate retarder. The polarisation apparatus may
comprise two circularly polarising elements, one for each chirality
of polarisation. The circularly polarising element may be actuable
to change the chirality of the circular polarisation imparted to
the laser beam. The circular polarising element(s) may be operable
to polarise a respective laser beam or may be operable not to
polarise a beam (e.g. by being moved from the beam path).
[0042] The labelling system may comprise a plurality of shutters
each operable to block a respective one of the plurality of laser
beams. Thus, the system may allow a region of the label to remain
unmodified.
[0043] Alternatively the system may comprise a plurality of
shutters and a single linear and circular polariser, so that all
beams are simultaneously polarised with the same polarisation
state, and the shutters may be operable to block the beams as
necessary so that only those needed for writing that present
polarisation are allowed to reach the sample and modify a region
thereof. A label could then be written in e.g. three steps, one for
each type of polarisation used (unmodified regions would not
require a writing step).
[0044] The labelling system may comprising focussing optics
arranged to focus each of the plurality of laser beams at a
respective predetermined location within the sample for laser
modifying a respective regions of the sample and writing the label.
The focussing optics may be common to each of the plurality of
laser beams, or may comprise a plurality of separate focussing
mechanisms for each of the laser beams respectively. The focussing
optics may be dynamic so that the location of the laser modified
regions may be controlled. Alternatively, the focussing optics may
be static and the system may comprise a translation stage to move
the sample relative to the location of the modifying laser beams'
foci.
[0045] The plurality of laser beams may be arranged to write in the
sample along a straight line. The label to be written may comprise
a two dimensional array having one dimension equal to the number of
modifying laser beams so that one row/column of the array may be
written all at once. The plurality of laser beams may be arranged
to write in the sample in a two-dimensional array. There may be as
many laser beams as elements of the array, so that an array may be
written all at once.
[0046] The light source may be arranged to provide a plurality of
different wavelengths of light. Thus, the system may be operable to
create light-modified regions of each type using different
wavelengths, so as to allow the same types of modified region to be
distinguished from each other and further increase the available
density of information in the label.
[0047] The light source of the labelling system, for example, a
laser may have a pulse duration between 1 femtosecond and 20
nanoseconds, and may have a pulse duration of between 5 and 15
nanosecond, and may be about 10 nanoseconds for modifying a sample.
The pulse duration may be less than 10 nanoseconds. The pulse
duration for modification may be determined by the sample
material.
[0048] The system may further comprise a controller for
predetermining properties of the label to include a plurality of
optically active laser modified regions and their locations within
the label.
[0049] The labelling system may be arranged to perform the method
according to any of the embodiments of the invention as described
with reference to the first aspect.
[0050] According to a third aspect of the invention there is
provided a sample comprising a label, wherein the label displays a
visible layout of light-modified regions in a predetermined spatial
arrangement and comprises: a first light-modified region of a first
type which has been modified using light of a first polarisation
state and has a first optical activity state characteristic of
having been formed by light of the first polarisation state.
[0051] The sample may comprise a second light-modified region of a
second type which has been modified using light of a second
polarisation state and has a second optical activity state
characteristic of having been formed by light of the second
polarisation state. The sample may comprise a third light-modified
region of a third type which has been modified using light of a
third polarisation state and has a third optical activity state
characteristic of having been formed by light of the third
polarisation state.
[0052] The light-modified regions may be laser-modified regions
formed by laser pulses having the appropriate polarisation
state.
[0053] The sample may comprise a plurality of laser modified
regions of the first type which have been modified using light of
the first polarisation state and which have a first optical
activity state characteristic of having been formed by light of the
first polarisation state.
[0054] The arrangement of the types of laser modified regions with
the sample may encode covert information readable by their
characteristic sculpted optical activity.
[0055] The sample may comprise a plurality of laser modified
regions of the second type which have been modified using light of
the second polarisation state and which have a second optical
activity state characteristic of having been formed by light of the
second polarisation state. The sample may comprising a plurality of
laser modified regions of the third type which have been modified
using light of the third polarisation state and which have a third
optical activity state characteristic of having been formed by
light of the third polarisation state.
[0056] The laser modified regions may be coplanar within the sample
(i.e. all disposed on the same flat plane within the sample). The
plane may be parallel to a surface of the sample. The modified
regions may be disposed in a two dimensional array, or may be
disposed along a straight line.
[0057] The modified regions within the sample may be separated by
unmodified regions of the sample and may be separated by more than
5 microns, or by more than 20 microns, or more than 200 microns.
The label may be less than 50 millimetres in size, and may be less
than 10 millimetres, and may be less than 3 millimetres in
size.
[0058] The sample may be a sample with a label written therein by
the method as described in any embodiment of the first aspect of
the invention. The label may be written using the labelling system
as described above with relation to any embodiment of the second
aspect of the invention.
[0059] According to a fourth aspect of the present invention there
is provided a method of reading a label within a sample, the label
comprising a plurality of light-modified regions having a
predetermined spatial arrangement therebetween, the modified
regions comprising light-modified regions of a first type having a
first optical activity state characteristic of having been formed
by light of a first polarisation state, the method comprising:
illuminating the label with light of a predetermined polarisation
state to reveal the locations of the first type of light-modified
regions to read covert information encoded by their locations.
[0060] The modified regions may comprises light-modified regions of
a second type having a second optical activity state characteristic
of having been formed by light of a second polarisation state, and
the method may comprise: illuminating the label with light of the
predetermined polarisation state to reveal the locations the second
type of modified regions to read covert information encoded by
their locations.
[0061] The label may comprise a third type of modified regions
having a third optical activity state characteristic of having been
formed by light of a third polarisation state, and the method may
comprising: illuminating the label with light of the predetermined
polarisation state to reveal the locations the third type of laser
modified regions to read covert information encoded by their
locations.
[0062] The method may comprise illuminating the second type of
light-modified region with the same polarity of light as that used
to illuminate the first type of light-modified region. The method
may include illuminating the third type of light-modified regions
with the same polarisation of light as the first type and second
type of light-modified regions. For example, for left and right
polarised laser modified regions the chirality of the region may be
determined using both right polarised light and left polarised
light, depending on whether the label is reflecting or transmitting
the illuminating light when being viewed.
