Optical connector and optical connector connection structure

Abstract

The present invention relates to an optical connector provided with at least one optical fiber, and a lens element having at least one lens that couples light to an end face of the optical fiber. A distance (FLh) between the end face of the optical fiber and the vertex of the lens is expressed by the sum of a distance (FL) from the vertex of the lens to a focal point (F) located in the back surface direction of the lens, and an interval (δ) between the end face of the optical fiber and the focal point (F), and the interval (δ) is longer than 10 μm.

Description

[Technical field]

[0001] The present invention relates to an optical connector and an optical connector connection structure, and more particularly to a lens connector that connects optical fibers using a lens system and an optical connector connection structure including the same. [Background technology]

[0002] In constructing optical wiring using optical fibers in data centers, the demand for optical connectors for backplanes (BP) is increasing to cope with the increasing density of optical wiring. In addition, there is an increasing demand for long-distance transmission and large-capacity transmission, and the use of single-mode (SM) optical fibers that can meet these requirements as BP optical connectors is on the rise. Furthermore, in order to cope with the large scale caused by the increase in data communication volume, the use of multi-core optical connectors for BP optical connectors is also being considered.

[0003] There are two known methods for connecting optical fibers in BP optical connectors: the physical contact (PC) method and the lens method. In the PC method, the optical fibers are physically connected by butting the end faces of the optical fibers in the optical fiber array to be connected against each other with a pressing force, which brings them into physical contact. However, since BP optical connectors are generally used in places that are difficult to clean, there is a concern that dust in the optical connection part may deteriorate the communication quality. For example, if the optical path is blocked by dust, the insertion loss (optical power loss) increases, and dust may be trapped and obstruct the physical contact. Furthermore, in the PC method, as the number of optical fiber cores increases, the pressing force per board becomes excessive, making it difficult to expand the number of cores.

[0004] Meanwhile, in recent years, lens-type multi-core connectors have been attracting attention due to the demand for even greater number of cores in optical connectors. In the lens type, a lens array having lenses corresponding to each optical fiber of an optical fiber array is provided in an optical connector, and the optical connectors provided with the lens array are fixed opposite each other to optically connect the optical fibers through the lenses. In such a lens type, the beam diameter of the optical fiber is expanded through the lens, so the effect of dust is reduced, and the burn of the end face of the optical fiber due to dust is also suppressed by reducing the power density of the connection part. Furthermore, since the optical fibers can be connected to each other without contact, the pressing force can be made constant regardless of the number of cores of the optical fiber.

[0005] As an example of a connection structure for such a lens-type multi-core connector, Patent Document 1 discloses an optical connector connection structure in which two optical connectors each having a multi-core optical fiber are joined via a lens array for optical connectors that has lenses formed from a transparent resin. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2003-107277 A

[0007] Incidentally, 100 Gigabit Ethernet (registered trademark) optical transmission systems are now widely used, and research is ongoing into improving transmission characteristics such as transmission distance and transmission speed. Such optical transmission systems are used with a maximum input optical power of approximately +10.5 dBm.

[0008] However, when a conventional optical connector structure that connects multi-core optical fibers using a lens method is used in a high-power optical transmission system exceeding +20 dBm, such as a wavelength division multiplexing system, a small amount of light is absorbed in the plastic lens and converted into heat, which causes the temperature of the plastic lens in the optical path to rise. When the temperature of the plastic lens rises, the effective refractive index changes, causing a shift in the distance from the lens to the ideal focal point. As the ideal focal position changes, the focus shifts relative to the optical fiber core, raising concerns that this could lead to increased insertion loss. Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been made in consideration of the above problems, and has an object to provide a lens-type optical connector that can suppress insertion loss even when high-power light is input. [Means for solving the problem]

[0010] An optical connector according to a representative embodiment of the present invention comprises at least one optical fiber and a lens element having at least one lens that couples light to an end face of the optical fiber, and is characterized in that the distance FLh (μm) between the end face of the optical fiber and the apex of the lens is expressed as the sum of the distance FL (μm) from the apex of the lens to a focal point F located toward the back surface of the lens and the distance δ (μm) between the end face of the optical fiber and the focal point F, and the distance δ is longer than 10 μm. Effect of the Invention

[0011] According to the optical connector of the present invention, it is possible to suppress insertion loss even when high light power is input. [Brief description of the drawings]

[0012] [Figure 1] 1 is a perspective view showing the appearance of an optical connector according to a first embodiment. [Diagram 2]FIG. 1 is an exploded perspective view showing a configuration of an optical connector according to a first embodiment. [Diagram 3] 3 is a diagram showing a schematic diagram of a joint portion between an optical fiber and a lens element in the optical connector according to the first embodiment. FIG. [Figure 4A] 5A to 5C are diagrams illustrating an example of a method for joining an optical fiber and a lens element in the optical connector according to the first embodiment. [Figure 4B] 5A to 5C are diagrams illustrating an example of a method for joining an optical fiber and a lens element in the optical connector according to the first embodiment. [Figure 4C] 5A to 5C are diagrams illustrating an example of a method for joining an optical fiber and a lens element in the optical connector according to the first embodiment. [Figure 5A] 5A to 5C are diagrams illustrating another example of a method for joining an optical fiber and a lens element in the optical connector according to the first embodiment. [Figure 5B] 5A to 5C are diagrams illustrating another example of a method for joining an optical fiber and a lens element in the optical connector according to the first embodiment. [Figure 5C] 5A to 5C are diagrams illustrating another example of a method for joining an optical fiber and a lens element in the optical connector according to the first embodiment. [Figure 5D] 5A to 5C are diagrams illustrating another example of a method for joining an optical fiber and a lens element in the optical connector according to the first embodiment. [Figure 6] FIG. 5B is a diagram showing another example of an optical fiber used in the joining method shown in FIGS. 5A to 5D. [Figure 7] 4 is a diagram showing a schematic diagram of the relationship between the distance FLh, the distance FL, and the interval δ in the optical connector according to the first embodiment. FIG. [Figure 8] FIG. 11 is a schematic diagram for explaining an equation for calculating a distance FL. [Figure 9] 10 is a diagram showing a schematic diagram of a joint portion between an optical fiber and a lens element in an optical connector according to a second embodiment. FIG. [Figure 10] 11 is a diagram showing a schematic diagram of the relationship between the distance FLh, the distance FL, and the interval δ in the optical connector according to the second embodiment. FIG. [Figure 11]4 is a diagram showing the relationship between the incident light power and the insertion loss when δ=approximately 23 for the optical connector according to the first embodiment. FIG. [Figure 12] 4 is a diagram showing the relationship between the incident light power and the insertion loss when δ=approximately 33 for the optical connector according to the first embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] 1. Overview of the embodiment First, an overview of a representative embodiment of the present invention will be described. In the following description, for example, reference numerals in the drawings corresponding to components of the present invention are given in parentheses.

