JP2006011280A - Vertex deviation measuring apparatus of ferrule for optical fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vertex deviation measuring instrument of a ferrule for an optical fiber with which repetitive reproducibility of high accuracy can be obtained in measurement of a vertex deviation of a ferrule end surface. <P>SOLUTION: The vertex deviation measuring instrument of the ferrule for the optical fiber is constituted by arranging the ferrule formed on a spherical surface at its front end surface and inserted and fixed with an optical fiber at its center on a ferrule holder, forms interference fringes by respectively receiving the light formed by irradiating the front end surface of the ferrule with light from a light source and reflecting the same and the light formed by irradiating the front end surface of the ferrule with the light varied in optical path length from the light source and reflecting the same, respectively, and measures the virtual distance from the central position Q of the interference fringes to the central position of the optical axis to be irradiated to the front end surface of the ferrule as the vertex deviation of the ferrule. A precision sleeve having an inner diameter slightly greater than the external diameter of the ferrule is used for the ferrule holder. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a measuring apparatus for inspecting the end face shape of an optical fiber ferrule used in a connection portion of an optical fiber that is a transmission line in optical communication technology.

  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.

  A receptacle-type optical module in which a connector is connected among the optical modules includes a light receiving / emitting element 22 at one end of an optical receptacle 18 as shown in FIG. 1, and a plug of an optical connector (SC connector) at the other end. The ferrule 17 is connected.

    As shown in FIG. 1, the optical receptacle 18 includes a ferrule 4 made of a ceramic material such as zirconia or alumina, and a stub 13 obtained by inserting and fixing an optical fiber 27 made of quartz glass or the like in a through hole of the ferrule 4. The rear end portion is fixed to the holder 20 by press-fitting, the tip end portion is inserted into the inner hole of the sleeve 19, and they are press-fitted or adhesively fixed to the sleeve case 21.

    In recent years, miniaturization of optical modules has been required due to the demand for high-density mounting, and the total length of the optical receptacle 18 has also been required to be shortened. As the total length of the optical receptacle 18 is shortened, the total length of the stub 13 needs to be shortened. The connector connected to the optical receptacle 18 is also a smaller connector such as an SC connector or an LC connector.

    The stub 13 used for the optical receptacle 18 has a cylindrical shape, and the tip surface 5 of the ferrule 4 is mirror-polished simultaneously with the optical fiber 27. The outer diameter tolerance of the ferrule 4 is ± 1 μm or less, and the concentricity of the insertion hole of the optical fiber is a very precise part of about 1 μm.

The optical fiber at the center has a core through which the optical signal propagates. To realize an optical connector with a small connection loss by connecting the cores, the tip surface 5 of the ferrule is polished into a spherical surface, and the apex of the spherical surface A PC polished optical connector having an optical fiber core is effective.

  As shown in FIG. 4, the tip surface 5 of the ferrule 4 has a vertex shift distance L from the vertex 71 of the tip surface 5 to the optical axis 87, which is the central axis of the optical fiber 27, of Telcordia GR-326. The standard (reliability standard established by Telcordia, which has been disseminated as a standard standard in the field of optical communication, and hereinafter simply referred to as Telcordia) is determined to be smaller than 50 μm.

  The reason why the standard is defined in this way is that, when the apex deviation L is large, for example, when two ferrules 4 are brought into contact with each other, physical contact between the optical fibers 27 is obstructed, thereby requiring a connector. This is to deteriorate the insertion loss.

  As a method for measuring this parameter, a three-dimensional interference fringe measuring device manufactured by DORC (Direct Optical Research Company) is widely used (see, for example, Patent Document 1).

  The structure and operating principle of such an interference fringe measuring apparatus will be described with reference to FIG.

  FIG. 2 is a diagram for explaining the internal structure of the three-dimensional interference measurement apparatus. The light source 80 emits light for measuring vertex deviation, the first lens 81 for converting light from the light source 80 into parallel light, A half mirror 82 for separating parallel light into two optical paths, a wavelength correction plate 83 for correcting the wavelength of the light that has passed through the half mirror 82, and a mirror 84 for totally reflecting the light that has passed through the wavelength correction plate 83. The objective lens 85 for condensing the light reflected by the half mirror 82 on the ferrule 60, the ferrule 4 and the second lens 86 for imaging the light from the mirror 84. Although the ferrule 4 is not shown, a mounting portion is disposed for measurement, and the ferrule 4 is disposed on the mounting portion for measurement.

