WO2023139794A1

WO2023139794A1 - Multicore fiber and optical transmission system

Info

Publication number: WO2023139794A1
Application number: PCT/JP2022/002468
Authority: WO
Inventors: 千里深井; 和秀中島; 裕之飯田; 隆松井; 悠途寒河江; 友宏谷口; 亜弥子岩城; 聖成川; 誉人桐原
Original assignee: 日本電信電話株式会社
Priority date: 2022-01-24
Filing date: 2022-01-24
Publication date: 2023-07-27

Abstract

The purpose of the present invention is to provide an optical transmission system that makes it possible to perform sterilization and viral inactivation of a subject by using ultraviolet light without requiring the complete absence of humans and that makes it possible to prevent humans from touching the subject by mistake during ultraviolet irradiation, as well as a multicore fiber provided in the optical transmission system.　An optical transmission system according to the present invention is provided with a multicore fiber (12) characterized in that: in a fiber cross section, the center of each peripheral core (21) lies on a circle concentric with a center core (19) and having a radius (R_core) greater than the radius (a_c) of the center core (19); the radius (a_o) of the peripheral core (21) is less than the radius (a_c) of the center core (19); and the refractive index of the center core (19) in relation to the wavelength of light propagated through the center core (19) differs from the refractive index of the peripheral core (21) in relation to the wavelength of light propagated through the peripheral core (21). Either ultraviolet light or visible light is introduced to the center core (19), and the other is introduced to the peripheral core (21).

Description

Multicore fiber and optical transmission system

The present disclosure relates to a multi-core fiber for transmitting light (electromagnetic waves) in the ultraviolet band and an optical transmission system including the same.

Many organisms on earth, including bacteria and viruses, have a macromolecular biological substance called DNA that is responsible for the inheritance and expression of genetic information. This DNA has an absorption spectrum near 260 nm, and absorption of light of this wavelength causes abnormalities in the DNA arrangement. Light in the 260 nm band is ultraviolet light. When bacteria and viruses are irradiated with this ultraviolet light, the normal replication of DNA is inhibited, resulting in sterilization and virus inactivation.

The effect of sterilization or virus inactivation by ultraviolet light is used as a means of preventing infectious diseases. For example, Non-Patent Document 1 discloses an autonomous mobile robot that irradiates ultraviolet light as a method for preventing contact infection by sterilizing elevator buttons and doorknobs and deactivating viruses.

Ultraviolet light affects not only bacteria and viruses, but also the DNA of the human body. Therefore, when ultraviolet light is used to prevent contact infection, it is necessary to devise ways to avoid irradiating people with ultraviolet light. Since the ultraviolet light irradiation robot described in Non-Patent Document 1 is irradiated with ultraviolet light over a wide range, it is necessary to irradiate ultraviolet light to sterilize and inactivate viruses in an unmanned building at night. Therefore, the ultraviolet light irradiation robot described in Non-Patent Document 1 has a problem that it is difficult to sterilize and inactivate viruses immediately after a person touches an object such as an elevator button or a doorknob.

For the omnidirectional ultraviolet light irradiation robot described in Non-Patent Document 1, there is also an ultraviolet light irradiation system that transmits ultraviolet light through an optical fiber, emits the ultraviolet light from the tip of the optical fiber, and irradiates the target with a pinpoint. This UV light irradiation system is capable of sterilizing and virus inactivating objects with UV light without being completely unmanned. However, ultraviolet light has a wavelength that cannot be detected by the human eye, and people cannot avoid being exposed to ultraviolet light. For this reason, the ultraviolet light irradiation system using an optical fiber has a problem that it is difficult to prevent a person from accidentally touching an object during ultraviolet light irradiation.

Therefore, in order to solve the above problems, the object of the present invention is to provide an optical transmission system capable of sterilizing an object with ultraviolet light and inactivating viruses without making the object completely unattended, and of avoiding a person accidentally touching the object during ultraviolet light irradiation, and a multi-core fiber provided therein.

In order to achieve the above objectives, the optical transmission system according to the present invention divides the core of the multi-core fiber into an ultraviolet core that transmits ultraviolet light and a visible core that transmits visible light, and the arrangement and refractive index of the cores are adjusted so that the diameters of the respective irradiation areas match.

