(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2005/0007582 A1
`(43) Pub. Date:
`Jan. 13, 2005
`Villers et al.
`
`US 2005.0007582A1
`
`(54) METHODS AND APPARATUS FOR
`COLLECTION OF OPTICAL REFERENCE
`MEASUREMENTS FOR MONOLITHIC
`SENSORS
`(75) Inventors: Philippe Villers, Concord, MA (US);
`Robert K. Rowe, Corrales, NM (US);
`Kristin A. Nixon, Albuquerque, NM
`(US); Karen E. Unruh, Albuquerque,
`NM (US)
`
`Correspondence Address:
`TOWNSEND AND TOWNSEND AND CREW,
`LLP
`TWO EMBARCADERO CENTER
`EIGHTH FLOOR
`SAN FRANCISCO, CA 94111-3834 (US)
`
`(73) Assignee: Lumidigm, Inc., Albuquerque, NM (US)
`(21) Appl. No.:
`10/886,941
`(22) Filed:
`Jul. 7, 2004
`
`Related U.S. Application Data
`(60) Provisional application No. 60/485,593, filed on Jul.
`7, 2003.
`
`Publication Classification
`
`(51) Int. Cl. ................................................. G01N 21/55
`(52) U.S. Cl. .............................................................. 356/300
`(57)
`ABSTRACT
`Methods and apparatus are provided for collecting optical
`data. Light is propagated through a reference Sample from a
`Source of light to a detector of light to produce a measured
`reference spectral distribution. Light is also propagated
`through a Subject Sample from the Source of light to the
`detector of light to produce a measured Subject spectral
`distribution. At least one of an intensity change and a
`wavelength shift between the measured reference spectral
`distribution and a Stored reference spectral distribution is
`identified. The measured subject spectral distribution is
`compared with a Stored Subject spectral distribution associ
`ated with the stored reference spectral distribution. Such
`comparison includes accounting for the identified one of the
`intensity change and the wavelength shift.
`
`
`
`Monolithic sensor - can have one or
`Jo more light sources and one or more
`detectOS
`
`of
`
`a DetectOr
`o Light Source
`
`1
`
`APPLE 1021
`
`

`

`Patent Application Publication Jan. 13, 2005 Sheet 1 of 6
`
`US 2005/0007582 A1
`
`Monolithic sensor - can have one or
`more light sources and one or more
`detectors
`
`Figure 1:
`
`too
`
`
`
`o
`
`Ba Detector
`o Light source
`
`Original
`
`f .2A
`
`2.
`
`C
`
`Change in intensity, at
`multiple wavelengths
`
`
`
`wavelength
`
`Wavelength shift
`
`
`
`wavelength
`
`wavelength
`
`2
`
`

`

`Patent Application Publication Jan. 13, 2005 Sheet 2 of 6
`
`US 2005/0007582 A1
`
`Figure 3:
`
`/10
`
`-Material 3
`NMaterial 2
`Material 1
`
`k Light source
`Y Detector
`
`
`
`
`
`
`
`Diffuse Reflecting
`Surface
`
`Filter (wavelengths
`vary as a function of
`angle)
`o
`
`k Light source
`Y Detector
`
`3
`
`

`

`Patent Application Publication Jan. 13, 2005 Sheet 3 of 6
`
`US 2005/0007582 A1
`
`Detector
`o Light source
`
`SeSOr
`
`
`
`
`
`11 ?t
`
`Cover in place,
`active elements
`exposed for subject
`measurement
`
`
`
`Side view, COver
`rotates for reference
`measurements
`
`4
`
`