[0014] [1] An optical connector (10) according to a representative embodiment of the present invention comprises at least one optical fiber (18) and a lens element (14) having at least one lens (44) that couples light to an end face of the optical fiber, wherein a distance FLh (μm) between an end face (180) of the optical fiber and a vertex (144) of the lens is expressed as the sum of a distance FL (μm) from the vertex of the lens to a focal point F located toward the back surface of the lens and a distance δ (μm) between the end face of the optical fiber and the focal point, and the distance δ is longer than 10 μm.

[0015] [2] The optical connector (10) may have an input power such that the connection loss at high input power is smaller than the connection loss at low input power.

[0016] [3] In the optical connector (10), the high power may be an input optical power of +20 dBm or more.

[0017] [4] In the optical connector (10), the low power may be an input optical power of less than +11 dBm.

[0018] [5] In the optical connector (10), the lens element (14) may include a resin material.

[0019] [6] The optical connector (10) may further include a ferrule (12) for holding the optical fiber (18), and the lens element (14) and the ferrule may contain the same resin material.

[0020] [7] In the optical connector (10) described above, the resin material may be a cycloolefin polymer or a polyetherimide.

[0021] [8] The optical connector (10) includes a filler medium (19) between the end face (180) of the optical fiber and the lens element, and the filler medium may be an adhesive.

[0022] [9] The optical connector (10) may include a plurality of optical fibers (18) and a plurality of lenses (44) corresponding to the plurality of optical fibers.

[0023]

[10] In the optical connector (10), the interval δ may be greater than 20 μm.

[0024]

[11] In the optical connector (10), the interval δ may be 100 μm or less.

[0025]

[12] In the optical connector (10), the optical fiber (18) may be a single mode fiber.

[0026]

[13] In the optical connector connection structure, at least one of the components to be connected may be the optical connector (10) described above.

[0027] 2. Specific Examples of Embodiments Hereinafter, specific examples of the embodiments of the present invention will be described with reference to the drawings. In the following description, components common to each embodiment will be given the same reference numerals, and repeated description will be omitted. The drawings are schematic, and the dimensional relationship and ratio of each element may differ from the reality. The drawings may also include parts with different dimensional relationships and ratios.

[0028] <Embodiment 1> Fig. 1 is a perspective view showing the appearance of the optical connector according to the first embodiment of the present invention, Fig. 2 is an exploded perspective view showing the configuration of the optical connector according to the first embodiment of the present invention.

[0029] 1 and 2, an optical connector 10 according to the first embodiment is a multi-core optical connector for connecting a plurality of optical fibers fixed to the optical connector 10 to a plurality of optical fibers fixed to another optical connector to which the optical connector 10 is to be connected. Specifically, the optical connector 10 has a plurality of optical fibers 18, a ferrule 12, a lens element 14, and a pair of guide pins 16.

[0030] 3, the optical fiber 18 is a silica-based optical fiber having a core 118 and a cladding 218. For example, the optical connector 10 uses an optical fiber ribbon 20 in which a predetermined number of optical fibers 18 are arranged in parallel and integrally coated with a coating 22 made of a resin such as an ultraviolet curing resin, and a plurality of such optical fiber ribbons 20 are stacked and fixed to the ferrule 12. The optical fiber 18 is, for example, a single mode fiber.

[0031] The ferrule 12 is a connector body that houses and aligns a plurality of optical fibers 18 arranged in an array. The ferrule 12 contains a mixture of a base material containing resin, which is used in general resin ferrules, and a filler, which is a solid material made of a material different from the base material. The ferrule 12 is formed by molding the mixture. The molding method of the ferrule 12 is not particularly limited, and may be, for example, a transfer molding method, an injection molding method, or the like.

[0032] The base material used for the ferrule 12 contains at least one of a thermoplastic resin and a thermosetting resin. Examples of the thermoplastic resin used for the base material of the ferrule 12 include polyphenylene sulfide (PPS), liquid crystal polymer (LCP), polyethersulfone (PES), polycarbonate (PC), and cycloolefin polymer (COP). Examples of the thermosetting resin used for the base material of the ferrule 12 include epoxy resin, phenol resin, urea resin, melamine resin, and unsaturated polyester resin.

[0033] The filler used in the ferrule 12 may be, for example, a solid material made by processing quartz glass or quartz crystal into a predetermined shape. The filler in the ferrule 12 is mixed into the base material in order to reduce the linear expansion coefficient of the ferrule 12.

