JP2003344147A - Optical fibering interference sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical fibering interference sensor capable of detecting the failure of facilities and devices constituting the optical fibering interference sensor. <P>SOLUTION: Light receiving elements 11-13 receive light propagated through optical fibering 5. Amplifiers 17-19 amplify output signals of the light receiving elements 11-13. The output levels of the amplifiers 17-19 are monitored by circuits 21-23 for monitoring the levels of output signals. An error determining circuit 27 determines the failure on the basis of whether the signal levels detected by the circuits 21-23 for monitoring the levels of output signals lie within a predetermined range or not. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber ring interferometric sensor, and more particularly to an optical fiber ring interferometric sensor having a failure detection function.

[0002]

2. Description of the Related Art As one of the techniques applying an optical fiber and a laser, various interference sensors utilizing the phase difference between optical signals propagating in an optical fiber have been proposed.

For example, in the direction of Japanese Patent Laid-Open No. 2000-046564, a physical change such as vibration applied to the optical fiber is detected by using a looped optical fiber (this is called an optical fiber ring) and a laser beam. A fiber optic ring interferometric sensor that is capable of doing so is disclosed.

In such a sensor device, laser light emitted from a light source is branched by a branch coupling element and is made incident from both open ends of an optical fiber ring in a loop shape, and the laser light is rotated clockwise in the optical fiber ring. And the counterclockwise propagating light propagating in the optical fiber ring are coupled by the branch coupling element to be incident on the light receiving element, and the clockwise propagating light output from this light receiving element. The vibration applied to the optical fiber ring is detected based on the signal indicating the change in the light intensity of the interference light due to the phase difference between the counterclockwise propagating light and the counterclockwise propagation light.

Such an optical fiber ring interference type sensor can be used, for example, for detecting vibrations and impacts such as rockfall detection and intruder detection.

[0006]

However, in the conventional optical fiber ring interference type sensor, when a failure occurs in the equipment or device that constitutes this sensor, for example, loss increase due to disconnection or deformation of the optical fiber, Increased loss or incorrect insertion due to dirty connectors, disconnection or failure of optical transmission lines and signal systems such as optical fibers, connectors, and optical couplers,
When a failure occurs in the light emitting element, light receiving element, amplifier circuit or other circuits, or the gain of the amplifier circuit is insufficient or excessive, the transmission loss due to these failures appears as a change in the light intensity of the interference light. There is a problem that this is erroneously detected as a phase difference due to vibration applied to the optical fiber.

The present invention has been made in view of the above,
It is an object of the present invention to provide an optical fiber ring interference type sensor having a function of detecting a failure in equipment or devices constituting the optical fiber ring interference type sensor.

[0008]

The invention according to claim 1 is
In order to solve the above problems, an optical fiber, an N × N optical branching / coupling element connected to both open ends of the optical fiber, and an N × N optical branching / coupling element are connected, and a laser beam is fed into the optical fiber. A light emitting element for incidence, N light receiving elements connected to the N × N optical branching / coupling element, an amplifier circuit for amplifying an optical signal received by the light receiving element, and a signal output from the amplifier circuit. An optical fiber ring interference type sensor having a signal level monitoring circuit for monitoring a level and a failure determination circuit for determining a failure based on whether or not the signal level detected by the signal level monitoring circuit is within a predetermined range. Is.

According to a second aspect of the present invention, in the optical fiber ring interference type sensor according to the first aspect, the failure determination circuit is used when the signal level detected by the signal level monitoring circuit exceeds a predetermined value, or When the signal level detected by the signal level monitoring circuit is less than a predetermined value, it is determined that there is a failure.

According to a third aspect of the present invention, in the optical fiber ring interference type sensor according to the second aspect, in the failure determination circuit, the signal level output from the amplification circuit is a predetermined steady level for a predetermined time. If it does not return to the above, the main point is to determine that there is a failure.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the structure of an optical fiber ring interference type sensor to which the present invention is applied.

In this optical fiber ring interferometric sensor, an optical fiber ring 5 is formed by connecting a 3 × 3 optical branch coupling element 3 to both open portions of a loop-shaped optical fiber 1 to form an optical branch coupling element 3. The first light receiving element 11 and the third light receiving element 1
3 is connected to the second light receiving element 1 via the optical branching and coupling element 7.
3 and the light emitting element 15 are connected, and further, the first to third light receiving elements 11, 12, and 13 are respectively connected to the first to third amplifier circuits 17, 18, and 19 for amplifying the received signal. Optical fiber ring interference type sensor.