`

`Patent Application Publication Jan. 13, 2005 Sheet 4 of 6
`
`US 2005/0007582 A1
`
`Solid cover slip, rotates around
`set point or slides to cover Sensor
`
`Rotating reference
`material with gaps,
`positioned above active
`sensor layer and below
`optically transparent
`layer.
`
`H. SG
`
`
`
`2 - - - - - - --- a-
`
`20elf
`
`Relaxed state - Optically
`clear button attached to
`cover slips (reference
`sample) - able to Collect
`reference
`measurementS.
`
`N1"
`
`-
`
`Active state - Cover
`slip slides away when
`button is depressed -
`able to collect sample
`measurements.
`
`5
`
`

`

`Patent Application Publication Jan. 13, 2005 Sheet 5 of 6
`
`US 2005/0007582 A1
`
`Relaxed State -
`reflecting
`
`Active State -
`optically transparent
`
`Zd
`
`194
`
`loo
`
`On
`
`Detector
`o Light Source
`
`hi. (, B
`
`Figure 7:
`
`chield housing, underSide
`Opbaé
`treated for use as reference
`Sample
`
`
`
`lot
`
`ld
`A Detector
`O Light Source
`
`6
`
`

`

`Patent Application Publication Jan. 13, 2005 Sheet 6 of 6
`
`US 2005/0007582 A1
`
`Sensor material that is not
`optically opaque
`
`
`
`Detector
`o Light Source
`
`
`
`u1 Sample
`
`% 24 Detectors isolated such that
`-
`they only collect light from
`sample or sensor body
`Sensor material that is not
`optically opaque
`
`m
`
`.
`3
`---
`fia. PB
`t :
`
`
`
`. Detector
`o Light Source
`
`7
`
`

