Connector for optical connector inspection and optical connector inspection method

Abstract

A connector (10) for optical connector inspection is provided with: an optical fiber (1); a ferrule (11) which holds the optical fiber (1) and has an end face (15) from which an end part (3) of the optical fiber (1) is exposed; an optically transparent spacer (20) which is provided to the end face (15); and a light-shielding mask (30) which is provided on the spacer (20) and has a mask hole (31) at a position at which a portion of test light, which is emitted from the end part (3) of the optical fiber (1) and passes through the spacer (20), reaches.

Description

Optical connector inspection connector and optical connector inspection method

[0001] The present disclosure relates to an optical connector inspection connector and an optical connector inspection method.

[0002] Optical connectors are used in optical communication networks to connect optical fibers. For example, SC (Single-fiber Coupling) connectors and MU (Miniature Universal Coupling) connectors are used as optical connectors for connecting single-core optical fibers together. These optical connectors use a cylindrical ferrule that holds a single optical fiber. On the other hand, MT (Mechanical Transfer) connectors and MPO (Multi-fiber Push On) connectors are used as optical connectors for connecting multiple optical fibers together in an optical fiber cable. MT and MPO connectors use MT ferrules that hold multiple optical fibers. MT ferrules have multiple optical fiber insertion holes for adhesively fixing and aligning optical fibers, and two guide holes for holding or inserting guide pins for mating MT ferrules together.

[0003] The relative misalignment between fiber cores in a connector connection has a significant impact on connection loss. However, with current manufacturing technology, it is difficult to perfectly align the fiber cores. To limit this connection loss, the International Electrotechnical Commission (IEC) specifies the fiber core position of an MPO connector and how to measure it. For example, IEC 61755-3-31, the standard for 12-fiber MPO connectors, specifies that the core center must not be misaligned from the design position by more than 0.8 μm. IEC 61300-3-48 specifies a method for measuring the fiber core position of multi-fiber optical connectors (MT connectors, MPO connectors) using optical microscope images of the connector end face.

[0004] T. Sakamoto et al., "Few-Mode Multi-Core Fiber Technologies for Repeated Dense SDM Transmission," 2018 IEEE Photonics Society Summer Topical Meeting Series (SUM), Waikoloa, HI, USA, 2018, pp. 145-146.

[0005] In recent years, with the increasing speed of optical communication networks, spatial multiplexing transmission technology has been actively researched. The spatial multiplexing transmission technology described in Non-Patent Document 1 transmits multiple signals using multiple cores and multiple propagation modes in a single fiber. In such spatial multiplexing transmission, if there is a transfer of optical power between at least one of the cores and the modes, this causes crosstalk between signals, resulting in degradation of signal quality. Therefore, in order to suppress the transfer of optical power between cores and the modes, there is a possibility that the relative positional misalignment between cores may be further limited. In such a case, the limit resolution of an optical microscope may be insufficient to evaluate the positional misalignment.

[0006] The present disclosure has been made in consideration of these circumstances, and aims to provide an optical connector inspection connector and an optical connector inspection method that are capable of measuring the fiber core position with higher resolution than an optical microscope without performing optical observation.

[0007] The connector for optical connector inspection according to a first aspect of the present disclosure comprises a ferrule that holds an optical fiber and has an end face from which the end of the optical fiber is exposed, an optically transparent spacer that is provided on the end face, and a light-shielding mask that is provided on the spacer and has a mask hole at a position where a portion of the test light that is emitted from the end of the optical fiber and passes through the spacer can pass through.

[0008] An optical connector inspection method according to a second aspect of the present disclosure includes a light-shielding mask having a mask hole at a position where a portion of test light emitted from an end of a first optical fiber passes through, measuring the connection loss of the test light while a second connector holding a second optical fiber is connected to a first connector holding the first optical fiber, and calculating, based on the measured connection loss, an amount of axial misalignment of the core of the second optical fiber relative to a design position of the center axis of the fiber hole in the first connector.

