Optical fiber and its manufacturing method, light emitting method and light emitting device

Abstract

To provide an optical fiber capable of generating a single photon and a manufacturing method for the same, a light-emitting method, and a light-emitting device.SOLUTION: Provided are an optical fiber, a manufacturing method for the same, a light-emitting method, and a light-emitting device. The optical fiber has an area containing rare earth elements therein. At least a portion of the rare earth element is separated into single atoms at a distance exceeding the diffraction limit.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an optical fiber and a method for manufacturing the same, a light emitting method, and a light emitting device. [Background technology]

[0002] Optical fibers are capable of transmitting optical signals at high speeds and are therefore widely used in the fields of information technology such as communications, computers, etc. Such optical fibers are disclosed, for example, in Patent Document 1. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-118663 Summary of the Invention [Problem to be solved by the invention]

[0004] In information technology using quantum technology (quantum information technology), the use of the quantum mechanical properties of single photons is being studied for quantum computers, quantum memories, quantum cryptography, etc. However, although various technologies have been studied, including the technology disclosed in Patent Document 1, the current situation is that there are insufficient technologies for obtaining single photons.

[0005] The present disclosure has been made in light of the above circumstances, and a problem that one embodiment of the present disclosure aims to solve is to provide an optical fiber capable of generating a single photon. Another problem to be solved by another embodiment of the present disclosure is to provide a method for manufacturing the optical fiber. Another problem to be solved by another embodiment of the present disclosure is to provide a light emitting method using the optical fiber. Another problem to be solved by another embodiment of the present disclosure is to provide a light-emitting device using the optical fiber. [Means for solving the problem]

[0006] The present disclosure includes the following aspects. <1> Contains rare earth elements inside, An optical fiber having a region in which at least a portion of the rare earth elements are separated into single atoms at a distance exceeding the diffraction limit. <2> The rare earth element includes at least one of Yb and Er; <1> The optical fiber according to claim 1. <3> a resonator that amplifies at least a portion of the light emitted from the region; <1> or <2> The optical fiber according to claim 1. <4> the resonator has a fiber Bragg grating; <3> The optical fiber according to claim 1. <5> <1> ~ <4> irradiating excitation light onto at least a part of the region of the optical fiber described in any one of the above items to cause the rare earth element to emit light. <6> Excitation light is irradiated through the longitudinal end of the optical fiber. <5> The light-emitting method according to claim 1. <7> Excitation light is irradiated through the outer wall of the optical fiber. <5> The light-emitting method according to claim 1. <8> <1> ~ <4> an optical fiber according to any one of the above items; a light source that irradiates excitation light onto at least a portion of the region of the optical fiber; A light emitting device comprising: <9> an external resonator; <8> The light emitting device according to claim 1. <10> a step of longitudinally stretching an optical fiber preform doped with a rare earth element to form a region in the stretched portion where at least a part of the rare earth element is separated into a single atom at a distance exceeding the diffraction limit; <1> ~ <4> 10. A method for producing an optical fiber according to any one of the preceding claims. [Effects of the Invention]

[0007] According to one embodiment of the present disclosure, an optical fiber capable of generating single photons is provided. According to another embodiment of the present disclosure, there is provided a method for manufacturing the optical fiber described above. According to another embodiment of the present disclosure, there is provided a light emitting method using the optical fiber. According to another embodiment of the present disclosure, there is provided a light emitting device using the optical fiber. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram showing an example of an optical fiber. [Figure 2] FIG. 2 is a schematic diagram showing an example of an optical fiber. [Figure 3] FIG. 3 is a schematic diagram showing an example of an optical fiber. [Figure 4] FIG. 4 is a schematic diagram showing an example of a light emission method using an optical fiber. [Figure 5] FIG. 5 is a schematic diagram showing an example of a light emission method using an optical fiber. [Figure 6] FIG. 6 is a schematic diagram showing an example of a light emitting device. [Figure 7] FIG. 7 is a schematic diagram showing an example of a light emitting device. DETAILED DESCRIPTION OF THE INVENTION

[0009] The optical fiber, its manufacturing method, light emitting method, and light emitting device according to the present disclosure will be described in detail below.

[0010] In the present disclosure, a numerical range indicated using "to" means a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in the examples. In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment. In the present disclosure, when there are multiple substances corresponding to each component, the amount of each component means the total amount of the multiple substances unless otherwise specified. In the present disclosure, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved.