[0034] As shown in FIGS. 1 and 2, the ferrule 12 has a ferrule body portion 24 and a flange portion 26.

[0035] The ferrule body 24 is provided on the connection end side of the optical connector 10, and the flange portion 26 is provided on the opposite side to the connection end of the optical connector 10. In the following description, the connection end side of the optical connector 10 is referred to as the “front” of the optical connector 10, and the side opposite to the connection end of the optical connector 10 is referred to as the “rear” of the optical connector 10.

[0036] The ferrule 12 is a ferrule for a multi-core optical connector. Specifically, the ferrule 12 is a MT (Mechanically Transferable) ferrule, and conforms to or complies with standards such as IEC 61754-5 by the International Electrotechnical Commission and JIS C 5981 by the Japanese Industrial Standards.

[0037] The flange portion 26 is formed with an optical fiber introduction port 28 for introducing the multiple optical fibers 18 into the ferrule 12. The optical fiber introduction port 28 is formed in the flange portion 26 so as to penetrate the optical connector 10 in the front-rear direction.

[0038] The ferrule body 24 has a hollow portion 30 formed therein, which is connected to the optical fiber introduction port 28 of the flange portion 26. In addition, an opening 32 connected to the hollow portion 30 is formed in the upper surface of the ferrule body 24. The opening 32 is a hole for introducing an adhesive 29 that fixes the optical fiber 18 to the ferrule 12.

[0039] The ferrule body 24 has a connection side end face 34 on the front side of the optical connector 10. The connection side end face 34 is inclined with respect to a plane perpendicular to the front-rear direction of the optical connector 10. The connection side end face 34 of the ferrule body 24 is formed with a plurality of optical fiber insertion holes 36 into which the plurality of optical fibers 18 are inserted along the optical axes of the optical fibers. The plurality of optical fiber insertion holes 36 are each formed along the front-rear direction of the optical connector 10. One end of each of the plurality of optical fiber insertion holes 36 opens at the connection side end face 34. The other end of each of the plurality of optical fiber insertion holes 36 opens so as to connect to the hollow portion 30.

[0040] The optical fiber insertion holes 36 are arranged in an array. For example, rows of a predetermined number of optical fiber insertion holes 36 arranged in parallel along the width direction of the optical connector 10 are formed in multiple stages parallel to the vertical direction of the optical connector 10. FIG. 2 shows, as an example, a case in which 12 optical fiber insertion holes 36 are formed in five stages. The arrangement of the optical fiber insertion holes 36, the total number of the optical fiber insertion holes 36, the number of optical fiber insertion holes 36 per row, and the number of stages of the rows of the optical fiber insertion holes 36 can be appropriately set according to the number of the optical fibers 18, etc. The hole diameter and pitch of the optical fiber insertion holes 36 can also be appropriately set according to the outer diameter and pitch of the optical fiber 18. The number of stages of the optical fiber insertion holes 36 does not need to be multiple stages, and may be one stage.

[0041] Each optical fiber 18 has an outer diameter (outer diameter of the glass portion consisting of the core and cladding) of 80 to 126 μm. In the optical connector 10, when the outer diameter of the optical fiber 18 is 80 μm, the pitch is, for example, 125 μm or 250 μm, and when the outer diameter of the optical fiber 18 is 125 μm, the pitch is, for example, 250 μm. The pitch is not limited to this and may be set to be equal to or larger than the outer diameter of the optical fiber 18.

[0042] In the ferrule 12 formed as described above, the tip portions of the multiple optical fiber ribbon core wires 20 are introduced into the hollow portion 30 of the ferrule body 24 from the optical fiber introduction port 28 of the flange portion 26. The multiple optical fiber ribbon core wires 20 are stacked in the vertical direction of the optical connector 10. The multiple optical fiber ribbon core wires 20 may be protected by being covered and held by a boot or the like at the rear end of the optical connector 10. At the tip portions of the multiple optical fiber ribbon core wires 20 introduced into the hollow portion 30, the coating 22 has been removed, and the end face 180 of the optical fiber 18 is exposed.

[0043] An optical fiber 18 is inserted and fixed in each of the multiple optical fiber insertion holes 36 formed in the ferrule body 24. The multiple optical fibers 18 inserted and fixed in the multiple optical fiber insertion holes 36 in the same row are included in the same optical fiber ribbon 20.

[0044] The optical fiber 18 is adhered and fixed in the optical fiber insertion hole 36 by an adhesive 29 introduced from an opening 32 on the top surface of the ferrule body 24. The ends of the multiple optical fiber ribbons 20 introduced into the hollow portion 30 are also adhered and fixed to the ferrule body 24 by the adhesive 29 introduced from the opening 32.

[0045] The optical fiber 18 inserted and fixed in the optical fiber insertion hole 36 may be in a state in which it is covered with a resin coating, or in a state in which the resin coating has been removed.

[0046] The end face of the optical fiber 18 fixed in the optical fiber insertion hole 36 is polished together with the connection side end face 34 of the ferrule body 24 so as to be flush with the connection side end face 34 .

[0047] In this manner, the ferrule 12 accommodates the optical fibers 18 such that the optical fibers 18 are arranged in an array. The ferrule 12 accommodating the optical fibers 18 has a fiber array including the optical fibers 18.

[0048] In addition, in the width direction of the optical connector 10, a pair of guide pin insertion holes 38 into which the guide pins 16 are inserted are formed at both end portions on both sides of the multiple optical fiber insertion holes 36 and the hollow portion 30 of the ferrule body 24. The pair of guide pin insertion holes 38 are each formed along the front-rear direction of the optical connector 10.

