Optical encoder

Abstract

The present invention is a bundled fiber comprising a fiber bundle part obtained by bundling a plurality of fibers each made up of a core and a cladding that surrounds the outer circumference of the core, the bundled fiber being characterized in that polarizers, the polarization axes of which are different, are formed respectively at end sections of the cores of the fibers at one end in the fiber bundle part.

Description

Technical Field

[0001] The present invention relates to a bundle fiber, a polarization sensor, an optical encoder, a light scattering detection sensor, and a method for manufacturing a bundle fiber. Background Art

[0002] In recent years, in the fields of precision measurement devices, industrial robots, and conveyors, high-precision encoders have been demanded in order to more accurately detect the amount of displacement of moving parts. An encoder is a sensor that converts the amount of mechanical displacement caused by rotation or the like into an electrical signal, processes this electrical signal, and detects the position, speed, and the like of a moving part. Among these, optical encoders that detect displacement using light can greatly improve detection resolution.

[0003] For example, Patent Document 1 discloses an encoder detection unit including a memory plate having a plurality of slits formed along the circumferential direction, a fiber that emits light toward one opening end of the slits, and a light receiving unit that receives light passing through the slits.

[0004] Further, for example, Non-Patent Document 1 discloses a polarization encoder including a light source, a rotating polarizer, four polarizers with polarization axes oriented differently from each other, and four light receiving elements respectively corresponding to the four polarizers. This polarization encoder allows light from the light source to transmit through the rotating polarizer, and converts the light into four types of linearly polarized light with different directions. Then, these four types of linearly polarized light are detected by respective light receiving elements, output as four types of electrical signals, and a Lissajous waveform is obtained. Then, based on this Lissajous waveform, the displacement angle of the rotating polarizer connected to the displaced member is detected. Prior Art Documents Patent Documents

[0005] Patent Document 1 Japanese Unexamined Patent Publication No. 2010-181279 Non-Patent Documents

[0006] [Non-Patent Document 1] Hideki Furukawa et al, 2017 Society for Precision Engineering Spring Conference, 2017, p507-508 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, the encoder detection unit disclosed in Patent Document 1 uses a memory plate with slits formed on it to detect the displacement angle, making it difficult to increase the density of the slits and thus difficult to significantly improve the detection resolution.

[0008] Furthermore, the polarization encoder described in Non-Patent Document 1 has the drawback of having low noise immunity and being limited in the locations where it can be used due to external electromagnetic waves, because it receives the polarized light transmitted through a rotating polarizer with a photodetector and transmits the intensity of each polarization as an electrical signal.

[0009] This invention was proposed in view of the above-mentioned problems, and aims to provide a bundle fiber that has high noise immunity to electromagnetic waves and can improve detection resolution when applied to an encoder, a polarization sensor using the same, an optical encoder, a light scattering detection sensor, and a method for manufacturing a bundle fiber. [Means for solving the problem]

[0010] To solve the above problems, the bundled fiber of one embodiment of the present invention proposes the following means. (1) A bundle fiber according to embodiment 1 of the present invention is a bundle fiber comprising a fiber bundling portion in which a plurality of fibers, each consisting of a core and a cladding surrounding the outer circumference of the core, are bundled together, characterized in that at one end of the fiber bundling portion, polarizers with polarization axes of different orientations are formed on the ends of the cores of each individual fiber.

[0011] (2) Aspect 2 of the present invention is characterized in that, in the bundled fiber according to aspect 1, the polarizer is a wire grid polarizer in which a plurality of light-shielding wires are arranged in a stripe pattern at equal intervals along one direction.

[0012] (3) Aspect 3 of the present invention is characterized in that, in the bundled fiber according to aspect 1 or 2, a fiber separating portion where the fibers are separated one by one is formed on the other end side of the fiber bundling portion.

[0013] (4) Aspect 4 of the present invention is characterized in that, in the bundled fiber according to any one of aspects 1 to 3, each of the polarizers is bonded to an end face of an individual one of the cores.

[0014] (5) Aspect 5 of the present invention is characterized in that, in the bundled fiber according to any one of aspects 1 to 3, each of the polarizers is integrally formed at an end portion of an individual one of the cores.

[0015] (6) Aspect 6 of the present invention is characterized in that, in the bundled fiber according to any one of aspects 1 to 5, the number of the fibers in the fiber bundling portion is N (0 < N < 180, where N is an integer and a divisor of 180), and the direction of the polarization axis of each of the polarizers formed at the end portion of each of the cores has rotational symmetry of (180 / N)°.

[0016] (7) Aspect 7 of the present invention is characterized in that, in the bundled fiber according to any one of aspects 1 to 6, among the plurality of fibers in the fiber bundling portion, at least one fiber emits light toward the outside from one end side of the fiber bundling portion, and at least one fiber among the plurality of fibers allows light to enter from one end side of the fiber bundling portion.

[0017] (8) A polarization sensor according to aspect 8 of the present invention is characterized by comprising the bundled fiber according to any one of aspects 1 to 7.

