WO2020130917A1 - Communication par lumière visible à l'aide de lasers incorporés dans du bois transparent - Google Patents

Communication par lumière visible à l'aide de lasers incorporés dans du bois transparent Download PDF

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Publication number
WO2020130917A1
WO2020130917A1 PCT/SE2019/051295 SE2019051295W WO2020130917A1 WO 2020130917 A1 WO2020130917 A1 WO 2020130917A1 SE 2019051295 W SE2019051295 W SE 2019051295W WO 2020130917 A1 WO2020130917 A1 WO 2020130917A1
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WIPO (PCT)
Prior art keywords
luminophores
product
vlc
light
pumping
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PCT/SE2019/051295
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English (en)
Inventor
Sergei Popov
Lars Berglund
Yuanyuan Li
Ilya Sychugov
Original Assignee
Cellutech Ab
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Publication of WO2020130917A1 publication Critical patent/WO2020130917A1/fr

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
    • B27K—PROCESSES, APPARATUS OR SELECTION OF SUBSTANCES FOR IMPREGNATING, STAINING, DYEING, BLEACHING OF WOOD OR SIMILAR MATERIALS, OR TREATING OF WOOD OR SIMILAR MATERIALS WITH PERMEANT LIQUIDS, NOT OTHERWISE PROVIDED FOR; CHEMICAL OR PHYSICAL TREATMENT OF CORK, CANE, REED, STRAW OR SIMILAR MATERIALS
    • B27K3/00—Impregnating wood, e.g. impregnation pretreatment, for example puncturing; Wood impregnation aids not directly involved in the impregnation process
    • B27K3/16—Inorganic impregnating agents
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
    • B27K—PROCESSES, APPARATUS OR SELECTION OF SUBSTANCES FOR IMPREGNATING, STAINING, DYEING, BLEACHING OF WOOD OR SIMILAR MATERIALS, OR TREATING OF WOOD OR SIMILAR MATERIALS WITH PERMEANT LIQUIDS, NOT OTHERWISE PROVIDED FOR; CHEMICAL OR PHYSICAL TREATMENT OF CORK, CANE, REED, STRAW OR SIMILAR MATERIALS
    • B27K3/00—Impregnating wood, e.g. impregnation pretreatment, for example puncturing; Wood impregnation aids not directly involved in the impregnation process
    • B27K3/02—Processes; Apparatus
    • B27K3/15—Impregnating involving polymerisation including use of polymer-containing impregnating agents
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
    • B27K—PROCESSES, APPARATUS OR SELECTION OF SUBSTANCES FOR IMPREGNATING, STAINING, DYEING, BLEACHING OF WOOD OR SIMILAR MATERIALS, OR TREATING OF WOOD OR SIMILAR MATERIALS WITH PERMEANT LIQUIDS, NOT OTHERWISE PROVIDED FOR; CHEMICAL OR PHYSICAL TREATMENT OF CORK, CANE, REED, STRAW OR SIMILAR MATERIALS
    • B27K5/00—Treating of wood not provided for in groups B27K1/00, B27K3/00
    • B27K5/02—Staining or dyeing wood; Bleaching wood
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/11—Arrangements specific to free-space transmission, i.e. transmission through air or vacuum
    • H04B10/114—Indoor or close-range type systems
    • H04B10/116—Visible light communication
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
    • B27K—PROCESSES, APPARATUS OR SELECTION OF SUBSTANCES FOR IMPREGNATING, STAINING, DYEING, BLEACHING OF WOOD OR SIMILAR MATERIALS, OR TREATING OF WOOD OR SIMILAR MATERIALS WITH PERMEANT LIQUIDS, NOT OTHERWISE PROVIDED FOR; CHEMICAL OR PHYSICAL TREATMENT OF CORK, CANE, REED, STRAW OR SIMILAR MATERIALS
    • B27K2240/00—Purpose of the treatment
    • B27K2240/10—Extraction of components naturally occurring in wood, cork, straw, cane or reed
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L97/00—Compositions of lignin-containing materials
    • C08L97/02—Lignocellulosic material, e.g. wood, straw or bagasse

Definitions

  • the present disclosure relates to system and products for visible light communication (VLC). More specifically, the proposed technique relates to VLC via laser emitting luminophores embedded into transparent wood.
  • the disclosure comprises a transparent wood product, a VLC system comprising the transparent wood product and methods for generating white light and providing VLC using the VLC system.
  • Visible light communication is an emerging technology in the field of wireless communication that provides communication alongside illumination, and that can be incorporated into existing lighting infrastructures as a complementary functionality, alleviating pressure on the limited radio frequency spectrum.
  • Traditional radio and microwave communication systems suffer from limited channel capacity and transmission rate due to the limited radio spectrum available.
  • VLC systems are among the promising solutions to the bandwidth limitation problem faced by radio frequency systems.
  • VLC utilizes a light source as its transmitter where information is modulated into the intensity of the emitted light.
  • Most VLC systems to date uses light emitting diodes (LEDs) because of their superior switching capabilities compared to traditional incandescent and fluorescent sources.
  • VLC systems have several advantages over radio systems, such as immunity against interference caused by adjacent channels with the possibility of frequency reuse in different parts of the same building, it also offers better security at the physical layer due to the fact that
  • VLC systems are energy efficient system due to its dual functionally of illumination and communication, it provides license-free bandwidth, and can be harmless for humans and other electronic devices.
  • ISI inter symbol interference
  • the modulation bandwidth available in the transmitters (LEDs) is typically less than the VLC channel bandwidth, which means that the former limits the transmission rates.
