JP2009031459A - Single mode optical fiber for visible light transmission - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a single mode optical fiber for visible light transmission having a low loss and high optical coupling efficiency even in a visible light transmission under single mode. <P>SOLUTION: The single mode fiber 5 for visible light transmission contains GeO<SB>2</SB>in its core, the clad of the fiber is made of pure quartz and has TEC part 3 whose core diameter is expanded in a taper shape toward the input/output end face of light in the vicinity of an input/output end face 6 of light of the single mode optical fiber, and a pure quartz rod 4 is connected to the input/output end face of light. Preferably, the length of the TEC part is 0.2 to 5.0 mm and the length of the pure quartz rod is 0.2 to 5.0 mm. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a single-mode optical fiber for transmitting visible light, and more particularly to a single-mode optical fiber for visible light transmission that can be optically coupled with a light source, a photodetector, an optical device, and the like with low insertion loss efficiently.

  Conventionally, various methods are used for optical coupling between a light source such as a laser or LED or a detector such as a photodetector and a single mode optical fiber (hereinafter referred to as SM fiber).

  For example, in the method shown in FIG. 7A, the light from the light source 74 is collected by the lens 75 and is incident on the SM fiber 73 having the core 71 and the clad 72. In such a method, it is extremely difficult to adjust the deviation of the optical axis and the deviation of the angle only with the lens.

  On the other hand, as shown in FIG. 7B, a method in which a GRIN (Graded Index) lens 77 is connected to the light incident / exit end face 76 of the SM fiber 73 is often used. When the GRIN lens is provided on the light incident / exit end face as described above, the light receiving area is increased, so that the optical coupling efficiency is increased. However, there is a disadvantage that the connection loss between the SM fiber 73 and the GRIN lens 77 is increased. There is also a disadvantage that it is difficult to maintain the length of the GRIN lens at the original design length by polishing the GRIN lens 77 when polishing the end face in the connector processing.

Further, as shown in FIG. 7 (c), a core expanding fiber whose core diameter is enlarged toward the light incident / exit end surface is connected to the light incident / exit end surface 76 of the SM fiber, and the light from the light source 74 is transmitted. It is also made to enter the SM fiber 73. The method of expanding the core diameter is called a TEC (Thermal Expanded Core) method, in which the vicinity of the light incident / exit end face 76 of the SM fiber is heated to diffuse GeO ₂ in the core to the cladding to thereby diffuse the core region. Is expanded to obtain a TEC fiber 78.

  When such a method is used, the light receiving area is increased, so that the optical coupling efficiency is increased, and the connection loss between the SM fiber 73 and the TEC fiber 78 can be reduced as compared with the GRIN lens system. However, this TEC fiber system also has a drawback that it is difficult to maintain the light receiving area of the TEC fiber in the original design state by polishing the TEC fiber 78 when polishing the end face in the connector processing.

  Therefore, a method of further connecting an SM fiber to the tip of the TEC fiber is also known (for example, see Patent Document 1). In this method, after connecting the SM fiber having a large core diameter and the SM fiber having a small core diameter, the core diameter in the vicinity of the connecting portion of the SM fiber having the small core diameter is expanded by the TEC method. In this case, since the TEC fiber is not polished, the light receiving area can be maintained as designed.

  By the way, in recent years, the application of the SM fiber for visible light transmission is expected in the medical field and the field of reading DVD disks. The SM fiber for visible light transmission has characteristics that the core diameter is smaller and the relative refractive index difference is smaller than that of a normal SM fiber (SM fiber having a zero dispersion wavelength at 1.31 μm). Specifically, the core diameter is 3.0 to 4.5 μm (9.0 to 10.0 μm for a normal SM fiber), and the relative refractive index difference is 0.1 to 0.3% (less for a normal SM fiber). Also, the mode field diameter (hereinafter referred to as MFD) is as small as less than 4.0 μm.

JP 2004-205654 A

  As described above, the visible light transmission SM fiber has a disadvantage that its optical coupling efficiency with the light source and the detector is poor because the core diameter and the relative refractive index difference are smaller than those of the normal SM fiber.

