Antenna

Abstract

To provide an antenna capable of supporting a transmission of a high frequency signal and a wide bandwidth.SOLUTION: An antenna 100 includes a phosphor 10, a waveguide 20, and a photodetector 30. The phosphor 10 includes an energy donor that absorbs light of a first wavelength and becomes an excited state, and an energy acceptor that receives an energy from the energy donor in the excited state and emits a light of a second wavelength longer than the first wavelength. The waveguide 20 propagates the light of a second wavelength. The photodetector 30 detects the light of the second wavelength propagating through the waveguide 20.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an antenna. [Background technology]

[0002] Optical wireless communication is a type of wireless communication that uses electromagnetic waves (light) with wavelengths ranging from infrared to visible light. Optical wireless communication is attracting attention as a promising means of short-range communication in the future, due to factors such as the growing demand for radio wave-based wireless communication in recent years, which has led to a shortage of radio wave resources. Optical wireless communication consists of a transmitter (light source) and a receiver. Conventional methods that use a focusing lens to improve the focusing gain of the receiver are subject to an etendue limit, which means that the etendue cannot be exceeded. Etendue is calculated by the formula (area of ​​the light source emitting light) x (solid angle of the light diverging from the light source). Therefore, when light from a light source is focused, the field of view is limited to a narrow range. To solve the problem of a narrow field of view due to the etendue limit, fluorescent antennas for optical wireless communication have been proposed.

[0003] Patent Document 1 discloses a fluorescent antenna including a wavelength-shifting element configured to receive an input optical signal, the wavelength-shifting element including a fluorescent material configured to absorb at least a portion of the received input optical signal and generate an emitted optical signal from the input optical signal. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent No. 10,511,383 Summary of the Invention [Problem to be solved by the invention]

[0005] The performance of fluorescent antennas in optical wireless communication is affected by three characteristics: (1) the photoluminescence (PL) lifetime of the phosphor, (2) the photoluminescence quantum yield (PLQY), and (3) the PL emission wavelength and the wavelength sensitivity of the photodetector. Specifically, (1) the shorter the PL lifetime, the wider the optical signal transmission bandwidth. (2) The higher the PLQY, the more efficiently absorbed light can be converted into fluorescence. (3) In optical wireless communication, blue light (wavelength 450 nm) from GaN light-emitting diodes is often used as the signal light source. However, existing fluorescent antennas often convert this blue light into green light (wavelength 530 nm). However, because Si photodiodes, a common photodetector, are most sensitive to red or near-infrared light (wavelengths 600–800 nm), existing fluorescent antennas suffer from low sensitivity. Furthermore, when the absorption and emission wavelengths of the phosphor overlap widely, self-absorption occurs during the fluorescence propagation through the fluorescent antenna waveguide, resulting in attenuation of the fluorescence intensity. Therefore, existing fluorescent antennas have difficulty supporting the transmission of high frequency signals and wide bandwidths.

[0006] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an antenna that can support transmission of high frequency signals and wide bandwidths. [Means for solving the problem]

[0007] In order to achieve the object of the present invention, one aspect of the antenna according to the present invention comprises: a phosphor including an energy donor that absorbs light of a first wavelength and becomes excited, and an energy acceptor that receives energy from the excited energy donor and emits light of a second wavelength that is longer than the first wavelength; a waveguide that propagates light of the second wavelength; a photodetector that detects the light of the second wavelength that has propagated through the waveguide; The present invention is characterized by comprising: [Effects of the Invention]

[0008] According to the present invention, an antenna can be provided that can support the transmission of high frequency signals and wide bandwidths. [Brief explanation of the drawings]

[0009] [Figure 1] 1A and 1B are diagrams illustrating an antenna according to an embodiment. [Figure 2] 1A and 1B are diagrams illustrating phosphors according to an embodiment. [Figure 3] FIG. 1 is a diagram showing fluorescent substance Forster resonance energy transfer according to an embodiment. [Figure 4] 3A and 3B are diagrams showing absorption and emission spectra of a phosphor according to an embodiment. [Figure 5] FIG. 10 is a diagram showing an antenna according to a modified example. [Figure 6] FIG. 10 is a diagram showing a fluorescent substance Forster resonance energy transfer according to a modified example. [Figure 7] FIG. 10 is a diagram showing a fluorescent substance Forster resonance energy transfer according to a modified example. [Figure 8] FIG. 10 is a diagram showing a fluorescent substance Forster resonance energy transfer according to a modified example. [Figure 9] FIG. 10 is a diagram showing a fluorescent substance Forster resonance energy transfer according to a modified example. [Figure 10] FIG. 10 is a diagram showing an antenna according to a modified example. [Figure 11] FIG. 2 is a diagram showing the absorption spectrum of a phosphor according to an example. [Figure 12] FIG. 2 is a diagram showing the emission spectrum of a phosphor according to an example. [Figure 13] FIG. 1 is a graph showing the PLQY and PL lifetime of phosphors according to examples. [Figure 14] FIG. 1 is a diagram showing normalized absorption spectra and emission spectra of phosphors according to examples. [Figure 15] FIG. 1 is a diagram showing the PL lifetime of a phosphor according to an example. [Figure 16] FIG. 1 is a block diagram of an experimental set according to an example. [Figure 17] 17(a) is a diagram showing a frequency response according to an embodiment, and FIG. 17(b) is a diagram showing raw data used to generate FIG. 17(a). [Figure 18] (a) is a diagram showing the relationship between BER and data rate in an embodiment, (b) is a diagram showing a QAM constellation received without an antenna, (c) is a diagram showing a QAM constellation received using an antenna in a comparative example, and (d) is a diagram showing a QAM constellation received using an antenna in an embodiment. [Figure 19] FIG. 10 is a diagram illustrating the relationship between received signal strength and data rate according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Antennas according to embodiments of the present invention will be described below with reference to the drawings.

