Optical fiber terminal structure and optical connection component

Abstract

The optical fiber terminal structure of the present application has a hollow optical fiber (1) having a hollow portion that transmits light, a flat glass (2) that covers the hollow portion, and an anti-reflection mechanism that prevents reflection of light transmitted through the flat glass (2). An example of the anti-reflection mechanism is a structure in which an anti-reflection film is applied to both surfaces of the flat glass (2). The thickness of the flat glass (2) is preferably 100 μm or less. The flat glass (2) can be bonded to the end surface of the hollow optical fiber (1) by a jig. Furthermore, the optical connection member of the present application brings the flat glasses (2) of two optical fiber terminal structures toward each other.

Description

Technical Field

[0001] This invention relates to fiber optic terminal structures and optical connection components. Background Technology

[0002] Optical connection components (optical connectors) that connect optical fibers, such as single-core FC connectors, SC connectors, MU connectors, LC connectors, or multi-core MT connectors, MPO connectors, will be developed based on technologies that allow the end faces of the optical fibers to physically contact each other. An overview of these technologies is described in detail in Non-Patent Document 1.

[0003] In recent years, hollow-core optical fibers have attracted attention as a potential breakthrough in breaking the limits of existing quartz-based optical fibers (see Patent Document 1). The core of this fiber is made of air, a significant difference from existing optical fibers with a solid glass core. Hollow-core optical fibers possess the following superior characteristics: (1) a transmission speed (group velocity) approximately 1.45 times higher; (2) a nonlinear coefficient as small as three digits; and (3) low dispersion. The characteristic in (1) is expected to reduce latency in online transactions and online games due to the lower refractive index of air compared to glass. The characteristics in (2) and (3) can significantly reduce the transmission capacity limitations of existing optical fibers with a glass (solid) core.

[0004] In existing optical fibers, the transmission capacity of each fiber is increased through multiplexing methods (wavelength division multiplexing, multi-level modulation). However, regardless of the multiplexing method used, the total energy required to transmit the total amount of data cannot be reduced. This means that the more capacity is increased, the more energy is required for transmission.

[0005] In existing glass-core optical fibers, signal degradation occurs due to nonlinear optical effects of the glass with increasing energy, and the glass core melts due to concentrated optical power, leading to transmission to the light source – a limitation known as the fiber melting limit (thermal damage limit). In single-mode fibers with a core diameter of around 10 μm, the limit is around 1 W, thus limiting the transmission capacity to around 100 Tbps. Therefore, it cannot cope with the exponentially increasing network traffic. By changing the core from solid (glass) to hollow (air), this limiting factor is expected to be significantly eliminated. Hollow-core optical fibers are anticipated to be the ultimate optical fiber achievable by humankind.

[0006] However, hollow optical fibers cannot utilize the detachable optical connection technology based on physical contact, as is possible with existing glass-core optical fibers (Non-Patent Document 1). As described in Patent Document 1, hollow optical fibers come in various forms, such as photonic bandgap fibers, Kagome fibers, and anti-resonance fibers, but all of them have a structure in which multiple thin-walled (less than 1 μm thick) glass inner tubes are arranged around the hollow region constituting the core (see Patent Document 1). Therefore, their ends are more fragile than those of solid optical fibers. If hollow optical fibers are brought into physical contact with each other, the ends may be damaged, and fragments may enter the hollow core, causing a deterioration in transmission characteristics. In addition to this factor, from the viewpoint of not deteriorating transmission characteristics, methods must be adopted to prevent foreign matter from entering the hollow core from the outside.

[0007] To address this problem, methods for protecting the hollow core have been investigated. For example, Patent Documents 2 and 3 provide methods that block the hollow core at the end of the optical fiber by melting the cladding portion, etc., to prevent the ingress of foreign matter and achieve a strength sufficient for physical contact. However, in such methods, it is difficult to maintain the transmission mode of the hollow optical fiber, and it is also difficult to suppress reflections generated at the boundary between the molten glass and air, leading to deterioration of transmission characteristics.

[0008] As a method other than melting, a terminal structure is disclosed that uses a protective portion with a cavity to cover the top of the hollow optical fiber, preventing foreign matter from entering the hollow portion (Patent Document 4). However, because there is a space (cavity) at the end face of the optical fiber, a gap of mm to cm is generated between the optical fiber end and the window on the top of the protective portion where an anti-reflective film is applied. Therefore, the light emitted from the optical fiber diffuses significantly, resulting in increased insertion loss when optically connected to each other via the window.

[0009] Existing technical documents

[0010] Non-patent literature

[0011] Non-patent literature 1: NTT Technology Journal, vol.12, No.12, 2007, pp.74-78

[0012] Patent documents

[0013] Patent Document 1: Japanese Patent Publication No. 2019-504350;

[0014] Patent Document 2: Japanese Patent Application Publication No. 2003-30765;

[0015] Patent Document 3: Japanese Patent Application Publication No. 2002-323625;

[0016] Patent document 4: U.S. Patent No. 7,373,062. Summary of the Invention

[0017] The problem the invention aims to solve

[0018] In view of this situation, the objective of this invention is to improve the transmission characteristics of hollow optical fibers.

[0019] Solution for solving the problem

[0020] To achieve the above objectives, the present invention is characterized by having: a hollow optical fiber having a hollow portion for transmitting light; a light-transmitting component covering the hollow portion; and an anti-reflection mechanism preventing reflection of light transmitted through the light-transmitting component.

[0021] A detailed description follows.

[0022] Invention Effects

[0023] According to the present invention, the transmission characteristics of hollow optical fibers can be improved. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the fiber optic terminal structure according to the first embodiment.

[0025] Figure 2 (a) is an end face view of the hollow optical fiber, and (b) is a view with adhesive coating.

[0026] Figure 3A Illustration (1 / 2) of an example of the bonding process.

[0027] Figure 3B Illustration diagram (2 / 2) for an example of the bonding process.