Specifically, the multi-core fiber according to the present invention is a multi-core fiber comprising a central core and a plurality of peripheral cores, the cross-section comprising:
the center of the peripheral core is on a concentric circle with a radius R _core [m] greater than the radius _ac [m] of the central core;
the radius _ao [m] of the peripheral core is smaller than the radius _ac [m] of the central core;
characterized by

The ultraviolet light and visible light emitted from the tip of the multi-core fiber irradiate the same area. Therefore, a person can visually recognize the region irradiated with the ultraviolet light. By using this multi-core fiber, it is possible to perform sterilization and virus inactivation on an object with ultraviolet light without leaving the object completely unmanned, and it is possible to avoid accidental touching of the object by a person during irradiation with ultraviolet light.

Specifically, it is designed as follows.
In the multi-core fiber according to the present invention, the relationship between the diameter D _uv [m] of the ultraviolet light emitted from the central core and the radius D _vis [m] of the minimum circumscribed circle enclosing the beams of visible light emitted from all the peripheral cores is D _uv ≦D _vis on a plane perpendicular to the optical axis, which is L [m] away from one end in the optical axis direction.
It is characterized by
however,

n _{core_uv} is the refractive index of the central core in the ultraviolet band;
n _{clad_uv} is the refractive index of the clad in the ultraviolet band;
n _{core_vis} is the refractive index of the peripheral core in the visible band, and n _{clad_vis} is the refractive index of the cladding in the visible band.

In the multi-core fiber according to the present invention, in a plane perpendicular to the optical axis, which is L [m] away from one end in the optical axis direction, the relationship between the beam diameter D _vis [m] of the visible light emitted from the central core and the radius D _uv [m] of the minimum circumscribed circle enclosing the beams of ultraviolet light emitted from all the peripheral cores is D _uv ≤ D _vis .
It is characterized by
however,

n _{core_uv} is the refractive index of the peripheral core in the ultraviolet band;
n _{clad_uv} is the refractive index of the clad in the ultraviolet band;
n _{core_vis} is the refractive index of the central core in the visible band, and n _{clad_vis} is the refractive index of the cladding in the visible band.

A multi-core fiber according to the present invention is a quartz fiber, characterized in that the central core and the peripheral core are doped with different amounts of germanium. The refractive index of the core can be adjusted by the doping amount of germanium.

A transmission system according to the present invention includes a multi-core fiber having a central core and a plurality of peripheral cores, and a light incidence section for injecting one of ultraviolet light and visible light into the central core and the other into the peripheral core. Here, if the multi-core fiber is the multi-core fiber described above, the ultraviolet light and visible light emitted from the tip of the multi-core fiber irradiate the same region. Therefore, a person can visually recognize the region irradiated with the ultraviolet light.

Therefore, the present invention can provide an optical transmission system that can sterilize an object with ultraviolet light and inactivate viruses without being completely unmanned, and that can prevent a person from accidentally touching the object while it is being irradiated with ultraviolet light.

The present invention can provide an optical transmission system capable of sterilizing an object with ultraviolet light and deactivating viruses without making the object completely unattended, and preventing a person from accidentally touching the object while the object is being irradiated with ultraviolet light, and a multi-core fiber provided therein.

1 is a diagram for explaining an optical transmission system according to the present invention; FIG. FIG. 3 is a schematic diagram illustrating the state of light emitted from the output end of an optical fiber; It is a schematic diagram explaining the cross section of the optical fiber which concerns on this invention. It is a schematic diagram explaining the cross section of the optical fiber which concerns on this invention. FIG. 3 is a diagram for explaining the configuration of an optical coupling section of the optical transmission system according to the present invention; FIG. 3 is a diagram for explaining the configuration of an optical coupling section of the optical transmission system according to the present invention; FIG. 4 is a schematic diagram explaining light emitted from the emission end of the multi-core fiber according to the present invention; FIG. 4 is a diagram illustrating the relationship between the refractive index of the core and the diameter of the irradiation area when ultraviolet light is propagated through the central core of the multi-core fiber according to the present invention; FIG. 4 is a diagram for explaining the relationship between the amount of germanium doping for a quartz fiber and the refractive index in the ultraviolet band; FIG. 4 is a diagram for explaining the relationship between the wavelength of light in the visible band and the refractive index of the cores of the peripheral cores of the multi-core fiber according to the present invention. FIG. 4 is a diagram for explaining the relationship between the amount of germanium doping for a quartz fiber and the refractive index in the visible band;

An embodiment of the present invention will be described with reference to the attached drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In addition, in this specification and the drawings, constituent elements having the same reference numerals are the same as each other.

FIG. 1 is a block diagram illustrating the ultraviolet light transmission system 301 of this embodiment. The ultraviolet light transmission system includes a multi-core fiber 12 having a central core and a plurality of peripheral cores, and a light incidence section 17 for injecting one of ultraviolet light and visible light into the central core and the other into the peripheral core.