[0009] An optical connector inspection method according to a third aspect of the present disclosure includes: a light-shielding mask having a mask hole at a position where a portion of test light emitted from an end of a first optical fiber passes; a second connector holding a second optical fiber is connected to a plurality of first connectors holding the first optical fiber; measuring the connection loss of the test light when each of the first connectors is connected to the second connector; and calculating, based on the measured connection losses, the amount of axial misalignment of the core of the second optical fiber relative to the design position of the central axis of the fiber hole common to the plurality of first connectors; and the mask hole of each of the first connectors is located at a different position from each other.

[0010] According to the present disclosure, it is possible to provide an optical connector inspection connector and an optical connector inspection method that are capable of measuring the fiber core position with a higher resolution than an optical microscope without optical observation.

[0011] FIG. 1 is an exploded perspective view of an optical connector according to the present embodiment. FIG. 2 is a partial cross-sectional view of the optical connector. FIG. 3 is a partial cross-sectional view showing a state in which the optical connector according to the present embodiment and a connector to be inspected are butted together. FIG. 4A is a diagram for explaining a first measurement example of the optical connector inspection method according to the present embodiment. FIG. 4B is a diagram for explaining the first measurement example of the optical connector inspection method. FIG. 5 is a graph showing an example of the relationship between the amount of axial misalignment and connection loss. FIG. 6 is a diagram showing an example of the arrangement of mask holes in a second measurement example of the optical connector inspection method according to the present embodiment. FIG. 7A is a partial cross-sectional view showing a state in which optical connectors are butted together in the second measurement example. FIG. 7B is a partial cross-sectional view showing a state in which optical connectors are butted together in the second measurement example. FIG. 8A is a diagram for explaining a second measurement example of the optical connector inspection method according to the present embodiment. FIG. 8B is a diagram for explaining a second measurement example of the optical connector inspection method according to the present embodiment. FIG. 8C is a diagram for explaining a second measurement example of the optical connector inspection method according to the present embodiment. FIG. 8D is a diagram for explaining a second measurement example of the optical connector inspection method according to the present embodiment. Fig. 9 is a graph showing an example of the relationship between the amount of axial misalignment and connection loss. Fig. 10 is a graph showing an example of the relationship between the difference between two connection losses and the amount of axial misalignment. Fig. 11 is a diagram showing an example of the arrangement of mask holes in another measurement example of the optical connector inspection method according to this embodiment.

[0012] An optical connector inspection connector and an optical connector inspection method according to an embodiment of the present disclosure will be described below with reference to the drawings. In the drawings, identical parts are designated by the same reference numerals and will not be described again. For ease of explanation, mutually orthogonal X, Y, and Z directions are defined. The X direction is the width direction of the ferrule. The Y direction is the height direction of the ferrule. The Z direction is the extension direction of the fiber hole (insertion hole) of the ferrule and the propagation direction of the test light.

[0013] Hereinafter, the optical connector inspection connector 10 according to this embodiment will be referred to as the connector 10. Fig. 1 is an exploded perspective view of the connector 10. Fig. 2 is a partial cross-sectional view of the connector 10. As shown in Fig. 1, the connector 10 includes a ferrule 11, a spacer 20, and a light-shielding mask 30.

[0014] The ferrule 11 holds the optical fiber 1. The type of ferrule 11 is appropriately selected according to the ferrule of the optical connector to be inspected. For example, if the optical connector to be inspected is a multi-fiber connector, the ferrule 11 is an MT ferrule as shown in FIG. 1. If the optical connector to be inspected is a single-fiber connector, the ferrule 11 is a cylindrical ferrule. However, the ferrule 11 is not limited to the two types of ferrules described above.

