WO2014143204A1 - Procédés et appareil de détection des rayonnements infrarouges moyens - Google Patents

Procédés et appareil de détection des rayonnements infrarouges moyens Download PDF

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Publication number
WO2014143204A1
WO2014143204A1 PCT/US2013/069687 US2013069687W WO2014143204A1 WO 2014143204 A1 WO2014143204 A1 WO 2014143204A1 US 2013069687 W US2013069687 W US 2013069687W WO 2014143204 A1 WO2014143204 A1 WO 2014143204A1
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μιη
silicon
waveguide
mid
germanium
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PCT/US2013/069687
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English (en)
Inventor
Pao Tai LIN
Yan Cai
Anuradha Murthy Agarwal
Lionel C. Kimerling
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Massachusetts Institute Of Technology
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Priority claimed from US14/076,655 external-priority patent/US9046650B2/en
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Publication of WO2014143204A1 publication Critical patent/WO2014143204A1/fr

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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
    • G01N21/25—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
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/48—Biological material, e.g. blood, urine; Haemocytometers
    • G01N33/483—Physical analysis of biological material

Definitions

  • Silicon-integrated photonics are based mainly on conventional silicon- on-insulator (SOI) technology, in which a thin layer of silicon dioxide serves as an undercladding between the top crystalline silicon waveguide and the bottom crystalline silicon substrate to prevent light leakage through the substrate.
  • SOI silicon- on-insulator
  • ⁇ 3 ⁇ to 8 ⁇
  • silicon dioxide becomes optically lossy at wavelengths greater than about 3.6 ⁇ .
  • conventional SOI devices are generally unsuitable for detecting absorption in the mid-IR portion of the electromagnetic spectrum.
  • Embodiments of the present invention include devices and methods for sensing at least one molecule with a mid-infrared beam.
  • a mid-infrared sensing device includes a silicon substrate, a silicon pedestal extending from the silicon substrate, and a semiconductor waveguide (e.g., a silicon or germanium waveguide) disposed on the silicon pedestal above the silicon substrate.
  • the semiconductor waveguide guides the mid-infrared beam, which has at least one spectral component in a range of about 1.5 ⁇ to about 12.0 ⁇ .
  • the semiconductor waveguide's outer surface receives at least one molecule so as to cause absorption of the at least one spectral component by the at least one molecule.
  • a fluid containing the molecule may be disposed on the semiconductor waveguide's outer surface. This absorption reduces the spectral component's intensity.
  • a detector at the semiconductor waveguide's output may sense the intensity of the spectral component at one end of the semiconductor waveguide (e.g., the detector may include a spectrometer that senses the spectrum of the detected intensity).
  • the semiconductor waveguide which may be made of silicon or germanium, confines only a first portion of the mid-infrared beam.
  • the semiconductor waveguide can have a width of about 1 ⁇ to about 30 ⁇ and a height of about 0.4 ⁇ to about 50 ⁇ .
  • the silicon pedestal that supports that semiconductor waveguide may have a minimum width of about 0.5 ⁇ to about 2.5 ⁇ and a height of about 1.0 ⁇ to about 20 ⁇ .
  • Examples of the sensor may also include a mid-infrared light source, such as a tunable laser, that is optically coupled to the semiconductor waveguide.
  • the light source generates the mid-infrared beam and launches or couples it into one end of the semiconductor waveguide.
  • the light source and the detector may be disposed or formed on the silicon substrate as well.
  • the mid-infrared beam may be narrowband or broadband (e.g., with a bandwidth of about 1.0 ⁇ to about 12.0 ⁇ ) depending on the application. If the mid-infrared light source is tunable, then the wavelength of the spectral component may be tuned as a function of time, e.g., so as to sweep across a particular spectral band. Detecting a change in the detected intensity of the spectral component as a function of time yields a representation of the molecule's absorption spectrum, which can be used to identify the molecule (and/or its presence).
  • Embodiments of the present technology also include methods of making a silicon waveguide on a silicon pedestal extending from a silicon substrate.
  • An exemplary method includes forming a silicon ridge on the silicon substrate, then disposing a conformal layer of silicon dioxide on the silicon ridge so as to form a coated silicon ridge adjacent to an exposed portion of the silicon substrate. Etching the exposed portion of the silicon substrate yields a silicon pedestal that extends from the silicon substrate and supports the coated silicon ridge. Removing the conformal layer of silicon dioxide from the coated silicon ridge yields the silicon waveguide on the silicon pedestal.
  • the silicon ridge can be formed by depositing a silicon dioxide layer on the silicon substrate; patterning the silicon dioxide layer (e.g., via reactive ion etching or wet anisotropic etching) so as to form a silicon dioxide ridge on the silicon substrate; and etching the silicon substrate adjacent to the silicon dioxide ridge so as to form the silicon ridge beneath the silicon dioxide ridge.
  • the silicon ridge's width can be about 1 ⁇ to about 30 ⁇ and its height can be about 1 ⁇ to about 30 ⁇ .
  • the conformal layer of silicon dioxide can be disposed on the silicon ridge by depositing a silicon dioxide layer on the silicon ridge and the silicon substrate. Once the silicon dioxide layer has been deposited, it can be anisotropically etched (e.g., via reactive ion etching or wet anisotropic etching) so as to form the exposed portion of the silicon substrate.
  • the exposed portion of the silicon substrate can be etched by exposure to SF 6 .
  • the exposed portion may etched to a depth of about 1 ⁇ to about 20 ⁇ so as to form the silicon pedestal with a height of about 1 ⁇ to about 20 ⁇ .
  • the exposed portion of the silicon substrate may also be etched to form the silicon pedestal with a width of about 0.5 ⁇ to about 2.5 ⁇ .
  • Embodiments of the present technology also include methods of making a germanium waveguide on a silicon pedestal extending from a silicon substrate.
  • An exemplary method comprises forming a germanium waveguide on the silicon substrate and
  • the germanium waveguide is formed by: forming an oxide layer on the silicon substrate; selectively etching the oxide layer to form a trench that extends to the silicon substrate; depositing germanium in the trench; and removing the oxide layer to form the germanium waveguide.
  • the germanium waveguide is formed by forming a germanium layer on the silicon substrate and selectively etching the germanium layer to form the germanium waveguide.
  • FIG. 1 A is a perspective diagram of an exemplary air-clad, silicon pedestal waveguide suitable for mid-infrared (mid-IR) sensing with a waveguide width w, a waveguide height h, a pedestal height s, and a pedestal width d.
  • mid-IR mid-infrared
  • FIG. IB is a diagram of the silicon pedestal waveguide of FIG. 1A used to sense organic molecules with an evanescent wave.
