WO2010140998A1 - Nanospectromètre intégré optique et procédé de fabrication de celui-ci - Google Patents

Nanospectromètre intégré optique et procédé de fabrication de celui-ci Download PDF

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Publication number
WO2010140998A1
WO2010140998A1 PCT/US2009/003343 US2009003343W WO2010140998A1 WO 2010140998 A1 WO2010140998 A1 WO 2010140998A1 US 2009003343 W US2009003343 W US 2009003343W WO 2010140998 A1 WO2010140998 A1 WO 2010140998A1
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nanospectrometer
grating
optical integrated
super
light
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PCT/US2009/003343
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English (en)
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Vladimir Yankov
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Vladimir Yankov
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Priority to PCT/US2009/003343 priority Critical patent/WO2010140998A1/fr
Publication of WO2010140998A1 publication Critical patent/WO2010140998A1/fr

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    • 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
    • G01J3/28—Investigating the spectrum
    • G01J3/2803—Investigating the spectrum using photoelectric array detector
    • 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
    • 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
    • G01J3/0208—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows using focussing or collimating elements, e.g. lenses or mirrors; performing aberration correction
    • 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
    • G01J3/0218—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows using optical fibers
    • 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
    • G01J3/024—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows using means for illuminating a slit efficiently (e.g. entrance slit of a spectrometer or entrance face of fiber)
    • 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
    • G01J3/0256—Compact construction
    • G01J3/0259—Monolithic
    • 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
    • G01J3/10—Arrangements of light sources specially adapted for spectrometry or colorimetry
    • 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
    • G01J3/12—Generating the spectrum; Monochromators
    • G01J3/18—Generating the spectrum; Monochromators using diffraction elements, e.g. grating
    • G01J3/1838—Holographic gratings
    • 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
    • G01J3/12—Generating the spectrum; Monochromators
    • G01J3/18—Generating the spectrum; Monochromators using diffraction elements, e.g. grating
    • G01J3/1895—Generating the spectrum; Monochromators using diffraction elements, e.g. grating using fiber Bragg gratings or gratings integrated in a waveguide
    • 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
    • G01J3/28—Investigating the spectrum
    • G01J3/44—Raman spectrometry; Scattering spectrometry ; Fluorescence spectrometry
    • 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
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
    • G01N21/65—Raman scattering
    • G01N21/658—Raman scattering enhancement Raman, e.g. surface plasmons
    • 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
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/71—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light thermally excited
    • G01N21/718—Laser microanalysis, i.e. with formation of sample plasma
    • 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
    • G01N21/75—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated
    • G01N21/77—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator
    • G01N21/7703—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator using reagent-clad optical fibres or optical waveguides
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B6/12007—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind forming wavelength selective elements, e.g. multiplexer, demultiplexer
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G02B6/29304—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating
    • G02B6/29316—Light guides comprising a diffractive element, e.g. grating in or on the light guide such that diffracted light is confined in the light guide
    • G02B6/29325—Light guides comprising a diffractive element, e.g. grating in or on the light guide such that diffracted light is confined in the light guide of the slab or planar or plate like form, i.e. confinement in a single transverse dimension only
    • G02B6/29328—Diffractive elements operating in reflection
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/04—Processes or apparatus for producing holograms
    • G03H1/0402—Recording geometries or arrangements
    • G03H1/0408—Total internal reflection [TIR] holograms, e.g. edge lit or substrate mode holograms
    • 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
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
    • G01N21/65—Raman scattering
    • G01N2021/653—Coherent methods [CARS]
    • G01N2021/656—Raman microprobe
    • 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
    • G01N21/75—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated
    • G01N21/77—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator
    • G01N21/7703—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator using reagent-clad optical fibres or optical waveguides
    • G01N2021/7706—Reagent provision
    • G01N2021/7736—Reagent provision exposed, cladding free
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/0005—Adaptation of holography to specific applications
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/02—Details of features involved during the holographic process; Replication of holograms without interference recording
    • G03H1/024—Hologram nature or properties
    • G03H1/0244—Surface relief holograms

Definitions

  • the present invention generally relates to optical spectrometry for detecting small quantities of analytes and for other related applications.
  • the present invention provides a miniature integrated optical spectrometer based on nano-structures embedded into planar waveguides.