[0028] Figure 4 This is an explanatory diagram of the installation process of the fiber optic terminal structure according to the second embodiment.

[0029] Figure 5 This is an explanatory diagram illustrating the installation process of the fiber optic terminal structure in the first variation of the second embodiment.

[0030] Figure 6 This is an explanatory diagram illustrating the installation process of the fiber optic terminal structure in the second variation of the second embodiment.

[0031] Figure 7 This is another example of a light-transmitting component.

[0032] Figure 8 (a) is a schematic diagram of the fiber optic terminal structure of other variations, and (b) is a diagram of the fiber optic terminal structure of (a) viewed from the right.

[0033] Figure 9 A schematic diagram (1) of an optical connection component using other variations of the optical fiber terminal structure.

[0034] Figure 10 A schematic diagram (2) of an optical connection component using other variations of the optical fiber terminal structure. Detailed Implementation

[0035] [First Implementation Method]

[0036] Figure 1 This illustrates the fiber optic terminal structure according to a first embodiment of the present invention. In this embodiment, a disc-shaped flat glass plate 2, with anti-reflective films (not shown) applied to both sides, is bonded to the end face of a hollow optical fiber 1 (sometimes simply referred to as "optical fiber") to serve as a light-transmitting component. For example... Figure 2 As shown in (a), the structure of the hollow optical fiber 1 is as follows: six thin-walled glass inner tubes 4 are arranged on the radial inner edge of the hollow part H covered by cylindrical glass 3. The core for transmitting light is located in the region at the radial center of the hollow part H (in Figure 2 (The area in (a) is represented by the dashed circle). The hollow region of the inner tube 4 constitutes the hollow portion H, but including this hollow region, the inner tube 4 functions as a cladding. In addition, a jacket (not shown) is sometimes applied to the outside of the glass 3 as needed. The outer diameter of the flat glass 2 is smaller than the through hole 61 of the ferrule 6 described later, and is approximately the same as the outer diameter of the hollow optical fiber 1.

[0037] Flat glass 2 is bonded to the end face of hollow optical fiber 1. During bonding, adhesive 5 is applied... Figure 2 As shown in (b), the adhesive 5 is applied only to the glass 3 at the end of the hollow optical fiber 1, so that the adhesive 5 does not adhere to the hollow portion H containing the inner tube 4. The flat glass 2 can cover the hollow portion H.

[0038] Figure 3A , Figure 3B This illustrates an example of a bonding process. After inserting the hollow optical fiber 1 into the ferrule 6, which has a through-hole 61 for accommodating the hollow optical fiber 1 ( Figure 3A (a) The top of the hollow fiber 1 is cut (cleave) and temporarily retracted into the ferrule 6. Figure 3A (b)). The material of the insert 6 is preferably zirconium oxide, but is not limited thereto.

[0039] On the other hand, adhesive 5 is coated onto the flat glass 2. This coating is performed using an adhesive transfer jig 8 and an adsorption jig 7 that adsorbs and holds the flat glass 2. The adhesive transfer jig 8 has a protruding annular portion 81 slightly smaller than the glass region of the hollow optical fiber 1. As the adhesive 5, for example, a thermosetting resin or an ultraviolet-curable resin can be used, but it is not limited to these. The adsorption jig 7 is, for example, composed of a ferrule 6a and a hollow optical fiber 1a. Figure 3A(c)). Here, the hollow optical fiber 1a is positioned with its tip as... Figure 3A As shown in (c), the spacer 6a is fixed in a state where only the gap A is exposed from the end face of the ferrule 6a. By having an adsorption pump (not shown) at one end of the hollow optical fiber 1a, the flat glass 2 can be adsorbed and held.

[0040] The transfer (coating) of adhesive 5 onto the flat glass 2 is performed using an adhesive transfer fixture 8. Figure 3A (d)). The adhesive transfer jig 8 has a protrusion 81 of an annulus slightly smaller than the glass region of the hollow optical fiber 1. By bringing the adhesive transfer jig 8 close to the adhesive 5 coated on the plate 5a and pressing the adhesive 5 against the protrusion 81, and then removing the adhesive transfer jig 8, the adhesive 5 is transferred to the protrusion 81. Figure 3A (d)

[0041] Next, the transferred adhesive 5 is transferred onto the flat glass 2 that is adsorbed and held by the adsorption fixture 7. Figure 3A (e)). For example Figure 3B As shown in (f), a flat glass plate 2 coated with adhesive 5 is inserted into a ferrule 6 containing a hollow optical fiber 1. The ferrule 6 is in contact with the end face of the ferrule 6a of the adsorption clamp 7, and the hollow optical fiber 1 is pressed in the direction of the arrow in the figure to contact the flat glass plate 2. Figure 3B (g)) cures the adhesive 5. Additionally, the adsorption fixture 7 and the adhesive transfer fixture 8 can also coat or transfer the adhesive 5 onto the hollow optical fiber 1, instead of onto the flat glass 2 (see reference). Figure 2 (b)

[0042] Through this process, the glass 3 at the end face of the hollow optical fiber 1 and the flat glass 2 are bonded together within the ferrule 6. This seals the end face of the hollow optical fiber 1, making the distance from the side of the flat glass 2 facing the end face of the hollow optical fiber 1 to the sealing surface of the hollow portion H (which is substantially the same as the end face of the hollow optical fiber 1) almost zero. Therefore, compared to existing examples with a cavity, the diffusion of light emitted from the hollow optical fiber 1 can be minimized, thus suppressing the increase in insertion loss of the optical connectors using it and improving transmission characteristics.

[0043] In this embodiment, the optical connection component refers to a component that connects two optical fiber terminal structures (a first optical fiber terminal structure and a second optical fiber terminal structure) with the flat glass plates 2, 2 of each optical fiber terminal structure facing each other. The facing of the flat glass plates 2, 2 is achieved by mating the ferrules 6, 6 of the two optical fiber terminal structures together. Furthermore, the optical connection component of this embodiment can be installed in a connector; an optical connection component installed in a connector can achieve the mating state of the ferrules 6, 6, thus realizing the optical transmission characteristics of the present invention.