[0015] The following description will be given taking an MT ferrule as an example of the ferrule 11 used in the connector 10. As shown in Figure 1, the ferrule 11 includes a plurality of fiber holes 12 aligned in the X direction, grooves 13 that guide the optical fibers 1 into the fiber holes 12, and windows 14 that communicate with the grooves 13.

[0016] The optical fiber 1 is, for example, a single-mode fiber (SMF). The optical fiber 1 is inserted from the back surface 16 of the ferrule 11 through the groove 13 and into the fiber hole 12. The optical fiber 1 is held in the ferrule 11 by filling an adhesive through the window 14. An end 3 (see FIG. 2 ) of the optical fiber 1 is exposed at an end face 15 of the ferrule 11.

[0017] The multiple fiber holes 12 extend along the Z direction within the ferrule 11 and open to an end face (front face) 15 of the ferrule 11. The end face 15 may be perpendicular to the Z direction (parallel to the XY plane) or may be inclined with respect to the Z and Y directions. In the latter case, the inclination angle is, for example, 8°.

[0018] Guide holes 17 are formed in the end face 15. The guide holes 17 are located on both sides of a group of a plurality of fiber holes 12 aligned in the X direction. When connecting the connector 10 and a connector 50 to be inspected to each other, positioning guide pins (not shown) are inserted into the guide holes 17.

[0019] The spacer 20 is provided on the end face 15. The spacer 20 is a plate member or sheet material having a predetermined thickness in the Z direction, and is made of an optically transparent material such as glass. The spacer 20 is provided on the end face 15 of the ferrule 11 and is in close contact with the end 3 of the optical fiber 1. A through hole 21 is formed in the spacer 20 so that the guide pin can be inserted into the guide hole 17.

[0020] As will be described later, test light 5 from a light source (laser light source) 61 (see FIG. 4A ) propagates through the core 2 of the optical fiber 1 in the Z direction and enters the spacer 20. The test light 5 then propagates through the spacer 20. The refractive index of the spacer 20 may be the same as that of the core 2 of the optical fiber 1. In this case, reflection at the boundary surface due to the difference in refractive index between the core 2 and the spacer 20 can be suppressed.

[0021] The light-shielding mask 30 is provided on the spacer 20 and has a light-shielding property against the test light 5. The light-shielding mask 30 may be formed in a layer shape having a predetermined thickness on the surface (front surface) 22 of the spacer 20 using, for example, photolithography.

[0022] Mask holes 31 are formed in the light-shielding mask 30. The mask holes 31 extend in the Z direction and penetrate the light-shielding mask 30. The same number of mask holes 31 as the fiber holes 12 are formed in the light-shielding mask 30, and are located at positions corresponding to the fiber holes 12. Specifically, the mask holes 31 are located at positions where a portion of the test light 5 that is emitted from the optical fiber 1 in the corresponding fiber hole 12 and passes through the spacer 20 passes through. As long as this condition is satisfied, the central axis M of the mask hole 31 may coincide with the central axis C1B of the core 2 or may be deviated from the central axis C1B.

[0023] The light-shielding mask 30, together with the spacer 20, is attached to the end face 15 using a precision alignment machine (not shown) of a well-known configuration. Therefore, the position of the central axis M of the mask hole 31 can be set with high precision with respect to the design position of the core 2 set in the ferrule 11. Figure 2 shows a state in which the central axis M of the mask hole 31 coincides with the central axis C1A of the core 2 when the core 2 is positioned at the design position. In the following description, for convenience, this central axis C1A may be referred to as the fiber core axis C1A.

[0024] As shown in Figure 2, the test light 5 propagates in the Z direction (i.e., from the back surface 16 (see Figure 1) of the ferrule 11 toward the end face 15). The test light 5 is emitted from the end face 15 at an emission angle of approximately 8° and propagates toward the light-shielding mask 30 while diffusing within the spacer 20. A portion of the test light 5 that reaches the light-shielding mask 30 passes through the mask holes 31 and exits the light-shielding mask 30.

