Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Diffraction Grating-Based
Optical Identification Element
Cross References to Related Applications
This application claims the benefit of US Provisional Patent Applications,
Serial No. 6014I0,S41 (CiDRA Docket No. CC-543), filed Sept. 12, 2002, and is
a
continuation-in-part of US Patent Applications, Serial No. (CiDRA Docket No.
CC-
0648), each of which are incorporated herein by reference in their entirety.
IO
US Patent Application Serial No. (CiDRA Docket No. CC-0650A), filed
contemporaneously herewith, contains subject matter related to that disclosed
herein,
which is incorporated by reference in its entirety.
15 Technical Field
This invention relates to optical identification, and more particularly to
optical
elements used for identification or coding using diffraction gratings.
Background Art
20 Many industries have a need for uniquely identifiable objects or for the
ability
to uniquely identify objects, for sorting, tracking, and/or
identification/tagging.
Existing technologies, such as bar codes, electronic rnicrochipsJtransponders,
radio-
frequency identification (RFID), and fluorescence and other optical
techniques, are
often inadequate. For example, existing technologies may be too large for
certain
2S applications, may not provide enough different codes, or cannot withstand
harsh
temperature, chemical, nuclear and/or electromagnetic environments.
Therefore, it would be desirable to obtain a coding element or platform that
provides the capability of providing many codes (e.g., greater than 1 million
codes),
that can be made very small, andlor that can withstand harsh environments.
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Summary of the Invention
Objects of the present invention include provision of an optical
identification
element or platform that allows for a large number of distinct codes, can be
made very
small, and/or can withstand harsh environments.
According to the present invention, an optical identification element,
comprises an optical substrate; at least a portion of the substrate having at
least one
diffraction grating disposed therein, the grating having at least one
refractive index
pitch superimposed at a common location; the grating providing an output
optical
signal when illuminated by an incident light signal; and the optical output
signal being
indicative of a code in the substrate.
The present invention provides an optical element capable of having many
optically readable codes. The element has a substrate containing an optically
readable
composite diffraction grating having one or more collocated index spacing or
pitches
A. The invention allows for a high number of uniquely identifiable codes
(e.g.,
millions, billions, or more). The codes may be digital binary codes and thus
are
digitally readable or may be other numerical bases if desired.
The element may be made of a glass material, such as silica or other glasses,
or may be made of plastic, or any other material capable of having a
diffraction
grating disposed therein. The element may be cylindrical in shape or any other
geometry, provided the design parameters are met.
Also, the elements may be very small "microbeads" (or microelements or
microparticles or encoded particles) for small applications (about 1-1000
microns), or
larger "macroelements" for larger applications (e.g., 1-1000mm or much
larger). The
elements may also be referred to as encoded particles or encoded threads.
Also, the
element may be embedded within or part of a larger substrate or object.
T'he code in the element is interrogated using free-space optics and can be
made alignment insensitive.
The gratings (or codes) are embedded inside (including on or near the surface)
of the substrate and may be permanent non-removable codes that can operate in
harsh
environments (chemical, temperature, nuclear, electromagnetic, etc.).
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The code is not affected by spot imperfections, scratches, cracks or breaks in
the substrate. In addition, the codes are spatially invariant. Thus, splitting
or slicing an
element axially produces more elements with the same code. Accordingly, when a
bead is axially split-up, the code is not lost, but instead replicated in each
piece.
The foregoing and other objects, features and advantages of the present
invention will become more apparent in light of the following detailed
description of
exemplary embodiments thereof.
Brief Description of the Drawings
Fig. 1 is a side view of an optical identification element, in accordance with
the present invention.
Fig. 2 is a side view of whole and partitioned optical identification element,
in
accordance with the present invention.
Fig. 3 is a side view of an optical identification element, in accordance with
the present invention.
Fig. 4 and 5 are perspective views of an optical identification element, in
accordance with the present invention.
Fig. 6 is a side view of an optical identification element showing one optical
reading embodiment, in accordance with the present invention.
Fig. 7 is an image on a CCD camera of Fig. 6, in accordance with the present
invention.
Fig. ~ is a graph showing an digital representation of bits in a code derived
from the image of Fig. 7, in accordance with the present invention.
Fig. 9 illustrations (a)-(c) show images of digital codes on a CCD camera, in
accordance with the present invention.
Fig. 10 illustrations (a)-(d) show graphs of different refractive index
pitches
and a summation graph, in accordance with the present invention.
Fig. 11 is a side view of an optical identification element and optics
associated
therewith, in accordance with the present invention.
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Figs. 12-15 are side and end views of an optical identification element and
optics associated therewith, in accordance with the present invention.
Fig. 16 is an end view of a beam for an optical identification element, in
accordance with the present invention.
Fig. 17 is a side view of an alternative embodiment of an optical
identification
element, in accordance with the present invention.
Fig. 18 is a graph of a plurality of bits within a Bragg envelope of an
optical
identification element, in accordance with the present invention.
Fig. 19 shows an alternative optical schematic for reading a code in an
optical
identification element, in accordance with the present invention.
Figs. 20-22 are a graphs of a plurality of bits and a Bragg envelope of an
optical identification element, in accordance with the present invention.
Figs. 23-24 are side views of a thin grating for an optical identification
element, in accordance with the present invention.
1$ Fig. 25 is a perspective view azimuthal multiplexing of a thin grating for
an
optical identification element, in accordance with the present invention.
Fig. 26 is side view of a blazed grating for an optical identification
element, in
accordance with the present invention.
Fig. 27 is a graph of a plurality of states for each bit in a code for an
optical
identification element, in accordance with the present invention.
Fig. 28 is a perspective view of a grooved plate for use with an optical
identification element, in accordance with the present invention.
Fig. 29 is a perspective view of a tube for use with an optical identification
element, in accordance with the present invention.
Fig. 30 is a side view an optical identification element having a reflective
coating thereon, in accordance with the present invention.
Figs. 31 and 32 are side views or a groove plate having a reflective coating
thereon, in accordance with the present invention.
Fig. 33-38 are alternative embodiments for an optical identification element,
in
accordance with the present invention.
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Fig. 39 is a view an optical identification element having a plurality of
grating
located rotationally around an optical identification element, in accordance
with the
present invention.
Fig. 40 is a view an optical identification element having a plurality of
gratings disposed on a spherical optical identification element, in accordance
with the
presentinvention.
Fig. 41 illustrations (a)-(e) show various geometries of an optical
identification element that rnay have holes therein, in accordance with the
present
invention.
Fig. 42 illustrations (a)-(c) show various geometries of an optical
identification element that may have teeth therein, in accordance with the
present '
invention.
Fig. 43 illustrations (a)-(c) show various geometries of an optical
identification element, in accordance with the present invention.
Fig. 44 is a perspective view of an optical identification element having a
grating that is smaller than the substrate, in accordance with the present
invention.
Fig. 45 is a side view of an optical identification element where light is
incident on an end face, in accordance with the present invention.
Fig. 46 is an illustration of input light and output light passing through two
mediums, in accordance with the present invention.
Figs. 47-48 are a side view of an optical identification element where light
is
incident on an end face, in accordance with the present invention.
Figs. 49-51 are side views of an optical identification element having a
blazed
grating, in accordance with the present invention.
Fig. 52 is a perspective view of a plate with holes for use with an optical
identification element, in accordance with the present invention.
Fig. 53 is a perspective view of a grooved plate for use with an optical
identification element, in accordance with the present invention.
Fig. 54 is a perspective view of a disc shaped optical identification element,
in
accordance with the present invention.
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Fig. 55 is a side view of Fig. 54, in accordance with the present invention.
Fig. 56 illustrations (a)-(b) are graphs of reflection and transmission
wavelength spectrum for an optical identification element, in accordance with
the
present invention.
Fig. 57 illustrations (a)-(b) are side views of an optical identification
element
polarized along an electric or magnetic field, in accordance with the present
invention.
Fig. 58 is a side view of an optical identification element having a coating,
in
accordance with the present invention.
Best Mode for Carrying Out the Invention
Refernng to Fig. l, an optical identification element 8 comprises a known
optical substrate 10, having an optical diffraction grating 12 disposed (or
written,
impressed, embedded, imprinted, etched, grown, deposited or otherwise formed)
in
the volume of or on a surface of a substrate 10. The grating 12 is a periodic
or
aperiodic variation in the effective refractive index and/or effective optical
absorption
of at least a portion of the substrate 10.