  • An object of the present disclosure is to provide methods and devices which seek to mitigate, alleviate, or eliminate the above-identified deficiencies in the art and disadvantages singly or in any combination.
  • This object is obtained by a VLC system comprising a transparent wood (TW) product and one or more pumping source for generation of light for illumination and transmission of information.
  • TW transparent wood
  • a transparent wood product for providing white light illumination and visible light communication, comprising a TW matrix doped with luminophores embedded into the fiber cavities (e.g. cellulose/wood fiber cavities) of the TW matrix, where the combined emitted light from the luminophores form white light, substantially white light or light perceived as white light.
  • a transparent wood product for providing white light illumination and visible light communication, comprising a TW matrix doped with luminophores embedded into the fiber cavities (e.g. cellulose/wood fiber cavities) of the TW matrix, where the combined emitted light from the luminophores form white light, substantially white light or light perceived as white light.
  • a VLC system comprising the transparent wood product of the previous embodiment, wherein the TW product comprises a TW matrix doped with luminophores embedded into fiber cavities of the TW matrix, and one or more pumping source for exciting the luminophores of the TW product.
  • a method of generating illumination and transmitting information using visible light communication comprising providing a VLC system of the previous embodiment, providing information to the one or more pumping source, encoding the information into a modulation pattern of the pumping source, and pumping the luminophores of the TW product according to the modulation pattern using the one or more pumping source, thereby generating emitted light for illumination and transmission of the information.
  • the pumping of the luminophores according to the modulation pattern comprises pumping the luminophores using a pulsed pumping source, producing pulsed emitted light from the luminophores of the same modulation pattern.
  • the provided TW product and VLC system enables the safe and efficient transmission of information in an indoor environment.
  • Figure la is an image of balsa wood showing the wood hollow cells, which constitute potential cavities for embedding luminophores in the TW matrix of the TW product.
  • Figure lb shows the cross section (edges) of the TW material and the hollow cells/fiber cavities, where the cross- section in figure lc shows the length of the hollow cells/fiber cavities.
  • Figure Id is an image similar to lb also showing the hollow structures of the wood cells.
  • Figure 2 is an illustration of the wood fibers of the TW matrix, where figure 2a shows a cluster of wood fibers with different sizes, figure 2b shows an individual fiber acting as resonator and figure 2c shows the potential dimensions of a single fiber.
  • Figure 3 is a block diagram illustrating a VLC process of the current disclosure.
  • Figure 4 is an illustration of the emission system of the current VLC system.
  • Figure 5 illustrates an example of the location of pumping sources in view of the TW product, such as arranged at a few points as in figure 5a, or arranged at the edges of the TW product as in 5b.
  • Figure 6 is a flowchart of a method of generating substantially white light and transmitting information, using the VLC system of the current disclosure.
  • FIG. 7 shows a schematic preparation of dye TW.
  • Figure 8 shows a schematic preparation of Quantum dots based luminescent components embedded TW.
  • a "wood material (wood template) is used for making transparent wood.
  • Wood have different types of wood cells such as tracheids, rays, fibers and vessels, which are mostly formed as tubes and the hollow void inside them is called the "lumen".
  • the wood material is a hollow structure, as wood is composed of wood cells that are hollow (the lumen of the wood cell is hollow).
  • the hollow structures forms tubular structures, as seen for example in figure 2, which upon polymer infiltration provide the lasing capability of the TW product.
  • the hollow wood cells or lumen or tubular structures are referred to as "wood fiber cavities", "cellulose fiber cavities”, “fiber cavities”, “fibers” or “cavities” in this disclosure, which can be infiltrated by a polymer to make transparent wood.
  • the polymer may contain the
  • the term "fibers" or "fiber cavities” of the TW product are not referring to hollow cavities, but cavities filled with polymer and luminophores.
  • a non-limiting term "transparent wood” is used.
  • the transparent wood herein is wood material that has been prepared, using any available method, to become transparent, i.e. by delignification or bleaching followed by polymer infiltration.
  • Transparent wood is a composite comprising a wood template and a polymer, and which is transparent due to treatment of the wood material, i.e. presents an optical transmittance of at least 60 % at a wavelength in the electromagnetic spectrum of wavelengths 400-1000nm.
  • Transparent wood may transmit certain amount of light energy, mainly in visible range, and provide a reasonable image visibility through this materia.
  • the term "transparent wood” is well known to the person skilled in the art.
  • the "transparent wood matrix” is a prepared, by e.g. delignification or bleaching, TW material (wood template) that may be used for embedding luminophores.
  • TW material wood template
  • the TW matrix is used for making transparent wood, but is not itself transparent before polymer infiltration due to comprising wood cells that are hollow.
  • the TW matrix is formed after the bleaching or delignification step, and become transparent after the polymer infiltration/impregnation step, where either normal TW is formed, or a TW product, depending on if the polymer infiltration step contains luminophores or not.
  • the "TW product” is thus the TW matrix comprising the embedded luminophores and, optionally, other components such as waveguides.
  • Embedding or doping refer to a method of impregnating, infiltrating or distributing the active fluorescent components/luminophores such that the luminophores enter and retain in the cavities or holes of the TW material/matrix. After polymer infiltration of the TW matrix with a polymer containing luminophores, the luminophores become embedded into the fiber cavities (the hollow structures of the TW matrix), which are no longer hollow but comprising the polymer and luminophores in the final TW product. The filled fiber cavities may now act as resonators in the TW product, as seen in figure 2b.
  • white light or “substantially white light”
  • white light/substantially white light or white light illumination is meant light/illumination that is perceived as white to the human eye.
  • White light can be achieved by color mixing of different fluorescent components/luminophores or by combinations of components/ luminophores and laser pumps.