The light input unit 17 includes a light source 10 that generates light including the ultraviolet band and the visible band, a control device 15 that controls the output of the light source 10, and an optical coupling unit 11 that couples the light generated from the light source 10 to the multi-core fiber 12 that transmits the light. The emitted light 13 emitted from the emitting end 12-2 of the multi-core fiber 12 is applied to the irradiation object . The ultraviolet light transmission system 301 can carry out sterilization or virus inactivation while allowing humans to recognize the irradiated area with visible light.

Here, the ultraviolet light transmission system 301 may include a remote control device 16 that remotely controls the control device 15 . Further, the ultraviolet light transmission system 301 may be combined with a sensor or the like and provided with a safety device (not shown) that does not emit light from the light source 10 when there is a person near the irradiation object 14 .

FIG. 2 is a schematic diagram illustrating the state of light emitted from one end 54 of a general optical fiber 50. As shown in FIG. The diameter D of the irradiation area at the distance L [m] from the one end 54 of the light can be expressed by Equation (1).
[Number 1]
D=2L tan θ _max +2a (1)
Here, θmax[°] and a[m] are the maximum output angle and core radius that can be output from the optical fiber 50, respectively. Also, the numerical aperture NA can be expressed by Equation (2) using θmax.

where n, n _core , and n _clad are the refractive indices of the medium, fiber core, and cladding around the fiber circumference, respectively, and n=1 when the fiber circumference is air.

Therefore, the diameter D[m] of the irradiated area can be expressed by Equation (3) using L, n _core , n _clad and a[m].

In order for a person to be able to confirm the irradiation region of ultraviolet light, as shown in formula (4), the diameter D _uv [m] of the irradiation region in the ultraviolet band must be equal to or less than the diameter D _vis [m] of the irradiation region in the visible band. That is, considering equations (3) and (4), since the refractive index of the core and clad in the ultraviolet band and the refractive index of the core and clad in the visible band are different, it is necessary to adjust the refractive index of the core and clad to satisfy equation (4).
[Number 4]
D _uv ≦D _vis (4)

(Example 1)
FIG. 3 is a schematic diagram illustrating a cross section of the multicore fiber 12. FIG. The multicore fiber 12 is a multicore fiber comprising a central core 19 and a plurality of peripheral cores 21, and in cross section:
the center of the peripheral core 21 is on a concentric circle with a radius R _core [m] larger than the radius _ac [m] of the central core 19;
the radius _ao [m] of the peripheral core 21 is smaller than the radius _ac [m] of the central core 19;
characterized by
Surrounding each core is a cladding 20 .

In this embodiment, an example in which ultraviolet light is propagated through the central core 19 and visible light is propagated through the peripheral core 21 will be described. Visible light may be propagated through the central core 19 and ultraviolet light may be propagated through the peripheral core 21 provided that the refractive index and radius conditions described below are satisfied.
As shown in FIG. 3, the core center of the peripheral core 21 is arranged on the circumference of a circle having a core arrangement radius R _core with respect to the center of the optical fiber 12 . FIG. 3 shows an example in which the eight peripheral cores 21 are evenly arranged on the core arrangement radius R _core , but the central core 19 and the peripheral cores 21 may be arranged with the clad 20 interposed therebetween, and the number of cores and the arrangement interval are not limited to this.

The central core 19 and the peripheral core 21 each have a higher refractive index than the clad 20, and light is transmitted by the light confinement effect due to the refractive index difference. For example, it is possible to form a core with a higher refractive index than the clad by forming a clad with pure silica and doping the pure silica with germanium. Also, as shown in FIG. 4, a plurality of holes 22 may be arranged so as to surround each core.

FIG. 5 is a diagram illustrating an example of the form of the optical coupling section 11 that couples the light from the light source 10 to the input end 12-1 of the multicore fiber 12. FIG. Light 23 including the ultraviolet band and the visible band emitted from the light source 10 is split into transmitted light 30 and reflected light 31 by the beam splitter 24 . The transmitted light 30 becomes light 28 of only the ultraviolet band by a wavelength filter 26 that transmits only the ultraviolet band, and is coupled to the central core 19 by the lens 32 . On the other hand, the reflected light 31 is further reflected by the reflector 25 , becomes light 29 only in the visible band by the wavelength filter 27 that transmits only the visible band, and is coupled to the peripheral core 21 by the lens 33 .

The

lenses

32 and 33 can be combined with condensing lenses and diffusing lenses to couple the ultraviolet band-only light 28 and the visible band-only light 29 into the central core 19 and the peripheral core 21, respectively.