  • FIG. 1C is an end-on view of an exemplary air-clad, germanium pedestal waveguide suitable for mid-IR sensing with a waveguide width w, a waveguide height h, a pedestal height s, a pedestal upper base width d ⁇ , and a pedestal lower base width ⁇ i 2 .
  • FIG. ID is a side view of the germanium pedestal waveguide of FIG. 1C.
  • FIG. 2 is a schematic diagram of a chip-based mid-IR sensor that includes a semiconductor pedestal waveguide (e.g., the silicon pedestal waveguide of FIGS. 1A and IB or the germanium pedestal waveguide of FIGS. 1C and ID).
  • a semiconductor pedestal waveguide e.g., the silicon pedestal waveguide of FIGS. 1A and IB or the germanium pedestal waveguide of FIGS. 1C and ID.
  • FIGS. 3A-3F illustrate a process for fabricating silicon pedestal waveguides and splitters.
  • FIG. 4A is a scanning electron microscope (SEM) image of an array of fabricated air-clad silicon pedestal waveguides suitable for mid-IR sensing (the box indicates the view shown in FIG. 4B).
  • SEM scanning electron microscope
  • FIG. 4C is another SEM image of the array of FIG. 4A (the box indicates the view shown in FIG. 4D).
  • FIG. 4D is an SEM image of the waveguide of FIG. 4A, taken at an angle of 45°, to inspect the waveguide's smooth sidewalk
  • FIG. 4E is an SEM image of a curved section of a silicon pedestal waveguide.
  • FIG. 4F is an SEM image of an array of forked silicon pedestal waveguides (the inset shows a magnified view of the fork (splitter) in the middle waveguide).
  • FIG. 5A is a plot of the refractive index profile of a silicon pedestal waveguide structure used for finite-difference simulations of waveguide performance (the dashed box indicates the light source used to couple light into the waveguide).
  • FIG. 6 is a schematic diagram of a system suitable for characterizing mid-IR sensing with a silicon pedestal waveguide.
  • FIG. 8 is a plot of measured optical power (dots) and a curve fit (line) versus wavelength for silicon pedestal waveguides (inset) with different relative length D.
  • FIG. 9 is a plot of the measured transmission spectrum of an exemplary fabricated crystalline silicon-based sensor platform (the dashed line indicates relatively high
  • FIG. 10 is a plot of relative optical power measurements (circles with error bars) versus waveguide length for the paperclip-shaped pedestal waveguide shown in the inset of FIG. 10.
  • FIG. 1 IB is a plot of the relative intensity versus lateral dimension across the x axis of the modes illustrated in FIG. 11 A.
  • FIG. 12 is a plot of waveguide mode intensities at different toluene/CCU
  • FIG. 13 is a real-time trace of intensity change over time measured at the output of a mid-IR silicon pedestal waveguide sensor exposed to toluene.
  • FIG. 16 is a plot of the effective mode index versus silicon pedestal top width d ⁇ for TE and TM modes guided in a germanium waveguide on a silicon pedestal.
  • FIG. 18 is a plot of the effective mode index versus waveguide thickness for a germanium waveguide on a silicon pedestal.
  • FIGS. 19A-19C show calculated 2D mode profiles on a logarithmic scale for the superimposed germanium waveguide/silicon pedestal structure with a waveguide widths of 0.75 ⁇ (FIG. 19A), 2.0 ⁇ (FIG. 19B), and 3.5 ⁇ (FIG. 19C).
  • FIGS. 20 A and 20B show calculated 2D mode profiles on a logarithmic scale for the superimposed germanium waveguide/silicon pedestal structure at wavelengths of 3.1 ⁇ and 3.7 ⁇ , respectively.
  • FIG. 20C is a plot of the effective mode index versus wavelength for the germanium waveguide/silicon pedestal structure shown in FIGS. 20A and 20B.
  • FIG. 21 A shows the refractive index profile of a protruded germanium waveguide with a variable protrusion height p on a silicon pedestal
  • FIG. 2 IB is a plot of effective mode index versus protrusion height for the germanium pedestal/silicoon waveguide structure of FIG. 21 A.
  • FIGS. 21C and 2 ID show calculated 2D mode profiles on a logarithmic scale for the superimposed germanium pedestal/silicon waveguide structures with protrusion heights p of 0.25 ⁇ and 2.0 ⁇ , respectively.
  • FIG. 22 shows process flows for making Ge-on-Si undercut waveguides by growing Ge waveguides selectively inside oxide trenches (left) and dry etching the as-grown Ge blanket film to form Ge waveguides (right).
  • FIGS. 23A-23C are cross-sectional SEM pictures of germanium waveguides on silicon substrates at various steps in fabrication process shown in FIG. 22: after germanium deposition (FIG. 23 A), after oxide removal (FIG. 23B), and in the final waveguide configuration (FIG. 23C).
  • Embodiments of the present technology include air-clad semiconductor straight waveguides, bent waveguides, and splitter waveguides. Each of these waveguides utilizes a pedestal structure for broadband mid-infrared (mid-IR) devices and is compatible with complementary metal-oxide-semiconductor (CMOS) processes and hence amenable to large- scale manufacturing.
  • CMOS complementary metal-oxide-semiconductor
  • Experimental results including scanning electron microscope (SEM) images, confirm that exemplary devices retain their structural integrity during fabrication processing.
  • Broadband mid-IR transmission characterization of exemplary devices shows a sharp fundamental waveguide mode, low mid-IR optical loss (e.g., 2.7 dB/cm), and, for certain waveguide splitters, a 50/50 power splitting ratio. These characteristics make exemplary air-clad semiconductor waveguides suitable for integrated mid-IR microphotonics, including mid-IR sensing applications.
  • an exemplary air-clad silicon or germanium pedestal waveguide can be used in mid-IR integrated photonics for spectroscopic sensing at wavelengths between 1.5 ⁇ and 12.0 ⁇ (e.g., between 1.5 ⁇ and 8.0 ⁇ , between 3.0 ⁇ and 6.5 ⁇ , between 5.0 ⁇ and 12.0 ⁇ , and so on).
  • SOI Silicon-On-Insulator
  • Air-clad semiconductor pedestal waveguides also offer advantages over Silicon- On-Sapphire (SOS) waveguides, including simpler (and less expensive) fabrication.
  • SOS Silicon- On-Sapphire
  • the cladding layer in an SOS waveguide weakens the interaction between the evanescent optical wave and the surrounding chemicals, consequently decreasing the SOS device's sensitivity.
