JP2009157262A - Optical fiber with boot - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical fiber with a boot that is usable as a single-mode and a multi-mode fiber in common, has small bending loss, and can reduce a storage space when mounted on an object device. <P>SOLUTION: The optical fiber 1000 with the boot includes a double-core optical fiber 1001, an optical connector 1002, and the boot 1003 which stores a portion of the double-core optical fiber 1001 led out of the optical connector 1002 from the opposite side from a joint portion 1006 and can hold the double-core optical fiber 1001 to a prescribed radius of curvature when it is bent. Further, a plurality of pairs of slits 1004 and 1005 along the length of the boot 1003 are formed in an exposed area of the boot 1003 orthogonally to the length. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical fiber with a boot, and more specifically, it is possible to connect optical communication in both a single mode and a multimode, and a bending loss is small and a rear end optical fiber cord can be bent small. The present invention relates to an optical fiber with an optical boot that is capable of being stored.

  With recent progress in optical communication technology, high-speed and large-capacity communication has become possible. Optical fibers are attracting attention as transmission media for constructing high-speed and large-capacity communication networks. Optical fiber is introduced not only to companies but also to homes, and users can receive various communication services. In such optical communication, an optical fiber connector is required as a detachable optical fiber connector.

  Here, the influence of the bending of the optical fiber will be described. Optical fibers leak due to bending, causing transmission loss. In particular, a single mode optical fiber is greatly affected by bending. In the JIS standard, model name SSMA-9.3 / 125 (wavelength 1310 nm zero dispersion, mode field diameter 9.3 μm, clad diameter 125 μm), which is the most commonly used silica-based glass single mode optical fiber for single mode optical communication. Since a loss occurs at a curvature radius of 20 mm, the bending radius is generally set not to be 20 mm or less.

  On the other hand, JIS standard, model name SGI-50 / 125 (core diameter 50 μm, clad diameter 125 μm), which is a silica-based glass multimode optical fiber most frequently used for multimode optical communication, has a relatively small bending loss. Even when the bending radius is about 10 mm, there is no problem in use.

  In consideration of the above-mentioned influence of bending of the optical fiber, the conventional optical fiber connector is devised in the boot at the rear of the main body. In particular, a device has been devised assuming that the optical fiber connector is horizontally fitted to the apparatus and the optical fiber cord hangs downward from the rear end by 90 °.

FIG. 1 is a cross-sectional view of a conventional SC-type optical fiber connector described in Patent Document 1. In FIG.
In FIG. 1, one end of an optical fiber cord 5 is covered with a boot 2 and connected to an optical connector 1. In the exposed area of the boot 2, a plurality of pairs of slits 3, 4 are formed in a shape orthogonal to the length direction of the boot 2 and two along the length direction.

  Thus, in the SC type optical fiber connector described in Patent Document 1 shown in FIG. 1, since the slits 3 and 4 whose sizes are adjusted are inserted in the boot 2, as shown in FIG. The optical fiber is not bent at the rear end of the optical connector 1 including the jacket tearing portion 7, and the optical fiber 2 is bent at a curvature radius of 20 mm as a whole.

  In the conventional simple conical boot 8 having no slit as shown in FIG. 3, when a tension is applied perpendicularly to the optical fiber cord, a caulking fitting 9 for fixing the outer cover of the optical fiber cord is provided. A bend with a small radius of curvature occurred at the rear edge. However, with the configuration as shown in FIG. 1, the rear end of the caulking metal fitting 6 can be bent at a gentle angle, and the occurrence of bending with a small radius of curvature can be suppressed (see Patent Document 1).

  2 and 3, the outer cover of the optical cord is cut and spread over the caulking seat inside the caulking fitting, and is caulked and fixed with the caulking fitting.

On the other hand, FIG. 4 is a side view of a conventional LC type optical fiber connector.
In FIG. 4, reference numeral 41 denotes an optical connector, reference numeral 42 denotes a boot, reference numeral 43 denotes a tube, and reference numeral 44 denotes an optical fiber. In this LC type optical fiber connector, bending tends to occur as shown in FIG. In the LC type optical fiber connector shown in FIG. 4, the boot 42 is not particularly devised, and the tube 43 which is a heat shrinkable tube is used to fix the jacket of the optical fiber cord 44, and the boundary between these is used. Bending occurs on the surface.

