WO2015030833A1 - Spectromètre à multiples guides d'ondes - Google Patents

Spectromètre à multiples guides d'ondes Download PDF

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WO2015030833A1
WO2015030833A1 PCT/US2013/057749 US2013057749W WO2015030833A1 WO 2015030833 A1 WO2015030833 A1 WO 2015030833A1 US 2013057749 W US2013057749 W US 2013057749W WO 2015030833 A1 WO2015030833 A1 WO 2015030833A1
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waveguide
waveguides
light
sample
measurement
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PANDATA RESEARCH LLC
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/55—Specular reflectivity
    • G01N21/552—Attenuated total reflection
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
    • G01J3/02—Details
    • G01J3/0205—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N2021/3129—Determining multicomponents by multiwavelength light
    • G01N2021/3133—Determining multicomponents by multiwavelength light with selection of wavelengths before the sample
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N2021/3129—Determining multicomponents by multiwavelength light
    • G01N2021/3137—Determining multicomponents by multiwavelength light with selection of wavelengths after the sample
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/314—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry with comparison of measurements at specific and non-specific wavelengths
    • G01N2021/3166—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry with comparison of measurements at specific and non-specific wavelengths using separate detectors and filters
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/314—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry with comparison of measurements at specific and non-specific wavelengths
    • G01N2021/317—Special constructive features
    • G01N2021/3177—Use of spatially separated filters in simultaneous way
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light

Definitions

  • the present invention relates generally to methods and apparatus for spectroscopic evaluation of a sample that include m ultiple waveguides; and more particularly wherein each waveguide is configured to direct light onto the sample at respective incident angle.
  • optical techniques are known for characterizing a sample, several of which involve launching a beam of light at the sample under a particular set of conditions, and measuring light reflected from the sample. Some such optical techniques tailor the set of conditions toward measuring a particular structure or characteristic. For instance, ellipsometry makes use of polarization state to perform measurements, and is particularly useful for measuring the refractive indices and the layer thicknesses for thin film structures. As another example, interferometry makes use of coherent light interference to perform measurements, and is particularly useful for measuring the physical profile of the surface of a sample.
  • a spectrometer In order to detect the composition of a sample, or the presence of a particular constituent in the composition of a sample, or to measure a concentration of such a particular constituent in a sample, a spectrometer may be used. I n one commonly known configuration of a spectrometer designed for detection of a selected constituent, power reflectivity is measured from the sample at a plurality of different wavelengths, at least one of which is sensitive to the presence of the selected constituent, and at least another of which is not sensitive to such constituent. The ratio of the measured reflectivity between at least two such wavelengths yields information about the presence and/or concentration of the constituent. In other configurations, the power reflectivity may be compared to a reference standard to determine the presence or concentration of the constituent.
  • a measurement of a particular analyte in a human or animal bloodstream in tissue typically requires that the light penetrate into the sample at least a threshold distance, interact with the analyte in the blood, return to the surface, and be collected by a measurement apparatus.
  • the light employed for such detection/measurement is in the infrared (IR) portion of the spectrum.
  • IR infrared
  • Attenuated total reflection (ATR) spectroscopy is especially well-suited for many forms of sample analysis, and methods have been proposed for implementing operational processes to obtain measurements at varying depths below the surface of a sample.
  • ATR Attenuated total reflection
  • a beam of light is propagated to a boundary between an incident medium, such as a waveguide having a waveguide refractive index, and a sample medium to be measured, such as the above-referenced tissue having a refractive index lower than the waveguide refractive index.
  • a relative portion of the light is reflected at the boundary, and a relative portion transmits into the sample medium.
  • the relative amounts of reflected and transmitted light depend on the angle at which the light strikes the boundary, which is referred to as an incident angle.
  • a critical angle which is a function of the refractive indices of the incident medium and the sample medium.
  • the evanescent wave may interact with the sample medium and may be absorbed by the sample medium. This absorption reduces the fraction of reflected light from the value of 100%.
  • the depth at which the evanescent wave penetrates into the sample varies with incident angle, and is typically greatest at incident angles at and near the critical angle.
  • the range of angles at and near the critical angle is referred to as the "peri-critical" region. Use of the peri-critical region is especially well- suited for measurements to be made at particular depths below the surface of the sample.
  • the reflectance from the sample medium is measured at multiple angles of incidence, typically but not necessarily including the peri-critical region.
  • these measurement schemes rely on movement of one or more optical elements in the optical path.
  • the incident angles may be varied by rotating and/or translating one or more mirrors in the optical path.