[0025] The intensity distribution 5a of the test light 5 is a normal distribution at the end face 15. The test light 5 is sufficiently diffused while propagating through the spacer 20, and a portion of it passes through the mask hole 31. As a result, the test light 5 emitted from the mask hole 31 forms a plane wave with a nearly uniform intensity distribution.

[0026] As shown by the dotted line in Figure 2, a GRIN (graded index) lens 4 may be provided between the end 3 of the optical fiber 1 and the spacer 20. The GRIN lens 4 is coupled to the end 3 of the optical fiber 1 and is housed in the fiber hole 12 together with the optical fiber 1. The GRIN lens 4 converts the test light 5 emitted from the end 3 into parallel light. Therefore, a plane wave can be obtained earlier than when the GRIN lens 4 is not provided. This allows the thickness of the spacer 20 to be thinned, thereby enabling the connector 10 to be made more compact.

[0027] 3, in the optical connector inspection method according to this embodiment, the connector 10 and a connector 50 to be inspected are connected (butted) to each other. The connector 50 holds an optical fiber 41. The proportion of the intensity of the test light 5 emitted from the connector 10 that is coupled to the core 42 of the optical fiber 41 and becomes propagating light is equal to the overlap integral between the intensity distribution of the test light 5 emitted from the mask hole 31 and the intensity distribution of the propagating light in the optical fiber 41. Therefore, the axial misalignment D of the core of the optical fiber 41 with respect to the center of the mask hole 31 can be derived from the measurement results of the connection loss of the connector 50.

[0028] For example, when the optical fiber 41 is a single-mode optical fiber, the intensity distribution of the propagating light is a normal distribution centered on the center of the core 42. This normal distribution can be calculated from the mode field diameter (MFD) of the optical fiber 41, which is known from specifications or measurements. On the other hand, the test light 5 emitted from the mask hole 31 can be considered a plane wave, and its intensity distribution is a uniform distribution. Therefore, the rate at which the test light 5 is coupled to the propagating light is greatest when the center of the core 42 and the center of the mask hole 31 are aligned, and decreases as the offset between the two centers increases.

[0029] [First Measurement Example] Next, a first measurement example of the optical connector inspection method using the connector 10 will be described. In the first measurement example, only one connector 10 is used as the connector for inspection. Also, as shown in Figure 3, the position of the central axis M of the mask hole 31 coincides with the position of the fiber core axis C1A.

[0030] In the first measurement example, the connector 10 serving as the first connector is connected to the connector 50 serving as the second connector, and the connection loss α of the test light 5 is measured. Then, based on the measured connection loss α, the axial misalignment D of the core 42 of the optical fiber 41 with respect to the fiber core axis C1A is calculated.

[0031] Specifically, as shown in FIG. 4A, an optical power meter 62 is connected to the light source 61 via the connector 10, and the intensity P ０ Next, as shown in FIG. 4B, the optical power meter 62 is connected to the light source 61 via the connector 10 and the connector 50 which are connected to each other, and the intensity P １ The difference between these two intensities (P ０ -P １ ) is the connection loss α [dB] of the connector 50.

[0032] FIG. 5 is a graph showing an example of the relationship between the axial misalignment D and the connection loss α. As described above, the intensity ratio of the test light 5 emitted from the connector 10 that couples with the core 42 of the optical fiber 41 and becomes propagating light is equal to the overlap integral between the intensity distribution of the test light 5 emitted from the mask hole 31 and the intensity distribution of the propagating light in the optical fiber 41. Furthermore, the optical intensity distribution of the propagating light can be calculated (back-calculated) from the known MFD of the optical fiber 41. Therefore, as shown in FIG. 5, the connection loss α of the connector 50 varies depending on the axial misalignment D. In other words, the axial misalignment D can be calculated by measuring the connection loss α.