[0049] The lens element 14 is attached to the connection side end surface 34 of the ferrule body 24. The lens element 14 is a lens array including a plurality of lenses 44 corresponding to the plurality of optical fibers 18 housed in the ferrule 12.

[0050] The lens element 14 preferably contains a resin material having a refractive index of 1.40 to 1.67. By forming the lens element 14 from a resin material, it is possible to improve processability and mass productivity. In addition, by making the properties, such as the linear expansion coefficient, of the resin material forming the lens element 14 and the resin material forming the ferrule 12 close to or identical to each other, it is possible to suppress the coupling loss in the optical connector. The lens 44 may contain the same resin material as the lens element 14, and the lens element 14 may be molded integrally with the lens 44.

[0051] Such a resin material may be any material that allows the light to be transmitted, and is preferably transparent. Examples of the resin material include cycloolefin polymer (COP: refractive index n=1.51), polyetherimide (PEI: refractive index n=1.66), polycarbonate (PC: refractive index n=1.58), polyethersulfone (PES: refractive index n=1.63), polymethyl methacrylate (PMMA: refractive index n=1.49), and silicone-based resin (refractive index n=1.40 to 1.50). The resin material may contain a filler. Since the lens element 14 is a resin plate, molding is easy and mass production is possible compared to glass. Furthermore, since the lens element 14 and the lens 44 are formed from the same resin material, it is possible to prevent a change in refractive index between different materials.

[0052] The lens element 14 has a lens array side end face 40 as a first main surface on which a lens array portion 42 including a plurality of lenses 44 corresponding to the plurality of optical fibers 18 is formed, and a lens array back surface 41 as a second main surface opposite the lens array side end face 40.

[0053] The lens array side end face 40 is a front surface of the optical connector 10 in the lens element 14, and is a surface that is disposed opposite to another optical connector 10 to be connected when two optical connectors 10 are connected. More specifically, the lens array side end face 40 is disposed opposite to the lens array side end face 40 of the lens element 14 of the other optical connector 10 to be connected.

[0054] The lens array portion 42 has a plurality of lenses 44 arranged in an array corresponding to the plurality of optical fibers 18 aligned on the connection side end face 34 of the ferrule body portion 24 .

[0055] Each of the lenses 44 has a convex curved surface on the lens array side end face 40, and is formed so that the optical axis is in the direction along the front-rear direction of the optical connector 10. Each lens 44 may be a spherical lens or an aspherical lens.

[0056] The lens array rear surface 41 is the surface of the lens element 14 at the rear of the optical connector 10, and is the surface that is joined to the connection side end surface 34 of the ferrule 12 by the adhesive 29. Specifically, as described below, the lens array rear surface 41 is a surface that is inclined with respect to a plane perpendicular to the front-rear direction of the optical connector 10, and is joined to the connection side end surface 34 of the ferrule main body 24 so that each lens 44 is optically coupled to the corresponding optical fiber 18. The details of the joint portion between the lens element 14 and the optical fiber 18 will be described later.

[0057] In this way, by joining the lens array rear surface 41 to the connection side end face 34 of the ferrule 12, the multiple lenses 44 can function as collimating lenses that collimate light emitted from the corresponding optical fiber 18 toward the lens 44 into parallel light and emit the parallel light toward the optical connector of the other connection. The multiple lenses 44 can also function as focusing lenses that focus parallel light incident toward the lens 44 from the optical connector of the other connection onto the end face of the corresponding optical fiber 18 and input it to the optical fiber 18.

[0058] In the width direction of the optical connector 10, a pair of guide pin insertion holes 46 into which the guide pins 16 are inserted are formed at both end portions on both sides of the lens array portion 42 of the lens element 14. The pair of guide pin insertion holes 46 are formed along the front-rear direction of the optical connector 10. The pair of guide pin insertion holes 46 are formed corresponding to the pair of guide pin insertion holes 38 of the ferrule body portion 24.

[0059] The lens element 14 is adhered and fixed to the connection side end face 34 of the ferrule 12 by an adhesive 29, with the lens element 14 being positioned relative to the ferrule 12 by a pair of guide pins 16. The guide pins 16 inserted into the guide pin insertion holes 46, 38 have portions that protrude from the lens element 14 to the front of the optical connector 10, so that they can be similarly inserted into the counterpart optical connector for connection.

[0060] As a result of the above, the optical connector 10 having the multiple optical fibers 18 accommodated and fixed in the ferrule 12 is realized.

[0061] Next, the joint between the lens element 14 and the optical fiber 18 will be described in detail.

[0062] Fig. 3 is a diagram showing a schematic diagram of a joint portion between an optical fiber 18 and a lens element 14 in the optical connector 10 according to the first embodiment. In Fig. 3, one optical fiber 18 is representatively shown among a plurality of optical fibers 18 fixed to a ferrule 12 as an example of the optical connector 10 for connecting single-mode multi-core optical fibers by the lens system.

[0063] As shown in FIG. 3, the lens array rear surface 41 is bonded to the connection side end face 34 of the ferrule 12 (ferrule body portion 24) and the end face 180 of the optical fiber 18 via an adhesive 19 serving as a filling medium.

[0064] The adhesive 19 is made of a material having an optimum refractive index depending on the resin material used for the lens element 14. The refractive index of the material used for the adhesive 19 is preferably a value between the refractive index of the optical fiber 18 (core 118) and the refractive index of the resin material used for the lens element 14. Moreover, the adhesive 19 is preferably made of a material that becomes transparent to light in the wavelength band to be transmitted after hardening. As such an adhesive 19, for example, an epoxy resin adhesive, an acrylic resin adhesive, or a silicone adhesive can be used.