  The light source 80 is an incoherent light source, and an LED having a wavelength λ of 500 nm is generally used. The light from the light source 80 is converted into parallel light by the first lens 81 and separated into two paths (optical path a and optical path b) by the above-described configuration to form interference fringes.

  Here, in the optical path a, the light generated from the light source 80 and converted in parallel by the first lens 81 hits the half mirror 82 (optical path a-1), and the reflected light hits the tip surface 5 of the ferrule 4 (optical path a -2), the reflected light is imaged by the second lens 86 through the half mirror 82 (optical path a-3). On the other hand, in the optical path b, the light generated from the light source 80 and converted in parallel by the first lens 81 passes through the half mirror 82 and passes through the wavelength correction plate 83 and hits the mirror 84 (optical path b-1). The light is reflected by the half mirror 82 (optical path b-2), and the reflected light is imaged by the second lens 86 through the half mirror 82 (optical path b-3). Here, interference occurs when the wavelength difference between the optical path a and the optical path b formed by the second lens 86 is λ / 2, and a bright and dark image (interference fringe 11) is generated as shown in FIG.

  By operating the mirror 84, the wavelength of the optical path b is adjusted, and the position information of the z component of the ferrule 4 is obtained by changing the wavelength difference between the optical path a and the optical path b. A method for obtaining the end face shape is a three-dimensional interference fringe measurement method.

  According to this interference fringe measuring apparatus, as shown in FIGS. 3 and 4, it is assumed that the center position Q of the interference fringe corresponds to the apex 71 on the ferrule tip surface 5, and light that is the center of the optical fiber 27. It is assumed that the end face 25 of the shaft 130 and the optical axis center position 87 irradiated with the light from the light source 80 on the optical fiber end face 5 coincide with each other, and interference is performed using the interference fringes 11 appearing every λ / 4. The measurement was performed using the distance from the center position Q of the stripe to the optical axis center position 87 as the virtual distance L of the apex deviation.

  However, in the conventional measurement, before the vertex deviation measurement, the lens 85 is a condensing lens, and the lens has aberration, so that the light from the light source 80 is accurately applied to the end face 25 of the optical fiber 27. However, prior to the vertex deviation measurement, the incident position of the ferrule 4 and the light source 80 is adjusted to correct the optical axis deviation.

  This point will be described in detail with reference to FIGS. First, the ferrule part 89 of the master connector is arranged in the V groove 7 and the interference fringe center position Q is measured. At this time, as a method of holding the ferrule part 89 of the master connector and the ferrule 4 which is the object to be measured, a method of placing a ferrule in the V groove 7 shown in FIG. In the optical axis deviation correction, the interference fringe center position Q is measured a plurality of times in the same manner as described above by rotating based on the ferrule center axis while pressing the ferrule portion 89 of the master connector. In this case, the interference fringe center position Q draws the locus of the circle S, and the center position R of this circle is calculated. The center position R is a center position with respect to the outer periphery of the ferrule and corresponds to the end face 25 of the optical axis 87 that is the central axis of the optical fiber 27. Therefore, as shown in FIG. 3, the optical axis center position 87 and the center position R from the light source 80 are actually shifted by a distance e (μm), which is called an optical axis shift. In the case of a three-dimensional interference fringe measuring apparatus manufactured by DORC, this value is indicated by the software correction value, and the upper limit is 20 μm.

Therefore, when the value of the optical axis deviation e is larger than 20 μm, correction is performed by changing the position of the half mirror 82 so that the light irradiation position becomes 20 μm or less.
Japanese Patent Laid-Open No. 5-118832

  However, since the conventional holding method holds the ferrule 4 over the entire surface of the V-groove 7, high-precision repeatability cannot be obtained when measuring the vertex deviation L of the ferrule end face 5. The reason is that it is difficult to form a flat surface of micron or less in units of several millimeters in the length of the V-groove 7, and the ferrule 4 cannot always maintain a stable posture because of the minute irregularities in the V-groove. Because. In addition, the V-groove 4 is worn every time the measurement is repeated, and there is a problem that large irregularities are formed in the V-groove 4 and the ferrule cannot be stably held.

  Further, when the ferrule 4 having a short length of 4 mm or less is pressed against the V groove 4 by the rod-shaped member 6, if the ferrule 4 is pressed near the end of the ferrule 4, the ferrule 4 is inclined, and the repetitive reproducibility of the apex deviation L is increased. There was a problem that it could not be obtained.