`

`US 2005/0007582 A1
`
`Jan. 13, 2005
`
`METHODS AND APPARATUS FOR COLLECTION
`OF OPTICAL REFERENCE MEASUREMENTS
`FOR MONOLITHIC SENSORS
`
`CROSS REFERENCE TO RELATED
`APPLICATIONS
`0001. This application is a nonprovisional of and claims
`the benefit of the filing date of Provisional Application No.
`60/485,593, filed Jul. 7, 2003, which is herein incorporated
`by reference in its entirety for all purposes.
`
`BACKGROUND OF THE INVENTION
`0002 This application relates generally to optical sen
`Sors. More specifically, this application relates to methods
`and Systems for collection of optical reference measure
`ments for Spectroscopic optical Sensors.
`0003. There are a variety of applications in which optical
`Sensors may be used in collecting data from living Subjects.
`In Such applications, a spectral distribution of light over
`Some wavelength range is examined and perhaps compared
`with other spectral distributions. These other spectral distri
`butions may represent data taken from the same Subject at a
`different time or may represent data taken from another
`Subject. Information is typically extracted by identifying
`Similarities or differences between the Spectral distributions,
`which is performed by comparing the Spectral distributions.
`One challenge in performing Such comparisons is to identify
`when differences in the Spectral distributions are actually
`artifacts, resulting from Such factors as wavelength shift or
`a change in intensity of the light Source(s), or a change in the
`responsivity of the detector, or a combination of Such effects.
`The accuracy of the comparison very much depends on an
`ability to distinguish Such artifacts from real, physically
`based differences in the Spectra.
`0004. There is, accordingly, a general need in the art for
`methods and Systems that permit compensation for Such
`effects to remove artifact-based differences in Spectral dis
`tributions.
`
`BRIEF SUMMARY OF THE INVENTION
`0005 Embodiments of the invention provide methods
`and apparatus for collecting optical data. Light is propagated
`through a reference Sample from a Source of light to a
`detector of light to produce a measured reference Spectral
`distribution. Light is also propagated through a Subject
`Sample from the Source of light to the detector of light to
`produce a measured Subject spectral distribution. At least
`one of an intensity change and a wavelength shift between
`the measured reference spectral distribution and a Stored
`reference Spectral distribution is identified. The measured
`Subject spectral distribution and its associated Stored refer
`ence spectral distribution is compared with a Stored Subject
`Spectral distribution and its associated Stored reference Spec
`tral distribution. Such comparison includes accounting for
`the intensity change and/or the wavelength shift. These
`methods may be implemented with an optical Sensor that
`comprises the Source of light, detector of light, and reference
`material.
`0006 There are a variety of compositions that may be
`used for the reference material and configurations of the
`optical Sensor that comprises it. For example, in one
`
`embodiment, the reference Sample comprises a Substantially
`homogeneous material, Such as collagen and water. In
`another embodiment, the reference Sample is heterogeneous.
`Such a heterogeneous reference Sample may comprise a
`plurality of areas of Substantially homogeneous material. In
`a particular embodiment where the Source of light comprises
`one or more Sources of light and the detector of light
`comprises a plurality of detectors of light, each of the areas
`of Substantially homogeneous material may be configured
`Such that different proportions of the homogeneous material
`are associated with different paths from the Sources of light
`to the detectors of light.
`0007. In other embodiments, the reference sample com
`prises a plurality of reference Samples, which have Substan
`tially different Spectral characteristics. In one Such embodi
`ment, the plurality of reference Samples comprise a plurality
`of optical filters. In Some embodiments, one of the reference
`Samples has a flat Spectral reflection characteristic. In Some
`embodiments, one of the reference Samples is optically
`black or non-reflecting. In further embodiments, the refer
`ence Sample comprises a Spectrally dispersive element. In
`Still other embodiments, the reference Sample comprises a
`filter having a wavelength-dependent profile, which may
`further have an angular-dependent profile in one embodi
`ment.
`0008. The optical sensor may also comprise a device
`adapted for Selective presentation of the reference Sample to
`the Source of light and detector of light. Such a device may
`be further adapted to act as a protective cover for the optical
`Sensor. In Some instances, the device may be adapted to
`dispense discrete units of the reference Sample.
`0009. In one embodiment, the reference sample com
`prises a plurality of holes arranged according to a geometri
`cal arrangement of the Source of light and the detector of
`light. In this embodiment, the device may be adapted to
`move the reference Sample to align the plurality of holes
`with the geometrical arrangement. In another embodiment,
`the reference Sample comprises a material having a first State
`that is opaque at a wavelength of the Source of light and a
`Second State that is transparent at the wavelength of the
`Source of light. In this embodiment, the device may be
`adapted to change the State of the material. In a further
`embodiment, the device is adapted to shield the detector of
`light from Some or all wavelengths of ambient light while
`light is propagated through the Subject Sample.
`BRIEF DESCRIPTION OF THE DRAWINGS
`0010) A further understanding of the nature and advan
`tages of the present invention may be realized by reference
`to the remaining portions of the Specification and the draw
`ings wherein like reference numerals are used throughout
`the Several drawings to refer to Similar components. In Some
`instances, a Sublabel is associated with a reference numeral
`and follows a hyphen to denote one of multiple Similar
`components. When reference is made to a reference numeral
`without Specification to an existing Sublabel, it is intended to
`refer to all Such multiple Similar components.
`0011 FIG. 1 provides a top view of a schematic illus
`tration of the Structure of a monolithic optical Sensor used in
`embodiments of the invention;
`0012 FIGS. 2A-2C provide exemplary spectral distribu
`tions that may be compared in performing functions with the
`monolithic optical sensor shown in FIG. 1;
`
`8
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`