The substrate 10 has an inner region 20 where the grating 12 is located. The
inner region may be photosensitive to allow the writing or impressing of the
grating
12. The substrate 10 has an outer region 18 which does not have the grating 12
therein.
The grating 12 is a combination of one or more individual spatial periodic
sinusoidal variations in the refractive index that are collocated along the
length of the
grating region 20 of the substrate 10, each having a spatial period (or pitch)
A. The
grating 12 (or a combination of gratings) represents a unique optically
readable code,
made up of bits. In one embodiment, a bit corresponds to a unique pitch A
within the
grating 12.
The grating 12 may also referred to herein as a composite or collocated
grating. Also, the grating 12 may be referred to as a "hologram", as the
grating 12
transforms, translates, or filters an input optical signal to a predetermined
desired
optical output pattern or signal.
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The substrate 10 comprises silica glass (Si02) having the appropriate chemical
composition to allow the grating 12 to be disposed therein or thereon. Other
materials
for the optical substrate 10 may be used if desired. For example, the
substrate 10 may
be made of any glass, e.g., silica, phosphate glass, borosilicate glass or
other glasses,
or made of glass and plastic, or solely plastic. For high temperature or harsh
chemical
applications, the optical substrate 10 made of a glass material is desirable.
If a
flexible substrate is needed, a plastic, rubber or polymer-based substrate may
be used.
The optical substrate 10 may be any material capable of having the grating 12
disposed in the grating region 20 and that allows light to pass through it to
allow the
code to be optically read.
The optical substrate 10 with the grating 12 has a length L and an outer
diameter Dl, and the inner region 20 diameter D. The length L can range from
very
small (about 1-1000 microns or smaller) to large (about 1.0 - 1000 mm or
greater). In
addition, the outer dimension D1 can range from small (less than 1000 microns)
to
large (1.0 - 1000 mm and greater). Other dimensions and lengths for the
substrate 10
and the grating 12 may be used.
The grating 12 may have a length Lg of about the length L of the substrate 10.
Alternatively, the length Lg of the grating 12 may be shorter than the total
length L of
the substrate 10, as shown in Fig. 11.
Moreover, refernng to Fig. 44, the size of any given dimension for the region
20 of the grating 12 may be less than any corresponding dimension of the
substrate
10. For example, if the grating 12 has dimensions of length Lg, depth Dg, and
width
Wg, and the substrate 12 has dimensions of length L, depth D, and width W, the
dimensions of the grating 12 may be less than that of the substrate 12. Thus,
the
grating 12, may be embedded within or part of a much larger substrate 12.
Instead of
rectangular dimensions or coordinates for size of the substrate 10, the
element 8, or
the grating 12, other dimensions/coordinates for size may be used, e.g., polar
or vector
dimensions.
Also, the element S may be embedded or formed in or on a larger object for
identification of the object.
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The substrate 10 may have end-view cross-sectional shapes other than
circular, such as square, rectangular, elliptical, clam-shell, D-shaped, or
other shapes,
and may have side-view sectional shapes other than rectangular, such as
circular,
square, elliptical, clam-shell, D-shaped, or other shapes. Also, 3D
geornetries other
than a cylinder may be used, such as a sphere, a cube, a pyramid, a bar, a
slab, a plate,
a brick, or a disc shape, or any other 3D shape. Alternatively, the substrate
10 may
have a geometry that is a combination of one or more of the foregoing shapes.
The dimensions, geometries, materials, and material properties of the
substrate
are selected such that the desired optical and material properties are met for
a
10 given application. The resolution and range for the optical codes are
scalable by
controlling these parameters (discussed more hereinafter).
The substrate 10 may be coated with a, polymer material or other material that
may be dissimilar to the material of the substrate 10, provided that the
coating on at
least a portion of the substrate, allows sufficient light to pass transversely
through the
substrate for adequate optical detection of the code using side illumination.
Referring to Fig. 2, the grating 12 is axially spatially invariant. As a
result, the
substrate 10 with the grating 12 (shown as a long substrate 21) may be axially
subdivided or cut into many separate smaller substrates 30-36 and each
substrate 30-
36 will contain the same code as the longer substrate 21 had before it was
cut. The
limit on the size of the smaller substrates 30-36 is based on design and
performance
factors discussed hereinafter.
Referring to Fig. 1, the outer region 18 is made of pure silica (SiOz) and has
a
refractive index n2 of about 1.458 (at a wavelength of about 1553 nm), and the
inner
grating region 20 of the substrate 10 has dopants, such as germanium and/or
boron, to
provide a refractive index nl of about 1.453, which is less than that of outer
region 18
by about 0.005. Other indices of refraction nl,n2 for the grating region 20
and the
outer region 18, respectively, may be used, if desired, provided the grating
12 can be
impressed in the desired grating region 20. For example, the grating region 20
may
have an index of refraction that is larger than that of the outer region 18 or
grating
region 20 may have the same index of refraction as the outer region 18 if
desired.
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Referring to Figs. 3, 4, and 5, one purpose of the outer region 18 (or region
without the grating 12) of the substrate 10 is to provide mechanical or
structural
support for the inner grating region 20. Refernng to Fig. 3, accordingly, the
entire
substrate 10 may comprise the grating 12, if desired. Refernng to Fig. 4,
alternatively
the support portion may be completely or partially beneath, above, or along
one or
more sides of the grating region 20, such as in a planar geometry (Fig. 4), or
a D-
shaped geometry (Fig. 5), or other geornetries. The non-grating portion 18 of
the
substrate 10 may be used for other purposes as well, such as optical Tensing
effects or
other effects (discussed hereinafter).
Also, the end faces of the substrate 10 need not be perpendicular to the sides
or parallel to each other. However, for applications where the elements 8 are
stacked
end-to-end, the packing density may be optimized if the end faces are
perpendicular to
the sides.
Referring to Fig. 6, an incident light 24 of a wavelength ~,, e.g., 532 nm
from a
known frequency doubled Nd:YAG laser or 632nm from a known Helium-Neon laser,
is incident on the grating 12 in the substrate 10. Any other input wavelength
~, can be
used if desired provided ~, is within the optical transmission range of the
substrate
(discussed more hereinafter).
A portion of the input light 24 passes straight through the grating 12 as
indicated by dashed lines 25. The remainder of the light 24 is reflected by
the grating
12 and forms a plurality of beams 26-36 (collectively referred to as reflected
light 27),
each having the same wavelength ~, as the input wavelength ~, and each having
a
different angle indicative of the pitches (Al-An) existing in the grating 12.
As discussed hereinbefore, the grating 12 is a combination of one or more
individual sinusoidal spatial periods or pitches A of the refractive index
variation
along the substrate, each collocated at substantially the same location on the
substrate
10 (discussed more hereinafter). The resultant combination of these individual
pitches
is the grating 12 comprising spatial periods (A1-An) each representing a bit
in the
code. Accordingly, the code is determined by which spatial periods (A1-An)
exist (or
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do not exist) in a given composite grating 12. The code may also be determined
by
additional parameters as well, as discussed hereinafter.
The reflected light 26-36 passes through a lens 37, which provides focused
light beams 46-56 which are imaged onto a CCD camera 60. Instead of or in
addition
to the lens 37, other imaging optics may be used to provide the desired
characteristics
of the optical image/signal onto the camera 60 (e.g., spots, lines, circles,
ovals, etc.),
depending on the shape of the substrate and input optical signals. Also,
instead of a
CCD camera other devices may be used to read/capture the output light.
Referring to Fig. 7, the image on the CCD camera 60 is a series of illuminated
stripes indicating ones and zeros of a digital pattern or code of the grating
12 in the
element 8.
Referring to Fig. 8, lines 68 on a graph 70 are indicative of a digitized
version
of the image of Fig. 7 as indicated in spatial periods (Al-An).
Each of the individual spatial periods (A1-An) in the grating 12 is slightly
different, thus producing an array of N unique diffraction conditions (or
diffraction
angles) discussed more hereinafter. When the element 8 is illuminated from the
side,
in the region of the grating 12, at the appropriate angle (discussed
hereinafter), with a
single input wavelength ~, (monochromatic) source, the diffracted (or
reflected) beams
26-36 are generated.
