JP3971742B2 - Optical connector connection loss calculation method and simulator using the same - Google Patents

Description

  The present invention relates to a method for estimating distribution data of connection loss values of optical connectors used for optical communication by simulation and a simulator using the method.

  In recent years, optical communication using an optical fiber has been used with an increase in the amount of information in communication. In this optical communication, an optical connector is used to connect optical fibers.

  As shown in FIGS. 6 and 7, the plug 10 used in the optical connector has an optical fiber protector 2 fixed in advance to a cylindrical ferrule 1, and the coating is removed from the through hole 1 a formed in the ferrule 1. The tip of the optical fiber 3 is inserted, held and fixed by the adhesive 4, and the pair of ferrules 1 are inserted from both ends of the split sleeve 5 and polished into a convex spherical shape inside the split sleeve 5. It is the structure which made 1b contact | abut.

  In the optical connector, in order to ensure low-loss and low-reflection optical connection, optical characteristics are measured after the optical connector is assembled. Measurement items include connection loss, which indicates the light transmittance at the connection part of the optical connector, and return loss, which indicates the reflectance of light. Currently, these connection loss and return loss are individually determined manually. Is measured.

  8A and 8B are diagrams for explaining a method of measuring the random connection loss of the optical connector. In this figure, an LD light source 11, a reference optical cord 12, an optical connector 12a, a reference optical connector 12b, an adapter 13, an optical cord 14 with optical connectors at both ends to be measured, an optical connector 14a to be measured, and a termination side Optical connector 14b, light receiving unit 15, and power meter 16.

  Here, the reference optical connector 12b is an optical connector having the same specifications as the optical connectors 14a and 14b to be measured. Usually, the optical connector randomly extracted from the same lot as the optical connector for measurement in manufacturing is used. .

  First, prior to the measurement of the connection loss of the optical connector, the connection loss reference is set in the measurement system shown in FIG. The optical connector 12 a at one end of the reference optical cord 12 is connected to the LD light source 11, and the reference optical connector 12 b is connected to the light receiving unit 15. Light emitted from the reference optical connector 12b is received by the light receiving unit 15 through the air layer. The output power P0 is read from the reference optical connector 12b by the power meter 16, and this value is defined as a reference value (connection loss is 0 dB) in the connection loss measurement.

  Next, in order to measure the connection loss of the optical connector 14a to be measured, the reference optical connector 12b is removed from the light receiving unit 15, and then, as shown in FIG. The light emitted from the optical connector 14b connected to the optical cord 14 is received by the light receiving unit 15 through the air layer as in the case of measuring the reference value. The output power P1 at this time is measured by the power meter 16 (see Patent Document 1).

The connection loss IL at the connection portion of the optical connector is expressed by the following equation using the output power P0, the output power P1, the transmission loss α (dB / Km) of the optical fiber, and the reflection loss β at the end face of the optical connector. Is done.

  Here, the reflection at the end face of the optical connector is usually 0.01% or less, and the reflection loss β is less than the resolution of the measuring device, so there is no need to consider it. In the case of a single mode optical fiber, the transmission loss α is 0.35 dB / Km or less. Accordingly, when the length of the optical cord to be measured is 30 m or less, the transmission loss α is about 0.01 dB, which is substantially equal to the resolution of the measuring instrument, and can be ignored. If the transmission loss (α / m) is measured or calculated in advance, the connection loss IL of the optical connector can be easily obtained from Equation 1 in any case.

  Factors of connection loss in optical connectors include axial misalignment between optical fiber cores, angular misalignment between optical fibers, end face gaps between optical connectors, and structural mismatch between optical fibers. In the connector, an axial misalignment between optical fiber cores (hereinafter referred to as “axial misalignment”) is a main factor.

  The main factor of the axis deviation is the processing accuracy of the through hole 1a of the ferrule 1. However, in the region where the amount of eccentricity required for a normal single mode optical connector is about 0.7 μm or less, there is almost no correlation between the measured eccentricity value of the through hole 1a and the actual connection loss value. This is because the eccentricity of the core of the optical fiber does not necessarily match the eccentricity of the through hole 1a. That is, a clearance of about 1 μm is required between the through hole 1a of the optical connector and the optical fiber inserted into the through hole 1a, and the optical fiber itself has a slight core with respect to the center of the outer diameter. Therefore, even if there is no eccentricity in the through-hole 1a, an axial deviation may occur.