[0018] (9) The optical encoder according to aspect 9 of the present invention comprises the bundle fiber according to any one of aspects 1 to 7, a rotating polarizing plate formed adjacent to one end side of the fiber binding portion, and a light source that irradiates light toward the rotating polarizing plate.

[0019] (10) The light scattering detection sensor according to aspect 10 of the present invention comprises the bundle fiber according to any one of aspects 1 to 7, a detector connected to the bundle fiber, and a light source that irradiates light toward a measurement object.

[0020] (11) The method for manufacturing a bundle fiber according to aspect 11 of the present invention is a method for manufacturing the bundle fiber according to aspect 2, comprising: a resist film forming step of forming a resist film on a surface of a light-transmissive base material; a lithography step of forming the resist film into a striped resist pattern; and a metal film forming step of forming a metal film on the surface of the light-transmissive base material using the resist pattern as a mask to obtain a wire grid polarizer provided with a striped wire grid.

[0021] (12) Aspect 12 of the present invention is characterized in that, in the method for manufacturing a bundle fiber according to aspect 11, the light-transmissive base material is made of the same material as the core constituting the fiber. Effects of the Invention

[0022] According to the present invention, it is possible to provide a bundle fiber which has high noise resistance against electromagnetic waves and can improve detection resolution when applied to an encoder, a polarization sensor using the same, an optical encoder, a light scattering detection sensor, and a method for manufacturing the bundle fiber. Brief Description of the Drawings

[0023] [Figure 1] FIG. 1 is a schematic diagram illustrating the bundle fiber according to the first embodiment, which is an example of the present invention. [Figure 2] FIG. 2 is an enlarged plan view of essential parts illustrating one end side of the fiber binding portion in the first embodiment, which is an example of the present invention. [Figure 3] This is an enlarged plan view of a key part showing one end of the fiber bundling portion in a bundled fiber according to a second embodiment, which is an example of the present invention. [Figure 4] These are enlarged cross-sectional view (a) and enlarged plan view (b) of a key part showing one end of the fiber bundling portion in a bundle fiber according to a third embodiment of the present invention, which is an example of the present invention. [Figure 5] This is a schematic diagram showing an optical encoder of one embodiment of the present invention. [Figure 6] This is a schematic diagram showing an optical encoder according to another embodiment of the present invention. [Figure 7] This is a schematic diagram illustrating, step-by-step, an example of a bundle fiber manufacturing process, up to the formation of a wire grid polarizer at the end of the core. [Figure 8] (a) is a design drawing of a chip equipped with a wire grid polarizer, and (b) is a magnified plan view of the thin wires that make up the wire grid polarizer. [Figure 9] (a) is an SEM image of a wire grid polarizer that was actually fabricated. (b) is a magnified image of the end face of a bundle fiber to which the wire grid polarizers that were actually fabricated are joined. [Figure 10] This is a photograph of the actual optical encoder that was manufactured. [Figure 11] This graph shows the measurement results for light with a wavelength of 850 nm. [Modes for carrying out the invention]

[0024] Hereinafter, with reference to the drawings, a bundle fiber according to one embodiment of the present invention, an optical encoder using the same, and a method for manufacturing the bundle fiber will be described. The embodiments shown below are provided specifically to better illustrate the spirit of the invention and do not limit the present invention unless otherwise specified. Furthermore, the drawings used in the following description may be enlarged for convenience to make the features of the present invention easier to understand, and the dimensional ratios of each component may not be the same as in reality.

[0025] (Bundled fiber: First embodiment) An example of the configuration of a bundle fiber according to a first embodiment of the present invention will be described. Figure 1 is a schematic diagram showing a bundled fiber of a first embodiment, which is an example of the present invention. Figure 2 is an enlarged plan view of a key part showing one end of the fiber bundle in the first embodiment, which is an example of the present invention. The bundled fiber 10 of this embodiment has a fiber bundling portion 11 and a fiber separation portion 12 connected to the other end 11b of the fiber bundling portion 11.

[0026] The fiber bundling section 11 is composed of multiple fiber bundles, in this embodiment four fiber bundles 21A, 21B, 21C, and 21D, bound together by a covering section 23. Each fiber 21A, 21B, 21C, and 21D has a core 21a, 21b, 21c, and 21d, and cladding 22a, 22b, 22c, and 22d surrounding these cores, respectively. Each fiber 21A, 21B, 21C, and 21D may be covered with a light-shielding coating 29.

[0027] Cores 21a, 21b, 21c, and 21d are each molded from quartz (SiO2) or a light-transmitting material such as optical glass or polymer. In this embodiment, cores 21a, 21b, 21c, and 21d are made of quartz. Cores 21a, 21b, 21c, and 21d can be single-mode cores with a diameter of 9 to 10 μm, or multi-mode cores with a diameter of approximately 50 μm to 3000 μm.