[0063] The light-modified regions of the label may be
laser-modified regions created by laser pulses having the relevant
polarisation state.
[0064] The method may comprise: illuminating the label with light
of a second polarisation state to reveal the locations the second
type of laser modified regions to read covert information encoded
by their locations. The method may further comprise illuminating
the label with light of a third polarisation state to reveal the
locations the third type of laser modified regions to read covert
information encoded by their locations. Since each type of laser
modified region exhibits optical activity characteristic of the
polarisation state used to create the modified region, the method
may comprise illuminating the label with each of the types of
polarisation state used to create each of the types of laser
modified regions in order to reveal covert information encoded by
the locations of the respective types of laser modified
regions.
[0065] The method may comprise revealing covert information by
illumination of the label by a particular polarisation of
light.
[0066] The method may comprise: alternately illuminating a laser
modified region of the label with a pulse of light of a first
polarisation state and a pulse of light of a second polarisation
state; timing detection of the illuminating light, for a first
predetermined period, so as to detect only light of the first
polarisation state; timing detection of the illuminating light, for
a second predetermined period, so as to detect only light of the
second polarisation state; and comparing signals detected in the
first predetermined period and the second predetermined period to
determine the type of the laser modified region. That is, the
method may comprise a type of dichroism measurement to generate a
relative signal response over the label to reveal LCP light
modified regions, RCP light modified regions, and LP light modified
regions.
[0067] The method may comprise reading covert information in a
label written by any of the embodiments described with respect to
the first aspect of the invention. The method may comprise reading
covert information written into a label using the system of any of
the embodiments described with respect to the second aspect of the
invention. The method may comprise reading a label in a sample of
any of the embodiments as described with respect to the third
aspect of the invention.
[0068] The method may comprise using different wavelengths of light
to illuminate the label, and may comprise determining the location
of types of modified regions of a predetermined wavelength.
[0069] According to a fifth aspect of the present invention there
is provided a label reader apparatus for reading a label in a
sample, the label displaying a visible layout of light-modified
regions in a predetermined spatial arrangement, and comprising
light-modified regions of a first type having a first optical
activity state characteristic of having been formed by light of a
first polarisation state, the apparatus comprising: an illumination
device for illuminating the label in the sample; a polarisation
device for imparting one of a plurality of polarisation states to
the illuminating light; a detection device arranged to detect light
from the illumination device; and a processor configured to
determine from the detected light locations of the first type of
modified regions and read covert information encoded by their
locations.
[0070] The illumination device may be arranged to illuminate only
part of the label at a time. The illumination device may be
arranged to illuminate the whole label all at once. Where the label
is an array, the reader apparatus may be arranged to read one
element of the array at each time and scan over the entire array to
read the whole label. Alternatively, the reader apparatus may be
arranged to illuminate the whole array all at once.
[0071] The label reader apparatus may be arranged to read covert
information from a label written according to any embodiment of the
first aspect of the invention. The label reader apparatus may be
arranged to read covert information written in a label using a
system according to any embodiment of the second aspect of the
invention. The label reader apparatus may be arranged to read
covert information from a label in a sample according to any
embodiment of the third aspect of the invention. The label reader
apparatus may be arranged to read covert information from a label
of a sample using the method of any embodiment of the fourth aspect
of the invention.
[0072] According to another aspect of the present invention there
is provided a system for writing a label and reading a label,
comprising a labelling system as described with respect to the
second aspect, and a label reader apparatus as described with
respect to the fifth aspect.
[0073] According to another aspect of the present invention there
is provided a computer-readable storage medium comprising
instructions which, when executed by a computer, cause the computer
to perform the method as described with respect to the first
aspect, or the method as described with respect to the fourth
aspect.
[0074] According to another aspect of the present invention there
is provided a method of encoding information including inputting
information into a processor that is to be assigned to a label,
encoding the information on the processor as covert information to
be hidden in a spatial arrangement of different types of chirality
or optical activity states at different addressable locations in an
array of laser modified regions in a material that is to form the
label, outputting a signal for a laser writing apparatus to control
the output of a laser between different output modes comprising at
least left-circularly polarised light, right circularly polarised
light, and linearly polarised light (e.g. vertical and/or
horizontal and/or any other tilted orientation between 0 degrees
(vertical) and 90 degrees (horizontal)) to induce different types
of laser modification at different locations of the label to write
the covert information within a visual layout of laser modified
regions.
LIST OF FIGURES
[0075] Certain preferred embodiments of the invention will now be
described by way of example only and with reference to the
accompanying drawings in which:
[0076] FIG. 1A shows a schematic of a label in a sample;
[0077] FIG. 1B shows an implementation of the schematic of FIG.
1A;
[0078] FIG. 1C shows a magnification of the label of FIG. 1B;
[0079] FIG. 1D shows the results of dichroism measurements of the
label of FIG. 1C;
[0080] FIG. 2 shows a labelling system for writing a label in a
sample;
[0081] FIG. 3 shows a label reading system;
[0082] FIG. 4 shows another label reading system;
[0083] FIG. 5 shows another label reading system;
[0084] FIG. 6 shows another label reading system;
[0085] FIG. 7 shows another label reading system;
[0086] FIG. 8A shows a schematic of a label in a sample;
[0087] FIG. 8B shows an implementation of the schematic of FIG.
8A;
[0088] FIG. 8C shows the implementation of FIG. 8B as a difference
between illumination of the label under left circularly polarised
light and right circularly polarised light;
[0089] FIG. 8D shows the results of dichroism measurements of the
label of FIGS. 8B and 8C;
[0090] FIG. 9A shows a schematic of a label comprising four types
of laser modified region;
[0091] FIG. 9B shows an implementation of the schematic of FIG.
9A;
[0092] FIG. 9C shows the implementation of FIG. 9B as a difference
between illumination of the label under left circularly polarised
light and right circularly polarised light;
[0093] FIG. 9D shows the results of dichroism measurements of the
label of FIGS. 9B and 9C;
[0094] FIG. 10 shows a transmission-type label reading system;
and
[0095] FIG. 11 shows a reflection-type label reading system.