  Therefore, as shown in FIGS. 6A and 6B, there is a boot that has a curvature radius determined in advance and is bent downward at 90 °. FIG. 6A shows an optical fiber connector for single mode, and the radius of curvature of the optical fiber cord 44 is 20 mm. On the other hand, FIG. 6B shows an optical fiber connector for multimode, and the radius of curvature of the optical fiber cord 44 is 10 mm. Thereby, since the radius of curvature is determined in advance, the bending loss does not increase any more. As shown in FIGS. 6A and 6B, a boot reinforcing portion 46 for maintaining a bent state is provided on the inner side of the bending curve of the boot 45 (see Non-Patent Document 1).

Japanese Patent No. 3361395 “LC DUPLEX CONNECTOR (90 ° BOOT)”, Internet <URL: http://www.molex.com/pdm_docs/sd/860253400_sd.pdf)

  In Patent Document 1, the boot 2 is tapered from the optical connector 1, the depth of the slits 3 and 4 is increased on the optical connector 1, and the depth of the slits 3 and 4 is gradually increased toward the rear end. Therefore, when a load is applied to the optical fiber cord 5, the optical connector 1 side of the boot 2 is less likely to bend and more easily bent toward the rear end. Therefore, the rear end of the caulking metal fitting 6 bends gently, and the transmission loss of light is reduced at the connection portion of the optical fiber cord 5 to the optical connector 1.

  That is, in Patent Document 1, a slit is formed in order to reduce transmission loss at the connection portion of the optical fiber cord 5 to the optical connector 1, and a large radius of curvature is obtained by the boot in which the slit is formed. .

  Thus, in an optical fiber connector, in order to suppress the transmission loss of light, the form which provides a slit in a boot as it describes in patent document 1 is influential, but in order to make it more convenient There are still issues to be solved. In particular, the SC-type optical connector boot 2 described in Patent Document 1 needs to ensure a large radius of curvature as a whole (a radius of curvature of 20 mm in the single mode) from the viewpoint of reducing transmission loss. In order to ensure a straight line at the rear end of the boot, the entire length of the boot was as long as 30 mm so as to be a length corresponding to a 90-degree arc having a radius of 20 mm. Thus, when the overall length of the boot becomes long, the storage space in the apparatus to which the optical fiber connector is attached becomes large.

  That is, in Patent Document 1, in order to realize the “reduction in transmission loss of light at the connection portion between the optical fiber cord and the optical connector” which is the object of Patent Document 1, it is gently bent at the bent portion of the optical fiber. That is, the curvature radius is increased. Therefore, although it is useful because transmission loss can be reduced, the problem of “reducing the storage space”, which has been desired in recent years, remains.

  However, in Patent Document 1, in the case of an optical fiber connector for multimode, the bending radius (curvature radius) can be set small, so that the length of the boot can be reduced and the storage space can be reduced. it can. However, when the multimode optical fiber connector is applied to a single mode optical fiber, the assumed radius of curvature is small, and therefore, if the optical fiber cord is bent, light transmission loss occurs. Therefore, it is necessary to prepare both a single-mode optical fiber connector and a multi-mode optical fiber connector, which increases costs.

  Furthermore, when connecting both a single mode optical fiber and a multimode optical fiber to a device to which an optical fiber connector is attached, the storage space needs to be designed so that an optical fiber connector for a single mode can be stored. As described above, the storage space cannot be made compact.

  On the other hand, the boot 45 provided with the boot reinforcing portion 46 shown in FIGS. 6A and 6B is exclusively used when the direction of the optical fiber cord 44 is bent by 90 °, and can be used for a linear connection. However, the usage is limited. Also in this case, it is necessary to prepare two types of boots for the single mode and for the multimode, which increases costs.