[0011] The antenna 100 according to this embodiment is a fluorescent antenna used for optical wireless communication, and as shown in Fig. 1, includes a phosphor 10, a waveguide 20, and a photodetector 30. Optical wireless communication is expected to enhance existing radio frequency systems and play an important role in future 6G networks.

[0012] The fluorophore 10 is disposed on the surface of the waveguide 20 and includes an energy donor 11 and an energy acceptor 12, as shown in FIG. 2. The energy donor 11 absorbs light of a first wavelength and enters an excited state. The energy acceptor 12 accepts energy from the excited energy donor and emits light of a second wavelength longer than the first wavelength. Specifically, as shown in FIGS. 3 and 4, the excited state energy of the energy donor 11 is transferred to the energy acceptor 12 via Förster resonance energy transfer (FRET) through dipole-dipole interactions, thereby generating an excited state for the energy acceptor 12. In this case, the greater the overlap between the emission of the energy donor 11 and the absorption of the energy acceptor 12 shown in FIG. 4, the more efficiently the excited state energy of the energy donor 11 can be transferred to the energy acceptor 12. Furthermore, when the distance between the energy donor 11 and the energy acceptor 12 shown in FIG. 2 is within the Förster radius (R0), FRET occurs efficiently, thereby enabling efficient energy transfer from the energy donor 11 to the energy acceptor 12. Here, R0 is the distance at which the rate at which the energy donor 11 in an excited state undergoes radiative transition to the ground state and the rate at which energy transfer from the energy donor 11 to the energy acceptor 12 occurs are 50%. R0 is determined by the luminescence quantum yield of the energy donor 11, the extent of overlap between the emission spectrum of the energy donor 11 and the absorption spectrum of the energy acceptor 12, and the relative orientation state between these molecules, and generally takes a value of several nm to 10 nm. When the excited state of the energy acceptor 12 returns to the ground state, the energy acceptor 12 emits light of a second wavelength. The first wavelength is, for example, 350 nm or more and 450 nm or less. The second wavelength is, for example, 500 nm or more and 1675 nm or less. Furthermore, the phosphor 10 may be provided with a protective layer. In this way, durability can be improved.

[0013] The energy donor 11 is, for example, tris(8-hydroxyquinolinato)aluminum (Alq3) represented by the following formula (a). The energy acceptor 12 is, for example, 4-dicyanomethylene-2-methyl-6-P-dimethylaminostyryl-4H-pyran (DCM) represented by the following formula (b). When Alq3 is used as the energy donor 11 and DCM is used as the energy acceptor 12, the mass ratio of DCM to Alq3 is preferably 1:20 to 1:400. This allows the excited state energy of Alq3 to be efficiently transferred to DCM by FRET.

[0014] [ka]

[0015] The waveguide 20 is made of a material that is transparent in the second wavelength range and propagates light of the second wavelength. The waveguide 20 may be made of glass or a resin such as a methacrylic resin or a fluorine-based resin. The shape of the waveguide 20 is not particularly limited, and may be a plate or a fiber. Specifically, the waveguide 20 may be a glass optical fiber or a plastic optical fiber.

[0016] The photodetector 30 detects the light of the second wavelength that has propagated through the waveguide 20, and includes, for example, a Si photodiode. The Si photodiode has high sensitivity in the red or near-infrared wavelength region (600 nm or more and 800 nm or less). When the waveguide 20 has a fiber-like shape, the photodetector 30 is disposed at the end of the waveguide 20.

[0017] As described above, according to the antenna 100 of this embodiment, an antenna capable of supporting the transmission of high frequency signals and wide bandwidths can be provided by absorbing an optical signal transmitted from a transmitter with the energy donor 11 and emitting the signal with the energy acceptor 12. In detail, the following technical effects can be obtained. (1) The PL (Photo Luminescence) lifetime and PL quantum yield (PLQY) are determined by the energy acceptor 12 and can be reduced by selecting materials with a short PL lifetime or a high PLQY. (2) The light detection sensitivity can be improved by selecting an energy donor 11 that has strong absorption at the wavelength of the light source and selecting a material for the energy acceptor 12 that emits light at a wavelength that the photodetector 30 has high detection sensitivity. (3) When light emitted from the phosphor 10 propagates through the waveguide 20, it undergoes repeated total reflection at the interface between the waveguide 20 and the phosphor 10. When FRET is used, the difference in wavelength between absorption and emission (the Stokes shift) increases significantly compared to when a single material is used, and the wavelength of the emitted light becomes longer, thereby reducing self-absorption by the phosphor 10. As a result, it is possible to suppress attenuation of light intensity when propagating through the waveguide 20. In optical wireless communications, a shorter PL lifetime can support the transmission of higher frequency signals and wider modulation bandwidths, while a high PL QY and large Stokes shift can achieve high optical harvesting gain, which leads to a higher signal-to-noise ratio (SNR). The effects will be explained in more detail in the examples described below.