[0044] Furthermore, preferably in this state, the hollow optical fiber 1 is bonded to the ferrule 6 by injecting adhesive 51 from the rear end of the ferrule 6. Figure 3B (h) Specifically, the hollow optical fiber 1 is first slightly inserted into the through hole 61 from the rear end of the ferrule 6. The insertion of the hollow optical fiber 1 is easily achieved by using the chamfered portion 62 formed around the through hole 61 in the rear end of the ferrule 6 as a guide. Next, adhesive 51 is applied to the chamfered portion 62. Then, the hollow optical fiber 1 is further inserted to a predetermined position. In this embodiment, the predetermined position refers to a position close to the flat glass 2 until it can be bonded to the flat glass 2. As a result, as ( Figure 3B As shown in (h), adhesive 51 is applied to a portion of the sidewall of the hollow optical fiber 1 in the through-hole 61 and cured. Meanwhile, the flat glass 2 is fixed at this time at a position where it is recessed inward by a distance A from the ferrule tip.

[0045] The thickness of the flat glass 2 is preferably 100 μm or less. The reasoning is as follows: When cutting optical fibers with a commercially available cleaver, the cutting angle deviates from 90 degrees, with this deviation ranging from approximately 1 degree. If the flat glass 2 is bonded to the end face of the optical fiber with the cutting angle deviating from 90 degrees, this deviation directly affects the optical axis offset (since both ends of the flat glass 2 are air, the optical axis is offset parallel to the ground). This optical axis offset is proportional to the thickness of the flat glass 2. The core diameter of the hollow optical fiber 1 is approximately 20 μm to 50 μm, as in Patent Document 1. Therefore, to construct a low-loss optical connection component, this optical axis offset needs to be set to approximately 1 μm or less. When the end face of the hollow optical fiber 1 is fitted with a flat glass 2 of refractive index 1.45 with a cutting angle deviation of 1 degree (the worst-case scenario), and its thickness is 100 μm, the optical axis offset is only about 0.5 μm. Therefore, if a flat glass 2 with a thickness of less than 100 μm is used, and the ferrule end faces of the optical fiber terminal structure of this embodiment are mated together to form an optical connection component, low-loss transmission can be achieved even considering manufacturing tolerances of mechanical components.

[0046] The spacing A is preferably 5 μm or more and 50 μm or less. This spacing A can be easily specified using the adsorption clamp 7. In this case, when the end faces of the inserts 6, 6 are brought together to form an optical connection component, the spacing between the flat glass plates 2, 2 (the distance between one side of one flat glass plate 2 and the side of the other flat glass plate 2 facing that side) can be set to 10 μm or more and 100 μm or less. Since the flat glass plates 2, 2 do not contact each other, there is no need to worry about damage to the flat glass plates 2, and stable optical connection (loading and unloading) can be repeatedly performed.

[0047] The following explains why the spacing between the two flat glass plates 2 and 2 should be less than 100 μm. When connecting single-mode fibers with an MFD (mode field diameter) of 10 μm and an NA of 0.11 with a gap, the insertion loss is approximately 0.5 dB when the spacing is 100 μm. Compared to single-mode fiber, hollow fiber 1 has a larger MFD and a smaller NA due to its structural characteristics. Therefore, when connecting hollow fibers 1 and 1 with a gap, the loss is less compared to the single-mode fiber case. This means that if the spacing is set to less than 100 μm, optical transmission can be achieved with an insertion loss of less than 0.5 dB.

[0048] In this embodiment, the distance between the fiber end faces is equal to two thicknesses (approximately 200 μm) of the flat glass plates 2, 2. However, in the case of an air-glass-air path, light diffusion is suppressed by refraction through the glass plates. Therefore, when the optical connection component is constructed with the spacing between the flat glass plates 2, which serve as the glass plates, set to 100 μm or less, low insertion loss transmission can be achieved. Furthermore, if the spacing between the flat glass plates 2, 2 is on the order of wavelength (a few μm or less), a small change in the gap may cause a large change in transmittance, but this problem can be avoided if the spacing is 10 μm or more.

[0049] The adhesive clamp 7 during adhesive curing can be configured in two ways: either adsorbing the flat glass 2 or pressurizing air (gas) onto the flat glass 2. When the adhesive 5 is cured in the adsorbed state, the surface of the flat glass 2 can be perpendicular to the axis of the ferrule 6 (the optical axis direction of the hollow optical fiber 1), allowing light from the hollow optical fiber 1 to exit from the end face of the ferrule 6 without optical axis deviation. Furthermore, when the adhesive 5 is cured under pressure, the end face of the hollow optical fiber 1 and the flat glass 2 can be tightly bonded together with the cut surface, resulting in a more reliable seal.

[0050] Taking into account the coefficients of thermal expansion of ferrule 6 and hollow fiber 1, the gap A can be determined in such a way that the flat glass 2 will not be exposed from the end face of ferrule 6 within the operating temperature range. With the glass fiber bonded only to the rear end of the 10mm long zirconia ferrule, when the temperature drops by 50 degrees Celsius, the fiber shifts 8μm in the exposed direction due to the difference in thermal expansion coefficients. Assuming such an operating environment, if the gap A is set to approximately 20μm, the flat glass 2 will not be exposed from the end face of ferrule 6 even with significant changes in ambient temperature, and the gap will not be on the order of wavelength. Therefore, a stable optical connection component can be provided under various temperature conditions.

[0051] Because anti-reflective coatings (not shown) are applied to both sides of the flat glass 2, no reflection occurs at the interfaces between the hollow optical fiber 1 (air) and the flat glass 2, and between the flat glass 2 and the space A located at the top of the ferrule 6, thus forming an optical connection component with good transmission characteristics. Based on the above effects, an optical connection component that does not suffer from transmission characteristic degradation due to melting and solidification, as is the case in the prior art, can be provided.