  • this type of optical chip can be used as a spectral device for limited amount of wavelengths; however, extending this type of optical chip to a large number of channels is not feasible, and this is the main disadvantage of the approach.
  • the gratings are separated spatially for sequential processing of light. As the number of channels and correspondingly the number of wavelengths to be processed grows, the size of the device increases, the path of light to the remote gratings grows, and, consequently, intrinsic losses grow as well. Also, building large devices is difficult and expensive due to limited precision of the lithographic process and limited uniformity of the waveguide used for gratings.
  • a new approach to spectral planar integrated devices is based on superposition of multiple sub-gratings on the same planar area. Each sub-grating resonates to a fixed wavelength, but a super-grating comprising many sub-gratings can be deployed as a spectral instrument.
  • U.S. Patent Applications such as U.S. Patent Application Ser. No. 405,160 filed by V. Yankov et al on April 2, 2003 entitled “Planar holographic multiplexer/demultiplexer"; U.S. Patent Application Ser. No. 137,152 filed by S. Babin et al on May 2, 2002 entitled "Photonic multi-bandgap lightwave device and methods for manufacturing thereof; U.S.
  • CCDs charge-coupled devices
  • the device comprises a CCD Planar spectrometer operable in either one- or two-dimensional modes.
  • An object of the present invention is to provide a nanospectrometer on the basis of digitally generated diffraction structures in planar optical waveguides. Another object of the invention is to provide a method of manufacturing the aforementioned nanospectrometer by means of microlithography. It is a further object to provide a nanospectrometer with super-gratings that comprise multiple sub-gratings consisting of standard binary features such as dashes or grooves etched or formed in a planar waveguide by means of microlithography.
  • the nanospectrometers of the invention use diffraction structures, which are combinations of numerous nano features placed in a configuration and providing multiple functionalities such as guiding light, resonantly reflecting light at multiple wavelengths, directing light to detectors, and focusing light on detectors.
  • a diffraction structure can be described as a super-grating because it is an optimized combination of overlaid sub-gratings, each of which is resonant to a single wavelength of light.
  • Each device includes at least one sensor, at least one light source of spectrum, at least one super-grating in an optical waveguide, and at least one array of detectors.
  • the device of the present invention allows detection of small amounts of analytes in gases and liquids or on solid surfaces and can be particularly advantageous for field analysis of environmental safety in multiple locations because of its miniature size and low cost.
  • the super-grating comprises multiple sub-gratings, which consist of standard binary features like dashes * or grooves * etched or otherwise formed in a planar waveguidejn order to generate local modulations of effective refractive index inside a planar optical waveguide. Positions of standard features are determined by a generating function, which is calculated based on desired parameters of the super-grating. Essentially, these gratings are sets of zeroes and ones engraved on the planar waveguide.
  • a typical grating consists of, several million features, which could be used in huge number of combinations, but only a few of them are appropriate for efficient operation; therefore, it is necessary to optimize the generating function.
  • each super-grating is generated as_a mathematical superposition of elliptic, parabolic, or hyperbolic sub-gratings with a spatial period of approximately one-half wavelength by a method characterized by the following steps.
  • the first to be created is a two-dimensional analog-generating function A(x,y) representing a superposition of modulation profiles of the refractive index.
  • Each modulation function corresponds to the equivalent of a sub-grating. Determined in this step is a two- dimensional generating function A(x,y), which resembles an interference pattern of wavelengths emitted from multiple sources at different wavelengths.
  • the generating function A(x,y) is a mathematical linear superposition of integration of elliptic sub- gratings, wherein each sub-grating is tuned to resonantly reflect at one of the N spectral channels.
  • the next step is binarization of a two-dimensional analog-generating function A(x,y), which was produced in the previous step. Binarization is achieved by applying a threshold value and assigning 1 to all areas above the predetermined threshold and 0 to the remaining areas in order to obtain a digital two-dimensional generating function B(x,y).
  • the last step is lithographic fabrication of the calculated standard microlithographic features by etching all binary features as function C(x,y) to a calculated depth on a planar waveguide.
  • the present invention further provides the step of applying an apodization function to a function representing a plurality of binary features to be written by using single-layer (binary) microlithography. This is necessary in order to suppress side lobes of the transfer function.
  • an apodization function g(r) is determined and applied to binary features by removing some of the binary features to the extent that an average density of the binary features becomes proportional to g(r).