  In order to increase the light receiving area, an optical fiber having a structure in which the core diameter is enlarged in the vicinity of the light incident / exit end surface by the TEC fiber method may be considered. However, as described above, when polishing the end surface in the connector processing There is a drawback in that it is difficult to maintain the light receiving area in the original design state by polishing the core diameter enlarged portion.

In addition, as described in Patent Document 1, the core diameter in the vicinity of the light incident / exit end face of the SM fiber with a small core diameter is expanded by the TEC fiber method, and an SM fiber with a large core diameter is used at the tip to increase the light receiving area Although an arrangement structure is conceivable, the SM fiber has a drawback that it is easily deteriorated by a laser because GeO ₂ is added to the core.

  The present invention has been made to solve the above problems, and provides a visible light transmission SM fiber capable of efficiently optically coupling a light source, a detector, an optical device or the like with an optical fiber with low loss. is there.

In order to achieve this object, the first aspect of the SM fiber for visible light transmission according to the present invention is a single mode optical fiber for transmitting visible light, and the single mode optical fiber contains GeO ₂ in the core. And an optical fiber having a clad made of pure quartz has an enlarged core portion in which the core diameter is tapered toward the light incident / exit end surface near the light incident / exit end surface, and a pure quartz rod on the light incident / exit end surface Are connected.

  The second aspect of the SM fiber for visible light transmission according to the present invention is characterized in that, in the first aspect, the core enlarged portion has a length of 0.2 mm to 5.0 mm.

  Furthermore, the third aspect of the SM fiber for visible light transmission according to the present invention is characterized in that, in the first or second aspect, the pure quartz rod has a length of 0.2 mm to 5.0 mm.

  The fourth aspect of the SM fiber for visible light transmission according to the present invention is the first to third aspects, wherein the single mode optical fiber to which the pure silica rod is connected is inserted into the ferrule, and the ferrule is inserted into the connector. It is arranged.

  In the first aspect of the SM fiber for visible light transmission according to the present invention, since a pure quartz rod is connected to the tip of the SM fiber, there is no deterioration due to the laser, and the light source, detector, optical device, etc. and the optical fiber are low loss. It is possible to provide a visible light transmission SM fiber that can be optically coupled efficiently.

  In the second and third embodiments of the SM fiber for visible light transmission according to the present invention, the TEC portion (portion in which the core diameter is enlarged) and the pure quartz rod are set to a predetermined length, so that the optical coupling efficiency is further improved. A high visible light transmission SM fiber can be provided.

  In the fourth aspect of the SM fiber for visible light transmission according to the present invention, since the SM fiber for visible light transmission is arranged in the connector, the connector polishing can be performed with the TEC portion maintained, so that the laser, LED, etc. It can be easily attached to or detached from a detector such as a light source or a photodetector or an optical device.

  Hereinafter, preferred embodiments of the SM fiber for visible light transmission according to the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing the configuration of a visible light transmission SM fiber according to the present invention. FIG. 1 shows a structure in which the SM fiber for visible light transmission according to the present invention is inserted into a ferrule, and the ferrule is arranged in a connector.

In FIG. 1, the SM fiber 5 for visible light transmission according to the present invention has a core expanded in the vicinity of the light incident / exit end face 6 of the SM fiber composed of the core 1 doped with GeO ₂ and the clad 2 made of pure quartz. This portion is referred to as “TEC portion 3”), and the pure quartz rod 4 is connected to the light incident / exit end face 6.

  The plastic resin coating 7 is removed near the tip of the visible light transmission SM fiber 5 and the ferrule 8 is inserted into the ferrule 8.

  Here, the length of the TEC portion 3 is preferably in the range of 0.2 mm to 5.0 mm. This is because if the thickness is less than 0.2 mm, the core region hardly expands, and if it exceeds 5.0 mm, the expansion of the core region becomes non-uniform and the insertion loss increases.

  The length of the pure quartz rod 4 is preferably in the range of 0.2 mm to 5.0 mm. If it is less than 0.2 mm, it is difficult to polish the end face in the connector processing. If it exceeds 5.0 mm, the light diffusion in the pure quartz rod 4 causes the disadvantage that the insertion loss with the optical fiber having the TEC portion 3 increases. It is.

