WO2022102548A1 - 光フィルタデバイス - Google Patents
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- WO2022102548A1 WO2022102548A1 PCT/JP2021/040855 JP2021040855W WO2022102548A1 WO 2022102548 A1 WO2022102548 A1 WO 2022102548A1 JP 2021040855 W JP2021040855 W JP 2021040855W WO 2022102548 A1 WO2022102548 A1 WO 2022102548A1
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- 230000003287 optical effect Effects 0.000 title claims abstract description 176
- 239000013307 optical fiber Substances 0.000 claims abstract description 100
- 238000000926 separation method Methods 0.000 claims abstract description 46
- 238000005498 polishing Methods 0.000 claims description 58
- 230000002093 peripheral effect Effects 0.000 claims description 44
- 238000005253 cladding Methods 0.000 claims description 3
- 238000000411 transmission spectrum Methods 0.000 description 50
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- 238000010586 diagram Methods 0.000 description 12
- 230000006399 behavior Effects 0.000 description 11
- 238000004458 analytical method Methods 0.000 description 8
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- 238000005516 engineering process Methods 0.000 description 6
- 230000001902 propagating effect Effects 0.000 description 5
- 238000004891 communication Methods 0.000 description 3
- 239000010408 film Substances 0.000 description 2
- 239000011521 glass Substances 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 239000010453 quartz Substances 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- 238000002834 transmittance Methods 0.000 description 2
- 230000001154 acute effect Effects 0.000 description 1
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- 230000001427 coherent effect Effects 0.000 description 1
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- 230000000149 penetrating effect Effects 0.000 description 1
- 238000012827 research and development Methods 0.000 description 1
- 239000010409 thin film Substances 0.000 description 1
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Classifications
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
- G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
- G02B6/29346—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by wave or beam interference
- G02B6/29361—Interference filters, e.g. multilayer coatings, thin film filters, dichroic splitters or mirrors based on multilayers, WDM filters
- G02B6/2937—In line lens-filtering-lens devices, i.e. elements arranged along a line and mountable in a cylindrical package for compactness, e.g. 3- port device with GRIN lenses sandwiching a single filter operating at normal incidence in a tubular package
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
- G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
- G02B6/29346—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by wave or beam interference
- G02B6/29361—Interference filters, e.g. multilayer coatings, thin film filters, dichroic splitters or mirrors based on multilayers, WDM filters
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
- G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
- G02B6/29379—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device
- G02B6/29395—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means characterised by the function or use of the complete device configurable, e.g. tunable or reconfigurable
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/02042—Multicore optical fibres
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/35—Optical coupling means having switching means
- G02B6/351—Optical coupling means having switching means involving stationary waveguides with moving interposed optical elements
Definitions
- the present invention relates to an optical filter device.
- WDM wavelength division multiplexing
- SDM Space Division Multiplexing
- the speed and capacity can be further increased.
- the optical filter device for example, a multi-core optical fiber, an optical filter composed of a dielectric multilayer film, and an optical fiber having the same number of cores as the multi-core optical fiber (typically, a multi-core optical fiber) are used.
- Devices arranged in this order along a certain axis are known.
- the optical filter has, for example, a function of transmitting light rays in a specific wavelength band.
- the light rays emitted from each core of the multi-core optical fiber are incident on the incident surface of the optical filter, pass through the optical filter, and are incident on the corresponding core of the optical fiber (see, for example, Patent Document 1).
- the optical filter device In such an optical filter device, if the optical filter is arranged so that its incident surface is parallel to the plane orthogonal to the axis, the light rays emitted from the multi-core optical fiber may be reflected at the incident surface. There is. Such reflected light is generally referred to as "reflected return light". The reflected return light may be incident on the communication device on the transmitting side via the multi-core optical fiber, or may be multiple-reflected to deteriorate the optical characteristics of the signal light.
- the reflected return light has been reduced by arranging the optical filter so that the incident surface of the optical filter is inclined with respect to the plane orthogonal to the axis line.
- FIG. 25A is a graph showing the transmission loss characteristics of a certain optical filter device.
- the optical filter device comprises two multi-core optical fibers having seven cores and an optical filter disposed between the two multi-core optical fibers.
- the two multi-core optical fibers have the same configuration. Specifically, one of the seven cores extends as a central core along the central axis of the multi-core optical fiber.
- the remaining six cores are located at the vertices of a regular hexagon centered on the central core and extend along the axial direction as peripheral cores.
- a short wavelength transmitted light filter an optical filter that transmits light in a wavelength band shorter than a specific wavelength
- the optical filter is tilted.
- FIG. 25A the cutoff wavelength of this optical filter is about 1520 nm.
- FIG. 25B is an enlarged graph of a portion of FIG. 25A where the transmission loss begins to increase.
- the solid line 101 located on the shortest wavelength side shows the transmission spectrum of the emitted light from a certain peripheral core
- the solid line located on the longest wavelength side shows the transmission spectrum of the emitted light from a certain peripheral core
- Reference numeral 102 shows a transmission spectrum of light emitted from another peripheral core.
- the number of transmission spectra (solid lines) in the graph does not match the number of cores.
- the transmission spectra shown in FIG. 25B are all shifted to the short wavelength side as compared with the transmission spectra of the emitted light from the same core (not shown) before the optical filter is tilted, but the shift of each transmission spectrum is performed.
- the amount varies from core to core.
- the shift amount of the transmission spectrum 101 is the maximum
- the shift amount of the transmission spectrum 102 is the minimum.
- the maximum value of the variation of the transmission spectrum that is, the transmission spectrum located on the shortest wavelength side and the transmission spectrum located on the longest wavelength side
- the maximum value of the variation in the transmission spectrum (cutoff wavelength) when the transmission loss is 3 dB is about 0.6 nm.
- the transmission loss of the emitted light from each core at an arbitrary wavelength will vary.
- the intensity of light rays propagating through each core of the optical fiber varies, and as a result, the optical signal may not be transmitted properly.
- the variation in transmission loss increases as the maximum value of variation in the transmission spectrum increases. Therefore, in order to properly transmit the light rays transmitted through the optical filter through the optical fiber, it is important to reduce the maximum value of the variation in the transmission spectrum.
- the present invention has been made to address the above-mentioned problems. That is, one of the objects of the present invention is to provide an optical filter device capable of appropriately transmitting an optical signal while reducing reflected return light.
- the optical filter device (10) is A th.I. 1 multi-core optical fiber (20) and It has an optical axis (z-axis) located on the central axis of the first multi-core optical fiber (20), and collimates and collimates the light rays emitted and emitted from each of the first cores (C1 to C7).
- the first lens (30) that collects the light rays from each of the first cores (C1 to C7), and The first surface (40a) on which the light rays emitted from the first lens (30) are incident, and the second surface (40b) on which the light rays transmitted through the first surface (40a) are opposed to each other and are emitted.
- An optical fiber (60) having a columnar shape and extending along the axial direction to which all the light rays from the first cores (C1 to C7) emitted from the second lens (50) are incident.
- This optical filter device (10) From a reference axis (y-axis) that passes through the optical axis (z-axis) and is parallel to the rotation axis (r1), an orthogonal axis (x-axis) that is orthogonal to the optical axis (z-axis) and the reference axis (y-axis).
- the direction toward one side with respect to the reference axis (y-axis) is defined as the first orthogonal direction (-x-axis direction), and the direction toward the other side with respect to the reference axis (y-axis). If the direction is defined as the second orthogonal direction (+ x-axis direction),
- the circumferential direction of the first multi-core optical fiber (20) is the first orthogonal direction from the reference axis (y-axis) when the end face (20a) is viewed along the central axis (z-axis).
- the optical fiber including a core in which "all light rays from each first core are incident" means an optical fiber including a core capable of incident light emitted from each core of the first multi-core optical fiber. That is, the reflected return light is not included in the above "all light rays".
- condensing means that the lens is one point of light rays (strictly speaking, the main light rays of light rays) from a plurality of light sources (for example, a plurality of first cores of a first multi-core optical fiber).
- Convergence (focusing) means that the lens narrows the diameter of the light rays from one light source (for example, each first core of the first multi-core optical fiber) and collects them at one point. do.
- an optical signal can be appropriately transmitted while reducing reflected return light.