  • chalcogenide glass (ChG) waveguide materials have a wider IR transparency
  • air-clad crystalline silicon is chemically and mechanically more robust because it is a single crystal (as opposed to a glass).
  • VLSI very-large-scale integration
  • one or more mid-IR air-clad semiconductor pedestal waveguide sensors can be integrated with one or more light sources and one or more photodetectors to form a mid-IR spectrometer-on-a-chip.
  • the robust air-clad pedestal semiconductor sensor(s) can be tailored to perform chemical analyte detection using characteristic mid-IR absorption spectra to simultaneously perform qualitative (compound recognition) and quantitative (target concentration) analyses.
  • mid-IR spectra can "fingerprint" molecular structures within functional groups present in the chemical analytes, enabling label-free detection.
  • These lab-on-a-chip broadband Mid-IR sensors can be used in many applications, including but not limited to remote real-time sensing of trace toxins and detection of contaminants.
  • SPR requires a highly smooth dielectric/metal interface in order to avoid polariton scattering loss.
  • a pedestal silicon or germanium waveguide can be built on a single mid-IR transparent material (silicon) that reduces or eliminates any complexity in device design and materials selection and provides very low propagation loss.
  • Semiconductor pedestal waveguides also provide advantages over optical sensors that use ultraviolet, visible, or near-infrared light to measure chemical concentration by sensing a shift of a resonant cavity's resonance frequency.
  • these optical sensors use a frequency-swept or narrow linewidth source to probe a change in the cavity's refractive index caused by a change in the chemical concentration.
  • measuring the absorption of an evanescent wave does not require a source with such a narrow linewidth or as great a frequency agility.
  • the sensors described below are made of silicon and germanium, one of skill in the art would readily understand that the sensor' and its components could each comprise any other suitable semiconductor material, including but not limited to pure semiconductor material, binary semiconductor materials (e.g., III-V compounds such as gallium arsenide), certain ternary compounds, and certain organic semiconductor materials.
  • binary semiconductor materials e.g., III-V compounds such as gallium arsenide
  • certain ternary compounds e.g., III-V compounds such as gallium arsenide
  • organic semiconductor materials e.g., silicon Pedestal Waveguide Sensors
  • FIGS. 1A and IB illustrate a silicon pedestal waveguide 100 suitable for sensing changes in concentration via evanescent absorption at wavelength(s) between about 3 ⁇ and about 8 ⁇ .
  • the silicon pedestal waveguide 100 includes a silicon substrate (wafer) 130, a silicon pedestal 120 extending from the silicon substrate 130, and a silicon waveguide 110 supported above the silicon substrate 130 by the silicon pedestal 120.
  • the silicon waveguide 110 also defines an exterior surface 112, through which an evanescent wave 1 1 associated with the supported waveguide mode(s) interacts with one or more organic molecules 10 or other analytes.
  • the waveguide's shape and dimensions may be selected to support propagation of one or modes of a mid-IR
  • the waveguide 110 shown in in FIGS. 1A and IB has a rectangular cross-section with a width w and a height h.
  • the waveguide width w may be about 1 ⁇ to about 30 ⁇ (e.g., 2.5 ⁇ , 5.0 ⁇ , 7.5 ⁇ , 10.0 ⁇ , 12.5 ⁇ , 15.0 ⁇ , 17.5 ⁇ , 20.0 ⁇ , 22.5 ⁇ , 25.0 ⁇ , or 27.5 ⁇ ) and the waveguide height h may be about 1 ⁇ to about 30 ⁇ (e.g., 2.5 ⁇ , 5.0 ⁇ , 7.5 ⁇ , 10.0 ⁇ , 12.5 ⁇ , 15.0 ⁇ , 17.5 ⁇ , 20.0 ⁇ , 22.5 ⁇ , 25.0 ⁇ , or 27.5 ⁇ ).
  • Other embodiments may have different cross-sectional shapes, including but not limited to circles, triangles, squares, pentagons, hexagon, octagons, etc.
  • the silicon waveguide's shape and dimensions may be chosen to support propagation of only a single mode (e.g., the TEM 0 o mode) of a beam with a wavelength of about 2 ⁇ to about 8 ⁇ . In other cases, the silicon waveguide's shape and dimensions may be chosen to support propagation of multiple modes at mid-IR wavelengths.
  • the silicon waveguide 110 may include stress members and/or have a shape or composition selected to preserve the polarization state of the mid-IR beam propagating through the silicon waveguide 110. In other words, the silicon waveguide 110 may be a polarization-maintaining waveguide as readily understood by those of skill in the art.
  • the waveguide's shape and dimensions may also be chosen to support an evanescent wave (tail) that extends laterally out of the waveguide 110.
  • an evanescent wave is a near- field wave whose intensity decays exponentially decay as a function of the distance from the boundary at which the evanescent wave is formed— in this case, the waveguide's outer surface 112.
  • at least a portion of the evanescent wave may be absorbed by one or more molecules (e.g., organic molecules 10) within a length about equal to the evanescent wave's decay constant.
  • the molecule(s) may absorb one or more of the evanescent wave's spectral components, leading to a spectrally selective reduction in intensity of the wave propagating through the waveguide 110. Detecting this spectrally selective reduction in intensity—e.g., by measuring the absorption spectrum— at the waveguide's output yields an indication of the type and concentration of molecules in the fluid surrounding the waveguide 110.
  • the waveguide's outer surface 112 may be configured to receive or support at least one molecule (e.g., organic molecule 10) in the fluid surrounding the pedestal waveguide sensor 100.
  • the outer surface 112 may be textured, patterned, and/or coated to promote adhesion of the molecules to the outer surface 112.
  • the outer surface 112 may be unlabeled and/or smooth.
  • a portion of the waveguide's outer surface 112 runs roughly parallel to the surface of the silicon substrate 130.
  • FIGS. 1 A and IB also show that the pedestal 120 has a rectangular cross section with a width d and a height s. These dimensions may be selected for ease of fabrication, and/or to provide desired performance.
  • the pedestal width d may be about 0.5 ⁇ ⁇ about 2.5 ⁇ (e.g., 0.75 ⁇ , 1.0 ⁇ , 1.25 ⁇ , 1.5 ⁇ , 1.75 ⁇ , 2.0 ⁇ , or 2.25 ⁇ )
  • the pedestal height s may be about 1.0 ⁇ to about 20 ⁇ (e.g., 2.5 ⁇ , 5.0 ⁇ , 7.5 ⁇ , 10.0 ⁇ , 12.5 ⁇ , 15.0 ⁇ , or 17.5 ⁇ ).
  • the pedestal may be smoothly tapered at its top and/or its bottom to provide increased stability and/or to reduce mechanical stress and strain on the sensor 100 and its components.
