JP3350873B2 - Inspection method for return loss of optical connector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting the return loss of an optical connector used for connecting optical fibers in optical communication.

[0002]

2. Description of the Related Art With the advancement of optical communication and the increase in capacity, it is necessary to reduce the reflection of light at a connection point of an optical connector on a transmission line to a certain value or less. Optical connectors with a large volume are positioned as key parts in video analog transmission and high-speed digital transmission, which are expected to develop in the future. The requirements imposed on optical connectors when designing and operating such optical transmission lines are:
This is the magnitude of the minimum return loss per connection point when connectors are connected at random.

The return loss test method for optical connectors is based on JIS.
4. of C 5961 “Optical fiber connector test method”
2. Return loss (2) Method 2 is currently commonly used. On the other hand, the reflection at the connection point of the optical connector occurs because a damaged layer having a different refractive index from that of the fiber core remains on the fiber end face due to polishing at the time of trimming.
The fact that the return loss at the connection point of the optical connector can be described based on the refractive index and the thickness of the processed deteriorated layer has been clarified in a report of the 1991 IEICE Spring National Convention C-279. However, a problem in the above-mentioned JIS test method is that the state of the processing layer of the optical connector of the master optical cord is not specified at all. Therefore, there is a problem that accurate measurement cannot be performed because the return loss distribution differs depending on the master optical code, the yield at the time of selection changes greatly, or reflection occurs below the standard value when the selected code is connected at random. . As a result, since the return loss of the optical code to be measured depends on the master optical code, highly reliable measurement and selection cannot be achieved.

[0004] In order to solve this problem, a method for inspecting the return loss of an optical connector has been proposed in Japanese Patent Application Laid-Open No. Hei 5-40074. FIG. 3 is a connection diagram for explaining a method of inspecting the return loss according to this conventional example. In FIG. 3, A1
Is a reference light code for measurement, B2 is a reference light code for measurement, 3
Is an optical cable to be measured with a connector at both ends; 5 is an adapter for connecting the optical connectors; 1a, 2a, 30a, 31a are optical connectors having an optical fiber end face polished into a flat or convex spherical surface; 1b, 2b, 13b is a regular end face. Is an obliquely polished optical connector which is inclined with respect to the optical axis propagating through the optical fiber, 11 is a light source for supplying measurement light, 12 is a light intensity detector for measuring the intensity of reflected light, and 13 is a light intensity detector for measuring reflected light intensity. It is an optical branching coupler for leading to a light intensity detector.

A conventional example will be described with reference to FIG. Here, the return loss standard value L _rs of the measured optical code is set to 45 [d
B], the refractive index n ₁ of the fiber core is 1.452, and the refractive index n _{2 of} air is 1.0. In the measurement, first, the light intensity detector 1 is connected to each branch end of the optical branching coupler 13.
2 is connected. Next, a method of defining the reference optical code A1 and the reference optical code B2 will be described with reference to FIG. The obliquely polished optical connector 1b of the measurement reference optical code A1 is connected to the obliquely polished connector 13b of the optical branching coupler 13, and the optical branching coupler 13 when the optical connector 1a of the measuring reference optical code A1 is an open end. the intensity of reflected light returns to the optical intensity detector and P ₈ watts. In this state, the optical connector 2a of the measurement reference optical code B2 is connected to the optical connector 1a of the measurement reference optical code A1 via the adapter 5,
The reflected light intensity when the oblique polishing connector 2b of the measurement reference beam code B2 to the open end and P ₁ watts.

In general, when the measuring light having the light intensity P ₀ is incident from the light source 11 and the reflected light intensity P ₈ is measured, the relationship is represented by the following equation [Equation 1].

(Equation 1) In the above [Equation 1], the left side is the return loss for the measurement reference optical code A1 having the connector 1a, and the right side is the return _loss standard value L _rs [dB] + M. M indirectly represents the state of the above-mentioned deteriorated layer.

The light P ₀ from the light source 11 is expressed by the following equation (2) using the reflected light intensity P ₈ and the refractive indexes n ₁ and n ₂ .

(Equation 2) In this [Equation 2], the second term on the right side corresponds to Fresnel reflection between the fiber core and air, and its value is 14.7 [dB]. As a result, M is obtained based on the following equation (3) by measuring the measurement reference codes A1 and B2.

(Equation 3) In addition, M in this equation generally indicates that the return loss distribution per connector connection point is approximately 40 to 60 [dB] and that the average value is 45 to 60 [dB].
Since it is 50 [dB], -10 ≦ M ≦ 10 [dB] so that an arbitrary optical connector can be used as a reference optical code for measurement.
B].