[0018] (Variation) In the antenna 100 of the above embodiment, the phosphor 10 is disposed on the surface of the waveguide 20. The location of the phosphor 10 is not particularly limited; for example, as shown in FIG. 5, the phosphor 10 may be disposed within the waveguide 20. In this case, the waveguide 20 may be made of a resin such as methacrylic resin or fluorine-based resin. This facilitates disposing the phosphor 10 within the waveguide 20. Specifically, the waveguide 20 is a plastic optical fiber, and the phosphor 10 is mixed into the plastic optical fiber. The Stokes shift of the phosphor 10 is significantly larger than that of a single material, resulting in a longer wavelength of emitted light and less self-absorption. This suppresses attenuation of light intensity during propagation through the waveguide 20, providing an antenna capable of supporting the transmission of high-frequency signals and wide bandwidths.

[0019] In the antenna 100 of the above-described embodiment, the phosphor 10 includes the energy donor 11 and the energy acceptor 12. However, the phosphor 10 may further include an intermediate. The energy donor 11 absorbs light of a first wavelength and enters a high-energy excited state. The intermediate between the excited state and the ground state of the energy donor 11 transfers energy from the energy donor 11 by FRET through dipole-dipole interaction, forming an excited state of the intermediate. Furthermore, when the energy of the excited state of the intermediate is transferred to the energy acceptor 12, the excitation energy of the intermediate is transferred to the energy acceptor 12 by FRET through dipole-dipole interaction without the emission of the intermediate or absorption by the energy acceptor 12. When the excited state of the energy acceptor 12 thus generated returns to the ground state, it emits light of a second wavelength. Note that the efficiency of FRET increases as the overlap between the wavelength emitted by the first phosphor (second wavelength) and the wavelength absorbed by the second phosphor increases, as shown in FIG. 4. In this way, it is possible to increase the difference between the absorption wavelength and the emission wavelength (Stokes shift). Note that any fluorescent substance can be used for the energy donor 11, the energy acceptor 12, and the intermediate.

[0020] To be more specific, for example, as shown in FIG. 6, when a first fluorescent substance that absorbs ultraviolet to violet light (wavelengths of 350 nm to 400 nm) and emits blue-violet to blue light (wavelengths of 400 nm to 490 nm) coexists with a second fluorescent substance that absorbs in the wavelength range of 400 nm to 490 nm and emits blue-green to green light (wavelengths of 500 nm to 550 nm), the first fluorescent substance does not emit light but causes a step of FRET1 in the second fluorescent substance, generating an excited state in the second fluorescent substance and causing light emission from the second fluorescent substance, resulting in a second wavelength of blue-green to green (wavelengths of 500 nm to 550 nm).

[0021] Furthermore, as shown in Figure 7, when a third fluorescent substance that has absorption in the blue-green to green (wavelength 500nm to 550nm) region and emits light in the yellow to red (560nm to 790nm) region is added in addition to the first fluorescent substance and the second fluorescent substance, a second stage FRET2 occurs from the second fluorescent substance to the third fluorescent substance, resulting in emission of light in the yellow to red (560nm to 790nm). In other words, the second wavelength is 560nm to 790nm.

[0022] Furthermore, as shown in Figure 8, if there is a fourth fluorescent substance that absorbs in the yellow to red (560nm to 790nm) region and emits in the near-infrared (800nm ​​to 1675nm) region, the second wavelength will be 800nm ​​to 1675nm through the third stage FRET3, i.e., the first fluorescent substance → the second fluorescent substance → the third fluorescent substance → the fourth fluorescent substance. When the second wavelength is near-infrared light, a detector that is sensitive to near-infrared light, such as an InGaAs photodiode, is used as the detector. In this case, for example, PBD: 2-(4-tert-butylphenyl)-5-(4-biphenylyl)-1,3,4-oxadiazole can be used as the first fluorescent substance, C490: coumarin 490 can be used as the second fluorescent substance, DCM2: 4-(dicyanomethylene)-2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)vinyl]-4H-pyran can be used as the third fluorescent substance, and LDS821: 2-[[3-[2-[4-(dimethylamino)phenyl]ethenyl]-5,5-dimethyl-2-cyclohexen-1-ylidene]methyl]-3-ethylbenzothiazolium perchlorate can be used as the fourth fluorescent substance.