DETAILED DESCRIPTION
[0096] An application of the invention may relate to photo-induced
optical activity in pure and doped Ge.sub.2Sb.sub.2Te.sub.5 (GST)
thin films in security labels, in which there are overt (visible)
and covert (invisible) features that provide increased security.
The labels may be individualised with never-repeating code or an
individual number may be encoded, if needed. The overt (visible)
features are provided by changing the originally amorphous GST film
into crystalline or photo-darkened form by laser light
illumination. The covert (invisible) features are defined by using
different states of polarisation of laser light that may be used to
change the state of the amorphous film to a crystalline form
comprising either an enantiometric excess of a chiral species, for
example a left or right enantiomer, or a racemic mixture where
there is no bias. Three different polarisation states of laser
light may be used to write the covert features, such as left
circular polarisation, right circular polarisation, and linear
polarisation.
[0097] The invention may relate to a method to encode an individual
number/image in a label. The label may be written by using overt
and covert features and may have a form of e.g. an N.times.N matrix
array, in which each position within the array can be either an
area of the original as-deposited amorphous GST film, or a dot on
the amorphous GST film that has been treated by a laser light. Each
position in the matrix may be assigned a number, for example,
starting from the left top corner, and going from left to right and
from top to bottom. For example, the top left position may be
assigned number 1, and the bottom right position may be number
N.sup.2. The positions may be the powers of the quaternary numeral
system. Such a matrix may be used to encode numbers which may be
individual for each of the security label using the overt and
covert features described above.
[0098] Using these features, four bits of information may be
defined as follows: original as-deposited amorphous area may be 1,
laser-treated area using left circularly polarised light may be 2,
laser-treated area using right circularly polarised light may be 3,
and laser-treated area using linearly polarised light may be 4. The
matrix may then be used to record a number of up to 4.sup.(N 2)
(i.e. 4 to the power of N squared), meaning that 4.sup.(N 2)
individual labels may be prepared. For example, a matrix of
6.times.6 dots may be enough to put more than 500 different labels
on every grain of sand on Earth (assuming there are
7.5.times.10.sup.18 grains of sand). Using the size of the spot of
500 microns, the size of the whole label may be about only
3.times.3 millimetres. The correct number of the label may only be
revealed if the covert features are correctly read.
[0099] The number may be further encoded by a secret key number to
further increase the security. An example is described below.
Suppose the number to be put in the label is 1 in decimal base. If
it is converted into quaternary base-- 1--to be put in the label,
the size of the number is easily recognised as just a single dot
used to represent it. If the secret key number is 123 (decimal),
the input number may be converted using some encryption method, for
example, bitwise XOR encryption into 1 XOR 123=122 (decimal). This
may be converted into base 4 numerical value-- 2433--which may then
be written as the label array-- LCPL LPL RCPL RCPL. The reading may
occur by reversing the above encoding operation. First, the encoded
base 4 number may be read. Then the corresponding decimal value may
be converted into encoded number by using the secret key and binary
XOR operation: 122 XOR 123=1.
[0100] As an alternative or in addition to the label design, a bar
code may be written using the technology, within which a covert QR
code may be encoded by using the polarisation of light, as shown by
the demonstration label in FIG. 1.
[0101] The invention may relate to a label writing device. The
writing device may include a pulsed laser and a writing head, where
a single beam from a laser may be split into multiple laser beams
arranged in a required N.times.N array by using suitable optical
cables. Each of the beams in the writing head may be fitted with
its own controlled polariser and quarter wave plate to prepare any
of the required polarisations--left circular, right circular, or
linear. The beams may then be focused on to the required size on
the GST material for writing. The laser beam may have a circular or
a square shape and may have a Gaussian or top hat profile.
[0102] The invention may relate to a reading device. The reading
device may examine differential light absorption of left and right
circularly polarised light at a given wavelength in the area where
the authenticity label is written. The device may consist of a
continuous laser that produces a narrow light beam for illumination
of only small area equivalent to the size of the written dot in the
label. The beam may be passed through a photoelastic modulator or
Pockels cell or Soleil-Babinet compensator or the like to prepare
alternating pulses of left and right circularly polarised light
that may then be scanned through the label. A photomultiplier
single beam detector may be behind the label and may be timed to
record only pulses of light with left or right circular
polarisation. The read signals as a function of position on the
label may then be converted into an image or a number using the
algorithm such as the one described above.
[0103] An alternative design of the reading device may use a wide
beam illumination of the laser that can illuminate the whole label.
The light beam may again be passed through a photoelastic modulator
or Pockels cell or Soleil-Babinet compensator to prepare
alternating pulses of left and right circularly polarised light.
These pulses may be passed through the label and the signal may be
recorded by a pixelated detector, for example, a photo diode or
avalanche photo diode array.
[0104] The design of a reading device that will allow fast reading
of the suggested security labels may be based on a laser
polarimeter design. In this design, a laser beam of the wavelength
that has shown to produce the largest response in the CD spectra,
in this case in the range of 500 to 560 nanometres (nm), more
preferably 515 to 545 nm, for example 532 nm, may be used. A
linearly polarised light from a small beam of the laser may be used
to scan the area of the label. The polarisation rotation may then
be measured by a set of polarises and a detector. In these
measurements the exact angle of polarisation rotation of light
passing through the label may not be important, only the direction
of rotation--left or right or no rotation--may be used to reveal
the covert information in the label.
[0105] Different wavelengths of light may be used to write the
spots in the same pattern to provide an additional parameter to
store information. Such a spot can be distinguished from another
spot written with another wavelength of light. For example, if 532
nanometres (nm) green light (G) is used with left (L) or right (R)
circular polarisation (CP) to write a spot, when reading, it will
give a response signal peaked at also 532 nm. If 266 nm blue laser
(B) is used with left (L) or right (R) circular polarisation (CP),
it gives a response peaked around 266 nm. Linearly polarised light
may give indistinguishable signals with respect to the inducing
light's wavelength. So in case of left and right circularly
polarised light and one direction of linearly polarised (LP) light,
it gives an opportunity to write information with increased
density. For example, BLCP, BRCP, GLCP, GRCP and BGLP spots. In
addition, adding different directions of linear polarisation may
further increase information density (and hence security of the
label). When the label is read, it can be read by blue light, green
light or any suitable wavelength, and therefore the different spots
can be distinguished.