  • the senor 100 is made of silicon with well-developed fabrication processes and a wide mid-IR transparency, it can accommodate broadband laser scanning, which is useful for multi-spectral and diverse chemical analysis.
  • silicon is a rugged material in response to harsh environments, since it is chemically inert when exposed to most organic chemicals. Therefore, the fabricated sensors can be utilized in tracing a variety of organic pollutants.
  • FIGS. 1C and ID show a sensor 150 that includes a mid-IR germanium waveguide 160 on a silicon pedestal 170 extending from a silicon wafer (substrate) 180. Like the silicon sensor 100 shown in FIGS. 1A and IB, the sensor 150 shown in FIGS.
  • the waveguide's shape and dimensions may be selected to support propagation of one or modes of a mid-IR electromagnetic wave.
  • FIG. 1C shows the germanium waveguide 160 as having a rectangular cross section with a width w and a height (thickness) h.
  • the top of the waveguide 160 may bulge slightly as described below with respect to FIGS.
  • the waveguide width w may be about 1 ⁇ to about 30 ⁇ (e.g., 2.5 ⁇ , 5.0 ⁇ , 7.5 ⁇ , 10.0 ⁇ , 12.5 ⁇ , 15.0 ⁇ , 17.5 ⁇ , 20.0 ⁇ , 22.5 ⁇ , 25.0 ⁇ , or 27.5 ⁇ ) and the waveguide height h may be about 1 ⁇ to about 30 ⁇ (e.g., 2.5 ⁇ , 5.0 ⁇ , 7.5 ⁇ , 10.0 ⁇ , 12.5 ⁇ , 15.0 ⁇ , 17.5 ⁇ , 20.0 ⁇ , 22.5 ⁇ , 25.0 ⁇ , or 27.5 ⁇ ).
  • Other embodiments may have different cross-sectional shapes, including but not limited to circles, triangles, squares, pentagons, hexagon, octagons, etc.
  • the germanium waveguide's shape and dimensions may be chosen to support propagation of only a single mode (e.g., the TEM 0 o mode) of a beam with a wavelength of about 2 ⁇ to about 12 ⁇ (e.g., about 5 ⁇ to about 12 ⁇ ). In other cases, the germanium waveguide's shape and dimensions may be chosen to support propagation of multiple modes at mid-IR wavelengths. If desired, the germanium waveguide 160 may include stress members and/or have a shape or composition selected to preserve the polarization state of the mid-IR beam propagating through the germanium waveguide 160.
  • the germanium waveguide 160 may be a polarization-maintaining waveguide as readily understood by those of skill in the art.
  • the germanium waveguide's shape and dimensions may also be chosen to support an evanescent wave (tail) that extends laterally out of the germanium waveguide 160 through its outer surface 162.
  • evanescent wave tail
  • at least a portion of the evanescent wave may be absorbed by one or more molecules within a length about equal to the evanescent wave's decay constant.
  • the molecule(s) may absorb one or more of the evanescent wave's spectral components, leading to a spectrally selective reduction in intensity of the wave propagating through the germanium waveguide 160.
  • Detecting this spectrally selective reduction in intensity—e.g., by measuring the absorption spectrum— at the waveguide's output yields an indication of the type and concentration of molecules in the fluid surrounding the germanium waveguide 160.
  • the germanium waveguide's outer surface 162 may be configured to receive or support at least one molecule (e.g., an organic molecule) in fluid surrounding the germanium pedestal waveguide sensor 150.
  • the outer surface 162 may be textured, patterned, and/or coated to promote adhesion of the molecules to the outer surface 162.
  • the outer surface 162 may be unlabeled and/or smooth. In the sensor 150 shown in FIGS. 1C and ID, a portion of the waveguide's outer surface 162 runs roughly parallel to the surface of the silicon substrate 180.
  • FIGS. 1C and ID also show that the germanium waveguide 160 sits atop a silicon pedestal 170 whose cross section is in the shape of an isosceles trapezoid.
  • the silicon pedestal's cross section has an upper base width a lower base width ⁇ i 2 , and a height s measured perpendicular to the upper and lower bases.
  • the base angle formed between the lower base and the sides may about 54.7° due to anisotropic etching of the (100) and (111) planes of crystalline silicon during fabrication.
  • the pedestal's dimensions may be selected for ease of fabrication, and/or to provide desired performance. For instance, the pedestal's upper base width may be selected to prevent or promote confinement of the TM mode within the pedestal 170 itself.
  • the pedestal's upper base width d ⁇ may be about 0.1 ⁇ to about 2.5 ⁇ (e.g., 0.25 ⁇ , 0.5 ⁇ , 0.75 ⁇ , 1.0 ⁇ , 1.25 ⁇ , 1.5 ⁇ , 1.75 ⁇ , 2.0 ⁇ , or 2.25 ⁇ ).
  • the pedestal height s may be about 0.4 ⁇ to about 50 ⁇ (e.g., 0.5 ⁇ , 1.0 ⁇ , 1.5 ⁇ , 2.0 ⁇ , 2.5 ⁇ , 5.0 ⁇ , 7.5 ⁇ , 10.0 ⁇ , 12.5 ⁇ , 15.0 ⁇ , 17.5 ⁇ , 20 ⁇ , 25 ⁇ , 30 ⁇ , 35 ⁇ , 40 ⁇ , or 45 ⁇ ) depending on the application and the etch ratio of (100) to (111) semiconductor planes.
  • ⁇ e.g., 0.5 ⁇ , 1.0 ⁇ , 1.5 ⁇ , 2.0 ⁇ , 2.5 ⁇ , 5.0 ⁇ , 7.5 ⁇ , 10.0 ⁇ , 12.5 ⁇ , 15.0 ⁇ , 17.5 ⁇ , 20 ⁇ , 25 ⁇ , 30 ⁇ , 35 ⁇ , 40 ⁇ , or 45 ⁇
  • mid-IR germanium waveguide 160 and the silicon pedestal 170 can be designed and optimized, e.g., using two- dimensional finite element method (FEM) and Finite Difference Time Domain (FDTD), to achieve a particular mode profile/confinement as explained in greater detail below.
  • FEM finite element method
  • FDTD Finite Difference Time Domain
  • FIG. 2 shows a chip 201 that includes a semiconductor pedestal waveguide sensor 200 (e.g., a silicon or germanium sensor) integrated with a light source 240 and a detector 250 onto a semiconductor substrate 230 (e.g., a silicon substrate).
  • the light source 240 which may include one or more narrowband/coherent emitters (e.g., quantum cascade lasers), broadband emitters, or tunable emitters, emits a beam of mid-IR light.