[0023] The above example describes a three-stage FRET process: first fluorescent substance → second fluorescent substance → third fluorescent substance → fourth fluorescent substance. On the other hand, as shown in Figure 9, if a combination of materials is used in which the emission spectrum of the first fluorescent substance overlaps with the absorption spectrum of the third fluorescent substance, a single-stage FRET1 from the first fluorescent substance that absorbs wavelengths of 350 nm to 400 nm to the third fluorescent substance can be achieved, resulting in yellow to red emission (560 nm to 790 nm) as the second wavelength.

[0024] Similarly, when a combination of a second fluorescent substance and a third fluorescent substance is used, FRET1 occurs from the second fluorescent substance that absorbs wavelengths of 400 nm to 490 nm to the third fluorescent substance, resulting in emission of yellow to red light (560 nm to 790 nm) as the second wavelength.

[0025] In this way, by selecting a fluorescent material that absorbs the wavelength of the optical signal output from the transmitter as the energy donor 11 and combining it with a fluorescent material that emits the wavelength to be emitted as the energy acceptor 12, it is possible to select a second wavelength that matches the sensitivity characteristics of the detector.

[0026] Specific examples of compounds that can be used as the first to fourth fluorescent substances are shown below.

[0027] The first fluorescent substance is a material that absorbs ultraviolet to purple light (wavelength 350 nm to 400 nm) and emits blue-purple to blue light (wavelength 400 nm to 490 nm), and examples thereof include diphenylanthracene, 2,5,8,11-tetra-tert-butylperylene, PBD (2-(4-tert-butylphenyl)-5-(4-biphenylyl)-1,3,4-oxadiazole), PVK (polyvinylcarbazole), These include 4,4-bis(N-carbazolyl)-1,1'-biphenyl, poly(9,9-di-n-octylfluorenyl-2,7-diyl), bis(3,5-difluoro-4-cyano-2-(2-pyridyl)phenyl-(2-carboxypyridyl)iridium(III)(*), bis(2,4-difluorophenylpyridinato)tetrakis(1-pyrazolyl)borateiridium(III)(*), etc.

[0028] The second fluorescent substance is a material that has absorption in the blue-violet to blue (wavelength 400 nm to 490 nm) region and emits light from blue-green to green (wavelength 500 nm to 550 nm), and is selected from Alq3 (tris(8-hydroxyquinolinato)aluminum), Coumarin 504 (ethyl 2,3,6,7-tetrahydro-11-oxo-1H,5H,11H-[1]benzopyrano[6,7,8-ij]quinolizine-10-carboxylate), BPEA (9,10-bis(phenylethynyl)anthracene), N ,N'-dimethylquinacridone, 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene, 2,3,5,6-tetrakis(carbazol-9-yl)-1,4-dicyanobenzene, 2,5-bis(2,2'-bipyridin-6-yl)-1,1-dimethyl-3,4-diphenylsilole, F8BT (poly(9,9-di-n-octylfluorenyl-2,7-diyl)), tris(2-phenylpyridinato)iridium(III)(*), etc.

[0029] The compounds marked with (*) are called phosphorescent materials. Fluorescence is a technical term that refers to light emission from a singlet excited state. In contrast, phosphorescence refers to light emission from a triplet excited state. Both fluorescent and phosphorescent materials can be used as energy donors 11 and energy acceptors 12 in FRET.

[0030] The third fluorescent substance is a material that absorbs light in the blue-green to green (wavelength 500 nm to 550 nm) region and emits light in the yellow to red (560 nm to 790 nm) region, and includes rubrene, diphenylpentacene, 2,8-di-tert-butyl-5,11-bis(4-tert-butylphenyl)-6,12-diphenyltetracene, 2,6-bis(4-(diphenylamino)phenyl)anthracene-9,10-dione, MEH-PPV (poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]), CN-PPV (poly(2,5-di(hexyloxy)cyano terephthalylidene)), etc.

[0031] The fourth fluorescent substance is a material that has absorption in the blue to green (wavelength 450 nm to 540 nm) or blue-green to green (wavelength 500 nm to 550 nm) region and emits near-infrared light (800 to 1675 nm), and includes Pt-TPTNP (Pt-tetraphenyltetranaphthoporphyrin), Pt-Ar4TAP (platinum (II)-5,10,15,20-(3,5-di-tert-butylphenyl)tetraanthroporphyrin), etc.

[0032] The antenna 100 of the above embodiment has been described as detecting light in one wavelength range, but as shown in FIG. 10, it can also be used as a stacked fluorescent antenna for wavelength division multiplexing (WDM) by using multiple antennas 100A to 100C.

[0033] Here, antennas 100A, 100B, and 100C function like filters that absorb light of blue B, green G, and red R, respectively. For example, we will explain a case where three LEDs in the visible light range, red R (wavelength approximately 620 nm), green G (wavelength approximately 530 nm), and blue B (wavelength approximately 450 nm), are used as transmitters to simultaneously send signals, but it is also possible to convert the final wavelength into a near-infrared wavelength.