  • the present invention further provides the step of correcting crosstalk by imposing a linear relationship on geometrical positions of input/output ports and central frequencies of channels.
  • crosstalk can be suppressed by precompensation of generating function A(x,y).
  • the present invention makes it possible to develop nanospectrometers of different types that can be integrated on a chip for detection of solid, liquid, or gas analytes.
  • these nanospectrometers are the following: a laser-induced breakdown (LIB) spectrometer, an absorption spectrometer, or a Raman spectrometer.
  • LIB laser-induced breakdown
  • Fig. 1 illustrates an exemplary super-grating embedded into a planar waveguide according to one modification of the present invention.
  • Fig. 2 illustrates a fragment of an exemplary realization of a function C(x, y) for a super- grating with eight resonant wavelengths made in accordance with the invention.
  • Fig. 3A shows the simulated transfer function for a 4-channel PBQC according to the invention.
  • Fig. 3B shows the transfer function for the same device as in Fig. 3 A, measured experimentally.
  • Fig. 4 A demonstrates the transfer function of a 4-channel super-grating with low channel isolation (high crosstalk) according to the invention.
  • Fig. 4B demonstrates the transfer function for the same device as in Fig. 4A, measured experimentally.
  • Fig. 5 shows the wave vectors of sub-gratings participating in the synthesis of a super- grating made in accordance with the invention.
  • Fig. 6 illustrates the grating apodization function g(r) formed by the method of the invention.
  • Fig. 7 shows the configuration of the laser-induced breakdown (LIB) nanospectrometer corresponding to the present invention.
  • LIB laser-induced breakdown
  • Fig. 8 shows the configuration of the absorption nanospectrometer of the invention with multiple super-luminescent diode light sources.
  • Fig. 9 demonstrates the absorption nanospectrometer of the invention with a bare fiber probe.
  • Fig. 10 presents the Raman nanospectrometer on a chip made in accordance with the invention.
  • Fig. 1 IA shows the layout of the Raman nanospectrometer with a fiber probe made in accordance with the invention.
  • Figs. 1 IB through 1 1C illustrate the shapes of the fiber face used in the spectrometer of Fig. HA.
  • Fig. 12 illustrates a folded nanospectrometer of the invention that has improved resolution.
  • the term "super-grating” means a digital planar hologram that performs multiple functions and operates for a plurality of channels incorporated into a nanospectrometer.
  • the term "sub-grating” means a virtual component of the aforementioned digital planar hologram that provides operation of a single light- signal-transmitting channel.
  • the same elements of different sub-gratings belong to the same super-grating.
  • the physics of a spectral super-grating, deployed in the invented spectrometers, is complicated, and for this reason several theoretical models should be used to explain the properties of transfer function.
  • the super-grating works like a superposition of elliptical sub-gratings, each of which connects an input port with one of multiple output ports.
  • the sub-gratings are structures that are composed of multiple nano- features that modulate the refractive index of a planar waveguide where propagating light is confined.
  • the nano-features are positioned in a manner to provide resonant reflection of light of a predefined wavelength.
  • the super-grating works like a superposition of sub- I gratings, reflecting multiple wavelengths to assigned output ports.
  • the super-grating can be also considered as a photonic bandgap quasi-crystal with a quasi- periodic structure and multiple periods corresponding to multiple bandgaps.
  • light propagates in any direction except specifically designed one, thus resulting in light reflection from one ellipse focus into another.
  • These photonic bandgap quasi- crystals can be made by means of binary lithography, nano-imprinting, or other methods on planar waveguides and contain nano-features that modulate the refractive index, and are made for example, into the form of dashes.
  • the super-grating is synthesized from multiple sub-gratings in a synergistic manner, which includes a mathematical superposition of modulation functions followed by binarization. This process is substantially different from direct superposition of sub- gratings because superposition originates as a mathematical step, which effectively averages a plurality of modulation functions having varying phases.
  • each super-grating is originally computed as a mathematical superposition of elliptic, parabolic, or hyperbolic sub-gratings with a spatial period of approximately one-half wavelength, for which this sub-grating will be resonant (reflective).