[0106] Embodiments of the invention may be used for manufacturing
and authentication of security labels for various products. An
advantage of the invention may be a combination of high security
and simplicity of manufacturing of individualised labels. Existing
technology typically relies on e-beam lithography to write ever
decreasing features in a metal matrix often down to several tens of
nanometres, which are difficult to reproduce reliably during large
scale production. In addition, the e-beam technique cannot be
easily used to individualise the labels. The disclosed technique
may be secure, because it may use several levels of encryption, and
may be easy to adapt to large scale manufacturing of labels each of
which may be unique.
[0107] The disclosed method may comprise any of the following
features. It may comprise use of chalcogenide materials to increase
the security level of authenticity labels. The disclosed method may
comprise storing and reading individual number/information in the
labels using polarisation of light.
[0108] The invention will now be described in more detail with
reference to an exemplary embodiment. Chiral light may be used,
such as left or right circularly polarised light, to crystallise
amorphous films of Ge.sub.2Sb.sub.2Te.sub.5. The treated regions of
the film become chiral, depending on the chirality of the light
used to crystallise the film. This may manifest in pronounced
mirror-symmetric circular dichroism spectra recorded from the areas
treated by light of opposite chirality, namely left and right
circularly polarised light. The mechanism of this phenomenon is
suggested to be that as the light induces crystallisation in the
film, the growing crystallites are aligned in the material along
rotating polarisation vectors of the propagating light. Depending
on the direction of rotation of the polarisation in the light,
chiral left- or right-handed crystallite groups are formed, and
preserved in the material. These chiral crystallite groups may then
produce the chiral response when circular dichroism spectra are
measured.
[0109] FIG. 1A shows a label design as a covert QR code within a
visible bar code. FIG. 1B shows its implementation in a sample of
GST film on a LiF substrate disk. FIG. 10 shows an enlarged bar
code in visible light, and FIG. 1D shows the QR code revealed by
circular dichroism measurements. As can be seen from FIG. 1D, the
label can be read using chiral illumination and a hidden QR code
represented by the chirality of the spots induced by chiral
illumination.
EXAMPLES
[0110] FIG. 1A is a schematic view of an exemplary label 120 in a
sample 110. The label 120 is made of an array of laser modified
regions 130 in the form of dots. Each laser modified region 130 is
modified by left circularly polarised light, right circularly
polarised light, or linearly polarised light (e.g. vertical,
horizontal, and/or tilted). Left circularly polarised modified
regions 132 are shown all the same colouring, as are right
circularly polarised modified regions 134, as are linearly
polarised modified regions 136. The label 120 also includes spaces
138 formed by unmodified regions of the sample 110. The label 120
shown in FIG. 1A comprises several columns of modified regions 130,
but it will be appreciated that any suitable array or shape can be
formed by the modified regions.
[0111] FIG. 1B shows an implementation of the schematic of FIG. 1A.
The sample 110 is a Ge.sub.2Sb.sub.2Te.sub.5 (GST) film carried on
a lithium fluoride (LiF) disc. The label 120 is defined within a
predetermined region of the sample 110. In this example, a total of
90 spots, each of about 500 micrometres in diameter, are
distributed in a 10.times.9 grid in a 8 mm.times.5 mm area. FIG. 10
shows an enlargement of the label 120 of FIG. 1B under visible
light (i.e. unpolarised light). As can be seen from FIG. 10, all of
the laser modified regions 130 appear to be substantially the same,
showing as dots within the sample 110. The spaces 138 do not show
any modification as compared to the sample 110. The label therefore
displays a visible layout of laser modified regions in a
predetermined spatial arrangement. The spatial arrangement
comprises laser modified regions separated by unmodified regions in
a predetermined way.
[0112] The left circularly polarised modified regions 132 formed by
light of left circular polarisation have a first type of optical
activity when measured e.g. using a circular dichroism (CD)
instrument. During formation of the laser modified region,
molecular fragments of the material align under the electromagnetic
field of the modifying light and so the material takes on a left
handed chirality. As such, the laser modified regions 132 interact
with left circularly polarised light differently to other
polarisations. In a similar way, right circularly polarised laser
modified regions 134 exhibit optical activity because of a right
handed chirality created during formation. Linearly polarised laser
modified regions 136 are created by molecular fragments aligning
with the linearly polarised electromagnet field of the modifying
light, and therefore exhibit optical activity with linearly
polarised light of the same orientation as the modifying light.
Thus, each laser modified region exhibits optical activity when
illuminated by light having the same polarisation as that which
created the region.
[0113] For example, the left circularly polarised laser modified
regions 132 have a first type of optical activity. They exhibit
increased transmission of left circularly polarised light, and an
increased reflection of right circularly polarised light. Right
circularly polarised laser modified regions 134 have a second type
of optical activity. They exhibit increased transmission of right
circularly polarised light, and an increased reflection of left
circularly polarised light. Linearly polarised laser modified
regions 136 have a third type of optical activity. They exhibit
increased transmission in transmission mode (see e.g. FIGS. 3 and
5) and increased reflection in reflection mode (see e.g. FIGS. 4
and 6) of linearly polarised light of the same orientation (e.g.
vertical, horizontal, and/or tilted), and a decreased transmission
in transmission mode (see e.g. FIGS. 3 and 5) and a decreased
reflection in reflection mode (see e.g. FIGS. 4 and 6) of other
polarisations It is therefore possible to distinguish types of
laser modified regions by illuminating them with light of a
particular polarisation.