- FIG. 9A is a graph defining the relationship between the incident angle ⁇ of the light beam emitted from each core of the multi-core optical fiber of FIG. 9A and the wavelength shift amount ⁇ . It is a figure which shows the end face when the multi-core optical fiber of FIG. 8A is set to the parallel type.
- FIG. 3 is a graph defining the relationship between the incident angle ⁇ of the light beam emitted from each core of the multi-core optical fiber of FIG. 10A and the wavelength shift amount ⁇ . It is a figure which shows the end face when the multi-core optical fiber of FIG. 8B is set diagonally.
- 11A is a graph defining the relationship between the incident angle ⁇ of the light beam emitted from each core of the multi-core optical fiber of FIG.
- FIG. 11A is a figure which shows the end face when the multi-core optical fiber of FIG. 8B is set to the parallel type.
- FIG. 12 is a graph defining the relationship between the incident angle ⁇ of light rays emitted from each core of the multi-core optical fiber of FIG. 12A and the wavelength shift amount ⁇ .
- FIG. 8C is set to the orthogonal type.
- FIG. 13A shows the end face when the multi-core optical fiber of FIG.
- FIG. 14 is a graph defining the relationship between the incident angle ⁇ of the light beam emitted from each core of the multi-core optical fiber of FIG. 14A and the wavelength shift amount ⁇ . It is a top view of the optical filter device which concerns on 2nd Embodiment of this invention. It is a figure used to explain the diagonal polishing direction of a multi-core optical fiber which functions as an emission member. It is a figure which shows the number of cores, and the core arrangement of the multi-core optical fiber whose end face is obliquely polished. It is a figure which shows the core number and core arrangement of another multi-core optical fiber whose end face is obliquely polished.
- FIG. 1 is a plan view showing an example of an optical filter device 10 according to the first embodiment of the present invention.
- the optical filter device 10 includes a multi-core optical fiber 20 as a first multi-core optical fiber, a first lens 30, an optical filter 40, a second lens 50, and a multi-core optical fiber as an optical fiber. 60 and. These members are arranged in the above order along the axis A1.
- An orthogonal coordinate system is set in the optical filter device 10. The z-axis extends on the axis A1 so that the direction from the first lens 30 toward the optical filter 40 is the positive direction.
- the y-axis is orthogonal to the z-axis (that is, the axis A1) and extends so that the front direction of the paper is the positive direction.
- the x-axis is orthogonal to the z-axis and the y-axis.
- the multi-core optical fiber is also referred to as “MCF”.
- MCF multi-core optical fiber
- the MCF 20 is columnar, and the central axis at least at the end in the + z axis direction coincides with the axis A1.
- the end face 20a of the MCF 20 is parallel to the plane (xy plane) orthogonal to the axis A1.
- FIG. 2 is a diagram showing an end face 20a of the MCF 20.
- the MCF 20 includes seven cores C1 to C7 as first cores and a common clad 21 surrounding these cores C1 to C7.
- the core C4 extends along the central axis of the MCF 20 (hereinafter, also referred to as “central core C4”).
- the cores C1 to C3 and C5 to C7 are located at the vertices of a regular hexagon centered on the central core C4 and extend along the axial direction (hereinafter, "peripheral cores C1 to C3 and C5, respectively". Also referred to as "C7").
- the peripheral cores C1 to C3 and C5 to C7 extend along the axis excluding the central axis of the MCF 20.
- the distance (core pitch) between adjacent cores is 38 ⁇ m.
- the cores C1 to C7 and the clad 21 are formed of glass containing quartz as a main component.
- the refractive index of the cores C1 to C7 is larger than the refractive index of the clad 21.
- the MCF 20 is a single mode optical fiber.
- the MCF 20 is an example of a multi-core optical fiber used in the optical filter device 10 (described later).
- the materials of the cores C1 to C7 and the clad 21 are not limited to glass containing quartz as a main component, and may be formed of other materials. Further, in the present specification, the cylinder includes a cylinder having a curved axis.
- the end portion of the MCF 20 in the + z-axis direction is inserted and held by a cylindrical ferrule 22.
- the end face 22a of the ferrule 22 is located on the same plane as the end face 20a of the MCF 20. This is because the end face 20a of the MCF 20 is collectively polished together with the end face 22a in a state of being inserted into the ferrule 22.
- the MCF 20 in the ferrule 22 is shown by a broken line, but the cores C1 to C7 are not shown.
- FIG. 1 illustrates only the main rays of the light rays emitted from the cores C1, C4 and C7 (see FIG. 2) among the light rays emitted from the cores C1 to C7.
- the rays B1, B4 and B7 correspond to the main rays of the emitted light from the cores C1, C4 and C7, respectively.
- the main rays of the emitted light from the cores C1 to C7 are parallel to each other (see the rays B1, B4 and B7 in FIG. 1), but each emitted light is a divergent light diverging as it progresses.
- the first lens 30 is an aspherical lens having a focal length of 2.5 mm.
- the central axis (optical axis) of the first lens 30 is located on the axis A1.
- the first lens 30 collimates (parallelizes) the light rays emitted from the cores C1 to C7 and emitted. In other words, the first lens 30 collimates, for example, a light ray emitted from the core C1 and emitted (only the main light ray B1 is shown in FIG. 1). That is, the first lens 30 is a so-called collimating lens.
- the first lens 30 focuses the light rays from the cores C1 to C7 collimated in this way at the focal point (only the light rays B1, B4 and B7 are shown in FIG. 1).
- the light rays collimated in this way are also referred to as "colimated light (parallel light)".
- the optical filter 40 is a short wavelength transmitted light filter. Since the short wavelength transmitted light filter is a well-known optical filter composed of a dielectric multilayer film, detailed description thereof will be omitted.
- the optical filter 40 includes an incident surface 40a as a first surface and an exit surface 40b as a second surface facing parallel to the incident surface 40a. The light beam emitted from the first lens 30 is incident on the incident surface 40a.
- the optical filter 40 is arranged so that the focal point of the first lens 30 is located on the incident surface 40a. Therefore, the light rays from the cores C1 to C7 are focused on the incident surface 40a via the first lens 30, pass through the optical filter 40, and are emitted from the exit surface 40b.
- the lens arranged between the MCF 20 and the optical filter 40 is not limited to the first lens 30, and may be a lens capable of substantially collimating the emitted light from the cores C1 to C7 of the MCF 20.
- it may be a spherical lens or a GRIN lens.
- the optical filter 40 has a rotation axis r1 extending in the y-axis direction at a position where the axis A1 intersects the incident surface 40a (that is, the focal point of the first lens 30).
- the optical filter 40 is rotated by a rotation angle ⁇ around the rotation axis r1 from a position where the incident surface 40a is parallel to the surface orthogonal to the axis A1.
- the magnitude of the rotation angle ⁇ is 0 ° ⁇ ⁇ 90 °. This reduces the reflected return light.
- the optical filter 40 is viewed from the + y-axis direction (that is, when viewed from the direction shown in FIG.
- the optical filter 40 is rotated counterclockwise by the rotation angle ⁇ when viewed from the + y-axis direction. Therefore, the position of the light beam emitted from the light emitting surface 40b is located in the + x-axis direction with respect to the position of the light ray incident on the incident surface 40a.
- the light rays emitted from the cores C1 to C7 emitted from the optical filter 40 are collimated light (parallel light), but the main light rays travel in directions away from each other (FIG. 1). Rays B1, B4 and B7).
- the main ray B4 emitted from the optical filter 40 is parallel to the axis A1.
- the second lens 50 is an aspherical lens having a focal length of 2.5 mm.
- the second lens 50 is shifted in the + x-axis direction by a predetermined distance so that the main ray B4 emitted from the optical filter 40 travels along the central axis (optical axis) of the second lens 50.
- the second lens 50 is arranged at a position separated by a focal length in the + z-axis direction from the intersection of the main rays of the light emitted from the optical filter 40 (not shown in FIG. 1).
- the second lens 50 refracts the light rays emitted from the cores C1 to C7 emitted from the optical filter 40 so that these main light rays are parallel to each other (see light rays B1, B4 and B7 in FIG. 1). Further, the second lens 50 converges the light rays from the cores C1 to C7, respectively (only the main light rays are shown in FIG. 1).
- MCF60 has the same configuration as MCF20. That is, the MCF 60 is columnar and includes seven cores (not shown) extending along the axial direction and a common cladding (not shown) surrounding these cores.
- the MCF 60 is a single mode optical fiber.