  • An analog-generating function A(x,y) that describes modulation of the refractive index in a planar waveguide and resembling a superposition of a plurality of interference fringes of diverging and converging light beams is implemented according to the following expression:
  • F is a vector connecting the input port to an arbitrary point (x,y) on the planar surface
  • F 1 0 "' is a vector that connects this point with coordinates (x,y) to the output port i for a chosen wavelength X 1 ;
  • Highlight a is a weight coefficient associated with wavelength / ; and ⁇ , is an arbitrary phase associated with wavelength; and f(x,y) is a function that compensates for variation of refractive index. (All of the parameters above are associated with wavelength Z 1 )
  • the A(x,y) function resembles holographic fringes with an omitted factor 1/r to avoid performance deterioration.
  • A(x,y) n(x,y) ⁇ A(x,y) (2) would have the best performance, but, unfortunately, it cannot be fabricated by mass production technologies (microlithography, nano-imprinting, or the like).
  • the analog-generating function A (x,y) can be implemented as its surface relief. This will modulate the effective refractive index as prescribed by formula (1), but fabricating that multilevel relief with modern lithography is very difficult if possible at all. Therefore, to make this approach practical, the relief must be reduced to a binary shape, meaning that there cannot be more than one nano-feature at each location. According to the present invention, this problem is solved by approximating the analog- generating function A(x,y) with proper positioning of standard nano-features, for example, dashes, or short straight grooves.
  • binarization of function A(x,y) is further implemented by applying a threshold value by assigning 1 to all areas above the predetermined threshold and 0 to the remaining areas.
  • a threshold value assigning 1 to all areas above the predetermined threshold and 0 to the remaining areas.
  • the shape of function B(x,y) is simplified by replacing ditches with curved boundaries by a combination of standard microlithographic nano-features (short straight grooves or dashes). This operation can be described as quantization of binary function B(x,y) to produce a discrete function C(x,y), which is nothing but a collection of standard nano-features (dashes) that can be formed according to the aforementioned mass-production methods.
  • the last parameter of the super-grating to be determined is the depth of dashes to be formed in a planar waveguide by microlithography or nano-imprinting.
  • Fig. 1 illustrates an exemplary nanospectrometer 20 having an integrated super-grating 30 with a planar waveguide 31 that comprises several flat layers of transparent optical materials, each associated with different refraction indices.
  • the materials are chosen so that one of them, referred to herein as the core 24, has a refractive index, which is higher than the refractive indices of the cladding 22. This provides a low-loss guiding of lightwaves through the core 24.
  • an input light signal 26 comprising multiple wavelengths to be spectrally analyzed enters the planar waveguide 31 through an input port 28 from an optical fiber or from a ridge waveguide (not shown in Fig. 1) and propagates within a sector determined by the angular aperture of the input port.
  • the super- grating 30 that incorporates multiple nano-features organized according to discrete generating function C(x,y) is embedded into one or more layer interfaces of the waveguide.
  • the super-grating 30 works as a thick (volume) digital hologram directing light of various wavelengths to the assigned output ports 32 and 34.
  • Fig. 2 illustrates a fragment of an exemplary realization of discrete generating function C(x, y) for an eight-channel super-grating 36 (dark lines that represent grooves etched on the layer interface(s) of the waveguide).
  • This super-grating 36 resonantly reflects eight various wavelengths to the assigned output ports 32 and 34 (Fig. 1).
  • FIG. 3A shows a simulated transfer function for a four-channel super-grating
  • the sub-grating (channel) transfer functions are denoted as A, B, C, and D.
  • wavelengths (nm) are plotted on the abscissa axis, and the intensity (arbitrary units) is plotted on the ordinate axis.
  • the effective refractive index for the TE mode is about 1.53, for the TM mode about 1.47, and for cladding modes about 1.44.
  • optimization of the super-grating design consists of finding an analog-generating function A(x,y) that provides best possible performance for the super-grating after the aforementioned binarization and quantization procedures.
  • Binarization of the analog- generating function A(x,y) is a strongly nonlinear transform. In accordance with the rules of nonlinear transform, if A(x,y) includes just three Fourier components with wave vectors
  • the Fourier spectrum of the generated binary relief would include the beating-generated wave vectors ⁇ ,* ⁇ expressed by a linear combination of the three original wave vectors: where m, n, and / are arbitrary positive or negative integers.
  • These parasitic Fourier harmonics may be responsible for high crosstalk (insufficient channel isolation). In fact, this effect was observed both in simulations and experiments, as illustrated in Fig. 4A (simulation) and Fig. 4B (experiment).