Here, the transmitted light may be coupled to the central core 19 as light of only the visible band by a wavelength filter that transmits only the visible band. In this case, the reflected light is coupled to the peripheral core 21 as light only in the ultraviolet band by a wavelength filter that transmits only the ultraviolet band.

Further, by configuring the beam splitter 24 with a dichroic mirror, it is possible to split the transmitted light 30 and the reflected light 31 into light 28 only in the ultraviolet band and light 30 only in the visible band, respectively. In this case, the filter 26 that transmits only the ultraviolet band and the filter 27 that transmits only the visible band are unnecessary.

Alternatively, as shown in FIG. 6, the light source 10 may be configured with a light source 34 that emits only the ultraviolet band and a light source 35 that emits only the visible band, and the light 28 only in the ultraviolet band may be coupled to the central core 19 by the lens 32, and the light 29 only in the visible band may be coupled to the peripheral core 21 by the lens 33.

FIG. 7 is a schematic side view of the vicinity of the output end 12-2 of the multi-core fiber 12. As shown in FIG. The diameter D _uv of the irradiation region in the ultraviolet band from the central core 19 can be expressed by Equation (5).

where n _{core_uv} and n _{clad_uv} are the refractive indices of the central core 19 and the clad 20 in the ultraviolet band, respectively. Also, _ac is the core radius of the central core 19 .

On the other hand, the diameter D _vis of the irradiation area in the visible band from all the peripheral cores 21 (minimum circle enclosing the range irradiated by the visible light from each peripheral core 21) can be expressed by Equation (6).

where n _{core_vis} and n _{clad_vis} are the refractive indices of the peripheral core 21 and cladding 20 in the visible band, respectively. Also, a _o and R _core are the core radius of the peripheral core 21 and the core placement radius of the peripheral core 21 , respectively.

FIG. 8 is a diagram for explaining the relationship between the refractive index n _{core_uv} of the central core and the diameter D _uv [m] of the irradiation region for light in the ultraviolet band in a germanium-doped silica fiber (the wavelength λuv of ultraviolet light is 266 nm). Here, the distance L from the fiber output end 12-2 and the core radius a _c of the central core 19 were set to 10 cm (1×10 ⁻¹ [m]) and 100 μm (1×10 ⁻⁴ [m]), respectively.

From FIG. 8, the diameter D _uv of the ultraviolet light irradiation region can be changed in the range of 2.5 to 6 [cm] (2, 5 to 6×10 ⁻¹ [m]) when the refractive index n _{core_uv} of the central core 19 is in the range of 1.505 to 1.525. For example, when the refractive index n _{core_uv} of the central core 19 is 1.525, the diameter Duv of the irradiation area is 5.4 cm (5.4×10 ⁻¹ [m]).

As shown in FIG. 9, it is possible to change the refractive index of the silica fiber by increasing or decreasing the doping amount of germanium. An optical fiber core with a refractive index n _{core_uv} of 1.505-1.525 can be achieved with a germanium doping amount of 2.2-11.2 mol %. The refractive index n _{core — uv} =1.525 mentioned above can be achieved with a germanium doping amount of 11.2 mol %.

FIG. 10 is a diagram for explaining the relationship between the wavelength λvis of visible light and the refractive index n _{core_vis} of the peripheral core for light in the visible band when the diameter D _vis of the irradiation region in the visible band is 3.3, 4.1, 4.8, and 5.4 cm (3.3×10 ⁻¹ , 4.1×10 ⁻¹ , 4.8×10 ⁻¹ , 5.4×10 ⁻¹ [m]) (wavelength λv of visible light The range of is is from 400 to 600 nm). Here, the core radius a _o of the peripheral core 21 and the core arrangement radius R _core were set to 5 μm (5×10 ⁻⁶ [m]) and 115 μm (1.15×10 −4 [m]), respectively.

From FIG. 10, it can be seen that the formula (4) can be realized by using the refractive index n _{core_vis} of the peripheral core 21 corresponding to the wavelength λvis of light in the visible band used for visual observation. Specifically, when using light in the visible band with a wavelength λvis of 400 to 600 nm, an irradiation area with a diameter Dvis of 3.3 to 5.4 cm can be realized by adjusting the refractive index n _{core_vis} of the fiber core in the visible band to 1.467 to 1.492.

For example, when the diameter D _uv of the irradiation region in the ultraviolet band is 5.4 cm, the diameter D _vis of the irradiation region in the visible band must also be 5.4 cm in order to visually observe the ultraviolet light irradiation region using the wavelength λvis of light in the visible band of 400 nm. This diameter D _vis can be achieved by setting the refractive index n _{core_vis} of the fiber core in the visible band to 1.479.