  The present invention has been made in view of such problems, and the object of the present invention is to be able to share a single mode and a multimode, have a small bending loss, and reduce the storage space when mounted on the target device. An object of the present invention is to provide an optical fiber with a boot that can be made small.

  In order to achieve such an object, an invention according to claim 1 is an optical fiber with a boot, which includes an optical fiber including a first core and a second core, and a part of the optical fiber. And a boot capable of holding the optical fiber at a predetermined radius of curvature when the optical fiber is bent, the optical fiber having a first refractive index disposed at the axial center of the optical fiber. A first material, a second material having a second refractive index smaller than the first refractive index, disposed on an outer periphery of the first material; and an outer periphery of the second material. A third material having a third refractive index smaller than the second refractive index, wherein the first material is the first core, and the first material and the second material The material is the second core, and the second material is the first to the first core. A clad, wherein the third material is a second clad for the second core, and the optical fiber selectively excites only the first core using an optical signal in the first wavelength band. In this case, the propagation mode has a single mode characteristic in which only the specified mode is present, and the mode field diameter of the specified mode is equal to the mode field diameter of the single mode optical fiber capable of single mode transmission in the first wavelength band. The diameter of the second core is equal to the core diameter of a graded index type multimode fiber or a step index type multimode fiber used as a transmission path for optical signals in the second wavelength band.

  The invention according to claim 2 is the invention according to claim 1, wherein the predetermined radius of curvature is 10 mm or more and less than 20 mm.

  According to the present invention, it is possible to provide an optical fiber with a boot that can share a single mode and a multimode, has a small bending loss, and can reduce a storage space when attached to a target device.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings described below, components having the same function are denoted by the same reference numerals, and repeated description thereof is omitted.
A first object of the present invention is to reduce the storage space of an optical fiber with a boot when the optical fiber with a boot is attached to a target device while reducing transmission loss of light. That is, in order to achieve the first object, it is important to use an optical fiber that is resistant to bending (a transmission loss is small even if it is bent) in consideration of a compact storage space. In this embodiment, it is preferable to use a double core optical fiber (dual mode optical fiber) as such an optical fiber.

  Here, the double-core optical fiber includes a single mode transmission core and a multimode transmission core in one optical fiber at the same time, and the single mode signal light and the multimode signal light are transmitted by the same optical fiber. An optical fiber that enables transmission.

  There are various optical fiber connectors, optical fiber strands, optical fiber core wires, optical fiber cords, and the like that are connected to the optical fiber connector. At least used. Therefore, in this specification, the optical fiber, the optical fiber strand, the optical fiber core wire, and the optical fiber cord are collectively referred to as “optical fiber”. Therefore, the double core optical fiber includes a double core optical fiber, a double core optical fiber strand, a double core optical fiber core wire, and a double core optical fiber cord.

The core for single mode transmission in the double-core optical fiber according to the present embodiment is a first material having a refractive index n ₁ at the innermost side of the optical fiber, and uses the optical signal in the long wavelength band. A mode field of a single-mode optical fiber that has a single-mode characteristic in which the propagation mode is only the specified mode when selectively excited, and the mode field diameter of the specified mode is capable of single-mode transmission in the long wavelength band. The same value as the diameter or substantially the same value. That is, the single-mode transmission core of the double-core optical fiber has an aperture ratio of a commonly used long-wavelength single-mode transmission optical fiber.

In addition, the multi-mode transmission core of the double-core optical fiber according to the present embodiment includes a first material that is a single-mode transmission core, and a refractive index n ₁ formed so as to cover the first material. A graded index multimode fiber that is formed by a combination with a second material having a smaller refractive index n ₂ , and whose core diameter is used as a transmission path for optical signals in a short wavelength band Alternatively, it is the same value as or substantially the same value as the core diameter of the step index type multimode fiber. That is, the multi-mode transmission core of the double-core optical fiber has an aperture ratio of a commonly used short-wavelength multi-mode transmission optical fiber.

  Therefore, when the double core optical fiber according to the present embodiment is used, both the single mode optical fiber and the multimode optical fiber can be connected with low loss.

  The second material functions as a cladding for a single mode transmission core, and functions as a multimode transmission core together with the first material for a multimode transmission core. To do.