- the central axis at least at the end of the MCF 60 in the ⁇ z axis direction coincides with the central axis of the second lens 50.
- the end of the MCF 60 in the ⁇ z axis direction is inserted and held by a cylindrical ferrule 62.
- the end face 60a of the MCF 60 is polished together with the end face 62a in a state of being inserted into the ferrule 62.
- the end surface 60a of the MCF 60 and the end surface 62a of the ferrule 62 are located on the same plane (xy plane).
- the MCF 60 in the ferrule 62 is shown by a broken line.
- the end face 60a of the MCF 60 is located at a position where the light rays from the cores C1 to C7 converge.
- the light rays emitted from the cores C1 to C7 emitted from the second lens 50 are incident on the corresponding cores of the MCF 60 with low loss. That is, the MCF 20 and the MCF 60 are optically coupled by the first lens 30 and the second lens 50 via the optical filter 40.
- the lens arranged between the optical filter 40 and the MCF 60 is not limited to the second lens 50, and may be, for example, a spherical lens or a GRIN lens.
- the MCF 60 functions as a light receiving member that receives the light emitted from the second lens 50, but the light receiving member is not limited to the multi-core optical fiber.
- the light receiving member is a group of single-core optical fibers having the same number of single-mode single-core optical fibers in which each core is surrounded by individual claddings, as many as the number of cores of MCF20 (7 in the example of FIG. 1). You may. The above is a description of the configuration of the optical filter device 10.
- FIG. 3 is a diagram showing incident angles ⁇ ( ⁇ 1, ⁇ 2, ⁇ 3) of the main rays B4, B1 and B7 incident on the optical filter 40 (angle ⁇ will be described later).
- the main light beam that passes through the optical filter 40 and is emitted from the emission surface 40b is not shown.
- the optical filter 40 is rotated counterclockwise by the rotation angle ⁇ ( ⁇ > 0) around the rotation axis r1, the normal N of the optical filter 40 is counterclockwise from the axis A1. Rotate by the angle ⁇ .
- the optical filter 40 is not rotated (that is, the incident surface 40a is parallel to the xy plane)
- the incident angle ⁇ 2 and the incident angle ⁇ 3 are due to the symmetry of the core C1 and the core C7 with respect to the core C4.
- the inventors of the present application have investigated the relationship between the incident angle ⁇ of the light ray incident on the optical filter 40 and the wavelength shift amount ⁇ (described later) of the transmission spectrum of the light ray, thereby examining the maximum value of the variation in the transmission spectrum.
- the circumferential orientation of the MCF 20 (and the MCF 120 and 220 described later) that can reduce the problem is examined. Hereinafter, it will be described in detail.
- FIG. 4 is a plan view of the optical filter 40 prepared for investigating the relationship between the incident angle ⁇ and the wavelength shift amount ⁇ .
- a ray R is incident on the incident surface 40a of the optical filter 40 along the axis A2.
- the light ray R passes through the optical filter 40 and is emitted from the emission surface 40b.
- the optical filter 40 can rotate about the rotation axis r1 by the rotation angle ⁇ with respect to the plane orthogonal to the axis A2. As a result, the incident angle ⁇ of the light ray R becomes equal to the rotation angle ⁇ .
- the inventors of the present application have changed the rotation angle ⁇ in the range of ⁇ 2.5 ° ⁇ ⁇ ⁇ 2.5 ° in 0.5 ° increments (in other words, the incident angle ⁇ of the light ray R is ⁇ 2.
- the transmission loss of the light ray R emitted from the optical filter 40 was measured.
- FIG. 5 is a graph showing the transmission loss characteristics based on the above measurement.
- the transmission spectrum of the ray R of ⁇ 2.5 ° is shown.
- the transmission spectra L2 and L3 are substantially the same and are shown superimposed.
- the transmission spectra L2 to L11 are all shifted from the transmission spectrum L1 to the short wavelength side, and the shift amount increases as the magnitude of the incident angle ⁇ increases.
- the shift amount of the wavelength at which the transmission spectra L2 to L11 are shifted from the transmission spectrum L1 when the transmittance is 3 dB is defined as “wavelength shift amount ⁇ ”. That is, the wavelength shift amount ⁇ is “the amount of wavelength shift of the transmission spectrum of the light ray having the incident angle ⁇ from the transmission spectrum of the light ray having the incident angle 0 ° when the transmission loss is 3 dB”.
- FIG. 6 is a graph defining the relationship between the incident angle ⁇ and the wavelength shift amount ⁇ .
- the 11 actually measured values in the graph are the values plotted based on the graph of FIG.
- the result of calculating the relationship between the incident angle ⁇ and the wavelength shift amount ⁇ based on the following analytical formula (1) is also shown.
- the analytical formula (1) was derived with reference to the following documents. Mitsunobu Kohiyama, "Optical Thin Film Filter Design", 1st Edition, Optronics Co., Ltd., 2006, p.301-346
- n 2 is.
- the analysis formula (1) is in good agreement with the behavior of the measured value. Therefore, in the following study, the wavelength shift amount ⁇ will be calculated based on the analysis formula (1). Further, according to the analysis formula (1), the wavelength shift amount ⁇ increases as the magnitude of the incident angle ⁇ increases.
- the wavelength shift amount ⁇ is defined as the wavelength shift amount when the transmission loss is 3 dB, but the present invention is not limited to this.
- the wavelength shift amount ⁇ may be defined as the wavelength shift amount when the transmission loss is 2 dB, 4 dB, or 5 dB. This is because, as shown in FIG. 5, when the transmission loss is at least in the range of 2 dB to 5 dB, the transmission spectra 1 to 11 are substantially parallel to each other, so that the shift amount of the wavelength of each transmission spectrum 2 to 11 has a transmission loss. This is because it is substantially the same as the wavelength shift amount ⁇ at 3 dB (that is, it is in good agreement with the analysis formula (1)).
- the incident angle ⁇ includes “the rotation angle ⁇ of the optical filter 40”, “the ray angle ⁇ at which the light ray emitted from the first lens 30 forms an acute angle with the axis A1 (see FIG. 3)”, and “each peripheral core. It can be derived from the angles ⁇ of C1 to C3 and C5 to C7 (described later). This will be described with reference to FIGS. 7A and 7B.
- FIG. 7A is a diagram showing the relationship between the incident angle ⁇ , the rotation angle ⁇ , the ray angle ⁇ , and the angle ⁇ in the Cartesian coordinate system
- FIG. 7B is a diagram showing the end face 20a of the MCF 20. As shown in FIG.
- the angle ⁇ of any peripheral core is defined as an argument.
- the declination is the angle from the positive part of the x-axis to the line segment connecting the center and origin of any peripheral core.
- the angles ⁇ of the peripheral cores C1, C2, C5, C7, C6 and C3 are 0 °, 60 °, 120 °, 180 °, 240 ° and 300 °, respectively.
- the angle ⁇ is not defined.
- the angle ⁇ is shown as an angle that increases counterclockwise from the “negative” portion of the x-axis when viewed from the + z-axis direction. This is because the light rays from the peripheral cores C1 to C3 and C5 to C7 of the MCF 20 are refracted by the first lens 30.
- the vector B in FIG. 7A is a ray vector representing a ray traveling from any core C1 to C7 through the first lens 30. If the half-line extending in the direction of the angle ⁇ from the origin is defined as the half-line b, the ray vector B is located on the plane passing through the half-line b and the z-axis, and the unit vector ez extending in the + z-axis direction (illustrated). (Omitted) and the ray angle ⁇ . Therefore, the ray vector B can be expressed as the following equation (2).
- the vector N in FIG. 7A is a normal vector from the emission surface 40b of the optical filter 40.
- the normal vector N is located on the zx plane and forms a rotation angle ⁇ with the unit vector ez.
- the normal vector N is defined as the normal vector from the emission surface 40b, which is opposite to the direction of the normal N shown in FIGS. 3 and 4, but this is + z. It should be noted that it is easier to explain by defining the angle with the unit vector ez extending in the axial direction as the rotation angle ⁇ , and it has the same value as the rotation angle ⁇ shown in FIGS. 3 and 4.
- the normal vector N can be expressed as the following equation (3).
- the incident angle ⁇ is an angle formed by the ray vector B (formula (2)) and the normal vector N (formula (3)). Therefore, according to the definition of the inner product, the incident angle ⁇ can be derived as the following equation (4).