  • narrowband/coherent emitters e.g., quantum cascade lasers
  • broadband emitters e.g., or tunable emitters
  • the light source 240 may emit a beam whose wavelength spans or is tuned over some or all of the mid-IR portion of the electromagnetic spectrum, e.g., over a bandwidth of about 1.0 ⁇ to about 12.0 ⁇ (e.g., about 2 ⁇ , 3 ⁇ , 4 ⁇ , 5 ⁇ , 6 ⁇ , 7 ⁇ , 8 ⁇ , 9 ⁇ , 10 ⁇ , or 11 ⁇ ,).
  • the light emitted by the light source 240 is coupled into a semiconductor waveguide 210, such as a silicon or germanium waveguide, in the sensor 200, e.g., via butt-coupling or with one or more lenses (not shown). Another lens (not shown) may focus light emitted by the waveguide 210 onto the detector 220.
  • the senor 200 on the chip 201 is exposed to a fluid (e.g., gas or liquid) to be analyzed for the presence (or absence) of one or more particular chemicals or compounds.
  • a fluid e.g., gas or liquid
  • the fluid may be a liquid that is dropped onto the chip 201 with a pipette.
  • the chip 201 may also be immersed in fluid or placed in a fluid flow.
  • the chip 201 may be integrated with one or more micro-fluidic devices to prevent evaporation and improve device stability.
  • At least some of the fluid extends over or near at least a portion of the sensor's waveguide 210.
  • the fluid may absorb some or all of one or more spectral components of the evanescent tail extending from the waveguide's exterior surface 212. This absorption reduces the intensity of the corresponding spectral component(s) of the mode propagating through the waveguide 210, producing a variation in the intensity of at least one spectral component of the beam emitted by the waveguide 210.
  • the detector 250 senses this spectrally selective variation in intensity of the emitted beam and emits a photocurrent or other electrical signal whose amplitude is proportional to the intensity of the emitted beam.
  • the detector 250 may include one or more broadband sensing elements and/or spectrally selective narrowband sensing elements.
  • the detector 250 may include a spectrometer formed by a grating or other dispersive element that directs different spectral components of a broadband beam into different angles, each of which is monitored by a respective detector element in a detector array (e.g., a charged coupled device (CCD) or complementary metal-oxide-semiconductor (CMOS) sensing array) to yield the absorption spectrum of the absorbers evanescently coupled to the sensor 200.
  • the detector 250 may include a single sensing element that detects the time- varying intensity of a spectrally swept (chirped) beam. Mapping the resulting time-varying intensity signal to the spectral sweep speed yields an absorption spectrum that can be used to identify any absorbers evanescently coupled to the sensor 200.
  • the chip 201 can be used to identify chemicals from an unknown solution by using the detected absorption spectrum as a chemical "fingerprint.”
  • FIGS. 3A-3F illustrate a process 300 for making a silicon pedestal waveguide, such as the waveguide 100 shown in FIGS. 1A and IB, that involves dry/wet etching and conformal oxide deposition.
  • photoresist 330 is deposited onto a thermal oxide layer 320 (e.g., a Si0 2 layer, other oxide layer, or nitride layer), which in turn is on a silicon wafer 310 (e.g., a 3 ⁇ thick oxide -on-silicon wafer).
  • the photoresist 330 may be patterned using photolithography to form a straight waveguide, curved waveguide, splitter, ring, or group of waveguides.
  • the patterns are transferred sequentially into the thermal oxide layer 320 and the silicon wafer 310 using inductively coupled plasma reactive ion etching (ICP-RIE), wet anisotropic patterning, or any other suitable type of anisotropic etching to form a silicon ridge 312 coated with an oxide layer 320 as shown in FIG. 3B.
  • ICP-RIE inductively coupled plasma reactive ion etching
  • wet anisotropic patterning any other suitable type of anisotropic etching to form a silicon ridge 312 coated with an oxide layer 320 as shown in FIG. 3B.
  • This technique can also be used to form a gallium arsenide ridge or germanium.
  • a gas mixture composed of H 2 /CHF 3 /CF 4 may be used to obtain an etching depth of 3 ⁇ in the thermal oxide layer 320.
  • a C 4 F 8 /SF 6 gas mixture can be used to obtain an etching depth of 10 ⁇ in the silicon wafer 310.
  • a thin oxide layer 340 (comprising, e.g., silicon dioxide, another oxide, or a nitride) with a thickness of about 0.5 ⁇ to about 3.0 ⁇ is conformally deposited on the oxide-coated silicon ridge 312 using plasma-enhanced chemical vapor deposition (PECVD) or any other suitable deposition technique.
  • PECVD plasma-enhanced chemical vapor deposition
  • Suitable materials for the thin oxide layer 340 include silicon dioxide, other oxides (e.g., thermal oxide), and nitrides.
  • the thin oxide layer 340 is anisotropically and preferentially etched back using ICP-RIE as shown in FIG. 3D.
  • the thin oxide layer 340 is etched back to reveal at least a portion of the silicon wafer's horizontal surface(s) and the thermal oxide layer's horizon surface(s), and to leave a vertical oxid layer 342 on the silicon ridge's vertical sidewall to protect the sidewall's surface.
  • the silicon ridge 312 is undercut, e.g., using isotropic etching with SF 6 gas, to form the sensor's waveguide 110 and the pedestal 120 as shown in FIG. 3E.
  • This isotropic silicon etching removes only silicon that is not covered by an oxide (thermal oxide layer 320 and thin oxide layer 340).
  • the remaining oxide may then removed by a buffered oxide etch (BOE) to reveal the completed sensor 100, which has a waveguide width w, waveguide height h, lift-off length s, and notch width d as shown in FIG. 3F.
  • BOE buffered oxide etch
  • FIGS. 4A-4F are scanning electron microscope (SEM) images of fabricated mid-IR waveguides, which are tilted at 54° during microscopy to improve the cross-sectional view.
  • FIG. 4A shows an array of parallel waveguides;
  • FIG. 4A and 4B also show that the waveguide edges (top of the structure) are smooth (no bumps or indentations appear in the pictures) and straight (no bending or distortion is observed), and that the waveguide structure is well resolved (no cracks or roughness appear on the waveguide edges).
  • FIG. 4C shows the waveguide array of FIG. 4A rotated by 45° to visualize the morphology of the waveguide sidewalls.
  • FIG. 4D is an enlarged image of the region indicated by the rectangle in FIG. 4C.
  • FIG. 4D shows that no defects appear in the vertical facets, confirming that the conformally deposited oxide layer protected the waveguide cores during the isotropic silicon etching.