[0011] The drawings referred to in the following description are illustrative and schematic, and the present disclosure is not limited to these drawings. The same reference numerals indicate the same components. Also, reference numerals in the drawings may be omitted.

[0012] <Optical fiber> The optical fiber according to the present disclosure contains a rare earth element therein, and has a region in which at least a portion of the rare earth element is present as a single atom separated at a distance exceeding the diffraction limit.

[0013] Rare earth elements have the property of emitting light when excited by excitation light, i.e., generating photons, and optical fibers doped with rare earth elements, such as those described in Patent Document 1, are being studied. However, it is difficult to generate single photons simply by doping an optical fiber with a rare earth element.

[0014] In contrast, the optical fiber according to the present disclosure has a region in which at least a portion of the rare earth elements contained therein are separated into single atoms at a distance exceeding the diffraction limit. Therefore, when excitation light is irradiated onto this region, the rare earth elements separated into single atoms at a distance exceeding the diffraction limit can be excited. The excited atoms of the rare earth elements then function as a single photon source, capable of generating single photons.

[0015] In the optical fiber according to the present disclosure, a region where at least a portion of the rare earth elements are present separated into single atoms at a distance exceeding the diffraction limit may be referred to as a "specific region."

[0016] For example, the optical fiber 100 shown in FIG. 1 contains rare earth elements and has a specific region 10 in which at least a portion of the rare earth elements are separated into single atoms at a distance exceeding the diffraction limit.

[0017] The diffraction limit of light is approximately the wavelength of the light emitted by the rare-earth element. The fact that at least a portion of the rare-earth element exists in a specific region as a single atom at a distance exceeding the diffraction limit can be confirmed by observing the generation of single photons when excitation light is irradiated onto the specific region.

[0018] The generation of single photons can be observed as follows. Excitation light is irradiated onto a specific region of an optical fiber, causing the rare earth element to emit light. The emission of the rare earth element can be confirmed by visually observing the specific region using an optical microscope (e.g., 30x to 40x magnification). Obtaining photon statistics for the emission of the rare earth element through photon correlation measurements can confirm that the photons emitted from the rare earth element atoms are in a single-photon state. Specifically, the emission of the rare earth element is split into two directions using a beam splitter, and the two separated light beams are observed using single-photon detectors, respectively, to perform simultaneous observation and measurement using two single-photon detectors. If the detection probability of photons observed simultaneously by both detectors is nearly zero, the photon emitted from the rare earth element atom is measured as being in a single-photon state. In this way, the generation of single photons can be observed.

[0019] Silica glass is preferably used as the material for the optical fiber, and the optical fiber may have a core / clad structure in which a central core is covered with a clad.

[0020] The diameter of the specific region is not particularly limited, and may be, for example, 0.3 μm to 2.0 μm. The diameter of the specific region can be measured by a method using an electron microscope or an optical microscope (for example, 30 to 40 times magnification). Alternatively, the diameter of the specific region can be measured by a method of calculating the diameter by simultaneously observing a test target or the like with a known scale.

[0021] An optical fiber may include regions other than the specific region. For example, as shown in FIG. 1 , an optical fiber 100 may include regions other than the specific region 10, i.e., a non-specific region 50 and a tapered section 30, and the specific region 10 and the non-specific region 50 may have a continuous structure via the tapered section 30. In one embodiment, in a portion of the tapered section 30, at least a portion of the rare earth element may be separated into single atoms at a distance exceeding the diffraction limit, and this portion may be part of the specific region 10. Such an optical fiber 100 can be manufactured, for example, by longitudinally stretching an optical fiber preform doped with a rare earth element, as described below. In an optical fiber manufactured in this manner, the specific region is a thinned optical fiber preform, while the non-specific region has the same structure as the optical fiber preform, for example, a core / clad structure in which a central core portion is covered with a clad portion. For example, the diameter of the non-specific region may be 5 μm to 50 μm, and the diameter of the core portion may be 0.3 μm to 2.0 μm. The diameters of the non-specific region and the core portion can be measured by a method using an electron microscope or an optical microscope (for example, 30 to 40 times magnification). Alternatively, the diameters of the non-specific region and the core portion can be measured by a method of calculating the diameter by simultaneously observing a test target or the like with a known scale.

[0022] [Rare earth elements] Rare earth elements are useful in the field of quantum information technology. For example, rare earth elements are optically active even at room temperature, and optical excitation and optical measurement of the excitation light are easy.