[0065] 3, the joint surface between the optical fibers 18 and the lens element 14 is not perpendicular to the optical axis 181 of each optical fiber 18. In other words, the joint surface between the optical fibers 18 and the lens element 14 is inclined with respect to a plane 182 perpendicular to the optical axis 181 of the optical fiber 18.

[0066] Here, the joint surface between the optical fiber 18 and the lens element 14 refers to the end surface 180 of the optical fiber 18 and the rear surface 41 of the lens array, which are joined together via an adhesive 19 .

[0067] That is, the end face 180 of the optical fiber 18 is inclined with respect to a plane 182 perpendicular to the optical axis 181 of the optical fiber 18, and the lens array rear surface 41 is inclined with respect to the plane 182. Here, the inclination angle of the end face 180 of the optical fiber 18 with respect to the plane 182 and the inclination angle of the lens array rear surface 41 with respect to the plane 182 are equal to each other.

[0068] When the inclination angle of the end face 180 of the optical fiber 18 relative to the plane 182 (the inclination angle of the lens array rear surface 41 relative to the plane 182) is θ [degrees (°)], 0°<θ<90°, preferably θ≧3°, and more preferably θ=approximately 8°.

[0069] As a specific example, in order to make the rate at which reflected light at the joint surface between lens element 14 and optical fiber 18 is coupled to optical fiber 18, i.e., the return loss at the joint surface between lens element 14 and optical fiber 18, -45 dB or less, it is preferable that θ≧3° when lens element 14 is made of COP (refractive index n=1.51), and θ≧6° when lens element 14 is made of PEI (refractive index n=1.66). Moreover, regardless of the material of lens element 14, θ may be approximately 8°.

[0070] In the optical connector 10 according to the first embodiment, when the lens 44 is coated with an anti-reflective (AR) coating, the return loss can be reduced to -45 dB or less. Depending on the application, the optical connector 10 preferably uses a wavelength band corresponding to the optical communication wavelength band from O-band to L-band (1260 nm to 1625 nm). For example, in the case of a single-mode optical fiber 18, wavelengths in the wavelength bands of O-band (1260 nm to 1360 nm), C-band (1530 nm to 1565 nm), and L-band (1565 nm to 1625 nm) are used.

[0071] Next, a description will be given of a method for joining the optical fiber 18 and the lens element 14 in the optical connector 10 according to the embodiment 1. Here, two methods for joining the optical fiber 18 and the lens element 14 will be illustrated.

[0072] 4A to 4C are diagrams showing an example of a method for joining optical fiber 18 and lens element 14 in optical connector 10 according to the first embodiment.

[0073] 4A, a ferrule 12 having a plurality of optical fiber insertion holes 36 formed therein is prepared, and an optical fiber 18 is inserted and fixed into each of the optical fiber insertion holes 36 of the ferrule 12 (step S11). For example, with the optical fibers 18 inserted into each of the optical fiber insertion holes 36, adhesive 19 is poured into the gap between each optical fiber insertion hole 36 and the optical fiber 18 to fix them.

[0074] 4B, one end face of the ferrule 12 to which the optical fiber 18 is fixed is polished (step S12). Specifically, the ferrule 12 is polished by a known polishing technique so that the connection side end face 34 of the ferrule 12 is non-perpendicular to the optical axis 181 of the optical fiber 18. At this time, the inclination angle θ of the connection side end face 34 of the ferrule 12 with respect to the plane 182 perpendicular to the optical axis 181 of the optical fiber 18 may be set to an appropriate value depending on the material forming the lens element 14, as described above.

[0075] 4C, lens element 14 is prepared with lens array rear surface 41 polished obliquely like ferrule 12, and lens array rear surface 41 of lens element 14 is bonded to connection side end surface 34 of ferrule 12 with adhesive 19 (step S13). At this time, ferrule 12 and lens element 14 are bonded so that end surface 180 of each optical fiber 18 adhesively fixed to ferrule 12 faces the corresponding lens 44.

[0076] Through the above processing steps, the joint portion between the optical fiber 18 and the lens element 14 in the optical connector 10 according to the first embodiment can be realized.

[0077] 5A to 5D are diagrams showing another example of a method for joining the optical fiber 18 and the lens element 14 in the optical connector 10 according to the first embodiment.

[0078] 5A, the ferrule 12 having a plurality of optical fiber insertion holes 36 formed therein is prepared, and one end face of the ferrule 12 is polished by a known polishing technique (step S21). The polishing method is the same as that of step S12 described above.

[0079] 5B, lens element 14 is prepared by polishing lens array rear surface 41 obliquely like ferrule 12, and lens array rear surface 41 of lens element 14 and connection side end surface 34 of ferrule 12 are bonded with adhesive 19 (step S22). At this time, ferrule 12 and lens element 14 are bonded so that optical fiber insertion hole 36 of ferrule 12 and corresponding lens 44 face each other.

[0080] Next, as shown in FIG. 5C, similar to the ferrule 12, a plurality of optical fibers 18 each having one end face 180 polished obliquely are prepared, and the optical fibers 18 are inserted into the corresponding optical fiber insertion holes 36 of the ferrule 12 (step S23).

[0081] Next, as shown in FIG. 5D, each optical fiber 18 is adhesively fixed to the lens array rear surface 41 of the lens element 14 via adhesive 19 (step S24).

[0082] Through the above processing steps, the joint portion between the optical fiber 18 and the lens element 14 in the optical connector 10 according to the first embodiment can be realized.