[0033] Figure 5 shows the change in splice loss α when the MFD of the optical fiber 41 is assumed to be 9 μm and the diameter of the mask hole 31 is assumed to be 2 μm. In this example, when the measured splice loss α is 8.9 dB or less, the central axis C2 of the core 42 is located within a ±0.3 μm range of the fiber core axis C1A. Furthermore, when the central axis C2 of the core 42 is deviated from the fiber core axis C1A by an absolute value of 1.5 μm or more, the splice loss α changes by 0.1 dB or more for an axial misalignment of 0.05 μm. Considering that the resolution of a typical optical power meter is 0.01 dB, it is clear that the axial misalignment D can be measured with higher resolution than with an optical microscope.

[0034] The central axis M of the mask hole 31 may be offset from the fiber core axis C1A. As described above, the mask hole 31 can be positioned with high precision with respect to the design position of the core 2 by a precision alignment machine. That is, the position (coordinates) of the mask hole 31 with respect to the design position of the core 2 is known, so the amount of axial misalignment of the central axis C2 of the core 42 with respect to the design position can be calculated by correcting the amount of axial misalignment D calculated by the above measurement, taking into account the amount of misalignment between the mask hole 31 and the design position.

[0035] [Second Example] Next, a second measurement example of the optical connector inspection method using the connector 10 will be described. In the second measurement example, two connectors 10 are used as connectors for inspection. For ease of explanation, one of the two connectors 10 will be referred to as connector 10A and the other as connector 10B. Furthermore, the mask holes 31 of connectors 10A and 10B will be referred to as mask hole 31A and mask hole 31B, respectively.

[0036] As shown in Fig. 6, the mask holes 31A and 31B are located at different positions. For example, the mask holes 31A and 31B are located on one side and the other side in the Y direction relative to the fiber core axis C1A. Specifically, as shown in Fig. 7A, in the connector 10A, the center axis Ma of the mask hole 31A is offset by a distance d from the fiber core axis C1A on the positive side in the Y direction. On the other hand, as shown in Fig. 7B, in the connector 10B, the center axis M of the mask hole 31B is offset by a distance d from the fiber core axis C1A on the negative side in the Y direction.

[0037] In the second measurement example, the connector 50 serving as the second connector is connected to the connector 10A serving as the first connector, and the connection loss α ａ Furthermore, in a state where the connector 50 is connected to the connector 10B as the first connector, the connection loss α ｂ Then, measure the two measured splice losses α ａ , α ｂ Based on this, the amount of axial misalignment D of the core 42 of the optical fiber 41 with respect to the fiber core axis C1A common to each connector 10 is calculated.

[0038] Specifically, as shown in FIG. 8A, an optical power meter 62 is connected to a light source 61 via a connector 10A, and the intensity P Ａ０ Next, as shown in FIG. 8B, the optical power meter 62 is connected to the light source 61 via the connector 10A and the connector 50 which are connected to each other, and the intensity P Ａ１ Measure [dBm].

[0039] Furthermore, as shown in FIG. 8C, an optical power meter 62 is connected to the light source 61 via the connector 10B, and the intensity P Ｂ０ Finally, as shown in FIG. 8D, the optical power meter 62 is connected to the light source 61 via the connector 10B and the connector 50 which are connected to each other, and the intensity P Ｂ１ Measure [dBm].

[0040] From the above measurements, the intensity difference (P Ａ０ -P Ａ１ ) is the connection loss α of the connector 50 when the connector 10A is used. Ａ [dB]. Also, the intensity difference (P Ｂ０ -P Ｂ１ ) is the connection loss α of the connector 50 when the connector 10B is used. Ｂ [dB].