[0052] Furthermore, as a fiber optic terminal structure, it is not limited to Figure 3B The way shown in (i) is to house the insert 6, for example, it could also be to remove the insert 6. Figure 1 ).

[0053] [Second Implementation]

[0054] Figure 4 This illustrates the fiber optic terminal structure according to a second embodiment of the present invention. The main difference between this embodiment and the first embodiment is that a recess 63 for receiving the flat glass 2 is provided at the top end of the ferrule 6, and the top end of the ferrule 6 (the portion where the through hole 61 communicates with the recess 63) is chamfered. Here, the outer diameter (diameter) of the flat glass 2 is set to be larger than the chamfer range L1 and is the diameter L2 of the recess 63 (see reference). Figure 4 Below (d). The flat portion 63a of the recess 63 is approximately perpendicular to the axial direction of the ferrule 6 (the optical axis direction of the hollow optical fiber 1). Furthermore, during bonding, in order to achieve a positional relationship where the flat glass 2 is retracted from the top surface of the ferrule 6, the depth of the recess 63 is greater than the thickness of the flat glass 2. The difference (depth of the recess 63 - thickness of the flat glass 2) is preferably set to be 5 μm or more and 50 μm or less.

[0055] The installation procedure of this embodiment is described below. After inserting the hollow optical fiber 1 into the ferrule 6, the top end is cut ( Figure 4 (a) Before retracting the hollow optical fiber 1, adhesive 5 is applied to the recess 63 of the chamfered portion 64, which includes the through hole 61 for the ferrule 6. Figure 4 (b)). Next, the flat glass 2 is pressed against the end face of the hollow optical fiber 1 and pressed into the flat portion 63a of the recess 63. Figure 4 (c)). This process can use, for example, Figure 3A The adsorption fixture 7 shown in (c) is used for this purpose. Alternatively, it can be performed as shown in [the diagram]. Figure 3A As shown in (e), adhesive 5 is transferred onto the flat glass 2 and bonded to the portion of the glass 3 at the end of the hollow optical fiber 1. Alternatively, adhesive 5 can be directly applied to the flat portion 63a of the recess 63 (prior art).

[0056] Furthermore, the outer diameter of the flat glass 2 is set to be greater than the chamfer range L1 and less than the diameter of the recess 63. When the flat glass 2 is housed in the ferrule 6, it is held in place by the flat portion 63a of the recess 63. During this series of processes, as the hollow optical fiber 1 retracts through the through hole 61, the adhesive 5 coated on the chamfer portion 64 flows into the through hole 61 through the side of the hollow optical fiber 1. Figure 4 (c) By adopting such a process, while the end face of the hollow optical fiber 1 is in contact with the flat glass 2, the bonding of the flat glass 2 to the recess 63 of the ferrule 6 and the bonding of the near end of the hollow optical fiber 1 to the ferrule 6 can be performed simultaneously, thereby simplifying the installation process and reducing the installation cost.

[0057] Here, because the flat glass 2 is bonded to the flat portion 63a of the recess 63 of the ferrule 6, the surface of the flat glass 2 is perpendicular to the axis of the ferrule 6 (the optical axis direction of the hollow fiber 1). Therefore, even if the cut angle of the hollow fiber 1 is not 90 degrees, the optical axis will not shift. The reason is that when the cut angle is not 90 degrees, a small gap is generated in the optical path between the two, but since this gap is air (by appropriately designing the amount of adhesive 5, etc., so that the adhesive 5 can reliably flow into the through hole 61), it becomes the same refractive index as the core of the hollow fiber 1, and the optical axis perpendicular to the surface of the flat glass 2 remains unchanged.

[0058] Furthermore, because the hollow optical fiber 1 is bonded near the top of the ferrule 6, their relative positions remain almost unchanged even with temperature variations. Therefore, there is no need to worry about applying excessive pressure to the flat glass 2 that the end face of the hollow optical fiber 1 contacts, or about deviations on the order of μm caused by pulling the optical fiber.

[0059] However, due to the difference in thermal expansion coefficients between glass and zirconium oxide, the optical fiber exhibits pistoning, resulting in axial displacement on the order of tens of nanometers. This displacement is directly transmitted to the flat glass 2 that contacts the end face of the hollow optical fiber 1, potentially leading to breakage in the worst-case scenario.

[0060] This concern can be eliminated by providing a chamfered portion 64 in the ferrule 6. This is because, in the fiber optic terminal structure of this embodiment, the chamfered portion 64 has an adhesive 5 or space with a hardness lower than that of zirconium oxide. Even if pressure caused by fiber protrusion is applied to the flat glass 2, causing the position of the flat glass 2 to shift along the axial direction (vertical direction in the figure) of the fiber, the presence of the adhesive 5 or space can mitigate the stress, thus preventing damage to the flat glass 2. The larger the area of ​​the chamfered portion 64, the more effective the stress mitigation. For example, when the radius of the hollow fiber 1 is a, the chamfering can be performed with a chamfering angle of Ca (obliquely chamfered at a distance a from the apex of the angle), Ra (rounded chamfered with radius a), or the apex angle θ of the chamfer can be set to 90 degrees or more (see reference). Figure 4 (d) can achieve sufficient stress relief.

[0061] Furthermore, the hollow optical fiber 1 protrudes from the through-hole 61 at the chamfered portion 64, but from the viewpoint of suppressing optical axis misalignment, it is preferable that the exposed length be short. On the other hand, from the viewpoint of stress relief, it is preferable to increase the bonding area between the flat glass 2 and the adhesive 5. If the apex angle θ of the chamfer is set to 90 degrees or more, it is possible to balance ensuring the bonding area between the flat glass 2 and the adhesive 5 and shortening the length of the hollow optical fiber 1 protruding from the through-hole 61.

[0062] Based on the above, compared with existing examples, the gap between the hollow optical fiber 1 and the flat glass 2 can be minimized, thus minimizing the diffusion of light emitted from the hollow optical fiber 1 and enabling an optical fiber termination structure without optical axis offset.