The beams 26-36 are imaged onto the CCD camera 60 to produce a pattern of
light and dark regions representing a digital (or binary) code, where light =
1 and dark
= 0 (or vice versa). The digital code may be generated by selectively creating
individual index variations (or individual gratings) with the desired spatial
periods
A1-An.
Referring to Fig. 9, illustrations (a)-(c), for the grating 12 in a
cylindrical
substrate 10 having a sample spectral 17 bit code (i.e., 17 different pitches
Al-A17),
the corresponding image on the CCD (Charge Coupled Device) camera 60 is shown
for a digital pattern of 7 bits turned on (10110010001001001); 9 bits turned
on of
(11000101010100111); all 17 bits turned on of (11111111111111111).
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For the images in Fig. 9, the length of the substrate 10 was 450 microns, the
outer diameter D 1 was 65 microns, the inner diameter D was 14 microns, 8n for
the
grating 12 was about 10~, nl in portion 20 was about 1.458 (at a wavelength of
about
1550 mn), n2 in portion 18 was about 1.453, the average pitch spacing A for
the
grating 12 was about 0.542 microns, and the spacing between pitches DA was
about
0.36 % of the adjacent pitches A.
Refernng to Fig. 10, illustration (a), the pitch A of an individual grating is
the
axial spatial period of the sinusoidal variation in the refractive index nl in
the region
20 of the substrate 10 along the axial length of the grating 12 as indicated
by a curve
90 on a graph 91. Refernng to Fig. 10, illustration (b), a sample composite
grating 12
comprises three individual gratings that are co-located on the substrate 10,
each
individual grating having slightly different pitches, Al, A2, A3,
respectively, and the
difference (or spacing) ~A between each pitch A being about 3.0 % of the
period of
an adjacent pitch A as indicated by a series of curves 92 on a graph 94.
Referring to
Fig. 10, illustration (c), three individual gratings, each having slightly
different
pitches, Al, A2, A3, respectively, are shown, the difference ~A between each
pitch A
being about 0.3% of the pitch A of the adjacent pitch as shown by a series of
curves
95 on a graph 97. The individual gratings in Fig. 9, illustrations (b) and (c)
are shown
to all start at 0 for illustration purposes; however, it should be understood
that, the
separate gratings need not all start in phase with each other. Refernng to
Fig. 10,
illustration (d), the overlapping of the individual sinusoidal refractive
index variation
pitches Al-An in the grating region 20 of the substrate 10, produces a
combined
resultant refractive index variation in the composite grating 12 shown as a
curve 96 on
a graph 98 representing the combination of the three pitches shown in Fig. 9,
illustration (b). Accordingly, the resultant refractive index variation in the
grating
region 20 of the substrate 10 may not be sinusoidal and is a combination of
the
individual pitches A (or index variation).
Referring to Fig. 11, to read codes of the grating 12, the light must be
efficiently reflected (or diffracted or scattered) off the grating 12. As is
known, two
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conditions must be met for light to be efficiently reflected. First, the
diffraction
condition for the grating 12 must be satisfied. This condition, as is known,
is the
diffraction (or reflection or scatter) relationship between input wavelength
~,, input
incident angle 8i, output incident angle 00, and the spatial period A of the
grating 12,
and is governed by the below equation:
sin(B; ) + sin(60 ) = m~, / nA Eq. 1
where m is the "order" of the reflection being observed, and n is the
refractive index
of the substrate 10. For Fig. 11, the input angle 8i and the output angle 0o
are defined
as outside the cylinder substrate 10. The value of m=1 or first order
reflection is
acceptable for illustrative purposes. Eq. 1 applies to light incident on outer
surfaces of
the substrate 10 which are parallel to the longitudinal axis of the grating
(or the kB
vector), or where a line 203 normal to the outer surface is perpendicular to
the the kB
vector. Because the angles 0i,6o are defined outside the substrate 10 and
because the
effective refractive index of the substrate 10 is substantially a common
value, the
value of n in Eq. 1 cancels out of this equation.
Thus, for a given input wavelength ~,, grating spacing A, and incident angle
of
the input light 8i, the angle 80 of the reflected output light may be
determined.
Solving Eq. 1 for 8o and plugging in m=1, gives:
9 0 = si~i ~(~1/dl - sin(B i)) Eq. 2
For example, for an input wavelength 7~ = 532 nm, a grating spacing A= 0.532
microns (or 532 nm), and an input angle of incidence 0i =30 degrees, the
output angle
of reflection will be Bo = 30 degrees. Alternatively, for an input wavelength
7~ = 632
nm, a grating spacing A = 0.532 microns (or 532 nm), and an input angle 8i of
30
degrees, the output angle of reflection 0o will be at 43.47 degrees, or for an
input
angle 8i = 37 degrees, the output angle of reflection will be 00 = 37 degrees.
Refernng to Table 1 below, for an input wavelength of ~.= 532 nrn and an
input angle 8i = 30 Degrees, for given grating pitches A, the output angle 0o
is shown.
Table 1
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Number A microns 80
1 0.5245 30.95
2 0.5265 30.69
3 0.529 30.38
4 0.5315 30.06
0.5335 29.81
6 0.536 29.51
7 0.538 29.27
8 0.54 29.03
9 0.542 28.79
0.5445 28.49
11 0.5465 28.26
12 0.549 27.97
13 0.551 27.74
14 0.5535 27.46
0.555 27.29
16 0.5575 27.02
17 0.5595 26.80
The second condition for reading the output light is that the reflection angle
Oo
of the output light must lie within an acceptable region of a "Bragg envelope"
200 to
provide an acceptable level of output light. The Bragg envelope defines the
reflection
5 (or diffraction or scatter) efficiency of incident light. The Bragg envelope
has a center
(or peak) on a center line 202 where refection efficiency is greatest (which
occurs
when 8; = 6o - discussed hereinafter), and it has a half width (8B) measured
in degrees
from the center line 202 or a total width (20B). For optimal or most efficient
reflection, the output light path angle 6o should be at the center of the
Bragg envelope.
10 In particular, for an input light beam incident on a cylinder in a plane
defined
by the longitudinal axis 207 of the cylinder and the line 203 normal to the
longitudinal
axis of the cylinder, the equation governing the reflection or scattering
efficiency (or
normalized reflection intensity) profile for the Bragg envelope is
approximately:
I (ki, ko) ~ ~KD~a sin c2 (ki -~ o)D gq, 3
15 where K = 2~8n/~,, where, 8n is the local refractive index modulation
amplitude of the
grating and ~, is the input wavelength, sinc(x) = sin(x)/x, and the vectors k;
_
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2~cos(8;)/7~ and ko= 2~ccos (00)/~ are the projections of the incident light
and the
output (or reflected) light, respectively, onto the line 203 normal to the
axial direction
of the grating 12 (or the grating vector kB), D is the thickness or depth of
the grating
12 as measured along the line 203 (normal to the axial direction of the
grating 12).
Other substrate shapes than a cylinder may be used and will exhibit a similar
peaked
characteristic of the Bragg envelope. We have found that a value for 8n of
about 10~
in the grating region of the substrate is acceptable; however, other values
may be used
if desired.
Rewriting Eq. 3 gives the reflection efficiency profile of the Bragg envelope
as:
I(ki,ko)~~2~r~8n~D~2~Sin(x)~Z E .4
x q
where: x =(ki-ko)Dl2 = (~Dl~,) *(cos 8 i - cos 8 0)
Thus, when the input angle 0i is equal to the output (or reflected) angle Oo
(i.e:, 8i = 80), the reflection efficiency I (Eqs. 3 & 4) is maximized, which
is at the
center or peak of the Bragg envelope. When 8i = 80, the input light angle is
referred
to as the Bragg angle as is known. The efficiency decreases for other input
and output
angles (i.e., 8i ~ 0o), as defined by Eqs. 3 & 4. Thus, for maximum reflection
efficiency and thus output light power, for a given grating pitch A and input
wavelength, the angle 8i of the input light 24 should be set so that the angle
80 of the
reflected output light equals the input angle 8i. An example of a since
function of Eq.
3 of the reflection efficiency associated with the Bragg envelope is shown as
the line
200.
