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Title:
VISIBLE LIGHT COMMUNICATION USING TRANSPARENT WOOD EMBEDDED LASERS
Document Type and Number:
WIPO Patent Application WO/2020/130917
Kind Code:
A1
Abstract:
The current 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 (TW). The VLC system comprises a TW product, 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. 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.

Inventors:
POPOV SERGEI (SE)
BERGLUND LARS (SE)
LI YUANYUAN (SE)
SYCHUGOV ILYA (SE)
Application Number:
PCT/SE2019/051295
Publication Date:
June 25, 2020
Filing Date:
December 17, 2019
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
CELLUTECH AB (SE)
International Classes:
H04B10/116; B27K3/15; B27K5/02; B27K3/02; C08L97/02
Domestic Patent References:
WO2017136714A12017-08-10
WO2018182497A12018-10-04
Foreign References:
CN108656276A2018-10-16
Other References:
POPOV SERGEI; MARININS ALEKSANDRS; SYCHUGOV ILYA; YAN MAX; VASILEVA ELENA; LI YUANYUAN; BERGLUND LARS; UDALCOVS ALEKSEJS; OZOLINS : "Polymer photonics and nano-materials for optical Communication", 2018 17TH WORKSHOP ON INFORMATION OPTICS (WIO), 16 July 2018 (2018-07-16), pages 1 - 3, XP033518800
VASILEVA ELENA, LI YUANYUAN, SYTJUGOV ILYA, BERGLUND LARS, POPOV SERGEI: "Transparent Wood as a Novel Material for Non-Cavity Laser", 2016 ASIA COMMUNICATIONS AND PHOTONICS CONFERENCE (ACP) , CONFERENCE PROCEEDINGS ARTICLE, vol. 4, 2 November 2016 (2016-11-02), pages 1 - 3, XP055719788
BI ZHIHAO, LI TUANWEI, SU HUI, NI YONG, YAN LIFENG: "Transparent Wood Film Incorporating Carbon Dots as Encapsulating Material for White Light-Emitting Diodes", ACS SUSTAINABLE CHEM. ENG., vol. 6, no. 7, 2018, pages 9314 - 9323, XP055719790
YUANYUAN LI ET AL.: "Lignin-Retaining Transparent Wood", CHEMSUSCHEM, vol. 10, 2017, pages 3445 - 3451, XP055547755
KOIVUROVA M. ET AL.: "Complete spatial coherence characterization of quasi-random laser emission from dye doped transparent Wood", OPTICS EXPRESS 13475, vol. 26, no. 1 0, 14 May 2018 (2018-05-14), XP027860919
VASILEVA ELENA, LI YUANYUAN, SYCHUGOV ILYA, MENSI MOUNIR, BERGLUND LARS, POPOV SERGEI: "Lasing from Organic Dye Molecules Embedded in Transparent Wood", ADV. OPTICAL MATER, vol. 5, no. 10, 2017, pages 1 - 6, XP055719795
Attorney, Agent or Firm:
AWA SWEDEN AB (SE)
Download PDF:
Claims:
CLAIMS

1. A visible light communication, VLC, system for generating illumination and

transmitting information, the system comprising a transparent wood, TW, product, the 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.

2. The VLC system of claim 1, wherein the one or more pumping source is an optical or electrical pumping source.

3. The VLC system of claim 2, wherein the optical pumping source is a laser, laser diode, LD, or light emitting diode, LED.

4. The VLC system of claims 1-3, wherein the excited luminophores in the fiber cavities form quasi-random lasers.

5. The VLC system of claims 1-4, wherein the one or more pumping source is

configured for exciting the luminophores according to a modulation pattern, the modulation pattern corresponding to information to be sent using the VLC system.

6. The VLC system of claims 1-5, wherein several pumping sources are used, the

different pumping sources being arranged so that different types of luminophores are excited using different pumping sources.

7. The VLC system of claims 1-6, wherein the VLC system further comprises one or more waveguide arranged for guiding electromagnetic waves from the one or more pumping source to the luminophores of the TW product.

8. The VLC system of claims 1-6, further comprising one or more receivers for receiving information transmitted using the VLC system.

9. A method of generating illumination and transmitting information using visible light communication, VLC, the method comprising:

providing (SI) a VLC system of claims 1-8;

providing (S2) information to the one or more pumping source;

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.

10. The method of claim 9, wherein pumping (S4) 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.

11. The method of claims 9-10, wherein the combined light generated by the different luminophores form white light, substantially white light and/or light perceived as white light.