[0063] Furthermore, since the flat glass 2 is positioned at a distance of 5μm to 50μm from the end face of the ferrule 6, when the ferrules 6 are joined end-to-end to form an optical connection component, contact between the flat glass 2 and 6 can be avoided over a wide temperature range, and their spacing can be maintained at 10μm to 100μm, thus providing a low-loss optical connection component. Additionally, since anti-reflective coatings are applied to both sides of the flat glass 2, no reflection occurs at the interfaces between the hollow fiber 1 (air) and the flat glass 2, and between the flat glass 2 and the space located at the top end of the ferrule 6, enabling the formation of an optical connection component with excellent transmission characteristics. Based on these effects, an optical connection component that does not suffer from transmission characteristic degradation due to melting and solidification, as is the case in the prior art, can be provided.

[0064] Alternatively, the hollow optical fiber 1 can be bonded to the rear end of the ferrule 6 by injecting adhesive 51 from the rear end of the ferrule 6 (see reference). Figure 3B (h)). In this way, the bonding strength between the hollow optical fiber 1 and the ferrule 6 can be made stronger.

[0065] [First variation of the second embodiment]

[0066] Figure 5 This illustrates a fiber optic terminal structure of a first variation of the second embodiment of the present invention. This embodiment is related to... Figure 4 The main difference in the illustrated embodiment is the absence of the chamfered portion 64 of the insert 6. The absence of the chamfered portion 64 allows for the use of a lower-cost insert. The outer diameter of the flat glass 2 is set to be larger than the through-hole 61 of the insert 6 and less than the diameter of the recess 63. Furthermore, during bonding, in order to achieve a positional relationship where the flat glass 2 recedes from the top surface of the insert 6, the depth of the recess 63 is greater than the thickness of the flat glass 2. The difference (depth of the recess 63 - thickness of the flat glass 2) is preferably set to be 5 μm or more and 50 μm or less.

[0067] The installation procedure of this embodiment is described below. The cut hollow optical fiber 1 is retracted into the through hole 61 of the ferrule 6. Figure 5 (a)). In this state, the flat glass 2 is pressed onto the flat portion 63a of the recess 63 of the insert 6 and bonded together. Figure 5 (b)). During this bonding process, it is possible to use, for example... Figure 3A The method of transferring adhesive to the portion of the flat glass 2 that abuts against the flat portion 63a of the recess 63, as shown, or the method of directly applying adhesive 5 to the flat portion 63a of the recess 63 (prior art) is performed.

[0068] After bonding, the hollow optical fiber 1 inside the ferrule 6 is raised to the specified position. Figure 5 (c)). The specified position refers to a position that does not contact the flat glass 2 but maintains a specified interval. For example, by placing a camera (not shown) above the figure (on the side of the flat glass 2 opposite to the ferrule 6), the tip of the hollow optical fiber 1 can be positioned at the specified position by monitoring the through-hole 61 of the ferrule 6 through the flat glass 2. In this state, adhesive 51 is injected from the rear end of the ferrule 6, thereby bonding ( Figure 5 (d) (refer to) Figure 3B (h)

[0069] Furthermore, the specified spacing is preferably set to approximately 10 μm. This is because, when the glass fiber is bonded only to the rear end of the 10 mm long zirconia ferrule, the fiber will move 8 μm towards the exposed direction due to the difference in thermal expansion coefficients when the temperature drops by 50 degrees. Therefore, if the spacing is set to approximately 10 μm, the tip of the hollow fiber 1 will not come into contact with the flat glass 2 even when the ambient temperature changes significantly.

[0070] Therefore, the gap between the hollow optical fiber 1 and the flat glass 2 can be minimized without worrying about damage to the flat glass 2, thus enabling an optical fiber termination structure that suppresses light diffusion. Furthermore, since the flat glass 2 is bonded to the recess 63 of the ferrule 6, the surface of the flat glass 2 is perpendicular to the axis of the ferrule 6 (the optical axis direction of the hollow optical fiber 1). Therefore, even if the cut angle of the hollow optical fiber 1 is not 90 degrees, the optical axis will not shift. Although there is a gap of approximately 10 μm in the optical path between them, since this gap is filled with air (by appropriately designing the amount of adhesive 5 to ensure reliable flow of adhesive 5 into the through-hole 61), it has the same refractive index as the core of the hollow optical fiber 1, and the optical axis perpendicular to the surface of the flat glass 2 remains unchanged.

[0071] Based on the above, compared with existing examples, by minimizing the spacing between the hollow optical fiber 1 and the flat glass 2, the diffusion of light emitted from the hollow optical fiber 1 can be minimized, and an optical fiber termination structure without optical axis offset can be achieved.

[0072] Because the top of the flat glass 2 is positioned 5μm to 50μm behind the end face of the ferrule 6, contact between the flat glass 2 can be avoided when the end faces of the ferrules 6 are brought together to form an optical connection component, and the spacing between them can be 10μm to 100μm. Therefore, light diffusion can be suppressed without worrying about damage to the flat glass 2, enabling repeated, stable, low-loss optical connections (installation and removal). Furthermore, since anti-reflective films are applied to both sides of the flat glass 2, reflections do not occur at the interfaces between the hollow fiber 1 (air) and the flat glass 2, or between the flat glass 2 and the space located at the top of the ferrule 6. Therefore, an optical connection component that does not suffer from transmission characteristic degradation due to melting and solidification, as is the case in the prior art, can be provided.

[0073] [Second variation of the second embodiment]

[0074] Figure 6 This describes a fiber optic terminal structure of a second variation of the second embodiment of the present invention. This embodiment is similar to... Figure 4 The main difference in the illustrated embodiment is that the insert 6 does not have a recess 63. Therefore, a chamfered portion 64 is formed on the end face of the insert 6 to chamfer the through hole 61 of the insert 6. Since there is no recess 63, it has the advantage of being able to use a lower-cost insert. The outer diameter of the flat glass 2 is set to be larger than the chamfered range L1 (see reference). Figure 4 (d) and smaller than the outer diameter of the ferrule 6.