[0083] In the latter joining method (FIGS. 5A to 5D) described above, an optical fiber 18 may be used in which one end is cut by melting using, for example, a laser cleaver (or a laser cutter), as shown in FIG. 6. The cut surface (end surface 180) of the optical fiber 18 becomes rounded due to the heat generated when melted. The laser of the laser cleaver is generally a laser having an absorption wavelength of the optical fiber, such as a CO2 laser or an ultraviolet laser. Here, the end surface 180 of the optical fiber 18 is a surface that contacts the center of the core 118.

[0084] Next, an approach for suppressing the insertion loss in the optical connector 10 when high power light is input will be described in detail.

[0085] Fig. 7 is a diagram showing a schematic relationship between the distance FLh between the end face of the optical fiber 18 and the apex of the lens 44, the distance FL from the apex of the lens 44 to a focal point F located in the rear direction of the lens 44, and the interval δ between the end face of the optical fiber 18 and the focal point F in the optical connector 10 according to the first embodiment. As in Fig. 3, Fig. 7 shows one optical fiber 18 representatively out of multiple optical fibers 18 fixed to a ferrule 12 as an example of the optical connector 10 for connecting single-mode multi-core optical fibers by the lens system.

[0086] As shown in FIG. 7, the lens array rear surface 41 is bonded to the end face 180 of the optical fiber 18 via an adhesive 19, similar to FIG. 3, and the end face 180 of the optical fiber 18 and the lens array rear surface 41 are inclined at equal angles to each other.

[0087] The distance FLh between the end face 180 of the optical fiber 18 and the apex 144 of the lens is expressed as the sum of the distance FL from the apex 144 of the lens to a focal point F located in the direction of the lens back surface 244, and the interval δ between the end face 180 of the optical fiber 18 and the focal point F. The position of the focal point F is the focal position of the light incident from the apex 144 of the lens when an optical power of an extent that hardly changes the refractive index of the lens element 14 and the lens 44 is incident, that is, the focal position at the time of low-power incident light. Hereinafter, the position of the focal point F is referred to as the ideal focal position F. Hereinafter, the low power means an incident light power of less than +11 dBm, which has been conventionally used.

[0088] Light incident from the lens vertex 144 at the time of low-power input is refracted through the lens 44 as shown by optical path A, and then passes through the lens element 14 to reach the ideal focal position F. The distance from the lens vertex 144 to the ideal focal position F is defined as the distance FL (μm). The focal position F is located at the bonding surface between the adhesive 19 and the lens element 14, i.e., the lens array rear surface 41. Therefore, in order to reduce the transmission loss of the light incident at the time of low-power input, it is preferable to position the end surface 180 of the optical fiber 18 as close as possible to the lens array rear surface 41.

[0089] On the other hand, the light incident from the vertex 144 of the lens at the time of high power input is refracted through the lens 44 as shown by the optical path B, and further passes through the lens element 14 and the adhesive 19 to reach the end face 180 of the optical fiber 18. Specifically, the focal point at the time of high power input is adjusted to be located at the end face 180 of the optical fiber 18. That is, the focal point at the time of high power input is shifted from the ideal focal position F by the distance δ so that the focal point is located at the end face 180 of the optical fiber 18 at the time of high power input. The distance from the vertex 144 of the lens to the focal position at the time of high power input is defined as the distance FLh (μm). Note that high power means an input power of +20 dBm or more, and although the upper limit is not particularly limited, it is sufficient that the input power is, for example, +30 dBm or less as a practically feasible input power.

[0090] The interval δ is the distance (interval) between the ideal focal position F and the focal position at high power incidence, and is set to be longer than 10 μm. By making the interval δ longer than 10 μm, insertion loss can be suppressed, and it is more preferable that the interval δ is longer than 20 μm. In this way, the distance FLh is adjusted so that the focal position at high power incidence is shifted by the interval δ longer than 10 μm from the ideal focal position F toward the end face 180 of the optical fiber 18, that is, so that the focal position at high power incidence reaches the core 118 of the optical fiber 18. The upper limit of the interval δ is not particularly limited, but may be 100 μm or less.

[0091] FIG. 8 is a schematic diagram for explaining an equation for calculating the distance FL. The distance FL can be calculated from the following formula (1) and is based on the lens formula. Since the distance FL is calculated from the following formula (1), the ideal focal position F is determined. Therefore, the focal position at the time of high power input can be adjusted from the relationship between the above-mentioned ideal focal position F and the interval δ. Note that in FIG. 8, the end face 180 of the optical fiber 18 and the lens array rear surface 41 are shown in a state where they are not inclined for convenience, but even if they are inclined, the distance FL can be calculated from the following formula (1) in the same manner.

[0092]

number

[0093] FL: Distance from the lens apex to the ideal focal position T: Distance from the lens apex to the lens element R: Radius of curvature of the lens surface near the central axis (in the case of an aspheric surface, r in the aspheric equation expressed by the following formula (2)) n L : Refractive index of lens medium n l : Refractive index of the filling medium (adhesive, etc.) (1 for air)

[0094]

number

[0095] r: radius of curvature h: Distance from the optical axis (radial direction) k: conic constant z: Sag amount (parallel to the optical axis of the lens) A, B, C...: Aspheric coefficients

[0096] Next, the insertion loss exhibited by the optical connector 10 when high power light is input will be described with a concrete example.

[0097] Fig. 11 is a diagram showing the relationship between the incident light power and the insertion loss for the optical connector 10 according to the first embodiment when δ is about 23. As shown in Fig. 11, when δ is about 23, the insertion loss is minimum when the incident light power is in the range of +20 to +23 dBm. In Fig. 11, values ​​calculated as the average value of 48 measurement results are plotted, and the straight lines extending above and below each plot indicate the range between the upper and lower limits of each measurement result.