`US 2005/0007582 A1
`
`Jan. 13, 2005
`
`0013 FIG. 3 provides a side view of a schematic illus
`tration of a structure for optical reference material used with
`a monolithic optical Sensor in one embodiment of the
`invention;
`0.014
`FIG. 4 provides a side view of a schematic illus
`tration of a structure for optical reference material used with
`a monolithic optical Sensor in another embodiment of the
`invention;
`0015 FIGS. 5A-5H provide schematic illustrations of
`combinations of a monolithic optical Sensor and reference
`material used in further embodiments of the invention;
`0016 FIGS. 6A and 6B provide side views of schematic
`illustrations of the use of optically dependent material
`properties of reference material used with a monolithic
`optical Sensor in another embodiment of the invention;
`0017 FIG. 7 provides a side view of a schematic illus
`tration of the use of an optical-shield housing that comprises
`reference material in a further embodiment of the invention;
`and
`0018 FIGS. 8A and 8B provide side views of schematic
`illustrations of embodiments in which leakage through a
`monolithic Sensor is used.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`0019 1. Introduction
`0020. The number of applications in which comparisons
`of spectral distributions derived from living subjects provide
`useful information is diverse. For example, in Some appli
`cations, optical Sensors may be used to determine analyte
`concentrations in individuals as an aid to diagnosing disease
`Such as diabetes. Examples of Such applications are
`described in U.S. Pat. Nos. 5,655,530 and 5,823,951, both of
`which are incorporated herein by reference in their entireties
`for all purposes. These applications relate to near-infrared
`analysis of a tissue analyte concentration that varies with
`time. Similarly, U.S. Pat. No. 6,152,876, which is also
`incorporated herein by reference in its entirety for all pur
`poses, discloses improvements in non-invasive living tissue
`analyte analysis.
`0021 U.S. Pat. No. 5,636,633, the entire disclosure of
`which is incorporated herein by reference, relates in part to
`another aspect of accurate non-invasive measurement of an
`analyte concentration. The apparatus described therein
`includes a device having transparent and reflective quadrants
`for Separating diffuse reflected light from Specular reflected
`light. Incident light projected into the Skin results in Specular
`and diffuse reflected light coming back from the skin.
`Specular reflected light has little or no useful information
`and is preferably removed prior to collection. U.S. Pat. No.
`5,935,062, the entire disclosure of which has been incorpo
`rated herein by reference, discloses a further improvement
`for accurate analyte concentration analysis which includes a
`blocking blade device for Separating diffuse reflected light
`from specular reflected light. The blade allows light from the
`deeper, inner dermis layer to be captured, rejecting light
`from the Surface, epidermis layer, where the epidermis layer
`has much leSS analyte information than the inner dermis
`layer, and contributes noise. The blade traps Specular reflec
`tions as well as diffuse reflections from the epidermis.
`
`In one specific application, optical Sensors may be
`0022.
`used to monitor blood-alcohol levels in individuals, as