  • white LED light blue diode with light converting luminophores made of rare-earth elements.
  • White light may for example be defined by a color rendering index, where white light is estimated to have a CRI>80.
  • White light typically has a color temperature of 4000-6000 Kelvin. The white light should preferably mimic daylight and be comfortable to the human eye.
  • Li-Fi refers to Light Fidelity which is a high speed bi-directional fully connected, visible light wireless communications system and is analogous to Wi-Fi, which uses radio frequency (RF) for communication. Li-Fi can be 250 times faster than Wi-Fi and could be used in places where the use of Wi-Fi is challenging.
  • RF radio frequency
  • a laser diode is an electrically pumped semiconductor device that produces coherent radiation in the visible or infrared spectrum when current passes through it.
  • LDs an effective laser resonance is stimulated due to the presence of coated or uncoated end facets that behave like mirrors with different reflectivities, resulting in an eventual gain in stimulated emission of highly directional photons.
  • VLC visible light communication
  • radio systems for example immunity against interference cause by adjacent channels with the possibility of frequency reuse in different parts of the same building, better security at the physical layer, energy efficiency due to dual functionality, harmless for humans and other electronic devices, easy to integrate in the existing lighting infrastructure, and a much wider bandwidth than RF communication.
  • LEDs light emitting diodes
  • ISI inter symbol interference
  • LDs laser diodes
  • VLC transmitters used are luminophores embedded into cavities of a transparent wood material which act as individual laser sources upon laser pumping, generating homogenous light and VLC being harmless to the health of the user.
  • Active dopants/luminophores are embedded into a TW matrix which consists of a vast amount of small-size cellulose/wood fibers (cavities). These fibers can, upon embedding with
  • luminophores operate as small-size laser resonators and emit laser light with high spectral brightness. Due to homogenous distribution of the dopants/luminophores in the TW material and resulting TW product, a whole TW panel comprising the TW product can work as the source of laser light radiation combining lighting and communication functionality.
  • Wood is a naturally occurring material that is widely used as a constructions and build ing material. Wood is mainly composed of elongated cells, oriented in the longitudinal direction of the stem. Wood is natu rally non-transparent due to light scattering at the interface between the cell wall tissue and the porous lumen space at the center of the wood cells (i.e. rays, fibers, tracheids and vessel cells) with diameters in the order of tens of micrometers.
  • lignin, tannins and other resinous compounds absorb light through chromophoric groups. Studies suggest that lignin accounts for 80-95% of the light absorption in wood.
  • TW Transparent wood
  • mechanical performance, high strength to weight ratio and toughness may be combined with good optical transmittance.
  • TW combines functional (optical transparency) properties with structural properties (mechanical) and has potential in light-transmitting building
  • TW can be prepared using several different processes.
  • One such process is delignification of the substrate followed by impregnation/infiltration with a polymer with matched refractive index to the wood substrate.
  • WO2017136714 discloses a method of preparing TW composite by lignin removal.
  • Another possibility is TW is prepared by bleaching the wood material and then impregnating it with a polymer, without the removal of lignin (Y. Li et al., ChemSusChem. 2017 Sep ll;10(17):3445-3451/WO2018182497). This will generally give better mechanical properties to the TW material.
  • a TW matrix is prepared from the wood material using any suitable method, such as delignification or bleaching, and then infiltrated by polymers to a become transparent.
  • Suitable polymers may have a refractive index that matches the refractive index of cellulose, such as a refractive index from 1.3 to 1.7.
  • the TW product of the current disclosure comprising a TW matrix infiltrated with a polymer comprising luminophores, may be prepared using any suitable method for preparing the TW matrix.
  • the TW material or matrix may be doped with components, polymers and particles suitable for lasing, e.g. luminophores, active fluorescent components such as organic dye molecules, nanocrystal quantum dots or rare earth elements, for example Si nano-crystals or carbon dots, to make the TW product.
  • active fluorescent components such as organic dye molecules, nanocrystal quantum dots or rare earth elements, for example Si nano-crystals or carbon dots.
  • Any component or particle suitable for lasing may be doped or embedded into the TW matrix material.
  • Organic dyes have a life-time and will bleach over time, compared to Quantum dots which are more stable and that don't bleach over time. Proper embedding will influence the photo bleaching of the luminophores.
  • the embedded TW product preparation is made using a modified process based on the normal TW preparation process.
  • the optically active components the luminophores
  • the infiltration step as described in detail in the example section below.
  • Proof of concept for this method has also been previously described by the inventor (E. Vasileva et al. Adv. Optical Mater. 5, 2017), where it was shown that embedding an organic dye into transparent wood may generate illumination.
  • Z. Bi, et al. Z. Bi, et al. ACS Sustainable Chem. Eng. 6: 9314-9323, 2018
  • the optically active components/luminophores can be embedded either by chemical bonding to cellulose or by impregnation into the polymer.
  • One way is to disperse the luminophores in pre-polymerized monomer solution, such as in methyl methacrylate (MMA) solution, and then fill the luminophores doped pre-polymerized monomer solution into TW matrix (bleached/delignified wood template) and then further cure in the oven to get the luminophore TW product.
  • pre-polymerized monomer solution such as in methyl methacrylate (MMA) solution
  • Another method is to infiltrate TW matrix into luminophore solution, remove the luminophore doped wood template and infiltrate with pre-polymerized monomer solution, such as for example pre-polymerized MMA solution, and then cure in the oven to get the luminophore TW product.
  • Doping the TW material/TW matrix with the luminophores makes the TW an optically active medium referred to as a TW product.
  • the TW product may also comprise additional elements, such as waveguides, as external modules.