[0114] FIG. 1D shows the label of FIG. 10 as revealed by circular
dichroism measurements using Diamond B23 beamline for synchrotron
radiation circular dichroism imaging with highly collimated
microbeam to achieve high spatial resolution. Such measurements
comprise sequential illumination under left circularly polarised
light and right circularly polarised light. A ratio of the results
under each type of illumination is taken to form a ratio of signals
and show their relative strengths (intensity magnitude). The left
circularly polarised modified regions 132 all appear, shown in the
same colouring, where the signal strength for left circularly
polarised light is stronger than that of right circularly polarised
light. The right circularly polarised modified regions 134 all
appear shown in another colouring, all the same, in regions where
the signal strength is greater for right circularly polarised light
than for left circularly polarised light. The optical activity and
behaviour of the laser modified regions is therefore revealed. Not
all of the laser modified regions 130 appear in this depicted case,
since some regions behave the same under both left and right
circularly polarised illumination. The linearly polarised modified
regions 136 do not appear in FIG. 1D. Similarly, the spaces 138 do
not show any activity since they behave the same way for both left
and right circularly polarised light, and hence do not create a
difference in signals. Thus, the left circularly polarised modified
regions 132 can be differentiated from the right circularly
polarised modified regions 134, which in turn can be differentiated
from the linearly polarised modified regions and unmodified
regions. Hence, a spatial arrangement that was not otherwise
visible may be revealed.
[0115] Although an exemplary array is shown in FIGS. 1A-D, it will
be appreciated that the laser modified regions 130, 132, 134 and
136, together with the spaces 138 can be arranged in any suitable
manner, with any suitable spacing therebetween. For example, a
square array of modified regions 130 may be written which under
visible light would appear to comprise identical dots regularly
spaced, but which under circular dichroism measurements, or under
illumination by a particular polarisation of light, could reveal a
covert pattern. Another covert pattern may be revealed by
measurements under linear polarisation to reveal the linearly
polarised modified regions 136. Moreover, the relative orientation
of the linear polarisation used to create the laser modified region
may also be distinguishable. Therefore, laser modified regions
created by different orientations of linear polarisation (e.g.
vertical, horizontal, tilted) may also be distinguished from each
other.
[0116] Although FIG. 1D shows the results of circular dichroism
measurements (i.e. a difference in signals for different
polarisation), the optical activity states of a laser modified
region may be revealed by illuminating the label 120 with light of
a single polarisation. For example, left circularly polarised laser
modified regions 132 will have an increased reflection of right
circularly polarised light. As such, they may be revealed by
illumination under right circularly polarised light and observation
of the increase in reflected light. Alternatively, they might be
revealed by transmission of left circularly polarised light. It is
therefore possible to reveal covert arrangements of laser modified
regions by illuminating the label with light of a predetermined
polarisation.
[0117] The array of FIG. 1 is a two-dimensional orthogonal
arrangement in Cartesian co-ordinates. However, the label 120 need
not be arranged on Cartesian orthogonal axes but could be based on
any coordinate system which is able to provide addressable
regions.
[0118] As another example, an array may be written using modified
regions 130 and spaces 138 to create a label 120 comprising
standard QR code when viewed under visible light. Measurements of
the label 120 using suitable polarisations may then reveal an
otherwise hidden array and pattern of modified regions. It may
further reveal another covert pattern under illumination of another
polarisation.
[0119] The label 120 may be written in any suitable material, and
may be written in a phase change material. The material may be a
chalcogenide material. Non-limiting examples of chalcogenide
materials include Ge-Sb-Te (GST), As-Sb-Te, As-Ge-Sb-Te, Sn-Sb-Te,
In-Sb-Te, Ag-In-Sb-Te, Ge-Te, In-Se, Sb-Te, Ga-Sb, In-Sb, As-Te,
Al-Te, Ge-Sb-Te, Te-Ge-As, In-Sb-Te, Te-Sn-Se, Ge-Se-Ga, Bi-Se-Sb,
Ga-Se-Te, Sn-Sb-Te, In-Sb-Ge, Te-Ge-Sb-S, Te-Ge-Sn-O, Te-Ge-Sn-Au,
Pd-Te-Ge-Sn, In-Se-Ti-Co, Ge-Sb-Te-Pd, Ge-Sb-Te-Co, Sb-Te-Bi-Se,
Ag-In-Sb-Te, Ge-Sb-Se-Te, Ge-Sn-Sb-Te, Ge-Te-Sn-Ni, Ge-Te-Sn-Pd and
Ge-Te-Sn-Pt. It will be appreciated that the hyphenated chemical
composition notation used herein indicates the elements included in
a particular mixture or compound, and is intended to represent all
stoichiometries involving the indicated elements. Moreover, where
chalcogenide compounds having particular stoichiometries are
specified, the chalcogenide compound may include the same
combination of elements having other stoichiometries.
[0120] The material may comprise Ge, Sb and Te. The material may
comprise one or more dopants. The one or more dopants may be
selected from Ag, Au, B, C, N, 0, Al, Si, P, S, Ga, Se, In, Sn, I,
Pb and Bi. The material may comprise one or more dopants, at least
one of which is N.
[0121] The material may be a chalcogenide material comprising Ge,
Sb, Te and one or more dopants. The one or more dopants may be
selected from Ag, Au, B, C, N, 0, Al, Si, P, S, Ga, Se, In, Sn, I,
Pb and Bi. The material may comprise one or more dopants, at least
one of which is N.
[0122] The material may comprise Ge, Te and Sb in the following
amounts (in atomic percent): from about 5% to about 60% Ge; from
about 20% to about 70% Te; and from about 5% to about 30% of one or
more dopants; with the remainder being Sb (e.g. from about 5% to
about 60% Sb). The atomic percentage of Ge in the material may be
from about 15% to about 50%, e.g. from about 17% to about 44%, e.g.
about 22%. The atomic percentage of Sb in the material may be from
about 15% to about 50%, e.g. from about 17% to about 44%, e.g.
about 22%. The atomic percentage of Te in the material may be from
about 23% to about 56%, e.g. from about 48% to about 56%, e.g.
about 55%. Ge, Sb and Te may be present in atomic percentages of
about 22%, about 22% and about 55% respectively.