[0098] Fig. 12 is a diagram showing the relationship between the incident light power and the insertion loss for the optical connector 10 according to the first embodiment when δ=approximately 33. As shown in Fig. 12, when δ=approximately 33, the insertion loss is reduced even when the incident light power exceeds +25 dBm, and is predicted to be minimum at +27 dBm or more. That is, the optical connector 10 according to the first embodiment may have an incident light power such that the connection loss at high incident power is smaller than the connection loss at low incident power. Note that Fig. 12 shows the results of 12 measurements.

[0099] As described above, in the optical connector 10 according to the first embodiment, the distance FLh is adjusted so that the focal point at the time of high-power input is shifted from the ideal focal position F by an interval δ longer than 10 μm toward the end face 180 of the optical fiber 18. In other words, the distance FLh is adjusted to be longer than the distance FL from the vertex 144 of the lens to the ideal focal position F by more than 10 μm. As a result, the focal point is located at the end face 180 (core 118) of the optical fiber 18 at the time of high-power input, so that it is possible to prevent the focal point from shifting from the core 118 of the optical fiber 18 even if the lens element 14 and the lens 44 are made of a resin material.

[0100] Therefore, according to the optical connector 10 of the first embodiment, it is possible to suppress the insertion loss even when high-power light is input.

[0101] In the optical connector 10 according to the first embodiment, it is possible to reduce return loss by applying an anti-reflection coating to the convex surface of the lens 44 in the lens element 14. When a multi-layer anti-reflection coating is applied to the convex surface of the lens 44, it is possible to reduce the reflection at the convex surface of the lens 44 to -40 dB or less and the coupling amount of the light reflected at the convex surface of the lens 44 to the optical fiber 18 to -55 dB or less in a band of ±40 nm centered on 1310 nm, for example.

[0102] In the optical connector 10 of embodiment 1, if there is a difference in the linear expansion coefficient between the ferrule 12 and the lens element 14, a shift will occur between the optical axis of each optical fiber 18 fixed to the ferrule 12 and the optical axis of the lens 44 due to temperature changes, and there is a risk that the insertion loss of light into the optical connector 10 will vary due to temperature changes.

[0103] Therefore, it is desirable to select materials for the ferrule 12 and the lens element 14 so as to reduce the difference in linear expansion coefficient between the ferrule 12 and the lens element 14 in the optical connector 10. For example, it is desirable to adjust (e.g., reduce) the amount of filler (e.g., quartz glass) mixed into the base material (e.g., polyphenylene sulfide (PPS)) of the ferrule 12 so that the difference in linear expansion coefficient between the ferrule 12 and the lens element 14 is 20 ppm / °C or less.

[0104] In addition, in the optical connector 10, the ferrule 12 and the lens element 14 may be formed of the same material. Examples of the material include resin materials such as cycloolefin polymer (COP, linear expansion coefficient: 60 to 80 ppm / °C) and polyetherimide (PEI, linear expansion coefficient: 56 ppm / °C).

[0105] <Embodiment 2> Fig. 9 is a diagram showing a schematic diagram of a joint portion between an optical fiber 18 and a lens element 14 in an optical connector 10 according to embodiment 2. Fig. 9 representatively shows a joint portion of one optical fiber 18 in a structure of a portion where a lens element 14 having a plurality of lenses 44 formed on its surface is joined to a ferrule 12 housing a plurality of optical fibers 18 in an optical connector 10 for connecting single-mode multi-core optical fibers by a lens system.

[0106] 9, the lens array rear surface 41 is joined to the connection side end face 34 of the ferrule 12 (ferrule body portion 24) and the end face 180 of the optical fiber 18 via an adhesive 19. Although not shown, the adhesive 19 is also filled in the gap between the inner wall of the optical fiber insertion hole 36 of the ferrule 12 and the optical fiber 18.

[0107] The joint surface between the optical fibers 18 and the lens element 14 is perpendicular to the optical axis 181 of each optical fiber 18. That is, the joint surface between the optical fibers 18 and the lens element 14 is parallel to a plane 182 perpendicular to the optical axis 181 of the optical fiber 18.

[0108] Here, the joint surface between the optical fiber 18 and the lens element 14 refers to the end surface 180 of the optical fiber 18 and the rear surface 41 of the lens array, which are joined together via an adhesive 19 .

[0109] That is, the end face 180 of the optical fiber 18 and the lens array rear surface 41 are parallel to a plane 182 perpendicular to the optical axis 181 of the optical fiber 18, and are joined without being inclined via the adhesive 19. The optical connector 10 according to the second embodiment shown in Fig. 9 has the same structure as the optical connector 10 according to the first embodiment shown in Fig. 3, except that the optical fiber 18 and the lens element 14 are not inclined.

[0110] Fig. 10 is a diagram showing a schematic relationship between the distance FLh between the end face of the optical fiber 18 and the apex of the lens 44, the distance FL from the apex of the lens 44 to a focal point F' located in the rear direction of the lens 44, and the interval δ between the end face of the optical fiber 18 and the focal point F' in the optical connector 10 according to the second embodiment. As in Fig. 7, Fig. 10 shows one optical fiber 18 representatively out of multiple optical fibers 18 fixed to a ferrule 12 as an example of the optical connector 10 for connecting single-mode multi-core optical fibers by the lens system.

[0111] The distance FLh between the end face 180 of the optical fiber 18 and the vertex 144 of the lens is expressed as the sum of the distance FL from the vertex 144 of the lens to the focal point F' (ideal focal position F') located in the direction of the back surface 244 of the lens, and the distance δ between the end face 180 of the optical fiber 18 and the focal point F'.