[0023] Furthermore, rare earth elements form stable intrinsic energy levels in solids (in optical fibers) and have a small intrinsic energy uniformity width that is less susceptible to the external environment, making them easy to photoexcite. In contrast, quantum dots cannot form stable intrinsic energy levels in solids.

[0024] Furthermore, single photons generated from atoms of rare earth elements can be easily guided into nanometer-order waveguides (eg, specific regions in some embodiments) and resonators.

[0025] The type of rare earth element is not particularly limited, but for example, Yb has an isotope with a nuclear spin of 1 / 2, making it preferable from the viewpoint of application to quantum computers, quantum memories, etc. Furthermore, Er is preferable from the viewpoint of application to optical communications, since the wavelength of the light it emits is very close to the wavelength used in optical communications.

[0026] The rare earth elements may be used singly or in combination of two or more. From the above viewpoint, it is preferable that the optical fiber contains at least one of Yb and Er.

[0027] Doping amount of rare earth elements into optical fiber (m -3 ) is not particularly limited as long as at least a part of the rare earth element is present separated into single atoms at a distance exceeding the diffraction limit.

[0028] [Resonator] The optical fiber may include a resonator that amplifies at least a portion of the emitted light from a particular region.

[0029] The configuration of the resonator is not particularly limited, but for example, a resonator consisting of two optical reflectors provided in an optical fiber and a section sandwiched between them can be mentioned.

[0030] The position of the resonator in the optical fiber is not particularly limited, and each of the two optical reflectors may be disposed in any of a specific region, a tapered portion, or a non-specific region.

[0031] For example, the resonator may be configured by two optical reflectors arranged to sandwich at least a part of the specific region 10. In this embodiment, for example, as shown in Fig. 2, optical reflectors 72 and 74 may be provided in part of the specific region 10 of the optical fiber 102, thereby forming a resonator 70 consisting of the two optical reflectors and the section sandwiched between them. This allows the resonator to amplify the generation efficiency of single photons generated in the specific region. In this embodiment, the length of the optical reflector in the longitudinal direction may be, for example, 10 μm to 100 μm, and the length of the section sandwiched by the optical reflectors may be, for example, 10 μm to 100 μm.

[0032] Also, for example, the resonator may be configured by arranging two optical reflectors so as not to sandwich the specific region 10. For example, as shown in Fig. 3, optical reflectors 77 and 79 may be provided in part of the non-specific region 52 of the optical fiber 104, thereby forming a resonator 75 consisting of two optical reflectors and the section sandwiched between them. This allows the resonator to amplify the generation efficiency of single photons generated in the specific region. In this embodiment, the length of the optical reflector in the longitudinal direction may be, for example, 10 μm to 100 μm, and the length of the section sandwiched by the optical reflectors may be, for example, 10 μm to 100 μm.

[0033] The structure of the resonator is not particularly limited and may be a known structure. For example, the resonator may have a fiber Bragg grating (FBG) or may have nanocraters. The FBG and the nanocraters function as optical reflectors. Examples of FBG include a structure in which a refractive index distribution is provided inside an optical fiber, and a structure in which a periodic structure is provided inside an optical fiber. Examples of nanocraters include a structure in which a plurality of recesses are provided on the outer wall of an optical fiber, and a structure in which a one-dimensional photonic crystal is provided on the outer wall of an optical fiber.

[0034] <Lighting method> In the light emission method according to the present disclosure, excitation light is applied to at least a portion of a specific region of the optical fiber according to the present disclosure to cause the rare earth element to emit light, whereby the excited atoms of the rare earth element function as a single-photon source and can generate single photons.

[0035] For example, there is a light emission method shown in FIGS. 4 and 5 using the optical fiber 100 shown in FIG.

[0036] In the light emission method shown in Fig. 4, excitation light (arrow A1) is irradiated from a light source 300 onto a specific region 10 via a longitudinal end 90 of an optical fiber 100. This causes the excited rare earth element to emit light, and a single photon is generated from the rare earth element atom. The emitted light from the rare earth element can be guided through the specific region 10 of the optical fiber 100 toward a longitudinal end 92 of the optical fiber 100. For example, the generation of a single photon can be observed by analyzing the light (arrow A2) guided to the longitudinal end 92 or the emitted light from the specific region 10 using the method described above.

[0037] In the light emission method shown in Fig. 5, excitation light (arrow A1) is irradiated from light source 300 onto specific region 10 through the outer wall of optical fiber 100. This causes the excited rare earth element to emit light, and a single photon is generated from the rare earth element atom. The emitted light from the rare earth element can be guided through specific region 10 of optical fiber 100 toward at least one of longitudinal end 90 and longitudinal end 92 of optical fiber 100. For example, the generation of a single photon can be observed by analyzing the light (arrow A2) guided to longitudinal end 90 or longitudinal end 92 using the method described above.

