(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2004/0130786 A1
`Putnam et al.
`(43) Pub. Date:
`Jul. 8, 2004
`
`US 20040130786A1
`
`(54) METHOD OF MANUFACTURING OF
`DIFFRACTION GRATING-BASED OPTICAL
`IDENTIFICATION ELEMENT
`
`(76)
`
`Inventors: Martin A. Putnam, Cheshire, CT (US);
`John Moon, Wallingford, CT (US);
`Paul S. Szczepanek, Middletown, CT
`(US); Tuo Li, East Lyme, CT (US);
`Anthony Rauseo, Kensington, CT
`(US); Joseph Traynor, Woburn, MA
`(US)
`
`Correspondence Address:
`Gerald L. DePardo
`
`CiDRA Corporation
`50 Barnes Park North
`Wallingford, CT 06492 (US)
`
`(21) Appl. No.:
`
`10/661,116
`
`(22)
`
`Filed:
`
`Sep. 12, 2003
`
`Related U.S. Application Data
`
`(60) Provisional application No. 60/410,541, filed on Sep.
`12, 2002.
`
`Publication Classification
`
`Int. Cl.7 ..................................................... .. G02B 5/18
`(51)
`(52) U.S.Cl.
`............................................... ..359/566; 359/2
`
`(57)
`
`ABSTRACT
`
`A method for manufacturing a diffusion grating-based opti-
`cal identification element is provided. The optical identifi-
`cation element includes a known optical substrate, having an
`optical diffraction grating disposed in the volume of the
`substrate. Alarge number of substrates or microbeads having
`unique identification codes can be manufactured Winding a
`substrate, such as a fiber, around a polygonal shaped cage/
`basket to form a fiber ribbon having flat sections. A grating
`Writing station Writes one or more gratings into each flat
`section to form a unique code to this section. Each flat
`section of fibers of the fiber ribbon is Written with the same
`
`gratings to provide the same identification code, or alterna-
`tively each flat section may be have a different grating(s)
`Written therein so that each section has a different identifi-
`
`cation code. The fiber ribbon is then removed from the cage
`and diced to form a groups of optical identification elements,
`each group having unique optical identification codes.
`
`sip L9
`
`189% ID
`
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`1
`
`Page 1
`
`ILLUMINA, INC. EXHIBIT 1025
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`Page 1
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`

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`Patent Application Publication
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`Jul. 8, 2004 Sheet 1 of 25
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`US 2004/0130786 A1
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`Patent Application Publication
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`Jul. 8, 2004 Sheet 2 of 25
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`US 2004/0130786 A1
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`800
`
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`
`Page 3
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`Page 3
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`

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`Patent Application Publication
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`Jul. 8, 2004 Sheet 3 of 25
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`US 2004/0130786 A1
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`Patent Application Publication
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`Patent Application Publication
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`Jul. 8, 2004 Sheet 12 of 25
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`Patent Application Publication
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`Jul. 8, 2004 Sheet 15 of 25
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`Patent Application Publication
`
`Jul. 8, 2004 Sheet 17 of 25
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`US 2004/0130786 A1
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`

`
`Patent Application Publication
`
`Jul. 8, 2004 Sheet 18 of 25
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`US 2004/0130786 A1
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`Patent Application Publication
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`

`
`US 2004/0130786 A1
`
`Jul. 8, 2004
`
`METHOD OF MANUFACTURING OF
`DIFFRACTION GRATING-BASED OPTICAL
`IDENTIFICATION ELEMENT
`
`CROSS REFERENCES TO RELATED
`APPLICATIONS
`
`[0001] This application claims the benefit of U.S. Provi-
`sional Patent Applications Serial No. 60/410,541 (CiDRA
`Docket No. CC-543), filed Sep. 12, 2002, and is a continu-
`ation-in-part of U.S. patent applications Ser. No.
`(CiDRA Docket No. CC-0648), filed Aug. 20, 2003, each of
`which are incorporated herein by reference in their entirety.