Here, by measuring the amount of eccentricity with respect to the center of the outer peripheral surface of the ferrule 1 of the core of the optical fiber 3 in the optical connector, the insertion loss IL due to the axial deviation d between the optical fibers in the optical connector connection of the single mode optical fiber. (DB) is given by the following equation.

Here, w is the mode field radius of the optical fiber. When this expression is expanded, the following expression is obtained.

  Assuming that w = 4.7 μm, the insertion loss ILΔ (dB) due to the axial deviation d between the optical fibers is about 0.05 dB when the axial deviation d is 0.5 μm, and about 0.20 dB when 1 μm. It becomes about 0.79 dB at 2 μm. Therefore, the amount of change in connection loss increases in order to increase the axial misalignment between optical fibers.

  There is a connection method called tuning as a method for suppressing an increase in connection loss due to shaft misalignment. All plugs are tested in advance with a plug called a master, and the plug is rotated every 90 degrees around the axis to find the direction in which the connection loss is the smallest of the four directions. Mark the direction of the plug. In actual connection, the connection is made so that the marks coincide with each other. As a result, the direction of axial misalignment of the two plugs to be connected is included in the same 90 degree range. As a result, the shaft misalignment is offset to some extent, and an increase in connection loss can be suppressed. General tuning is intended to be in the same 90-degree range, and one direction is selected from the four directions, so here it is referred to as four-time tuning. Therefore, the tuning that limits the axis deviation in the range of (360 / m) degrees, where m is a natural number, is called m-time tuning.

Next, the main factor of the angle shift between optical fibers (hereinafter referred to as “angle shift”) is the angle shift with respect to the outer peripheral surface 1 c of the through hole 1 a of the ferrule 1. Here, in the optical connector, when the angular deviation of the emission angle of the optical fiber 3 with respect to the outer peripheral surface 1c is θ, the insertion loss ILθ (dB) is expressed by the following equation.

Here, n is the refractive index of the optical fiber, and λ represents the wavelength of light in vacuum. Here, when a general refractive index of 1.46 of an optical fiber is substituted for λ and developed, the following equation is obtained.

  Here, the insertion loss ILθ (dB) due to the angular deviation θ between the optical fibers is about 0.014 dB when the angular deviation θ is 0.2 °, and about 0.089 dB when the angular deviation θ is 0.5 °. As the angular deviation θ increases, the amount of change in connection loss increases. However, the influence is small compared to the connection loss with respect to the axis deviation d.

From the above equations 1 and 2, as shown in FIG. 9, a graph showing the axis deviation, the angle deviation, and the connection loss is simply used, and a rough connection loss is estimated from the angle deviation and the axis deviation of each optical connector. (See Non-Patent Document 1).
Japanese Patent No. 3323919 (paragraphs 0003 to 0008) Research Practical Report Vol. 32 No. 3 (1983) P675, “Optical Circuit for Single Mode Fiber”, Section 3.1

  However, in the conventional method of estimating the connection loss, the axial misalignment is intricately intertwined with the amount of eccentricity of the ferrule, the outer diameter difference between the through hole 1a of the ferrule and the optical fiber, the concentricity of the core of the optical fiber, etc. It is necessary to measure how much the position of the core of the optical fiber after the fiber is bonded and fixed to the ferrule is decentered with respect to the center of the outer peripheral surface. How long the angle of the optical fiber after bonding and fixing is inclined with respect to the outer peripheral surface is not measured after the light is emitted from the tip of the optical fiber and the emission angle is measured. Could not be estimated.

  In other words, since all the samples had to be actually manufactured and then measured, it took a lot of man-hours for the preparation of the samples and the measurement of the axis deviation and the angle deviation.

  Also, if you actually make a sample, you can get the actual measurement value by measuring the connection loss directly, without measuring the exit angle and axis deviation, but measure the connection loss anyway. Therefore, it took a lot of man-hours.

  In addition, the axial and angular deviations measured by conventional methods can be analogized to determine which parameters affect splice loss due to complex intertwining of optical fiber and ferrule dimensional parameters. Was difficult.