[0075] The installation procedure of this embodiment is described below. After inserting the hollow optical fiber 1 into the ferrule 6, the top end is cut ( Figure 6(a) Before retracting the hollow optical fiber 1, adhesive 5 is applied to the chamfered portion 64. Figure 6 (b) Next, press the flat glass 2 onto the end face of the hollow optical fiber 1 and make it contact the end face of the ferrule 6. Figure 6 (c)). Here, the application of adhesive 5 to the chamfered portion 64 is done using, as shown in the image. Figure 3A The method of transferring adhesive 5 onto the part of the flat glass 2 that abuts against the insert 6 as shown, or the method of directly applying adhesive to the chamfered portion 64 of the end face of the insert 6 (prior art).

[0076] During this series of processes, as the hollow optical fiber 1 retracts through the through hole 61, the adhesive 5 coated on the chamfered portion 64 flows into the through hole 61 through the side of the hollow optical fiber 1. Figure 6 (c) By adopting such a process, while the end face of the hollow optical fiber 1 is in contact with the flat glass 2, the bonding of the flat glass 2 to the end face of the ferrule 6 and the bonding of the near top part of the hollow optical fiber 1 to the ferrule 6 can be performed simultaneously, thereby simplifying the installation process and reducing the installation cost.

[0077] Here, since the flat glass 2 is bonded to the end face of the ferrule 6, the surface of the flat glass 2 is perpendicular to the axis of the ferrule 6 (the optical axis direction of the hollow fiber 1). Therefore, even if the cut angle of the hollow fiber 1 is not 90 degrees, the optical axis will not shift. Even if a small gap is generated in the optical path between the two when the cut angle is not 90 degrees, since this gap is filled with air (by appropriately designing the amount of adhesive 5, etc., so that the adhesive 5 can reliably flow into the through hole 61), it has the same refractive index as the core of the hollow fiber 1, and the optical axis perpendicular to the surface of the flat glass 2 remains unchanged.

[0078] Furthermore, since the hollow optical fiber 1 is bonded to the top of the ferrule 6, their relative positions remain almost unchanged even with temperature variations. Therefore, there is no need to worry about applying excessive pressure to the flat glass 2 that the end face of the hollow optical fiber 1 contacts, or about deviations on the order of μm caused by pulling the optical fiber.

[0079] However, the fiber optic protrusion caused by the difference in thermal expansion coefficients between glass and zirconium oxide results in a positional shift on the order of tens of nanometers along the axial direction. This positional shift is directly transmitted to the flat glass 2 that contacts the end face of the hollow fiber 1, raising concerns that, in the worst-case scenario, it could lead to breakage.

[0080] This concern can be eliminated by providing a chamfered portion 64 in the ferrule 6. This is because, in the fiber optic terminal structure of this embodiment, the chamfered portion 64 has an adhesive 5 or space with a hardness lower than that of zirconium oxide. Even if pressure caused by the protrusion of the optical fiber is applied to the flat glass 2, causing the position of the flat glass 2 to shift along the axial direction of the optical fiber (vertical direction in the figure), the presence of the adhesive 5 or space can mitigate the stress, thus preventing damage to the flat glass 2. The larger the area of ​​the chamfered portion, the more effective the stress mitigation.

[0081] For example, when the radius of the hollow optical fiber 1 is a, the chamfer can be made by using a chamfer of Ca or Ra or higher, or by setting the apex angle θ of the chamfer to 90 degrees or higher (see reference). Figure 4 (d) can achieve sufficient stress relief. If the apex angle θ of the chamfer is set to 90 degrees or more, it can ensure the bonding area between the flat glass 2 and the adhesive 5, and shorten the length of the hollow optical fiber 1 exposed from the through hole 61.

[0082] Based on the above, compared with existing examples, by minimizing the spacing between the hollow optical fiber 1 and the flat glass 2, the diffusion of light emitted from the hollow optical fiber 1 can be minimized, and an optical fiber termination structure without optical axis offset can be achieved.

[0083] like Figure 6 As shown in (d), the optical connection components connecting the fiber optic terminal structures are configured to have spacers 9. The spacer 9 is preferably annular in shape, with its inner diameter being larger than the outer diameter of the flat glass 2, and its outer diameter being less than or equal to the outer diameter of the ferrule 6. Furthermore, the thickness of the spacer 9 is greater than the thickness of the flat glass 2. Preferably, the thickness of the spacer 9 is 5 μm or more but less than 50 μm thicker than the thickness of the flat glass 2. Additionally, the structure having this spacer 9 can also be used as a fiber optic terminal structure.

[0084] Here, the optical connection component in this embodiment refers to a component that connects two optical fiber terminal structures having spacer 9, with the flat glass plates 2, 2 of each optical fiber terminal structure facing each other. Furthermore, the spacer 9 can surround the flat glass plate 2 bonded to the end face of the ferrule 6. Additionally, the spacer 9 can be appropriately bonded to the end face of the ferrule 6 (in... Figure 6 (Illustration omitted in (d)).

[0085] In through Figure 6The fiber optic terminal structure shown has a spacer 9 between its end faces. When the ferrules 6 and 6 are positioned with their end faces facing each other to form an optical connection component, the flat glass plates 2 and 2 can be prevented from contacting each other, and their spacing is between 10 μm and 100 μm. Therefore, when fiber optic terminal structures without optical axis misalignment are connected, light diffusion can be suppressed without worrying about damage to the flat glass plates 2, and stable, low-loss optical connections (installation and removal) can be repeatedly performed.