[0028] The cladding layers 22a, 22b, 22c, and 22d are formed from light-transmitting materials such as quartz (SiO2) or polymers, which have a lower refractive index than the cores 21a, 21b, 21c, and 21d. In this embodiment, the cladding layers 22a, 22b, 22c, and 22d are made of quartz. With this configuration, the fiber bundling section 11 constitutes a multi-core fiber in which four fibers 21A, 21B, 21C, and 21D are arranged at equal intervals inside the covering section 23.

[0029] The covering portion 23 is a bundling member that connects the four fibers 21A, 21B, 21C, and 21D, and can be made of, for example, a resin that does not transmit light or a thin metal film. In this embodiment, a heat-shrinkable resin is used as the covering portion 23.

[0030] One end 11a of the fiber bundling section 11 is provided with wire grid polarizers (polarizers) 24a, 24b, 24c, and 24d, which correspond to the respective end faces of the cores 21a, 21b, 21c, and 21d.

[0031] In this embodiment, a wire grid type polarizer is used as the polarizer, but such polarizers are not limited to wire grid polarizers. For example, various types of polarizers can be used, such as crystal type polarizers that control the polarization component by birefringence of crystalline materials, PBS (Polarizing Beam Splitter) type polarizers using optical multilayer films, resin polarizers formed by stretching a resin sheet impregnated with a dichroic dye in a certain direction, Grant-Thomson prism type polarizers that remove the linear polarization component in one direction by total internal reflection by combining with a calcite prism, photonic crystal type polarizers, metamaterial / metasurface type polarizers, and structural birefringence type polarizers.

[0032] The wire grid polarizers 24a, 24b, 24c, and 24d of this embodiment are made of a light-transmitting substrate consisting of a light-transmitting material containing SiO2 or a light-transmitting material containing a polymer, and in this embodiment, a light-shielding material, such as a metal film 27, is formed in a striped pattern on one surface of a quartz substrate (light-transmitting substrate) 26.

[0033] In this embodiment, aluminum is used as the metal film 27. The formation pitch of the individual fine wires 27a of the striped metal film 27 can be, for example, about 140 nm to 250 nm. In addition, the width of each fine wire 27a can be about 30 nm to 140 nm, and the thickness (height) can be about 10 nm to 150 nm.

[0034] These wire grid polarizers 24a, 24b, 24c, and 24d are joined to one end face of the cores 21a, 21b, 21c, and 21d of the fiber bundling section 11, respectively. For example, the wire grid polarizer 24a is joined to the core 21a of the fiber bundling section 11 so that their centers coincide.

[0035] The wire grid polarizer 24a and the core 21a are joined by a bonding layer 28 made of a light-transmitting resin, with the striped metal film 27 constituting the wire grid polarizer 24a facing the end face side of the core 21a. In this embodiment, a light-transmitting ultraviolet-curing resin is used as the bonding material.

[0036] The wire grid polarizers 24b, 24c, and 24d are also joined to one end face of the cores 21b, 21c, and 21d of the fiber bundling section 11 via the bonding layer 28, similar to the wire grid polarizer 24a.

[0037] The wire grid polarizers 24a, 24b, 24c, and 24d are joined to one end face of the cores 21a, 21b, 21c, and 21d of the fiber bundling section 11, respectively, so that the angles of the extension direction of the striped thin wires 27a are different for each of them.

[0038] In other words, when the angle perpendicular to the extension direction of the striped thin lines 27a of the wire grid polarizer 24a is taken as 0°, the wire grid polarizer 24b is mounted at 45°, the wire grid polarizer 24c at 90°, and the wire grid polarizer 24d at 135°.

[0039] The fiber separation section 12 is connected to the other end 11b of the fiber bundling section 11 and consists of four single fibers 31A, 31B, 31C, and 31D, each comprising a single core 31a, 31b, 31c, and 31d, cladding 32a, 32b, 32c, and 32d surrounding the outer circumference of these four cores, and a coating 29 surrounding the outer circumference of these four cladding 22.

[0040] Fiber 31A can be any series of cores in which core 31a is integrally formed with core 21a of fiber bundling portion 11. Similarly, core 31b can be any series of cores integrally formed with core 21b, core 31c with core 21c, and core 31d with core 21d.

[0041] With this configuration, light incident from one end 11a of the fiber bundling section 11 to the cores 21a, 21b, 21c, and 21d respectively is branched and propagated in the fiber separation section 12 to the separated fibers 31A, 31B, 31C, and 31D, respectively.

[0042] One end 11a of the fiber bundling section 11 may be fixed with a fixing member such as a connector. That is, the bundle fiber 10 may have a fixing member provided on one end 11a of the fiber bundling section 11 to fix multiple fibers. In this case, the fiber bundling section 11 is connected to the fiber holder, for example, via the connector. The bundle fiber 10 does not have to have a connector, but in that case, a fixing member may be provided on the outermost part near one end 11a of the bundle fiber 10, for example, on the outer circumference of the covering section 23, or an optical fiber probe, which is made up of a tubular body and houses the bundle fiber 10 inside, may be provided. This makes it possible to firmly fix multiple fibers and multiple polarizers to each other, and to improve the accuracy of setting the angle of each polarizer.