`
`[0002] U.S. patent application Ser. No.
`Docket No. CC-0648A) and application Ser. No.
`(CiDRA Docket No. CC-0650), filed contemporaneously
`herewith, contains subject matter related to that disclosed
`herein, which is incorporated by reference in its entirety.
`
`(CiDRA
`
`TECHNICAL FIELD
`
`[0003] This invention relates to identification elements,
`and more particularly to method of manufacturing diffrac-
`tion grating based optical identification elements.
`
`BACKGROUND ART
`
`[0004] Many industries have a need for uniquely identi-
`fiable objects or for the ability to uniquely identify objects,
`for sorting, tracking, and/or identification/tagging. Existing
`technologies, such as bar codes, electronic microchips/
`transponders,
`radio-frequency identification (RFID), and
`fluorescence and other optical techniques, are often inad-
`equate. For example, existing technologies may be too large
`for certain applications, may not provide enough different
`codes, or cannot withstand harsh temperature, chemical,
`nuclear and/or electromagnetic environments.
`
`[0005] 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, and/or that can withstand harsh environ-
`ments.
`
`SUMMARY OF THE INVENTION
`
`[0006] Objects of the present invention include a method
`of manufacturing a plurality of diffraction grating based
`optical identification elements (microbeads) having unique
`codes.
`
`[0007] According to the present invention, a method of
`manufacturing an optical identification element is provided.
`The method includes providing a substrate and winding the
`substrate around a device to provide at least one grating
`writing section. The method further includes writing at least
`one grating into the substrate disposed in grating writing
`section, and splitting the substrate disposed in the grating
`writing section to form a plurality of optical identification
`elements.
`
`features and
`[0008] The foregoing and other objects,
`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
`
`[0010] FIG. 2 is a top level optical schematic for reading
`a code in an optical identification element, in accordance
`with the present invention.
`
`[0011] FIG. 3 is a block diagram of the steps of manu-
`facturing a diffraction grating-based optical identification
`element or microbead, in accordance with the present inven-
`tion.
`
`[0012] FIG. 4 is an elevational view of a fiber stripping
`station, in accordance with the present invention.
`
`[0013] FIG. 5 is a perspective view of a cage having a pair
`of fiber ribbons wound thereabout, in accordance with the
`present invention.
`
`[0014] FIG. 6 is a side view of a cage having a fiber ribbon
`wound thereabout, in accordance with the present invention.
`
`[0015] FIG. 7 is a perspective view of a disk having a fiber
`ribbon wound thereabout, in accordance with the present
`invention.
`
`[0016] FIG. 8 is a top view of a grating writing station, in
`accordance with the present invention.
`
`[0017] FIG. 9 is a top view of another embodiment of a
`grating writing station, in accordance with the present inven-
`tion.
`
`[0018] FIG. 10 is a front view of a section of a fiber ribbon
`and a projection of a UV beam from a laser for writing a
`grating that is narrower than the width of the fiber ribbon, in
`accordance with the present invention.
`
`[0019] FIG. 11 is a front view of a section of a fiber ribbon
`and a projection of a UV beam from a laser for writing a
`grating that is wider than the width of the fiber ribbon, in
`accordance with the present invention.
`
`[0020] FIG. 12 is a front view of a section of a fiber ribbon
`and a projection of a UV beam from a laser and a phase mask
`tilted at a blaze angle,
`in accordance with the present
`invention.
`
`[0021] FIG. 13 is a perspective view of a plurality of fiber
`ribbons adhered to a test fixture, in accordance with the
`present invention.
`
`[0022] FIG. 14 is a side view of a plurality of fiber ribbons
`adhered to a test fixture,
`in accordance with the present
`invention.
`
`[0023] FIG. 15 is an expanded top view of a portion of the
`diced fiber ribbon, in accordance with the present invention.
`
`[0024] FIG. 16 is a side view of separation station having
`a section of fiber ribbon disposed in a vessel, in accordance
`with the present invention.