A third material as a clad for the multimode transmission core is formed so as to cover the multimode transmission core. The refractive index n ₃ of the _third material is smaller than the refractive index n ₂ of the second material. That is, since the third material functions as a clad for the multimode transmission core made of the first material and the second material, a satisfactory multimode signal light transmission can be realized.

  Even if the double-core optical fiber is bent by providing a third material having a refractive index smaller than that of the second material around the second material included in the core for multimode transmission, the outer periphery of the bend The generation of a region having a higher refractive index than that of the first material guided by the single mode signal light can be reduced.

Furthermore, by providing the third material having a refractive index smaller than that of the second material, bleeding of light from the second material to the third material is suppressed. This suppression effect of the bleeding becomes even more prominent by providing a fourth material having a refractive index n ₄ smaller than the refractive index n ₃ of the third material around the third material. Therefore, it is a more preferable form to form the fourth material so as to cover the third material.

  Although it is desirable that the refractive index of the fourth material be smaller than that of the third material, the coating material that protects the glass fiber has a higher refractive index than glass, and the coating material is made of the fourth material. Generally, it corresponds to the position and the refractive index is higher than that of the third material. However, the arrangement of the materials from the first to third materials has a sufficient effect of suppressing the oozing out.

  In the double core optical fiber according to the present embodiment, it is not essential to propagate signal light in a long wavelength band with single mode signal light and propagate signal light with a short wavelength band in multimode signal light. It is important to be able to transmit single-mode signal light and multi-mode signal light in the same optical fiber, and the wavelength of signal light that propagates as single-mode signal light and multi-mode signal light is any. Is also good. Therefore, the single mode signal light may be signal light in the short wavelength band, and the multimode signal light may be signal light in the long wavelength band.

  Therefore, the core for single mode transmission has the aperture ratio of the optical fiber for single mode transmission, and the core for multimode transmission only has to have the aperture ratio of the optical fiber for multimode transmission.

  In the double-core optical fiber according to the present embodiment, the first to fourth materials have the above-described refractive index relationship and function as a core or cladding of the optical fiber. Any material such as an organic substance such as polymer and acrylic may be used.

  FIGS. 7A and 7B are explanatory diagrams of a double core optical fiber which is an optical fiber suitable for use in the present embodiment. FIG. 7A is a refractive index profile of the double core optical fiber, and FIG. 7B is a cross-sectional view of the double core optical fiber having the refractive index profile of FIG.

  In FIG. 7A, reference numeral 112 denotes the refractive index of the core 111, reference numeral 122 denotes the refractive index of the first cladding 121, reference numeral 132 denotes the refractive index of the second cladding 131, and reference numeral 142 denotes the third cladding. 141 is a refractive index of the fourth cladding or covering material 151. As can be seen from FIG. 7A, the refractive index 122 of the first cladding 121 is smaller than the refractive index 112 of the core 111, the refractive index 132 of the second cladding 131 is smaller than the refractive index 122 of the first cladding 121, The refractive index 142 of the third cladding 141 is smaller than the refractive index 132 of the second cladding 131. In addition, the refractive index 152 of the fourth cladding 151 is higher than the refractive index 142 of the third cladding 141.

  In such a configuration, the core 111 functions as a core for single mode transmission, and the core 111 and the first cladding 121 function as a core for multimode transmission. In the double-core optical fiber, the optical signal wavelength for single mode transmission (the wavelength of the optical signal that excites the specified mode of the core 111 and transmits the single mode) is changed to the C-Band band (1530 nm to 1560 nm) or the L-Band band ( 1570 nm to 1610 nm), or alternatively, any of the 1300 nm band can be designed. Further, the mode field diameter can be set to 7.0 to 10.0 μm. That is, the mode field diameter of the above-mentioned specified mode can be set to 7.0 to 10.0 μm.