- the value of the second term in parentheses in the equation (4) is 0 when calculating the incident angle ⁇ of the light ray from the central core C4. (Because the value of sin ⁇ is 0). That is, in this case, the angle ⁇ is not included in the equation (4). Therefore, there is no particular problem even if the angle ⁇ is not defined for the central core C4, and the incident angle ⁇ of the light beam from the central core C4 can be appropriately calculated using the equation (4).
- the angle of incidence ⁇ of the light rays from the cores C1 to C7 on the optical filter 40 is calculated from the rotation angle ⁇ of the optical filter 40, the light ray angle ⁇ of the light rays, and the angle ⁇ of the core corresponding to the light rays. It turns out that it can be done.
- the wavelength shift amount ⁇ can be calculated using the equation (1).
- the inventors of the present application can apply MCFs having various core numbers and core arrangements to the optical filter device 10 and use the equations (4) and (1) to reduce the maximum value of the variation of the transmission spectrum. I examined the direction of the direction.
- FIGS. 8A to 8C are views showing the end faces of the MCF used in the study.
- the MCF in FIG. 8A is the MCF 20. Since the configuration of the MCF 20 has been described with reference to FIG. 2, detailed description thereof will be omitted.
- the ray angle ⁇ of the light beam from the central core C4 is 0 °.
- the ray angles ⁇ of the rays from the peripheral cores C1 to C3 and C5 to C7 are equal to each other due to the symmetry with respect to the rays from the central core C4, and are 0.87 °, respectively (see FIG. 1).
- the rotation angle ⁇ is set to 2.9 °. This also applies to the examples of FIGS. 8B and 8C.
- the peripheral cores C1 to C3 and C5 to C7 correspond to an example of the "outermost core".
- the MCF in FIG. 8B is an MCF 120 that differs from the MCF 20 only in the number of cores and the core arrangement.
- the MCF 120 includes four cores C1 to C4 as first cores and a common clad 121 surrounding these cores C1 to C4.
- the cores C1 to C4 are located at the vertices of a square centered on the center of the end face 120a. That is, the cores C1 to C4 are "peripheral cores".
- the core pitch is 50 ⁇ m.
- the ray angles ⁇ of the rays from the cores C1 to C4 are equal to each other due to the symmetry with respect to the central axis of the MCF 120, and each is 0.81 °.
- the cores C1 to C4 correspond to an example of the "outermost core”.
- the MCF in FIG. 8C is an MCF 220 that differs only from the MCF 120 in the core arrangement.
- the MCF 220 includes four cores C1 to C4 as first cores and a common clad 221 that surrounds these cores C1 to C4.
- the cores C1 to C4 are linearly arranged so as to be twice symmetrical about the center of the end face 220a. That is, the cores C1 to C4 are "peripheral cores".
- the core pitch is 50 ⁇ m.
- the ray angles ⁇ of the rays from the cores C1 and C4 are equal to each other due to the symmetry with respect to the central axis of the MCF 220, and each is 1.7 °.
- the ray angles ⁇ of the rays from the cores C2 and C3 are equal to each other due to the symmetry with respect to the central axis of the MCF 220, and each is 0.57 °.
- FIG. 9A shows the circumferential direction of the MCF20 (see FIG. 8A) in which a straight line passing through the cores C1, C4 and C7 passes through the y-axis as a reference axis (that is, an axis passing through the axis A1 and parallel to the rotation axis r1). It is a figure which shows the end face 20a when it is set to be orthogonal to. Hereinafter, such an orientation is also referred to as an “orthogonal type”.
- the core most distant from the y-axis in the ⁇ x-axis direction is defined as the “first distant core”
- the core most distant from the y-axis in the + x-axis direction is defined as the “second distant core”.
- the first separated core is the core C7
- the second separated core is the core C1.
- the separation distance is 75 ⁇ m in this example.
- the ⁇ x-axis direction corresponds to an example of a “first orthogonal direction” toward one side of the y-axis along the x-axis as an orthogonal axis
- the + x-axis direction is y along the x-axis. It corresponds to an example of the "second orthogonal direction” toward the other side with respect to the axis.
- the rotation axis r1 since the rotation axis r1 is also an axis passing through the axis A1, the rotation axis r1 may be used as the reference axis.
- FIG. 9B is a graph defining the relationship between the incident angle ⁇ of the light rays from the cores C1 to C7 and the wavelength shift amount ⁇ when the MCF 20 is set to the orthogonal type.
- the incident angle ⁇ can be calculated from the equation (4), and the wavelength shift amount ⁇ can be calculated from the equation (1).
- the broken line 70 in the graph represents the analysis formula (1).
- the incident angle ⁇ of the light beam from the first distance core C7 is the minimum
- the incident angle ⁇ of the light ray from the second distance core C1 is the maximum. Therefore, the wavelength shift amount ⁇ of the light beam from the first distance core C7 is the minimum
- the wavelength shift amount ⁇ of the light ray from the second distance core C1 is the maximum.
- the maximum value of the variation in the transmission spectrum is equal to the difference between the minimum value ⁇ min and the maximum value ⁇ max of the wavelength shift amount ⁇ .
- this difference ( ⁇ max ⁇ min) is referred to as “maximum value Dmax of variation in transmission spectrum” or simply “maximum value Dmax of variation” or “Dmax”.
- the maximum value Dmax of the variation of the transmission spectrum when the MCF 20 was set to the orthogonal type was 0.87 nm.
- the angle of incidence ⁇ of the light beam from the central core C4 is equal to the rotation angle ⁇ (see FIGS. 3 and 4). Therefore, according to the graph of FIG. 9B, the incident angle ⁇ of the light beam from the central core C4 is 2.9 °. The same applies to FIG. 10B.
- FIG. 10A is a diagram showing an end face 20a when the circumferential direction of the MCF 20 is set so that the straight line passing through the cores C1, C4 and C7 is parallel to the y-axis.
- such an orientation is also referred to as a "parallel type".
- the first separated cores are cores C2 and C5
- the second separated cores are cores C3 and C6.
- the separation distance is 65 ⁇ m.
- FIG. 10B is a graph defining the relationship between the incident angle ⁇ of the light rays from the cores C1 to C7 and the wavelength shift amount ⁇ when the MCF 20 is set to the parallel type.
- the incident angle ⁇ of the light rays from the first separated cores C2 and C5 is the minimum
- the incident angles ⁇ of the light rays from the second separated cores C3 and C6 are the maximum. Therefore, the wavelength shift amount ⁇ of the light rays from the first distance cores C2 and C5 is the minimum
- the wavelength shift amount ⁇ of the light rays from the second distance cores C3 and C6 is the maximum.
- the maximum value Dmax of the variation of the transmission spectrum when the MCF 20 was set to the parallel type was 0.75 nm.
- the separation distance (65 ⁇ m) in the parallel type is shorter than the separation distance (75 ⁇ m) in the orthogonal type. Further, since the variation in the incident angle ⁇ in the parallel type is smaller than the variation in the incident angle ⁇ in the orthogonal type, the variation in the wavelength shift amount ⁇ is smaller in the parallel type (that is, Dmax).
- the separation distance becomes shorter, the variation in the incident angle ⁇ becomes smaller, and as a result, the variation in the wavelength shift amount ⁇ ( ⁇ max ⁇ min) can be reduced, that is, the maximum value Dmax of the variation in the transmission spectrum can be obtained. It can be seen that it can be reduced.
- the orthogonal type is the orientation in the circumferential direction of the MCF 20 when the separation distance is maximum (that is, Dmax is maximum), and the parallel type is when the separation distance is minimum (that is, Dmax is minimum). Is the orientation of the MCF 20 in the circumferential direction.
- the Dmax (0.75 nm) in the parallel type is about 13% smaller than the Dmax (0.87 nm) in the orthogonal type. This means that Dmax can be reduced by up to about 13% by setting the circumferential orientation of the MCF 20 to be parallel.
- the peripheral cores C1 to C3 and C5 to C7 are axisymmetric with respect to the y-axis regardless of whether the MCF 20 is set to the orthogonal type or the parallel type.
- the MCF 20 is set to be orthogonal, two of the six peripheral cores (cores C1 to C3 and C5 to C7) are located on the x-axis.
- the MCF 20 is set to the parallel type, none of the peripheral cores is located on the x-axis. From this, the orientation of the MCF 20 in the circumferential direction when the separation distance is minimized (that is, Dmax is minimized) can also be specified as follows.