`
`[0025] FIG. 17 is a side view of the vessel of FIG. 16
`having a vial disposed on one end of the vessel, in accor-
`dance with the present invention.
`
`[0026] FIG. 18 is a side view of the vessel and vial of
`FIG. 16 in a turned over orientation, in accordance with the
`present invention.
`
`[0009] FIG. 1 is a side view of an optical identification
`element, in accordance with the present invention.
`
`[0027] FIG. 19 is a side view of microbeads disposed
`within a vial, in accordance with the present invention.
`
`Page 27
`
`Page 27
`
`

`
`US 2004/0130786 A1
`
`Jul. 8, 2004
`
`[0028] FIG. 20 is a top View of another embodiment of a
`grating writing station, in accordance with the present inven-
`tion.
`
`[0046] FIG. 39 is a side view of an optical identification
`element where light is incident on an end face, in accordance
`with the present invention.
`
`[0029] FIG. 21 is a perspective of another embodiment of
`a grating writing station, in accordance with the present
`invention.
`
`[0047] FIGS. 40-41 are side views of an optical identifi-
`cation element where light is incident on an end face, in
`accordance with the present invention.
`
`[0030] FIG. 22 is a side view of a pair of lasers scoring
`opposing sides of a fiber to form microbeads, in accordance
`with the present invention.
`
`[0048] FIG. 42, illustrations (a)-(c) are side views of an
`optical identification element having a blazed grating, in
`accordance with the present invention.
`
`[0031] FIG. 23 is a side view of a laser scoring one side
`of a fiber to form microbeads, in accordance with the present
`invention.
`
`[0049] FIG. 43 is a side view of an optical identification
`element having a coating, in accordance with the present
`invention.
`
`[0032] FIG. 24 is a side view of an anvil and support used
`to separate the microbeads from the scored fiber, in accor-
`dance with the present invention.
`
`[0033] FIG. 25 is a schematic illustration of another
`method of manufacturing microbeads, in accordance with
`the present invention.
`
`[0034] FIG. 26 is a side view of another embodiment for
`cutting a fiber to form microbeads, in accordance with the
`present invention.
`
`[0035] FIG. 27 is an optical schematic for reading a code
`in an optical identification element, in accordance with the
`present invention.
`
`[0036] FIG. 28 is an image of a code on a CCD camera
`from an optical identification element, in accordance with
`the present invention.
`
`[0037] FIG. 29 is a graph showing an digital representa-
`tion of bits in a code in an optical identification element, in
`accordance with the present invention.
`
`[0038] FIG. 30 illustrations (a)-(c) show images of digital
`codes on a CCD camera, in accordance with the present
`invention.
`
`[0039] FIG. 31 illustrations (a)-(d) show graphs of differ-
`ent refractive index pitches and a summation graph,
`in
`accordance with the present invention.
`
`[0040] FIG. 32 is an alternative optical schematic for
`reading a code in an optical
`identification element,
`in
`accordance with the present invention.
`
`[0050] FIG. 44 is a side view of whole and partitioned
`optical identification element, in accordance with the present
`invention.
`
`[0051] FIG. 45 is a side view of an optical identification
`element having a grating across an entire dimension,
`in
`accordance with the present invention.
`
`[0052] FIG. 46, illustrations (a)-(c), are perspective views
`of alternative embodiments for an optical
`identification
`element, in accordance with the present invention.
`
`[0053] FIG. 47, illustrations (a)-(b), are perspective views
`of an optical identification element having multiple grating
`locations, in accordance with the present invention.
`
`[0054] FIG. 48, is a perspective view of an alternative
`embodiment for an optical identification element, in accor-
`dance with the present invention.
`
`[0055] FIG. 49 is a view an optical identification element
`having a plurality of gratings located rotationally around the
`optical identification element, in accordance with the present
`invention.
`
`[0056] FIG. 50 illustrations (a)-(e) show various geom-
`etries of an optical identification element that may have
`holes therein, in accordance with the present invention.
