JP2007148091A - Fiber stub, and optical receptacle and optical receptacle module using the fiber stub - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical receptacle in which tracking error characteristics and wiggle characteristics are improved significantly. <P>SOLUTION: In a fiber stub where a graded index fiber is fixed in the through hole of a ferrule, expression L=π×P×r×(2/Δ)<SP>1/2</SP>(P=0.5N+P1, where N is an integer that is 0 or larger, and 0.4≤P1≤0.6) is satisfied, where L is the length of the graded index fiber, r is the core radius, Δ is the refractive index difference between the core and the clad, and P is the pitch of a light beam locus inside the graded index fiber. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical receptacle and an optical receptacle module, and more particularly to an optical receptacle for optical communication and a module using the same.

  An optical module for converting an optical signal into an electrical signal has a structure in which an optical element such as a semiconductor laser or a photodiode is housed in a case, and the optical signal is introduced or derived through an optical fiber (Patent Document). 1).

  A receptacle-type optical module 21 in which an optical connector 23 is connected to the optical module 21 includes an optical element 24 at one end of an optical receptacle 22 as shown in FIG. 5, and an optical connector 23 (SC connector or the like) at the other end. ) Plug ferrule 25 is connected.

  The optical receptacle 22 is fixed by press-fitting the rear end portion of the stub 12 obtained by inserting and fixing the optical fiber 11 into a ferrule 10 made of a ceramic material such as zirconia or alumina as shown in FIG. The distal end portion is inserted into the inner hole of the sleeve 9, and they are press-fitted or adhesively fixed to the case 27.

  Further, the case 27 has its rear end portion pressed into and fixed to the holder 26, so that the inner diameter of the insertion portion for guiding the inner plug ferrule 25 of the case 27 to the sleeve 9 is set larger than the inner diameter of the sleeve 9. It is press-fitted or bonded and fixed so as not to interfere with the inner diameter of the sleeve 9.

  At this time, the outer diameter of the ferrule 25 is about φ2.5 mm for the type to which the SC connector is connected, about φ1.25 mm for the small type to which the LC connector is connected, and the outer diameter tolerance is ± 1 μm or less. The outer diameter of the optical fiber 11 provided in the hole is about 125 μm, and the outer diameter tolerance is about ± 1 μm, which is defined by the JIS standard or the IEC standard. Conventionally, the optical signal formed at the center of the optical fiber In order to connect the cores (not shown) having a diameter of about 10 μm to each other with low loss, the sleeve 9 and the ferrule 25 are processed with high precision, and the stub 12 and the plug ferrule 25 are stably and highly accurate by the sleeve 9. It has a structure to hold.

  Further, the end face of the optical fiber 11 in the stub 12 is mirror-polished to a curved surface having a curvature radius of about 5 to 30 mm in order to reduce connection loss at the time of contact, and the opposite end face is formed from an optical element such as an LD. In order to prevent the emitted light from being reflected at the tip of the optical fiber 11 and returning to the optical element, it is mirror-polished to an inclined surface of about 4 to 10 ° together with the ferrule 10 inserted through the optical fiber 11.

In addition, as a receptacle for a light receiving element such as a PD, a method of reducing a connection loss by using a graded index fiber as an optical fiber in a stub has been proposed (see Patent Document 2).
JP 2001-66468 A Japanese Patent Laid-Open No. 10-68843

  However, in recent years, the output stability (wiggle characteristics) of the optical communication module with respect to the load applied to the plug ferrule 25 in the direction perpendicular to the optical axis has been regarded as important, and the load is directly applied to the sleeve 9 as shown in FIG. It has a structure.

  This is because the conventional optical receptacle 22 as shown in FIG. 4 is press-fitted and adhesively fixed so that the outer periphery of the rear end side of the case 27 is covered with the holder 26, so that these inner and outer diameters are concentric. In addition to the processing accuracy, the sleeve is easily deformed until it comes into contact with the inner diameter of the case 27 due to the collapse when the stub 12 and the case 27 are fixed to the holder 26, and interference between the connector housing portion and the outer diameter portion of the case 27 occurs. . For these reasons, there is a problem that the optical fiber 11 and the optical fiber fixed to the plug ferrule 25 are relatively displaced, and the connection loss of the joint portion is deteriorated.

In addition, since the light is coupled to the optical element side of the stub, there is a problem in that the connection loss is deteriorated due to the deviation of the optical system at high and low temperatures.

Furthermore, in the structure proposed in Patent Document 2, since the length of the graded index fiber is not optimized, the light emitting element module and the light receiving element module having a small light receiving diameter for high-speed communication can stably realize low loss. There was a problem that I could not.