- the peripheral cores are line-symmetrical with respect to the y-axis.
- FIG. 11A is a diagram showing an end face 120a when the circumferential direction of the MCF 120 (see FIG. 8B) is set so that the straight line passing through the core C2 and the core C4 is orthogonal to the y-axis.
- such an orientation is also referred to as a “diagonal type”.
- the first distance core is core C2 and the second distance core is core C4.
- the separation distance is 71 ⁇ m.
- FIG. 11B is a graph defining the relationship between the incident angle ⁇ of the light rays from the cores C1 to C4 and the wavelength shift amount ⁇ when the MCF 120 is set diagonally.
- the incident angle ⁇ and the wavelength shift amount ⁇ of the light beam from the first distance core C2 are the minimum
- the incident angle ⁇ and the wavelength shift amount ⁇ of the light ray from the second distance core C4 are the maximum.
- the maximum value Dmax of the variation of the transmission spectrum when the MCF 120 was set diagonally was 0.81 nm.
- FIG. 12A is a diagram showing an end face 120a when the circumferential direction of the MCF 120 is set so that the straight line passing through the core C2 and the core C3 (or the core C1 and the core C4) is parallel to the y-axis. ..
- such an orientation is also referred to as a "parallel type".
- the first separated cores are cores C2 and C3
- the second separated cores are cores C1 and C4.
- the separation distance is 50 ⁇ m.
- FIG. 12B is a graph defining the relationship between the incident angle ⁇ of the light rays from the cores C1 to C4 and the wavelength shift amount ⁇ when the MCF 120 is set to the parallel type. According to the graph of FIG. 12B, the incident angle ⁇ and the wavelength shift amount ⁇ of the light rays from the first separated cores C2 and C3 are minimized, and the incident angle ⁇ and the wavelength shift amount ⁇ of the light rays from the second separated cores C1 and C4 are minimized. Is the maximum. The maximum value Dmax of the variation of the transmission spectrum when the MCF 120 was set to the parallel type was 0.57 nm.
- the separation distance (50 ⁇ m) in the parallel type is shorter than the separation distance (71 ⁇ m) in the diagonal type. Further, since the variation of the incident angle ⁇ of the parallel type is smaller than the variation of the incident angle ⁇ of the diagonal type, the variation of the wavelength shift amount ⁇ is smaller in the parallel type (that is, Dmax).
- the diagonal type is the circumferential orientation of the MCF 120 when the separation distance is maximum
- the parallel type is the circumferential orientation of the MCF 120 when the separation distance is minimum.
- the Dmax (0.53 nm) in the parallel type is about 29% smaller than the Dmax (0.81 nm) in the diagonal type. This means that Dmax can be reduced by up to about 29% by setting the circumferential orientation of the MCF 120 to be parallel.
- the peripheral cores C1 to C4 are axisymmetric with respect to the y-axis regardless of whether the MCF 120 is set to be diagonal or parallel.
- the MCF 120 is set diagonally, two of the four peripheral cores (cores C1 to C4) are located on the x-axis, whereas the MCF 120 is located on the x-axis.
- the orientation of the MCF 120 in the circumferential direction when the separation distance is minimized can be specified as follows, as in the case of the MCF 20.
- an MCF MCF120 having "a core arrangement in which the peripheral core is located at the apex of a square centered on the center of the end face of the MCF", two types (diagonal type and parallel) in which the peripheral core is axisymmetric with respect to the y-axis.
- FIG. 13A is a diagram showing an end face 220a when the circumferential direction of the MCF 220 (see FIG. 8C) is set so that the straight line passing through the cores C1 to C4 is orthogonal to the y-axis.
- such an orientation is also referred to as an “orthogonal type”.
- the first distance core is core C1 and the second distance core is core C4.
- the separation distance is 150 ⁇ m.
- FIG. 13B is a graph defining the relationship between the incident angle ⁇ of the light rays from the cores C1 to C4 and the wavelength shift amount ⁇ when the MCF 220 is set to the orthogonal type.
- the incident angle ⁇ and the wavelength shift amount ⁇ of the light beam from the first distance core C1 are the minimum
- the incident angle ⁇ and the wavelength shift amount ⁇ of the light ray from the second distance core C4 are the maximum.
- the maximum value Dmax of the variation of the transmission spectrum when the MCF 220 was set to the orthogonal type was 1.7 nm.
- FIG. 14A is a diagram showing an end face 220a when the circumferential direction of the MCF 220 is set so that the straight line passing through the cores C1 to C4 is parallel to the y-axis.
- such an orientation is also referred to as a "parallel type".
- the cores C1 to C4 are arranged along the y-axis, the cores C1 to C4 are both the first separated core and the second separated core. Therefore, the separation distance is 0 ⁇ m.
- FIG. 14B is a graph defining the relationship between the incident angle ⁇ of the light rays from the cores C1 to C4 and the wavelength shift amount ⁇ when the MCF 220 is set to the parallel type.
- the incident angle ⁇ and the wavelength shift amount ⁇ of the light rays from the cores C2 and C3 are minimized
- the cores C1 and C4 that is, the core closer to the axis A1 (z axis)
- the incident angle ⁇ and the wavelength shift amount ⁇ of the light beam from the core) farther from the axis A1 are the maximum.
- the maximum value Dmax of the variation of the transmission spectrum when the MCF 220 was set to the parallel type was 0.23 nm.
- the separation distance (0 ⁇ m) in the parallel type is shorter than the separation distance (150 ⁇ m) in the orthogonal type. Further, since the variation of the incident angle ⁇ of the parallel type is smaller than the variation of the incident angle ⁇ of the orthogonal type, the variation of the wavelength shift amount ⁇ is smaller in the parallel type (that is, Dmax).
- the orthogonal type is the circumferential orientation of the MCF 220 when the separation distance is maximum
- the parallel type is the circumferential orientation of the MCF 220 when the separation distance is minimum.
- the Dmax (0.23 nm) in the parallel type is about 87% smaller than the Dmax (1.7 nm) in the orthogonal type. This means that Dmax can be reduced by up to about 87% by setting the circumferential orientation of the MCF 220 to be parallel.
- the peripheral cores C1 to C4 are axisymmetric with respect to the y-axis regardless of whether the MCF 220 is set to the orthogonal type or the parallel type.
- all four peripheral cores (cores C1 to C4) are located on the x-axis, whereas when the MCF 220 is set to be parallel.
- None of the peripheral cores are located on the x-axis. From this, the orientation of the MCF 220 in the circumferential direction when the separation distance is minimized can be specified as follows, as in the case of the MCF 20 and 120.
- MCF220 having "a core arrangement in which the peripheral cores are arranged along a straight line passing through the center of the end face of the MCF", two types (orthogonal type and parallel type) in which the peripheral cores are line-symmetrical with respect to the y-axis. )
- the separation distance can be minimized by setting the MCF to the type (parallel type) in which the peripheral core is not located on the x-axis.
- the MCF When the MCF has "a core arrangement in which the peripheral core is located at the apex of the regular polygon centered on the center of the end face of the MCF", the MCF is one or more radially inward from the peripheral core. It may have another peripheral core as an inner core.
- the inner cores do not have to have a symmetric relationship and may be arranged in any way. This is because the separation distance should be minimized in order to minimize the maximum value Dmax of the variation, and the separation distance is a value determined (independently) regardless of the core arrangement of the inner peripheral core. That is why.
- the number of cores and the arrangement of cores of MCF are not limited to the examples given in FIGS. 8A to 8C. Further, the core arrangement of the MCF does not have to have symmetry with respect to the center of the end face of the MCF.
- the first separated core and the second separated core may be displaced from each other in the y-axis direction, and the distance from the y-axis to the first separated core is the distance from the y-axis to the second separated core. May be different from. Even in such a case, by setting the orientation of the MCF in the circumferential direction so that the separation distance is minimized, the variation in the incident angle ⁇ can be minimized, so that the above-mentioned effect can be obtained. ..
- the optical filter 40 may be rotated so that the rotation angle ⁇ has a negative value. Even in this case, the above-mentioned effect can be obtained by setting the orientation of the MCF in the circumferential direction so that the separation distance is minimized.
- FIG. 15 is a plan view showing an example of the optical filter device 310 according to the second embodiment of the present invention.
- the same members as those in the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted for the same configurations as those in the first embodiment.