`
`[0057] FIG. 51 illustrations (a)-(c) show various geom-
`etries of an optical identification element that may have teeth
`thereon, in accordance with the present invention.
`
`[0058] FIG. 52 illustrations (a)-(c) show various geom-
`etries of an optical identification element, in accordance with
`the present invention.
`
`[0041] FIG. 33 illustrations (a)-(b) are graphs of reflection
`and transmission wavelength spectrum for an optical iden-
`tification element, in accordance with the present invention.
`
`[0059] FIG. 53 is a side view an optical identification
`element having a reflective coating thereon, in accordance
`with the present invention.
`
`[0042] FIGS. 34-35 are side views of a thin grating for an
`optical identification element, in accordance with the present
`invention.
`
`[0060] FIG. 54 illustrations (a)-(b) are side views of an
`optical identification element polarized along an electric or
`magnetic field, in accordance with the present invention.
`
`[0043] FIG. 36 is a perspective view showing azimuthal
`multiplexing of a thin grating for an optical identification
`element, in accordance with the present invention.
`
`[0044] FIG. 37 is side view of a blazed grating for an
`optical identification element, in accordance with the present
`invention.
`
`[0045] FIG. 38 is a graph of a plurality of states for each
`bit in a code for an optical identification element, in accor-
`dance with the present invention.
`
`BEST MODE FOR CARRYING OUT THE
`INVENTION
`
`[0061] Referring to FIG. 1, a diffraction grating-based
`optical
`identification element 8 (or encoded element or
`coded element) 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
`
`Page 28
`
`Page 28
`
`

`
`US 2004/0130786 A1
`
`Jul. 8, 2004
`
`variation in the effective refractive index and/or effective
`optical absorption of at least a portion of the substrate 10.
`
`identification element 8 described
`[0062] The optical
`herein is the same as that described in Copending patent
`application
`Ser. No.
`(CiDRA Docket No.
`CC-0648A), filed contemporaneously herewith, which is
`incorporated herein by reference in its entirety.
`
`In particular, the substrate 10 has an inner region 20
`[0063]
`where the grating 12 is located. The inner region 20 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.
`
`[0064] The grating 12 is a combination of one or more
`individual spatial periodic sinusoidal variations (or compo-
`nents) in the refractive index that are collocated at substan-
`tially the same location on the substrate 10 along the length
`of the grating region 20, each having a spatial period (or
`pitch) A. The resultant combination of these individual
`pitches is the grating 12, comprising spatial periods (A1-An)
`each representing a bit in the code. Thus, the grating 12
`represents a unique optically readable code, made up of bits,
`where a bit corresponds to a unique pitch A within the
`grating 12. Accordingly, for a digital binary (0-1) code, the
`code is determined by which spatial periods (A1-An) exist
`(or do not exist) in a given composite grating 12. The code
`or bits may also be determined by additional parameters (or
`additional degrees of multiplexing), and other numerical
`bases for the code may be used, as discussed herein and/or
`in the aforementioned patent application.
`
`[0065] The grating 12 may also be 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 predeter-
`mined desired optical output pattern or signal.
`
`[0066] The substrate 10 has an outer diameter D1 and
`comprises silica glass (SiO2) having the appropriate chemi-
`cal 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, borosili-
`cate glass, or other glasses, or made of glass and plastic, or
`solely plastic. For high temperature or harsh chemical appli-
`cations, the optical substrate 10 made of a glass material is
`desirable. If a flexible substrate is needed, 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.
`
`[0067] The optical substrate 10 with the grating 12 has a
`length L and an outer diameter D1, and the inner region 20
`diameter D. The length L can range from very small “micro-
`beads” (or microelements, micro-particles, or encoded par-
`ticles), about 1-1000 microns or smaller, to larger “macro-
`beads” or “macroelements” for larger applications (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.
`
`[0068] 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.