12. The method of claims 9-11, wherein the pumped luminophores in the fiber cavities form quasi-random lasers.

13. The method of claims 9-12, wherein the modulation pattern uses intensity

modulation, IM, where the information is modulated into the intensity of the emitted light.

14. The method of claims 9-13, wherein the pumping of the luminophores is performed using different pumping sources for the different types of luminophores.

15. The method of claims 9-14, wherein the encoded information, transmitted in the emitted light as an optically modulated signal, is received by a receiver, and wherein the receiver decodes the encoded information by converting the optically modulated signal of into an electrical signal.

16. 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.

17. The TW product of claim 16, wherein the luminophores emit light upon excitation by one or more pumping source.

18. The TW product of claim 17, wherein 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.

19. The TW product of claims 17-18, wherein the luminophores and the fiber cavities form quasi-random lasers.

20. The TW product of any of claims 16-19, wherein the luminophores are selected from organic dye molecules, nanocrystal quantum dots and rare-earth elements.

21. The TW product of claims 17-20 further comprising one or more waveguide modules arranged for guiding electromagnetic waves from the one or more pumping source to the luminophores of the TW product. 22. The TW product of claims 16-21, wherein the TW product constitutes an indoor construction material for generating white light and providing VLC inside a building. 23. The TW product of claim 22, wherein the indoor construction material is a tile or a panel, such as a ceiling tile, floor tile or wall panel.

24. Use of a TW product of claims 16-23 for providing white light illumination and visible light communication.

Description:
VISIBLE LIGHT COMMUNICATION USING TRANSPARENT WOOD EMBEDDED LASERS

TECHNICAL FIELD

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.

BACKGROUND

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. There is a potential optical band of the electromagnetic spectrum available that may be able to provide tens of gigabit per second, especially for indoor

users. 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

light does not penetrate through opaque barriers, which means there is no eavesdropping possible as with radio systems. 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. However, there are also downsides, including the low modulation bandwidth of the LEDs used and inter symbol interference (ISI). 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.

The growing demands for higher data rates in the gigabit class range has deviated focus toward the consideration of laser diodes (LDs) as potential sources for VLC due to their unique features of high modulation bandwidth, efficiency, and beam convergence (A.T. Hussein et al. J of lightwave technology, 33(15), 2015; and F. Zafar et al. IEEE Communications Magazine, Feb 2017). Despite numerous advantages, the use of LDs for VLC is still uncertain due to high cost, health hazard issues, color mixing complexity and efficient homogeneous illumination. Hence, there is a need to provide VLC systems that provides high data rates and efficient homogenous illumination without being harmful to the health of the end user.

SUMMARY

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.

In one embodiment is provided 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.

In one embodiment, use of the TW product for providing white light illumination and visible light communication is disclosed. According to a further embodiment, a VLC system is provided 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.

According to another embodiment, a method of generating illumination and transmitting information using visible light communication is provided, the method 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. In one aspect 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.

Other objects and advantages will become apparent to those skilled in the art from a review of the ensuing detailed description, which proceeds with reference to the following illustrative drawings, and the attendant claims.

BRIEF DESCRIPTION OF THE DRAWINGS

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.

Figure 7 shows a schematic preparation of dye TW.

Figure 8 shows a schematic preparation of Quantum dots based luminescent components embedded TW.

DETAILED DESCRIPTION

Aspects of the present disclosure will be described more fully hereinafter with reference to the accompanying drawings. The system and method disclosed herein can, however, be realized in many different forms and should not be construed as being limited to the aspects set forth herein. Like numbers in the drawings refer to like elements throughout.

The terminology used herein is for the purpose of describing particular aspects of the disclosure only, and is not intended to limit the disclosure. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

In some embodiments 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

luminophores, upon which the luminophores become embedded into the fiber cavities of the final TW product. The fiber cavities are thus filled with polymer and luminophores in the TW product, hence the fiber cavities of the final product are no longer hollow. Accordingly, the term "fibers" or "fiber cavities" of the TW product are not referring to hollow cavities, but cavities filled with polymer and luminophores.

In some embodiments 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. 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. Hence, 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.

The term "embedded" as in luminophore embedded TW, or "doped" as in luminophore doped TW is used interchangeably herein. 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.

Also in some embodiments the terminology "white light", or "substantially white light", is used. With 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. One example is 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.

The term "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.

A laser diode (LD) is an electrically pumped semiconductor device that produces coherent radiation in the visible or infrared spectrum when current passes through it. In 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.