  • Doping a TW matrix with optically active luminophores results in an optically active TW product, where each cavity having embedded luminophores act as individual lasers upon excitation, e.g. illumination by an external light source.
  • the TW matrix comprises an immense number of cavities, the cavities realized by the wood cells (i.e. tracheids, fibers, rays and vessels) existing in the wood material used. Theoretically, the cavity number in TW could be the same as the lumen numbers in the wood. Calculating from the diameter of the wood cells (e.g. fibers), gives a value between 2.6*10 4 /cm 2 to 1.27*10 6 /cm 2 .
  • the cavity size is dependent on the type of cells in the wood as well as wood types (i.e. softwood or hardwood), which differ in sizes.
  • wood types i.e. softwood or hardwood
  • wood cells in softwoods and hardwoods may have lengths that vary from 0.5-10 mm, and a diameter from 10-70 pm.
  • hardwoods contains a very high percentage of vessels wood cells, which may have a length up to 700 mm and a diameter up to 400 pm. Since the luminophores are so small in relation to the wood cell/fiber cavities, the luminophores being in nano scale while the cell walls are in the micro scale, a large number of particles will be present in each cavity.
  • Figures la-d show scanning electron microscope, SEM, images of a wood template, which may be used as a TW material, made of balsa with cavities present, showing 3D structural (figure la), cross sectional (figure lb and d), and surface morphology (figure lc).
  • Figures la-d are showing the wood hollow cells, which are the potential cavities for embedding luminophores in embedded TW, including the fibers and vessels.
  • the fibers and vessels have an estimated length from 200 pm up to several mm (vessels usually being longer than fibers, potentially up to 700 mm), and a diameter of 10-70 urn for the fibers and 150-300 pm for the vessels.
  • FIG 2a shows a schematic illustration of a group of wood fibers from a TW matrix of the invention where it is shown that the fibers may have different dimensions and be structurally ordered in a hierarchically but random manner.
  • FIG 2b is shown an individual fiber acting as resonator for the emitted light from the embedded active dopants/luminophores upon doping the fiber cavity with luminophores, hence creating mini lasers.
  • organic dyes in a free medium for illumination instead or the defined wood cells/cavities in the wood as in the present disclosure, would not work as well since the dyes tend to agglomerate.
  • no quasi-random lasers would be formed.
  • An illustration of the exemplary dimensions of a single wood fiber is shown in Figure 2c.
  • Any type of wood may be used for the optical function.
  • high density wood such as birch, ash, pine, and oak, may be better for load-bearing.
  • Any wood thickness direction is possible, longitudinal may be preferred for the illumination application, but might be a drawback as a construction element as the mechanical properties of the longitudinal will not be as good as the transversal.
  • using the TW product as an illumination panel may not require very strong material properties.
  • the transversal direction will not have as good illumination properties, but VLC does not require very strong radiation, it is the narrow band application that is most important.
  • the TW product of the present disclosure may have a varying thickness depending on the product it is used in. In terms of loading bearing purpose, the thicker and larger, the better. Flowever, thicker TW sample shows lower transmittance. Flence, the TW product should not be too thick, for example no more than 10 mm. It should be thick enough to comprise the active dopants (luminophores) and eventual additional components, such as waveguides, but still thin enough to be transparent.
  • One method to control the transparent wood mechanical properties and optical properties is to laminate transparent wood layers, as described in Q. Fu et al. Composites Science and Technology 164: 296-303, 2018. VLC and light generation
  • Luminophores embedded into cavities, such as fiber cavities, of the transparent wood matrix act as individual lasers upon pumping, such as illumination by an external light source.
  • the external light source also referred to as a pump or pumping source, excites the
  • luminophores which emits visible light that can be used for illumination and communication (VLC).
  • an optical pumping source light source
  • an electrical pumping source may be used for direct electrical pumping. This may be realized using e.g. electrically conductive nanowires present for example in the holes of the wood.
  • TW product a dye embedded TW
  • SEM image of a dye embedded TW pumped by a laser beam showed that all the hollow cells in the wood template (TW matrix) constitute the possible cavities, which may be filled with polymer and luminophores in the TW product.
  • Impregnation of active dopants/luminophores inside TW panels can be scaled up to very large geometrical sizes which can be used as components of internal building and construction material.
  • the TW product may be used as a construction material in walls or roofs for example, or as an indoor construction material in walls, floors and ceiling or even furniture.
  • the TW product may for example be formed as floor or ceiling tiles, or wall panels, enabling e.g. the use of optically active wood panels as construction elements, with data
  • the panels or tiles may comprise fastening means for arranging and/or fastening the panels or tiles to the floors or ceilings, and optionally to each other.
  • the emitted light will be evenly and homogenously distributed, hence providing homogenous illumination and VLC coverage in the area of the TW product.
  • TW product as, for example, ceiling tiles in a room will provide homogenous illumination as well as uniform VLC coverage in the room.
  • LEDs distributed as "spotlights" are often used as a VLC source, and VLC via LEDs won't have a uniform coverage in the whole room. LEDs also suffer from shadowing and broad linewidth, e.g. 20nm. This is not mitigated using a LD, since also a LD acts as a spot like illumination source, because each LD is one illumination spot, one device.
  • LDs have a safety issue and is that as the source is very narrow, it acts as a direct laser, with too high spectral brightness which is dangerous for the human eyes.
  • TW can be used for VLC thanks to its narrowband-lasing capability, and thanks to its structure homogenous and diffuse light is obtained instead of the "laser spot light" which pose danger to the human eye and is too direct, compared to the cloud of lasers obtained from the TW product.