  In view of the above problems, the apex deviation measuring device for an optical fiber ferrule of the present invention has a ferrule in which a tip surface is formed into a spherical surface and an optical fiber is inserted and fixed in the center on a ferrule holder. Interference fringes are formed by receiving light reflected from the tip surface of the ferrule and light reflected from the light source with different light path lengths from the light source. In addition, in the optical fiber ferrule vertex deviation measuring apparatus that measures the virtual distance from the center position Q of the interference fringe to the optical axis center position L irradiating the tip surface of the ferrule as the vertex deviation distance of the ferrule, The tool is characterized in that a precision sleeve having an inner diameter slightly larger than the outer diameter of the ferrule is used.

  Further, a through hole in which a part of the side surface of the ferrule can be exposed is formed in the side wall of the precision sleeve, and a rod-shaped member is configured to be able to press the side surface of the ferrule from the through hole. is there.

  Furthermore, the precision sleeve is formed of zirconia ceramics.

  Further, the distance between the center position R of the circle drawn by the center position Q of the interference fringes and the center position L of the optical axis is determined by rotating while pressing with a rod-shaped member around the center axis of the ferrule. It measures as follows.

  According to the present invention, when the ferrule as the object to be measured is inserted into the inner diameter of the precision sleeve, since the clearance between the outer diameter of the ferrule and the inner diameter of the precision sleeve is minimal, the measurement error of the vertex deviation amount of the ferrule end face When the outer periphery near the end of the ferrule having a short overall length is pressed, the tilt of the ferrule can be suppressed and high-accuracy measurement is possible.

  Also, with regard to optical axis deviation correction, when the ferrule part of the master connector is rotated while being pressed with a rod-like member, the rotation is further smoothed. improves.

  Further, since the precision sleeve is made of zirconia ceramic, wear of the holder due to measurement does not occur, so that stable holding of the ferrule can be realized, and high-precision repeatability can be realized.

  Here, an embodiment of the present invention will be described.

  FIG. 6 is a diagram showing an embodiment of the apex deviation measuring apparatus for an optical fiber ferrule of the present invention.

  As the ferrule holder 1 of the apex deviation measuring device for an optical fiber ferrule of the present invention, a precision sleeve 9 having an inner diameter slightly larger than the outer diameter of the ferrule 4 which is a measurement object is used. The reason for this is that if the clearance between the precision sleeve 9 and the outer diameter of the ferrule 4 is large, when the ferrule 4 is pressed against the side surface of the ferrule 4 with the rod-shaped member 6 for high-precision measurement, the end of the ferrule 4 Although the vicinity is pressed, since the end face 5 of the ferrule 4 is inclined with respect to the optical path a-2, the apex deviation of the end face of the ferrule 4 cannot be measured with good reproducibility.

  Furthermore, in recent years, miniaturization of optical modules has been demanded due to the demand for high-density mounting, and the overall length of the ferrule 4 has been shortened accordingly. When the entire length of the ferrule 4 is shortened, the ferrule end face 5 is easily inclined with respect to the optical path a-2, and the reproducibility of the vertex shift is further deteriorated. Therefore, it is necessary to minimize the clearance between the outer diameter of the ferrule 4 and the inner diameter of the precision sleeve 9 so that the ferrule end face 5 does not tilt no matter where the side surface of the ferrule 4 is pressed by the rod-shaped member 6.

  Further, as shown in FIG. 6, a through hole 10 in which a part of the side surface of the ferrule 4 can be exposed is formed in the side wall of the precision sleeve 9, and a rod-like member can press the side surface of the ferrule 4 from the through hole 10. It is preferable that it is comprised.

  The reason for pressing is that, as explained in the prior art, it is necessary to correct the optical axis deviation at the time of apex deviation measurement, rotate the ferrule part 89 of the master connector by 45 degrees and plot the center of the interference fringe. However, the circular locus S must be drawn. If the ferrule portion 89 of the master connector is not pressed at this time, a beautiful circular locus S with good reproducibility cannot be drawn, and the optical axis deviation cannot be corrected.

  The precision sleeve 9 is preferably a zirconia ceramic. Zirconia ceramics generally have a Young's modulus of 210 GPa and a Vickers hardness of 12.3 GPa, and are excellent in wear resistance, so that there is no wear of the holder due to measurement, so stable holding of the ferrule can be realized, and high-precision repetition Reproducibility can be realized.