[0086] Furthermore, since anti-reflective films are applied to both sides of the flat glass 2, no reflection occurs at the interfaces between the hollow optical fiber 1 (air) and the flat glass 2, and between the flat glass 2 and the space located at the top of the ferrule 6, thus enabling the formation of an optical connection component with excellent transmission characteristics. Therefore, it is possible to provide an optical connection component that does not suffer from transmission characteristic degradation due to melting and solidification, as is the case in the prior art.

[0087] In addition, not limited to Figure 6 The fiber optic termination structure of the example implementation can also be used in a shape where the ferrule 6 does not have the chamfer 64. In this case, it has the advantage of being able to use a lower-cost ferrule. In this case, as Figure 5 As in the example implementation, it is preferable to ensure that the hollow optical fiber 1 and the flat glass 2 do not come into contact, and to bond them together with a predetermined interval in a manner that prevents them from coming into contact even when the temperature changes.

[0088] Furthermore, the spacer 9 does not need to be provided for each fiber optic terminal structure; it can be a single optical connection component. In this case, it is preferable that the thickness of the spacer 9 is at least 10 μm and less than 100 μm thicker than twice the thickness of the flat glass 2 (the combined thickness of the two flat glass pieces 2). The optical connection component in this embodiment refers to a component that connects two fiber optic terminal structures (a first fiber optic terminal structure with the spacer 9 and a second fiber optic terminal structure without the spacer 9) with the flat glass pieces 2, 2 of each fiber optic terminal structure facing each other. Additionally, the spacer 9 can surround the flat glass 2 bonded to the end face of the ferrule 6. Furthermore, the spacer 9 can be appropriately bonded to the end face of the ferrule 6.

[0089] [Other variations]

[0090] (a) In the above embodiments, flat glass 2 is used as the light-transmitting component, but it is not limited to this as long as it is a light-transmitting material; it can also be Si, resin, etc. The shape of the light-transmitting component does not necessarily have to be disc-shaped; it can also be a quadrilateral or other shapes. Furthermore, it can also be as follows: Figure 7The shape shown has the function of a plano-convex lens 10 or a prism 11. When the plano-convex lens 10 or prism 11 is used, the connection distance and connection direction can be freed, thus enabling the diversification of the structure of the optical connection component.

[0091] (b) As a hollow optical fiber, it is not limited to Figure 2 The optical fiber exemplified in (a) can be of various forms, such as photonic bandgap fiber, Kagome fiber, anti-resonance fiber, and NANF, as long as the core is hollow.

[0092] (c) The material of the insert 6 is not limited to zirconium oxide, but can also be other materials such as resin, glass, and metal.

[0093] (d) This embodiment illustrates a fiber optic termination structure using ferrule 6, but it can also be applied to other methods such as V-groove arrays (fiber optic termination structures without ferrules).

[0094] (e) An example of the end face or recess 63 of the ferrule 6, which serves as the bonding surface of the flat glass 2, is perpendicular to the axial direction of the ferrule 6 (the optical axis direction of the hollow optical fiber 1) (the optical axis direction of the hollow optical fiber 1 is aligned with the normal direction of the flat surface of the end face or recess 63 of the ferrule 6). For example, it may not be perpendicular, but rather tilted at any (prescribed) angle (preferably 8 degrees or less) relative to the axial direction of the ferrule 6. That is, the normal direction of the flat surface of the end face or recess 63 of the ferrule 6 may also be tilted relative to the axial direction of the ferrule 6. Figure 8 Example (a) illustrates an optical fiber termination structure in which the flat portion 63a of the recess 63 formed on the end face of the ferrule 6 is tilted. In this case, corresponding to the tilt angle of the flat portion 63a of the recess 63, the reflection angle of the returned light from the flat glass 2 becomes larger, and even without applying an anti-reflective coating with extremely low reflection to the flat glass 2, the specified reflection attenuation (e.g., 40 dB) can be achieved with good reproducibility. Since glass with an anti-reflective coating with extremely low reflection is not used, it has the advantage of being able to use lower-cost components. Furthermore, in the structure where the flat glass 2 has an anti-reflective coating with extremely low reflection, the wavelength band in which extremely low reflection can be achieved is limited due to factors such as the choice of material for the anti-reflective coating. In contrast, in the structure where the flat portion 63a of the recess 63 is tilted and the flat glass 2 does not have an anti-reflective coating with extremely low reflection, it also has the advantage of obtaining good characteristics of extremely low reflection over a wide wavelength range. However, although it is not extremely low reflection, by tilting the flat glass 2 based on the application of an anti-reflective coating, the connection loss caused by Fresnel reflection can be reduced. The anti-reflective film applied to both sides of the flat glass 2 and the inclination of the recess 63 (the flat portion 63a) described in this embodiment are related to... Figure 10 The example shown is an anti-reflective mechanism that uses the inclined fit of the end face of the insert 6 to prevent the reflection of light transmitted through the flat glass 2.

[0095] Figure 9 Show and explain how Figure 8 of (a), Figure 8 The preferred example of the optical connection components facing each other in the optical fiber termination structure shown in (b) is as follows. The optical fiber termination structure has: a ferrule 6 for housing a hollow optical fiber 1; a flange 20 for pressing into the ferrule 6; and a housing 21 for housing the flange 20. The optical connection components connect the optical fiber termination structures facing each other via an adapter 30.

[0096] When the housing 21 accommodates the flange 20, the keyway 22 of the housing 21 engages with the protrusion 23 of the flange 20, thus uniquely determining the relative rotation angle between the flange 20 and the housing 21. Here, when the ferrule 6 is pressed into the flange 20, for example, the shallowest part of the flat portion 63a of the inclined recess 63 engages with the keyway 22 of the housing 21. That is, the relative rotation angle between the ferrule 6 and the housing 21 is determined. Furthermore, when the fiber optic termination structures face each other to form an optical connection component, the protrusions 23 of the flanges 20 face each other by embedding the keys 24 of the housings 21 into the keyways 31 of the adapter 30. As a result, as... Figure 9 As shown, the optical connection component can be configured such that the shallowest portions of the flat portions 63a of the recess 63 face each other, and the inclined apex portions 2a of the flat glass 2 disposed on the flat portion 63a (the portions of the flat glass 2 disposed on the shallowest portion of the flat portion 63a of the recess 63) face each other (including the meaning of being roughly facing each other).