  In the double-core optical fiber, in the multimode signal light having a wavelength of 850 nm, an electric field strength distribution is formed over the core 111, the first cladding 121, and the second cladding 131, and the step index type multimode fiber having a wavelength of 850 nm or a wavelength of 850 nm. It is designed to be equivalent to the aperture ratio of band graded index type multimode fiber. The optical signal wavelength for multimode transmission (the wavelength of the optical signal for multimode transmission by exciting the core for multimode transmission including the core 111 and the first cladding 121) is designed to be 850 nm. Furthermore, the diameter of the core for multimode transmission, that is, the diameter of the first cladding 121 can be set to 50 μm or 62.5 μm.

  In the double core optical fiber, the diameter of the first clad 121 that defines the diameter of the core for multimode transmission is set to be the same as or substantially the same as the diameter of the optical fiber for multimode transmission, Since the aperture ratio of the optical fiber is set, an optical fiber for multimode transmission (for example, a multimode optical fiber having an optical signal wavelength of 850 nm as introduced in a LAN (Local Area Network)) and a low loss are provided. The multimode signal light can be transmitted with low loss.

  Further, in the double-core optical fiber, the core 111 included in the multi-mode transmission core also functions as a single-mode transmission core. Mode signal light can be transmitted.

  That is, both the single-mode signal light and the multi-mode signal light, and one each can be transmitted through the same optical fiber.

  FIG. 9 shows a refractive index profile when the double core optical fiber is bent in the shape shown in FIG. In FIG. 8, reference numeral 21 denotes a center of curvature, reference numeral 22 denotes a radius of curvature, reference numeral 23 denotes an outer peripheral side of the optical fiber when the optical fiber is bent, and reference numeral 24 denotes an optical fiber when the optical fiber is bent. It is the inner circumference side. In FIG. 9, reference numeral 175 denotes the maximum value of the refractive index of the core 111 when the radius of curvature R is.

  At this time, the refractive index on the outer periphery side of the second cladding 121 (the right side in FIG. 9) becomes higher, but the refractive index 132 of the second cladding 131 is made smaller than the refractive index 122 of the first cladding 121, and further the third cladding. Since the refractive index 142 of 141 is set to be smaller than the refractive index 132, the refractive index 112 of the core 111 can be obtained even in the case of a radius of curvature in which a region having a higher refractive index than that of the core is generated in the conventional optical fiber. It is possible to eliminate the generation of a region having a higher refractive index than that. Therefore, the deterioration of the transmission characteristics of the optical signal transmitted through the core is not given, and no increase in error at the time of demodulation at the optical signal receiving end that may occur when a conventional optical fiber is used. That is, when the optical fiber is bent, a part of the single mode signal light leaking from the core 111 is trapped in the first clad 121, the second clad 131, and the third clad 141, or reflected from each of them and returned to the core 111. Without reaching the fourth cladding 151, it can be absorbed. Therefore, when the optical fiber is bent, stable single mode transmission and further multimode transmission can be performed simultaneously.

  In addition, by reducing the radius of curvature R (tightening the bend), there may be a region where the refractive indexes 132 and 142 are larger than the maximum value 175. Even if a region larger than the maximum value 175 is generated in this way, the region is smaller than the region generated in the conventional optical fiber when bent at the same curvature radius R. Accordingly, it is possible to reduce multimode transmission due to the radiation mode of the single mode signal light guided through the core 111 when the optical fiber is bent.

  As described above, in the double-core optical fiber, even if the region is eliminated or the region is generated in the radius of curvature R in which a region higher than the refractive index of the core is generated in the conventional optical fiber, the region is generated even if the region is generated. Can be made smaller than in the prior art, so that multimode transmission of signal light guided through the core can be reduced.

  In the double core optical fiber, the second cladding 131 having a refractive index 132 lower than the refractive index 122 has a function of confining the multimode signal light in the core for multimode transmission, and further, When bent, it has a function of reducing multimode transmission of single-mode signal light guided through the core 111.

  Further, the third cladding 141 having a refractive index 142 lower than the refractive index 132 has a function of better confining the multimode signal light in the core for multimode transmission. In other words, the third clad 141 with a low refractive index to which the F element is added plays a role of further reducing the multimode signal light being guided to the fourth clad 151 which is a coating formed of a polymer resin. .