  Therefore, the present invention has been made in view of the above-described problems. Distribution data of axial misalignment of a single plug comprising a ferrule having a through hole in the longitudinal direction and an optical fiber inserted into the ferrule, and the outer diameter of the ferrule. From the distribution data, the n-th moment (n-th moment product) of the amount of shaft misalignment in the connected state when tuning is performed, which is a technique for aligning the direction of the shaft misalignment of a single plug, is calculated, and the n of the connection loss is calculated therefrom. A connection loss calculation method for an optical connector, characterized by calculating a second moment.

  That is, the present invention is characterized in that the average value is calculated from the first moment of the connection loss, and the standard deviation / dispersion is calculated from the first moment and the second moment.

    Furthermore, the distribution data of the dimensional parameter or angle parameter of the split sleeve or the distribution data of the connection loss value of the split sleeve is combined.

  In addition, the amount of the axial deviation is obtained from a gap generated from the inner diameter of the ferrule and the outer diameter of the optical fiber, the concentricity of the outer peripheral portion of the ferrule and the through hole, and the concentricity of the core and the clad of the optical fiber. And

    Further, the angle deviation amount is obtained from the inclination in the longitudinal direction with respect to the outer peripheral portion of the ferrule through hole.

Furthermore, the n-order moment of the connection loss is calculated from the n-order moment of the paired angular deviation calculated by combining two n-order moments of the ferrule angular deviation. By connecting the connection loss value calculated from the shaft misalignment, the connection loss value calculated from the paired angle misalignment, and the connection loss value of the split sleeve to obtain the total connection loss value, the nth moment of the connection loss value is obtained. It is characterized by calculating.

  In the optical connector connection loss calculation simulator, at least one of the optical connector connection loss calculation methods is used.

  As described above, according to the present invention, a single plug is obtained from distribution data of axial misalignment of a single plug comprising a ferrule having a through hole in the longitudinal direction and an optical fiber inserted into the ferrule, and distribution data of an outer diameter of the ferrule. By calculating the n-th moment of the amount of shaft misalignment in the connected state when tuning is performed, which is a technique for aligning the direction of the shaft misalignment, and calculating the n-th moment of the connection loss from there, a great amount of man-hours and costs are saved. Connection loss distribution can be estimated easily without the need.

  Embodiments of the present invention will be described below.

  According to the present invention, the direction of axial misalignment of a single plug is determined from the distribution data of axial misalignment of a single plug comprising a ferrule having a through hole in the longitudinal direction and an optical fiber inserted into the ferrule, and distribution data of the outer diameter of the ferrule. It is characterized in that an n-order moment (n-order moment factor) of the amount of axial misalignment in a connected state when tuning is performed, which is a technique for aligning, and calculating an n-order moment of connection loss therefrom. The axial displacement distribution data for a single plug includes the distribution of gaps generated from the inner diameter of the ferrule and the outer diameter of the optical fiber, the distribution of the concentricity between the outer periphery of the ferrule and the through hole, and the concentricity of the core and cladding of the optical fiber. Obtain from the distribution of degrees.

The n-th moment of the discrete random variable x (i) is expressed by the following equation using the probability distribution P (i).

The first moment is an average value as expressed by the following equation.

Further, using the second moment and the first moment, the variance can be expressed as the following equation.

  Thus, the average value and variance of the probability distribution can be calculated by using the nth moment. Specifically, the first moment of the connection loss is required to obtain the average value of the connection loss, and the first moment and the second moment of the connection loss are required to obtain the dispersion. On the other hand, the connection loss itself is proportional to the square of the amount of axial deviation and the amount of angular deviation. Therefore, in order to obtain the average value of the connection loss, the first moment and the second moment of the deviation amount are required, and in order to obtain the variance, the first to fourth moments of the deviation amount are necessary.

  As an example of the present invention, a method for simulating the n-th moment of the splice loss value is shown in FIG.

  The axial displacement distribution of a single plug is obtained from the gap generated from the inner diameter of the ferrule and the outer diameter of the optical fiber, the concentricity of the outer peripheral portion of the ferrule and the through hole, and the concentricity of the core and cladding of the optical fiber. Then, the n-order moment of the axis deviation paired by tuning is calculated from the two n-order moments of the axis deviation of the single plug and the n-order moment of the outer diameter difference of the ferrule.