Also, as the thickness or diameter D of the grating decreases, the width of
the
sin(x)/x function (and thus the width of the Bragg envelope) increases and,
the
coefficient to or amplitude of the sincz (or (sin(x)/x) 2 function (and thus
the efficiency
level across the Bragg envelope) also increases, and vice versa. Further, as
the
wavelength ~, increases, the half width of the Bragg envelope as well as the
efficiency
level across the Bragg envelope both decrease. Thus, there is a trade-off
between the
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brightness of an individual bit and the number of bits available under the
Bragg
envelope. Ideally, 8n should be made as large as possible to maximize the
brightness,
which allows D to be made smaller.
From Eq. 3 and 4, the half angle of the Bragg envelope AB is defined as:
B ~D sin(~; ) Eq. 5
where rl is a reflection efficiency factor which is the value for x in the
sinc2(x)
function where the value of sincz(x) has decreased to a predetermined value
from the
maximum amplitude as indicated by points 204,206 on the curve 2Q0.
While an output light angle 80 located at the center of the Bragg envelope
provide maximum reflection efficiency, output angle within a predetermined
range
around the center of the Bragg envelope provide sufficient level of reflection
efficiency.
We have found that the reflection efficiency is acceptable when ~ <_ 1.39.
This
value for ~ corresponds to when the amplitude of the reflected beam (i.e.,
from the
sinc2(x) function of Eqs. 3 & 4) has decayed to about 50°f° of
its peak value. In
particular,.when x = 1.39 = ~, sinc2(x) = 0.5. However, other values for
efficiency
thresholds or factor in the Bragg envelope may be used if desired.
It is known that a focused light beam diverges beyond its focal point at a
divergence half angle 8R, which is defined as:
6R = ~1(atw) Eq. 6
where ~, is the wavelength of the light and w is the beam half width (HW) at
the focal
point (or "beam waist") measured at the point of 1 /e2 of the peak beam
intensity (for a
Gaussian beam). The beam half width w is determined at the point of incidence
on the
element 8. As the beam width w decreases, the divergence angle increases (and
vice
versa). Also, as the wavelength ~, of light increases, the beam divergence
angle 0R
also increases.
Portions of to above discussion of side grating reflection and the Bragg
effect
are also described in Krug P., et al, "Measurement of Index Modulation Along
an
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Optical Fiber Bragg Grating", Optics Letters, Vol. 20 (No.l7), pp.1767-1769,
Sept.
1995, which is incorporated herein by reference.
Referring to Figs. 12, 13 & 16, we have found that the outer edges of the
substrate 10 may scatter the input light from the incident angle into the
output beam
angular space, which may degrade the ability fo read the code from the
reflected
output light. To minimize this effect, the beam width 2w should be less than
the outer
dimensions of the substrate 10 by a predetermined beam width factor (3, e.g.,
about
50% to 80% for each dimension. Thus, for a cylinder, the beam should be
shorter than
the longitudinal length L in the axial dimension (side view) and narrower than
the
diameter of the cylinder in the cross-sectional dimension (end view).
Accordingly, for
a cylinder substrate 10, the input beam 24 may have a non-circular cross-
section. In
that case, the beam 24 half width w will have a half width dimension wl along
one
dimension (e.g., the length) of the grating 12 and a half width dimension w2
along the
other dimension (e.g., the cross-sectional diameter) of the grating 12. Other
spot sizes
may be used if desired, depending on the amount of end scatter that can be
tolerated
by the application (discussed more hereinafter).
The beam width factor (3 thus may be defined as the ratio of the full width
(2w) of the incident beam (along a given axis) to the length L of the
substrate 10 as
follows:
(3 = 2w/L Eq. 7
For example, when the full beam width 2w is 50% of the length of the
substrate 10, the factor (3 has a value of 0.5.
Accordingly, the divergence equation may be rewritten in terms of the
substrate length L and the beam width factor (3 as:
~R = ~/(~w)= 2~1/(~iL) Eq. 8
For example, for a substrate having an overall length L of about 400 microns,
having the grating 12 length Lg along its entire length L, the half width wl
of the
incident beam along the grating length L may be about 100-150 microns to avoid
end
scatter effects. Similarly, for a substrate 12 having an outer diameter of
about 65
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microns and a grating region 20 diameter of about 10 microns, the other half
width
w2 of the incident beam 24 may be about 15 microns. Other spot dimensions may
be
used if desired, depending on the amount of end scatter that can be tolerated
by the
application.
In view of the foregoing, the number of bits N, which is equal to the number
of different grating pitches A (and hence the number of codes), that can be
accurately
read (or resolved) using side-illumination and side-reading of the grating 12
in the
substrate 10 is determined by numerous factors, including: the beam width w
incident
on the substrate (and the corresponding substrate length L and grating length
Lg), the
thickness or diameter D of the grating 12, the wavelength ~, of incident
light, the beam
divergence angle 8R, and the width of the Bragg envelope 6B. Note that in Fig.
11
both the Bragg envelope 0B and the beam divergence 0R are defined as half
angles
from a central line.
Thus, the maximum number of resolvable bits N for a given wavelength is
approximately as shown below.
N - ~B Eq. 9
R
plugging in for 0B and 0 R from Eqs. S and 8, respectively, gives:
_ r~~3L q
N 2D sin( ~; ) E . 10
Table 2 below shows values of number of bits N, for various values of the
grating thickness D in microns and substrate length L in microns (the length
Lg of the
grating 12 is the same as the length L of the substrate- the grating length Lg
controls),
for 0i = 30 degrees and (3 = 0.5.
Table 2
Grating Thickness7 10 20 30
D
(microns) _>
Substrate Len N N N N
th L
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microns ~
0 0 0 0
2p 2 1 1 0
50 5 3 2 1
100 10 7 3 2
200 20 14 7 5
400 40 28 14 9
500 50 35 17 12
1000 99 70 35 23
As seen from Table 2, and shown by the equations discussed hereinbefore, as
the grating thickness or depth D is made smaller, the Bragg envelope ~B
increases
and, thus, the number of bits N increases. Also, as the length of the grating
Lg gets
shorter (and thus the beam width gets smaller), the number of bits N
decreases, as the
divergence angle 8R increases for each bit or pitch A. Accordingly, the number
of bits
N is limited to the number of bits that can fit within the Bragg envelope
(28B).
18
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Referring to Figure 18, an example of the Bragg envelope half width (6B) is
shown for an input wavelength ~,i = 532nm, an input angle 8i = 30 degrees, a
grating
thickness D = 20 microns, a beam half width w = 150 microns, corresponding to
a
total of 15 bits across the entire Bragg envelope (28B) separated in angular
space by 2
half widths.
It should be understood that depending on the acceptable usable Bragg
envelope 0B relating to acceptable reflection efficiency discussed
hereinbefore, the
achievable number of bits N may be reduced from this amount, as discussed
hereinbefore.
Also, it should be understood that Eq. 5 is based on the beam spacing in the
"far field". Thus, even though the output beams may overlap near to the
substrate
(i.e., in the "near field"), if the lens 37 is placed in the near field it
will separate out
the individual beams and provide separately resolved beams having a desired
spot size
to provide an effective far field effect shown by Eq. 5. Alternatively, the
beams may
be optically detected in the far field without the lens 37, or with other
imaging optics
as desired.
Referring to Figs. 12 & 13, in addition, the outer diameter D 1 of the
substrate
10 affects how much power is scattered off the ends of the substrate 10. In
particular,
even if the HW beam size is within the outer edges of the substrate 10, the
intensity
fringes outside the HW point on the incident beam 24 may reflect off the front
or rear
faces of the substrate 10 toward the output beam. Therefore, the smaller the
outer
diameter D 1 of the substrate, the smaller the amount of unwanted beam
scatter.
Alternatively, certain edges of the substrate may be bowed (see Fig. 17) or
angled or
otherwise have a geometry that minimizes such scatter or the ends may be
coated with
a material that minimizes scatter.
Referring to Fig. 15, the circular outer surface of the cylindrical substrate
10
causes a convex Tensing effect which spreads out the reflected light beams as
indicated by a line 294. The lens 37 collimates the reflected light 290 which
appears
as a line 295. If the bottom of the substrate 10 was flat as indicated by a
line 296
instead of curved (convex), the reflected light beam would not be spread out
in this
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dimension, but would substantially retain the shape of the incident light
(accounting
for beam divergence), as indicated by dashed lines 297. In that case, the
output light
would be spots or circles instead of lines.