FIG. 10 is a side view of an optical fiber with a boot according to the present embodiment, and FIG. 11 is a side view of the optical fiber with a boot when the optical fiber with a boot shown in FIG. 10 is bent.
In FIG. 10, the optical fiber with boots 1000 includes the double core optical fiber 1001 shown in FIG. 7B, the optical connector 1002, and the double core optical fiber 1001 drawn from the opposite side of the joint portion 1006 of the optical connector 1002. A boot 1003 is provided that can accommodate a part thereof and can hold the double core optical fiber 1001 with a predetermined curvature radius when the double core optical fiber 1001 is bent. That is, one end of the double core optical fiber 1001 is covered with the boot 1003 and connected to the optical connector 1002. Further, in the exposed area of the boot 1003, a plurality of pairs of slits 1004 and 1005 are formed in a shape orthogonal to the length direction of the boot 1003 and two along the length direction.

  In the present embodiment, the overall length of the boot is 15 mm. Further, as shown in FIG. 11, when the double core optical fiber 1001 extending from the optical connector 1002 is bent 90 degrees from the long axis direction of the optical connector 1002, the radius of curvature of the double core optical fiber 1001 is 10 mm. It is said. That is, the boot 1003 can hold a curvature radius of 10 mm as the minimum curvature radius when bent in the 90-degree direction.

  In this embodiment, the shape of the optical connector, the shape and material of the boot, and the connection method between the connector and the boot are not essential, and any conventional form may be used.

  Since the optical fiber used in this embodiment is a double core optical fiber shown in FIG. 7B, the double core optical fiber 1001 has a refractive index profile shown in FIG. 7A. Therefore, the double-core optical fiber 1001 has a profile in which a single-mode refractive index profile and a multi-mode refractive index profile are fused, and realizes both single-mode and multi-mode optical communication using the same optical fiber. Can do. Further, the first clad 121 that is the multimode core part of the double core optical fiber 1001 and the second clad 131 that is the clad of the multimode core part are used for single mode communication light when the double core optical fiber 1001 is bent. Therefore, the bending loss of single mode communication light can be reduced.

  What is important in the present embodiment is that, for example, while reducing the bending loss when the optical fiber is bent 90 degrees, the storage space of the optical fiber 1000 with a boot when the optical connector 1002 is attached to a predetermined device is reduced. For this reason, it is the essence of this embodiment that the length of the boot 1003 that plays a role of holding a bent optical fiber (for example, 90 degrees) with a predetermined radius of curvature is shortened.

  That is, in order to reduce the storage space, it is necessary to reduce the radius of curvature when the optical fiber is bent so as not to impair the bending loss. In order to maintain the radius, it is necessary to shorten the length of the boot.

  For example, as described above, suppressing the bending loss when the optical fiber is bent by 90 degrees can be achieved by the method disclosed in Patent Document 1. However, in Patent Document 1, in order to suppress the bending loss, a gentle bending is performed. Under the technical idea of securing the optical fiber, the optical fiber is configured to suppress sudden bending. That is, the loss is reduced by adopting a configuration that maintains the curvature radius of 20 mm required for loss reduction compared to the conventional optical fiber in which loss occurs at the curvature radius of 20 mm. Therefore, the configuration of Patent Document 1 does not realize space saving.

  On the other hand, in the present embodiment, under the idea that single mode signal light and multimode signal light can be transmitted through the same optical fiber, due to the presence of the multimode core part and the multimode clad part, Even if the bending of the double core optical fiber 1001 is tight (the radius of curvature is reduced), the radiation mode is suppressed, and the idea is completely different from that of Patent Document 1.

FIG. 12 is a diagram showing excess loss characteristics due to bending (360 degrees) during single-mode signal light transmission for the double-core optical fiber 1001. FIG. 13 is a diagram showing excess loss characteristics due to bending (360 degrees) during transmission of multimode signal light with respect to the double core optical fiber 1001.
As shown in FIGS. 12 and 13, in both the single mode and the multimode, even when the double core optical fiber 1001 is bent 360 degrees with a curvature radius of 5 mm, almost no loss occurs. Therefore, in both the single mode and the multi mode, the minimum value of the radius of curvature that suppresses the loss can be made smaller than the conventional value.