Next, the procedure for measuring the return loss of the optical code under test 3 with connectors at both ends using the standard optical code for measurement A1 and the standard optical code for measurement B2 will be described with reference to the numbers in FIG. In this state, the optical connector 1a of the measuring reference optical code A1 and the optical connector 30a of the measured optical code 3 are connected to the optical connector 31a of the measured optical code 3 and the measuring reference optical code B.
The two optical connectors 2a are connected via the adapter 5, and the reflected light intensity when the obliquely polished connector 2b of the reference optical cord for measurement B2 is used as the open end is P ₂ + P ₃ watts. The return loss of the optical cable under test 3 with connectors at both ends is represented by the left side of the following equation, and the standard value L _rs = 45 [d]
If it is equal to or more than N [dB] higher than B], it is regarded as good.

[0009]

(Equation 4) This N is obtained from the probability that the return loss at the connection point exceeds the standard value L _rs [dB] when the optical connector of the connector under test that has passed the inspection is randomly connected.

[0010]

In the above conventional example, the return loss when the optical connector 2a of the measurement reference optical code B2 is connected via the adapter 5 to the optical connector 1a of the measurement reference optical code A1. Measuring and measuring the optical connector 1a of the reference optical code A1 and the optical code 3 to be measured
The optical connector 30a is connected to the optical connector 31a of the optical code under test 3 and the optical connector 2a of the standard optical code B2 for measurement via the adapter 5, and the oblique polishing connector 2b of the standard optical cord for measurement B2 is opened. It is necessary to measure the return loss when That is, the optical connector 1a and the optical connector 2a, the optical connector 1a and the optical connector 30a, and the optical connector 2a and the optical connector 31a must be connectable optical connectors. However, for example, the optical connector 30a is an F04 type optical fiber connector according to JIS, and the optical connector 31a is also the F11 type optical fiber connector.
In the case of an optical fiber connector, the optical connector 1
a and the optical connector 2a must be F04 and F11, respectively. As a result, in order to connect the optical connector 1a and the optical connector 2a, it is necessary to change the housing of the optical connector or to connect only the ferrule to which the optical fiber is fixed, which complicates the inspection process. There was a point. Further, in the case of an optical connector having a different diameter of the ferrule, connection of the optical connectors 1a and 2a becomes impossible, and there is a problem that inspection cannot be performed.

In view of the above problems, an object of the present invention is to provide a simple and reliable method for inspecting the return loss of an optical connector even if the form of the connector is changed.

[0012]

SUMMARY OF THE INVENTION To achieve the above object of the present invention, (1) light polishing the end face of the first optical fiber cord said first optical fiber attached to both ends of the flat or convex spherical Flatten one end of the optical fiber with one of the connectors.
When the optical connector is randomly connected to another optical connector polished to a surface or a convex spherical surface, the return loss from the connection point is a specified value L.
_rs [dB] or more, which is an inspection method for determining whether or not the optical connector is polished into a flat or convex spherical shape.
Third optical connector having a flat or convex spherically polished optical connector
Measuring the return loss L _r1 [dB] generated from the connection point when the optical connector of the measurement reference optical cord is connected to the optical connector of the second measurement reference optical cord; The optical connector of the fifth measurement reference optical cord having an optical connector polished into a flat or convex spherical shape, which can be fitted with the optical connector of the fourth measurement reference optical cord having the optical connector polished into a shape and measuring the time of connecting the fourth measurement reference light code of the optical connector, the return loss L _r2 [dB] resulting from the connection point between the L _r1 [d
B] and L _r2 [dB], a step of _obtaining a value of M (−10 ≦ M ≦ 10 [dB]) so that the following expression (1) is satisfied; (L _r1 + L _r2 ) / 2-M ≦ L _rs (Equation 1) connecting the optical connector of the second measuring reference optical cord to the optical connector at the one end, which can be fitted to the optical connector at one end of the first optical fiber cord; Connecting the optical connector of the fourth measuring reference optical cord to the optical connector at the other end, the optical connector being capable of being fitted to the optical connector at the other end of the first optical fiber cord; And the return loss L ₁ [dB] generated from the connection point between the optical connector at one end of the first optical fiber cord and the optical connector, and the optical connector at the other end of the first optical fiber cord and the fourth measurement. Return loss L ₃ [d generated from the connection point of the optical connector of the reference optical cord for use
B] a step of determining the sum L _{1 + 2} [dB] of, and determining whether the value obtained by the process satisfies the following (Formula _{2), L rs ≦ L 1} + 2 ( Equation 2) It is characterized by consisting of.