`
`Page 29
`
`[0069] The outer region 18 is made of pure silica (SiO2)
`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 n1 of about 1.453, which is less
`than that of outer region 18 by about 0.005. Other indices of
`refraction n1,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.
`
`light 24 of a
`[0070] Referring to FIG. 2, an incident
`wavelength A, e.g., 532 nm from a known frequency
`doubled Nd:YAG laser or 632 nm from a known Helium-
`
`Neon laser, is incident on the grating 12 in the substrate 10.
`Any other input wavelength A can be used if desired
`provided k is within the optical transmission range of the
`substrate (discussed more herein and/or in the aforemen-
`tioned patent application). A portion of the input light 24
`passes straight through the grating 12, as indicated by a line
`25. The remainder of the input light 24 is reflected by the
`grating 12, as indicated by a line 27 and provided to a
`detector 29. The output light 27 may be a plurality of beams,
`each having the same wavelength A as the input wavelength
`A and each having a different output angle indicative of the
`pitches (A1-An) existing in the grating 12. Alternatively, the
`input light 24 may be a plurality of wavelengths and the
`output light 27 may have a plurality of wavelengths indica-
`tive of the pitches (A1-An) existing in the grating 12.
`Alternatively,
`the output light may be a combination of
`wavelengths and output angles. The above techniques are
`discussed in more detail herein and/or in the aforementioned
`patent application.
`
`[0071] The detector 29 has the necessary optics, electron-
`ics, software and/or firmware to perform the functions
`described herein. In particular, the detector reads the optical
`signal 27 diffracted or reflected from the grating 12 and
`determines the code based on the pitches present or the
`optical pattern, as discussed more herein or in the afore-
`mentioned patent application. An output signal indicative of
`the code is provided on a line 31.
`
`[0072] FIG. 3 shows a method 800 of manufacturing a
`microbead 8 similar to that described hereinbefore in accor-
`
`dance with the present invention. The first step 802 includes
`providing a photosensitive substrate or fiber 830. To sim-
`plify the description of the method of manufacturing, the
`substrate will be referred to as a fiber with the understanding
`that the microbeads 8 may be formed of any photosensitive
`substrate.
`
`[0073] The fiber 830 may be made of any material that has
`sufficient photosensitivity to allow a diffraction grating 12 to
`be disposed therein,
`that represents a code that can be
`interrogated as described herein and/or in the aforemen-
`tioned patent application. The fiber 830 may be doped or
`loaded with any dopant now known or later discovered that
`allows the fiber to exhibit the necessary level of photosen-
`sitivity for the incident radiation (e.g., UV or other actinic
`radiation) used for writing the grating 12, such as, hydrogen,
`deuterium, boron, germanium, lead, or other dopants that
`provide photosensitivity, some of which are described in
`
`Page 29
`
`

`
`US 2004/0130786 A1
`
`Jul. 8, 2004
`
`Patent Nos.: U.S. Pat. No. 6,436,857 to Brueck et al, U.S.
`Pat. No. 5,287,427 to Atkins et al, U.S. Pat. No. 5,235,659
`to Atkins et al, U.S. Pat. No. 6,327,406 to Cullen et al, WO
`00/44683 to Samsung Electronics Co. LTD, U.S. Pat. No.
`6,221,566 to Kohnke et al, U.S. Pat. No. 6,097,512 to
`Ainslie et al; and U.S. Pat. No. 6,075,625 to Ainslie et al.
`
`In step 804, the photosensitive fiber 830 is then
`[0074]
`stripped of the coating or buffer disposed on its outer surface
`and then cleaned. The stripped fiber is then wound around a
`cage or basket 832 having a generally polygon shape so that
`the wound fiber has sections 831 of flat areas.