  In particular, for the single mode, conventionally, the minimum value of the radius of curvature that suppresses the loss is about 20 mm, but the occurrence of bending loss can be suppressed even if the radius of curvature is 10 mm as in this embodiment. That is, according to the present embodiment, the minimum value of the radius of curvature with reduced loss for the single mode can be significantly reduced.

  That is, since a bending loss can be suppressed even with a small radius of curvature without securing a large radius of curvature as in the prior art, the length of the boot 1003 for maintaining the small radius of curvature can be made smaller than before. It is possible to reduce the storage space in the apparatus to be mounted.

  Moreover, in this embodiment, since the radius of curvature that suppresses loss can be reduced to the same level in both single mode and multimode, the optical fiber with boot 1000 suppresses bending loss while saving space, Both single-mode and multi-mode optical communication connections can be made possible.

  In addition, since the bending loss of the single mode is small, it is not necessary to distinguish between the single mode and the multimode for the boot structure. That is, conventionally, the minimum value of the radius of curvature with reduced loss is larger for single-mode optical fibers than for multi-mode optical fibers, and when multi-mode boots are applied to single-mode optical connectors. The radius of curvature when the optical fiber is bent becomes smaller than the appropriate value of the optical fiber for single mode, which leads to the generation of a large bending loss. Since the radius of curvature to be suppressed can be made as small as the radius of curvature that suppresses the occurrence of bending loss with respect to the multimode, both the single mode and the multimode can be supported by the boot having the same structure.

  That is, by using the double core optical fiber 1001, single mode signal light and multimode signal light can be transmitted through the same optical fiber, and the minimum value of the radius of curvature that suppresses the occurrence of bending loss is defined as single mode. It can be made substantially the same in the multi mode. Therefore, when it is desired to communicate in both single mode and multimode, one double-core optical fiber 1001 can be used without preparing two optical fibers, a single mode optical fiber and a multimode optical fiber. For example, even when the double core optical fiber 1001 is bent so as to have a radius of curvature corresponding to a conventional multimode and a radius of curvature of 10 mm that suppresses the occurrence of bending loss, bending in the transmitted single mode signal light is possible. Loss generation can be suppressed.

  Accordingly, the length of the boot 1003 can be reduced in a state where the single mode signal light and the multimode signal light can be transmitted while suppressing loss, and when the boot-equipped optical fiber 1000 is attached to a device to be attached. The storage space can be made compact. That is, as described above, the boot 1003 can be shortened and can be bent easily, and the accommodation space at the rear end can be reduced.

  As described above, the configuration shown in FIGS. 10 and 11 is the case of the SC type optical connector. When the optical fiber 1000 with a boot is pulled in the 90-degree direction, the notch of the boot is maintained so that the radius of curvature is 10 mm. Slits 1004 and 1005 are formed, and the boot 1003 realizes a short length of 15 mm, which is a length corresponding to a 90-degree arc with a radius of curvature of 10 mm, and saves space in the occupied portion in the apparatus. Realized.

  In this embodiment, as can be seen from FIGS. 12 and 13, even when the radius of curvature is 5 mm, almost no bending loss occurs. Therefore, the boot 1003 may be a boot that is held at a radius of curvature of 5 mm. It is a brittle material made of glass, and if it is held with a small radius of curvature, it may break.

  The optical fiber is subjected to screening by applying an elongation strain at the time of manufacture. By subjecting to screening with an elongation strain of 1%, the possibility of breakage can be eliminated even if the curvature radius is 20 mm. In the case of the double-core optical fiber 1001 according to the present embodiment, the risk of breakage when held at a radius of curvature of 10 mm is eliminated by screening with an elongation strain of 2%.

  However, it is difficult to guarantee that the radius of curvature is less than this. Therefore, the radius of curvature held by the boot 1003 is 10 mm. In order to further reduce the radius of curvature, screening with a larger elongation strain can be ensured, but retention at a smaller radius of curvature can be guaranteed, but the number of breaks during screening increases and yield decreases. On the other hand, the structure that holds the curvature radius of 10 mm has a margin for bending loss, and is a structure that holds the minimum curvature radius in consideration of the strength of the current optical fiber.