[0034] By using a receiver consisting of a fluorescent antenna 100A that absorbs blue B light (wavelength approximately 450 nm) and emits and detects green G fluorescence (wavelength approximately 530 nm), antenna 100B that absorbs green G light (wavelength approximately 530 nm) and emits and detects red R fluorescence (wavelength approximately 620 nm), and fluorescent antenna 100C that absorbs red R light (wavelength approximately 620 nm) and detects near-infrared light (wavelength approximately 800 nm), it is possible to receive signals from three independent transmitters. [Example]

[0035] The effects of the antenna 100 and the phosphor 10 are demonstrated below by examples. These examples show one embodiment of the present disclosure, and the present disclosure is not limited to these examples in any way.

[0036] (phosphor) The energy donor 11 contained in the phosphor 10 was tris(8-hydroxyquinolinato)aluminum (Alq3) represented by the following formula (a), and the energy acceptor 12 was 4-dicyanomethylene-2-methyl-6-P-dimethylaminostyryl-4H-pyran (DCM) represented by the following formula (b).

[0037] [ka]

[0038] Samples 1 to 7 of phosphor 10 were prepared using Alq3 as energy donor 11 and DCM as energy acceptor 12 in the proportions shown in Table 1 below. Sample A was a comparison sample containing no DCM.

[0039] [Table 1]

[0040] In Samples 1 to 7, energy is transferred by FRET from Alq3, the energy donor 11, to DCM, the energy acceptor 12. In contrast, in Sample A, which does not contain the energy acceptor 12, energy transfer by FRET does not occur.

[0041] The efficiency of energy transfer in FRET strongly depends on the distance between the energy donor 11, Alq3, and the energy acceptor 12, DCM. The distance between Alq3 and DCM depends on the relative concentrations of the energy donor 11 and the energy acceptor 12. Therefore, the initial focus of research on FRET-based antennas is optimizing the concentration ratio of Alq3 to DCM. The results after this optimization showed that employing FRET increased the PLQY of sample 5 to 0.53, more than three-fold compared to the PLQY of sample A (0.16). Furthermore, FRET shortened the PL lifetime of sample 5 to 3.52 ns, compared to 9.31 ns for sample A.

[0042] DCM emits red light with a high PL QY and short PL lifetime, which is efficiently detected by conventional Si-based photodiodes. Furthermore, the significant overlap between the emission spectrum of Alq3 and the absorption spectrum of DCM, as shown in Figure 14, implies efficient energy transfer between these molecules during FRET.

[0043] First, the absorption spectra of Samples 1 to 7 and Sample A were measured. For this measurement, the materials were dissolved in chloroform to prepare solution-based samples. The concentration of Alq3 in chloroform was set to 0.1 mg / mL, which is 0.218 × 10 -5 This corresponds to a molar concentration in mol / L. Next, as shown in Table 1, samples 1 to 7 with different mass ratios of DCM to Alq3 were prepared by changing the amount of DCM added to Alq3.

[0044] The mole fractions of DCM in Alq3 were 7.04%, 2.93%, 1.49%, 1.00%, 0.75%, 0.50%, and 0.38%, respectively. As shown in Figure 11, with much higher concentrations of Alq3 compared to DCM, the absorption spectra were primarily dominated by Alq3. However, at higher concentrations, DCM caused absorption at wavelengths longer than 450 nm. When the concentration of DCM in Alq3 was reduced below 1:150, this additional absorbance from DCM was almost negligible.

[0045] Next, the emission spectra of the samples were measured to determine the effect of energy transfer. Energy transfer occurs effectively when the energy acceptor 12 and the energy donor 11 are close enough to each other within the Förster radius (R0). For this measurement, thin-film samples consisting of Alq3 and DCM were prepared. Chloroform was used as the solvent for the thin-film samples, and the concentration of Alq3 in chloroform was fixed at 10 mg / ml. Next, samples 1 to 7 were prepared by varying the amount of DCM added to each sample. For reference, pure Alq3, sample A, was also prepared. These samples were then dropped onto a quartz substrate and spin-coated. The spin-coating process was performed at a speed of 2000 RPM for 30 seconds. After spin-coating, the samples were left on the holder for several minutes to allow the chloroform to evaporate. Figure 12 shows the measured emission spectra of samples 1 to 7 and sample A when the excitation light wavelength was 365 nm. It was found that the emission wavelength increased with increasing the concentration of DCM in Alq3. The results also show that the emitted light intensity differs for Samples 1 to 7 and Sample A. Because emission intensity is directly related to PLQY, we also measured the PLQY of Samples 1 to 7 and Sample A, obtaining the results shown by the circles in Figure 13. Sample 5 at 1:200 (0.75 mol%) yielded the highest PLQY. This is consistent with the emission spectrum measurements shown in Figure 12, which confirmed that higher PLQY corresponds to higher intensity peaks. As shown in these results, the PLQY was found to initially increase with increasing DCM concentration and then decrease at higher concentrations.