(2) The value of M is -10 ≦ M ≦ 5 [dB].

[0014]

The optical connector of the reference optical code for measurement A1 and the optical connector
The optical connector of the fixed reference optical cord A10 can be fitted.
You. The optical connector of the measurement reference optical cord B2 and the optical connector
The optical connector of the reference optical cord for measurement B20 can be fitted.
is there. Further, an optical connector at the right end of the optical fiber cord and
The optical connector of the measurement reference optical code A1 can be fitted.
Yes, the optical connector at the left end of the optical fiber cord and the measurement
The optical connector of the reference optical cord for use B2 can be fitted.
Therefore, the housing of any of the above optical connectors is rearranged.
No need, and a ferrule that fixes the optical fiber
It is not necessary to connect only with
You. In order to satisfy (Equation 1), the above L_r1[DB] and
L_r2Average value of [dB] (L _r1+ L_r2) / 2 is
Since the value of M is determined to satisfy, the measurement is indirectly performed.
The optical connector of the reference optical code A1 and the reference light for measurement
Processing of code B2 on the fiber surface of the optical connector
The state of the deteriorated layer is determined, and the
Return loss from the optical connector on the right end of the barcode and the return loss on the left end.
The sum of the return loss from the optical connector exceeds a certain value
As a result, the right and left connectors are added.
Optical fiber cords whose deterioration layer is above a certain level are sorted out.
You. Therefore, the selected optical fiber cord optical connector
When connected randomly, the reflection per connector is reduced.
The amount of decay is the standard value L_rs[DB]. Also,
Since the value of M is set to 5 [dB] or less, the measurement reference
Processing of the optical connector of the optical cord
As a result, the optical fiber cord at the time of sorting according to (Equation 2) is obtained.
Of the optical fiber cord after sorting
If optical connectors are connected at random,
The return loss is set to the standard value L with a high probability._rs[DB] up
Will spin.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the method for testing return loss of an optical connector according to the present invention will be described with reference to FIGS. FIG. 1 is a connection diagram showing one embodiment of an optical connector inspection method according to the present invention, and FIG. 2 is a diagram showing one example of a measured optical code with a double-ended optical connector and a measured optical code before being sorted by the one embodiment.
It is a figure which shows the relationship between the return loss converted per connection point, and a cumulative probability. In FIG. 1, A1 is a reference optical code for measurement, A10 is a reference optical code for measurement, B2 is a reference optical code for measurement, B20 is a reference optical code for measurement, 3 is an optical code to be measured with connectors at both ends, and 5 is an optical connector. , 1a, 10a, 2a, 20a, 30a, 31
a is an optical connector in which the end face of an optical fiber is polished into a flat or convex spherical shape, and 1b, 10b, 2b, 20b, and 13b are obliquely polished optical connectors whose regulated end faces are inclined with respect to the optical axis propagating through the optical fiber. , 11 is a light source for supplying measurement light, 12 is a light intensity detector for measuring reflected light intensity,
Reference numeral 13 denotes an optical branching coupler for guiding the reflected light to a light intensity detector.

First, a method for inspecting the return loss of an optical connector according to this embodiment will be described with reference to FIG. In this embodiment, the standard value L _rs of the return loss of the optical code to be measured is 41.5.
[DB], and the refractive index of the measurement fiber core and the refractive index of air are the same as those described in the above-described conventional technique. In the measurement, first, the light intensity detector 12 is connected to each branch end of the optical branching coupler 13. Next, a method of defining the reference optical code A1 and the reference optical code A10 and the reference optical code B2 and the reference optical code B20 will be described with reference to FIG.

The obliquely polished optical connector 1 b of the reference optical code for measurement A 1 is connected to the obliquely polished connector 1 of the optical branching coupler 13.
3b, and further connected to the optical connector 1a of the measurement reference optical code A1 by the optical connector 10a of the measurement reference optical code A10.
a via the adapter 5 and the reference optical cord A for measurement
Return loss when the oblique polishing connector 10b and the open end 10 of the L _r1 [dB]. In this case, the reference value of the return loss is, as described in the above-mentioned prior art, the return loss when the optical connector 1a is set to the open end, and the Fresnel reflection 1 generated from the refractive index difference between the fiber core and air.
It is good to set it to 4.7 [dB].