Refernng to Fig. 14, in the side view, the lens 37 focuses the reflected light
290 to a point or spot having a diameter of about 30 microns (full width, at
the lle2
intensity point) for a 65 micron diameter substrate. The lens 37 focuses the
reflected
light onto different spots 293 along a line 292.
Referring to Fig. 19, instead of having the input light 24 at a single
wavelength
7~i (monochromatic) and reading the bits by the angle 80 of the output light,
the bits
(or grating pitches A) may be read/detected by providing a plurality of
wavelengths
and reading the wavelength spectrum of the reflected output light signal. In
this case,
there would be one bit per wavelength, and thus, the code is contained in the
wavelength information of the reflected output signal.
In this case, each bit (or A) is defined by whether its corresponding
wavelength falls within the Bragg envelope, not by ifs angular position within
the
Bragg envelope. As a result, it is not limited by the number of angles that
can fit in the
Bragg envelope for a given composite grating 12, as in the embodiment
discussed
hereinbefore. Thus, using multiple wavelengths, the only limitation in the
number of
bits N is the maximum number of grating pitches A that can be superimposed and
optically distinguished in wavelength space for the output beam.
Referring to Figs. 19 and 56, illustration (a), the reflection wavelength
spectrum (~,1-~,n) of the reflected output beam 310 will exhibit a series of
reflection
peaks 695, each appearing at the same output Bragg angle 00. Each wavelength
peak
695 (~,1-~,n) corresponds to an associated spatial period (Al-An), which make
up the
grating 12.
One way to measure the bits in wavelength space is to have the input light
angle 0i equal to the output light angle 80, which is kept at a constant
value, and to
provide an input wavelength ~, that satisfies the diffraction condition (Eq.
1) for each
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grating pitch A. This will maximize the optical power of the output signal for
each
pitch A detected in the grating 12.
Refernng to Fig. 56, illustration (b), the transmission wavelength spectrum of
the transmitted output beam 330 (which is transmitted straight through the
grating 12)
S ~ will exhibit a series of notches (or dark spots) 696. Therefore, instead
of detecting the
reflected output light 310, the transmitted light 330 may be detected at the
detectorlreader 308. Alternatively, the detector/reader 308 may read the both
the
transmitted light 25 and the reflected light 310. It should be understood that
the
optical signal levels for the reflection peaks 695 and transmission notches
696 will
depend on the "strength" of the grating 12, i.e., the magnitude of the index
variation n
in the grating 12.
Referring to Fig. 21, for a wavelength-based readout, the grating 12 thickness
D may be made large to make the width of the Bragg envelope 200 narrow, and
thus
the reflection efficiency large, so it is comparable to or slightly smaller
than the
angular width of the output beam corresponding to one of the bits 340.
In Fig. 19, the bits may be detected by continuously scanning the input
wavelength. A known optical source 300 provides the input light signal 24 of a
coherent scanned wavelength input light shown as a graph 304. The source 300
provides a sync signal on a line 306 to a known reader 308. The sync signal
may be a
timed pulse or a voltage ramped signal, which is indicative of the wavelength
being
provided as the input light 24 to the substrate 10 at any given time. The
reader 308
may be a photodiode, CCD camera, or other optical detection device that
detects
when an optical signal is present and provides an output signal on a line 309
indicative of the code in the substrate 10 or of the wavelengths present in
the output
light, which is directly related to the code, as discussed herein. The grating
12 reflects
the input light 24 and provides an output light signal 310 to the reader 308.
The
wavelength of the input signal is set such that the reflected output light 310
will be
substantially in the center 314 of the Bragg envelope 312 for the individual
grating
pitch (or bit) being read.
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Alternatively, the source 300 may provide a continuous broadband wavelength
input signal such as that shown as a graph 316. In that case, the reflected
output beam
310 signal is provided to a narrow band scanning filter 318 which scans across
the
desired range of wavelengths and provides a filtered output optical signal 320
to the
reader 308. The filter 318 provides a sync signal on a line 322 to the reader,
which is
indicative of which wavelengths are being provided on the output signal 320 to
the
reader and may be similar to the sync signal discussed hereinbefore on the
line 306
from the source 300. In this case, the source 300 does not need to provide a
sync
signal because the input optical signal 24 is continuous. Alternatively,
instead of
having the scanning filter being located in the path of the output beam 310,
the
scanning filter may be located in the path of the input beam 24 as indicated
by the
dashed box 324, which provides the sync signal on a line 323.
Alternatively, instead of the scanning filters 318,324, the reader 308 may be
a
lenown optical spectrometer (such as a lenown spectrum analyzer), capable of
measuring the wavelength of the output light.
The desired values for the input wavelengths 7~ (or wavelength range) for the
input signal 24 from the source 300 may be determined from the Bragg condition
of
Eq. 1, for a given grating spacing A and equal angles for the input light 0i
and the
angle light 80. Solving Eq. 1 for ~, and plugging in m=1, gives:
~, =~1 (sin(B o)+ sin(8 i)J Eq. 11
Referring to Table 3 below, for 8i = 00 = 30 degrees, the above equation
reduces to ~, = A. Thus, for given grating pitches A, the corresponding values
of the
input (and associated output) wavelength ~, are shown in Table 3.
Table 3
Number A microns ~, nm
1 0.5245 524.5
2 0.5265 526.5
3 0.529 529
4 0.5315 531.5
S 0.5335 533.5
6 0.536 536
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7 O.S38 538
8 O.S4 540
9 O.S42 542
O.S44S S44.S
11 O.S46S S46.S
12 O.S49 549
13 O.SSl SS1
14 O.SS3S 553.5
1S O.SSS SSS
16 O.SS75 SS7.S
17 O.SS9S S59.S
Refernng to Fig. 20, is an example of bit readout with two different input
wavelengths, e.g., ~,I,~,2. The rightmost bit 342 falls outside the Bragg
envelope 200
when ~.l is the source, but falls within the Bragg envelope 200 for ~,2. Thus,
the
effective position of the bit 342 shifts based on input wavelength as
indicated by a
line 344.
Refernng to Fig. 22, it is also possible to combine the angular-based code
detection with the wavelength-based code detection, both discussed
hereinbefore. In
10 this case, each readout wavelength is associated with a predetermined
number of bits
within the Bragg envelope. Bits (or grating pitches A) written for different
wavelengths do not show up unless the correct wavelength is used. For example,
the
Bragg envelope 400 is set so that about 3 bits (or pitches A) 402 fit within
the Bragg
envelope 400 for a given input wavelength ~,1, as indicated by a solid line
404, so that
1 S a second set of 3 bits (or pitches A) 402 fit within the Bragg envelope
400 for second
input wavelength ~,2, as indicated by a dashed line 406, and so that a third
set of 3 bits
(or pitches A) 402 fit within the Bragg envelope 400 for a third input
wavelength ~,3
as indicated by a dashed line 408. It should be understood that each of the
sets of bits
may not lie on top of each other in the Bragg envelope as shown in Fig. 22.
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In view of the foregoing, the bits (or grating pitches A) can be read using
one
wavelength and many angles, many wavelengths and one angle, or many
wavelengths
and many angles.
Refernng to Fig. 23, the grating 12 may have a thickness or depth D which is
comparable or smaller than the incident beam wavelength ~,. This is known as a
"thin"
diffraction grating (or the full angle Bragg envelope is 1 ~0 degrees). In
that case, the
half angle Bragg envelope 0B is substantially 90 degrees; however, 8n must be
made
large enough to provide sufficient reflection efficiency, per Eqs. 3 and 4. In
particular,
for a "thin" grating, D*8n ~ ~,/2, which corresponds to a ~ phase shift
between
adjacent minimum and maximum refractive index values of the grating 12.
It should be understood that there is still the trade-off discussed
hereinbefore
with beam divergence angle OR and the incident beam width (or length L of the
substrate), but the accessible angular space is theoretically now 90 degrees.
Also, for
maximum efficiency, the phase shift between adjacent minimum and maximum
refractive index values of the grating 12 should approach a ~ phase shift;
however,
other phase shifts may be used.
In this case, rather than having the input light 24 be incident at the
conventional Bragg input angle 0i, as discussed hereinbefore and indicated by
a
dashed line 701, the grating 12 is illuminated with the input light 24
oriented on a line
705 orthogonal to the longitudinal grating vector 705. The input beam 24 will
split
into two (or more) beams of equal amplitude, where the exit angle Ao can be
determined from Eq. 1 with the input angle A0 (normal to the longitudinal axis
of
the grating 12).