  That is, in this embodiment, from the viewpoint of suppressing the occurrence of bending loss, the minimum value of the radius of curvature when bent in the 90 degree direction is 5 mm, but from the viewpoint of manufacturing, the minimum value is 10 mm. Is preferred. That is, it is preferable to set the radius of curvature when bent in the 90-degree direction to be 10 mm or more.

  Moreover, the length of a boot can be shortened rather than before by setting so that the curvature radius at the time of bending in a 90 degree direction may be 10 mm or more and less than 20 mm. Therefore, from the viewpoint of space saving, it is more preferable to set the radius of curvature when bent in the 90 degree direction to 10 mm or more and less than 20 mm.

  That is, in consideration of downsizing of the storage space and the effect of breakage of the optical fiber, the curvature radius of the difference bent in the 90-degree direction is preferably 10 mm or more and less than 20 mm, and the radius of curvature is smaller. However, it is more preferable that the radius of curvature is 10 mm.

It is a side view of the conventional SC type optical fiber connector. It is sectional drawing which shows the conventional boots bent by the load to an optical fiber. It is sectional drawing which shows the conventional boots bent by the load to an optical fiber. It is a side view of the conventional LC type optical fiber connector. It is a figure which shows a mode that the LC type optical fiber connector shown in FIG. 4 was bent. (A) And (b) is a side view of the conventional LC type optical fiber connector. (A) is a refractive index profile of the double core optical fiber which concerns on one Embodiment of this invention, (b) is a cross-section figure of the double core optical fiber which has the refractive index profile of (a). It is explanatory drawing in the case of bending an optical fiber centering on one point which is a curvature radius R. 5 is a refractive index profile that is changed when a double-core optical fiber suitable for use in an embodiment of the present invention is bent at a radius of curvature R. It is a side view of an optical fiber with a boot concerning one embodiment of the present invention. It is a side view of this optical fiber with a boot at the time of bending the optical fiber with a boot shown in FIG. It is a figure which shows the excess loss characteristic by the bending (360 degree | times) at the time of single mode signal light transmission about the double core optical fiber which concerns on one Embodiment of this invention. It is a figure which shows the excess loss characteristic by the bending (360 degree | times) at the time of multimode signal light transmission about the double core optical fiber which concerns on one Embodiment of this invention.

Explanation of symbols

111 Core 112 Refractive index of core 121 First clad 121 Refractive index of first clad 131 Second clad 132 Refractive index of second clad 141 Third clad 142 Refractive index of third clad 151 Fourth clad 152 Refraction of fourth clad Rate 1000 Optical fiber with boot 1001 Double core optical fiber 1002 Optical connector 1003 Boot 1004, 1005 Slit 1006 Joint

Claims (2)

An optical fiber comprising a first core and a second core;
A boot that houses a part of the optical fiber and can hold the optical fiber at a predetermined radius of curvature when the optical fiber is bent;
The optical fiber is
A first material having a first refractive index disposed at the axial center of the optical fiber;
A second material having a second refractive index smaller than the first refractive index, disposed on an outer periphery of the first material;
A third material having a third refractive index smaller than the second refractive index, disposed on the outer periphery of the second material,
The first material is the first core;
The first material and the second material are the second core;
The second material is a first cladding for the first core;
The third material is a second cladding for the second core;
The optical fiber has a single mode characteristic in which a propagation mode is only a prescribed mode when only the first core is selectively excited using an optical signal in a first wavelength band, and The mode field diameter is equal to the mode field diameter of a single mode optical fiber capable of single mode transmission in the first wavelength band,
The diameter of the second core is equal to the core diameter of a graded index type multimode fiber or step index type multimode fiber used as an optical signal transmission path in the second wavelength band. Optical fiber.   The optical fiber with a boot according to claim 1, wherein the predetermined radius of curvature is 10 mm or more and less than 20 mm.

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