The obliquely polished optical connector 2 b of the measurement reference optical code B 2 is connected to the obliquely polished connector 1 of the optical branching coupler 13.
3b, and further connected to the optical connector 2a of the measurement reference optical code B20.
a via the adapter 5 and the reference light cord for measurement B
The return loss when the oblique polishing connector 20b of FIG. 20 is the open end is represented by L _r2 [dB]. In this case, the reference value of the return loss is the return loss when the optical connector 2a is set to the open end, and the Fresnel reflection 14.7 [dB] caused by the difference in the refractive index between the fiber core and the air. Is good.

Next, the average value of the measured L _r1 and L _r2 (L _r1 +
L _r2 ) / 2 and the standard return loss L _r2 are _{expressed by} the following (Equation 1).
Is determined so as to satisfy the following equation. (L _r1 + L _r2 ) / 2−M ≦ L _rs (Equation 1) The value of M is the return loss at the connection point even if the optical connector of the cable under test that has passed the inspection described later is connected at random. Is determined so that the probability of exceeding the standard value L _rs [dB] is sufficiently high. According to the inspection method of the return loss of the optical connector according to the above-mentioned Japanese Patent Application Laid-Open No. Hei 5-40074, the measured optical code with the double-sided optical connector exceeds L _rs [dB] with a probability of 99% or more at the time of the random connection. M for
Is N ≧ 0.4M−2.0 in relation to N described above.
, The condition of N = 0 is satisfied, so that M ≦ 5. Therefore, if M ≦ 5 [dB], the return loss per connection point at random connection is a standard value L _rs [dB] with a sufficiently high probability.
Will be exceeded. In this embodiment, M = 2.5 [dB]
And That is, according to (Equation 1), the average value ( _Lr1 + _Lr2 ) /
2 may be 41.5 + 2.5 = 44 [dB].

Further, the procedure for inspecting the return loss of the measured optical code 3 with connectors at both ends using the measuring reference optical code A1 and the measuring reference optical code B2 will be described with reference to FIG. Oblique polishing optical connector 1b for measurement reference optical code A1
To the optical branching coupler 13 obliquely polished connector 13b,
The optical connector 1a of the measuring reference optical code A1 and the optical connector 30a of the measured optical code 3, the optical connector 31a of the measured optical code 3 and the optical connector 2a of the measuring reference optical code B2.
And the return loss when the obliquely polished connector 2b of the measurement reference optical cord B2 is set to the open end is L _{1 + 2.}
[DB]. Then, when L _{1 + 2} is larger than the standard value L _rs as in the following equation (2), the measured optical code is regarded as a non-defective product, that is, a passed product. L _rs ≦ L _{1 + 2} (Equation 2)

FIG. 2 shows the distribution of the return loss when the optical codes to be measured selected in this embodiment are randomly connected, and the distribution before the selection. In the figure, L _rs = 41.5 [dB],
M = 2.5 [dB]. From FIG. 2, the probability that the return loss is equal to or less than the standard value of 41.5 [dB] before selection is 70.
%, But after sorting in the present embodiment, all the values are above the standard value.

As described above, the method for inspecting the return loss of an optical connector according to the present embodiment has the following features. First, since two sets of measurement reference optical codes are used, the optical connector 1a of the measurement reference optical code A1, the optical connector 10a of the measurement reference optical code A10, and
As the optical connector 2a of the measurement reference optical code B2 and the optical connector 20a of the measurement reference optical code B20, those that can be fitted can be used. Further, the optical connector 30a at the left end of the optical code 3 to be measured and the optical connector 1a of the reference optical code A1 for measurement can be used, and the optical connector 31a at the right end of the optical code to be measured and the reference optical code B2 for measurement can be used. Can be used as the optical connector 2a. Therefore, there is no need to change the housing of any optical connector, and it is not necessary to connect only the ferrule to which the optical fiber is fixed, so that the inspection can be performed easily.

[0023] As the second point, so as to satisfy (Equation 1), L _r1 [dB] and L _r2 average of [dB] (L _r1 +
Since the value of M is obtained from L _r2 ) / 2, the state of the damaged layer formed on the fiber surface of the optical connector 1a of the measurement reference optical code A1 and the optical connector 2a of the measurement reference optical code B2 indirectly. Is determined according to (Equation 2) so that the sum of the return loss from the right end optical connector and the return loss from the left end optical connector of the optical code under test 3 is equal to or more than a certain value. Then, the optical fiber cords whose processed deteriorated layer of the left end connector has a certain level or more are selected. Therefore, when the optical connectors of the selected optical fiber cords are connected at random, the return loss per connection point of the connector exceeds the standard value L _rs [dB], and the simple and reliable optical connector is selected. Becomes possible.