`described in copending, commonly assigned U.S. ProV. Pat.
`Appl. No. 60/460,247, entitled “NONINVASIVE ALCO
`HOL MONITOR,” filed Apr. 4, 2003 by Robert K. Rowe
`and Robert M. Harbour, the entire disclosure of which is
`incorporated herein by reference for all purposes.
`0023. In other applications, optical sensors may be used
`in biometric identification or identity-verification applica
`tions. Examples of Such applications for optical Sensors are
`disclosed in the following copending, commonly assigned
`applications, the entire disclosure of each of which is
`incorporated herein by reference for all purposes: U.S. Prov.
`Pat. Appl. No. 60/403,453, entitled “BIOMETRIC
`ENROLLMENTSYSTEMS AND METHODS,” filed Aug.
`13, 2002 by Robert K. Rowe et al.; U.S. Prov. Pat. Appl. No.
`60/403,452, entitled “BIOMETRIC CALIBRATION AND
`DATAACQUISITION SYSTEMS AND METHODS,” filed
`Aug. 13, 2002 by Robert K. Rowe et al.; U.S. Prov. Pat.
`Appl. No. 60/403.593, entitled “BIOMETRIC SENSORS
`ON PORTABLE ELECTRONIC DEVICES.” filed Aug. 13,
`2002 by Robert K. Rowe et al.; U.S. Prov. Pat. Appl. No.
`60/403.461, entitled “ULTRA-HIGH-SECURITY IDENTI
`FICATION SYSTEMS AND METHODS,” filed Aug. 13,
`2002 by Robert K. Rowe et al.; U.S. Prov. Pat. Appl. No.
`60/403,449, entitled “MULTIFUNCTION BIOMETRIC
`DEVICES.” filed Aug. 13, 2002 by Robert K. Rowe et al.;
`U.S. patent application Ser. No. 09/415,594, entitled
`“APPARATUS AND METHOD FOR IDENTIFICATION
`OF INDIVIDUALS BY NEAR-INFRARED SPECTRUM,”
`filed Oct. 8, 1999 by Robert K. Rowe et al.; U.S. patent
`application Ser. No. 09/832,534, entitled “APPARATUS
`AND METHOD OF BIOMETRIC IDENTIFICATION
`AND VERIFICATION INDIVIDUALS USING OPTICAL
`SPECTROSCOPY,” filed Apr. 11, 2001 by Robert K. Rowe
`et al., U.S. patent application Ser. No. 09/874,740, entitled
`“APPARATUS AND METHOD OF BIOMETRIC DETER
`MINATION USING SPECIALIZED OPTICAL SPEC
`TROSCOPY SYSTEM," filed Jun. 5, 2001 by Robert K.
`Rowe et al.; and U.S. patent application Ser. No. 10/407,589,
`entitled “METHODS AND SYSTEMS FOR BIOMETRIC
`IDENTIFICATION OF INDIVIDUALS USING LINEAR
`OPTICAL SPECTROSCOPY,” filed Apr. 3, 2003 by Robert
`K. Rowe et al.
`0024 Optical sensors may also be used to make “live
`ness' determinations by identifying whether specific tissue
`Samples are currently alive, even distinguishing from tissue
`that was once alive but is no longer. The physiological
`effects that give rise to spectral features that indicate the
`liveneSS State of a Sample include, but are not limited to,
`blood perfusion, temperature, hydration Status, glucose and
`other analyte levels, and overall State of tissue decay.
`0025. A structure of a typical monolithic sensor that may
`be used for Such varied applications is illustrated Schemati
`cally in FIG.1. The monolithic sensor 100 may include one
`or more light Sources 104 and one or more light detectors
`102. The light sources 104 could comprise LEDs, laser
`diodes, VCSELS, or other solid-state optoelectronic devices.
`The detectors 102 may comprise, for example, Si, PbS,
`PbSe, InSb, InCaAS, MCT, bolometers and micro-bolometer
`arrayS. The wavelength range of the light Sources 104, and
`the wavelength detection range of the light detectorS 102, is
`usually defined by the Specific intended application for the
`
`9
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`