  • the fiber cavities with embedded luminophores will act as individual lasers upon excitation by a pumping source. All the fibers should be impregnated with the one or more different luminophores, since each embedded fiber acts as one laser source.
  • the luminophores should be inside the laser cavity, i.e. inside the fiber cavity filled with polymer after polymer infiltration.
  • the lasing action from the embedded luminophores has been attributed to the collective effect of the wood cells, e.g. cellulose fibers, working as an assembly of small Fabry-Perot resonators that are partially ordered due to the natural growth of internal wood components.
  • the lasing from these lasers will not be harmful or pose health hazards, as the use of conventional coherent lasers.
  • the emission of the generated lasers has features of random lasing and act as quasi random lasers, hence not posing any harm to the health of the user.
  • Wood is an ideal material to use as substrate for the embedding of luminophores, due to the hierarchical structure and that the fibers are quite well aligned and that there are plenty of them. To prepare a similar artificial material would be difficult due to the structure and the number of the fiber cavities, and it would probably also be more precisely ordered, hence producing more coherent lasing, hence potentially more dangerous to the human eye.
  • white light illumination substantially white light
  • an external light source of high spectral brightness e.g. LED or laser with a wavelength suitable for the efficient absorption by embedded luminophores
  • the TW active matter Upon being illuminated by e.g. an external light source of high spectral brightness, e.g. LED or laser with a wavelength suitable for the efficient absorption by embedded luminophores, the TW active matter emits light of different wavelengths (colors), which are defined by the embedded luminophores chemical and physical structure.
  • Proper luminophore modification provides an opportunity for the tuning of total emission spectrum, and to adjust it according to environmental requirements.
  • embedding different organic dyes, with different colors white color could be obtained.
  • a single type of luminophore with a broad yellow spectrum may generate white light under a blue pump.
  • the white light or substantially white light (perceived as white light to the human eye) will be uniformly spread due to the nature of the TW product, hence generating homogenous illumination, or illumination of a desirable spectral content.
  • the organic dyes could be randomly or homogeneously distributed in the matrix, in order to obtain white light and homogenous VLC coverage.
  • the luminophore solution should be a homogenous dispersion. This will make sure that the luminophores are uniformly distributed into the TW.
  • all cavities in the TW material/matrix of the TW product should have basically the same amount of embedded luminophores, and if different types of luminophores are used, such as organic dyes of different colors, then these different types should also be homogenously spread over the TW matrix. This solves both the health and coverage issues of using spot-light devices.
  • the VLC system is the VLC system.
  • Modern VLC systems are used for indoor applications to transmit data signal in visible range (Li- Fi), and they can substitute in future Wi-Fi communication since VLC offers higher data transmission rate, and can be used for ambient illumination, thus saving the energy.
  • Current state-of-the-art systems use light emitting diodes as the light source, which have broad spectral linewidth (30-40 nm), and only several different wavelengths (3-4) can be used simultaneously due to limited spectral range in visible. It would be useful to implement lasers in VLC, since they have very narrow spectral linewidth, and more channels could be placed in a given spectral range.
  • DAM dynamic amplitude modulation
  • a VLC system of the current disclosure comprises a TW product as described above, comprising optically active luminophores which may be pumped using one or more pumping sources, hence emitting light for illumination and VLC.
  • the luminophores and pumping sources may be chosen to obtain white light illumination.
  • the energy from the pumping source may be guided to the luminophores by waveguides present in or in relation to the TW product.
  • the VLC system may be operated by providing a digital data stream of information to be transmitted using the system to the pumping source(s), encoding the information into a modulating pattern and pumping the luminophores according to the modulation pattern using the pumping source(s), thereby generating light comprising the encoded information.
  • a pulsed excitation light source/pumping source with high repetition rate, it is possible to encode digital data stream (in the simplest case, in "on-off' modulation format) into excitation radiation. Active dopants will be excited according to the stream modulation pattern, and will produce pulsed fluorescence of the same modulation pattern. Since the data pulse rate is very high, typically 100 MHz (100 Mbit/s data rate), the human perception of the illumination performance will not be affected
  • a digital data stream is modulated with one of possible advanced modulation formats.
  • the simplest example is PAM4, where four different signal amplitudes correspond to 2-digit binary combinations, i.e. 00, 01, 10, 11.
  • two bits are transmitted in one-time slot, which in traditional intensity modulation would be allocated to one bit only.
  • More complicated modulation formats allow to "pack" more bits in one slot.
  • Several parallel streams of modulated signals are sent to pumping source containing several carrier wavelengths, so called “comb” laser, one laser with several emission wavelengths simultaneously.
  • Pumping "lasers” with encoded information (as varying intensity in each wavelength channel) pump active material i.e. the active TW material which incorporates different types of optically active luminophores with corresponding absorption wavelengths.
  • TW active material generates laser emission on several wavelengths, which carry information signals, and can be used for illumination at the same time.
  • the emitted light may be detected by a receiver, which can be a very generic photodetector of wide FOV, and is typically placed in computers, indoor routers or other user equipments.
  • a conventional photodetector in visible (with a proper wavelength filter) registers the signal and transfers it further to demodulation block, which converts the received modulated signal into data stream.
  • FIG. 3 shows a VLC block-diagram of the current disclosure, with the above mentioned principle of operation.
  • Two directions showing emitting light from box “active material TW" (down and right) is a functionality principle. Physically, it is the same light radiating from the material uniformly in all directions in space.
  • a data stream, 100 comprising the information to be transmitted is provided and the data/information encoded (modulated) to provide encoded information 101.
  • the encoded information is then provided to one or more multi-wavelength pumping source, 102, which pumps the active material, the TW product 103, preferably using one or more waveguides (not shown).