[0123] The phase change material may comprise a chalcogenide
compound of the formula Ge.sub.2Sb.sub.2Te.sub.5X.sub.n, wherein X
represents one or more dopants and n is from about 0.1 to about 2.
X may represent one or more dopants selected from Ag, Au, B, C, N,
0, Al, Si, P, S, Ga, Se, In, Sn, I, Pb and Bi. X may be N. The
value n may be from about 1 to about 2, e.g. about 1 or about
2.
[0124] The phase change material may be produced in accordance with
various techniques known in the art. For instance, the phase change
material may be produced by vapour deposition on a suitable
substrate. Suitable deposition techniques include physical vapour
deposition (PVD), chemical vapour deposition (CVD). Physical vapour
deposition techniques include sputtering, evaporation and ionized
deposition techniques.
[0125] The material may be formed as a layer of material. The layer
may have a thickness ranging from about 40 to about 1000 nm, e.g.
from about 60 to 100 nm, or from about 200 to about 300 nm.
[0126] The material may be formed as a layer on a substrate. The
substrate may be a silicon substrate or another bulk substrate
including polymer or a layer of semiconductor material. For
example, the substrate may be selected from silicon wafers,
silicon-on-insulator substrates, silicon-on-sapphire substrates,
epitaxial layers of silicon on a base semiconductor foundation, and
other semiconductor or optoelectronics materials, such as
silicon-germanium, germanium, gallium arsenide, or indium
phosphide. The material of the substrate may be doped or undoped.
The material may also be formed on another material overlying the
substrate, depending on the intended application of the phase
change material.
[0127] The material may comprise a chiral species. The material may
comprise a plurality of chiral species. A chiral species may be a
chiral molecule or complex, or a chiral fragment, i.e. a molecular
fragment or crystallite cluster which can exist in a plurality of
non-superimposable forms.
[0128] The material may comprise a dopant which forms one or more
chiral species in the material. The material may be doped with
nitrogen such that one or more chiral species are formed in the
material.
[0129] The material may comprise a chiral species containing a
nitrogen atom, wherein the nitrogen atom is bound to three
different moieties in a substantially non-planar geometry and
comprises a lone pair of electrons. The nitrogen atom may be bound
to Ge, Sb and Te in a non-planar geometry. The sum of the bond
angles about the nitrogen atom may be less than 360.degree., e.g.
from about 320.degree. to about 355.degree.. The sum of the bond
angles about the nitrogen atom is about 355.degree..
[0130] FIG. 2 shows a schematic of a labelling system for writing a
label in a sample. The system comprises a laser 140 which generates
a laser beam 142. The laser beam 142 propagates to defocussing
optics 160 which are arranged to divide the laser beam 142 into a
plurality of beams 143, 144, 145, 146. A plurality of optical
fibres 150 are arranged to guide each of the plurality of beams
143, 144, 145, 146 to a polarisation apparatus 170. The
polarisation apparatus comprises linear polarisers 172 and quarter
wave plates 174. The linear polarisers 172 and quarter wave plates
174 may be individually addressable.
[0131] As each of the plurality of laser beams 143, 144, 145 146,
passes through the polarisation apparatus 170, the desired
polarisation state is imparted. The polarisation apparatus 170
comprises elements for each of the beams 143, 144, 145 146
respectively. The elements of the polarisation apparatus 170 are
individually addressable and can be controlled so as to polarise
each laser beam 143, 144, 145, 146 with the desired polarisation
state. For example, the top-most beam 143 may be polarised by the
linear polariser 172 to a linear polarisation state (e.g. vertical,
horizontal and/or tilted). The quarter wave plate 174 in the path
of the top-most beam 143 is not used. The next beam 144 may be
polarised by the quarter wave plate 174 to a left circular
polarisation state. Beam 145 may be polarised by the quarter wave
plate 174 to a right circular polarisation state.
[0132] The system may also include blocks or shutters 176 to stop
propagation of any and all of the lasers beams 143, 144, 145, 146.
For example, shutters 176 may be disposed in the path of each beam
143, 144, 145, 146 and between the polarisation apparatus 170 and
the sample 110, or between the optical fibres 150 and the
polarisation apparatus 170. The shutters 176 may be operable to
stop propagation of a beam and thereby stop formation in the sample
110 of a laser modified region. In this way, spaces 138 may be
`formed` in the label 120.
[0133] According to the system of FIG. 2, each beam 143, 144, 145,
146 may be given the desired polarisation state. The beams are then
focussed by focussing optics 162 into the sample 110. Each beam
thus writes a laser modified region 130 within the sample, each
laser modified region 130 having an optical property characteristic
of having been formed by light of the respective polarisation.
Where shutters 176 are included in the system, any of the beams may
be prevented from reaching the sample 110 and writing a modified
region 130, instead resulting in a space 138 in the label 120.
[0134] The system of FIG. 2 comprises four beams 143, 144, 145, 146
for writing modified regions 130. The system may then write four
laser modified regions 130 within the sample 110 by each exposure.
After an exposure, the sample 110 may be translated so that the
next exposure writes laser modified regions 130 in the next
location within the sample 110. Alternatively the focussing optics
162 may re-focus each of the beams 143, 144, 145, 146 to another
location within the sample 110.
[0135] Although four beams are shown in FIG. 2, it will be
appreciated that any suitable number may be used. In FIG. 2, the
beams are arranged linearly and the written laser modified regions
130 are disposed on a line within the sample 110 and below its
surface. However, the beams may be arranged in any suitable manner
and the focussing optics may be configured to write each laser
modified region 130 in a predetermined location within the sample
110 as needed. The focussing optics 162 may be dynamic and may be
controlled to write laser modified regions 130 within the sample
110 as desired or in accordance with a controlling program.
[0136] The sample 110 may be labelled in advance of being fixed to
a product. For example, the sample 110 may be a sticker that first
has a label 120 written therein, then is stuck to a product.
[0137] The sample 110 may be a coating applied to a product which
then has a label 120 written therein. The sample may be the product
itself, so that the label 120 is written directly therein.