  • measurements are typically taken between the movements, so that the measurements are taken serially, one after another. While such systems offer a maximum range of incremental angles, not all applications require that degree of flexibility.
  • This disclosure addresses methods and apparatus for measuring optical properties of a sample at multiple angles of incidence, which are particularly well adapted for use with ATR spectroscopy, though their applicability is not limited to such use.
  • multiple incident beams are directed onto an interface between multiple waveguides and a sample.
  • the amount of optical power reflected from the interface is measured.
  • the light is in the infrared (IR) portion of the electromagnetic spectrum, although other portions of the spectrum may be used, including the various portions of the IR band, such as near-IR, mid-IR and far-IR, as well as the visible light and the ultraviolet (UV) wavelength bands.
  • measurements at multiple incident angles are taken, where each measurement is made through use of a respective waveguide configured to direct light onto the sample at a corresponding incident angle.
  • at least two of incident angles are different.
  • at least two of the waveguides have different internal geometries that direct light onto the sample at different incident angles.
  • Figure 1 depicts a side-view schematic representation of an example reflectance spectrometer system, with an example waveguide.
  • Figure 2 is a side-view schematic representation of an alternative spectrometer system.
  • Figure 3 is a side-view schematic representation of another alternative spectrometer system.
  • Figure 4 is a cutaway perspective depiction showing a spectrometer housing and processing unit, with an example arrangement of waveguides, light sources, spectral filters, and detectors.
  • Figure 5 is a top-view schematic depiction of an alternative arrangement of waveguides.
  • Figure 6 is a top-view schematic depiction of another alternative arrangement of waveguides.
  • Figure 7 is a top-view schematic depiction of another alternative arrangement of waveguides.
  • Figure 8 is a top-view schematic depiction of another alternative arrangement of waveguides.
  • Figure 9 is a flowchart of an example measurement process.
  • references to "one example” or “an example” mean that the feature being referred to is, or may be, included in at least one example of the invention.
  • the methods and apparatus disclosed herein are particularly well suited for use with attenuated total reflection (ATR) spectroscopy.
  • ATR attenuated total reflection
  • the reflectance is measured in the angular region at and near the critical angle. This angular region is sometimes referred to as being "peri-critical.”
  • peri-critical region the evanescent wave penetrates beyond the surface of the material, and at the critical angle the wave will extend to a greater depth into the sample material than at many other incident angles.
  • ATR through use of angles within this peri- critical region is adapted to perform measurements beneath the sample surface.
  • a stratified sample is human or animal tissue, which has different levels of composition beneath the epidermis and before reaching a vascularized region substantially below the epidermis layers at the sample surface.
  • ATR through angles within this peri-critical region may be used to measure these different levels and potentially also the vascularized regions at which blood analytes can be sensed.
  • Figure 1 shows an example reflectance spectrometer 100, which is suitable for performing reflectance measurements on a sample 118 through use of ATR spectroscopy.
  • the example spectrometer 100 includes a waveguide 104, and a plurality of optical elements associated with the production, direction, and detection of light in the
  • the processing unit 120 which can direct electrical power to the optical element(s) as needed, and can receive and interpret electrical signals produced by the light-sensing element(s).
  • the processing unit 120 (which may be a conventional "computer” (in any of a variety of known forms) will provides a suitable user interface and can provide and control storage and retrieval of data.
  • the processing unit 120 will include one or more processors in combination with additional hardware as needed (volatile and/or non-volatile memory; communication ports; I/O device(s) and ports; etc.) to provide the control functionality as described herein.
  • An example processing unit 120 can serve to both control functions of the measurement system and to receive and process measurements from the detectors from the various waveguides; and to perform such processing as is needed to determine the presence and/or concentration of constituents in the sample.
  • one or more a non-volatile, machine-readable storage devices i.e., a memory device (such as DRAM, FLASH, SRAM, or any other known form), a hard drive, or other mechanical, electronic, magnetic, or optical storage mechanism, etc.
  • these functions may be implemented by separate processing units, as desired, and additional functions may be performed by such one or more processing units in response to similarly stored instructions.
  • Spectrometer 100 depicts an example geometry for a single waveguide 104, including various angles and dimensions that may be varied or scaled from waveguide to waveguide within a single device.
  • a single device can include multiple waveguides, where at least two of the waveguides are scaled differently so that they deliver light onto the sample interface at different incident angles.
  • the optical path P includes a reflection off the measurement face 110 at an incident angle of ⁇ .
  • the sample interface includes at least a portion of each measurement face from the multiple waveguides within the device.
