WO2022024336A1

WO2022024336A1 - Optical fiber and solar transmission system

Info

Publication number: WO2022024336A1
Application number: PCT/JP2020/029405
Authority: WO
Inventors: 悠途寒河江; 千里深井; 隆松井; 和秀中島; 一貴原; 敦子河北; 友宏谷口
Original assignee: 日本電信電話株式会社
Priority date: 2020-07-31
Filing date: 2020-07-31
Publication date: 2022-02-03
Also published as: JP7435789B2; JPWO2022024336A1

Abstract

The purpose of the present invention is to eliminate the necessity for a wavelength filter or power-supply-driven light source unit having a specific wavelength when using sunlight.　The present invention relates to an optical fiber in which the periphery of a core is covered by cladding, wherein the optical fiber transmits a predetermined wavelength among the wavelengths included in sunlight, and has a core radius and a difference in the relative refractive index of the cladding with respect to the core.

Description

Fiber optics and photovoltaic transmission systems

This disclosure relates to optical fibers and systems for transmitting sunlight.

Currently, light of various wavelength bands is used for various purposes. The visible light region is not only used for household lighting, but also lighting having a visible light spectrum optimized for growing conditions is used in a plant factory (Non-Patent Document 1). The ultraviolet region is used in a sterilization system for the purpose of preventing infectious diseases, for example (Non-Patent Document 2). Further, in the infrared region, various products are used as heater appliances (Non-Patent Document 3).

In Non-Patent Documents 1 to 3, it is necessary to prepare power-driven light sources having wavelengths according to the intended use of light, and there is a problem that power consumption and device cost increase. There is a technique for selectively extracting and irradiating an arbitrary wavelength from sunlight, which is a power-free source, using a wavelength filter, but it is not economical from the viewpoint of equipment cost.

It is an object of the present disclosure to eliminate the need for a power source-driven light source unit and a wavelength filter having a specific wavelength in the use of sunlight.

In the present disclosure, an arbitrary wavelength is extracted by designing the transmittance of an optical fiber that collects sunlight and transmits light to an irradiation target. This eliminates the need for a power source-driven light source unit and a wavelength filter having a specific wavelength, which are required for conventional light utilization, so that an economical system can be configured by saving power and reducing equipment cost.

The optical fiber according to the present disclosure is
An optical fiber whose core is covered with a clad.
It has a radius of the core and a difference in the specific refractive index of the clad with respect to the core, which transmits a predetermined wavelength among the wavelengths contained in sunlight.

The solar transmission system according to this disclosure is
A condensing unit that collects sunlight and
An irradiation part that irradiates the irradiation target with light,
An optical transmission unit including an optical fiber or an optical fiber bundle of the present disclosure, which connects the light collecting unit and the irradiation unit and is bent at least in a part with a predetermined bending radius.
To prepare for.

According to the present disclosure, in a system using a specific wavelength, a power supply-driven light source unit and a wavelength filter having a specific wavelength, which are required in the conventional light utilization, are not required, and thus problems in the prior art are solved. And an economical system can be realized.

An example of wavelength selection by optical fiber design of the optical transmission unit is shown. An example of the structure dependence of the transmission peak wavelength in a pure quartz core step index fiber is shown. An example of the Δ dependence of K1 is shown. A first configuration example of the present disclosure is shown. A first configuration example in which the wavelength can be selected is shown. A second configuration example in which the optimum wavelength can be selected is shown. A configuration example that realizes two irradiation methods is shown. A first configuration example that realizes an increase in irradiation intensity is shown. A second configuration example that realizes an increase in irradiation intensity is shown. An example of the function of distributing light to two or more irradiation targets is shown.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The present disclosure is not limited to the embodiments shown below. Examples of these implementations are merely examples, and the present disclosure can be implemented in various modified and improved forms based on the knowledge of those skilled in the art. In addition, the components having the same reference numerals in the present specification and the drawings shall indicate the same components.