[0046] The initial increase in PLQY with increasing DCM concentration was consistent with an increased probability of energy transfer as the average distance between DCM and Alq3 molecules decreased. The decrease in PLQY at high concentrations was consistent with DCM molecules quenching each other as they approached each other, a phenomenon known as concentration quenching (CQ). To confirm that these processes lead to the observed behavior, we calculated various distances between DCM molecules and between DCM and Alq3 molecules in the prepared thin film samples. The results, summarized in Table 1, showed that as the DCM mole fraction changed from 7.04% to 0.38%, the average distance between DCM molecules increased from 2.73 nm to 7.23 nm. Due to the uniform distribution of Alq3 molecules between DCM molecules, this meant that the distance between DCM and Alq3 molecules changed from 1.37 nm to 3.62 nm. The fluorescence decay rate (k) as a function of DCM-DCM distance was fl ), non-emissivity (k nr ) and concentration quenching rate (k CQ The sum of the σ and σ values ​​showed that in this system, the nonradiative decay of DCM was significantly increased with increasing DCM. Another quantitative comparison was made by comparing the average distance between Alq3 and DCM with the Förster radius. The Förster radius is defined as the average intermolecular distance at which the probability of an exciton in the energy donor (Alq3) either deactivating on the energy donor 12 or transferring nonradiatively to the nearest energy acceptor 12 molecule (DCM) is equal.

[0047] The R0 for Alq3-DCM has been reported to be 3.3 nm. Since the average Alq3-DCM distance for sample 6 with a concentration ratio of 1:300 coincides with R0, samples 1 through 5 with DCM ratios above 1:200 favor efficient energy transfer. Therefore, the maximum PLQY arises from a combination of an increase in PLQY due to the improved transfer efficiency from Alq3 to DCM molecules, on the one hand, and a decrease in PLQY due to the improved efficiency of CQ, on the other hand. The normalized absorption and emission spectra for sample 5 with a DCM concentration of 1:200 in Alq3 are shown in Figure 14. These are compared with both the Alq3 thin film sample and the DCM solution sample (0.1 mg / ml in chloroform). In the case of DCM, we investigated the solution rather than the thin film because the strong CQ effect of DCM prevents emission in DCM films. The results shown in Figure 14 indicate that the absorption spectra of Alq3 and Alq3 + DCM are nearly identical, suggesting that the 365 nm excitation light used in the experiment is primarily absorbed by Alq3. In contrast, the emission spectra of these samples are significantly different. In the case of Alq3 + DCM, the emission is primarily from DCM. This confirms the occurrence of energy transfer from Alq3 to DCM. Note that the emission spectrum of Alq3 + DCM is not the same as that of DCM. This is because the DCM sample is a solution, whereas the Alq3 + DCM sample is a thin film. In other words, the difference in matrix polarity between the two samples results in differences in the emission spectra from DCM.

[0048] Another important parameter of the antenna 100 is the PL lifetime τ, which is the 3 dB bandwidth f of the antenna 100. 3dBThe PL decay data for Samples 1 to 7 and Sample A were measured using a streak camera system (Hamamatsu Photonics, C4780). The corresponding PL lifetimes are indicated by squares in Figure 13. The PL lifetime of Alq3 was found to be 9.31 ns, corresponding to a 3 dB bandwidth of 17 MHz. Adding DCM to Alq3 also shortened the PL lifetime. Furthermore, the results showed a direct correlation between the PL lifetime and the amount of DCM mixed with Alq3. Energy transfer causes DCM to emit light, resulting in a shorter PL lifetime. This is because the PL lifetime of DCM is shorter than that of Alq3. Furthermore, as previously mentioned, increasing the DCM concentration increases the CQ. As a result, the PLQY decreases, but the PL lifetime also shortens. Sample 5, with a concentration ratio of 1:200, yielded the highest PLQY, and therefore antenna 100 was fabricated using this ratio. The results in Figure 15 indicate that the PL lifetime of the antenna 100 using Sample 5 with a concentration ratio of 1:200 is 3.52 ns, and therefore the 3 dB bandwidth is 45 MHz. Note that the PL lifetime τ and the 3 dB bandwidth f 3dB The relationship is calculated by the following formula (1).

[0049]

number

[0050] (antennas and transmission systems) The antenna 100 of Example 1 comprises a phosphor 10, a waveguide 20, and a photodetector 30. A glass substrate measuring 75 mm in length, 8 mm in width, and 1.1 mm in thickness was used to form the waveguide 20. Next, to fabricate the phosphor 10, a solution containing DCM and Alq3 at a weight ratio of 1:200 was drop-cast onto the surface of the glass substrate (the waveguide 20). After the solvent evaporated, a thin-film fluorescent layer was formed. Furthermore, two fluorescent layers composed of phosphor 10 were formed by coating both sides of the glass substrate, allowing the lower layer to absorb light not absorbed by the upper layer. When incident light of a first wavelength reaches the fluorescent layer, it is absorbed if its wavelength is within the absorption range of Alq3. A portion of this absorbed energy causes the DCM to emit photons of a second wavelength longer than the first wavelength. Because the photons emit at random angles, many photons are trapped within the glass and directed toward the edge of the glass substrate where the photodetector 30 is located. However, because the perimeter of the antenna 100 is much larger than the light receiving area (1 mm diameter) of the photodetector 30, only a portion of the guided light is detected. Despite this inefficiency, the use of the antenna 100 can increase the intensity of the light reaching the photodetector 30.