  • the light is collimated along the optical path P.
  • an x, y, z coordinate system is established around the measurement face 110 of the waveguide 104, so that the measurement face 110 is within the x-y plane, and a longitudinal axis of the waveguide 104 is parallel to the y-axis.
  • the incident and exiting beams, which direct light into and out of the waveguide 104 through a rear face 108 of the waveguide 104 can, in many examples, be cooperatively arranged with waveguide 104 to propagate along the +z-axis and the -z-axis, respectively.
  • the light source 102 produces a collimated incident beam, which in the depicted example is directed parallel to the +z-axis.
  • the incident beam refracts through a back face 108 of the waveguide 104 and propagates as the internal beam inside the waveguide 104.
  • normal incidence is intended to provide angular relationships that are satisfied to within typical manufacturing and alignment tolerances. Angular descriptions used throughout this document also include typical manufacturing and alignment tolerances.
  • near-normal incidence is intended to include a deliberate misalignment between a beam and a surface normal, typically on the order of +/- 1 degree or less, which in some cases may reduce undesirable interference fringing effects in the beam. Use of such near-normal incidence is well-known to those skilled in the art.
  • the transmission through the back face 108 of the waveguide 104 will preferably be as complete (i.e., as close to 100%) as is practical.
  • An anti-reflection coating applied to the back face 108 of the waveguide 104 in an area that is expected to fully subtend the incident beam (for example, close to the light source 102), may eliminate reflections at the surface, or reduce the reflections down to a sufficiently low level.
  • the anti-reflection coating is intended to work at normal incidence or near-normal incidence, at either a single wavelength or a plurality of wavelengths.
  • a simple example of anti-reflection coating is a single, quarter-wave-thick layer, having a refractive index equal to the square root of the product of the refractive index of waveguide 3 and the refractive index of air.
  • a quarter-wave anti-reflection layer should have a refractive index of about 1.55.
  • V-coat a two-layer coating known as a "V-coat,” which can achieve especially good performance at a single wavelength, at the expense of typically worse performance than the single quarter-wave layer at wavelengths far from the single wavelength.
  • W-coat a three-layer coating known as a "W-coat” or a “broadband AR coating,” which can achieve a very low reflection at two distinct wavelengths.
  • W-coat a three-layer coating known as a "W-coat” or a “broadband AR coating”
  • these and other anti- reflection coatings are well-known to those skilled in the art, and may be readily designed using common software without undue experimentation.
  • Other suitable anti-reflection coatings may be used, or the back face 108 may remain uncoated in the region that receives the incident beam (i.e., near the light source 102).
  • a first inclined reflective face 106 receives the internal beam from the back face 108.
  • the first inclined reflective face 106 has a surface normal SNi 0 6 that lies in the y-z plane, and is angled away from the z-axis by ( ⁇ / 2).
  • the first inclined reflective face 106 is directly adjacent to the measurement face 110 on the waveguide, with the first inclined reflective face 106 adjoining the measurement face 110 along a line that extends along the x-axis.
  • the angle formed in air between the first inclined reflective face 106 and the measurement face 110 is 180 degrees plus ( ⁇ / 2).
  • the incident angle at the first inclined reflective face 106 (with respect to the surface normal SNi 0 6) is ( ⁇ / 2), which is half the incident angle ⁇ at the measurement face 110.
  • Light reflects off the first inclined reflective face 106 with an exit angle (with respect to the surface normal SNi 0 6) of ( ⁇ / 2).
  • the reflection off the first inclined reflective face 106 is preferred to be as complete (i.e., as close to 100%) as is practical.
  • a high-reflectance coating applied to the first inclined reflective face 106 of the waveguide 104 in an area that is expected to fully subtend the internal beam, may increase reflections up to a sufficiently high level.
  • the high- reflectance coating is intended to work at an incident angle of ( ⁇ / 2), at either a single wavelength or a plurality of wavelengths.
  • An example of a high-reflectance coating may be a single metallic layer, such as of gold.
  • Another example of a high-reflectance coating may be a thin-film structure having alternating layers of dielectric materials with relatively high and relatively low refractive indices.
  • these and other high-reflection coatings are well-known to those skilled in the art, and may be readily designed using common software without undue experimentation.
  • Other suitable high-reflection coatings may be used, or the first inclined reflective face 106 may remain uncoated in the region that receives the internal beam.
  • the back face 108 receives the light reflected from the first inclined reflective face 106, and reflects it toward the measurement face 110.
  • the reflection off the back face 108 is at a high enough incident angle so that the internal beam undergoes total internal reflection at the back face 108.