(Wavelength selection by optical fiber design of optical transmission unit)
An optical fiber in which the core of quartz glass is covered with a cladding behaves like a wavelength bandpass filter due to light leakage loss and Rayleigh scattering loss due to bending. FIG. 1 shows the core radius dependence of the light transmission spectrum when the difference in the specific refractive index of the clad with respect to the core of the pure quartz core fiber is −0.35% and the bending radius is 30 mm. The vertical axis is standardized by the transmittance at the peak wavelength. Since the wavelength characteristic of bending loss changes depending on the core radius, the transmission wavelength band can be designed. The same effect can be obtained with an optical fiber using quartz glass to which GeO ₂ is added as a core. In addition, it can be applied to any optical fiber in which light leakage loss and Rayleigh scattering loss occur due to bending, and it is considered that it can be applied to a rare earth-added optical fiber containing an element other than _GeO2 , for example. A more flexible wavelength filter can also be realized by adding a grating structure to the optical fiber. By using an optical fiber having a hollow core, it is possible to select a wavelength with relatively low loss even in the ultraviolet region.

FIG. 2 shows an example of the structure dependence of the transmission peak wavelength in the optical fiber. The figure shows the core radius of the transmission peak wavelength in a step index fiber having a pure quartz core, and the Δ dependence of the specific refractive index difference of the clad with respect to the core. In any of the specific refractive index differences Δ, the peak wavelength is linearly lengthened as the core radius increases. This is because the bending loss on the long wavelength side is suppressed by increasing the core radius. Each straight line can be written by the following equation, where K ₁ is a coefficient depending on Δ.

Here, a is the core radius.

FIG. ₃ shows the Δ dependence of K1. The curve can be expressed by the following equation.

From the above, the desired transmission peak wavelength (λ _pk ) is a pure quartz core step index fiber having a core radius a determined by the following equation when Δ is −0.7% or more and −0.35% or less.

(First Embodiment)
FIG. 4 shows an example of the basic configuration of the present disclosure. The system of the present disclosure is a solar transmission system in which a condensing unit 91 and an irradiation unit 92 are connected by an optical transmission unit 93. The light collecting unit 91 collects sunlight. For example, the condensing unit 91 includes an arbitrary device that includes a condensing system using one or more lenses or mirrors and is capable of optical coupling to the optical transmission unit 93. In the present disclosure, the sunlight collected by the condensing unit 91 may be referred to as condensing light.

The irradiation unit 92 irradiates the irradiation target 101 with light of an arbitrary wavelength transmitted by the optical transmission unit 93 (the light may be referred to as transmission light). For example, the irradiation unit 92 emits the transmitted light directly from the end face of the optical fiber and irradiates the irradiation target 101. Further, the irradiation unit 92 may irradiate the transmitted light by propagating it by a spatial optical system using one or more lenses. Further, the irradiation unit 92 may irradiate the transmitted light by using the light leaked from the side surface due to bending of the optical fiber or the like.

The optical transmission unit 93 transmits the condensed light to the irradiation unit 92. The optical transmission unit 93 uses an optical fiber having a core having a transmission wavelength designed as shown in FIGS. 1 to 3. Therefore, by bending the optical transmission unit 93 with a predetermined length and a predetermined bending radius according to the wavelength characteristics, it is operated like a wavelength bandpass filter by light leakage loss and Rayleigh scattering loss due to bending, which is desired. It is possible to extract the wavelength of. The predetermined length of the optical fiber of the present disclosure provided in the optical transmission unit 93 may be a length capable of attenuating an unnecessary wavelength band.

For example, if the wavelength band is 280 nm to 340 nm, an optical fiber having a core radius of 0.5 μm and a clad specific refractive index difference of −0.35% with respect to the core is bent with a bending radius of 30 mm. When the wavelength band is 380 nm to 620 nm, an optical fiber having a core radius of 1.0 μm and a clad specific refractive index difference of −0.35% with respect to the core is bent with a bending radius of 30 mm. When the wavelength band is 400 nm to 840 nm, an optical fiber having a core radius of 1.5 μm and a clad specific refractive index difference of −0.35% with respect to the core is bent with a bending radius of 30 mm. The optical fiber of the present disclosure included in the optical transmission unit 93 is not limited to one, and optical fibers having different core radii may be continuously connected.