  • the pumped TW product emits lighting for illumination, 105a, and light comprising a signal 105b encompassing the encoded information 101.
  • the signal may then be detected using a receiver/photo detector, 106, and is demodulated, generating the original information (demodulated information) 107, hence providing the data
  • a pumping source can be located in virtually any place provided that suitable optical waveguide delivers pumping radiation to the active material.
  • the waveguide is present in a module external of the TW product.
  • the waveguide can be thin-film or glass (organic or nonorganic) layer implementing an effect of total internal reflection of light.
  • Figure 4 shows a schematic drawing, a technical scheme of the emission system.
  • the active embedded TW material/TW product, 103 is pumped using one or more pumping sources, 102, via the optical pumping waveguide, 104. Electrical pumping sources and waveguides may also be used.
  • the one or more waveguide, 104 is typically located external from the TW product, 103, as shown in figure 4.
  • the TW product 103 Upon excitation by the one or more pumping source 102, the TW product 103 emits quasi-random laser light 105. The emitted light comprising the encoded information may then be detected by one or more detectors (not shown).
  • the active material can be pumped from any direction, preferably to cover the largest area from top, as in figure 4.
  • orientation of fibers inside the material can be both horizontal and vertical referring to the direction of pumping light coming from the waveguide, as seen in the cross- sections of the TW product, 108 and 109 respectively, in figure 4.
  • the lasing emission is formed in micro-cavities oriented along the fibers, the output emission leaves the material without certain direction due to strong scattering from the fiber walls.
  • Embedded TW with fiber in plain could be used with the load bearing purpose for roofs, with the pumping sources located on one side of the TW.
  • the side exiting the illumination is referred to as the "downside" of the TW product/panels/tiles, while the pumping source(s), 102, typically is arranged on the opposite side of the generated light, 105, referred to as the
  • the pumping source need to cover all the area to make sure transmitted light can cover as large area as possible.
  • the pumping source can be used to only cover a few points as the transmitted light can spread to a large area as shown in Figure 5a, where a few points on the upside is covered by pumping sources, 102.
  • the pumping source, 102 can also be arranged on the edges of the transparent wood as shown in Figure 5b.
  • the waveguides may thus be arranged in vicinity of the pumping sources to guide the emitted waves of the pumping source to the luminophores, such as between the pumping source and the TW product.
  • the current disclosure discloses a TW product and its use in VLC.
  • a transparent wood, TW, product for providing white light illumination and visible light communication, VLC, comprising a TW matrix doped with luminophores embedded into the fiber cavities of the TW matrix, where the combined emitted light from the luminophores form substantially white light or light perceived as white light.
  • the luminophores of the TW product emit light upon excitation by one or more pumping source.
  • the pumping sources may be optical or electrical. Several pumping sources may be used for pumping/exciting the luminophores.
  • the illumination being emitted from the TW product is visible light, perceived as substantially white light, i.e. a person in room illuminated by the TW product would not consider the illumination to have any specific color besides white.
  • the fiber cavities of the TW matrix act as resonators for the luminophores such that each fiber cavity having embedded luminophores forms an individual laser source, wherein the luminophores and the fiber cavities form quasi random lasers.
  • the luminophores are selected from e.g. organic dye molecules, nanocrystal quantum dots and rare-earth elements.
  • the TW product may comprise one or more waveguide modules arranged for guiding electromagnetic waves from the one or more pumping source to the luminophores of the TW product.
  • the waveguides are typically arranged external to the TW product itself.
  • the TW product may be used as an indoor construction material for generating white light and providing VLC inside a building.
  • the indoor construction material may be a tile or a panel, such as a ceiling tile, floor tile or wall panel.
  • the current TW product may thus be used for providing visible illumination, (substantially) white light illumination, and visible light communication, by encoding a data stream into a modulating pattern of the pumping source.
  • a visible light communication, VLC, system for generating illumination and transmitting information comprising the above described TW product (a TW product comprising a TW matrix doped with luminophores embedded into fiber cavities of the TW matrix), and one or more pumping source arranged for exciting the luminophores of the TW product.
  • the one or more pumping source used may be an optical or electrical pumping source, wherein the optical pumping source may be a laser, laser diode, LD, or light emitting diode, LED.
  • the excited luminophores in the fiber cavities of the TW product in the VLC system form quasi-random lasers.
  • the one or more pumping source of the VLC system may be configured for exciting the luminophores according to a modulation pattern, the modulation pattern corresponding to information to be sent using the VLC system.
  • several pumping sources are used, wherein the different pumping sources may be arranged so that different types of luminophores are excited using different pumping sources.
  • the VLC system may further comprise one or more waveguide arranged for guiding electromagnetic waves from the one or more pumping source to the luminophores of the TW product.
  • the waveguides are typically an external module present on one side of the TW product that is not providing illumination.
  • the VLC system may further comprise one or more receivers for receiving information transmitted using the VLC system.
  • Figure 6 comprises some operations and modules which are illustrated with a solid border and some operations and modules which are illustrated with a dashed border.
  • the operations and modules which are illustrated with solid border are operations which are comprised in the broadest example embodiment.
  • the operations and modules which are illustrated with dashed border are example embodiments which may be comprised in, or a part of, or are further embodiments which may be taken in addition to the operations and modules of the broader example embodiments. It should be appreciated that the operations do not need to be performed in order. Furthermore, it should be appreciated that not all of the operations need to be performed.
  • FIG. 6 is a flowchart of a method of generating light, such as substantially white light, for illumination and transmission of information, using the VLC system of the current disclosure.