[0038] The excitation light may be, for example, a laser beam having an appropriate excitation wavelength depending on the type of rare earth element doped into the optical fiber, for example, 915 nm and 975 nm for Yb, and 980 nm and 1480 nm for Er.

[0039] <Light-emitting device> The light emitting device according to the present disclosure comprises: an optical fiber according to the present disclosure; a light source that irradiates excitation light onto at least a portion of a specific region of the optical fiber; This allows the excited rare earth element atom to function as a single photon source and generate a single photon.

[0040] The light source is not particularly limited as long as it can irradiate the above-mentioned excitation light. Details of the optical fiber and the excitation light are as described above.

[0041] The manner in which excitation light is irradiated onto at least a part of the specific region of the optical fiber is not particularly limited, and the light emission method described above may be used.

[0042] For example, a light-emitting device 700 shown in FIG. 6 includes an optical fiber 100 and a light source 300. Excitation light (arrow A1) emitted from the light source 300 is irradiated onto a specific region 10 via a longitudinal end 90 of the optical fiber 100. This causes the excited rare earth element to emit light, and a single photon is generated from the atom of the rare earth element. The emitted light from the rare earth element is guided through the specific region 10 of the optical fiber 100 toward a longitudinal end 92 of the optical fiber 100, and the guided light (arrow A2) can be extracted from the longitudinal end 92.

[0043] The light emitting device may include other resonators such as an external resonator in addition to the above-described resonators that may be included in the optical fiber. The configuration of the other resonators such as the external resonator is not particularly limited, and any known configuration may be used. An example of the external resonator is one that includes an optical reflector (for example, a mirror).

[0044] For example, the light-emitting device 702 shown in FIG. 7 includes an optical fiber 100, a light source 300, and an external resonator 500. The external resonator 500 includes an optical reflector 520 and an optical reflector 540. Excitation light (arrow A1) emitted from the light source 300 is irradiated onto the specific region 10 via the longitudinal end 90 of the optical fiber 100. This causes the excited rare earth element to emit light, and a single photon is generated from the rare earth element atom. The emitted light from the rare earth element is guided through the specific region 10 of the optical fiber 100 toward the longitudinal end 92 of the optical fiber 100. The guided light (arrow A2) is introduced into the external resonator 500 and amplified. The amplified light (arrow A3) can be extracted from the external resonator 500.

[0045] <Optical fiber manufacturing method> The method for producing an optical fiber according to the present disclosure is not particularly limited, but the following method for producing an optical fiber according to the present disclosure can be suitably used. The method for manufacturing an optical fiber according to the present disclosure includes a step of longitudinally stretching an optical fiber preform doped with a rare earth element to form a region (i.e., a specific region) in the stretched portion where at least a portion of the rare earth element is separated into single atoms at a distance exceeding the diffraction limit (hereinafter, this may be referred to as the "stretching step").

[0046] [Stretching process] An optical fiber preform doped with a rare earth element (hereinafter, sometimes simply referred to as an "optical fiber preform") can be stretched in the longitudinal direction, for example, as follows.

[0047] First, a part of the optical fiber preform is heated to a temperature equal to or higher than the melting point of the optical fiber preform. The heating method is not particularly limited, and for example, a ceramic heater, a gas burner, or the like may be used.

[0048] Next, while holding two points of the optical fiber preform via the heating section of the optical fiber preform, the heating section is stretched in the longitudinal direction. This increases the distance between the rare earth elements in the stretched section, allowing a specific region to be formed in the stretched section, and for example, optical fiber 100 shown in FIG. 1 can be produced. In one embodiment, at least a portion of the rare earth elements in a portion of tapered section 30 may be separated into single atoms at a distance exceeding the diffraction limit, and this portion may be part of specific region 10.

[0049] When stretching an optical fiber preform, the degree of stretching depends on the amount of rare earth elements doped into the optical fiber preform (m -3 That is, the doping amount (m -3 ) is the number of rare earth elements per unit volume of the optical fiber preform, so it is possible to estimate how much the distance between the rare earth elements will be if the optical fiber preform is stretched. Based on this estimation, the degree of stretching can be determined so that the distance exceeds the diffraction limit.