[0112] Light incident on the lens vertex 144 at low input power is refracted through the lens 44 as shown by optical path A', and then passes through the lens element 14 to reach the ideal focal position F'. The focal position F' is located between the lens array rear surface 41 and the end face 180 of the optical fiber 18, i.e., in the adhesive 19.

[0113] On the other hand, light incident from the vertex 144 of the lens when the light is incident at high power is refracted through the lens 44 as shown by optical path B', and then passes through the lens element 14 and adhesive 19 to reach the end face 180 of the optical fiber 18. Specifically, the focal point when the light is incident at high power is adjusted to be located at the core 118 of the optical fiber 18.

[0114] The interval δ is the distance (spacing) between the ideal focal position F' and the focal position when the light enters at high power, and is set to be longer than 10 μm. In this manner, the distance FLh is adjusted so that the focal position when the light enters at high power is shifted from the ideal focal position F' toward the end face 180 of the optical fiber 18 by the interval δ that is longer than 10 μm.

[0115] As described above, in the optical connector 10 according to the second embodiment, the distance FLh is adjusted so that the focal point at high power input is shifted from the ideal focal position F' by an interval δ longer than 10 μm toward the end face 180 (core 118) of the optical fiber 18. As a result, the focal point is located at the end face 180 (core 118) of the optical fiber 18 at high power input, so that even if the lens element 14 and the lens 44 are made of a resin material, it is possible to prevent the focal point from shifting from the core 118 of the optical fiber 18.

[0116] <Extension of the embodiment> The invention made by the present inventors has been specifically described above based on an embodiment, but the present invention is not limited thereto and can be modified in various ways without departing from the gist of the invention.

[0117] For example, in each of the above embodiments, the ferrule 12 is formed as a separate component from the lens element 14, but the ferrule 12 may be formed integrally with the lens element 14.

[0118] In addition, in each of the above embodiments, the case where a plurality of optical fibers 18 are provided is illustrated, but the present invention is not limited to this, and a single optical fiber may be used. In addition, the optical fiber 18 may be built into a cable, a cord, or the like.

[0119] In addition, in each of the above embodiments, the optical fiber 18 is a single mode (SM) optical fiber, but the optical fiber 18 may be a multimode (MM) optical fiber. When the optical fiber 18 is a multimode (MM) optical fiber, wavelengths in the wavelength bands of 850 nm (850nn±50 nm range), 1060 nm (1060nn±50 nm range), and 1310 nm (1310nn±50 nm range) are used.

[0120] In addition, in each of the above embodiments, the optical connector 10 is a male connector equipped with the guide pins 16, but the optical connector 10 may be a female connector without the guide pins 16. In addition, the optical connector 10 may be an MPO connector (multi-fiber push-on connector) in which the guide pins 16 are incorporated in a housing such as an adapter.

[0121] Moreover, the optical connector 10 in each of the above-described embodiments may be used as the optical connector connection structure, and in such an optical connector connection structure, at least one of the connected components may be the optical connector 10 . [Explanation of symbols]

[0122] 10 Optical Connector 12 Ferrule 14 Lens elements 16 Guide pin 18 Optical Fiber 19,29 Adhesive 24 Ferrule body 34 Connection side end face 36 Optical fiber insertion hole 38 Guide pin insertion hole 40 Lens array side end face 41 Lens array back 44 Lens 46 Guide pin insertion hole 118 cores 144 Lens apex 180 Optical fiber end face 181 Optical fiber optical axis 182 Plane perpendicular to the optical axis 218 Clad 244 Lens back θ Tilt angle F,F' focus (ideal focus) FL: Distance from the apex of the lens to the ideal focal position FLh is the distance between the end face of the optical fiber and the apex of the lens. δ Distance between the ideal focal position and the focal position when high power input light is applied A,A',B,B' light path

Claims

1. a lens element having at least one optical fiber and at least one lens for coupling light to an end face of the optical fiber; a distance FLh (μm) between the end face of the optical fiber and the apex of the lens is expressed as the sum of a distance FL (μm) from the apex of the lens to a focal point F located in the direction toward the back surface of the lens and a distance δ (μm) between the end face of the optical fiber and the focal point F; An optical connector, characterized in that the interval δ is longer than 20 μm and 100 μm or less, The optical connector further includes a ferrule for holding a plurality of the optical fibers, an adhesive layer between the ferrule and the lens element;

2. 2. The optical connector according to claim 1, having an input power such that a connection loss at high input power is smaller than a connection loss at low input power.

3. 3. The optical connector according to claim 2, wherein the high power is an input optical power of +20 dBm or more.

4. 3. The optical connector according to claim 2, wherein the low power is an input optical power of less than +11 dBm.

5. The optical connector according to claim 1 , wherein the lens element comprises a resin material.

6. An optical connector as described in any one of claims 1 to 5, wherein the lens element and the ferrule comprise the same resin material.

7. 7. The optical connector according to claim 6, wherein a difference in linear expansion coefficient between the ferrule and the lens element is 20 ppm / [deg.] C. or less.

8. 8. The optical connector according to claim 5, wherein the resin material is a cycloolefin polymer or a polyetherimide.

9. a filler medium is provided between the end face of the optical fiber and the lens element; 9. The optical connector according to claim 1, wherein the filling medium is an adhesive.

10. 10. The optical connector according to claim 1, comprising: a plurality of optical fibers; and a plurality of lenses corresponding to the plurality of optical fibers.

11. 11. The optical connector according to claim 1, wherein the optical fiber is a single mode fiber.

12. An optical connector connection structure, wherein at least one of the connecting members comprises the optical connector according to any one of claims 1 to 11.

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