`US 2005/0007582 A1
`
`Jan. 13, 2005
`
`Sensor. For example, biometric identifications might use a
`wavelength range of about 350-1100 nm, alcohol-monitor
`ing applications might use a wavelength range of about
`1.5-2.5 tim, analyte-concentration analysis might use a
`wavelength range that includes identifiable spectral features
`of the particular analyte, etc. Furthermore, it will be appre
`ciated that the arrangement of light Sources 104 and light
`detectors 102 is intended merely to be illustrative and that
`many other configurations may be used in various embodi
`ments, also often depending on the Specific application
`intended for the Sensor. In Some embodiments, only a single
`light source 104 may be used and, in other embodiments,
`only a single light detector 102 may be used.
`0026. The mechanisms by which spurious differences in
`Spectra may arise when performing spectral comparisons,
`particularly when the Spectra being compared were obtained
`under different conditions, is illustrated schematically with
`FIGS. 2A-2C. In FIG. 2A, a reference spectrum taken at a
`first time is shown Schematically as having a wavelength
`distribution, with certain features in the Spectrum being
`manifested at certain wavelengths. FIG. 2B illustrates a
`Spectrum taken at a Second time from the same Subject in
`which a change in intensity of the light Source(s) causes an
`apparent change in Spectral Strength at various wavelengths.
`These changes, however, do not correspond to actual physi
`cal changes in the Subject, but are rather artifacts resulting
`from differences in measurement conditions. FIG. 2C illus
`trates a Spectrum taken at a third time from the Same Subject.
`In this case, the relative spectral Strength over the spectrum
`is substantially identical to that of FIG. 2A, but includes a
`Spectral shift towards higher wavelengths. A comparison of
`Spectral Strength at Specific wavelengths thus shows appar
`ent differences, but these differences are again artifacts of
`the different measurement conditions and do not indicate a
`Spectral difference indicative of, Say, a change in analyte
`concentration or of a difference in identity of the Subject. In
`Some instances, artifacts may arise from a combination of
`Spurious intensity and wavelength-shift changes.
`0027. In some embodiments, the presence of such arti
`facts is avoided by performing optical background measure
`ments with light that has interacted with a reference sample,
`thereby providing a Standard calibration measure for analy
`sis of Spectra obtained from actual Subjects. Such embodi
`ments described herein may be used in applications involv
`ing Sensors for making measurements on biological tissue,
`Such as for making biometric identifications, for analyzing
`analyte concentrations, making liveness determinations, and
`the like. Measurements of the spectral distribution of a
`Subject are associated with one or more of the Stored
`reference spectra that represent the Spectral qualities of the
`Sensor at the time the Subject measurement was made. When
`a comparison is to be made between two spectra for actual
`Subjects, it includes a comparison of the associated reference
`Spectra. If differences exist between the reference spectra, a
`correction is made to the comparison of the Subject spectra.
`Such a correction may comprise modifying one or both of
`the Spectra being compared in accordance with differences
`between the reference Spectra before the comparison is
`made. Alternatively, in Some embodiments a post-compari
`Son correction may be made to a resulting difference Spec
`trum or other measure of the Similarity of the Subject spectra.
`The embodiments described herein may generally be used in
`applications when the Sensor has one or more light Sources
`and one or more light detectors.
`
`0028 2. Reference Sample Structures
`0029. In some embodiments, the reference sample com
`prises a Substantially homogeneous gel that is spectrally
`Similar to a typical living tissue Sample. For example, in
`applications where the living Sample comprises human
`tissue, the homogeneous gel may be configured to have
`Spectral characteristics of a mean human tissue Sample. This
`reference Sample thus provides composite information on
`both light-Source changes and wavelength shifts. Because
`the gel has similar spectral characteristics to the Subject(s),
`there is good reliability in using the information on these
`changes to compensate for Such factors. In one embodiment,
`the gel comprises a polymeric material. The polymeric
`material may be chosen So that electromagnetic absorption,
`reflection, and Scattering characteristics are similar to Such
`characteristics in human tissue, at least over the wavelengths
`used to obtain the Spectra. In another embodiment, the gel
`comprises Specific chemical Substances found in the relevant
`human tissue. For example, in the case where the human
`tissue comprises Skin, the gel may comprise collagen, hemo
`globin and water.
`0030. In other embodiments, a plurality of spectrally
`heterogeneous Samples are used to provide information both
`about light-source intensity changes and about wavelength
`changes. These embodiments are Suitable when used with a
`sensor 100 that has one or more light sources 104 and a
`plurality of light detectors 102. In one such embodiment,
`illustrated in FIG. 3, the spectrally heterogeneous reference
`Sample 108 comprises a plurality of Spectrally homogeneous
`materials 110. Merely by way of example, suitable homo
`geneous materials include diffuse reflecting materials, gels,
`pastes, and blasted aluminum.
`0031 Merely for illustrative purposes, FIG.3 shows the
`Spectrally homogeneous materials 110 in a particular geom
`etry, namely with equal-thickness horizontal sheets of mate
`rial having planes parallel with a plane containing the light
`detectors 102. It will be appreciated, however, that the
`invention is not limited to Such a geometry and that other
`geometries may be used in alternative embodiments. For
`example, the sheets of material could have different thick
`nesses. The sheets of material could have Surface planes
`parallel with a different plane, Such as with a vertical plane
`orthogonal to the plane containing the light detectorS 102, or
`parallel with a plane inclined at a non-right-angle to the
`plane containing the light detectors 102. In another embodi
`ment, the sheets of material could have varying thickness So
`that their Surfaces do not define planes at all. To have a
`Spectrally heterogeneous reference Sample 108, at least two
`of the spectrally homogeneous materials 110 have different
`Spectral characteristics, but Some or all of the remaining
`homogeneous materials may have spectral characteristics in
`common. The different spectrally homogeneous areas 110
`may interface directly in Some embodiments, although in
`other embodiments they are separated; Such separations may
`be provided through the use of intermediate optically opaque
`or optically transparent materials at certain wavelengths.
`0032. The exemplary geometrical configuration of homo
`geneous materials 110 shown in FIG. 3 is an example of a
`configuration in which the distance between a specific light
`Source 102 and a specific light detector 104 allow light to
`travel to a separate area of homogeneous material 110. In
`this way, the resulting spectral-correction information when
`
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`