[0041] FIG. 9 shows the relationship between the amount of axial misalignment D and the splice loss α Ａ , α Ｂ 9 is a graph showing an example of the relationship between the splice loss α when the MFD of the optical fiber 41 is assumed to be 9 μm and the diameter of the mask hole 31 is assumed to be 2 μm. Ａ , α Ｂ As shown in FIG. 9, in the second measurement example, the change in the connection loss α Ａ , α Ｂ changes depending on the amount of axial misalignment D. As shown in FIG. 10, the difference Y (=α Ｂ -α Ａ ) changes with the amount of axial misalignment D. In other words, by calculating the difference Y in the connection loss, the amount of axial misalignment D corresponding thereto can be immediately obtained.

[0042] 10, it can be seen that the amount of axis misalignment D can be measured with a resolution of 0.0125 μm / 0.1 dB. As mentioned above, considering that the resolution of a typical optical power meter is 0.01 dB, it can be seen that the amount of axis misalignment D can be measured with a higher resolution than when using an optical microscope.

[0043] The number of connectors 10 used in the optical connector inspection method may be three or more. In this case, as in the second measurement example, the mask holes 31 of the connectors 10 are located at different positions. For example, when three connectors 10A to 10C are used as the connectors 10, as shown in FIG. 11, the mask hole 31A of the connector 10A is located at (+d, +d) in the XY coordinate system with the design position as the origin. Furthermore, the mask hole 31B of the connector 10B is located at (+d, -d), and the mask hole 31C of the connector 10C is located at (-d, +d). In this example, the connection loss of the connector 50 using the connectors 10A, 10B, and 10C is α Ａ , α Ｂ , α Ｃ When this is the case, the amount of axial misalignment of the fiber core axis in the X direction D Ｘ is (α Ｃ -α Ａ ) and the amount of axial misalignment of the fiber core axis in the Y direction D Ｙ is (α Ｃ -α Ａ ), (α Ｂ -α Ａ ) can be obtained from

[0044] It is also possible to use four connectors 10 in the optical connector inspection method. For example, when four connectors 10A to 10D are used as the connectors 10, the coordinates (x, y) of the mask holes 31 of the connectors 10A, 10B, 10C, and 10D can be set to (-d, 0), (d, 0), (0, -d), and (0, d), respectively. In either case, it is possible to measure the amount of axial misalignment D with a higher resolution than measurement using an optical microscope.

[0045] REFERENCE SIGNS LIST 1 Optical fiber 2 Core 3 End 4 GRIN lens 5 Test light 10 Connector for optical connector inspection 11 Ferrule 12 Fiber hole 15 End face (front face) 20 Spacer 30 Light-shielding mask 31, 31A, 31B, 31C Mask hole 41 Optical fiber 42 Core 50 Connector C1A Fiber core axis

Claims

1. An optical connector inspection connector comprising: a ferrule that holds an optical fiber and has an end face at which the end of the optical fiber is exposed; an optically transparent spacer that is provided at the end face; and a light-shielding mask that is provided on the spacer and has a mask hole at a position that allows a portion of the test light that is emitted from the end of the optical fiber and passes through the spacer to pass through.

2. The optical connector inspection connector according to claim 1, further comprising a GRIN lens provided between the end of the optical fiber and the spacer, for converting the test light into parallel light.

3. An optical connector inspection method comprising: a light-shielding mask having a mask hole at a position where a portion of test light emitted from the end of a first optical fiber passes through; measuring the connection loss of the test light while a second connector holding a second optical fiber is connected to a first connector holding the first optical fiber; and calculating the amount of axial misalignment of the core of the second optical fiber relative to the design position of the center axis of the fiber hole in the first connector based on the measured connection loss.

4. An optical connector inspection method comprising: a light-shielding mask having a mask hole at a position where a portion of the test light emitted from the end of a first optical fiber passes; a second connector holding a second optical fiber is connected to a plurality of first connectors holding the first optical fiber; measuring the connection loss of the test light when each of the first connectors is connected to the second connector; calculating the amount of axial deviation of the core of the second optical fiber from the design position of the central axis of the fiber hole common to the plurality of first connectors based on each of the measured connection losses; and wherein the mask hole of each of the first connectors is located at a different position from each other.

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