The first to third light receiving elements are optical branching and coupling elements 3
The clockwise propagating light and the counterclockwise propagating light propagating through the optical fiber ring 5 are received via the optical fiber ring 5, and an electric signal corresponding to the received light intensity signal is output.

Each of the first to third amplifier circuits 17 to 19 is an amplifier circuit having a variable gain, and each of the light receiving elements 11 to 11.
The electric signal output from 13 is amplified by a desired gain.

The output signals from the first to third amplifier circuits 17 to 19 are input to the phase difference calculating circuit 25 which calculates the phase difference between the optical signals propagating in the optical fiber ring 5 in the clockwise and counterclockwise directions. Has been done.

Further, the first to third amplifier circuits 17, 18, 1
Reference numeral 9 denotes first to third output signal level monitoring circuits 21 and 22 for respectively monitoring the signal levels output from them.
23 is connected.

The signals from the output signal level monitoring circuits 21 to 23 are input to an error determination circuit 27 for detecting and determining a failure in the equipment or device that constitutes the optical fiber ring interference type sensor.

The optical fiber ring 5 is provided with an optical delay element 9 in order to adjust the total extension of the optical fiber ring 5. This is because when the position where vibration is applied to the optical fiber ring 5 is just at the midpoint of the ring, the phase difference of the light propagating in the optical fiber ring in the clockwise and counterclockwise directions may be canceled out. Therefore, in order to prevent the excitation point from becoming the middle point of the ring by increasing the total length of the optical path, for example, a long optical fiber is inserted as a delay element.

The operation of this embodiment will be described below.

First, the phase difference calculating operation, which is the basic function of the optical fiber ring interference type sensor, will be described.

In this optical fiber ring interference type sensor,
The laser light output from the light emitting element 15 is incident on the 3 × 3 optical branching / coupling element 3 via the optical branching / coupling element 7.

The light incident on the optical branching / coupling element 3 propagates in the optical fiber ring 5 clockwise and counterclockwise. Then, the optical fiber ring 5 is rotated once, and the branch coupling element 3 is again provided.
The clockwise light and the counterclockwise light are coupled by and the optical signals appearing due to the intensity change of the interference light due to the phase difference between the two enter the first to third light receiving elements 11 to 13.

At this time, the 3 × 3 optical branching / coupling element 3 outputs the interference light having the phase bias from the respective output terminals. Actually, the respective phases are outputs shifted by 2π / 3.

The light incident on the first to third light receiving elements 11 to 13 is converted into an electric signal, and the first to third amplifying circuits 17 to 19 are formed.
Is amplified by.

In each of the amplifier circuits 17 to 19, a section in which the correlation between the amplified light intensity output and the phase difference between the clockwise light and the counterclockwise light is close to a straight line is determined in advance.

For example, when an output having a phase shift of 2π / 3 is used as the 3 × 3 optical branching / coupling element 3, the signals output from the light receiving elements 11 to 13 are shifted by 2π / 3. , Between the respective phases of π / 3 and 2π / 3 corresponds to a section in which the correlation between the phase difference between the clockwise light and the counterclockwise light is close to a straight line.

The outputs from the amplifier circuits 17 to 19 are input to the phase difference calculation circuit 25. In the phase difference calculation circuit 25,
When the signal from the amplifier circuit connected to one light receiving element reaches the intensity corresponding to the above section, the phase difference is calculated by the output of the amplifier circuit, and it exceeds the upper or lower limit of the section. Switches to the output from the amplifier circuit connected to the next light receiving element and calculates the phase difference. For example, when the light intensity signal from the first amplification circuit 17 that amplifies the signal received by the first light receiving element 11 reaches the above section, the phase difference is caused by the light intensity signal from the first amplification circuit 17. The second amplifier circuit 1 that amplifies the signal received by the second light receiving element when the upper limit of the above section is exceeded.
If the signal of the light intensity from the first amplifier circuit 17 is below the lower limit of the above-mentioned section, the signal received by the third light receiving element is amplified. The calculation is switched to the phase difference calculation based on the signal of the light intensity from the third amplifier circuit 19 that is present.

As a result, when vibration is applied to the optical fiber 1, a phase difference occurs in the light carried clockwise and counterclockwise in the optical fiber ring, and the optical intensity of the phase difference causes the optical fiber to have a phase difference. The vibration applied to 1 will be detected.

Next, a failure detecting operation in the optical fiber ring interference type sensor will be described.

The failure detection is carried out by the error judgment circuit 27 based on the output signal levels detected by the output signal level monitoring circuits 21-23 attached to the amplifier circuits 17-19.