`US 2005/0007582 A1
`
`Jan. 13, 2005
`
`applied to actual Spectral data includes information for
`Specific Source-detector combinations.
`0033. In a further set of embodiments, multiple reference
`Samples are used. These embodiments may be used in
`applications involving Sensors having one or more light
`Sources and one or more light detectors. The multiple
`reference Samples may all be spectrally homogeneous, may
`all be spectrally heterogeneous, or may comprise a combi
`nation of distinct Spectrally homogeneous and Spectrally
`heterogeneous Samples. AS an example, one of the reference
`Samples may be Substantially Spectrally flat So that it is
`Sensitive to intensity changes but insensitive to wavelength
`changes. Another of the reference Samples is Sensitive both
`to intensity and wavelength changes. AS Such, comparisons
`between spectra that include both intensity and wavelength
`differences may be performed by using the following cor
`rection methodology. Comparisons between the Spectrally
`flat and spectrally nonflat reference samples are used to
`identify which changes in the Spectrally nonflat Sample
`result Solely from wavelength changes. The combination of
`this wavelength-change information and the intensity
`change information from the Spectrally flat Sample is then
`used to correct the Subject-Sample comparison for both
`intensity and wavelength changes. In addition, another of the
`multiple reference Samples might be optically black. The
`measurements that result from Such a reference Sample
`provide further information about effects Such as electronic
`drift and optical light leakage that may be affecting the
`measurements of actual Subjects. This information might be
`used alone or in conjunction with one or more spectral
`reflectors to correct the Subject-sample comparison.
`0034. The correction of spectral analyses may be facili
`tated in Some embodiments by using a plurality of reference
`Samples that are Sensitive to both intensity and wavelength
`changes. This may be particularly useful where the Specific
`characteristics of the intensity- and wavelength-dependent
`behaviors differ among the reference Samples. In particular,
`Such an embodiment permits both intensity and wavelength
`changes to be assessed by combining information from
`measurements collected on each of the plurality of Samples.
`0035) In one such embodiment, multiple samples that
`comprise layers of optical filters are used. For example, in
`one Set of filters, the filter closest to the Sensor is broadest,
`allowing most of the relevant wavelengths to pass through.
`Each Subsequent layer, as distance from the Sensor increases,
`is increasingly restrictive, allowing a progressively Smaller
`Subset of the relevant wavelengths to pass through. The filter
`closest to the Sensor thus corresponds to the Spectrally flat
`Sample, with the remaining Samples corresponding to
`Samples Sensitive to both intensity and wavelength changes,
`and having different Such characteristics. In another
`example, the passband or transmission edge of the filters is
`progressively shifted relative to the others for each filter in
`the Stack.
`0036). In still a further set of embodiments, the reference
`Sample comprises a spectrally dispersive optical element,
`Such as grating, prism, grism, or other Spectrally dispersive
`element. The optical character of the dispersive element thus
`Simultaneously provides information about light-Source
`intensity and about wavelength changes, effectively provid
`ing information Similar to that provided by a grating Spec
`trometer. These embodiments may be used in applications
`
`involving Sensors having one or more light Sources and
`having a plurality of light detectors.
`0037. In one specific embodiment, the dispersive element
`is combined with a monolithic Sensor that includes one or
`more light Sources and a plurality of light detectors. Illumi
`nation of one of the light Sources onto the dispersive element