[0097] When the inclination of the flat portion 63a of the recess 63 is 8 degrees and the thickness of the flat glass 2 is 100 μm, the deviation of the optical axis in the flat glass 2 increases to about 4 μm. Figure 9 When the tilted apex portions 2a of the flat glass 2 arranged as shown face each other, no optical axis shift occurs as an optical connection component. When the optical fiber termination structures with the same tilt angle of the end face of the ferrule 6 or the flat portion 63a of the recess 63 are arranged facing each other to form an optical connection component, no optical axis shift occurs even if the tilt angle is arbitrary (even greater than 8 degrees). Therefore, by giving the flat glass 2 a specified tilt, a specified amount of reflection attenuation can be achieved with good reproducibility, and an optical connection component with low insertion loss can be constructed.

[0098] In addition, the above explanation also applies to Figure 10 The structure shown depicts inserts 6, 6, with their end faces inclined relative to their axial direction. For example... Figure 10As shown, most of the end faces of ferrules 6 and 6 are inclined, but a portion 65 and 65 radially outward from the central axis of ferrules 6 and 6 are not inclined, and become the contact surfaces when the fiber optic terminal structures face each other to form an optical connection component. The thickness and diameter of the flat glass plates 2 and 2, as well as the inclined portion of the end faces of ferrules 6 and 6, are determined in such a way that the flat glass plates 2 and 2 on the end faces of ferrules 6 and 6 do not contact each other when forming an optical connection component with a specified inclination angle.

[0099] Furthermore, the above explanation also applies to... Figure 1 The hollow optical fiber 1 is cut at an angle in the way shown in the method of bonding the hollow optical fiber 1 to the flat glass 2.

[0100] (f) In addition, it is also possible to implement a technology that appropriately combines the various technologies described in this embodiment.

[0101] (g) In addition, the shape, material, function, etc. of the constituent elements of the present invention may be appropriately changed without departing from the spirit of the present invention.

[0102] Explanation of reference numerals in the attached figures

[0103] 1, 1a: Hollow optical fiber

[0104] 2: Flat glass (light-transmitting component)

[0105] 3: Glass

[0106] 4: Inner tube

[0107] 5, 51: Adhesive

[0108] 5a: Board

[0109] 6, 6a: ferrule

[0110] 61: Through hole

[0111] 62: Chamfered section

[0112] 63: Concave

[0113] 63a: Flat area

[0114] 64: Chamfered section

[0115] 65: (partial area of ​​the inclined end face of the ferrule)

[0116] 7: Adsorption clamp (clamp)

[0117] 8: Adhesive transfer fixture (clamp)

[0118] 81: convex part

[0119] 9: Spacer

[0120] 10: Plano-convex lens

[0121] 11: Prism

[0122] 20: Flange

[0123] 21: Shell

[0124] 22: Keyway

[0125] 23: Protrusion

[0126] 24: Key

[0127] 30: Adapter

[0128] H: Hollow section

Claims

1. A fiber optic terminal structure, characterized in that, have: Hollow optical fiber has a hollow section for transmitting light; The light-transmitting component is a flat glass plate covering the hollow portion. The end face of the ferrule through which the hollow optical fiber is inserted has a recess for accommodating the light-transmitting component. The light-transmitting component is bonded to the flat portion of the recess. The fiber optic terminal structure has a chamfered portion where the bottom of the flat portion of the recess bevels the through hole of the ferrule. The outer diameter of the light-transmitting component is larger than the chamfer range of the chamfered portion. The light-transmitting component is recessed from the end face of the insert.

2. The optical fiber terminal structure according to claim 1, characterized in that, The thickness of the light-transmitting component is less than 100 μm.

3. The optical fiber terminal structure according to claim 1, characterized in that, The light-transmitting component is bonded to the end face of the hollow optical fiber by coating or transferring an adhesive onto the light-transmitting component or the hollow optical fiber.

4. The optical fiber terminal structure according to claim 1, characterized in that, The light-transmitting component is bonded to the end face of the ferrule through which the hollow optical fiber is inserted. The fiber optic terminal structure has spacers surrounding the light-transmitting component.

5. The optical fiber terminal structure according to claim 4, characterized in that, The thickness of the spacer is greater than the thickness of the light-transmitting component.

6. The optical fiber terminal structure according to claim 1, characterized in that, The normal direction of the end face of the hollow optical fiber is tilted at a specified angle relative to the axial direction of the hollow optical fiber.

7. The optical fiber terminal structure according to claim 1, characterized in that, The normal direction of the flat portion of the recess is inclined at a predetermined angle relative to the axial direction of the insert.

8. The optical fiber terminal structure according to claim 1, characterized in that, The light-transmitting component is positioned back from the end face of the insert.

9. The optical fiber terminal structure according to claim 4, characterized in that, The end face of the insert is inclined at a specified angle relative to the axial direction of the insert.

10. An optical connection component that connects a first optical fiber termination structure as claimed in claim 1 and a second optical fiber termination structure as claimed in claim 1. The light-transmitting component of the first optical fiber terminal structure faces the light-transmitting component of the second optical fiber terminal structure.

11. An optical connection component that connects a first optical fiber termination structure, which is the optical fiber termination structure according to claim 4, and a second optical fiber termination structure that does not have said spacer. The spacer of the first optical fiber terminal structure has a thickness twice that of the light-transmitting component, and the light-transmitting component of the first optical fiber terminal structure faces the light-transmitting component of the second optical fiber terminal structure.

12. An optical connection component that connects a first optical fiber termination structure and a second optical fiber termination structure as described in claim 6. The inclined apex of the light-transmitting component of the first optical fiber terminal structure faces the inclined apex of the light-transmitting component of the second optical fiber terminal structure.

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