According to the present invention, in a fiber stub in which a graded index fiber is fixed to a through hole of a ferrule, the length of the graded index fiber is L, the core radius is r, the refractive index difference between the core and the clad is Δ, When the pitch of the ray trajectory in the dead index fiber is P,
L = π · P · r · (2 / △) ^1/2
(P = 0.5N + P1, N is an integer of 0 or more, 0.4 ≦ P1 ≦ 0.6)
It is characterized by becoming.

  Furthermore, a coreless fiber is bonded to at least one end of the graded index fiber.

  Furthermore, one end of the fiber stub is arranged so as to be directly connectable with a plug ferrule.

  Further, the optical receptacle module is characterized in that the other end of the fiber stub is disposed so as to be optically connectable to an optical element.

  In the optical receptacle according to the present invention, the optical connection loss part is provided at one place, and the tolerance characteristic of this part is less than that of the conventional one, so that the tracking error characteristic and the wiggle characteristic can be greatly improved.

  In addition, the above characteristics can be stably produced by using a coreless fiber.

According to the present invention, in a fiber stub in which a graded index fiber is fixed to a through hole of a ferrule, the length of the graded index fiber is L, the core radius is r, the refractive index difference between the core and the clad is Δ, When the pitch of the ray trajectory in the dead index fiber is P,
L = π · P · r · (2 / △) ^1/2
(P = 0.5N + P1, N is an integer of 0 or more, 0.4 ≦ P1 ≦ 0.6)
It is characterized by becoming.

  As shown in FIG. 1, the stub 3 includes a stub ferrule 5 and a GI fiber 6. The GI fiber 6 is inserted into a through hole extending in the axial direction of the ferrule 5, and is bonded and fixed by, for example, an adhesive. It is a member constituted by doing. Moreover, the single side | surface 3a of the stub 3 is a round surface (for example, a curvature radius is 5-30 mm). Such a configuration is suitable for reducing connection loss with a connector (not shown). The other surface 3 b of the stub 3 is an inclined surface that is inclined at a predetermined angle (for example, 4 to 10 °) with respect to the axis of the stub 3. Such a configuration is suitable, for example, for preventing light emitted from an optical element (such as an LED or LD) from being reflected by the end face of the optical fiber 11 and returning to the optical element as reflected light.

The ferrule 5 is a member that protects the GI fiber 6 and contributes to increasing the concentricity of the stub 3 and the plug ferrule (not shown) together with the sleeve 2 described later. Ferrule 5 is made of a material such as zirconium oxide (zirconia), aluminum oxide (alumina), mullite, silicon nitride, silicon carbide, aluminum nitride, or the like, ceramics containing these as main components, or glass ceramics such as crystallized glass. Metal such as phosphor bronze, beryllium copper, brass and stainless steel, plastics such as epoxy and liquid crystal polymer, etc. Among them, zirconia-based ceramics (ceramics based on zirconia) having excellent weather resistance and toughness are preferred. It is. Further, among zirconia ceramics, zirconium oxide (ZrO ₂ ) is the main component, and at least one selected from the group consisting of Y ₂ O ₃ , CaO, MgO, CeO ₂ , Dy ₂ O _{3 and the} like is used as a stabilizer. The partially stabilized zirconia ceramics (mainly tetragonal crystals) are preferred from the viewpoints of wear resistance and elastic deformation.

  The GI fiber 6 generally has a structure similar to a graded index lens (hereinafter referred to as a GRIN lens) and has a lens effect. The central axis of the cylindrical shape has the highest refractive index, and the refractive index gradually decreases toward the outer periphery. In addition, the GRIN lens has an amount called a pitch (hereinafter referred to as P), which is a parameter indicating the light collection state of the GRIN lens. In the case of P = 0.5, it indicates that what was a point light source at the incident end face is condensed again on the point at the outgoing end face, and in the case of P = 0.25, if it is a point light source at the incident end face, it is emitted. The end face becomes collimated light and the maximum beam diameter is obtained.

This relationship is shown in FIG. The beam diameter is zero at the origin. The light gradually spreads, reaches a maximum at P = 0.25, and converges to a point again at P = 0.5. In this way, the GRIN lens periodically changes the outgoing beam diameter in the longitudinal direction. P is determined by the core radius r of the GRIN lens and the refractive index difference Δ. The same applies to the GI fiber 6. In order to satisfy the characteristics described below, the length of the GI fiber 6 is
L = π · P · r · (2 / Δ) ^1/2 , P = 0.5N (N is an integer of 0 or more)
Is optimal. However, considering manufacturing variations, P = 0.5N + P1, 0.4 ≦ P1 ≦ 0.6
Is desirable. Examples of the material of the GI fiber 6 include a quartz optical fiber, a plastic optical fiber, and a multicomponent glass optical fiber.