`acts to provide angular separation of the component wave
`lengths. Reflected light collected by the detectors then gives
`information both on the wavelengths of the light reflected
`and on the intensity of the light at each Such wavelength.
`0038. In a further set of embodiments, the reference
`Sample comprises a wavelength-dependent filter, which is
`used to provide information about both light-source intensity
`and about wavelength changes. Such embodiments are Suit
`able for applications in which the Sensor comprises one or
`more light Sources and a plurality of light detectors. One
`Such embodiment is illustrated in FIG. 4 where the wave
`length-dependent filter also comprises an angular-dependent
`profile to allow tracking of light intensity at Specific wave
`lengths. In particular, in this embodiment the reference
`sample 120 includes one or more light sources 104 and a
`plurality of light detectors 102. Light from the light
`source(s) 104 is reflected from a diffuse reflecting surface
`124, which may have a Surface plane parallel to a plane
`containing the plurality of light detectors 102. The wave
`length-dependent filter 122 is disposed So that it is encoun
`tered by light from the light source(s) 104 reflected from the
`reflecting Surface 124. The geometrical arrangement causes
`light received by different light detectors 102 to be incident
`on the wavelength-dependent filter 122 at different angles.
`The combination of wavelength- and angular-dependent
`profiles of the filter 122 thus permit the light intensity to be
`tracked for changes at Specific wavelengths. In another
`embodiment, the filter may be a linear variable filter or other
`Similar filter where the wavelength characteristics vary by
`position. In different embodiments, the filter may comprise
`a quarter-wave variable filter, an edge filter, a bandpass filter,
`a band-reject filter, etc.
`0039) 3. Reference-Sample Interfaces
`0040. There are a variety of ways in which the reference
`Samples described above may be interfaced with a Sensor in
`different embodiments as data are collected. For example, in
`one Set of embodiments, an external user-controlled device
`is used to collect periodic reference measurements. The
`external device may be structured Such that it comprises a
`reference Sample, Such as described above, disposed to be
`Substantially adjacent to the Sensor when presented to the
`Sensor. The external device may have Supplementary func
`tionality in Some embodiments, permitting it to be used as a
`cover or cap Secured to the Sensor when the Sensor is not in
`use, but this is not required. In other embodiments, the
`external device is used exclusively for the collection of
`reference measurements and is presented by the user only
`when a reference measurement is to be collected.
`0041. In other embodiments, an external user-controlled
`device may instead have a structure that permits dispensing
`a reference Sample, Such as described above, onto the Sensor.
`Such a configuration has the advantage that the user-con
`trolled device may be designed to be disposable. In Some
`embodiments, the reference Samples comprised by the exter
`nal device may be discrete reference Samples, Such as in the
`form of wafers, membranes, or thin films that are dispensed
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`US 2005/0007582 A1
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`Jan. 13, 2005
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`from the device onto the sensor by the user. In other
`embodiments, the reference samples are comprised by a
`volume of dispensable reference material, Such as a gel or
`paste that the user spreads onto the Sensor with the external
`device.
`0042 Specific examples of external devices and how they
`may be used with monolithic optical Sensors are illustrated
`for some embodiments in FIGS. 5A-5H. FIG. 5A provides
`a top view of a sensor 100' having a somewhat different
`geometrical configuration from the Sensor shown in FIG.
`1A. In