`
`[0075] FIG. 4 illustrates a fixture/set-up 834 for accom-
`plishing steps 802-804. The photosensitive fiber 830 is
`threaded through a blade 836 for stripping the buffer from
`the fiber. A heater 838 is disposed prior to the stripper 836
`to heat and soften the buffer to ease the removal of the buffer
`
`from the fiber. The stripped fiber then passes through or
`between a pair of pads 840 soaked with a solvent, such as
`acetone, to clean the fiber. The fiber 830 is then wound about
`the cage 832. While not shown, the set-up 834 may include
`one or more pulleys or rollers to provide tension on the fiber
`when winding the fiber onto the cage.
`
`[0076] As best shown in FIGS. 5 and 6, the cage 832 has
`a lower plate 842 and an upper ring support 844 with a
`plurality of rods 846 connected therebetween. The rods are
`equi-spaced about the circumference of the cage. In the
`embodiment shown, the cage 832 includes 16 openings 848,
`however, the invention contemplates having any number of
`openings. When wound around the rods 846 of the cage 832,
`each wrap of fiber is adjacent to and touches each adjacent
`wrap to form a single layer of fiber ribbon 850 around the
`cage. The fiber is wrapped around the cage between 100-120
`times to effectively form a single layer ribbon of fibers. The
`invention contemplates any number of wraps of fiber around
`the cage. The fiber ribbon 850 forms a polygonal shape when
`wrapped around the change to provide a plurality of flat
`sections (16 sections) 831. These fiat sections 831 of the
`fiber ribbon 850 provides the area of the fiber that a grating
`12 is written in, which will be described in greater detail
`hereafter. As best shown in FIG. 6, one section 831 of the
`fiber ribbon 850 is tape together at 852, including the ends
`of the fiber, to maintain the tension of the fiber around the
`cage and to maintain the single layer of the fiber ribbon.
`
`[0077] While FIG. 6 shows a single fiber ribbon 850
`disposed on the cage 832, the present invention contem-
`plates that a plurality of fiber ribbons 850 may be axially
`spaced on the cage, as shown in FIG. 5.
`
`In FIG. 7 illustrates that the stripped fiber 830 may
`[0078]
`by wound around a disk 854 having a plurality of circum-
`ferentially spaced dovetailed slots 856, wherein the fiber
`ribbon 850 is taped at 858 to the outer circumference of the
`disk.
`
`[0079] The next step 808 of FIG. 3 is to write or shoot the
`diffraction grating(s) 12 into each section 846 of the fiber
`ribbon 850. The grating 12 may be impressed in the fiber 830
`by any technique for writing,
`impressed, embedded,
`imprinted, or otherwise forming a diffraction grating in the
`volume of or on a surface of a substrate 10. Examples of
`some known techniques are described in U.S. Pat. Nos.
`4,725,110 and 4,807,950, entitled “Method for Impressing
`Gratings Within Fiber Optics”, to Glenn et al; and U.S. Pat.
`
`Page 30
`
`No. 5,388,173, entitled “Method and Apparatus for Forming
`Aperiodic Gratings in Optical Fibers”,
`to Glenn, respec-
`tively, and U.S. Pat. No. 5,367,588, entitled “Method of
`Fabricating Bragg Gratings Using a Silica Glass Phase
`Grating Mask and Mask Used by Same”, to Hill, and U.S.
`Pat. No. 3,916,182, entitled “Periodic Dielectric Waveguide
`Filter”, Dabby et al, and U.S. Pat. No. 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.
`
`instead of the grating 12 being
`[0080] Alternatively,
`impressed within the fiber 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 U.S. Pat. No. 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, pro-
`vided the resultant optical refractive profile for the desired
`code is created.
`
`[0081] 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.
`
`[0082] FIG. 8 shows the method of writing a grating 12
`into the fibers 830 of the ribbon 850 using at least one phase
`mask 860. Alaser 862, such as an excimer laser or CO2 laser,
`provides an ultra-violet
`(UV) beam 864, which passes
`through the phase mask to write a grating 12 having a
`predetermined profile corresponding to the phase mask. In
`one embodiment, one phase mask 860 may be used to write
`the grating into the fiber 830 to provide one unique