- the optical filter device 310 differs from the optical filter device 10 in that it includes the MCF 320 and the ferrule 322 instead of the MCF 20 and the ferrule 22, and the MCF 360 and the ferrule 362 instead of the MCF 60 and the ferrule 62.
- the positions of the second lenses 50 are different from those positions in the optical filter device 10.
- the end face 320a of the MCF 320 is diagonally polished (oblique polishing) so as to be inclined by a predetermined polishing angle (for example, 8 °) in a predetermined inclination direction with respect to the xy plane. This reduces the reflected return light on the end face 320a.
- the end face 320a has an elliptical shape when viewed from a direction perpendicular to the end face 320a. In the following, along the long axis of the end face 320a (an example of the oblique polishing reference axis), the direction from the distal end farther from the optical filter 40 toward the proximal end closer to the center of the end face 320a. The direction when viewed along the axis is defined as the "oblique polishing direction".
- FIG. 16 is a diagram showing an end face 320a.
- the solid line arrow 81 in FIG. 16 indicates the diagonal polishing direction of the end face 320a
- the broken line arrow 80 indicates the reference direction which is a reference for calculating the diagonal polishing angle described later.
- the reference direction 80 extends along the + y-axis direction.
- the angle formed by any certain oblique polishing direction counterclockwise from the reference direction 80 is defined as "oblique polishing rotation angle ⁇ having a positive value”.
- the oblique polishing rotation angle ⁇ in the oblique polishing direction 81 is 270 ° (in other words, ⁇ 90 ° C.). °).
- the end portion of the MCF 320 in the + z-axis direction is inserted and held by a cylindrical ferrule 322.
- the end face 320a of the MCF 320 is obliquely polished together with the end face 322a of the ferrule 322.
- the end portion 322a1 of the end surface 322a of the ferrule 322 in the oblique polishing direction 81 is not obliquely polished and is parallel to the xy plane.
- the end portion 322a1 is a so-called polishing allowance.
- the MCF 320 includes seven cores C1 to C7 and a common clad 321 surrounding these cores C1 to C7.
- the MCF 320 has a core arrangement similar to that of the MCF 20. Further, the circumferential direction of the MCF 320 is set to be a parallel type (that is, a direction in which the separation distance is minimized).
- the light rays propagating through the cores C1 to C7 of the MCF 320 are emitted from the end face 320a toward the first lens 30.
- FIG. 15 only the main rays B3, B4 and B2 of the light rays emitted from the cores C3, C4 and C2 (see FIG. 16) are shown, respectively.
- the main rays B3, B4, and B2 are inclined with respect to the axis A1 because they are inclined toward the diagonal polishing direction 81 side (in this example, the + x-axis direction side).
- the first lens 30 is arranged at a position on the end face 320a separated from the center of the central core C4 by the focal length in the + z-axis direction. Therefore, the main ray B4 emitted from the first lens 30 is parallel to the axis A1. The first lens 30 collimates and collects the light rays from the cores C1 to C7.
- the optical filter 40 is arranged so that the focusing point of the light emitted from the first lens 30 is located on the incident surface 40a.
- the light rays incident on the incident surface 40a pass through the optical filter 40 and are emitted from the emitting surface 40b.
- the optical filter 40 has a rotation axis r2 extending in the y-axis direction at a position where light rays are focused on the incident surface 40a.
- the optical filter 40 is rotated about the rotation axis r2 by a rotation angle ⁇ from a position parallel to the xy plane. This reduces the reflected return light.
- the main ray B4 emitted from the optical filter 40 is parallel to the axis A1.
- the second lens 50 is arranged so that its central axis coincides with the axis A1.
- the second lens 50 refracts the light rays emitted from the cores C1 to C7 emitted from the optical filter 40 so that these main light rays are parallel to each other (see light rays B3, B4 and B2 in FIG. 15). Further, the second lens 50 converges the light rays from the cores C1 to C7, respectively (only the main light rays are shown in FIG. 15).
- MCF360 has the same configuration as MCF320.
- the end of the MCF 360 in the ⁇ z axis direction is inserted and held by a cylindrical ferrule 362.
- the end face 360a of the MCF 360 is diagonally polished together with the end face 362a of the ferrule 362. This reduces the reflected return light on the end face 360a.
- the end surface 362a of the ferrule 362 has a polishing allowance at the end portion 362a1 in the oblique polishing direction.
- the MCF 360 has an axisymmetric relationship with the MCF 320 with respect to the x-axis.
- the positional relationship between the second lens 50 and the MCF 360 is determined so that the end faces 360a are located at positions where the light rays emitted from the cores C1 to C7 emitted from the second lens converge.
- the above is a description of the configuration of the optical filter device 310.
- the inventors of the present application apply two types of MCFs, which will be described later, in which the orientations in the circumferential direction are set to be parallel to the optical filter device 310, and change the oblique polishing rotation angle ⁇ in the range of 0 ° ⁇ ⁇ ⁇ 360 °. By doing so, the relationship between the oblique polishing rotation angle ⁇ and the maximum value Dmax of the variation in the transmission spectrum was considered.
- FIG. 17A and 17B are views showing the end faces of the MCF used in the discussion.
- the MCF in FIG. 17A is the MCF 320. Since the configuration of the MCF 320 has been described with reference to FIG. 16, detailed description thereof will be omitted.
- the diagonal polishing direction 82 can rotate 360 ° counterclockwise from the reference direction 80 (not shown).
- the ray angle ⁇ of the rays from the central core C4 is 0 ° (see FIG. 15).
- the average value of the ray angles ⁇ of the rays from the peripheral cores C1 to C3 and C5 to C7 is 0.87 °.
- the MCF in FIG. 17B is an MCF 420 that differs from the MCF 320 only in the number of cores and the core arrangement.
- the MCF 420 comprises four cores C1 to C4 and a common clad 421 that surrounds these cores C1 to C4.
- the MCF 420 has a core arrangement similar to that of the MCF 220.
- the diagonal polishing direction 83 can rotate 360 ° counterclockwise from the reference direction 80 (not shown).
- the ray angle ⁇ of the rays from the cores C1 and C4 is 1.7 °, respectively.
- the ray angle ⁇ of the rays from the cores C2 and C3 is 0.57 °, respectively.
- the rotation angle ⁇ is set to 2.9 °.
- the end face 320a of the MCF 320 is obliquely polished so that the oblique polishing rotation angle ⁇ is 90 °.
- the light rays transmitted through the optical filter 40 and emitted from the emission surface 40b are not shown. The same applies to FIG. 20.
- FIG. 19 shows the relationship between the “oblique polishing rotation angle ⁇ ” and the “maximum variation Dmax” when the oblique polishing rotation angle ⁇ of the MCF 320 shown in FIG. 18 is changed in the range of ⁇ 180 ° ⁇ ⁇ ⁇ 180 °.
- the solid line 90 in the graph indicates the maximum value Dmax of the variation when the MCF whose end face is not diagonally polished (that is, the parallel type MCF20 of the first embodiment (see FIGS. 10A and 10B)) is used.
- Dmax 0.75 nm, but this is because it is described with two significant figures, and the exact value is slightly smaller than 0.75 nm as shown by the solid line 90. ..
- the Dmax of the obliquely polished MCF320 is equal to or smaller than the Dmax of the non-obliquely polished parallel MCF20.
- the end face 320a is obliquely polished so that the oblique polishing rotation angle ⁇ is ⁇ 90 °.
- FIG. 21 shows the relationship between the “oblique polishing rotation angle ⁇ ” and the “maximum variation Dmax” when the oblique polishing rotation angle ⁇ of the MCF 320 shown in FIG. 20 is changed in the range of ⁇ 180 ° ⁇ ⁇ ⁇ 180 °. It is a graph that defines. According to FIG. 21, when ⁇ 180 ° ⁇ ⁇ 0 °, the Dmax of the obliquely polished MCF320 is equal to or smaller than the Dmax of the non-obliquely polished parallel MCF20. ..
- FIG. 22 shows “oblique” when the rotation angle ⁇ of the optical filter 40 shown in FIG. 18 is changed to 1.8 ° and the oblique polishing rotation angle ⁇ of the MCF 320 is changed in the range of ⁇ 180 ° ⁇ ⁇ ⁇ 180 °.
- It is a graph which defined the relationship between "polishing rotation angle ⁇ " and "maximum value Dmax of variation”.