  Furthermore, the present invention is characterized in that one end of the fiber stub is disposed so as to be directly connectable with a plug ferrule, and the other end of the fiber stub is disposed so as to be optically connectable with an optical element. Features.

  The GI fiber 6 may have a structure in which coreless fibers 6b and 6c are connected to both sides of the GI fiber 6a having the fiber length as shown in FIG. In this case, even if the length of the coreless fiber varies, since the influence on the optical characteristics is small, the length accuracy of the stub 3 can be relaxed.

  The sleeve 2 has a through hole for inserting the stub 3 and the plug ferrule, and is a member that bears the aligning function between the stub 3 and the plug ferrule. There are two types of the sleeve 2, a so-called split sleeve having a slit (not shown) extending in the longitudinal direction and a so-called precision sleeve having no slit. When the sleeve 2 having a slit generally used in an optical receptacle is employed, the hole diameter of the through hole is larger than the outer diameter of the plug ferrule so as to increase the gripping force acting on the plug ferrule inserted into the sleeve 2. It is preferable to set it slightly smaller (for example, so that the pressure acting on the stub 3 becomes 0.98 N or more when the stub 3 is inserted into the through hole). Examples of the material constituting the sleeve 2 include the same materials as the ferrule 5 described above.

  The holder 4 is a member for holding the stub 3 and fixing the stub 3 to parts on the optical element side by welding or the like. The holding part which bears the holding function of the stub 3 is provided, and the stub 3 is configured to be fitted. Further, the holder 3 is fixed by laser welding or the like through the outer peripheral portion or the upper surface portion of the holder 3 with the optical element side components. Examples of the material constituting the holder 3 include metals (stainless steel, copper, iron, nickel, and the like). Among them, stainless steel, particularly SUS304, is preferable from the viewpoint of corrosion resistance and weldability.

  The case 1 is a substantially cylindrical member for housing the sleeve 2. The diameter of the space for accommodating the sleeve 2 in the case 1 is configured to be slightly larger (for example, 60 μm) than the outer diameter of the sleeve 2. The opening is a portion for guiding the inside of the sleeve 2 when a plug ferrule (not shown) is inserted, and has a tapered shape. The opening diameter of the opening is slightly larger (for example, 0.2 mm) than the outer diameter of the stub 3. Examples of the material constituting the case 1 include weldable materials such as stainless steel, copper, iron, and nickel, and stainless steel is preferable from the viewpoint of corrosion resistance and weldability.

  FIG. 4A is a diagram of an optical system of a conventional optical receptacle. In this case, there are two optical connection loss generation parts B and C. Further, when this optical receptacle is modularized using an optical element, the loss is adjusted at part B in order to adjust the optical output of the optical module.

  FIG. 4B is a diagram of the optical system of the optical receptacle in the present invention, and the optical fiber is composed only of the GI fiber 6. In FIG. 4, the pitch of the GI fiber 6 is 0.5. In this case, the optical connection loss part is only one part A part, and the optical output adjustment of the optical module is performed at this part at the same time. For this reason, the spot diameter of light on the stub side is larger than that on the connector side, so the optical axis of part A shifts due to temperature changes and load on the connector, but the optical output fluctuations even with the same amount of deviation from part B of FIG. Becomes smaller. Moreover, since the optical connection loss part is one part of the A part with respect to the two parts of the B and C parts in FIG. 4A, the loss can be suppressed small, and the fluctuation of the optical connection loss with respect to temperature and load change is also possible. Get smaller.

  FIG. 4C is an optical system of an optical receptacle according to another embodiment of the present invention, and the optical fiber is a case where coreless fibers 6 b and 6 c are formed on both sides of the GI fiber 6.

  Similar to FIG. 4B, the pitch of the GI fiber 6 is set to 0.5. In this case, the same effect as in FIG. 4B can be obtained.

  Hereinafter, an embodiment of the present invention will be described with reference to FIG.