  In FIG. 2A, the optical fiber protector 2 is fixed to the ferrule 1 having the through hole 1 a, and the optical fiber 3 is inserted and fixed from the opening of the optical fiber protector 2 to form the plug 10. Since the axial deviation means a deviation of the position of the ferrule tip surface 1b from the center of the outer peripheral portion 1c, a view viewed from A is shown in FIG. 2 (b).

Here, the center of the outer peripheral portion 1C is O ₁ . When the center of the through hole of the ferrule and O _2, positional deviation of O ₂ becomes a half value of the concentricity. Next, the center position of the optical fiber is O ₃ , and the distance between O ₂ and O ₃ is half the value obtained by subtracting the optical fiber outer diameter from the ferrule inner diameter. Further, the center position of the optical fiber core is O ₄ , and the distance between O ₃ and O ₄ is a half value of the concentricity of the optical fiber core. Finally, the distance between O ₁ and O ₄ becomes the total axial deviation dT with respect to the ferrule outer peripheral portion 1c.

  As described above, since the single axis deviation in each parameter has a random axis deviation direction, the total axis deviation does not necessarily increase if the axis deviation in each parameter is large.

  As described above, the axis deviation of a single plug is obtained. However, as an optical connector, it is necessary to calculate it under the condition that a pair of two plugs are in contact with each other. A calculation method will be described.

  FIG. 3A shows a state in which the ferrule 1 ′ is in contact with the ferrule 1, and the tip surfaces 1 b and 1 b ′ are in contact with the split sleeve 5.

Here, as shown in FIG. 3B, the inner peripheral surface of the facing portion 5b of the slit 5a of the split sleeve 5 serves as a position reference point for the ferrule 1 and the ferrule 1 ', and the large-diameter ferrule 1' is the direction of the slit 5a. A position shift will occur. The center of the total axial misalignment with respect to the center O ₁ of the outer peripheral portion of the small-diameter ferrule 1 and O _4, the center of the total axial misalignment with respect to the center O _{1 'of} the outer peripheral portion of the large-diameter ferrule 1' is taken as O _4, O ₁ And O ₁ ′ is displaced by a distance dS in the direction of the slit 5a. Here, the distance d _S between O ₁ and O ₁ ′ is a half value of the difference between the outer diameter of the large-diameter ferrule 1 ′ and the outer diameter of the small-diameter ferrule 1.

Accordingly, the center of the final axis shift which is paired with tuning the axis shift distance d _P is paired with O ₅ becomes O ₄ and O _5. At this time, as an effect of tuning, the angle formed by the line segments O ₁ O ₄ and O ₁ ′ O ₄ ′ is within 90 degrees, and as a result, d _P remains small.

  Next, as for the angle deviation, the n-order moment of the paired angle deviation is calculated from the distribution data of the angle deviation of the single ferrule as described above.

  4A is a cross-sectional view of a state in which the ferrules 1 and 1 ′ are in contact with the front end surfaces 1b and 1b ′ inside the split sleeve 5, and the through holes 1a and 1a ′ have θ ° and θ ′ on the cross section. ° Inclined. However, it is also necessary to take into account that φ and φ ′ are inclined in the angular direction in the contact surface, and finally, the relative angle vector r of ferrule 1 and vector r ′ of ferrule 1 ′ The angle becomes a paired angle deviation.

  Here, a method for synthesizing the n-th moments of the two dimension parameters in consideration of the angle formed by the two dimension parameters will be described.

  FIG. 5 shows that the dimension parameter 1 vector and the dimension parameter 2 vector are combined to generate a dimension parameter 3 vector. Regarding the direction of the vector, in the four-time tuning that is usually used, the vector is uniformly distributed in the same 90-degree range. The size of the dimension parameter 3 is expressed by the dimension parameters 1 and 2 and the angle (θ2−θ1) when using the cosine theorem of trigonometric function. Therefore, the n-th moment of the dimension parameter 3 can also be expressed by using the dimension parameters 1 and 2, the angles θ1 and θ2, and the probability distribution thereof. If this is integrated with the angles θ 1 and θ 2, the n-order moment of the dimension parameter 3 is expressed only by the n-order moments of the dimension parameters 1 and 2.