  • Portions near the longitudinal ends of the back face 108 may optionally be anti-reflection coated for entry and exit of the beam though the back face 108 of the waveguide 104; such anti-reflection coatings are not needed in the central portion of the back face 108 away from the longitudinal ends.
  • the measurement face 110 which is parallel to the back face 108, receives the light reflected from the back face 108.
  • the measurement face 110 lies in the x-y plane and has a surface normal SN 0 that lies along the z-axis.
  • the incident angle at the measurement face 110 (with respect to the surface normal SNn 0 ) is ⁇ .
  • ⁇ will be at or near the critical angle formed between the waveguide 104, with refractive index n W a Ve guide, and the sample 118, with refractive index n sam pie-
  • the critical angle is given by the numerical value of sin 1 (n samp i e / n waveg uide)-
  • the reflectivity from the measurement face 110 will be close to 100%, with the drop from 100% being caused by absorption of a transmitted evanescent wave by the sample 118.
  • Light reflects off the measurement face 110 with an exit angle (with respect to the surface normal SNn 0 ) of ⁇ .
  • the back face 108 receives the light reflected from the measurement face 110, and again reflects it through total internal reflection.
  • the back face 108 may again be uncoated in the area that is expected to fully subtend the internal beam at this reflection.
  • a second inclined reflective face 112 then receives the internal beam reflected from the back face 108.
  • the second inclined reflective face 112 has a surface normal SN 2 that lies in the y-z plane, and is angled away from the z-axis by ( ⁇ / 2) but in the opposite direction as the first inclined reflective face 106.
  • the second inclined reflective face 112 is directly adjacent to the measurement face 110 on the waveguide, with the second inclined reflective face 112 adjoining the measurement face 110 along a line that extends along the x-axis.
  • the angle formed in air between the second inclined reflective face 112 and the measurement face 110 is 180 degrees plus ( ⁇ / 2).
  • the incident angle at the second inclined reflective face 112 (with respect to the surface normal SN112) is ( ⁇ / 2).
  • Light reflects off the second inclined reflective face 112 with an exit angle (with respect to the surface normal SNi 0 6) of ( ⁇ / 2).
  • the reflected light from the second inclined reflective face 112 travels along the -z-axis.
  • the second inclined reflective face 112 may have a high-reflectance coating, similar in function and construction to that on the first inclined reflective face 106.
  • the back face 108 of the waveguide 104 receives the light from the second inclined reflective face 112 at normal incidence or near-normal incidence.
  • the back face 108 may have an anti-reflection coating in an area that is expected to fully subtend the internal beam received from the second inclined reflective face 112.
  • Such an anti-reflection coating may be similar in function and construction to that on the back face 108 face in the area adjacent to the light source 102.
  • the internal beam strikes the back face 108, refracts through the back face 108 and forms the exiting beam, which propagates away from the waveguide 104 along the -z- axis.
  • the exiting beam passes through a spectral filter 114 and strikes a detector 116, where it is converted into an electrical signal for communication to a processing unit 120.
  • the waveguide has a thickness denoted by T, which is the separation along the z-axis between the measurement face 110 and the back face 108.
  • T a thickness denoted by T
  • a rough approximation of the center-to-center spacing along the y-axis between the incident and exiting beams is (4T tan ⁇ ), where ⁇ is the incident angle at the measurement face 110.
  • Such an approximation is helpful for estimating component sizes for a variety of operating conditions.
  • the waveguide 104 will be configured to direct the beam sufficiently close to the critical angle that the evanescent wave extends beneath the surface of the sample to a desired degree.
  • the waveguide 104 should have a refractive index close to, but greater than that of the sample 118.
  • the refractive index is typically between about 1.15 and about 1.5 over a wide range of wavelengths, from about 0.2 ⁇ to about 11 ⁇ . At wavelengths in the mid-infrared spectrum (about 3.5 ⁇ to about 13 ⁇ ), a reasonable approximation for the refractive index of water, and therefore also of tissue, is about 1.33.
  • suitable materials for the waveguide 104 can include: zinc selenide (ZnSe), having a refractive index of about 2.43 at wavelength of 5 ⁇ ; germanium (Ge), having a refractive index of about 4.0 at a wavelength of 5 ⁇ ; CVD diamond, having a refractive index of 2.38 at a wavelength of 10 ⁇ ; or polymethylpentene (PMP), having a refractive index of 1.46 at a wavelength of 5 ⁇ .