The third point is that the value of M is set to 5 [dB] or less, which limits the state of the work-affected layer of the optical connector of the measurement reference optical cord. In the case where the yield of the optical fiber cords is increased and the optical connectors of the selected optical fiber cords are randomly connected, the return loss per connection point of the connector is likely to exceed the standard value L _rs [dB] with a high probability. Thus, the cost of the optical connector-equipped cord can be reduced by improving the yield.

In this embodiment, the same effect can be obtained even if the means for measuring the return loss is an OTDR type comprising a pulse light source and an optical switch or an OLCR type comprising an interferometer. Needless to say.

[0026]

As described above, the method for inspecting the return loss of an optical connector according to the present invention provides a measuring reference light that can be fitted to an optical cord to be measured having any optical connector. Since a code can be prepared, inspection can be performed easily. When the optical connectors of the selected optical fiber cords are randomly connected, the amount of return loss per connection point of the connector exceeds the standard value, and it is possible to easily and reliably select the optical connectors. The yield of the optical fiber cord at the time of sorting can be increased, and the cost of the cord with an optical connector can be reduced by improving the yield. Therefore, it is possible to easily and reliably provide an optical connector in which the return loss per connection point is equal to or more than the standard value,
As a result, the effect of configuring a high-quality optical fiber transmission line is great.

[Brief description of the drawings]

FIG. 1 is a connection diagram illustrating an embodiment of a method for detecting return loss of an optical connector.

FIG. 2 is a diagram showing the relationship between the return loss calculated per connection point of the selected optical code with a double-ended optical connector and the optical code before the selection and the cumulative probability.

FIG. 3 is a connection diagram illustrating a conventional method for inspecting the return loss of an optical connector.

[Explanation of symbols]

A1 Reference optical cord for measurement A10 Reference optical cord for measurement B2 Reference optical cord for measurement B20 Reference optical cord for measurement 3 Optical cord to be measured with connectors at both ends 5 Adapter 1a, 10a, 2a, 20a, 30a, 31a Optical connector 1b, 10b , 2b, 20b, 13b Oblique polishing optical connector 11 Light source 12 Light intensity detector 13 Optical branching coupler

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Ryo Nagase 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) References JP-A-5-40074 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01M 11/00-11/02

Claims (2)

(57) [Claims] And any one of claims 1] optical connector polished end face of the first optical fiber cord said first optical fiber attached to both ends of the flat or convex spherical, the end face of the optical fiber Rights
When the optical connector is randomly connected to another optical connector polished to a surface or a convex spherical surface, the return loss from the connection point is a specified value L.
_rs [dB] or more, comprising: an optical connector polished into a flat or convex spherical shape;
The optical connector of the third measurement reference optical code and the optical connector of the second measurement reference optical code having an optical connector polished into a flat or convex spherical shape, which can be fitted with the optical connector of the measurement reference optical code. A step of measuring the return loss L _r1 [dB] generated from the connection point when the optical connector is connected; and a fourth step having the optical connector polished into a flat or convex spherical shape.
The optical connector of the fifth reference optical code for measurement having the optical connector polished into a flat or convex spherical shape and the optical connector of the fourth reference optical code for measurement, which can be fitted with the optical connector of the reference optical code for measurement. The step of measuring the return loss L _r2 [dB] generated from the connection point when the optical connector is connected, and the relationship between L _r1 [dB] and L _r2 [dB] satisfies the following (formula 1). M (however, −10 ≦ M ≦ 10 [d
B]) , and (L _r1 + L _r2 ) / 2−M ≦ L _rs (Equation 1) The second measurement reference that can be fitted to the optical connector at one end of the first optical fiber cord. Connecting the optical connector of the optical cord to the optical connector at one end; and connecting the optical connector of the fourth measurement reference optical cord, which can be fitted to the optical connector at the other end of the first optical fiber cord. Connecting to an optical connector at the other end; a return loss L ₁ [dB] generated from a connection point between the optical connector at one end of the first optical fiber cord and the optical connector of the second reference optical cord for measurement; The sum L of the return loss L ₃ [dB] generated from the connection point of the optical connector at the other end of the first optical fiber cord and the optical connector of the fourth measurement reference optical cord.
_{1 + 2} [dB], a step of determining whether the value obtained by the above step satisfies the following (Equation 2), and L _rs ≦ L _{1 + 2} (Equation 2). Inspection method for return loss of optical connector. 2. The method according to claim 1, wherein the value of M satisfies −10 ≦ M ≦ 5 [dB].