[0050] The optical fiber base material is not particularly limited, and any known material may be used. Silica glass is preferably used as the material for the optical fiber preform. The optical fiber may have a core / clad structure in which a central core is covered with a clad. For example, the diameter of the optical fiber preform may be 5 μm to 50 μm, and the diameter of the core may be 5 μm to 50 μm.

[0051] The method for producing the optical fiber preform is not particularly limited, and it may be produced by a known method, such as the MCVD (Modified Chemical Vapor Deposition) method or the VAD (Vapor Phase Axial Deposition) method. Alternatively, an optical fiber preform produced by the above method without doping with a rare earth element may be doped by sublimating the rare earth element by a vapor phase method.

[0052] Details of the rare earth elements are as described above. The amount of rare earth element doped into the optical fiber preform is not particularly limited as long as the specific region can be formed in the drawn portion when the optical fiber preform is drawn in the longitudinal direction.

[0053] [Other processes] The method for producing an optical fiber according to the present disclosure may include other steps in addition to the above step of drawing the optical fiber.

[0054] For example, the method for manufacturing an optical fiber according to the present disclosure may include a step of forming a resonator in the optical fiber that amplifies at least a portion of the light emitted from the specific region (hereinafter, this may be referred to as a "resonator forming step"). Details of the resonator are as described above. The resonator formation process is not particularly limited, and a known process may be used. [Example]

[0055] The present disclosure will be described in more detail below with reference to examples, although the present disclosure is not limited to these examples.

[0056] <Stretching process> A portion (a region of 2 mm to 3 mm in the longitudinal direction) of an Yb-doped optical fiber preform (YB1200-4 / 125 manufactured by nLight, Inc.) was heated using a gas burner to a temperature above the melting point of the optical fiber preform.

[0057] Next, while holding the optical fiber preform at two points via the heating section of the optical fiber preform, the heating section was stretched 2.5 cm in the longitudinal direction, thereby forming a specific region 10 in the stretched section, where at least a portion of the rare earth elements exist as single atoms separated at a distance exceeding the diffraction limit, and thus producing the optical fiber 100 shown in FIG.

[0058] <Lighting> Using the obtained optical fiber 100, the rare earth element in the specific region was made to emit light in the following manner. As a light source of excitation light, a laser light source was used in which a laser diode manufactured by DigiKey was attached to a laser diode mount with a temperature control function manufactured by Thorlabs. As shown in Fig. 4, excitation light (excitation wavelength: 980 nm, arrow A1) was irradiated from light source 300 onto specific region 10 via longitudinal end 90 of optical fiber 100. As a result, luminescence of the excited rare earth elements was confirmed at five points separated by distances of 24 nm to 77 µm in specific region 10. The luminescence of the rare earth elements was confirmed by visually observing specific region 10 using an optical microscope (30x magnification).

[0059] The emission of the rare earth element in the specific region 10 was analyzed in the following manner to observe the generation of a single photon. By obtaining photon statistics from photon correlation measurements of rare-earth element luminescence, we confirmed that the photons emitted from rare-earth element atoms are in a single-photon state. Specifically, the rare-earth element luminescence was split into two directions using a beam splitter, and the two separated light beams were observed using single-photon detectors, respectively, to perform simultaneous observation measurements using two single-photon detectors. When the detection probability of photons observed simultaneously by both detectors was nearly zero, we measured the photons emitted from the rare-earth element atoms as being in a single-photon state. In this way, we observed the generation of single photons. [Explanation of symbols]

[0060] 10 Specific areas 30 Tapered area 50, 52 Non-specific area 70, 75 resonator 72, 74, 77, 79 light reflector 90, 92 Longitudinal ends 100, 102, 104 Optical fiber 300 light source 500 external resonator 520, 540 light reflector 700, 702 Light-emitting device A1 excitation light

Claims

1. A method for manufacturing an optical fiber containing a rare earth element therein, comprising the step of longitudinally stretching an optical fiber preform doped with a rare earth element, thereby forming a region in the stretched portion in which at least a portion of the rare earth element is separated into single atoms at a distance exceeding the wavelength of the light emitted by the rare earth element.

2. A method for manufacturing an optical fiber as described in claim 1, wherein the rare earth element includes at least one of Yb and Er.

3. A method for manufacturing an optical fiber as described in claim 1, wherein the optical fiber is provided with a resonator that amplifies at least a portion of the light emitted from the region.

4. A method for manufacturing an optical fiber as described in claim 3, wherein the resonator has a fiber Bragg grating or a nanocrater.

Images