  • ZnSe zinc selenide
  • Ge germanium
  • CVD diamond having a refractive index of 2.38 at a wavelength of 10 ⁇
  • PMP polymethylpentene
  • a good approximation for the length (along the y-axis) of a waveguide having thickness T (along the z-axis) is (4T tan ⁇ ).
  • the waveguide length may be scaled up or down with the thickness T.
  • An example thickness of 1 mm is chosen for the examples below, with the understanding that other thicknesses may also be used.
  • the value of (4T tan ⁇ ) is used only as a rough estimate of size, with the assumption that during the actual design phase of the waveguide, proper raytracing simulation may be done to more properly account for the waveguide size and shape.
  • the critical angle is sin 1 (1.33 / 2.4), or about 34 degrees.
  • one envisioned configuration of a multiple waveguide spectrometer has five waveguides configured to direct a beam to the sample at angles in increments of 4 degrees.
  • One such example would increment from the critical angle, with incident angles ( ⁇ ) of 34 degrees, 38 degrees, 42 degrees, 46 degrees, and 50 degrees; and such a configuration would result in waveguides with estimated lengths of 2.7 mm, 3.1 mm, 3.6 mm, 4.1 mm, and 4.8 mm, respectively.
  • the critical angle is sin 1 (1.33 / 1.59), or about 57 degrees.
  • An example with five waveguides, and incident angles ( ⁇ ) of 57 degrees, 61 degrees, 65 degrees, 69 degrees, and 73 degrees would result in waveguides having estimated lengths of 6.2 mm, 7.2 mm, 8.6 mm, 10.4 mm, and 13.1 mm, respectively.
  • the critical angle is sin 1 (1.33 / 2.0), or about 42 degrees.
  • An example with five waveguides, and incident angles ( ⁇ ) of 42 degrees, 46 degrees, 50 degrees, 54 degrees, and 58 degrees would result in waveguides having estimated lengths of 3.6 mm, 4.1 mm, 4.8 mm, 5.5 mm, and 6.4 mm, respectively.
  • an example light source 102 is a broadband infrared source. Such a broadband source produces a range of wavelengths, and relies on one or more spectral filters downstream to select one or more wavelengths of interest.
  • broadband infrared sources in which a current is passed through a thin film, which heats the thin film to a relatively high temperature.
  • the heated thin film emits light as if it were a blackbody light source with a temperature equal to that of the thin film.
  • the emitted blackbody radiation extends over a relatively wide range of wavelengths, so that filtering the output can produce a useable amount of light over a relatively wide range of wavelengths.
  • these thin film emitters produce significantly more heat than comparable laser diodes or LEDs, and heat sinking may be required when using the thin film emitters in a relatively small mechanical package.
  • An example of a commercially available thin film broadband infrared source is sold by Scitec Instruments Ltd.
  • the IR- 43 accepts a voltage of 14 volts, either AC or DC, generates a current of 90 mA, and uses an electrical power of 1.3 watts.
  • the active area is square with dimensions of 1.5 mm on a side.
  • the emissivity is 0.80, meaning that the light output, for each wavelength over the full emission spectrum, is 80% of that of a blackbody emitter.
  • the temperature achieved by running at 90 mA is 600 degrees C, or about 875 K.
  • the film is expected to last over three years running at 600 degrees C.
  • the thin film of the IR-43 is packaged as free standing on a TO-5 header. With proper heat dissipation, the thin film may alternatively be packaged on a suitable chip as needed. Scitec also sells suitable reflectors with a parabolic shape that can collimate the output of the thin film source.
  • the wavelength at which the radiant intensity peaks is 3.32 ⁇ ; a significant amount of light is emitted on either side of this peak, so that the light output from the thin film emitter may be considered to be relatively broadband.
  • particular thin film emitters may be somewhat tunable, by varying the amount of current flowing through the thin film. The more current flowing through the film, the higher the temperature of the film, and the lower the peak wavelength of the broadband output.
  • the light source 102 is intended to include both the light producing element, such as thin film broadband infrared emitter, and a collimating element, such as a lens or a parabolic collimating mirror that collimates the light from the light emitting element.
  • the output from the light source 102 is a collimated, broadband beam.
  • the optical path P includes a spectral filter 114 that blocks all but a relatively narrow band of wavelengths.
  • the narrow band of transmitted wavelengths may be referred to as a "pass band,” which is commonly specified by a center wavelength and a bandwidth.
  • the spectral filter 114 is located in the optical path P between the waveguide 104 and the detector 116, as is shown in Figure 1.
  • a spectral filter 206 is located in the optical path P between the light source 202 and the waveguide 204, rather than between the waveguide 204 and the detector 208.