[0138] FIG. 3 shows a label reading device for a transmission-type
reader. The label reading device comprises a laser 140 for
generating a laser beam 142, defocussing optics 160 to expand the
laser beam 142 to a desired coverage, and focussing optics 162 to
collimate the laser beam 142. The collimated beam 142 passes
through a linear polariser 172 and a retarder 174 (e.g. a
left-handed, right-handed 1/4 wave static retarder, Pockels Cell,
PEM, motorised Soleil Babinet, etc.) for imparting a left or right
circular polarisation to the laser beam 142. The beam 142 is sized
to illuminate the whole label 120 within the sample 110. After
transmission through the sample 110 and label 120, the beam 142 is
incident on a detector 190.
[0139] The retarder 174 may be removed from the path of the laser
beam in order to illuminate the sample 110 with linearly polarised
light. Alternatively, the retarder 174 may be kept in the path of
the beam 142 to illuminate the sample 110 with a first circular
polarisation of light (e.g. left), and further may be flipped to
illuminate the sample 110 with a second type of circular
polarisation of light (e.g. right).
[0140] The detector 190 detects light transmitted through the
sample 110 during use. The signal received at the detector 190 will
depend on the polarisation of the light illuminating the sample
110, and on the spatial arrangement and type of laser modified
regions 130 within the sample 110. A covert spatial arrangement may
be revealed. By comparing the signals received at the detector to
the known polarisation of light applied to the sample, the type of
laser modified region can be revealed, and a covert arrangement of
region types can be revealed.
[0141] Optionally, a controller (not shown) may be used to control
switching of the retarder 174 to switch circular polarisation
illumination of the sample 110 from left to right and vice versa.
The controller may also be used in coordinating circular dichroism
measurements by timing detection by the detector so as to record
only light of a first polarisation for a period of time, then only
light of a second polarisation for another period of time. The
controller may then compare those measurements to generate e.g. a
dichroism measurement as shown in FIG. 1D.
[0142] FIG. 4 shows a label reading device for a reflection-type
reader. The depicted reader comprises similar elements to those
shown in FIG. 3, and further comprises a dichroic mirror 180
arranged so that the laser beam 142 can pass from the laser 140 to
the sample 110, then reflect from the dichroic mirror 180 onto the
detector 190. Upon reflection from the sample 110, the handedness
or the polarisation of the light (e.g. sculpted left circularly
polarised light) is flipped to the opposite handedness (e.g. right
circularly polarised), which in turn is flipped back to its
original polarisation (e.g. left circularly polarised) when
reflected by the dichroic mirror 180. The linear polarisations are
maintained upon transmission through the dichroic mirror 180 and
reflection from the sample 110 and the mirror 180,
respectively.
[0143] The reader of FIG. 4 may be used to read a label by
reflection of different polarisations of light from the label 120
in the sample 110. The reader of FIG. 3 may be used to read a label
by transmission of different polarisations of light through the
label 120 in the sample 110. In order to increase signal strength,
the thickness of the sample 110 may be increased so that the laser
modified regions 130 forming the label 120 may be made larger and
hence provide a stronger response to light incident thereon.
However, increased thickness of the sample 110 may reduce
transmission of light therethrough, so a reflection type reader may
be used where thicker or non-transparent samples 110 are needed in
order to obtain a stronger signal at the detector 190.
[0144] FIG. 5 shows a label reading device for a transmission-type
reader. The label reading device comprises a light source, for
example a laser, 140 for generating a light beam 142, defocussing
optics 160 to expand the light beam 142 to a desired coverage, and
focussing optics 162 to collimate the light beam 142. The
collimated beam 142 passes through a linear polariser 172 and a
Fresnel's multi prism (several Cornu quartz prisms) 182, from which
two beams, one for left circularly polarised components and the
other for right circularly polarised components will exit and will
be converted into linear polarised components by a rotating quarter
wave retarder 175 from each Fresnel's beam. The beam 142 is sized
to illuminate the whole label 120 within the sample 110. After
transmission through the sample 110 and label 120, the beam 142 is
split by the Fresnel's multi prism 182 into two beams: one for left
circularly polarised components and one for right circularly
polarised components that, being converted into linear polarisation
by rotatable quarter wave retarders 175, are incident on detectors
190.
[0145] Both rotatable quarter wave plates 175 may be removed from
the path of the laser beam and replaced by rotatable linear
polarisers as analysers 173 to image the sculpted linear
polarisation (vertical, horizontal or tilted) of label 120 of
sample 110.
[0146] FIG. 6 shows a label reading device for a reflection-type
reader. The depicted reader comprises similar elements to those
shown in FIG. 5, and further comprises a dichroic mirror 180
arranged so that the laser beam 142 can pass through from the laser
140 to the sample 110, then reflect from the dichroic mirror 180
onto the Fresnel's multi prism (several Cornu quartz prisms) 182,
rotatable quarter wave retarders 175 and detectors 190. The
replacement of rotatable quarter wave retarders 175 with linear
polarises 173 will identify the linear polarisation components of
label 120 when in crossed polarised position with respect to
172.
[0147] The reader of FIG. 6 may be used to read a label by
reflection of different circular polarisations of light from the
label 120 in the sample 110.
[0148] FIG. 7 shows a label reading device for a reflection-type
reader. The label reading device comprises a laser 140 for
generating a laser beam 142, defocussing optics 160 to expand the
laser beam 142 to a desired coverage, and focussing optics 162 to
collimate the laser beam 142. The collimated beam 142 passes
through a linear polariser 172 and a rotatable quarter wave plate
174 for imparting a left or right circular polarisation to the
laser beam 142. The beam 142 is incident on the label 120 in the
sample 110 and reflects therefrom. After reflection from the sample
110 and label 120, the beam 142 is incident on a detector 190.
[0149] The quarter wave plate 174 may be operated (e.g. removed
from the path of the laser beam) in order to illuminate the sample
110 with linearly polarised light. Alternatively, the quarter wave
plate 174 may be kept in the path of the beam 142 to illuminate the
sample 110 with a first circular polarisation of light (e.g. left),
and further may be flipped to illuminate the sample 110 with a
second type of circular polarisation of light (e.g. right).