  Next, application examples of the SM fiber for visible light transmission according to the present invention will be described below.

  FIG. 2 is a diagram showing a situation in which light emitted from a light source is incident on the visible light transmission SM fiber of the present invention. FIG. 2A shows a situation in which the light indicated by the wavy line emitted from the light source 10 is directly incident on the visible light transmission SM fiber 5 of the present invention. The light emitted from the light source 10 and spread is pure. The light enters the quartz rod 4 and is coupled to the TEC portion 3 having a large core region with low loss. The propagating light that has passed through the TEC portion 3 propagates to the core 1 while maintaining single mode propagation.

  FIG. 2B shows an example in which a lens 11 is provided between the visible light transmission SM fiber 5 and the light source 10. The TEC portion 3 is also used in a configuration in which a lens is used to stop the light emitted from the light source and spread. Since the light receiving area is maintained as originally designed, high optical coupling efficiency can be realized, and alignment can be easily performed even when the optical axis is deviated.

FIG. 3 is a view showing a situation where light emitted from the visible light transmission SM fiber 5 of the present invention enters the photodetector 12. Since the refractive index of the TEC portion 3 is lowered by the diffusion of GeO ₂ , the propagation light from the visible light transmission SM fiber 5 is emitted as light having a large MFD. The propagating light that has passed through the pure quartz rod 4 propagates in space and is optically coupled to the photodetector 12 with low loss.

  FIG. 4 is a diagram showing an example in which the visible light transmission SM fiber of the present invention is applied to an optical device such as an optical isolator, an optical attenuator, or an optical switch.

  4A shows an example in which the visible light transmission SM fibers 5 of the present invention are connected to each other via the optical device 13, and FIG. 4B shows the visible light transmission SM fiber 5 of the present invention via the optical device 13. The example which has arrange | positioned and connected in the connector 9 is shown.

  4 (a) and 4 (b), the propagating light is expanded as indicated by a broken line in the TEC portion 3 of one visible light transmission SM fiber 5, and enters the optical device 13 while maintaining the single mode state. Then, the light passes through the pure quartz rod 4 of the other visible light transmission SM fiber 5 and is further propagated from the TEC portion 3 to the core 1. As a result, single mode transmission having high optical coupling efficiency with low loss can be realized even if an optical device is interposed.

  Next, an embodiment using the visible light transmission SM fiber of the present invention will be described. In this embodiment, the visible light transmission SM fiber in the state where the core diameter is not enlarged is an optical fiber having a core diameter of 4.0 μm and a length of the TEC portion of 1.0 mm.

<Example 1>
With the configuration shown in FIG. 2A, a blue laser with a wavelength of 405 nm is used as the light source 10 and light is incident on the visible light transmission SM fiber 5 of the present invention. The maximum outer diameter of the TEC portion 3 was 12.0 μm, the relative refractive index difference between the core 1 and the clad 2 was 0.30%, and the length of the pure quartz rod 4 was 1.0 mm. The incident light was maintained in a single mode state, and the insertion loss into the visible light transmission SM fiber 5 was 1.0 dB.

<Example 2>
With the configuration shown in FIG. 2B, a blue laser having a wavelength of 435 nm was used as the light source 10, and light was incident on the visible light transmission SM fiber 5 of the present invention. The maximum outer diameter of the TEC portion 3 was 15.0 μm, the relative refractive index difference between the core 1 and the clad 2 was 0.25%, and the length of the pure quartz rod 4 was 1.5 mm. The incident light was maintained in a single mode state, and the insertion loss into the visible light transmission SM fiber 5 was 0.5 dB.

<Example 3>
With the configuration shown in FIG. 3, red laser light having a wavelength of 630 nm is transmitted to the visible light transmission SM fiber 5 of the present invention, and the light is detected by the photodetector 12. The maximum outer diameter of the TEC portion 3 was 9.0 μm, the relative refractive index difference between the core 1 and the clad 2 was 0.28%, and the length of the pure quartz rod 4 was 1.0 mm. At this time, the insertion loss of the light emitted in the single mode state into the photodetector 12 was 0.5 dB.