[0043] The operation of the bundle fiber 10 in this embodiment, configured as described above, will now be explained. When, for example, natural light (unpolarized) is incident on one end 11a of the fiber bundling portion 11 of the bundle fiber 10, the wire grid polarizers 24a, 24b, 24c, and 24d cause the transmittance of polarization at an angle perpendicular to the extension direction of each striped thin wire 27a to be the highest, and the transmittance of polarization at an angle along the extension direction of the thin wire 27a to be the lowest.

[0044] As a result, only the polarization with the strongest component at an angle of 0° from the incident natural light (unpolarized) propagates through core 21a. Similarly, only the polarization with the strongest component at an angle of 45° propagates through core 21b, only the polarization with the strongest component at an angle of 90° propagates through core 21c, and only the polarization with the strongest component at an angle of 135° propagates through core 21d.

[0045] Then, the polarized light with different angles propagating through each of the cores 21a, 21b, 21c, and 21d is split and propagated in the fiber separation section 12 into independent fibers 31A, 31B, 31C, and 31D. From the end faces of the cores 31a, 31b, 31c, and 31d of each fiber 31A, 31B, 31C, and 31D, four polarized lights with different angular components of their strongest light intensity are emitted, separated by the wire grid polarizers 24a, 24b, 24c, and 24d.

[0046] Thus, in the bundle fiber 10 of this embodiment, light incident from one end 11a of the fiber bundling portion 11 is divided into polarizations with different angles by the wire grid polarizers 24a, 24b, 24c, and 24d, making it easy to obtain multiple polarizations with different angular components.

[0047] Furthermore, with the bundle fiber 10 of this embodiment, the polarization separated into each angular component by the wire grid polarizers 24a, 24b, 24c, and 24d is not converted into an electrical signal by a photodetector and transmitted as in the conventional method, but is propagated as polarization by the fibers 31A, 31B, 31C, and 31D. Therefore, it is not affected by external electromagnetic waves or other factors that would cause noise in an electrical signal. Therefore, it has high noise immunity, and even in places with strong external electromagnetic waves, it is possible to detect the polarization of each angular component separated by the wire grid polarizer with high precision.

[0048] In this embodiment, four cores are formed in the fiber binding portion, and the configuration is provided with four wire-grid polarizers in which the fine wire (wire) angles are shifted from each other by 45°. However, the number of wire-grid polarizers and the number of cores in the fiber binding portion are not limited.

[0049] For example, three cores may be formed in the fiber binding portion, and the configuration may be provided with three wire-grid polarizers in which the fine wire (wire) angles are shifted from each other by 60°. In this case, the bundle fiber can be produced at a lower cost.

[0050] Further, for example, six cores may be formed in the fiber binding portion, and the configuration may be provided with six wire-grid polarizers in which the fine wire (wire) angles are shifted from each other by 30°. In this case, the detection accuracy of polarized light of each angular component can be further improved.

[0051] Further, the number of said fibers in the fiber binding portion may be N (0 < N < 180, N is an integer and a divisor of 180). In this case, the orientation of the polarization axis of each of said polarizers formed at the end portions of the cores of the N fibers is rotationally symmetric by (180° / N). In this case, each polarizer only needs to be arranged in an orientation that can divide 180° into N equal parts, and the number N of said fibers may be an even number or an odd number. Increasing the number N of fibers in the fiber binding portion in this manner can further improve detection accuracy.

[0052] (Bundle Fiber: Second Embodiment) A configuration example of the bundle fiber according to the second embodiment of the present invention will be described. The same reference numerals are given to configurations similar to those of the bundle fiber according to the first embodiment, and overlapping descriptions are omitted. FIG. 3 is an enlarged plan view of essential parts showing one end side of a fiber binding portion in a bundle fiber according to the second embodiment of the present invention.

[0053] The fiber bundling portion 41 of the bundle fiber 40 in this embodiment is composed of multiple, in this embodiment four, fibers 51A, 51B, 51C, and 51D bundled together by a covering portion 23 (see Figure 1). Each fiber 51A, 51B, 51C, and 51D has a core 51a, 51b, 51c, and 51d, and cladding 52a, 52b, 52c, and 52d that surrounds these cores 51a, 51b, 51c, and 51d, respectively.

[0054] The configuration of the cores 51a, 51b, 51c, 51d and the cladding 52a, 52b, 52c, 52d is the same as in the first embodiment.

[0055] Wire grid polarizers 54a, 54b, 54c, and 54d are integrally formed at each end of the cores 51a, 51b, 51c, and 51d, which are one end 11a of the fiber bundling portion 11.

[0056] The wire grid polarizers 54a, 54b, 54c, and 54d of this embodiment consist of a metal film 57 directly deposited in a striped pattern on each end of the cores 51a, 51b, 51c, and 51d. The structure of the metal film 57 in this embodiment is the same as in the first embodiment.

[0057] Furthermore, each of the wire grid polarizers 54a, 54b, 54c, and 54d has a light-transmitting protective film 58 formed on it to protect the fine wires 57a, covering the striped metal film 57. The protective film 58 can be made of any light-transmitting material, and in this embodiment, a light-transmitting ultraviolet-curing resin is used.