  This method is also used when the n-order moments of two angle parameters are combined in consideration of the angle formed by the two angle parameters.

  As described above, the n-order moment of the angular deviation paired with the n-order moment of the paired axis deviation can be calculated.

  Next, referring back to FIG. 1, the n-th moment of the connection loss value due to the axis deviation is obtained from Equation 3 from the n-order moment of the axis deviation that is tuned and paired. Further, the n-th moment of the connection loss value due to the angle deviation is obtained from Equation 5 from the n-order moment of the paired angle deviation.

The total n-th moment of the total connection loss can be calculated by summing up the n-th moment of the connection loss value due to the axial deviation and the n-th moment of the connection loss value due to the angle deviation and the n-th moment of the connection loss of the split sleeve. If the given data is not a split sleeve splice loss distribution but a dimensional or angular parameter distribution, it is converted to a splice loss distribution using Equation 3 or 5, and the nth moment is obtained. Specifically: As an example, the case of the first moment, that is, the average value will be described. The connection loss including different factors can be obtained by adding together the connection loss due to individual factors when each of them is sufficiently low. Therefore, it can be said that the total connection loss is the sum of the connection loss due to the shaft misalignment, the connection loss due to the angle misalignment, and the connection loss of the split sleeve. This is expressed by the following equation, where IL _{Δ is the} connection loss due to axial misalignment, IL _{θ is the} connection loss due to angular misalignment, IL _{sl is} the connection loss of the split sleeve, and IL is the total connection loss.

However, any connection loss is non-negative. In addition, those first moments, that is, average values are represented as <IL _Δ >;<IL _θ >;<IL _sl >;<IL>, respectively. Since the shaft misalignment, the angle misalignment, and the connection loss of the split sleeve are independent, the first moment of the total connection loss, that is, the average value is expressed by the following equation.

  The number of dimensional parameter data used in the present invention is preferably at least 10 data, and particularly preferably 100 or more data. This is because the larger the number of data, the smoother the probability distribution of the dimension parameter histogram.

  The data increment of the dimension parameter is desirably 0.1 μm or less, and particularly desirably 0.05 μm or less. This is because the smaller the data increment, the more accurate the n-th moment can be calculated.

  In the above embodiment, the connection loss is calculated using both the amount of axial deviation and the amount of angular deviation.For example, when the amount of angular deviation is very small compared to the amount of axial deviation, the connection loss is calculated only by the amount of axial deviation. It is also possible to calculate, and in the opposite case, it is also possible to calculate with only the amount of angular deviation.

    In order to reduce the connection loss of the optical connector, a centering technique has been introduced in which the direction of the axis misalignment is adjusted to a certain direction, but it is also possible to use the connection loss calculation method of the optical connector of the present invention. .

  In the present invention, simulation software is characterized by using the above-described optical connector connection loss calculation method.

  The method of creating with the personal computer spreadsheet software “Excel” is particularly desirable because it is simple, inexpensive and most commonly used, but it is possible to use Basic, Fortran, C language, etc. Similarly, the effects of the present invention can be obtained.

  The optical connector connection loss calculation method and the simulator using the optical connector according to the present invention have been described using a single mode optical fiber, but can also be applied to a multimode optical fiber.

  Examples of the present invention will be described below.

  Using the connection loss calculation simulator of the optical connector of the present invention shown in FIG. 1, the inner diameter of the ferrule is φ125.2 to 125.7 μm, the concentricity is 0 to 0.8 μm, the outer diameter is φ2.4892 to 2.4992 mm, The simulation was performed as distribution data in which the angle deviation was 0.02 to 0.14 °, the concentricity of the optical fiber was 0 to 0.4 μm, and the outer diameter was 124.8 to 125.3 μm. FIG. 10A shows the axial displacement distribution and ferrule outer diameter difference distribution of a single plug obtained from the dimension data. Here, the ferrule outer radius difference distribution is a distribution of ferrule outer radius differences that appear when two plugs are paired, and is obtained from the ferrule outer diameter distribution. From the above, the average value and standard deviation of the connection loss values are as shown in FIG.

  As a comparison, the result of another simulator was 0.07 dB when the average connection loss was not tuned. On the other hand, in the case of infinite tuning, the direction of shaft misalignment of the plugs to be paired is the same, so that it was 0.01 dB.