  Conventionally, the V-groove 7 in which the ferrule 4 is arranged is often made of a metal such as stainless steel, and the V-groove 7 is worn out as the number of measurements is increased, and the surface of the V-groove 7 is uneven and cannot be stably held. The ferrule holder is preferably made of the same material as the ferrule 4 that is the object to be measured.

  The precision sleeve 9 is made by inserting a stainless steel pin with excellent outer diameter accuracy coated with abrasive grains into the inner diameter of a molded and fired zirconia ceramic sleeve, and rotating the pin at high speed for polishing. The inner diameter of the sleeve can be precisely finished. The abrasive grains used are a mixture of oil and diamond with a fine particle size of about several μm.

  Here, the ferrule 4 as the object to be measured will be described. The ferrule 4 includes the ferrule 4 and the optical fiber 27 shown in FIG. The ferrule 4 is a cylindrical body made of ceramic, plastic, glass, etc., and the optical fiber 27 is inserted and held in the central through hole, and the end face of the ferrule 4 and the end face of the optical fiber 27 are polished at the same time to finish a mirror surface. It is to be produced. As the PC end face shape after polishing, as a standard standard in the field of optical communication, the radius of curvature is 7 to 25 mm in the case of the LC type optical connector, 10 to 25 mm in the case of the SC type optical connector, and the apex deviation is 50 μm. It is stipulated that it is smaller than.

  The reason why the standard is defined in this way is that, when the apex deviation L is large, for example, when two ferrules 4 are brought into contact with each other, physical contact between the optical fibers 27 is obstructed, thereby requiring a connector. This is to deteriorate the insertion loss.

  Next, the measurement method will be described.

First, in order to correct the optical axis deviation, as shown in FIG. 6C, the ferrule part 89 of the master connector is inserted into the precision sleeve 9 as the ferrule holder, and the ferrule part 89 of the master connector is inserted by the rod-like member 6. Press the side wall. Thereafter, the optical path a-2 is irradiated onto the ferrule end face 5 of the master connector, and this reflected light is imaged by the second lens 86 through the half mirror 82 (optical path a-3). On the other hand, in the optical path b, the light generated from the light source 80 and converted in parallel by the first lens 81 passes through the half mirror 82 and passes through the wavelength correction plate 83 and hits the mirror 84 (optical path b-1). The light is reflected by the half mirror 82 (optical path b-2), and the reflected light is imaged by the second lens 86 through the half mirror 82 (optical path b-3). Here, interference occurs when the wavelength difference between the optical path a and the optical path b formed by the second lens 86 is λ / 2, and a bright and dark image (interference fringe 11) is generated as shown in FIG. Thereafter, the interference fringe center position Q is measured a plurality of times by rotating based on the ferrule center axis. In this case, the interference fringe center position Q draws the locus of the circle S, and the center position R of this circle is calculated. This center position R is a center position with respect to the outer periphery of the ferrule and corresponds to the end face 25 of the optical axis 87 which is the center axis of the optical fiber 27. The center position R of the optical axis 87 and the circle S is Optical axis deviation correction can be performed by changing the position. At this time, by using a precision sleeve for the ferrule holder, the ferrule portion 89 of the master connector can be smoothly rotated. Therefore, the position of R can be calculated with high reproducibility, and highly accurate optical axis deviation correction can be performed.

  After the optical axis deviation correction, as shown in FIGS. 6A and 6B, the ferrule 4 as the object to be measured is inserted into the precision sleeve 9 and the side wall of the ferrule 4 is pressed by the rod-like member 6. Thereafter, the ferrule end face 5 is irradiated with the optical path a-2, an interference fringe is generated, and the distance between the center Q of the interference fringe and the optical axis 87 is calculated, whereby the apex deviation can be measured.

  Next, examples of the present invention will be described. Here, the experiment was conducted by the following method. As the ferrule for measurement, a ferrule for LC type optical connector having a total length of 2.4 mm and an outer diameter of 1.250 mm was used.

  As an embodiment of the present invention, as shown in FIGS. 6 (a) and 6 (b), an approximately 0.6 mm square through hole 10 is formed in the side wall of a precision sleeve having an inner diameter of 1.251 to 1.253 mm. The ferrule 4 inserted into the precision sleeve inner diameter was pressed through a rod-shaped member 6 having a diameter of about 0.5 mm.

  The holder 1 of the optical fiber ferrule vertex deviation measuring apparatus of the present invention holding the ferrule 4 as described above was placed in front of the optical path a-2, and the repeatability of the vertex deviation of the ferrule end face was investigated. The material of the precision sleeve is zirconia ceramics.