The optical transmission unit 93 includes, at least in part, a multi-core optical fiber having two or more cores designed with transmission wavelengths shown in FIGS. 1 to 3, or an optical fiber bundle in which optical fibers having one of the cores are bundled. include. It is preferable to use an optical fiber bundle because a larger light intensity can be transmitted.

The optical transmission unit 93 may use an optical fiber having a grating structure. This makes it possible to select any transmission wavelength in the present disclosure. Further, the optical transmission unit 93 may use an optical fiber having a hollow core. This makes it possible to transmit the present disclosure even with ultraviolet region light with relatively low loss.

(Second embodiment)
FIG. 5 shows a first system configuration example in which the wavelength can be selected. This system includes a wavelength selection unit 81, and an optical transmission unit 93 includes a transmission path selection unit 82 and an optical extraction unit 83. A plurality of optical transmission lines 84 are connected between the transmission line selection unit 82 and the optical extraction unit 83. By having one or more optical fibers of the present disclosure optimized for transmission in different wavelength bands, the plurality of optical transmission lines 84 can combine the transmission bands of each optical fiber to enable arbitrary wavelength extraction. ..

The wavelength selection unit 81 selects the transmission wavelength in the optical transmission unit 93, and transmits the selected wavelength information to the transmission path selection unit 82 and the optical extraction unit 83.

The transmission line selection unit 82 selects an optical transmission line 84 capable of extracting light of a desired wavelength from sunlight based on the selection wavelength information transmitted from the wavelength selection unit 81. Here, the method of selecting light is arbitrary, and can be realized by, for example, a mechanical optical switch or a MEMS (Micro Electro Mechanical Systems) optical switch whose optical path switching characteristic has no wavelength.

The light extraction unit 83 extracts transmission light from one or more arbitrary optical transmission paths 84 based on the selection wavelength information transmitted from the wavelength selection unit 81 and transmits the transmission light to the irradiation unit 92. Here, the light extraction method is arbitrary, and can be realized by, for example, a mechanical optical switch, a MEMS optical switch, an optical coupler, or the like whose optical path switching characteristic has no wavelength.

(Third embodiment)
FIG. 6 shows a second system configuration example in which the optimum wavelength can be selected. This system includes a wavelength selection unit 81, and an optical transmission unit 93 includes a core selection unit 85 and an optical extraction unit 86. A multi-core optical fiber 87 is connected between the core selection unit 85 and the optical extraction unit 86. The multi-core optical fiber 87 has one or more cores optimized for transmission in different wavelength bands, so that the transmission bands of the cores can be combined to enable arbitrary wavelength extraction.

The wavelength selection unit 81 selects the transmission wavelength in the optical transmission unit 93, and transmits the selected wavelength information to the core selection unit 85 and the optical extraction unit 86.

The core selection unit 85 selects a core capable of extracting a desired wavelength from sunlight based on the selection wavelength information transmitted from the wavelength selection unit 81. Here, the method of selecting the core is arbitrary, and it can be realized by combining a mechanical optical switch or a MEMS optical switch whose optical path switching characteristic has no wavelength, and a fan-in device using a spatial optical system or a planar waveguide. ..

The light extraction unit 86 extracts transmission light from an arbitrary core based on the selection wavelength information transmitted from the wavelength selection unit 81 and transmits it to the irradiation unit 92. Here, the extraction of light from each core can be realized by combining a mechanical optical switch, a MEMS optical switch, or an optical coupler whose optical path switching characteristics have no wavelength, and a fan-out device using a spatial optical system or a planar waveguide. Is.

(Fourth Embodiment)
FIG. 7 shows an example of a system configuration that realizes two irradiation methods. In this system, the irradiation unit 92 includes a wave packet forming unit 21 of a centralized irradiation method, a light diffusing unit 22 of a wide area irradiation method, and an irradiation control unit 23. The irradiation control unit 23 guides the light transmitted by the optical transmission unit 93 to at least one of the wave packet forming unit 21 and the light diffusion unit 22.