[0150] The detector 190 detects light reflected from the sample 110
during use. The signal received at the detector 190 will depend on
the polarisation of the light illuminating the sample 110, and on
the spatial arrangement and type of laser modified regions 130
within the sample 110. A covert spatial arrangement may be revealed
by appropriate illumination as described herein. By comparing the
signals received at the detector to the known polarisation of light
applied to the sample 110 and label 120, the type of laser modified
region 130 can be revealed, and a covert arrangement of region
types can be revealed.
[0151] FIG. 8A is a schematic view of an exemplary label 120 in a
sample 110. The label 120 comprises an array of laser modified
regions 130. In this case the laser modified regions are dots, but
it will be appreciated that any suitably shaped region may be
formed by laser modification of a portion of the sample 110. Each
laser modified region 130 of the label 120 is formed using left
circularly polarised light, right circularly polarised light, or
linearly polarised light (e.g. vertical, horizontal, and/or
tilted). Left circularly polarised modified regions 132 are shown
all in the same colouring, as are right circularly polarised
modified regions 134, as are linearly polarised modified regions
136. The label 120 also includes spaces 138 formed by unmodified
regions of the sample 110. The label 120 shown in FIG. 8A comprises
several columns of laser modified regions 130, but it will be
appreciated that any suitable array or shape can be formed by the
modified regions 130.
[0152] FIG. 8B shows an implementation of the schematic label 120
of FIG. 8A in a sample 110 comprising left circularly polarised
modified regions 132 formed by left circularly polarised light,
right circularly polarised modified regions 134 formed by right
circularly polarised light, and linearly polarised modified regions
136 formed by linearly polarised light. The label of FIG. 8B is
read using a scheme according to FIG. 3 and by a reader system as
shown in FIG. 10. The label 120 is illuminated under left
circularly polarised light and the intensity range of the image is
displayed in FIG. 8B. Since the intensity range of the image is
shown in FIG. 8B, the laser modified regions 130 therein appear
similar to each other.
[0153] FIG. 8C shows the difference between two images of the label
120 obtained by the reader of FIGS. 3 and 10 under left and right
circularly polarised light illumination. The different
polarisations reflect differently from the different types of laser
modified regions 130, and therefore comparison of the images under
different polarisations (in this case a difference of the images)
reveals the different types of laser modified regions 130 and each
type of laser modified region 130 is distinguishable from the
other. Left circularly polarised modified regions 132 are disclosed
corresponding to their locations in the schematic of FIG. 8A.
Similarly, right circularly polarised modified regions 134 are
revealed, as are linearly polarised modified regions 136. Spaces
138 are also clearly seen as unmodified regions, thereby allowing
the modified regions 130 to be seen.
[0154] FIG. 8D shows a circular dichroism signal of the label 120
of FIGS. 8A to 8C (with ellipticity in millidegrees). Again the
types of laser modified regions 130 are clearly distinguishable
from each other and their locations and arrangements are revealed
by the measurement.
[0155] FIG. 9A shows a schematic of an exemplary label 120
comprising laser modified regions 130 in the form of dots. Each of
the four depicted laser modified regions 130 corresponds to a
different type of laser modified region. The first (left-most in
FIG. 9A) laser modified region 130 is a left circularly polarised
modified region 132 formed by left circularly polarised light. The
second (second left in FIG. 9A) is a right circularly polarised
modified region 134 formed by right circularly polarised light. The
third and fourth laser modified regions (the two regions on the
right in FIG. 9A) are linearly polarised modified regions 136
formed by linearly polarised light. However, the third modified
region is a vertical linearly polarised modified region 137 formed
using vertically linearly polarised light, and the forth region
(right-most in FIG. 9A) is a horizontal linearly polarised modified
region 139 formed using horizontally linearly polarised light.
[0156] FIG. 9B shows an implementation of the label 120 of FIG. 9A
read using a reader according to the scheme of FIG. 7 and shown in
FIG. 11. Similarly to FIG. 8B, FIG. 9B shows the intensity range of
the label 120 illuminated with left circularly polarised light.
Since the image displays the intensity range, each of the laser
modified regions 130 in FIG. 9B appears similar to the others
despite being of different types.
[0157] FIG. 9C shows a difference between two images of the label
obtained by the reader of FIGS. 7 and 11 under left and right
circularly polarised light illumination. By comparison of images
obtained under illumination by different polarisations (in this
case the difference between left circularly polarised illumination
and right circularly polarised illumination) the differences
between the laser modified regions 130 are revealed and each type
of laser modified region 130 is distinguishable from the other. The
left circularly polarised modified region 132 is disclosed
corresponding to its location in the schematic of FIG. 9A.
Similarly, the right circularly polarised modified region 134 is
revealed. Moreover, the vertical linearly polarised modified region
137 is distinguished from the horizontal linearly polarised
modified region 139.
[0158] FIG. 9D shows a circular dichroism signal of the label 120
of FIGS. 9A to 9C (with ellipticity in millidegrees). Again the
types of laser modified regions 130 are clearly distinguishable
from each other and their locations and arrangements are revealed
by the measurement. In particular, the laser modified regions 130
formed by vertically linearly polarised light and horizontally
linearly polarised are distinguished from each other. Therefore,
four distinct types of laser modified region 130 are formed in the
label 120.
[0159] FIG. 10 shows a practical implementation of the reader
design shown in FIG. 3. It comprises an illumination device 1040
comprising a laser or LED light source and necessary optics for
illumination of the label 120. The label 120 positioned so that
light is transmitted through it to a detector 190 comprising a
sensor and/or camera. The reader device of FIG. 10 therefore
operates as a transmission-type reader.
[0160] FIG. 11 shows a practical implementation of the reader
design shown in FIG. 7. It comprises an illumination device 1040
comprising a laser or LED light source and optics, a label 120 in a
sample 110, and a detector 190 comprising a sensor and/or camera.
The reader device of FIG. 11 operates as a reflection-type reader
so that light from the illumination device 1040 reflects from the
label before being sensed by the detector 190.
* * * * *