In particular, from Eq. 1, for a given grating pitch A1, the +!-1St order
beams
(m=+1 and m=-1), corresponds to output beams 700,702, respectively. For the +/-
2"a
order beams (m=+2 and m=-2), corresponds to output beams 704,706,
respectively.
The 0'h order (undefracted) beam (m=0), corresponds to beam 70~ and passes
straight
through the substrate. The output beams 700-70~ project spectral spots or
peaks 710-
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718, respectively, along a common plane, shown from the side by a line 709,
which is
parallel to the upper surface of the substrate 10.
For example, for a grating pitch A = 1.0 um, and an input wavelength ~, = 400
nrn, the exit angles ~o are ~ +/- 23.6 degrees (for m = +/-1), and +/- 53.1
degrees
S (from m = +/-2), from Eq. 1. It should be understood that for certain
wavelengths,
certain orders (e.g., m = +/- 2) may be reflected back toward the input side
or
otherwise not detectable at the output side of the grating 12.
Alternatively, one can use only the +/-1 St order (m = +/-1 ) output beams for
the
code, in which case there would be only 2 peaks to detect, 712, 714.
Alternatively,
one can also use any one or more pairs from any order output beam that is
capable of
being detected. Alternatively, instead of using a pair of output peaks fox a
given order,
an individual peak may be used.
Referring to Fig. 24, if two pitches Al,A2 exist in the grating 12, two sets
of
peaks will exist. In particular, for a second grating pitch A2, the +/-1St
order beams
1S (m=+1 and m=-1), corresponds to output beams 720,722, respectively. For the
+/-2°a
order beams (m=+2 and m=-2), corresponds to output beams 724,726,
respectively.
The 0th order (un-defracted) beam (m=0), corresponds to beam 718 and passes
straight
through the substrate. The output beams 720-726 corresponding to the second
pitch
A2 project spectral spots or peaks 730-736, respectively, which are at a
different
location than the point 710-7I6, but along the same common plane, shown from
the
side by the line 709.
Thus, for a given pitch A (or bit) in a grating, a set of spectral peaks will
appear at a specific location in space. Thus, each different pitch corresponds
to a
different elevation or output angle which corresponds to a predetermined set
of
2S spectral peaks. Accordingly, the presence or absence of a particular peak
or set of
spectral peaks defines the code.
In general, if the angle of the grating 12 is not properly aligned with
respect to
the mechanical longitudinal axis of the substrate 10, the readout angles may
no longer
be symmetric, leading to possible difficulties in readout. With a thin
grating, the
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angular sensitivity to the alignment of the longitudinal axis of the substrate
10 to the
input angle 0i of incident radiation is reduced or eliminated. In particular,
the input
light can be oriented along substantially any angle 0i with respect to the
grating 12
without causing output signal degradation, due the large Bragg angle envelope.
Also,
S if the incident beam 24 is normal to the substrate 10, the grating 12 can be
oriented at
any rotational (or azimuthal) angle without causing output signal degradation.
However, in each of these cases, changing the incident angle 8i will affect
the output
angle 00 of the reflected light in a predetermined predictable way, thereby
allowing
for accurate output code signal detection or compensation.
Referring to Fig. 2S, for a thin grating, in addition to multiplexing in the
elevation or output angle based on grating pitch A, the bits can,also be
multiplexed in
an azimuthal (or rotational) angle 0a of the substrate. In particular, a
plurality of
gratings 7S0,7S2,7S4,7S6 each having the same pitch A are disposed in a
surface 701
of the substrate 10 and located in the plane of the substrate surface 701. The
input
1S light 24 is incident on all the gratings 7S0,7S2,7S4,7S6 simultaneously.
Each of the
gratings provides output beams oriented based on the grating orientation. For
example, the grating 7S0 provides the output beams 764,762, the grating 7S2
provides
the output beams 766,768, the grating 7S4 provides the output beams 770,772,
and the
grating 7S6 provides the output beams 774,776. Each of the output beams
provides
spectral peaks or spots (similar to that discussed hereinbefore), which are
located in a
plane 760 that is parallel to the substrate surface plane 701. In this case, a
single
grating pitch A can produce many bits depending on the number of gratings that
can
be placed at different rotational (or azimuthal) angles on the surface of the
substrate
10 and the number of output beam spectral peaks that can be spatially and
optically
2S resolved/detected. Each bit may be viewed as the presence or absence of a
pair of
peaks located at a predetermined location in space in the plane 760. Note that
this
example uses only the m =+/-1St order for each reflected output beam.
Alternatively,
the detection may also use the m = +/-2"d order. In that case, there would be
two
additional output beams and peaks (not shown) for each grating (as discussed
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hereinbefore) that may lie in the same plane as the plane 760 and may be on a
concentric circle outside the circle 760.
In addition, the azimuthal multiplexing can be combined with the elevation (or
output angle) multiplexing discussed hereinbefore to provide two levels of
multiplexing. Accordingly, for a thin grating, the number of bits can be
multiplexed
based on the number of grating pitches A and/or geometrically by the
orientation of
the grating pitches.
Furthermore, if the input light angle 0i is normal to the substrate 10, the
edges
of the substrate 10 no longer scatter light from the incident angle into the
"code
angular space", as discussed hereinbefore.
Also, in the thin grating geometry, a continuous broadband wavelength source
may be used as the optical source if desired.
Refernng to Fig. 26, instead of or in addition to the pitches A in the grating
12
being oriented normal to the longitudinal axis, the pitches may be created at
a angle
8g. In that case, when the input light 24 is incident normal to the surface
792, will
produce a reflected output beam 790 having an angle 8o determined by Eq. I as
adjusted for the blaze angle ~g. This can provide another level of
multiplexing bits in
the code.
Referring to Fig. 27, instead of using an optical binary (0-1) code, an
additional level of multiplexing may be provided by having the optical code
use other
numerical bases, if intensity levels of each bit are used to indicate code
information.
This could be achieved by having a corresponding magnitude (or strength) of
the
refractive index change (bn) for each grating pitch A. In Fig. 27, four
intensity ranges
are shown for each bit number or pitch A, providing for a Base-4 code (where
each bit
corresponds to 0,1,2, or 3). The lowest intensity level, corresponding to a 0,
would
exist when this pitch A is not present in the grating. The next intensity
level 450
would occur when a first low level 8n1 exists in the grating that provides an
output
signal within the intensity range corresponding to a 1. The next intensity
level 452
would occur when a second higher level ~n2 exists in the grating 12 that
provides an
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output signal within the intensity range corresponding to a 2. The next
intensity level
452, would occur when a third higher level 8n3 exists in the grating 12 that
provides
an output signal within the intensity range corresponding to a 3. Accordingly,
an
additional level of multiplexing may be provided
Referring to Figs. 33-37, alternatively, two or more substrates 10,250, each
having at least one grating therein, may be attached together to form the
element 8,
e.g., by an adhesive, fusing or other attachment techniques. In that case, the
gratings
12,252 rnay have the same or different codes.
Refernng to Figs. 36,38, alternatively, the substrate 10 may have more than
one region 20 having codes. For example, there may be two gratings side-by-
side, or
spaced end-to-end, such as that shown in Figs. 33,38, respectively.
Referring to Fig. 37, the length L of the element 8 may be shorter than its
diameter D, such as a plug or puck or wafer or disc.
Referring to Fig. 39, illustrations (a) and (b), to facilitate proper
alignment of
the grating axis with the angle 8i of the input beam 24, the substrate 10 may
have a
plurality of the gratings 12 having the same codes written therein at numerous
different angular or rotational positions of the substrate 10. In particular,
in illustration
(a), there are two gratings 550, 552, having axial grating axes 551, 553,
respectively.
The gratings 550,552 have a common central (or pivot or rotational) point
where the
two axes 551,553 intersect. The angle 8i of the incident light 24 is aligned
properly
with the grating 550 and is not aligned with the grating 552, such that output
light 555
is reflected off the grating 550 and light 557 passes through the grating 550
as
discussed herein. In illustration (b), the angle 8i of incident light 24 is
aligned
properly with the grating 552 and not aligned with the grating 550 such that
output
light 555 is reflected off the grating 552 and light 557 passes through the
grating 552
as discussed herein. When multiple gratings are located in this rotational
orientation,
the bead may be rotated as indicated by a line 559 and there may be many
angular
positions that will provide correct (or optimal) incident input angles 8i to
the grating.