  • a method of generating illumination and transmitting information using visible light communication, VLC comprising providing (SI) a VLC system of the current disclosure comprising a TW product and one or more pumping source, providing (S2) information to the one or more pumping source, wherein the information could be data to be transmitted, encoding (S3) the information into a modulation pattern of the pumping source, and pumping (S4) the luminophores of the TW product according to the modulation pattern using the one or more pumping source, thereby generating emitted light for illumination and transmission of the information.
  • the providing of the information, the encoding and the pumping may be performed step wise or more or less simultaneously.
  • Encoding the information into a modulation pattern or using a modulation pattern could be for example modulating using amplitude modulation or intensity modulation, where the modulation pattern uses intensity modulation, the information is modulated into the intensity of the emitted light.
  • Pumping (S4) the luminophores according to the modulation pattern may comprise pumping the
  • luminophores using a pulsed pumping source producing pulsed emitted light from the luminophores of the same modulation pattern.
  • the light generated by the combined emittance from the luminophores i.e. the combined light generated by the different luminophores, form white light, substantially white light and/or light perceived as white light to the human eye, due to specific election of the luminophores and pumping sources.
  • white light may be obtained, as well as different channels for transmitting information.
  • the light emitted from the pumped luminophores in the fiber cavities form quasi-random lasers due to the resonance of the cavities.
  • the information (data) to be transmitted may be encoded using a modulation pattern, which may give rise to an optically modulated signal comprised in the emitted light.
  • the encoded information transmitted in the emitted light as an optically modulated signal may be received by a receiver, which may then decode the encoded information by converting the optically modulated signal of into an electrical signal in the receiver.
  • the electrical signal will then comprise the information that was provided to the pumping source in the first step.
  • the normal TW preparation is mainly divided into two main steps, the first step is to make the wood template and the second step is to infiltrate the wood template with a polymer with a matching refractive index to obtain TW.
  • a polymer with a matching refractive index to obtain TW.
  • PMMA polymethyl methacrylate
  • many other polymers can be used.
  • the first step i.e. the preparation of the wood template, can be done by two methods; the delignification method or the lignin-retaining method. Both methods can be used in order to produce a TW matrix that can later be used for embedding luminescent components/ luminophores.
  • Wood veneer in this specific example Balsa
  • the dried samples were extracted using 1 wt% of sodium chlorite (NaCI02, Sigma-Aldrich) with acetate buffer solution (pH 4.6) at 80°C.
  • the sample dimension was 20 mm x 20 mm with thickness of 1.5 mm.
  • the reaction time for samples was 6 h.
  • the extracted samples were carefully washed with deionized water followed by dehydration using first pure ethanol, then 1:1 (volume ratio) mixture of ethanol and acetone and finally pure acetone (step by step). Each step was repeated three times.
  • Wood veneer in this specific example Balsa
  • Balsa Wood veneer with thickness of 1.5 mm was purchased from Wentzels Co. Ltd, Sweden with dimension of 20 mm* 20 mm.
  • the pieces of balsa wood were dried at 105 ⁇ 3 °C for 24 h before bleaching procedure.
  • the lignin modification solution i.e.
  • bleaching liquor was prepared by mixing chemicals in the following order: deionized water, sodium silicate (Fisher Scientific UK, 3.0 wt%), sodium hydroxide solution (Sigma-Aldrich, 3.0 wt%), magnesium sulfate (Scharlau, 0.1 wt%), diethylene-triaminepentaacetic acid, DTPA (Acros Organics, 0.1 wt%), and then H 2 0 2 (Sigma-Aldrich, 4.0 wt%), wherein all weight percentages are in relation to the weight of water in bleaching liquor.
  • the wood substrate was submerged in the bleaching liquor (200ml) at 70 °C until the wood became white. The samples were then thoroughly washed with deionized water and then solvent exchanged to acetone for further use as described in above (same steps as in the delignification method).
  • Transparent wood was made by infiltrating the wood template with a pre-polymerized PMMA solution and heated in an oven at 70 °C for 4 hours. Pure MMA monomer was pre-polymerized at 75 °C for 15 min in a two-necked round bottom flask with 0.3 wt% 2,2'-azobis (2- methylpropionitrile) (AIBN) as initiator. The pre-polymerized PMMA was cooled down to room temperature in ice-water bath to terminate the reaction. After that, the wood template, i.e. the delignified or bleached wood template obtained from the delignification or lignin-retaining methods above, was infiltrated with the pre-polymerized PMMA solution under vacuum for 30 min.
  • AIBN 2,2'-azobis (2- methylpropionitrile
  • Vacuum infiltration was repeated 3 times to ensure the full infiltration. Finally, the infiltrated wood was sandwiched between two glass slides and packaged in aluminum foil before further polymerization. The polymerization process was completed by heating the infiltrated wood sample in an oven at 70°C for 4 hours.
  • the TW matrix can be doped with luminophores in the infiltration step to become an optically active medium, also referred to as the TW product or embedded TW matrix.
  • an optically active medium also referred to as the TW product or embedded TW matrix.
  • the first step above, the delignification or lignin-retaining will be performed as above to prepare the TW matrix, while the second infiltration step will be performed differently when preparing a luminophore doped TW product.
  • the first step is to prepare a wood template (TW matrix) and secondly to infiltrate the matching refractive index polymer and the optically active component. This second part can be done in different ways, two examples are presented below.
  • the first example describes polymer dye based luminescent components embedded TW
  • the second example describes quantum dots based luminescent components embedded TW preparation. These two examples show two different methods that may be applied to all types of the luminophores or luminescent components embedded TW preparation.