  • the function of the spectral filter 114; 206 is the same, which is to block light with wavelengths outside a predetermined pass band.
  • Such spectral filters 114; 206 may be known as notch filters, and are well-known to those skilled in the field of optics.
  • FIG. 3 The system of Figure 3 includes two spectral filters 306, 308, with one spectral filter 306 disposed in the optical path P between the light source 302 and the waveguide 304, and one spectral filter 308 disposed between the waveguide 304 and the detector 310.
  • the spectral filters 306, 308 are movable into and out of the optical path P, and are controlled by processing unit 312, so that only one spectral filter 306, 308 appears in the optical path P at a given time.
  • a first measurement is performed at a first wavelength
  • a second measurement is performed at a second wavelength after the first measurement.
  • one of the spectral filters 306 is present in the optical path P, as is shown in Figure 4, while the other spectral filter 308 is located outside the optical path.
  • the measurement at the first wavelength is taken, using the configuration of Figure 3.
  • the processing unit 320 moves spectral filter 306 out of the optical path P and moves spectral filter 308 into the optical path P.
  • the measurement at the second wavelength is then taken.
  • the spectral filters do not appreciably alter the location or direction of the optical path P.
  • the optical path remains in essentially the same location and the same direction if the spectral filters are inserted into or removed from the optical path P. (See, for example, the portion of the path passing through the dashed outline of spectral filter 308.)
  • the filters may be located at any suitable location in the incident beam (i.e., between the light source and the waveguide) and/or in the exiting beam (i.e., between the waveguide and the detector).
  • the light source may use a relatively narrow-band light producing element, such as a laser diode or a light-emitting diode (LED).
  • a relatively narrow-band light producing element such as a laser diode or a light-emitting diode (LED).
  • the output from the laser diode or LED may be collimated with a small lens and/or mirror next to the laser diode or LED. This option may omit all the spectral filters, since the wavelength of the light is determined by the relatively narrow spectrum of the source.
  • detectors 116; 208; 310 there are various types of detectors that are suitable for the mid-infrared spectrum. Suitable types include thermopiles, LiTa0 3 pyroelectrics, and PZT pyroelectrics. These detectors are commercially available in a range of sizes and configurations, and may be readily adapted to particular packaging aspects of miniaturization.
  • an example system includes multiple waveguides, each of which produces a respective measurement of a sample.
  • Each waveguide has a corresponding measurement face thereon.
  • the measurement faces of the waveguides are physically arranged so that a sample interface presents at least a portion of the sample to measurement faces of all the waveguides.
  • Each waveguide directs light onto its respective measurement face at a respective incident angle and collects light reflected from the respective measurement face.
  • At least two of the waveguides direct light onto the respective measurement faces at different incident angles.
  • each waveguide directs light onto the sample at a unique incident angle.
  • measurements are performed at discrete, predefined incident angles.
  • An example arrangement of waveguides is shown in Figure 4.
  • An example spectrometer 400 includes a housing 416, shown in a cutaway view, in communication with a processing unit 420.
  • the example spectrometer includes five waveguides 402A-E, each with a corresponding measurement face 404A-E.
  • each waveguide 402A-E has a corresponding light source 408A-E that directs light through a respective spectral filter
  • the light source may be bonded (such as through adhesive optically transparent at the wavelengths of interest) directly to the waveguide. Or, where a spectral filter is present, the light source may be attached to the filter; which is in turn bonded to the waveguide.
  • a sample interface 406 is a region configured to contact a sample (not shown) to be measured.
  • the sample interface 406 may be an area that spans across the measurement faces 404A-E of several or all of the waveguides 402A-E.
  • the sample interface 406 may be bounded by a mask or an opening on a face 416 of the housing 414, so that inside the opening, contact may be obtained with the
  • the sample interface 406 includes a physical surface that spans across the waveguides 402A-E, such as a cover glass. In other examples, the sample interface 406 comprises portions of the individual waveguides 402A-E, with no dedicated cover glass or transparent sheet that extends among the individual waveguides 402A-E.
  • the sample interface 406 may be planar, or may be shaped or contoured to a desired shape, for instance, to facilitate optimal contact with a particular body part. For instance, if the sample interface 406 is intended to contact a wrist of a patient, the sample interface 406 may have a concave, generally cylindrical shape to improve contact with the patient's wrist. Other suitable shapes are contemplated.
  • a sample to be measured may be placed into contact with the sample interface 406, thereby exposing the sample simultaneously to the measurement faces 404A-E of the waveguides 402A-E.