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While this example shows a circular cross-section, this technique may be used
with
any shape cross-section.
Referring to Fig. 58, the substrate 10 may have an outer coating 799, such as
a
polymer or other material that may be dissimilar to the material of the
substrate 10,
provided that the coating 799 on at least a portion of the substrate, allows
sufficient
light to pass through the substrate for adequate optical detection of the
code. The
coating 799 may be on any one or more sides of the substrate 10. Also, the
coating
799 may be a solid, liquid, gas or powder, a chemical polymer, metal, or other
material, or they may be coated with a material that allows the beads to
float, sink,
glow, reflect light, repel or absorb a fluid (liquid and/or gas) or material,
align, have a
predetermined electrical or magnetic polarization, moment or field, or have
other
properties.
Also, the substrate 10 may be made of a material that is less dense than
certain
fluid (liquids and/or gas) solutions, thereby allowing the elements 8 to float
or be
buoyant or partially buoyant. Also, the substrate may be made of a porous
material,
such as controlled pore glass (CPG) or other porous materials, which may also
reduce
the density of the element 8 and may make the element 8 buoyant or partially-
buoyant
in certain fluids.
Alternatively, the substrate 10 may be made of a material that dissolves in
the
presence of certain chemicals or over time.
Refernng to Fig. 40, the substrate may have a spherical geometry. In that
case,
the substrate 10 may have multiple gratings 554, 556 located in different
three-
dimensional planes. In that case, input light 24 is incident on the gratings
554,556
and the gratings 554,556 provide reflected output light 560,562 as discussed
hereinbefore.
Refernng to Fig. 41 illustrations (a), (b), (c), (d), and (e) the substrate 10
may
have one or more holes located within the substrate 10. In illustration (a),
holes 560
may be located at various points along all or a portion of the length of the
substrate
10. The holes need not pass all the way through the substrate 10. Any number,
size
and spacing for the holes 560 may be used if desired. In illustration (b),
holes 572
-29-
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may be located very close together to form a honeycomb-like area of all or a
portion
of the cross-section. In illustration (c), one (or more) inner hole 566 may be
located in
the center of the substrate 10 or anywhere inside of where the grating
regions) 20 are
located. The inner hole 566 (or any holes described herein) may be coated with
a
reflective coating 573 to reflect light to facilitate reading of one or more
of the
gratings 12 and/or to reflect light diffracted off one or more of the gratings
12. The
incident light 24 may reflect off the grating 12 in the region 20 and then
reflect off the
surface 573 to provide output light 577. Alternatively, the incident light 24
may
reflect off the surface 573, then reflect off the grating 12 and provide the
output light
575. In that case the grating region 20 may run axially or circumferentially
571
around the substrate 10. In illustration (d), the holes 579 may be located
circumferentially around the grating region 20 or transversely across the
substrate 10.
In illustration (e), the grating 12 may be located circumferentially (and
running up-
down) around the outside of the substrate 10, and there rnay be holes 574
inside the
substrate 10. Alternatively, the grating 12 may be located circurnferentially
(and
running circurnferentially) around the outside of the substrate 10.
Also, any of the holes described herein for the element 8 or substrate 10 may
be filled with a solid, liquid, gas or powder, a chemical polymer, metal, or
other
material, or they may be coated with a material that allows the beads to
float, sink,
glow, reflect light, repel or absorb a fluid or material, align, have a
predetermined
electrical or magnetic polarization, moment or field, or have other
properties, or may
be similar to or the same as the coating 799 (Fig. 58) or the reflective
coating S 14 of
Fig. 30, discussed hereinbefore.
Referring to Fig. 42, illustrations (a), (b), and (c), the substrate 10 may
have
one or more protruding portions or teeth 570, 578,580 extending radially
and/or
circumferentially from the substrate 10. Alternatively, the teeth 570, 578,580
may
have any other desired shape.
Refernng to Fig. 43, illustrations (a), (b), (c) a D-shaped substrate, a flat-
sided
substrate and an eye-shaped (or clam-shell or teardrop shaped) substrate 10,
respectively, are shown. Also, the grating region 20 may have end cross-
sectional
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shapes other than circular and may have side cross-sectional shapes other than
rectangular, such as any of the geometries described herein for the substrate
10. For
example, the grating region 20 may have a oval cross-sectional shape as shown
by
dashed lines 581, which may be oriented in a desired direction, consistent
with the
teachings herein. Any other geometries for the substrate 10 or the grating
region 20
may be used if desired, as described herein. In the case of an oval shaped
grating
region 20 may provide high diffraction efficiency, when light is incident on
the long
side of the oval.
Referring to Fig. 28, the elements 8 may be placed in a tray or plate 207 with
grooves 205 to allow the elements 10 to be aligned in a predetermined
direction for
illumination and reading/detection as discussed herein. Alternatively, the
grooves 205
may have holes 2I0 that provide suction to keep the elements 8 in position.
The
groove plate may be illuminated from the top, side or the bottom of the plate.
Referring to Fig. 29, instead of a flat plate, the beads may be aligned in a
tube
502 that has a diameter that is only slightly larger than the substrate 10,
e.g., about 1-
50 microns, and that is substantially transparent to the incident light 24. In
that case,
the incident light 24 may pass through the tube 502 as indicated by the light
500 or be
reflected back due to a reflective coating on the tube 500 or the substrate as
shown by
return Light 504. Other techniques can be used for alignment if desired.
Referring to Fig. 30, at least a portion of a side of the substrate I O may be
coated with a reflective coating 514 to allow incident light 510 to be
reflected back to
the same side from which the incident light came, as indicated by reflected
light S 12.
Refernng to Figs. 28 and 31, alternatively, the surfaces inside the V-grooves
205 may be made of or coated with a reflective material that reflects the
incident light.
A light beam is incident onto the substrate and diffracted by the grating 12.
In
particular, the diffracted beam may be reflected by a surface 520 of the V-
groove 205
and read from the same direction as the incident beam 24. Alternatively,
referring to
Figs. 28 and 32, the incident light beam 24 may be diffracted by the
grating'12 and
pass through the upper surface 529 of the v-groove and reflected off two
surfaces 526,
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528 which are made or coated with a reflective coating to redirect the output
beam
upward as a output light beam 530 which may be detected as discussed
hereinbefore.
Referring to Fig. 57, illustrations (a) and (b), alternatively, the substrate
10 can
be electrically and/or magnetically polarized, by a dopant or coating, which
may be
used to ease handling and/or alignment or orientation of the substrate 10
and/or the
grating 12, or used for other purposes. Alternatively, the bead may be coated
with
conductive material, e.g., metal coating on the inside of a holy substrate, or
metallic
dopant inside the substrate. In these cases, such materials can cause the
substrate 10 to
align in an electric or magnetic field. Alternatively, the substrate can be
doped with an
element or compound that fluoresces or glows under appropriate ilrumination,
e.g., a
rare earth dopant, such as Erbium, or other rare earth dopant or fluorescent
or
luminescent molecule. In that case, such fluorescence or luminescence may aid
in
locating andlor aligning substrates.
Referring to Fig. 45, the input light 24 may be incident on the substrate 10
on
an end face 600 of the substrate 10. In that case, the input light 24 will be
incident on
the grating 12 having a more significant component of the light (as compared
to side
illumination discussed hereinbefore) along the longitudinal grating axis 207
of the
grating (along the grating vector kB), as shown by a line 602. The light 602
reflects
off the grating 12 as indicated by a line 604 and exits the substrate as
output light 608.
Accordingly, it should be understood by one skilled in the art that the
diffraction
equations discussed hereinbefore regarding output diffraction angle 8o also
apply in
this case except that the reference axis would now be the grating axis 207.
Thus, in
this case, the input and output light angles 0i,0o, would be measured from the
grating
axis 207 and length Lg of the grating 12 would become the thickness or depth D
of
the grating 12. As a result, for a grating 12 that is 400 microns long, this
would result
in the Bragg envelope 200 being narrow. It should be understood that because
the
values of nl and n2 are close to the same value, the slight angle changes of
the light
between the regions 18,20 are not shown herein.