  From the above, the respective axis deviations obtained from the distribution data of the dimensional parameters of the ferrule and the optical fiber of the present invention, and the angle deviations obtained from the distribution data of the angular parameters of the ferrule, are perpendicular to the axial direction of the optical fiber and the ferrule. The method of calculating the n-th moment of the axial deviation amount and the angular deviation amount in the connected state by calculating the sum as the vector amount in the vector, and calculating the n-th moment of the connection loss therefrom is a method using a different simulator. It was confirmed that almost equivalent values were obtained.

  The required time was several tens of minutes including data input in the present invention, whereas the method of actual measurement of the comparative example takes several tens of hours including sample preparation, measurement, and data summarization. Connection loss distribution data could be easily obtained without requiring a lot of man-hours and expenses.

It is a flowchart which shows the flow of the connection loss calculation simulator of this invention. (A) And (b) is a figure explaining the axial shift of the single plug of this invention. (A) And (b) is a figure explaining the axial deviation which carried out the 4 times tuning of this invention, and was paired. (A) And (b) is a figure explaining the angle shift which made the pair of this invention. It is a figure explaining the method of synthesize | combining the n-th moment of a dimension parameter regarding the case of 4 times tuning. It is sectional drawing which shows a general plug. It is sectional drawing which shows a common optical connector. It is a figure which shows the measuring method of the connection loss of an optical connector. It is a diagram showing an axis shift, an angle shift, and a connection loss. (A) is the axis deviation distribution and ferrule outer diameter difference distribution of a single plug, and (b) illustrates the relationship between the number of tunings, the average value of connection loss, and the standard deviation.

Explanation of symbols

1: Ferrule 1 ': Ferrule 1a: Through hole 1b: Tip surface 1c: Outer peripheral portion 1d: Tip surface 1e: Chamfered portion 2: Fiber protector 3: Optical fiber 3a: Core 3b: Clad 4: Adhesive 5: Split Sleeve 10: Plug 11: LD light source 12: Reference optical cord 12a: Optical connector 12b: Optical connector 13: Adapter 14: Optical cord for measurement 14a: Optical connector 14b: Optical connector 15: Light receiving unit 16: Power meter IL: Connection loss

Claims (8)

This is a method for aligning the axial direction of a single plug from the distribution data of the axial displacement of a single plug comprising a ferrule having a through hole in the longitudinal direction and an optical fiber inserted into the ferrule, and the distribution data of the outer diameter of the ferrule. A connection loss calculation method for an optical connector, characterized in that an n-order moment (n-order moment factor) of an axis deviation amount in a connected state when tuning is performed, and an n-order moment of a connection loss is calculated therefrom. . 2. The connection loss calculation method for an optical connector according to claim 1, wherein the average value is calculated from the primary moment of the connection loss, and the standard deviation / dispersion is calculated from the primary moment and the secondary moment. 3. The connection loss calculation method for an optical connector according to claim 1, wherein the distribution data of the dimensional parameter or angle parameter of the split sleeve or the distribution data of the connection loss value of the split sleeve is combined. The above-mentioned axial deviation amount is obtained from the gap generated from the inner diameter of the ferrule and the outer diameter of the optical fiber, the concentricity of the outer peripheral portion of the ferrule and the through hole, and the concentricity of the core and the clad of the optical fiber. The connection loss calculation method of the optical connector in any one of Claims 1-3. The method of calculating a connection loss of an optical connector according to claim 1, wherein the amount of angular deviation is obtained from the inclination in the longitudinal direction with respect to the outer peripheral portion of the ferrule through hole. 4. The n-th moment of the connection loss is calculated from the n-order moment of the paired angular deviation calculated by combining two n-order moments of the ferrule angular deviation. A method for calculating connection loss of an optical connector according to claim 1. By connecting the connection loss value calculated from the paired axis deviation, the connection loss value calculated from the paired angle deviation, and the connection loss value of the split sleeve, the total connection loss value is obtained. The method of calculating a connection loss of an optical connector according to claim 1, wherein a next moment is calculated. A connection loss calculation simulator for an optical connector using any one of the connection loss calculation methods for an optical connector according to claim 1.

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