  • the waveguides 402A-E may all perform their respective measurements simultaneously, or in succession, thereby producing
  • the measurement process may be relatively rapid, since the waveguides may take their respective measurements in parallel.
  • This example spectrometer 400 includes five waveguides 402A-E. In other examples, more or fewer than five waveguides may be used. As will be apparent to those skilled in the art, the precise number of waveguides used will typically be dependent on the intended use of the system and the required accuracy of the system, which may, in some cases, be balanced against the size, complexity, and cost of the system.
  • Figure 5 shows a top view of measurement faces similar to those depicted in
  • the measurement faces 504A-E are parallel and are directly adjacent to each other. In this example, there is little or no space between adjacent measurement faces 504A-E; in other examples, some of the adjacent measurement faces 504A-E may have some space between them.
  • the waveguides are arranged to have a longitudinal edge of each measurement face (at the intersection of the inclined reflection face with the measurement face for each waveguide), aligned with one another along a line 502, and each waveguide extends in the same direction from this line 502. In other examples, the waveguides may have their opposite longitudinal edges aligned along a line, may have their longitudinal centers along a line, or may be irregularly arranged.
  • the depicted configuration provides a maximum width of a sample area, as the measurement face 504A of the shortest waveguide defines the shortest dimension for the sample interface, and that dimension is aligned through all waveguides.
  • the relative positions might be adjusted, such as by having a longitudinal end of each waveguide aligned, though that may lead to a reduced or non-contiguous sample area across all waveguides depending on the specific conformation of each waveguide.
  • Figure 6 shows an example sample interface 606 extending across five
  • measurement faces 604A-E The measurement faces 604A-E are arranged roughly beside one another, but with increasing angulation with each measurement face 604A-E. As a result of this angulation, there is space between the measurement faces in wedge-shaped portions.
  • the example sample interface 606 is an elongated rectangle that extends across portions of the measurement faces 604A-E, and also include the wedge-shaped portions between measurement faces 604A-E. Such a configuration may be useful if it is desired to utilize more of the largest measurement face 604E, as compared with some other configurations.
  • the increasingly angulated geometry of Figure 6 is merely one example; other suitable geometries may also be used.
  • the waveguides are configured to share the functions of one or more optical components, such as a light source or a detector. Such an arrangement may reduce the complexity and the number of optical components in the device, which is desirable. Such an arrangement may also allow the housing to be made smaller, which may be desirable for particular applications.
  • One potential advantage to sharing light sources among waveguides is that fewer number of broadband light sources may be required, which may ease the burden of heat dissipation from the housing.
  • Another potential advantage to sharing light sources is that only a single, central set of spectral filters is required for each light source. It will be understood that use of a central set of one or more spectral filters may eliminates the need for including spectral filters with each waveguide, and may simplify the switching mechanism in the housing. If the detectors are shared, the signals from the waveguides may use time-division multiplexing to collate a particular measured reflectivity with the corresponding waveguide.
  • each waveguide has a particular longitudinal end in close proximity to the corresponding longitudinal ends of the other waveguides.
  • This close-proximity configuration 700 is shown in Figure 7.
  • the example configuration 700 has each waveguide 704A-E extending radially from a common center point, thereby providing a sample interface 706 of an annular configuration.
  • This configuration also places the inner end all the waveguides in close relation to one another such that each waveguide may receive light from a single broadband source assembly 708.
  • the waveguides may extend longitudinally inward past the inner portion of the annulus, so that the waveguides may all have one longitudinal end in close proximity to those of the other waveguides.
  • the annular geometry of the sample interface 706 and the radial orientations of the measurement faces 704A-E of Figure 7 are merely one example; other suitable geometries may also be used.
  • FIG 8 that figure depicts an alternative configuration 800, which in this example includes 8 waveguides 802A-H arranged in an end to end orientation to form a rectangle.
  • one or more light sources may be arranged at adjacent waveguide ends, such as schematically indicated at 804A-D; and one or more detectors may be arranged at the opposite waveguide ends, as schematically indicated at 806A-D.
  • a common light source might be used to illuminate both waveguides at each source location 804A-D, in many examples, with spectral filters oriented in the light path between each such light source and the respective waveguide 802A-H.
  • an individual detector may be used with each waveguide, or an array detector might be used to separately measure signals from each of the adjoining waveguides.
  • FIG. 9 is a flow chart of one example method 900 for performing the reflectivity measurement.
  • the flow chart described a system in which various optional elements are included, including moveable spectral filters. But simpler systems have been described herein, and the method of operation of such systems would be similarly simpler than that described below.