[0051] Figure 16 shows a block diagram of the experimental setup. In this experimental setup, an arbitrary waveform generator (AWG, Siglent SDG2082X) was used to generate the transmit signal, which was then amplified through a power amplifier (Mini-circuits, ZHL-32A-S). The amplified signal was superimposed on a DC current through a bias-T (Mini-circuits, ZFBT-4R2GW) to drive a 365 nm LED transmitter (Thorlabs, M365D2). On the receiver side, the antenna 100 in Example 1 collected light and guided it to a commercially available avalanche photodiode (APD, Thorlabs, APD130A). The APD output was then captured using a digital storage oscilloscope (DSO, LeCroy, 204Xi-A). For bandwidth measurements, sine waves of various frequencies were generated by the AWG, and the peak-to-peak voltage detected by the DSO was measured. For the measurements of data transmission, Orthogonal Frequency Division Multiplexing (OFDM) modulation was considered.

[0052] This signal was generated offline using numerical analysis software, and the main signal processing steps are shown in Figure 16. To create an OFDM signal suitable for intensity modulation, we first mapped the binary data sequence to quadrature amplitude modulation (QAM) symbols. These QAM symbols were constrained to be Hermitian symmetric, ensuring that the output time-domain signal sequence from the inverse fast Fourier transform (IFFT) contained only real numbers suitable for directly driving an LED transmitter. The signal sequence then underwent parallel-to-serial (P / S) conversion, a cyclic prefix (CP) was added, and both the top and bottom of the signal were clipped to address the high peak-to-average power ratio (PAPR). In this case, the clipping level was fixed at 10 dB, which means that the clipping level was 3.16 times greater than the standard deviation of the Gaussian distribution. This enabled us to remove obvious signal peaks while maintaining negligible distortion in the clipped signal. At the receiver, we performed OFDM demodulation to recover the transmitted data. This involved converting the received signal into the frequency domain using a Fast Fourier Transform (FFT) and applying a single-tap equalizer to each individual subcarrier. After equalization, the received QAM symbols were converted into binary bits based on the maximum likelihood (ML) detection principle. Finally, the transmitted and received bit sequences were compared to obtain the bit error rate (BER) for evaluating the performance of the transmission link.

[0053] (Communication measurement) Figure 17(a) shows the measured frequency response of the antenna 100 of Example 1, which uses Alq3 and DCM, the antenna of Comparative Example 1, which uses only Alq3, and the system without an antenna. These results show that the 3 dB bandwidth of the system without the antenna is 7.5 MHz. Because the 3 dB bandwidth of the ADP (Avalanche Photo Diode) is 50 MHz, this means that the bandwidth of this system, like other LED-based optical wireless communication systems, is limited by the LED. The results also show that the bandwidth of the system is not reduced by 3 dB because the bandwidth of both antennas is much higher than 7.5 MHz. However, at frequencies higher than the system's 3 dB frequency, the antenna slightly degraded the system's response.

[0054] Figure 17(b) shows the raw data used to generate Figure 17(a). Because this data is measured peak-to-peak voltage, it can be used to determine the signal gain obtained using either antenna. In particular, this data shows that using the antenna of Comparative Example 1 increased the signal by 1.3 times. However, this was significantly lower than the gain (6.5) obtained using the antenna 100 of Example 1. Most of the gain increase obtained by using the antenna 100 of Example 1 occurred due to an increase in PLQY. However, the change in the spectrum of the emitted light also means that self-absorption losses are reduced, allowing the APD to detect the emitted light more efficiently. These two processes combined contributed approximately 33% of the gain increase obtained using the antenna 100 of Example 1.

[0055] Figure 18(a) shows the BER (Bit Error Rate) measured when a transmission distance is 20 cm, with no antenna, the antenna of Comparative Example 1 using only Alq3, and the antenna 100 of Example 1 using Alq3 and DCM. In this measurement, the transmission data rate was changed from low to high by adjusting the transmission sampling rate. It was found that the BER increased as the data rate increased. 3.8 x 10 -3Considering the forward error correction (FEC) limitations of the BER, the best transmission data rate without an antenna was only 7 Mbps. This increased to 14 Mbps using the antenna of Comparative Example 1 using only Alq3 and to 50 Mbps using the antenna 100 of Example 1 using Alq3+DCM. This significant improvement achieved using the antenna 100 of Example 1 using Alq3+DCM was due to its high gain. Figures 18(b) to 18(d) show received QAM constellations for a transmission data rate of 20 Mbps. Figure 18(b) shows a QAM constellation received without an antenna. Figure 18(c) shows a QAM constellation received using the antenna of Comparative Example 1. Figure 18(d) shows a QAM constellation received using the antenna of Example 1. It was found that using the antenna 100 of Example 1 using Alq3+DCM resulted in a clearer constellation distribution with a BER of 0.