  • the wavelengths (nm) are plotted on the abscissa axis, and the intensity (arbitrary units) is plotted on the ordinate axis.
  • the transfer function of a four-channel super-grating demonstrates high crosstalk and low channel isolation about 8 dB only, while it is typically required that isolation be not less than 25 dB.
  • the above problem can be solved by properly positioning the output ports. Let us assume now that at some point the directions of wave vectors vary with absolute value of sub-grating wave vectors linearly so that the tips of the vectors lie on a straight line, as shown in Fig. 5, where E, F, G, and H are the wave vectors of channel sub-gratings.
  • any linear combination of wave vectors lies on the same straight line that is frequency of reflected light is a function of reflection direction and, consequently, crosstalk is avoided, [is unclear as written.]
  • ⁇ t is the central frequency of the channel
  • the wave vectors of the channel sub- gratings will lie on straight lines, as shown in Fig. 5.
  • the positions of the input port as well as channel spacing are arbitral. It is understood that the input port receives light having specific spectral characteristics or a spectrum obtained from a light source, which is conventionally shown by reference numeral 37 in Fig. 1.
  • apodized super-grating Inside the apodized super-grating the modulation function smoothly grows in a central zone of the super-grating from zero (no n(x,y) modulation) to unit (maximum n(x,y) modulation) and then slowly drops to zero at its end.
  • Full-scale modulation occurs only in the central part of the super-grating, which is surrounded with areas of variable modulation depth to provide a smooth transition from a nonmodulated to a fully modulated refractive index. Because the present invention uses binary nano-features, apodization can be implemented by removing some nano-features in the transitional areas so that the average density of the binary nano-features becomes proportional tog(r) .
  • a compensation function is applied in order to compensate for variations in the average refractive index.
  • a digital planar hologram creates a variation of the average effective refractive index so that the light wavelength within the digital planar hologram differs from that within the blank part of a planar waveguide.
  • a compensation function can be defined by the following equation:
  • An is the averaged variation of the effective refractive index in the vicinity of a given point, a is the scaling parameter, and r is the distance to an input port.
  • the super-grating apodization is illustrated in Fig. 6, where 23 and 25 are transitional areas and 24 is the central super-grating zone with the area of maximum modulation of the planar waveguide refractive index.
  • the super-grating is the main component of any nanospectrometer made in accordance with the present invention; however, as explained below, in order to improve functionality, the spectrometer should include some additional components. It should be understood that depending on the proposed nanospectrometer configuration, all or almost all components will be integrated on the same planar waveguide as the super-grating.
  • the first configuration of the nanospectrometer is a laser-induced breakdown (LIB) spectrometer, shown in Fig. 7.
  • the LIB nanospectrometer is integrated on a base 100, which can be a piece of silicon wafer or any other substance appropriate for attaching all components.
  • the super-grating 108 is embedded into a planar waveguide 104.
  • a laser 101 is integrated on the same base 100 and is coupled with a ridge waveguide 102, which, in turn, is coupled with the planar waveguide 104 so that the laser beam propagates directly to a narrowband concave grating 103.
  • This grating is embedded into the same planar waveguide 104 and is implemented as a sub-grating component of the super-grating with the function to reflect and focus the laser beam for coupling it into an optical fiber 105.
  • the laser beam is delivered by the fiber to an object having a solid or liquid surface 107, which needs to be studied and on which the laser beam must be focused through a focusing lens 106. In a small focus, the laser intensity gets high enough to ionize the superficial layer on the surface of the object, and the created plasma emits optical radiation, the spectrum of which is a unique determinant for the ionized substance.
  • This optical radiation is acquired with the focusing lens 106 and is coupled back to the fiber 105, which delivers it to the super-grating 108 for analysis.
  • the super-grating separates light into channels and focuses them on the arrays 109 and 1 10 of detectors for converting them into electrical signals that can be displayed and processed.
  • the device is made as an absorption nanospectrometer, as shown in Fig. 8. All spectrometer components are integrated on a single chip.
  • the device comprises a base 200, which can be a piece of silicon wafer or any other substance appropriate for attaching all components, several super-luminescent laser-emitting diodes (SLED) 201, 202, 203, 204, and 205, which radiate in various spectral bands in order to cover the spectral range appropriate for absorption analysis.