The increased demand of wireless communication poses a lot of pressure on the limited resources of the radio frequency spectrum. As an alternative, an optical wireless

communication technology called visible light communication, VLC, that utilizes a light source as its transmitter has emerged. VLC have several advantages compared to 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.

Most VLC systems uses light emitting diodes (LEDs) as transmitters, however limitations such as low modulation bandwidth of the LEDs used and inter symbol interference (ISI) degrades performance. To increase the performance of the VLC systems, laser diodes (LDs) have been proposed as an alternative to LEDs (A.H Hussein et al. and F. Zafar et al.). However, even though these systems provide higher data rates that the LED VLC systems, some major problems still remain, such as the lasers being hazardous to human beings, the light being localized to the transmitters hence not providing homogenous white light or efficient illumination. For example, in F. Zafar et al. is mentioned that health problems are related to the fact of using lasers (classl is recommended under all conditions for indoor systems), and the presence of speckle patterns due to high coherence of lasers can also be virtually disturbing which might induce health complications for the users. Hence, there is a need to provide a VLC system that generates efficient and safe VLC and homogenous efficient illumination.

The current disclosure provides solutions to the above-mentioned problems and drawbacks by providing a VLC system, where the 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.

Transparent wood

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. In addition, 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.

Transparent wood (TW) opens a novel set of possible applications where 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

applications. 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 for example 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. Hence, 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. 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. To prepare the doped TW matrix (TW product), the optically active components, the luminophores, can be added in 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) also describe a transparent wood film incorporating carbon dots for generating light.

Generally, 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. 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. For example, in general tracheids and libriform fibres wood cells in softwoods and hardwoods may have lengths that vary from 0.5-10 mm, and a diameter from 10-70 pm. As a difference from softwoods, 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. Figure 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. In figure 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. To distribute e.g. 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. Further, without the filled cavities acting as resonators, 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. For building applications, 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. Flowever, 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

Current VLC systems using LEDs suffer from low data rates, and the proposed VLC systems using LDs pose health hazards and lack homogenous white light generation. To achieve a higher gain, homogenous white light generation and avoid health hazards, it is proposed to use a TW matrix doped with luminophores for generating both homogenous light and VLC with higher data rates.

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). Besides 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. In one example (not shown), a SEM image of a cross section of a dye embedded TW (TW product) and a 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. Hence, 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

communication integrated with adjustable illumination. This, in turn, means uniform homogenous illumination covering practically all indoor area without shading zones blocking the data transmission. Only a limited number of exciting sources/pumping sources, e.g. one per TW panel, are required provided efficient excitation of the luminophores. 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.

Due to the immense number of cavities and the millions of embedded luminophores, the emitted light will be evenly and homogenously distributed, hence providing homogenous illumination and VLC coverage in the area of the TW product. Using the TW product as, for example, ceiling tiles in a room will provide homogenous illumination as well as uniform VLC coverage in the room. In comparison, 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. Moreover, 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.

However, using ceiling tiles of present TW product, as the tiles are used in the whole room and as each fiber is one laser source, the result is more like a diffuse light source, but still strong enough to be used as VLC source due to the laser (narrow band) optical properties. This creates millions of lasers of narrow line (about lnm), with many incoherently contribute to broadening the line (<10nm, such as 7nm). 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.

Due to the unique properties of the TW and especially the TW fiber cavities, 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.

It is further possible to generate white light illumination (substantially white light) using the current approach. 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. By, for example, embedding different organic dyes, with different colors, white color could be obtained. Also a single type of luminophore with a broad yellow spectrum may generate white light under a blue pump. By using several different types of luminophores, e.g. dyes of different colors, several signals/channels may be transmitted, such as encoding different signals in each color by using different pumping sources. Hence, preferably a large number of different types of particles are used to increase the communication channel. 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. Randomly means that the process of how the luminophores are distributed cannot be exactly controlled, but that it is performed in as way such that the luminophores are well distributed or uniformly distributed. To make the luminophores randomly distributed in the TW, the luminophore solution should be a homogenous dispersion. This will make sure that the luminophores are uniformly distributed into the TW. Hence 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

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. However, it is currently not possible to use lasers due to health hazards, that they have high coherence and emission directionality - photodetectors should be on a direct visibility line against the source, and since coherence can cause interference and degrading transmission on different wavelengths (inter-channel interference). Instead, quasi-random lasers based on TW- material are suggested for VLC use, i.e. lasers having emission properties resembling random lasers, but still being fairly narrow as coherent lasers. The formation of quasi-random lasers has previously been described by the inventor in M. Koivurova et al. Optics Express Vol. 26 No 10, 2018. Benefits of such lasers in comparison with traditional one is low coherence, no interference effects, nondirectional radiation i.e. sending light in all directions with no shadowed or faded places, while still providing high spectral brightness at the wavelength of emission, being narrow (nearly classical laser linewidth 5-7 nm) hence more wavelength channels than for LEDs can be transmitted simultaneously and being safe for human eyes.