The wave packet forming unit 21 performs selective intensive irradiation on the irradiation target 101. In the wave bundle forming unit 21, when light is propagated by an optical fiber, it can be realized by collimating or condensing the propagated light by imparting a lens function to the end face of the optical fiber. When light propagates in space, it can be realized by collimating or condensing the propagated light by using one or more lenses or mirrors.

The light diffusing unit 22 irradiates a wide area using the diffused light. When the light is propagated by the optical fiber, the light diffusing unit 22 imparts distributed bending to the optical fiber and imparts a plurality of scatterers such as bubbles in the longitudinal direction of the optical fiber to leak from the side surface of the optical fiber. It can be realized by using the light that is used. When the light of the irradiation unit 92 propagates in the space, it can be realized by using the light diffusion film for the light diffusion unit 22.

(Fifth Embodiment)
FIG. 8 shows a first system configuration example that realizes an increase in irradiation intensity. In this system, N condensing units 91 (N is an integer of 2 or more) are connected to the optical combine unit 94 by the condensing light transmission unit 95.

In the optical combine unit 94, the collected light from two or more condensing units 91 is combined and aggregated in the optical transmission unit 93. When the optical transmission unit 93 is composed of an optical fiber, the optical combiner unit 94 can be realized by one or more optical couplers. When space propagating light is used in the optical transmission unit 93, the photosynthetic unit 94 can be realized by using one or more half mirrors.

This system is expected to improve the following two performances by installing the condensing unit 91 at two or more geographically different points.
(I) Increased light intensity: When each condensing unit 91 condenses sunlight of the same intensity, it is possible to irradiate light with N times the intensity by using N condensing units 91.
(Ii) Improving stability: By installing two or more condensing units 91 at positions with different environmental conditions, the risk of a decrease in the amount of sunshine due to obstacles is dispersed, and stable light irradiation is applied to the irradiation target 101. Is possible.

(Sixth Embodiment)
FIG. 9 shows a second system configuration example that realizes an increase in irradiation intensity. When the angle of the position of the sun with respect to the ground surface and the installation angle of the condensing unit 91 are different, the condensing efficiency decreases. Therefore, this system includes two or more light collecting units 91 having different angles with respect to the ground plane _PH . As a result, each condensing unit 91 condenses light incident on the ground plane _PH at different angles. The figure shows an example in which a plurality of condensing units 91 having different installation angles are arranged in only one row, but there may be two or more rows. Further, the arrangement of the plurality of condensing units 91 having different installation angles is not limited to the uniaxial direction, but may be orthogonal to each other or may be biaxially intersecting at any angle.

This embodiment is preferable because the following two performance improvements are expected.
(I) Increased light intensity: Since light can be collected by two or more light collecting units 91 installed at an angle near the angle of the sun with respect to the ground surface, the irradiation light intensity is increased.
(Ii) Improved stability: Even if the angle of the sun with respect to the earth's surface changes throughout the day, the light condensing unit 91 with the same angle enables highly efficient condensing, so that stable condensing does not depend on the angle of the sun. Is possible.

(7th Embodiment)
FIG. 10 shows an example of a function of distributing light to two or more irradiation targets 101. This system includes a light intensity determining unit 31, a light amount adjusting unit 32, and an optical branching unit 33 between the optical transmission unit 93 and the irradiation unit 92.

The optical branching unit 33 branches the transmitted light to two or more irradiation units 92. When the optical transmission unit 93 is composed of an optical fiber, the optical branching unit 33 can be realized by using one or more optical couplers. When spatial propagation light is used in the optical transmission unit 93, the optical branching unit 33 can be realized by using one or more half mirrors.

The light intensity determination unit 31 determines the light transmission intensity to two or more irradiation units 92 for each irradiation unit 92. This function enables flexible switching of irradiation intensity according to irradiation demand.