  • FIG. 4D also shows that the waveguide edges are smooth and straight.
  • FIG. 4E is an image of an individual waveguide with two regions that are bent to form a paper clip shape. Each bent region's radius of the curvature is about 50 ⁇ .
  • FIG. 4E shows that the strip (pedestal) underneath the waveguide supports the waveguide well.
  • the pedestal waveguide can be formed in an arc, undulating curve, sinusoid, or ring.
  • the waveguide can be formed into a Y-shaped splitter with gently curved arms extending from a single waveguide as shown in FIG. 4F.
  • the magnified image in the inset of FIG. 4F shows that the splitter region has a highly symmetric structure for achieving a 50/50 power splitting ratio.
  • splitters with multiple ports e.g., n x m splitters, where n and m are positive integers.
  • the splitter may also be tunable, e.g., via one or more heaters that heat the waveguide(s) so as to modulate their refractive indices.
  • FIGS. 5 A and 5B illustrate two dimensional finite difference method (FDM) simulations of an exemplary silicon pedestal waveguide's light-guiding performance in the mid-IR spectral range.
  • FIG. 5A illustrates the pedestal configuration used in the FDM modeling.
  • a light source of 9 ⁇ x 9 ⁇ is chosen so its size is comparable to a single-mode fiber with 9 ⁇ core diameter.
  • FIG. 1 finite difference method
  • FIG. 5B shows that a fundamental mode is clearly resolved where the lightwave is highly confined inside the upper silicon waveguide.
  • FIG. 5B shows that negligible variation is observed in the mode profiles when the wavelength is scanned over a broad spectral range.
  • FIG. 5B also shows that a portion of the mode profile extends beyond the waveguide's edges to enhance the interaction with the fluid/chemical analyte being monitored.
  • the pulsed laser beam is coupled into a mid-IR fluoride fiber 630 with a 9 ⁇ core and 125 ⁇ cladding using a reflective lens 620.
  • the reflective lens 620 collimates the pulsed laser beam, then butt couples the collimated beam into the fiber 630.
  • the mid-IR fiber 630 extends onto a first six-axis stage 640, which can be used to align the mid-IR fiber's core with the smooth, cleaved front facet of the silicon waveguide 100. If desired, the silicon waveguidge 100 can be mounted on a second six-axis stage 650 to provide additional degrees of freedom.
  • a calcium fluoride biconvex lens 660 at the waveguide's output focuses the light emitted by the waveguide 660 onto the active area of a mid-IR camera 670, such as a liquid nitrogen cooled 320 pixel x 256 pixel InSb camera or other suitable mid-IR detector, which produces a photocurrent or other electrical signal whose amplitude is proportional to the intensity of the detected mid-IR radiation.
  • a mid-IR camera 670 such as a liquid nitrogen cooled 320 pixel x 256 pixel InSb camera or other suitable mid-IR detector, which produces a photocurrent or other electrical signal whose amplitude is proportional to the intensity of the detected mid-IR radiation.
  • the system 600 also includes a microscope 680 with a long working distance objective for fine adjustment of the fiber's tip with respect to the waveguide 100.
  • the microscope 680 projects a magnified image of the waveguide 100 onto a monitor 690 for use in aligning the mid-IR fiber 630, the waveguide 100, and/or the mid-IR camera 670 with respect to each other.
  • the alignment between the fiber 630 and the waveguide 100 can be performed under microscope guidance using the positioning stages 640 and 650, which provide full control of six axes (x, y, z, ⁇ , ⁇ , ⁇ ) with 0.02 ⁇ sensitivity.
  • Each image shows a sharp, clearly resolvable fundamental mode as predicted by the FDM simulation. No scattering or distortion appears in FIG. 7, which implies that the mid-IR probe light is confined inside the silicon pedestal waveguide.
  • the images show that the fundamental mode remains dominant within a wide spectral range, indicating that a silicon pedestal waveguide can efficiently deliver broadband mid-IR signals on-chip.
  • FWHM full-width half-maximum
  • the profile of an exemplary waveguide's fundamental mode can be evaluated over a wide range of operating wavelengths (e.g., 1.0-8.0 ⁇ , 1.3-6.5 ⁇ , 2.7-3.7 ⁇ , etc.).
  • the resulting measurements can be used to set the sensor's baseline transmittance profile as a function of wavelength (in other words, a baseline spectral profile) for use in chemical sensing and monitoring, among other applications.
  • the baseline transmittance can be subtracted from a raw signal provided by a photodetector to account for spectrally dependent variations in the source's output, the waveguide's absorption, and/or the detector's responsivity.
  • Subsequent profile evaluations can be used to track and account for changes can caused by changes in the sensor's performance due to aging, temperature changes, pressure changes, etc.
  • FTIR Fourier transform infrared spectroscopy
  • FIG. 10 is a plot of relative optical power measurements (circles) versus waveguide length for the paperclip-shaped pedestal waveguide shown in the inset of FIG. 10.
  • the error bars indicate a measurement error of less than 0.15 dB/cm.
  • the paper clip center distance D varies from about 1 mm to about 4 mm, which corresponds to a variation in waveguide length from about 2 mm to about 8 mm.
  • FIGS. 11 A and 1 IB illustrate the performance of a Y-branch silicon waveguide splitter supported by a pedestal structure (e.g., as shown in FIG. 4F).
  • FIG. 1 IB is a plot of the intensity profile (relative intensity versus transverse dimension) measured across the x axis indicated in FIG. 11 A. It shows two peaks with similar shapes and nearly identical maximum intensities, which indicates that the splitting ratio is 50/50.
  • the beam splitter can be used to couple light into multiple waveguide channels, e.g., for use in mid-IR planar array devices.
  • FIG. 12 is a plot of toluene concentration (by weight) in carbon tetrachloride versus waveguide mode intensity measured using a mid-IR sensor in the set-up of FIG. 6.
  • FIG. 12 shows that increasing the toluene concentration from 0 to 1 causes the light intensity measured at the output end of the waveguide to decrease monotonically, which indicates that the sensor can be used to distinguish different concentrations.
  • the evanescent light from the Mid-IR waveguide is absorbed by the surrounding chemical analyte molecules of interest, and consequently the intensity of the guided light decreases.
  • the change in intensity is proportional to the analyte concentration and reveals quantitative information regarding the concentration of the chemical.
  • the time-resolved response of mid-IR detection was obtained by recording the waveguide's transmitted intensity upon exposure to toluene.
  • the transmitted intensity dropped instantly as the analyte reached the sensor, where the intensity variation is indicated by the arrows.