- the solid line 91 in the graph shows the maximum value Dmax of the variation when the MCF whose end face is not diagonally polished (that is, the parallel type MCF20 of the first embodiment) is used.
- the Dmax of the obliquely polished MCF320 is equal to or smaller than the Dmax of the non-obliquely polished parallel MCF20.
- Dmax 0.23 nm, but this is because it is described with two significant figures, and the exact value is slightly smaller than 0.23 nm as shown by the solid line 92. .. According to FIG. 24, when the rotation angle ⁇ has a positive value, the Dmax of the obliquely polished MCF420 is larger than the Dmax of the non-obliquely polished parallel MCF220.
- the MCF320 when “ ⁇ > 0, the MCF320 is obliquely ground so as to satisfy 0 ° ⁇ ⁇ 180 °, and ⁇ .
- the maximum value Dmax of variation can be maintained or further reduced as compared with the configuration without oblique polishing, but the MCF420 It can be seen that such an effect cannot be obtained when the separation distance is "zero" as in the core arrangement of.
- the MCF may have an inner peripheral core. Further, the number of cores and the core arrangement of the MCF are not limited to the examples given in FIGS. 17A and 17B. Further, the core arrangement of the MCF does not have to have symmetry with respect to the center of the end face of the MCF. Even in this case, when the separation distance is larger than zero, the variation in the incident angle ⁇ can be further reduced by diagonally polishing the MCF in the diagonal polishing direction described above, so that the above-mentioned effect can be obtained.
- optical filter device according to the embodiment has been described above, the present invention is not limited to the above embodiment, and various modifications can be made as long as the object of the present invention is not deviated.
- the optical filter 40 is not limited to the short wavelength transmitted light filter, and is not limited to other optical filters that transmit light in a specific wavelength band with an arbitrary transmission intensity (for example, a long wavelength transmitted light filter, a band transmitted light filter, or gain equivalent). It may be an optical filter).
- a long wavelength transmitted light filter is used as the optical filter
- ⁇ 0 can be appropriately set according to the wavelength profile.
- the MCF since the end face of the MCF is obliquely polished, the ray angle ⁇ of the light rays emitted from each core emitted from the first lens 30 varies. Therefore, the MCF may be moved in the direction opposite to the diagonal polishing direction by a predetermined distance to reduce the variation in the ray angle ⁇ .
- the incident surface 40a of the optical filter 40 does not have to be located on the condensing point of the light emitted from the first lens 30.
- the rotation axes r1 and r2 of the optical filter 40 can be set as arbitrary axes penetrating the optical filter 40 in the y-axis direction.
- the MCF is not limited to a columnar shape, and may be, for example, a columnar shape having an elliptical or polygonal cross section orthogonal to the axis.
- the oblique polishing direction of the MCF is "a plane that passes through the center of the end face of the MCF, is orthogonal to the end face, and is parallel to the tilt direction (the direction in which the end face of the MCF is tilted with respect to the xy plane)".
- the "diagonal polishing reference axis" which is a line segment intersecting the end face, the direction from the distal end closer to the optical filter 40 toward the proximal end closer to the optical filter 40 is the central axis of the end face. It is defined as the direction when viewed along.
- the MCF60 (or MCF360) has the same number of cores and core arrangement as the MCF20 (or MCF320), but is not limited to this.
- the MCF60 (or MCF360) may have a different number of cores and core arrangement from the MCF20 (or MCF320) as long as it has a core capable of incident light emitted from each core of the MCF20 (or MCF320).
- the MCF 60 (or MCF 360) may have one or more cores in addition to the seven cores described above.
- the single-core optical fiber group includes a single-mode single-core optical fiber capable of incident light emitted from each core of the MCF20 (or MCF320)
- the number of cores is the number of cores of the MCF20 (or MCF320). It may be more than the number.
- the MCF 20 may be a multimode optical fiber.
- the MCF 60 may be a multimode optical fiber having seven or more cores.
- the single-core optical fiber group may include seven or more multimode single-core optical fibers.
- the second lens 50 may be a lens array including the same number of lenses as the number of cores of the MCF 20 (or MCF 320). Each lens in the lens array converges the light beam from each corresponding core of the MCF 20 (or MCF 320) so that it is incident on each corresponding single core optical fiber.
- all cores C1 to C7 of MCF20 may not be used for light ray propagation.
- the MCF 60 may have more cores than the number of cores of the MCF 20 (or MCF 320) used for propagating the light beam. That is, the MCF60 (or MCF360) does not necessarily have the same number of cores as the number of cores of the MCF20 (or MCF320).
- the single-core optical fiber group may include a single-core optical fiber having a number of cores of MCF20 (or MCF320) or more used for propagating light rays. That is, the single-core optical fiber group does not necessarily have to include the same number of single-core optical fibers as the number of cores of the MCF 20 (or MCF 320).