<Example 4>
As shown in FIG. 5, the visible light transmission SM fiber 5 of the present invention is connected to a pure silica rod having a core diameter of 3.9 μm with GeO ₂ added to the core and the visible light transmission SM fiber 14 having no TEC portion. Further, after the visible light transmission SM fiber 5 was connected to the optical coupler 15, blue laser light having a wavelength of 405 nm was incident on the photodetector 12 through the SM fiber 16. The maximum outer diameter of the TEC portion 3 of the SM fiber 5 for visible light transmission according to the present invention is 10.0 μm, the relative refractive index difference between the core 1 and the cladding 2 is 0.25%, and the length of the pure quartz rod 4 is It was 1.0 mm. At this time, the insertion loss from the visible light transmission SM fiber 5 to the optical coupler 15 was 0.5 dB. The visible light transmission SM fiber 14 and the visible light transmission SM fiber 5 of the present invention were mechanically aligned using a fine adjustment stage.

<Example 5>
As shown in FIG. 6, a pure silica rod having a core diameter of 4.1 μm with GeO ₂ added to the core and a visible light transmission SM fiber 14 having no TEC portion and the visible light transmission SM fiber 5 of the present invention are provided. A connector was connected via the sleeve 17, and blue-violet laser light having a wavelength of 375 μm was incident from the visible light transmission SM fiber 14. The maximum outer diameter of the TEC portion 3 of the SM fiber 5 for visible light transmission is 7.0 μm, the relative refractive index difference between the core 1 and the cladding 2 is 0.30%, and the length of the pure quartz rod 4 is 1.5 mm. Met. At this time, the insertion loss from the visible light transmission SM fiber 14 to the visible light transmission SM fiber 5 of the present invention was 0.7 dB.

<Comparative example>
In the same configuration as in Example 1, light was incident from a light source into a visible light transmission SM fiber having no pure quartz rod and TEC portion instead of the visible light transmission SM fiber 5. The visible light transmission SM fiber used had a core diameter of 3.8 μm, and the relative refractive index difference between the core and the clad was 0.28%. At this time, the insertion loss into the visible light transmission SM fiber used in this comparative example was 2.5 dB.

  From the above examples and comparative examples, the visible light transmission SM fiber of the present invention has a very low insertion loss compared to the insertion loss of the comparative example despite the small core diameter and relative refractive index difference, and single mode. It was clear that the optical coupling efficiency was high while maintaining the state. Further, even when various laser beams were made incident on the visible light transmission SM fiber of the present invention, no damage due to the laser was observed.

It is a figure which shows one Embodiment of a structure of SM fiber for visible light transmission of this invention. It is a figure which shows the example of application of SM fiber for visible light transmission of this invention. It is a figure which shows the other application example of SM fiber for visible light transmission of this invention. It is a figure which shows the further another application example of SM fiber for visible light transmission of this invention. It is a figure which shows the further another application example of SM fiber for visible light transmission of this invention. It is a figure which shows the further another application example of SM fiber for visible light transmission of this invention. It is a figure explaining the example of the optical coupling of the conventional SM fiber.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Core 2 Clad 3 TEC part 4 Pure quartz rod 5 Visible light transmission SM fiber 6 Light incident / exit end face 7 Plastic resin coating 8 Ferrule 9 Connector

Claims (4)

A single mode optical fiber for transmitting visible light, wherein the single mode optical fiber contains GeO ₂ in a core, and the core diameter is in the vicinity of the light incident / exit end face of the optical fiber whose cladding is made of pure quartz. A single mode optical fiber for visible light transmission, characterized in that it has a core expansion portion that is enlarged in a tapered shape toward a light incident / exit end face, and a pure quartz rod is connected to the light incident / exit end face.   The single-mode optical fiber for visible light transmission according to claim 1, wherein the enlarged core portion has a length of 0.2 mm to 5.0 mm.   The single mode optical fiber for visible light transmission according to claim 1 or 2, wherein the pure quartz rod has a length of 0.2 mm to 5.0 mm.   The single-mode optical fiber to which the pure quartz rod is connected is inserted into a ferrule, and the ferrule is disposed in the connector. Single mode optical fiber for visible light transmission.

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