[0058] According to the bundle fiber 40 of this embodiment, by directly depositing the fine wires 57a of the metal film 57 constituting the wire grid polarizers 54a, 54b, 54c, and 54d onto one end of the cores 51a, 51b, 51c, and 51d, respectively, compared to a configuration in which wire grid polarizers are formed separately from the core and then joined, there are no concerns about angular misalignment during bonding, and a high-precision bundle fiber 40 can be obtained with fewer manufacturing steps.

[0059] (Bundled fiber: Third embodiment) A configuration example of a bundle fiber according to a third embodiment of the present invention will be described. Note that components with the same numbering as the bundle fiber in the first embodiment are given the same numbering, and redundant explanations are omitted. Figure 4(a) is an enlarged cross-sectional view of a key part showing one end of the fiber bundling portion in a bundled fiber according to the third embodiment of the present invention. Figure 4(b) is an enlarged plan view of a key part showing the end side of Figure 4(a). The fiber bundling portion 61 of the bundle fiber 60 in this embodiment is composed of multiple bundles, in this embodiment two fibers 71A and 71B, bound together by a covering portion 23. Each fiber 71A and 71B has cores 71a and 71b, and cladding 72a and 72b that surround these cores 71a and 71b, respectively.

[0060] The configuration of the cores 71a, 71b and the cladding 72a, 72b is the same as in the first embodiment. With this configuration, the fiber bundling section 61 constitutes a multicore fiber in which two fibers 71A and 71B are arranged at equal intervals inside the covering section 23.

[0061] Wire grid polarizers 74a and 74b are provided at one end 61a of the fiber bundling portion 61, corresponding to the respective end faces of the cores 71a and 71b. The wire grid polarizers 74a and 74b of this embodiment consist of a core 71a and 71b with a metal film 77 formed in a striped pattern at each end.

[0062] Furthermore, each wire grid polarizer 74a and 74b has a protective film 78 that covers the fine wires 77a that make up the metal film 77. Note that, as in the first embodiment, the wire grid polarizers 74a and 74b may also be formed by bonding a metal film, which is formed in a striped pattern on one surface of a quartz substrate, to the respective ends of the cores 71a and 71b.

[0063] The wire grid polarizers 74a and 74b are configured such that the angles of the extension direction of the striped thin wires 77a are different for each other. That is, when the angle perpendicular to the extension direction of the striped thin wires 77a of the wire grid polarizer 74a is defined as 0°, the wire grid polarizer 74b is mounted so that the angle is 90°.

[0064] The bundled fiber 60 of this embodiment, as described above, can be used, for example, as a detector for a sensor that detects the surface state of a material. As shown in Figure 4(a), when visible light is emitted from the core 71a at one end 61a of the fiber bundle 61, only the polarization with the strongest component at an angle of 0° is emitted as inspection light towards the material M to be inspected by the wire grid polarizer 74a.

[0065] When this inspection light is reflected from the surface of material M, it generates specular and diffuse reflected light depending on the surface condition (reflectance, surface roughness) of material M. The wire grid polarizer 74b selectively transmits only the diffuse reflected light from these specular and diffuse reflected lights, and propagates the incident diffuse reflected light through the core 71b. Therefore, by measuring the diffuse reflected light propagating through the core 71b, the surface condition of material M can be detected.

[0066] Furthermore, the bundle fiber 60 of this embodiment can also be used as a detection sensor to detect the surface state of a material by measuring the ratio of near-infrared light to visible light based on the difference in reflectivity between visible light and near-infrared light, which varies depending on the material.

[0067] (Optical encoder) An example configuration of an optical encoder according to one embodiment of the present invention will be explained using Figures 1, 2, and 5. Figure 5 is a schematic diagram showing an optical encoder according to one embodiment of the present invention. The optical encoder 80 of this embodiment includes a bundle fiber 10 of the first embodiment, a rotating polarizing plate 81 formed adjacent to one end 11a of the fiber bundling portion 11 of the bundle fiber 10, a light source 82 that irradiates light toward the rotating polarizing plate 81, and a control unit 83 that receives polarized light emitted from the four fibers 31A, 31B, 31C, and 31D that constitute the fiber separation portion 12 of the bundle fiber 10, and calculates the rotation angle of the rotating polarizing plate 81 according to the change in the amount of light.

[0068] The light source 82 may be, for example, a non-polarizing light source device such as an LED or a tungsten halogen light source. Such a light source 82 may also be equipped with optical lenses such as a focusing lens.

[0069] The rotating polarizer 81 only needs to have its rotation axis 81m connected to a detection target that detects the rotation of a mechanically movable part. Such a rotating polarizer 81 may be, for example, a transparent disc-shaped substrate on which material molecules are oriented and formed, a wire grid polarizer, a photonic crystal type polarizer, a metamaterial / metasurface type polarizer, or a structural birefringence type polarizer. In this embodiment, a resin rotating polarizer was used, in which iodine compound molecules were adsorbed and oriented on a light-transmitting resin disc.