- Optical filter device 20, 120, 220: Multi-core optical fiber, 20a, 120a, 220a: End face of multi-core optical fiber, 21, 121, 221: Clad, 22: Ferrule, 22a: End face of ferrule, 30: First Lens, 40: Optical filter, 40a: Incident surface, 40b: Exit surface, 50: Second lens, 60: Multi-core optical fiber, 60a: End face of multi-core optical fiber
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Abstract
Description
このような光フィルタデバイスにおいて、光フィルタが、その入射面が軸線と直交する面と平行となるように配置されている場合、マルチコア光ファイバから出射された光線がその入射面において反射する可能性がある。このような反射光は、一般に、「反射戻り光」と称される。反射戻り光は、マルチコア光ファイバを経由して送信側の通信装置に入射したり、多重反射したりすることにより信号光の光学特性を低下させる可能性がある。
本発明による光フィルタデバイス(10)は、
柱状であり、軸線方向に沿って延在している複数の第1コア(C1乃至C7)と、前記複数の第1コア(C1乃至C7)を取り囲む共通のクラッド(21)と、を備える第1マルチコア光ファイバ(20)と、
前記第1マルチコア光ファイバ(20)の中心軸線上に位置する光軸(z軸)を有し、前記第1コア(C1乃至C7)のそれぞれから出射されて発散する光線をコリメートし、コリメートされた各第1コア(C1乃至C7)からの光線を集光する第1レンズ(30)と、
前記第1レンズ(30)から出射された光線が入射する第1面(40a)と、前記第1面(40a)と対向しており、自身を透過した光線が出射される第2面(40b)と、を備え、特定の波長帯域の光線を任意の透過強度で透過させる光フィルタであって、前記第1面(40a)が前記第1レンズ(30)の光軸(z軸)と直交する面(xy平面)と平行となる位置から、前記光軸(z軸)に垂直な特定の方向に延びる回転軸(r1)周りに所定の回転角度(η)だけ回転されている光フィルタ(40)と、
前記光フィルタ(40)から出射された各第1コア(C1乃至C7)からの光線をそれぞれ収束する第2レンズ(50)と、
柱状であり、前記第2レンズ(50)から出射された各第1コア(C1乃至C7)からの全ての光線が入射する、軸線方向に沿って延在しているコアを備える光ファイバ(60)と、
を備える。
この光フィルタデバイス(10)では、
前記光軸(z軸)を通り前記回転軸(r1)と平行な基準軸(y軸)から、前記光軸(z軸)及び前記基準軸(y軸)と直交する直交軸(x軸)に沿って、前記基準軸(y軸)に対して一方の側に向かう方向を第1直交方向(-x軸方向)と規定し、前記基準軸(y軸)に対して他方の側に向かう方向を第2直交方向(+x軸方向)と規定すると、
前記第1マルチコア光ファイバ(20)の周方向の向きは、その中心軸線(z軸)に沿ってその端面(20a)を見たときに、前記基準軸(y軸)から前記第1直交方向(-x軸方向)に最も離間している第1コア(第1離間コア)の前記基準軸(y軸)からの距離と、前記基準軸(y軸)から前記第2直交方向(+x軸方向)に最も離間している第1コア(第2離間コア)の前記基準軸(y軸)からの距離と、の和である離間距離が最小となるように設定されている。
なお、「各第1コアからの全ての光線が入射する」コアを備える光ファイバとは、第1マルチコア光ファイバの各コアからの出射光が入射可能なコアを備える光ファイバを意味する。即ち、反射戻り光は、上記「全ての光線」には含まれない。
また、本明細書において、「集光」とは、レンズが複数の光源(例えば、第1マルチコア光ファイバの複数の第1コア)からの光線(厳密には、光線の主光線)を1点に集めることを意味し、「収束(集束)」とは、レンズが1つの光源(例えば、第1マルチコア光ファイバの各第1コア)からの光線の径を絞って1点に集めることを意味する。
本発明によれば、反射戻り光を低減しつつ、光信号を適切に伝送することができる。
図1は、本発明の第1実施形態に係る光フィルタデバイス10の一例を示す平面図である。図1に示すように、光フィルタデバイス10は、第1マルチコア光ファイバとしてのマルチコア光ファイバ20と、第1レンズ30と、光フィルタ40と、第2レンズ50と、光ファイバとしてのマルチコア光ファイバ60と、を備える。これらの部材は、軸線A1に沿って上記の順に配置されている。光フィルタデバイス10には、直交座標系が設定されている。z軸は、軸線A1上に、第1レンズ30から光フィルタ40に向かう方向が正方向となるように延びている。y軸は、z軸(即ち、軸線A1)と直交しており、紙面手前方向が正方向となるように延びている。x軸は、z軸及びy軸と直交している。以下、マルチコア光ファイバを「MCF」とも称する。なお、本明細書では、図を見易くするために、特定の部材(例えば、MCF20及びMCF60)の寸法及び角度等を変更して図示している。
以上が光フィルタデバイス10の構成に関する説明である。
小檜山光信著、「光学薄膜フィルターデザイン」、第1版、株式会社オプトロニクス社、2006年、p.301-346
図15は、本発明の第2実施形態に係る光フィルタデバイス310の一例を示す平面図である。本実施形態では、第1実施形態と同一の部材については同一の符号を付し、第1実施形態と同様の構成についてはその詳細な説明を省略する。図15に示すように、光フィルタデバイス310は、MCF20及びフェルール22の代わりにMCF320及びフェルール322を備え、MCF60及びフェルール62の代わりにMCF360及びフェルール362を備える点で光フィルタデバイス10と相違している。また、第2レンズ50の位置が、光フィルタデバイス10におけるそれらの位置と相違している。
以上が光フィルタデバイス310の構成に関する説明である。
同様に、シングルコア光ファイバ群は、MCF20(又はMCF320)の各コアからの出射光が入射可能なシングルモード・シングルコア光ファイバを備えていれば、その数は、MCF20(又はMCF320)のコア数より多くてもよい。
これらの場合、MCF20(又はMCF320)の各コアC1乃至C7からの出射光が入射しないコア又はシングルコア光ファイバが存在することになるが、このような構成であっても、第1実施形態と同一の作用効果を奏することができる。
Claims (6)
- 柱状であり、軸線方向に沿って延在している複数の第1コアと、前記複数の第1コアを取り囲む共通のクラッドと、を備える第1マルチコア光ファイバと、
前記第1マルチコア光ファイバの中心軸線上に位置する光軸を有し、前記第1コアのそれぞれから出射されて発散する光線をコリメートし、コリメートされた各第1コアからの光線を集光する第1レンズと、
前記第1レンズから出射された光線が入射する第1面と、前記第1面と対向しており、自身を透過した光線が出射される第2面と、を備え、特定の波長帯域の光線を任意の透過強度で透過させる光フィルタであって、前記第1面が前記第1レンズの光軸と直交する面と平行となる位置から、前記光軸に垂直な特定の方向に延びる回転軸周りに所定の回転角度だけ回転されている光フィルタと、
前記光フィルタから出射された各第1コアからの光線をそれぞれ収束する第2レンズと、
柱状であり、前記第2レンズから出射された各第1コアからの全ての光線が入射する、軸線方向に沿って延在しているコアを備える光ファイバと、
を備え、
前記光軸を通り前記回転軸と平行な基準軸から、前記光軸及び前記基準軸と直交する直交軸に沿って、前記基準軸に対して一方の側に向かう方向を第1直交方向と規定し、前記基準軸に対して他方の側に向かう方向を第2直交方向と規定すると、
前記第1マルチコア光ファイバの周方向の向きは、その中心軸線に沿ってその端面を見たときに、前記基準軸から前記第1直交方向に最も離間している第1コアの前記基準軸からの距離と、前記基準軸から前記第2直交方向に最も離間している第1コアの前記基準軸からの距離と、の和である離間距離が最小となるように設定されている、
光フィルタデバイス。 - 請求項1に記載の光フィルタデバイスにおいて、
前記複数の第1コアは、前記第1マルチコア光ファイバの前記中心軸線を除く軸線に沿って延在する複数の周辺コアを含み、
前記第1マルチコア光ファイバの中心軸線に沿ってその端面を見たときに、
前記周辺コアは、前記端面の中心を通る直線に沿って配置されているか、又は、前記周辺コアのうち前記中心から最も離間している複数の最外周コアが、前記中心を中心とする正多角形の頂点に位置しており、
直線状に配置されている前記周辺コア、又は、前記最外周コアは、前記基準軸に関して線対称であり、且つ、前記直交軸上に位置していない、
光フィルタデバイス。 - 請求項1又は請求項2に記載の光フィルタデバイスにおいて、
前記光ファイバは、前記コアが共通のクラッドで取り囲まれている第2マルチコア光ファイバであり、
前記第2レンズは、前記光フィルタから出射された各第1コアからの光線を、それらの主光線が互いに平行となるように屈折させる、
光フィルタデバイス。 - 請求項1又は請求項2に記載の光フィルタデバイスにおいて、
前記光ファイバは、複数のシングルコア光ファイバを備えるシングルコア光ファイバ群であり、前記シングルコア光ファイバの各々が、1つの前記コアと、それを取り囲むクラッドと、を含む、
光フィルタデバイス。 - 請求項1乃至請求項4の何れか一項に記載の光フィルタデバイスにおいて、
前記光フィルタの前記回転角度の大きさは、0°超90°未満である、
光フィルタデバイス。 - 請求項1乃至請求項5の何れか一項に記載の光フィルタデバイスにおいて、
前記第1マルチコア光ファイバの端面は、前記光軸と直交する面に対して所定の傾斜方向に所定の研磨角度だけ傾斜するように斜めに研磨されており、
z軸が、前記光軸上に、前記第1レンズから前記光フィルタに向かう方向が正方向となるように延びており、y軸が、前記基準軸上に、前記基準軸の一端から他端に向かう方向が正方向となるように延びており、x軸が、前記第1直交方向及び前記第2直交方向に延びていると規定し、
前記光フィルタを前記y軸の正方向から見た場合において前記光フィルタが前記回転軸周りに反時計回りに回転されたときの前記回転角度が正の値を有し、前記光フィルタが前記回転軸周りに時計回りに回転されたときの前記回転角度が負の値を有すると規定し、
前記第1マルチコア光ファイバの前記端面の中心を通り前記端面と直交し且つ前記傾斜方向と平行な平面が前記端面と交差する線分である斜研磨基準軸に沿って、前記光フィルタからより離間している遠位端からより近接している近位端に向かう方向を、前記端面の中心軸線に沿って見たときの方向を斜研磨方向と規定し、前記斜研磨方向が、前記y軸の前記正方向から反時計回りに成す角を、正の値を有する斜研磨回転角度と規定すると、
前記離間距離が0より大きい場合において、
前記光フィルタの前記回転角度が正の値を有するときは、前記第1マルチコア光ファイバの前記端面は、前記斜研磨回転角度が0°超180°未満の値となるように斜めに研磨され、
前記光フィルタの前記回転角度が負の値を有するときは、前記第1マルチコア光ファイバの前記端面は、前記斜研磨回転角度が-180°超0°未満の値となるように斜めに研磨されている、
光フィルタデバイス。
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JP2001264572A (ja) * | 2000-03-21 | 2001-09-26 | Sun Tec Kk | 干渉光フィルタモジュール装置 |
US20030174937A1 (en) * | 2002-03-15 | 2003-09-18 | Yonglin Huang | Integrated WDM coupler for duplex communication |
JP2004264739A (ja) * | 2003-03-04 | 2004-09-24 | Tdk Corp | 光フィルタ及び光フィルタモジュール |
JP5598882B2 (ja) * | 2011-06-16 | 2014-10-01 | 古河電気工業株式会社 | 光ファイバ増幅器 |
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JPH0572411A (ja) * | 1991-06-13 | 1993-03-26 | Mitsubishi Electric Corp | 入射角調整装置 |
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