There are two operations in this failure detection operation,
The first is the operation of detecting the device failure together with the adjustment of the output signal level of the amplifier circuit, and the second is the operation of detecting the failure during the normal operation.

The output signal level adjustment of the amplifier circuit is performed when the optical fiber ring interferometric sensor itself calculates the phase difference.
As described above, since the light receiving element is switched in each section (phase is π / 3 to 2π / 3) where the light intensity output and the phase difference have a nearly linear relationship, amplification is performed to determine the level corresponding to each section. This is for adjusting the gain of the amplifier circuit within the range of the maximum value (the level at which the interference lights are added) and the minimum value (the level at which the interference lights cancel each other) of the output signal levels from the circuits 17 to 19.

In this adjustment, as shown in FIG. 2, the phase difference exceeds the upper and lower folding levels of the light intensity, that is, the output signal level from the amplifier circuit 17 (or 18, 19) is the maximum value and the minimum value. Vibration causing phase modulation that reaches both is applied to the optical fiber ring 5 so that the maximum and minimum values of the output signal level from the amplifier circuit 17 (or 18, 19) at that time fall within the allowable range. Adjust to. For convenience of description, FIG. 2 shows only one light receiving element 11 and the amplifying circuit 17, and other light receiving elements and the amplifying circuit are omitted.

FIG. 3 is a flow chart showing the procedure of the fault detection operation during the normal operation by the error judgment circuit 27. Note that this failure detection operation is performed individually for each amplifier circuit, but since it is the same process for all amplifier circuits, it will be described here as a failure detection operation based on a signal from one amplifier circuit. .

The output signal level in the state where no vibration is applied to the optical fiber ring 5 is set as a steady level and the variable NL is set.
(S20).

Then, the output signal level of the light intensity signal output from the amplifier circuit is obtained from the output signal level monitoring circuit and stored in the variable SL (S21).

Then, the output signal level stored in the variable SL and the steady level previously stored in the variable NL are compared (S22). As a result of the comparison, if the absolute value of these differences does not exceed the allowable level fluctuation range PL (S22, No),
The process directly returns to step S21.

On the other hand, if the absolute value of the difference between the variable SL and the variable NL is not less than the allowable level fluctuation range PL, (S22, Ye
s), counting of time t is started (S23).

The permissible level PL mentioned here is a permissible level of signal fluctuation estimated from electrical noise and vibration noise superimposed on the output signal in a steady state where no vibration or shock is applied.

Then, the value of the variable SL is compared with a predetermined maximum value Lmax suitable for calculating the phase difference (S24).

As a result of the comparison, the value of the variable SL is the maximum value Lma.
If it exceeds x (Yes in S24), an alarm is given that the output signal level from the amplifier circuit has become too high (S31), and the process ends.

On the other hand, as a result of the comparison, if the value of the variable SL does not exceed the maximum value Lmax (S24, No), then the value of the variable SL and a predetermined minimum value Lmin suitable for phase difference calculation are set. Are compared (S25).

As a result of the comparison, the value of the variable SL is the minimum value Lmi.
If it is less than n (S25, Yes), an alarm is given that the output signal level from the amplifier circuit is too low (S32), and the process is terminated.

On the other hand, as a result of the comparison, if the value of the variable SL is not less than the minimum value Lmin, the time t is compared with the predetermined time Lt (S26).

As a result of the comparison, if the time t does not exceed the predetermined time Lt (S26, No), the step S2 is directly performed.
After returning to 1, the failure detection process during normal operation is continued.

On the other hand, when the time t exceeds the predetermined time Lt (S26, Yes), an alarm is output as a time-out (S33), and the process ends.

Here, the predetermined time Lt is the maximum time in which vibration is considered to be applied in the fiber ring, and varies depending on the situation in which this optical fiber ring interference type sensor is used. Usually, the vibration applied to the optical fiber ring is intermittent, or only for a moment, and is rarely applied continuously for a long time, so when the signal of the phase difference indicating that the vibration is detected continues for a predetermined time, This is determined as a failure. If it is known from the beginning that vibration is continuously applied for a long period of time depending on the usage status of this sensor, steps S23, S26, and S
33 may be omitted.

Here, the estimation of the cause of failure when an alarm is issued in the above-described failure detection processing during normal operation will be described.

First, when the alarm is issued in step S31, it means that a very large signal is received as the light intensity of the phase difference signal. Therefore, for example, an output signal due to a failure of the amplifier circuit or a failure of the light receiving element. It is possible to estimate fluctuations in level or oscillation, strong light emission or oscillation due to a failure of the light receiving element or circuit.