[0070] The control unit 83 consists of a photodetector that detects the amount of polarized light emitted from each of the four fibers 31A, 31B, 31C, and 31D, and a computer (PC) that calculates the rotation angle of the rotating polarizer 81 based on the amounts of four polarized lights with different angles detected by these photodetectors.

[0071] With the optical encoder 80 configured as described above, when a constant amount of light is irradiated from the light source 82 while the rotating polarizing plate 81 is stationary, the output polarization (detection light) that has passed through the rotating polarizing plate 81 is then polarized by the wire grid polarizers 24a, 24b, 24c, and 24d, with a polarization amount corresponding to its angular component, and is incident on and propagated from the end faces of the cores 21a, 21b, 21c, and 21d.

[0072] Then, from fiber 31A of the fiber separation unit 12, polarization with the strongest component at an angle of 0° is emitted. Similarly, from fiber 31B, only polarization with the strongest component at an angle of 45° is emitted, from fiber 31C, only polarization with the strongest component at an angle of 90° is emitted, and from fiber 31D, only polarization with the strongest component at an angle of 135° is emitted.

[0073] When the rotating polarizer 81 is stationary and not rotating, the ratio of polarized light emitted from each of the fibers 31A, 31B, 31C, and 31D remains unchanged.

[0074] On the other hand, if the object whose rotation amount is to be detected rotates from this state, the rotating polarizer 81 rotates via the rotation axis 81m. When the rotating polarizer 81 rotates, the angular component of the output polarization (detection light) transmitted through the rotating polarizer 81 changes. Then, in accordance with this change in the angular component of the output polarization (detection light), the amount of polarized light transmitted through the wire grid polarizers 24a, 24b, 24c, and 24d changes, respectively.

[0075] The control unit 83 detects how much the object to be detected has rotated by calculating the rotation angle of the rotating polarizer 81 in accordance with the change in the amount of polarized light emitted from each of the four fibers 31A, 31B, 31C, and 31D.

[0076] Thus, with the optical encoder 80 of this embodiment, light is propagated by fibers 31A, 31B, 31C, and 31D to the control unit 83 that calculates the rotation angle, thus eliminating the influence of external electromagnetic noise. Therefore, it can be suitably used, for example, as an encoder for detecting the motion of robots in medical, industrial, and aerospace applications, or as an encoder for detecting the mechanical motion of equipment placed in environments with strong electromagnetic waves.

[0077] In the embodiment described above, the light source 82 is positioned to transmit light through the rotating polarizer 81, but the light source is not limited to this. For example, as shown in Figure 6, a bundle fiber 90 having a fiber bundling section 92 containing five fibers 91A, 91B, 91C, 91D, and 91E can be used, with four of these fibers 91A, 91B, 91C, and 91D used for the propagation of the output polarization (detection light) as described above, and one fiber 91E used for the emission of light incident from a light source connected to the other end. In this case, a reflective rotating polarizer 93 with a light-reflective film formed on its back surface can be used. By using such a configuration, the optical encoder can be made even smaller and lighter.

[0078] (Manufacturing method for bundled fibers) A method for manufacturing bundled fibers according to one embodiment of the present invention will be described. Figure 7 is a schematic diagram illustrating the steps involved in the manufacturing process of bundled fibers, up to the formation of a wire grid polarizer at the end of the core.

[0079] First, a substrate made of glass material containing SiO2, such as a quartz substrate 26, is prepared, and an electron beam (EB) resist film 102 is formed on one side of this quartz substrate 26 by a film deposition method such as spin coating (resist deposition process: see Figure 7(a)).

[0080] Next, a resist pattern 103 is obtained on the EB resist film 102 by EB lithography, in which the resist is solidified in a striped pattern on one side of the quartz substrate 26 (lithography process: see Figure 7(b)). In this embodiment, EB lithography is used as the lithography process, but other methods such as nanoimprint lithography or stepper lithography may also be used, and the lithography method is not limited.

[0081] Next, using the striped resist pattern 103 as a mask, a metal film, such as an aluminum film, is deposited on the surface of the quartz substrate 26, for example, by electron beam deposition. The metal film can also be made of gold, silver, copper, platinum, or other materials.

[0082] As a result, a metal film 27 is deposited in a striped pattern on the portion of the quartz substrate 26 surface exposed from the striped resist pattern 103, forming numerous fine wires 27a on the surface of the quartz substrate 26 (see Figure 7(c)). After this, by removing the striped resist pattern 103, a wire grid polarizer (assembly) 24 having the striped metal film 27 is obtained (metal deposition process: see Figure 7(d)).

[0083] In addition to the procedure described above, the wire grid polarizer (assembly) 24 can also be formed by, for example, forming a metal film on the surface of a quartz substrate, forming a striped resist pattern on this metal film by lithography, etching the metal film using this resist pattern as an etching mask, and then removing the resist pattern.