  • the example method 900 begins at 902, in which a sample is placed on a sample interface (such as 406 in Figure 4), which simultaneously spans first and second waveguides, (such as 402A, 402B in Figure 4).
  • a sample interface such as 406 in Figure 4
  • first and second waveguides such as 402A, 402B in Figure 4
  • each waveguide will provide light to the sample interface at a fixed incident angle that depends on the geometry of the particular waveguide; in this example, the first and second waveguides have different internal geometries, and therefore provide light to the sample interface at different incident angles.
  • light at a first wavelength is directed onto the sample interface (406), at a first incident angle in the first waveguide.
  • light at a second wavelength is directed onto the sample interface at a second incident angle in the second waveguide.
  • the second wavelength will be the same as the first wavelength.
  • a first reflectivity measurement is made from light reflected from the sample through the first waveguide; and at 910, a second reflectivity measurement is made from light reflected from the sample through the second waveguide.
  • the sample will be evaluated through reference to the first and second reflectivity measurements. Such evaluation can be through techniques generally known to those skilled in the art. But with the current method, implemented through systems such as the example systems described herein, the sample can be evaluated at different depths into the sample. As noted previously, this is of particular value with striated samples.
  • the method facilitates measuring a sample at two incident angles and at a single wavelength.
  • the light source is a narrowband light source, such as a laser diode or an LED, since narrowband light sources may not require spectral filters.

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Abstract

La présente invention porte sur un dispositif et un procédé de mesure de réflectivité d'échantillon à une pluralité d'angles incidents prédéfinis, discrets. Le dispositif comprend une interface d'échantillon qui s'étend sur des faces de mesure de multiples guides d'ondes. Chaque guide d'ondes est associé à un angle incident unique, respectif. Au moins deux des angles incidents sont différents. Dans certains cas, les angles incidents sont invariants pour chaque guide d'ondes et varient de guide d'ondes à guide d'ondes. Selon certains exemples, le dispositif comprend une source lumineuse de bande large et au moins un filtre spectral. Pour des configurations dans lesquelles un guide d'ondes particulier réalise des mesures à plus d'une longueur d'onde, le dispositif comprend un filtre spectral pour chaque longueur d'onde, qui est apte à être commuté dans et hors du trajet optique. Selon certains exemples, la géométrie de guide d'ondes détermine l'angle incident sur l'échantillon et la géométrie varie de guide d'ondes à un guide d'ondes.
PCT/US2013/057749 2013-08-31 2013-08-31 Spectromètre à multiples guides d'ondes Ceased WO2015030833A1 (fr)

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WO2018190358A1 (fr) * 2017-04-14 2018-10-18 国立研究開発法人産業技術総合研究所 Puce de détection de substance souhaitée, dispositif de détection de substance souhaitée, et procédé de détection de substance souhaitée
JP2018179784A (ja) * 2017-04-14 2018-11-15 国立研究開発法人産業技術総合研究所 目的物質検出チップ、目的物質検出装置及び目的物質検出方法
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US20220071521A1 (en) * 2019-01-31 2022-03-10 Tohoku University Blood-sugar-level measuring apparatus and blood-sugar-level measuring method
EP4508415A4 (fr) * 2022-04-13 2026-04-08 Services Petroliers Schlumberger Appareil et procédé de mesure d'un échantillon

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Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2018190358A1 (fr) * 2017-04-14 2018-10-18 国立研究開発法人産業技術総合研究所 Puce de détection de substance souhaitée, dispositif de détection de substance souhaitée, et procédé de détection de substance souhaitée
JP2018179784A (ja) * 2017-04-14 2018-11-15 国立研究開発法人産業技術総合研究所 目的物質検出チップ、目的物質検出装置及び目的物質検出方法
US11112359B2 (en) 2017-04-14 2021-09-07 National Institute Of Advanced Industrial Science And Technology Target substance detection chip, target substance detection device, and target substance detection method
JP2019020181A (ja) * 2017-07-13 2019-02-07 国立研究開発法人産業技術総合研究所 目的物質検出装置及び目的物質検出方法
JP7097563B2 (ja) 2017-07-13 2022-07-08 国立研究開発法人産業技術総合研究所 目的物質検出装置及び目的物質検出方法
US20220071521A1 (en) * 2019-01-31 2022-03-10 Tohoku University Blood-sugar-level measuring apparatus and blood-sugar-level measuring method
EP4508415A4 (fr) * 2022-04-13 2026-04-08 Services Petroliers Schlumberger Appareil et procédé de mesure d'un échantillon

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