  • Example 1 Polymer dye based luminescent components embedded TW:
  • the samples with polymer dye embedded into TW structure were prepared in three technological steps. 1) At the first step, 2 pieces of balsa wood (Ochroma pyramidale, purchased from Wentzels Co. Ltd, Sweden) of thickness of 1.0 mm and 3.0 mm were delignified using 1 wt% of sodium chlorite (NaCI02, Sigma-Aldrich) in acetate buffer solution (pH 4.6) at 80 °C, until the wood was totally bleached. Then the delignified wood was dehydrated with ethanol and acetone, sequentially; each procedure was repeated three times.
  • This first step is the same step used in order to obtain the wood template as when producing normal TW by the delignification method, but the next steps, as schematically illustrated in figure 7, differs.
  • the wood template was inserted for 2 hours into a dye acetone solution (may be any suitable solvent besides acetone, such as ethanol, methanol etc. as long as the dye can be dissolved in the solvent) with a concentration of lxlO -3 mole/L.
  • a two-hour long infiltration time may be used to make sure that the dye molecules can diffuse into the whole wood template.
  • a bit longer time is better for the homogeneous diffusion of dye molecule, especially for large and thick samples.
  • the wood template was fully infiltrated with the pre-polymerized MMA solution and then cured at 75 °C for 4 hours.
  • Pure MMA monomer was pre-polymerized into PMMA at 75 °C for 15 min in a two-necked round bottom flask with 0.3 wt% AIBN as initiator.
  • the pre-polymerized PMMA was cooled down to room temperature in ice-water bath to terminate the reaction.
  • the dye- wood template was infiltrated with the pre-polymerized PMMA solution under vacuum for 30 min. Vacuum infiltration was repeated 3 times to ensure the full infiltration.
  • the infiltrated wood was sandwiched between two glass slides and packaged in aluminum foil before further polymerization.
  • the polymerization process was completed by heating the infiltrated wood sample in an oven at 75 °C for 4 hours.
  • the first step for this example is also to obtain a wood template/TW matrix.
  • the wood template was obtained by delignification of wood veneer (balsa, Ochroma pyramidale, purchased from Wentzels Co. Ltd, Sweden) with dimension of 20 mm x 20 mm x 2 mm to remove the main light-absorbing component.
  • the thickness direction of the veneer is the tangential direction of the cross-section of the tree stem.
  • wood veneer was treated using 1 wt. % of sodium chlorite (NaCI0 2 , Sigma-Aldrich) in acetate buffer solution (pH 4.6) at 80 °C. The reaction was stopped when the wood appeared almost uniformly white.
  • the delignified samples were washed with deionized water and kept in water until further use. Prior to polymer infiltration, wood samples were dehydrated upon sequential exposure to ethanol and acetone with each solvent exchange step repeated 3 times.
  • This first step is the same step as when producing normal TW by delignification method in order to obtain the wood template.
  • QDs are dispersed in toluene with a concentration of about 0.1 wt%.
  • the MMA monomer was pre polymerized before mixing with QDs.
  • the pre-polymerization was completed by heating the MMA at 75 °C for 15 min with 0.3 wt.
  • the delignified wood template was fully vacuum-infiltrated with the pre-polymerized MMA/QDs solution in a desiccator under house vacuum with pressure of 13 mbar. Finally, the infiltrated wood was sandwiched between two glass slides, wrapped with aluminum foil, and heated in an oven at 70 °C for 4 hours in ambient atmosphere.
  • the content of this disclosure thus enables a novel approach for cost effective VLC for indoor implementation combining increased data transmission capability with adjustable ambient illumination (lighting spectral profile), without potential health hazards to the user, hence enabling Li-Fi.
  • the approach includes the combined use of environmentally and easily disposable organic material having a natural structure allowing to form small-size optical resonators capable of generating laser-like radiation, and the property of the laser light to provide narrow bandwidth radiation of high spectral brightness, by doping the material with active fluorescent components/ luminophores to provide narrowband multi-wavelength radiation for data transmission and spectrally adjustable lighting.
  • This enables more efficient use of light spectrum for both communication and illumination, increased data transmission capacity due to the multi-wavelength approach, homogenous distribution of light sources over large surface areas. This allows for combining the lighting and communication functionalities, and provides for enhancement of data transmission capacity in Local Area Networks (LANs).
  • LANs Local Area Networks
  • the decrease of radio frequency (RF) radiation achieved by the proposed solution improves communication security (no network intrusion outside the indoor area) and decreases potential health risks due to e.g. background RF pollution, as well as decreases net energy consumption. Due to a minimized number of external light sources/pumping sources and lack of RF antennas requiring separate power supply, the total amount of energy consumed can be decreased.
  • RF radio frequency

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  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Wood Science & Technology (AREA)
  • Forests & Forestry (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Chemical & Material Sciences (AREA)
  • Inorganic Chemistry (AREA)
  • Lasers (AREA)

Abstract

La présente invention concerne un système et des produits destinés à une communication par lumière visible (VLC). Plus spécifiquement, la technique proposée se rapporte à une VLC par l'intermédiaire de luminophores émettant un laser incorporés dans du bois transparent (TW). Le système VLC comprend un produit TW, le produit TW comprenant une matrice TW dopée avec des luminophores incorporés dans des cavités de fibres de la matrice TW, et une ou plusieurs sources de pompage pour exciter les luminophores du produit TW. L'invention comprend un produit en bois transparent, un système VLC comprenant le produit en bois transparent et des procédés de génération de lumière blanche et de fourniture de la VLC à l'aide du système VLC.
PCT/SE2019/051295 2018-12-20 2019-12-17 Communication par lumière visible à l'aide de lasers incorporés dans du bois transparent WO2020130917A1 (fr)

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