These lasers cannot be modulated using all possible modulation formats, hence intensity modulation, e.g. using dynamic amplitude modulation (DAM) i.e. pulsed modulation systems are typically used.

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. By using 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

For example, 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. Thus, 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.

Figure 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

stream/information 100 to the receiver.

A pumping source can be located in virtually any place provided that suitable optical waveguide delivers pumping radiation to the active material. Typically, the waveguide is present in a module external of the TW product. For example, 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. 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.

Further, the 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. Although 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

"upside", 103 in page 5b, or on the perpendicular sides compared to the upside and downsides referred to as the "edges", 103 in fig 5a. The advantage of TW compared to glass is that with glass as the transparent load bearing component, the pumping source need to cover all the area to make sure transmitted light can cover as large area as possible. With TW as the transparent load bearing component, 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. Alternatively, the pumping source, 102, can also be arranged on the edges of the transparent wood as shown in Figure 5b. Any arrangement of the pumping sources may be used, as long as the transmitted light can spread into a large enough area. 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. Example embodiments

The current disclosure discloses a TW product and its use in VLC.

In one embodiment is provided 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.

In a further embodiment is provided a visible light communication, VLC, system for generating illumination and transmitting information, the system 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. In some embodiments, 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.

In one embodiment a method of generating illumination and transmitting information using visible light communication, VLC, using the VLC system is provided. The proposed method will now be described in more detail referring to Figure 6. It should be appreciated that 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. Figure 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. In one aspect, a method of generating illumination and transmitting information using visible light communication, VLC, is provided, the method 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. By pumping different types of luminophores using different 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.

Examples

Preparation of transparent wood (TW)

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. In this example polymethyl methacrylate (PMMA) is used, but 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.

Delignification method:

Wood veneer (in this specific example Balsa), (Ochroma Lagopus, purchased from Wentzels Co. Ltd, Sweden) was dried at 105±3 °C for 24 h before chemical extraction. 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.

Lignin-retaining method:

Wood veneer (in this specific example Balsa) 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 fabrication (infiltration step):

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. 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.

Preparation of transparent wood matrix with embedded luminophores/luminescent components

After the first step of producing the wood template/TW matrix, 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. 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. In order to convert the TW host material into an optically active medium 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, and 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. At the second step, 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. In the third step, 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. After that, 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. 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 75 °C for 4 hours.

Example 2, Quantum dots (QDs) based luminescent components embedded TW:

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. Specifically, 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. In the second step, pre-polymerization of MMA and mixing with the luminophores, 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. % AIBN followed by cooling to room temperature and obtaining this way pre-polymerized MMA. Then the QDs in toluene solution are added into the pre-polymerized MMA solution. The solution is mixed by a magnetic stirrer for ~30 min. The QDs concentration in the pre-polymerized PMMA/QDs solution is less than 0.01 wt%.

Subsequently, in the third step, 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. These second and third steps are illustrated in figure 8. Conclusion

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).

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.

In the drawings and specification, there have been disclosed exemplary aspects of the disclosure. Flowever, many variations and modifications can be made to these aspects without substantially departing from the principles of the present disclosure. Thus, the disclosure should be regarded as illustrative rather than restrictive, and not as being limited to the particular aspects discussed above. Accordingly, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation.

The description of the example embodiments provided herein have been presented for purposes of illustration. The description is not intended to be exhaustive or to limit example embodiments to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of various alternatives to the provided embodiments. The examples discussed herein were chosen and described in order to explain the principles and the nature of various example embodiments and its practical application to enable one skilled in the art to utilize the example embodiments in various manners and with various modifications as are suited to the particular use contemplated. The features of the embodiments described herein may be combined in all possible combinations of methods, products, and systems. It should be appreciated that the example embodiments presented herein may be practiced in any combination with each other.

It should be noted that the word "comprising" does not necessarily exclude the presence of other elements or steps than those listed and the words "a" or "an" preceding an element do not exclude the presence of a plurality of such elements. It should further be noted that any reference signs do not limit the scope of the claims, that the example embodiments may be realized in the broadest sense of the claims.

All references cited herein are incorporated by reference to the extent allowed.