[0056] To investigate how bandwidth affects transmission performance, we varied the distance between the transmitter and receiver and quantified the received signal strength using the measured peak-to-peak voltage when transmitting a 1 MHz sine wave. Figure 19 shows the performance of a 3.8 × 10 -3The data rates corresponding to BERs of 1000 s are shown in Figure 19. As expected, the results in Figure 19 demonstrate that the achievable data rate increases as the signal strength increases. However, because the signal strength is relatively high, increasing the signal strength only slightly increases the data rate. Furthermore, it was found that, for the same signal strength, the highest data rate was supported without an antenna. This is because the use of a fluorescent antenna reduces the system bandwidth due to the PL lifetime of the fluorescent material. However, when comparing the antenna of Comparative Example 1, which uses only Alq3, with the antenna 100 of Example 1, which uses Alq3 and DCM, the antenna 100 of Example 1, which uses Alq3 and DCM, supported a higher data rate. This is due to the shorter PL lifetime of the antenna 100 of Example 1, as shown in Figure 15.

[0057] More importantly, the results shown in FIG. 19 indicated that the gain of the antenna 100 of Example 1 achieved the same receiver output voltage at a significantly longer transmission distance than the other two receivers. For example, when the voltage was approximately 600 mV, the transmission distance was only 10 cm when no antenna or the antenna of Comparative Example 1 was used. In contrast, the transmission distance was 30 cm when the antenna 100 of Example 1 was used. This means that in certain scenarios, the system incorporating the antenna 100 of Example 1 performed significantly better than the other two systems.

[0058] As described above, the use of the antenna 100 of Example 1 using Alq3 and DCM in optical wireless communication demonstrated that the use of Alq3 and DCM can enhance all aspects of the antenna 100's performance. In particular, using Alq3 as the energy donor and DCM as the energy acceptor, FRET shortened the PL lifetime from 9.3 ns to 3.5 ns. This means that FRET significantly increases the transmission bandwidth of the antenna 100. Furthermore, FRET increased the PLQY from 0.16 to 0.53. Furthermore, shifting the antenna's emission spectrum peak from 525 nm to 610 nm had two effects: reducing losses due to self-absorption and improving the efficiency with which the second wavelength of emitted light is detected by the photodetector 30. The combination of a high PLQY and a very long emission wavelength improved the antenna concentration gain from only 1.3 to 6.5. As a result, the SNR at the output of the optical wireless communication receiver was significantly improved. The results show that the improvement achieved by using the antenna 100 of Example 1 significantly increases the transmission data rate from a mere 7 Mbps to 50 Mbps. The above example describes the use of Alq3 as the energy donor 11 and DCM as the energy acceptor 12. The energy donor 11 may be a material other than Alq3, as long as it absorbs light of a first wavelength and becomes excited. The energy acceptor 12 may also be a material other than DCM, as long as it accepts energy from the excited energy donor 11 and emits light of a second wavelength longer than the first wavelength. Even in such cases, an antenna 100 capable of supporting the transmission of high-frequency signals and wide bandwidths can be provided.

[0059] The present invention allows various embodiments and modifications without departing from the broad spirit and scope of the present invention. Furthermore, the above-described embodiments are intended to explain the present invention and do not limit the scope of the present invention. That is, the scope of the present invention is defined by the claims, not the embodiments. Various modifications made within the scope of the claims and the meaning of the invention equivalent thereto are considered to be within the scope of the present invention. [Explanation of symbols]

[0060] 10...phosphor, 11...energy donor, 12...energy acceptor, 20...waveguide, 30...photodetector, 100, 100A, 100B, 100C...antenna

Claims

1. a phosphor including an energy donor that absorbs light of a first wavelength and becomes excited, and an energy acceptor that receives energy from the excited energy donor and emits light of a second wavelength that is longer than the first wavelength; a waveguide that propagates light of the second wavelength; a photodetector that detects the light of the second wavelength that has propagated through the waveguide; An antenna comprising:

2. The phosphor is disposed on the surface of the waveguide.

2. The antenna according to claim 1 .

3. The phosphor is disposed within the waveguide.

2. The antenna according to claim 1 .

4. The energy donor is tris(8-hydroxyquinolinato)aluminum (Alq3) represented by the following formula (a): The energy acceptor is 4-dicyanomethylene-2-methyl-6-P-dimethylaminostyryl-4H-pyran (DCM) represented by the following formula (b):

4. An antenna according to claim 1, wherein the antenna is a conductor. 【Chemistry 1】

5. the photodetector includes a Si photodiode; the second wavelength is equal to or greater than 600 nm and equal to or less than 800 nm; 4. An antenna according to claim 1, wherein the antenna is a conductor.

6. the first wavelength is equal to or greater than 350 nm and equal to or less than 450 nm; 6. The antenna according to claim 5.

7. The waveguide has a fiber shape, the photodetector is disposed at an end of the waveguide; 4. An antenna according to claim 1, wherein the antenna is a conductor.

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