[0084] Furthermore, the wire grid polarizer (assembly) 24 is diced to a size suitable for attachment to the core (see Figure 7(e)). Then, a bonding material, such as a transparent ultraviolet-curing resin R, is applied to the small piece 24S on which the wire grid polarizers 24a, 24b, 24c, and 24d are formed (see Figure 7(f)). After positioning these pieces on the end faces of the cores 21a, 21b, 21c, and 21d of the fiber bundling section 11, ultraviolet light is irradiated, thereby manufacturing a bundle fiber 10 in which the wire grid polarizers 24a, 24b, 24c, and 24d are bonded to the end faces of the cores 21a, 21b, 21c, and 21d via a bonding layer 28 (see Figure 7(g)).

[0085] Furthermore, the small piece 24S formed with the wire-grid polarizers 24a, 24b, 24c, 24d may be further chipped for each of the wire-grid polarizers 24a, 24b, 24c, 24d, and individually bonded to the end faces of the cores 21a, 21b, 21c, 21d, respectively.

[0086] The embodiments of the present invention have been described above. These embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and alterations can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, as well as in the scope of the invention described in the claims and equivalents thereof.

[0087] For example, the bundle fiber of the present embodiment can also be used in a light scattering detection sensor. The light scattering detection sensor includes a bundle fiber, a detector connected to the bundle fiber, and a light source that irradiates light toward a measurement object. In this case, similarly to the encoder described above, information on the polarization direction and intensity is detected by the light scattering detection sensor. The configuration of the bundle fiber can be the same as that of the bundle fiber provided in the encoder. The number of fibers in the fiber bundling portion of the bundle fiber may be N (0<N<180, N is an integer and a divisor of 180), and detection accuracy can be further improved by increasing the number of fibers N in the fiber bundling portion.

[0088] When the object being measured is a non-scattering material such as a mirror, the incident light (linearly polarized) is reflected while maintaining its linear polarization state, and therefore cannot pass through a polarizer oriented 90 degrees differently from its polarization direction. However, when a linearly polarized light source is shone on a scattering material, diffuse reflection occurs, causing the reflection direction to change to an angle other than specular reflection, and simultaneously changing the polarization direction, resulting in reflection with various components of different polarization directions. As a result, light is generated that passes through polarizers oriented 90 degrees differently, making it possible to distinguish whether the object being measured is a scattering material or a non-scattering material, and in the case of a scattering material, its degree of scattering can also be detected. Thus, the bundle fiber of this embodiment can be used as a polarization sensor such as an encoder or a light scattering detection sensor. Furthermore, the polarization sensor only needs to be equipped with a bundle fiber, and can be used as a sensor other than an encoder and a light scattering detection sensor. [Examples]

[0089] The following describes an example in which an optical encoder with the configuration shown in Figure 5 was actually designed and manufactured using the bundle fiber shown in Figure 1.

[0090] [Angle detection principle] The intensity of light (unpolarized light) emitted from the light source 82 when it passes through the rotating polarizer 81 is set as I0, and the intensities of the polarization after passing through the four wire grid polarizers (WGP) 24a, 24b, 24c, and 24d are set as I1, I2, I3, and I4, respectively. When the transmission axis of WGP 24a is set to 0°, WGP 24b is 45°, WGP 24c is 90°, and WGP 24d is 135°. It is also assumed that the light that passes through the rotating polarizer 81 becomes perfectly polarized. If the angle of the transmission axis of each WGP, i.e., the linear polarization angle, is θ, then I1, I2, I3, and I4 are expressed by the following equations (1) to (4), respectively. In the equations, α is the initial tilt angle (°) of θ with respect to the transmission axis of WGP 24a.

[0091] I1=I0(1+cos2(θ+α)) / 2···(1) I2=I0(1+sin2(θ+α)) / 2···(2) I3=I0(1-cos2(θ+α)) / 2···(3) I4=I0(1-sin2(θ+α)) / 2···(4)

[0092] Based on equations (1) to (4) described above, θ can be found by equation (5). θ=Arctan2(I1-I3,I2-I4)-α...(5) Here, Arctan2(x,y) is a function that returns θ that satisfies equations (6) and (7) below, for arguments x and y. cosθ = x / √(x 2 +y 2 )···(6) sinθ = y / √(x 2 +y 2 )···(7)

[0093] [Wire grid polarizer design] A chip equipped with a WGP was designed so that the WGP is positioned at the end face of the bundle fiber core. An example of the chip design is shown in Figure 8. Figure 8(a) is the chip design drawing, and Figure 8(b) is an enlarged plan view of the thin wires that make up the WGP.

[0094] For the bundled fiber, a bundled fiber (BF74LS01: manufactured by SoLab Japan Co., Ltd.) consisting of seven fibers bundled together was used. The tip was 2 mm square for a ferrule diameter of 3.2 mm. The WGP was made circular with a diameter of 0.43 mm so that the end face of the 0.4 mm diameter core was covered. The width of each wire was set to 80 nm, the height to 30 nm, and the formation pitch between wires to 180 nm.