  As a comparative example, as shown in FIG. 5, a V-shaped groove 7 is formed in a cylindrical stainless steel SUS303, and a through hole 10 having a side of about 0.6 mm is formed in the side wall, and the diameter of the through hole 10 is about 0. The ferrule 4 arranged in the V-groove 7 was pressed through the rod-shaped member 6 having a thickness of 5 mm.

The holder 2 of the conventional optical fiber ferrule apex deviation measuring device holding the ferrule 4 as described above was placed in front of the optical path a-2, and the repeatability of the apex deviation of the ferrule end face was investigated. The V groove depth T was 1.25 mm. The measured ferrule was made the same sample in the case of the holder 1 of the apex deviation measuring device of the optical fiber ferrule of the present invention and the case of the apex deviation measuring holder 2 of the conventional optical fiber ferrule. The results are as shown in Table 1.

  From Table 1, the repeatability of the vertex deviation of the ferrule end face 5 is σ = 0.6 when the holder 1 of the optical fiber ferrule vertex deviation measuring apparatus of the present invention is used. On the other hand, when the holder 2 of the conventional optical fiber ferrule apex deviation measuring apparatus 2 was used, σ = 16.9, which greatly improved reproducibility.

It is sectional drawing which shows an optical module. It is a figure which shows one Example of the vertex shift | offset | difference measuring apparatus of the ferrule end surface for optical fibers. It is a figure which shows one Example when measuring the vertex shift | offset | difference of the ferrule end surface for optical fibers from an interference fringe. It is an expanded sectional view of the ferrule end face for optical fibers. (A) is a front view which shows the holder of the vertex shift measuring apparatus of the conventional ferrule for optical fibers, (b) It is sectional drawing which shows the holder of the vertex shift measuring apparatus of the conventional ferrule for optical fibers, c) It is sectional drawing which shows having hold | maintained the master connector to the holder of the vertex deviation measuring apparatus of the conventional ferrule for optical fibers. (A) is a front view which shows the holder of the vertex deviation measuring apparatus of the ferrule for optical fibers of this invention, (b) It is sectional drawing which shows the holder of the vertex deviation measuring apparatus of the ferrule for optical fibers of this invention. (C) It is sectional drawing which shows having hold | maintained the master connector to the holder of the vertex deviation measuring apparatus of the ferrule for optical fibers of this invention.

Explanation of symbols

1: holder 2: holder 4: ferrule 5: ferrule end face 6: rod-like member 7: V groove 9: precision sleeve 10: through hole 11: interference fringe 13: stub 17: plug ferrule 18: optical receptacle 19: sleeve 20: holder 21: sleeve case 22: optical element 23: lens 24: case 25: optical fiber end face 27: optical fiber 71: vertex of ferrule 80: light source 81: first lens 82: half mirror 83: wavelength correction plate 84 : Mirror 85: Second lens 86: Objective lens 87: Optical axis 88: Master connector 89: Ferrule part of master connector

Claims (4)

A ferrule having a tip surface formed into a spherical surface and an optical fiber inserted and fixed in the center is disposed on the ferrule holder, and light reflected from the light source by irradiating the tip surface of the ferrule and the optical path length from the light source An optical axis for irradiating the tip surface of the ferrule from the center position Q of the interference fringe by forming the interference fringes by receiving light reflected from the tip surface of the ferrule and receiving the reflected light respectively In the optical fiber ferrule vertex misalignment measuring apparatus that measures the virtual distance to the center position L as the ferrule apex misalignment distance, the ferrule holder uses a precision sleeve having an inner diameter slightly larger than the outer diameter of the ferrule. An apex deviation measuring device for an optical fiber ferrule. The through hole in which a part of the side surface of the ferrule can be exposed is formed in the side wall of the precision sleeve, and a rod-shaped member is configured to be able to press the side surface of the ferrule from the through hole. The apex deviation measuring device of the ferrule for optical fibers described. 3. The optical fiber ferrule apex deviation measuring device according to claim 1, wherein the precision sleeve is made of zirconia ceramics. The distance between the center position R of the circle drawn by the center position Q of the interference fringes and the center position L of the optical axis is measured as the apex misalignment distance by rotating while pressing with a rod-shaped member around the center axis of the ferrule. The apex deviation measuring device for an optical fiber ferrule according to any one of claims 1 to 3.

Images