  • SLED super-luminescent laser-emitting diodes
  • All SLEDs are coupled at a point of coupling with ridge waveguides 206, 207, 208, 209, and 210 into a bare ridge guide 211.
  • the ridge guide is referred to as "bare” because it does not have the upper cladding that provides better interaction with the environment and higher sensitivity.
  • the bare waveguide spirals around the chip to accumulate a longer length for better sensitivity and is coupled into a slab waveguide 212 where the super-grating 212a is embedded.
  • Light, analyzed by the super-grating is focused on arrays 213 and 214 of detectors for conversion into electrical signals, which can be displayed and processed. This nanospectrometer can analyze liquids and gases.
  • the third modification which is shown in Fig. 9, provides an absorption nanospectrometer with a fiber sensor.
  • This nanospectrometer is similar to the previous one, but the sensor is implemented as a bare fiber (a fiber without a cladding) rather than as a ridge waveguide on a chip. This provides more convenient access to narrow channels or small gaps. All spectrometer components, in addition to the fiber sensor, are integrated on a single chip.
  • the nanospectrometer comprises a base 300, which can be a piece of silicon wafer or other substance appropriate for attaching all components, several super-luminescent laser- emitting diodes (SLED) 301, 302, 303, 304, and 305, which radiate in various spectral bands in order to cover the spectral range appropriate for absorption analysis. All SLEDs are coupled with ridge waveguides 306, 307, 308, 309, and 310 into an optical fiber, which consists of a core 31 1 and a cladding 312, which participates in guiding the light. At some distance from the chip, the cladding is removed, and a bare fiber 313 (core only) is used for guiding the light.
  • SLED super-luminescent laser- emitting diodes
  • the fiber probe is again coated with a cladding 314.
  • the fiber core 315 is coupled into a slab waveguide 316, where the super-grating 317 is embedded.
  • Light, analyzed by the super- grating 317, is focused on arrays 318 and 319 of detectors for conversion into electrical signals, which can be displayed and processed.
  • This nanospectrometer can analyze liquids and gases by submerging the bare fiber probe into them.
  • the fourth preferred modification is a Raman nanospectrometer on a chip. All spectrometer components are integrated on a base 400, which can be a piece of silicon wafer or other substance appropriate for attaching all components.
  • the spectrometer comprises a laser 401 coupled to a ridge waveguide without an upper cladding 402, a spiraling for higher sensitivity around a planar slab waveguide 404 and coupled thereto, a super-grating 405 embedded into the slab waveguide, and arrays 406, 407 of a detector.
  • a Raman-enhancing layer 404 comprising nanoparticles of silver or other metal used for increasing the Raman- effect cross-section by many orders of magnitude, typically by 10 9 -10 12 times and sometimes even more.
  • the laser beam propagates through the ridge waveguide, and each time it reflects from the top, the Raman spectrum caused by the environment is generated. After multiple reflections, the spectrum acquires higher intensity and can be analyzed by the super-grating 405, which is designed to freely transmit the laser wavelength and to focus the Raman spectrum on the arrays of detectors 406 and 407 for converting light signals into electrical signals that can be displayed and processed.
  • the fifth modification is a Raman nanospectrometer with a fiber probe. All spectrometer components, in addition to the fiber sensor, are integrated on a single chip, which has a base 500 that may be a piece of silicon wafer or other substance appropriate for attaching all components.
  • the spectrometer comprises a laser 501 coupled to a ridge waveguide 502 for guiding laser radiation to a planar slab waveguide 503. The laser beam propagates directly to a narrowband concave grating 504.
  • the grating of this modification is embedded into the same planar waveguide and is implemented as any sub- grating component of the super-grating with the function to reflect and focus the laser beam for coupling it into an optical fiber 506.
  • the laser beam is delivered to the fiber end, which is coated with a Raman-effect enhancing layer 507 that comprises nanoparticles of silver or other metal for increasing the Raman-effect cross-section by many orders of magnitude, typically by an increase of 10 9 -10 12 times and sometimes even more.
  • a Raman-effect enhancing layer 507 that comprises nanoparticles of silver or other metal for increasing the Raman-effect cross-section by many orders of magnitude, typically by an increase of 10 9 -10 12 times and sometimes even more.