  As the product 1 of the present invention, a GI fiber 6a having a core radius r = 25 μm, a refractive index difference Δ = 1%, and a fiber outer diameter 125 μm is bonded and fixed to a through-hole of a ferrule 5 made of zirconia ceramics. Thereafter, the one end face 3a is a rounded face (curvature radius: 20 mm), and then the other end face 3b is polished so as to be an inclined face (inclination angle: 8 °), thereby producing the stub 3. At that time, the total length of the fiber 6 in the stub 3 was set to 1.555 mm, 1.666 mm, and 1.777 mm. These 1.555 mm, 1.666 mm, and 1.777 mm correspond to 1.4 pitch, 1.5 pitch, and 1.6 pitch. Next, the holder 4 was produced by cutting stainless steel (SUS304), and the case was produced by cutting stainless steel (SUS303). The material of the sleeve 2 was zirconia ceramics. The rear end portion side of the stub 3 was press-fitted into the holding portion of the produced holder 4. Next, the tip end side of the stub 3 press-fitted into the holder 4 was inserted into the through hole of the split sleeve 2 made of zirconia from one end side.

  Next, the case 1 was fixed to the holder 4 by press fitting so as to cover the sleeve 2 into which a part of the stub 3 was inserted.

  As the product 2 of the present invention, a GI fiber 6 having a core radius r = 25 μm, a refractive index difference Δ = 1%, and a fiber outer diameter 125 μm is fused to a coreless fiber 6b having a fiber outer diameter 125 μm. Next, the GI fiber 6 is cut so that the length L of the GI fiber 6 is 1.555 mm, 1.666 mm, and 1.777 mm. Further, the coreless fiber 6 c is fused to the tip of the GI fiber 6. Next, the produced coreless fiber 6b + GI fiber 6 + coreless fiber 6c is bonded and fixed to the through hole of the ferrule 5 made of zirconia ceramics. Thereafter, the one end face 3a is a rounded face (curvature radius: 20 mm), and then the other end face 3b is polished so as to be an inclined face (inclination angle: 8 °), thereby producing the stub 3. At that time, the total length of the fiber in the stub 3 was set to 1.800 mm. Thereafter, it is manufactured in the same manner as the product 1 of the present invention.

  Further, in order to compare the characteristics, an optical receptacle having the structure of Patent Document 1 in which the optical fiber 6 of the present invention 1 is a single mode fiber was also produced.

  Furthermore, since the GI fiber 6 length is not specified in the comparative example corresponding to Patent Document 2, the fiber length is shifted so that the GI fiber 6 length of the product 1 of the present invention is 1.444 mm and 1.888 mm, and the pitch is set. Optical receptacles with 1.3 pitch and 1.7 pitch were also produced.

  Ten optical receptacles of nine types with all four structures were produced, and a module was produced using an LD element with a lens, and insertion loss and tracking error (−40 ° C., 85 ° C.) were measured.

Further, the plug ferrule 25 of the optical connector 23 was inserted from the tip side of the optical receptacle sample, a load of 500 gf was applied to the plug ferrule 25 in the direction perpendicular to the optical axis, and the connection loss fluctuation was measured. The results are shown in Table 1. It was.

  From Table 1, the products 1 and 2 of the present invention have an insertion loss equal to or greater than the comparative examples corresponding to the structures of Patent Documents 1 and 2, and the characteristics of tracking error and lateral load characteristics are improved. .

It is sectional drawing showing the optical receptacle which concerns on embodiment of this invention. It is a graph which shows the light ray locus in a GRIN lens. It is sectional drawing showing the (a) stub and (b) optical receptacle which concern on another embodiment of this invention. (A) A conventional stub (b) is a cross-sectional view for explaining the characteristics of an optical receptacle according to an embodiment of an optical module of the present invention. It is sectional drawing showing the optical module using the conventional optical receptacle.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Case 2 Sleeve 3 Stub 4 Holder 5 Ferrule 6 GI fiber 9 Sleeve 10 Ferrule 11 Optical fiber 12 Fiber stub 13, 26 Holder 21 Optical module 22 Optical receptacle 23 Connector 24 Optical element 25 Plug ferrule 27 Case

Claims (4)

In a fiber stub in which a graded index fiber is fixed to a through-hole of a ferrule, the length of the graded index fiber is L, the core radius is r, the difference in refractive index between the core and the clad is Δ, Let P be the pitch of the ray trajectory at
L = π · P · r · (2 / △) ^1/2
(P = 0.5N + P1, N is an integer of 0 or more, 0.4 ≦ P1 ≦ 0.6)
A fiber stub characterized by   The fiber stub according to claim 1, wherein a coreless fiber is bonded to at least one end of the graded index fiber.   An optical receptacle characterized in that one end of the fiber stub according to claim 1 or 2 is disposed so as to be directly connectable to a plug ferrule.   4. An optical receptacle module, wherein the other end of the fiber stub according to claim 3 is disposed so as to be optically connectable to an optical element.

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