Next, when the alarm is issued in step S32, it means that a very small signal is received as the light intensity of the phase difference signal. Therefore, for example, the output due to the failure of the amplifier circuit or the failure of the light receiving element. Signal level drop,
The output level of the light source decreases due to the failure of the light receiving element or the circuit, the failure, dropout or dirt of the optical connector, the increase of the loss of the optical fiber, the disconnection of the optical fiber, the loss of the optical transmission line due to the failure of the optical branching coupler, etc. Can be estimated.

Next, if an alarm is issued in step S33, is the vibration applied for a longer time than expected?
Or, since there is a long phase difference between the clockwise and counterclockwise signals, for example, when an optical fiber that constitutes an optical fiber ring is installed outdoors, If it is not fixed properly and shakes, the optical output level of the light source fluctuates due to the failure of the amplifier circuit or the failure of the light receiving element, the failure, dropout or dirt of the optical connector, the increase of the loss of the optical fiber, the disconnection of the optical fiber, the optical It can be estimated that the loss of the optical transmission line is increased due to the failure of the branch coupler, and the strong light emission of the light source or the decrease of the output level due to the failure of the light receiving element and the light emitting circuit.

In this case, since a small fluctuation in the output level can be detected, it is possible to estimate the failure even if the fluctuation is smaller than that in steps S31 and S32.

As described above, according to the embodiments of the present invention, it is possible to accurately detect a failure in the equipment or device constituting the sensor, which has been difficult to detect with the optical fiber ring interference type sensor, and to judge the failure. It becomes possible. Therefore, it is possible to prevent malfunction due to a failure of the sensor itself.

Although the embodiment to which the present invention is applied has been described above, the present invention is not limited to this embodiment. For example, although the case where the 3 × 3 optical branch-coupling element is used has been described in the present embodiment, the present invention has an initial phase difference of nπ (n = 0, n = 0,
1, 2, ...) other than at least 2
The present invention can also be applied to the case where the phase difference is calculated using N × N optical branching / coupling elements having three or more.

[0056]

According to the present invention described above, by monitoring the output from the amplifier circuit for amplifying the signal received by the light receiving element, the sensor function of the optical fiber ring interferometric sensor is deteriorated or lost. Promptly for failures and obstacles,
Further, it becomes possible to detect accurately and the reliability of the sensor function can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an optical fiber ring interference type sensor to which the present invention is applied.

FIG. 2 is a diagram for explaining vibration applied to an optical fiber ring.

FIG. 3 is a flowchart showing a procedure of a failure detection operation during normal operation by the error determination circuit.

[Explanation of symbols]

1 optical fiber 3 Optical branch coupling element 5 Optical fiber ring 11 First light receiving element 12 Second light receiving element 13 Third light receiving element 17 First amplifier circuit 18 Second amplifier circuit 19 Third amplifier circuit 21 First Output Signal Level Monitoring Circuit 22 Second output signal level monitoring circuit 23 Third Output Signal Level Monitoring Circuit 25 Phase difference calculation circuit 27 Error judgment circuit

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Toru Takashima             1440 Rokuzaki, Sakura City, Chiba Prefecture Fujikura Ltd.             Sakura office (72) Inventor Shinichi Niimi             1440 Rokuzaki, Sakura City, Chiba Prefecture Fujikura Ltd.             Sakura office F term (reference) 2F055 AA40 BB20 CC59 DD20 EE31                       FF49 GG31                 2F103 BA18 CA08 EB02 EB16 EC09                       FA01                 2G064 AB22 BC06 BC12 BC32 CC54

Claims (3)

[Claims] 1. An optical fiber, an N × N optical branching / coupling element connected to both open ends of the optical fiber, and an N × N optical branching / coupling element connected to allow laser light to enter the optical fiber. A light emitting element, an N number of light receiving elements connected to the N × N optical branching / coupling element, an amplifier circuit for amplifying an optical signal received by the light receiving element, and a signal level output from the amplifier circuit. An optical fiber ring interference type sensor, comprising: a signal level monitoring circuit for monitoring; and a failure determination circuit for determining a failure based on whether or not the signal level detected by the signal level monitoring circuit is within a predetermined range. 2. The failure determination circuit determines that there is a failure when the signal level detected by the signal level monitoring circuit exceeds a predetermined value or when the signal level detected by the signal level monitoring circuit is less than a predetermined value. The optical fiber ring interferometric sensor according to claim 1, characterized in that the determination is made. 3. The failure determination circuit determines that there is a failure when the signal level output from the amplifier circuit does not return to a predetermined steady level for a predetermined time. Fiber optic ring interferometric sensor.