In the case where incident light 610 is incident along the same direction as
the
grating vector 207, i.e., Ai=0 degrees, the light sees the length Lg of the
grating 12 and
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the grating provides a reflected output light angle 80 = 0 degrees, and the
Bragg
envelope 612 becomes extremely narrow as the narrowing effect discussed above
reaches a limit. In that case, the relationship between a given pitch A in the
grating 12
and the wavelength of reflection ~, is governed by a known "Bragg grating"
relation:
7~, = 2 ne~-A Eq. 12
where nep-is the effective index of refraction of the substrate, ~, is the
input (and
output wavelength) and A is the pitch. This relation, as is known, may be
derived
from Eq. 1 where 8i = 00 = 90 degrees.
In that case, the code information is readable only in the spectral wavelength
of the reflected beam, similar to that discussed hereinbefore for wavelength
based
code reading with Fig. 19. Accordingly the input signal in this case may be a
scanned
wavelength source or a broadband wavelength source. In addition, as discussed
hereinbefore with Fig. 19, the code information may be obtained in reflection
from
the reflected beam 614 or in transmission by the transmitted beam 616 that
passes
1 S through the grating 12.
Refernng to Fig. 46, it should be understood that for shapes of the substrate
10
or element 8 other than a cylinder, the effect of various different shapes on
the
propagation of input light through the element 8, substrate 10, and/or grating
12, and
the associated reflection angles, can be determined using known optical
physics
including Snell's Law, shown below:
n;~ sin Oin = noUt sin Gout Eq. 13
where n;~ is the refractive index of the first (input) medium, and no"t is the
refractive index of the second (output) medium, and Bin and Gout are measured
from a
line 620 normal to an incident surface 622.
Refernng to Fig. 47, if the value of nl in the grating region 20 is greater
than
the value of n2 in the non-grating region 18, the grating region 20 of the
substrate 10
will act as a known optical waveguide for certain wavelengths. In that case,
the
grating region 20 acts as a "core" along which light is guided and the outer
region 18
acts as a "cladding" which helps confine or guide the light. Also, such a
waveguide
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will have a known "numerical aperture" (0na) that will allow light that is
within the
aperture 0na to be directed or guided along the grating axis 207 and reflected
axially
off the grating 12 and returned and guided along the waveguide. In that case,
the
grating 12 will reflect light having the appropriate wavelengths equal to the
pitches A
S present in the grating 12 back along the region 20 (or core) of the
waveguide, and
pass the remaining wavelengths of light as the light 632. Thus, having the
grating
region 20 act as an optical waveguide for wavelengths reflected by the grating
12
allows incident light that is not aligned exactly with the grating axis 207 to
be guided
along and aligned with the grating 12 axis 207 for optimal grating reflection.
If an optical waveguide is used any standard waveguide may be used, e.g., a
standard telecommunication single mode optical fiber (125 micron diameter or
80
micron diameter fiber with about a 8-10 micron diameter), or a larger diameter
waveguide (greater than 0.5 mm diameter), such as is describe in U.S. Patent
Application, Serial No. 09/455,868,. filed December 6, 1999, entitled "Large
Diameter
Waveguide, Grating". Further, any type of optical waveguide may be used for
the
optical substrate I0, such as, a mufti-mode, birefringent, polarization
maintaining,
polarizing, mufti-core, mufti-cladding, or microsturctured optical waveguide,
or a flat
or planar waveguide (where the waveguide is rectangular shaped), or other
waveguides.
Referring to Fig. 48, if the grating 12 extends across the entire dimension D
of
the substrate, the substrate 10 does not behave as a waveguide for the
incident or
reflected light and the incident light 24 will be diffracted (or reflected) as
indicated by
lines 642, and the codes detected as discussed hereinbefore for the end-
incidence
condition discussed hereinbefore with Fig. 45, and the remaining light 640
passes
straight through.
Refernng to Fig. 49, for the end illumination condition, if a blazed or angled
grating is used, as discussed hereinbefore, the input light 24 is coupled out
of the
substrate IO at a known angle as shown by a line 650.
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Refernng to Fig. 50, alternatively, the input light 24 may be incident from
the
side and, if the grating I2 has the appropriate blaze angle, the reflected
light will exit
from the end face 652 as indicated by a line 654.
Refernng to Fig. 51, the grating 12 may have a plurality of different pitch
angles 660,662, which reflect the input light 24 to different output angles as
indicated
by lines 664, 666. This provides another level of multiplexing (spatially)
additional
codes, if desired.
Referring to Fig. 52, if the light 240 is incident along the grating axis 207
(Figs. 11 & 45), alignment may be achieved by using a plate 674 having holes
676
slightly larger than the elements 8. The incident light 670 is reflected off
the grating
and exits through the end as a light 672 and the remaining light passes
through the
grating and the plate 674 as a line 678. Alternatively, if a blazed grating is
used, as
discussed hereinbefore with Fig. 51, incident light 670 may be reflected out
the side
of the plate (or any other desired angle), as indicated by a line 680.
Alternatively,
1 S input light may be incident from the side of the plate 674 and reflected
out the top of
the plate 474 as indicated by a tine 684. The light 672 may be a plurality of
separate
light beams or a single light beam that illuminates the entire tray 674 if
desired.
Refernng to Fig. 53, the v-groove plate discussed hereinbefore with Fig. 28
may be used for the end illumination/readout condition. In that case, the
grating 12
may have a blaze angle such that light incident along the axial grating axis
will be
reflected upward, downward, or at a predetermined angle for code detection.
Similarly, the input light may be incident on the grating in a downward,
upward, or at
a predetermined angle and the grating 12 may reflect light along the axial
grating axis
for code detection.
Referring to Figs. 54 and 55, the substrate 10 may have a plurality of
gratings
688 disposed therein oriented for end illumination and/or readout, where input
light is
shown as a line 690 and output light is shown as a line 692 for reading in
reflection
and/or a line 694 for reading in transmission.
The grating 12 may be impressed in the substrate I O by any technique for
writing, impressed, embedded, imprinted, or otherwise forming a diffraction
grating
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in the volume of or on a surface of a substrate 10. Examples of some known
techniques are described in US Patent No. 4,725,110 and 4,807,950, entitled
"Method
for Impressing Gratings Within Fiber Optics", to Glenn et al; and US Patent
No.
5,388,173, entitled "Method and Apparatus for Forming Aperiodic Gratings in
Optical Fibers", to Glenn, respectively, and US Patent 5,367,588, entitled
"Method of
Fabricating Bragg Gratings Using a Silica Glass Phase Grating Mask and Mask
Used
by Same", to Hill, and US Patents 3,916,182, entitled "Periodic Dielectric
Waveguide
Filter", Dabby et al, and US Patent 3,891,302, entitled "Method of Filtering
Modes in
Optical Waveguides", to Dabby et al, which are all incorporated herein by
reference
to the extent necessary to understand the present invention.
Alternatively, instead of the grating 12 being impressed within the substrate
material, the grating 12 may be partially or totally created by etching or
otherwise
altering the outer surface geometry of the substrate to create a corrugated or
varying
surface geometry of the substrate, such as is described in US Patent
3,891,302,
entitled "Method of Filtering Modes in Optical Waveguides", to Dabby et al,
which is
incorporated herein by reference to the extent necessary to understand the
present
invention, provided the resultant optical refractive profile for the desired
code is
created.
Further, alternatively, the grating 12 may be made by depositing dielectric
layers onto the substrate, similar to the way a known thin film filter is
created, so as to
create the desired resultant optical refractive profile for the desired code.
Unless otherwise specifically stated herein, the term "microbead" is used
herein as a label and does not restrict any embodiment or application of the
present
invention to certain dimensions, materials andlor geometries.
The dimensions and/or geometries for any of the embodiments described
herein are merely for illustrative purposes and, as such, any other dimensions
and/or
geometries may be used if desired, depending on the application, size,
performance,
manufacturing requirements, or other factors, in view of the teachings herein.
It should be understood that, unless stated otherwise herein, any of the
features, characteristics, alternatives or modifications described regarding a
particular
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embodiment herein may also be applied, used, or incorporated with any other
embodiment described herein. Also, the drawings herein are not drawn to scale.
Although the invention has been described and illustrated with respect to
exemplary embodiments thereof, the foregoing and various other additions and
omissions may be made therein and thereto without departing from the spirit
and
scope of the present invention.
37