[0095] [Fabrication of wire grid polarizers] First, an EB resist film was formed by coating a cleaned glass substrate with EB resist, and a resist pattern was fabricated on this EB resist film using EB lithography. Next, an Al film was deposited to a thickness of 30 nm using this resist pattern as a mask by EB deposition. Subsequently, a wire grid polarizer was formed by arranging multiple Al wires in a striped pattern using a lift-off process.

[0096] Figure 9(a) shows an SEM image of a WGP that was actually fabricated. In Figure 9(a), the thin white lines are wires made of Al, and the gray area between them is the base glass substrate (SiO2). From the SEM image in Figure 9(a), it was confirmed that the width of each wire was 74 nm. Next, the glass substrate on which the WGP was formed was diced into 2 mm square pieces. These pieces were then aligned so that the WGP overlapped the cores of each end face of one end of the bundle fiber. Alignment was performed by shining light into each fiber from the other end face of the bundle fiber and observing with a magnifying camera to ensure that the center of the WGP aligned with the center of the core end face. UV-curable resin was used for bonding. Figure 9(b) shows a magnified image of the end face of the bundle fiber with the WGP bonded to it.

[0097] [Verification of operation of an optical encoder using a wire grid polarizer] As described above, we confirmed the operation of an optical encoder using a bundled fiber equipped with a wire grid polarizer. The configuration of the optical encoder is shown in Figure 5. Figure 10 shows a photograph of the actual optical encoder that was fabricated.

[0098] Light (unpolarized light) was shone from a light source onto a rotating polarizer and incident on one end face of a fiber bundle equipped with wire grid polarizers in four directions. The intensity of the transmitted light from each of the four wire grid polarizers was then measured while varying the angle of the rotating polarizer.

[0099] The measurement involved irradiating a rotating polarizer with parallel light from a light source via an optical fiber and collimating lens, while rotating the polarizer in 10° increments. A spectrometer (HR4000CG-UV-NIR: Ocean Photonics Co., Ltd.) was connected to each of the four fibers separated for each core at the other end of the bundle fiber, and the polarization intensity was measured.

[0100] Figure 11 shows a graph of the measurement results for light at a wavelength of 850 nm, using commercially available LED light sources. For the four-directional wire grid polarizer, the measurement results were normalized so that the maximum intensity was 1 and the minimum intensity was 0. The measurement results were in close agreement with the theoretical values ​​(calculated values) when the intensity I0 was set to 1 and the initial tilt angle α was set to 31.2° in equations (1) to (4) described above.

[0101] From the above results, it was confirmed that by pre-normalizing the measurement results and applying equation (5), the rotation angle θ of the rotating polarizer can be calculated, and that an optical encoder (rotary encoder) using a rotating polarizer as the rotor can be realized. [Industrial applicability]

[0102] The bundled fiber of the present invention, and the optical encoder using it, can be used in equipment installed in locations with strong external electromagnetic waves, as motion detection sensors for medical, industrial, and aerospace robots, and as rotation angle detection sensors for equipment susceptible to electromagnetic interference. Therefore, it has industrial applicability. [Explanation of Symbols]

[0103] 10… Bundle Fiber 11…Fiber bundling section 12…Fiber separation section 21A, 21B, 21C, 21D… Fiber 21a, 21b, 21c, 21d… Core 22a, 22b, 22c, 22d... clad 23... Covering part 24a, 24b, 24c, 24d… Wire grid polarizers

Claims

1. A polarization sensor including a bundle fiber having a fiber bundling portion which bundles multiple fibers consisting of a core and a cladding surrounding the outer circumference of the core, A reflective rotating polarizer is formed adjacent to one end of the aforementioned fiber bundling portion, with a light-reflective film formed on its back surface, An optical encoder having a light source that irradiates light toward the rotating polarizing plate, At one end of the fiber bundle, polarizers with polarization axes facing different directions are formed at the ends of the cores of each individual fiber. Of the plurality of fibers in the fiber bundling portion, at least one emits light outward from one end of the fiber bundling portion, and at least one of the plurality of fibers receives light from one end of the fiber bundling portion. An optical encoder characterized in that at least one of the fibers that emit light outward from one end of the fiber bundle is used for emitting light incident from a light source connected to the other end of the fiber bundle, and at least one of the plurality of fibers in the fiber bundle is used for propagating output polarization from the rotating polarizer.

2. The optical encoder according to claim 1, characterized in that the polarizer is a wire grid polarizer in which a plurality of light-shielding wires are arranged in a striped pattern at equal intervals along one direction.

3. The optical encoder according to claim 1 or 2, characterized in that a fiber separation section is formed on the other end of the fiber bundling section, in which each fiber is separated.

4. The optical encoder according to claim 1 or 2, characterized in that each of the polarizers is bonded to the end face of each of the cores.

5. The optical encoder according to claim 1 or 2, characterized in that each of the polarizers is integrally formed with the end of each of the cores.

6. The optical encoder according to claim 1 or 2, characterized in that the fiber bundle portion has N fibers (0 < N < 180, where N is an integer and a divisor of 180), and the orientation of the polarization axis of each polarizer formed at the end of each core is rotationally symmetrical by (180 / N)°.

Images