  • the end of the probe is partially stripped of cladding and is made "D- shaped." Shapes of fiber faces that are designated by reference numerals 505, 508, and 507, respectively, are shown in Figs. 1 I B to 1 1C. Such shapes are needed to provide direct contact over a significant area between the Raman-enhancing layer and the fiber probe core 505.
  • the fiber end is cleaved at an oblique angle to prevent direct reflection of the laser beam back to the chip.
  • the laser beam After multiple reflections and acquiring the Raman shift, which is the signature of the environment around the probe, the laser beam returns to the chip, where the narrowband mirror reflects the laser wavelength and transmits the Raman-shifted part of the spectrum to a super-grating 504 for analysis.
  • the super-grating embedded into the slab waveguide 503 focuses the light spectrum on arrays 509 and 510 of the detectors for conversion into electrical signals, which can be displayed and processed.
  • the sixth preferred modification is a folded nanospectrometer of high resolution.
  • the folded layout allows for more compact design and for compensation of optical nonuniformities in a planar waveguide.
  • All spectrometer components are integrated on a single chip that has a base 600, which can be a piece of silicon wafer or other substance, appropriate for attaching the components.
  • the spectrometer comprises an input port 601, from which the light beam to be spectrally analyzed propagates directly to a broadband concave grating 602 that is embedded into the same planar waveguide and operates as a folding mirror.
  • the light beam sequentially goes through the multiple super- grating knees 604, 607, and 610 steered with folding mirrors 605, 606, 608, and 609, all of which are broadband gratings embedded into the same planar waveguide as are the other nanospectrometer components.
  • Each of the super-grating knees reflects spectrally dispersed light to array 61 1 of the detectors for converting light into electrical signals to be processed, analyzed, and displayed.
  • the present invention provides a nanospectrometer on the basis of digitally generated diffraction structures in planar optical waveguides.
  • the invention also provides a method of manufacturing the aforementioned nanospectrometer by means of microlithography.
  • the super-gratings of the proposed nanospectrometer comprise multiple sub-gratings consisting of standard binary features such as dashes or grooves etched in the planar waveguide by means of microlithography.

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Abstract

L'invention porte sur un nanospectromètre plan formé sous la forme d'une unique puce qui utilise des structures de diffraction, qui sont des combinaisons de nombreuses nanocaractéristiques placées suivant une configuration prédéterminée et assurant de multiples fonctionnalités, telles que le guidage de la lumière, la réflexion en résonance de la lumière à de multiples longueurs d'onde, la direction de la lumière vers des détecteurs et la concentration de la lumière sur les détecteurs. La structure de diffraction peut être décrite comme étant un hologramme plan numérique qui comprend une combinaison optimisée de sous-réseaux virtuels superposés, chacun d'eux étant en résonance à une unique longueur d'onde de la lumière. Chaque dispositif comprend au moins un capteur, au moins une source de lumière et au moins un hologramme plan numérique dans un guide d'onde optique. Le dispositif selon la présente invention permet la détection de petites quantités d'analytes dans des gaz et des liquides ou sur des surfaces de solides et peut être particulièrement avantageux pour une analyse sur le terrain de la sécurité environnementale dans de multiples emplacements en raison de sa taille miniature et de son coût bas.
PCT/US2009/003343 2009-06-02 2009-06-02 Nanospectromètre intégré optique et procédé de fabrication de celui-ci WO2010140998A1 (fr)

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WO2014129970A1 (fr) 2013-02-19 2014-08-28 National University Of Singapore Instrument et procédé de diagnostic
US9612402B2 (en) 2012-01-12 2017-04-04 Hewlett Packard Enterprise Development Lp Integrated sub-wavelength grating system
CN107636432A (zh) * 2015-01-06 2018-01-26 玛斯特股份有限公司 用于检测磨损金属的mems实现方式
CN110595619A (zh) * 2018-06-13 2019-12-20 浙江澍源智能技术有限公司 一种光电一体化复合芯片的制造方法
CN112997058A (zh) * 2018-11-07 2021-06-18 应用材料公司 用于波导计量的方法与设备
WO2022090728A1 (fr) * 2020-10-30 2022-05-05 Heriot-Watt University Spectromètre à puce photonique

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CN112997058A (zh) * 2018-11-07 2021-06-18 应用材料公司 用于波导计量的方法与设备
WO2022090728A1 (fr) * 2020-10-30 2022-05-05 Heriot-Watt University Spectromètre à puce photonique

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