  • the intensity decreased as the toluene interacted with the waveguide mode.
  • the toluene covered the entire surface of the sensor and the signal stabilized due to the toluene's absorbtion of the mid-IR evanescent wave.
  • the waveguide intensity remained stable and low until most of the toluene evaporated at between about 370 seconds and about 400 seconds, at which point the transmitted intensity increased sharply.
  • the increase in intensity became slower after about 400 seconds because the surface tension at the toluene-silicon interface caused a thin toluene layer to remain on the waveguide.
  • the intensity recovered to the original intensity at 0 seconds after complete evaporation of the toluene from the sensor surface.
  • the sensor's response to the transient characteristics of the toluene solvent demonstrates that an exemplary sensor can monitor a chemical analyte in situ for applications including pollution control and early alarm systems.
  • Simulation can also be used to characterize the performance of germanium-based waveguide sensors.
  • a germanium waveguide can be simulated using FDTD to pick germanium waveguide and silicon pedestal parameters suitable for confining the guided mode(s) within the waveguide and preventing leakage of the mode into the silicon pedestal.
  • the following examples examine three parameters of the waveguide/pedestal structures are optimized— pedestal width, waveguide thickness (height), and protrusion height— and two parameters of the mode supported by the waveguide.
  • FIG. 15 shows the simulated refractive index profile of a rectangular germanium waveguide on an isosceles trapezoidal silicon pedestal.
  • the waveguide has a height
  • FIG. 15 shows that, at the wavelengths of interest (e.g., 3.1-3.7 ⁇ ), the silicon pedestal has a bulk refractive index of about 3.42-3.43 and the germanium waveguide has a bulk refractive index of about 4.02-4.04.
  • the germanium waveguide and silicon pedestal are surround by a material with a refractive index of about 1.0 (e.g., air). This refractive index profile is used to generate the simulations shown in FIGS. 16-20.
  • FIG. 16 also shows that the effective index of the TM mode increases more with increasing pedestal upper base width than the TE mode, which indicates that mode confinement in the vertical direction improves as pedestal upper base gets wider. It also indicates that the TM mode is more sensitive to changes in pedestal upper base width d ⁇ that the TE mode. Thus, the following simulations focus on the TM mode because it is more sensitive to changes in confinement in the vertical direction.
  • FIGS. 17A, 17B, and 17C depict the calculated 2D mode profiles of rectangular germanium waveguides on silicon pedestals with upper base widths of 0 ⁇ , 0.5 ⁇ , and 2.5 ⁇ , respectively, on a logarithmic scale (darker shading indicates higher intensity). Each plot also shows an outline of the corresponding germanium waveguide/silicon pedestal structure superimposed onto the mode profiles.
  • FIG. 17A shows that, at a pedestal upper base width of 0 ⁇ , the effective index is low because the evanescent wave expands into the surrounding air, which has an index of 1.
  • the area of the germanium waveguide's outer surface exposed to air decreases and the contact between the waveguide and silicon increases, causing the effective index to increase.
  • the mode expands into the silicon pedestal, resulting in the loss of confinement shown in FIG. 17C.
  • the loss of the mode into air is balanced with the loss of the mode into the silicon pedestal. Because silicon absorbs at IR wavelengths above about 6.5 ⁇ , reducing the pedestal upper base width may improve the germanium waveguide's efficiency even though it results in loss of the mode into the air.
  • a pedestal upper base width of 0.5 ⁇ is selected for the following simulations.
  • FIG. 18 is a plot of the effective index for the TM mode versus waveguide height (thickness) for a rectangular germanium waveguide on an isoceles trapezoidal silicon pedestal with an upper base width of 0.5 ⁇ and a base angle of about 54.7°.
  • FIGS. 19A, 19B, and 19C depict the calculated 2D mode profiles of rectangular germanium waveguides on silicon pedestal with waveguide widths of 0.75 ⁇ , 2.0 ⁇ , and 3.5 ⁇ , respectively, on a logarithmic scale (darker shading indicates higher intensity.
  • Each plot also shows an outline of the corresponding germanium waveguide/silicon pedestal structure superimposed onto the mode profiles.
  • the mode is supported by both the germanium waveguide and the silicon pedestal.
  • a thicker waveguide tends to confine the mode better than a thinner waveguide.
  • FIGS. 21C and 2 ID show the mode profiles on a logarithmic scale for protrusion heights of 0.25 ⁇ and 2.0 ⁇ , respectively, with darker shading indicating higher intensity. (The corresponding protruded germanium waveguide/silicon pedestal structures are superimposed onto the mode profiles.)
  • FIGS. 21B-21D shows that increasing the protrusion height increases the mode confinement and changes the mode's shape, which has implications for coupling light into and out of the waveguide.
  • FIGS. 22 and 23A-23C illustrate two processes for fabricating a germanium waveguide on a silicon pedestal: a first process 800 that involves selectively growing germainium in an oxide trench and a second process 850 that involves dry etching a germanium layer on a silicon substrate.
  • Both processes 800 and 850 start with a blanket silicon wafer (step 802).
  • silicon oxide is thermally grown or deposited on Si substrate (step 804).
  • the silicon oxide is patterned by lithography or any other suitable process to define a trench that extends to the surface of the silicon substrate (step 806).
  • the trench defines the shape of the germanium waveguide and can be made using a combination of dry etching and wet etching to prevent damage to the surface of the silicon substrate.
  • step 808 single crystalline germanium is grown epitaxially on the exposed silicon inside the silicon oxide trench by chemical vapor deposition (CVD), such as ultra-high- vacuum CVD or reduced pressure CVD, or any other suitable germanium deposition technique.
  • FIG. 23A is an annotated SEM image that shows the cross section of germanium waveguide grown on a silicon substrate within a trench formed in a layer of silicon dioxide on the silicon substrate's surface.
  • the germanium is intrinsic (undoped) to reduce free carrier absorption. Because the silicon oxide is not transparent in the mid-IR range, it is removed by wet etching with a chemical, such as a buffered oxide etchant, that selectively etches silicon oxide over germanium and silicon (step 810).
  • FIG. 23B is an annotated SEM image that shows the cross section of germanium waveguide on a silicon substrate after removal of the silicon dioxide.
  • step 812 a portion of the silicon under the germanium is selectively etched away to form a Ge-on-Si undercut waveguide.
  • Suitable etchants include, but are not limited to tetramethylammonium hydroxide (TMAH) solution and potassium hydroxide (KOH), each of which wet etches silicon but not germanium.
  • TMAH tetramethylammonium hydroxide
  • KOH potassium hydroxide
  • Anisotropic etching of the silicon (100) planes and (111) planes causes sidewalls of the silicon pedestal to form an angle of about 54.7° with the bottom of the germanium waveguide.