FIG. 11 is a diagram for explaining the relationship between the refractive index n _{core_vis} and the amount of germanium doping. The refractive index n _{core_vis} of the peripheral core 21 in the visible band from 1.467 to 1.492 can be achieved with a germanium doping amount of 5.1 to 14.4 mol %. The refractive index n _{core — vis} =1.479 mentioned above can be achieved with a germanium doping amount of 13.8 mol %.

That is, the multi-core fiber 12 is a silica fiber, and is characterized in that the central core 19 and the peripheral core 21 are doped with different amounts of germanium.

(Example 2)
This embodiment describes an ultraviolet light transmission system that uses the multicore fiber 12 described with reference to FIG. 3, transmits visible light through the central core 19, and transmits ultraviolet light through the peripheral core 21. In order to satisfy the expression (4) in the system of this example, the following expression must be satisfied.

where n _{core_uv} is the refractive index of the peripheral core 21 in the ultraviolet band, n _{clad_uv} is the refractive index of the clad 20 in the ultraviolet band, n _{core_vis} is the refractive index of the central core 19 in the visible band, and n _{clad_vis} is the refractive index of the clad 20 in the visible band.

This example can also be realized by adjusting the refractive index of each core with the doping amount of germanium, as described with reference to FIGS.

(effect)
In this optical transmission system, a core that transmits ultraviolet light is arranged at the center of an optical fiber, and a core that transmits visible light is arranged around the central core to transmit both ultraviolet light and visible light. Therefore, when preventing contact infection due to sterilization and virus inactivation by ultraviolet light, this optical transmission system can prevent erroneous irradiation of the human body and realize safe infection prevention because the person can see the ultraviolet light irradiation area with visible light.

The ultraviolet light transmission system according to the present disclosure can be applied to infection prevention measures.

10: Light source 11: Optical coupler 12: Multi-core fiber 12-1: Input end 12-2: Output end 13: Output light 14: Irradiation target 15: Control device 16: Remote device 17: Light input unit 19: Central core 20: Cladding 21: Peripheral core 22: Hole 23: Light including ultraviolet band and visible band 24: Beam splitter 25: Reflector 26: Wavelength filter 27 that transmits only ultraviolet band: Only visible band Wavelength filter 28 for transmitting: light only in the ultraviolet band 29: light only in the visible band 30: transmitted light 31: reflected light 32: lens 33: lens 34: light source that emits only the ultraviolet band 35: light source that emits only the visible band 50: optical fiber 51: core 52: cladding 54: one end 301: ultraviolet light transmission system

Claims

A multicore fiber comprising a central core and a plurality of peripheral cores,
In cross section,
the center of the peripheral core is on a concentric circle with a radius R core [m] greater than the radius ac [m] of the central core;
the radius ao [m] of the peripheral core is smaller than the radius ac [m] of the central core;
A multicore fiber characterized by:
In a plane perpendicular to the optical axis, which is L [m] away from one end in the optical axis direction, the relationship between the diameter D uv [m] of the ultraviolet light emitted from the central core and the radius D vis [m] of the minimum circumscribed circle containing the beams of visible light emitted from all the peripheral cores is D uv ≦D vis
The multicore fiber according to claim 1, characterized in that:
however,

n core_uv is the refractive index of the central core in the ultraviolet band;
n clad_uv is the refractive index of the clad in the ultraviolet band;
n core_vis is the refractive index of the peripheral core in the visible band, and n clad_vis is the refractive index of the cladding in the visible band.
In a plane perpendicular to the optical axis, which is L [m] away from one end in the optical axis direction, the relationship between the beam diameter D vis [m] of the visible light emitted from the central core and the radius D uv [m] of the minimum circumscribed circle containing the beams of ultraviolet light emitted from all the peripheral cores is D uv ≦D vis
The multicore fiber according to claim 1, characterized in that:
however,

n core_uv is the refractive index of the peripheral core in the ultraviolet band;
n clad_uv is the refractive index of the clad in the ultraviolet band;
n core_vis is the refractive index of the central core in the visible band, and n clad_vis is the refractive index of the cladding in the visible band.
The multi-core fiber is a quartz fiber,
4. The multi-core fiber according to any one of claims 1 to 3, wherein the central core and the peripheral core are doped with different amounts of germanium.
a multicore fiber comprising a central core and a plurality of peripheral cores;
a light incident part that makes one of ultraviolet light and visible light incident on the central core and the other on the peripheral core;
An optical transmission system comprising:
The optical transmission system according to claim 5, wherein the multicore fiber is the multicore fiber according to any one of claims 1 to 4.