The light amount adjusting unit 32 arbitrarily adjusts the light transmission intensity to two or more irradiation units 92. When light is transmitted using an optical fiber, it can be dimmed by adding bending or the like. In the case of spatial propagation light transmission, dimming is possible by using two or more polarizing plates or a dimming filter.

It is possible to combine the first to seventh embodiments that adopt the above-mentioned principle of the present disclosure. For example, the condensing unit 91, the condensing light transmission unit 95, and the optical combine unit 94 shown in FIG. 9 may be applied to the condensing unit 91 at each point shown in FIG. In this case, the optical transmission unit 93 shown in FIG. 9 functions as the focused optical transmission unit 95 shown in FIG. 8, and is combined by the optical combine unit 94.

This disclosure can be applied to the information and communication industry.

21: Wave bundle forming unit 22: Light diffusion unit 31: Light intensity determination unit 32: Light amount adjustment unit 33: Optical branch unit 81: Wave frequency selection unit 82: Transmission path selection unit 83: Light extraction unit 84: Optical transmission path 85: Core Selection unit 86: Optical extraction unit 87: Multi-core optical fiber 91: Condensing unit 92: Irradiation unit 93: Optical transmission unit 94: Optical confluence unit 95: Condensed light transmission unit 101: Irradiation target

Claims

An optical fiber whose core is covered with a clad.
It has a radius of the core and a difference in the specific refractive index of the clad with respect to the core, which transmits a predetermined wavelength among the wavelengths contained in sunlight.
Optical fiber.
A condensing unit that collects sunlight and
An irradiation part that irradiates the irradiation target with light,
The optical transmission unit including the optical fiber according to claim 1, which connects the light collecting unit and the irradiation unit and is bent at least in a part with a predetermined bending radius.
A solar transmission system equipped with.
Further, a wavelength selection unit for selecting a transmission wavelength in the optical transmission unit is provided.
The optical transmission unit
Multiple optical transmission lines that transmit different wavelength bands,
A transmission line selection unit that connects the plurality of optical transmission lines and transmits the condensed light from the light collecting unit to an optical transmission line that includes the wavelength selected by the wavelength selection unit as a transmission wavelength.
An optical extraction unit that is connected to the plurality of optical transmission lines and extracts transmission light of the optical transmission line that includes the wavelength selected by the wavelength selection unit as a transmission wavelength.
The solar transmission system according to claim 2.
The plurality of optical transmission lines are multi-core optical fibers including a plurality of cores that transmit different wavelength bands.
The transmission path selection unit is a core selection unit that transmits condensed light from the condensing unit to a core that includes the wavelength selected by the wavelength selection unit as a transmission wavelength.
The light extraction unit extracts the transmission light of the core including the wavelength selected by the wavelength selection unit as the transmission wavelength.
The solar transmission system according to claim 3.
The irradiation part is
A wave packet forming unit that concentrates the transmitted light of the optical transmission unit on the irradiation target,
A light diffusing unit that diffuses the transmitted light of the optical transmission unit and irradiates the irradiation target,
An irradiation control unit that guides the transmitted light of the optical transmission unit to at least one of the irradiation unit and the light diffusion unit.
The solar transmission system according to any one of claims 2 to 4.
With two or more of the light collectors,
A photosynthetic unit that combines the condensed light of two or more condensing units, and a photosynthetic unit.
The solar transmission system according to any one of claims 2 to 5.
The two or more light collectors collect light incident on a predetermined surface at different angles.
The solar transmission system according to claim 6.
An optical branching section that splits the transmitted light of the optical transmitting section into two or more,
Two or more of the irradiation units provided for each branch light branched at the optical branch, and
A light intensity determining unit that determines the intensity of each irradiation unit, and a light intensity determining unit.
A light amount adjusting unit connected between the light branching portion and each irradiation unit and adjusting the light transmission intensity to the irradiation unit to the intensity determined by the light intensity determining unit.
The solar transmission system according to any one of claims 2 to 7.