  • the anisotropic etching in step 812 can be carried out with solution temperatures ranging from room temperature (about 25° C) to about 90° C and at solution concentrations selected based on the desired etching rates of the silicon (100) and (111) planes.
  • solution temperatures ranging from room temperature (about 25° C) to about 90° C and at solution concentrations selected based on the desired etching rates of the silicon (100) and (111) planes.
  • solution temperatures ranging from room temperature (about 25° C) to about 90° C and at solution concentrations selected based on the desired etching rates of the silicon (100) and (111) planes.
  • TMAH solution a 25% TMAH solution at 70° C for 150 minutes yield the germanium waveguide/silicon pedestal shown in FIG. 23C.
  • FIG. 23C shows that the angle between the pedestal sidewall and the bottom of the waveguide is about 54.7°, the pedestal upper base width d ⁇ is about 500 nm, and the waveguide width w is about 2.2 ⁇ .
  • a germanium layer is grown epitaxially on the silicon substrate using CVD or any other suitable deposition technique in step 852.
  • the germanium layer is patterned lithographically and dry etched down to the surface of the silicon substrate to form a germanium waveguide in step 854.
  • the germanium waveguide is then undercut in step 812 (described above) to form a silicon pedestal underneath the germanium waveguide.
  • the second process 850 has fewer steps that the first process 800, it includes dry etching that may result in a germanium waveguide with rougher sidewalls. It may also be difficult to find dry etching chemicals that etch germanium without etching silicon (much).
  • inventive embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described and claimed.
  • inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and/or method described herein.
  • embodiments of designing and making the coupling structures and diffractive optical elements disclosed herein may be implemented using hardware, software or a combination thereof.
  • the software code can be executed on any suitable processor or collection of processors, whether provided in a single computer or distributed among multiple computers.
  • a computer may be embodied in any of a number of forms, such as a rack-mounted computer, a desktop computer, a laptop computer, or a tablet computer. Additionally, a computer may be embedded in a device not generally regarded as a computer but with suitable processing capabilities, including a Personal Digital Assistant (PDA), a smart phone or any other suitable portable or fixed electronic device.
  • PDA Personal Digital Assistant
  • a computer may have one or more input and output devices. These devices can be used, among other things, to present a user interface. Examples of output devices that can be used to provide a user interface include printers or display screens for visual presentation of output and speakers or other sound generating devices for audible
  • Examples of input devices that can be used for a user interface include keyboards, and pointing devices, such as mice, touch pads, and digitizing tablets.
  • a computer may receive input information through speech recognition or in other audible format.
  • Such computers may be interconnected by one or more networks in any suitable form, including a local area network or a wide area network, such as an enterprise network, and intelligent network (IN) or the Internet.
  • networks may be based on any suitable technology and may operate according to any suitable protocol and may include wireless networks, wired networks or fiber optic networks.
  • the various methods or processes may be coded as software that is executable on one or more processors that employ any one of a variety of operating systems or platforms. Additionally, such software may be written using any of a number of suitable programming languages and/or programming or scripting tools, and also may be compiled as executable machine language code or intermediate code that is executed on a framework or virtual machine.
  • inventive concepts may be embodied as a computer readable storage medium (or multiple computer readable storage media) (e.g., a computer memory, one or more floppy discs, compact discs, optical discs, magnetic tapes, flash memories, circuit configurations in Field Programmable Gate Arrays or other semiconductor devices, or other non-transitory medium or tangible computer storage medium) encoded with one or more programs that, when executed on one or more computers or other processors, perform methods that implement the various embodiments of the invention discussed above.
  • the computer readable medium or media can be transportable, such that the program or programs stored thereon can be loaded onto one or more different computers or other processors to implement various aspects of the present invention as discussed above.
  • program or “software” are used herein in a generic sense to refer to any type of computer code or set of computer-executable instructions that can be employed to program a computer or other processor to implement various aspects of embodiments as discussed above. Additionally, it should be appreciated that according to one aspect, one or more computer programs that when executed perform methods of the present invention need not reside on a single computer or processor, but may be distributed in a modular fashion amongst a number of different computers or processors to implement various aspects of the present invention.
  • Computer-executable instructions may be in many forms, such as program modules, executed by one or more computers or other devices.
  • program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types.
  • functionality of the program modules may be combined or distributed as desired in various embodiments.
  • data structures may be stored in computer-readable media in any suitable form.
  • data structures may be shown to have fields that are related through location in the data structure. Such relationships may likewise be achieved by assigning storage for the fields with locations in a computer-readable medium that convey relationship between the fields.
  • any suitable mechanism may be used to establish a relationship between information in fields of a data structure, including through the use of pointers, tags or other mechanisms that establish relationship between data elements.
  • inventive concepts may be embodied as one or more methods, of which an example has been provided.
  • the acts performed as part of the method may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include performing some acts simultaneously, even though shown as sequential acts in illustrative embodiments.
  • a reference to "A and/or B", when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.
  • the phrase "at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements.
  • This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase "at least one" refers, whether related or unrelated to those elements specifically identified.
  • At least one of A and B can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another

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Abstract

La présente invention concerne un guide d'onde semi-conducteur à socle, à gaine d'air et de la taille d'une puce, le guide d'onde pouvant être utilisé comme capteur de rayonnement infrarouge moyen (mid-IR) capable de surveiller in situ des solvants organiques et d'autres analytes. Le capteur utilise un couplage évanescent provenant d'un guide d'onde en silicium ou en germanium qui est hautement transparent dans la partie mid-IR du spectre électromagnétique (par exemple, entre = 1,3 m et = 6,5 m pour le silicium et = 1,3 m et = 12,0 m pour le germanium), pour sonder le spectre d'absorption du fluide entourant le guide d'onde. L'envoi d'un faisceau mid-IR dans le guide d'onde exposé à un analyte particulier entraîne l'atténuation des composants spectraux des ondes évanescentes due à une absorption par les liaisons carbone, oxygène, hydrogène et/ou azote dans le fluide environnant. La détection de ces changements au niveau de la sortie du guide d'onde fournit une indication sur le type et la concentration d'un ou de plusieurs composés dans le fluide environnant. Si cela est souhaité, le capteur peut être intégré sur un substrat de silicium avec une source de lumière mid-IR et un détecteur mid-IR pour former un spectromètre à base de puce.
PCT/US2013/069687 2013-03-12 2013-11-12 Procédés et appareil de détection des rayonnements infrarouges moyens WO2014143204A1 (fr)

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