JPH04344417A - Optical fiber gyro - Google Patents

Abstract

PURPOSE:To provide an optical fiber gyro with a stable property, for cancelling variation in the zero point output caused by temerature variation or the like of optical parts in a sensing loop of the optical fiber gyro. CONSTITUTION:Until a beam exiting a luminescent module 1 is branched by a beam coupler 5, the branched beams turn round in an optical fiber coil 10 in the left and right directions reverse to each other and again return to the beam coupler 5, the beams are disposed to turn around depolarizers 6, 7, phase modulators 8, 9 and the optical fiber coil 10 in the same order of both left and right directions within a sensing loop. Thus, the phase difference between both left and right beams generated by the depolarizer 6 is cancelled by the depolarizer 7, and the phase difference between both beams generated by the phase modulator 8 is cancelled by the phase modulator 9, so that an optical fiber gyro having a stable property generating no variation, in the zero point output can be realized.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber gyro used for detecting the angular velocity of a moving body.

0002

[Prior Art] An optical fiber gyro uses a loop-shaped optical fiber coil to propagate light in opposite directions, and detects the phase difference between the two lights caused by the Sagnac effect, thereby determining the rotational angular velocity of a moving body relative to inertial space. To detect.

[0003] Such optical fiber gyros include a phase bias method, a phase modulation method, a frequency modulation method, and the like. Here, the principle will be explained using the phase modulation method as an example.

FIG. 5 shows an example of a conventional optical fiber gyro. In FIG. 5, 51 is a light emitting module, and 52 is a light receiving module.
It is connected to No. 3 optical coupler. 54 is a polarizer for blocking unnecessary component light, and the optical coupler 53 and 55
It is inserted between the optical coupler and the optical coupler. A depolarizer 56 depolarizes the passed light, and is made by fusing 1:2 polarization maintaining optical fibers with their principal axes tilted at 45 degrees. After exiting the light emitting module 51 and passing through the optical coupler 53 and the polarizer 54, the light split by the optical coupler 55 passes through the depolarizer 56 on one side, and then the optical fiber coil 60 on the right. The light passes through the phase modulator 59 and returns to the optical coupler 55 again. The other light first passes through 59 phase modulators and then 60
The light passes through the optical fiber coil 56 in a counterclockwise direction, passes through the depolarizer 56, and returns to the optical coupler 55. At this time 6
When the zero optical fiber coil rotates with respect to inertial space, a phase difference occurs between the left and right beams due to the Sagnac effect. The optical fiber gyro detects the rotational angular velocity with respect to the inertial space by detecting the phase difference between the left and right rotation lights, and is branched from 55 optical couplers, where a phase difference occurs in the left and right rotation spaces due to the Sagnac effect. The path through which the light returns to the optical coupler 55 is called a sensing loop. The light returned to the optical coupler 55 passes through a polarizer 54, passes through an optical coupler 53, and is converted into an electrical signal by a light receiving module 52. Reference numeral 61 denotes a control circuit for the light emitting module, which controls the amount of light emitted from the light emitting module to always be constant. An oscillation circuit 63 generates a reference signal for phase modulation, and a phase modulator drive circuit 66 receives the reference signal 63 and drives a phase modulator 59. The output of the light receiving module 52 is amplified by an amplifier 62 and then synchronously detected by a synchronous detection circuit 67. The output of the synchronous detection circuit 67 corresponds to the phase difference between the light that rotated clockwise and the light that rotated counterclockwise through the optical fiber coil 60, and this output value determines the rotational angular velocity of the optical fiber coil relative to the inertial space. can be detected.

[0005] When there is uneven temperature fluctuation in an optical fiber coil composed of such a loop-shaped optical fiber due to fluctuations in environmental temperature, the left and right lights propagating in the optical fiber coil may change at the same time. It is known that because the two lights pass through different temperature fluctuations, a phase difference occurs between the two lights, causing a drift in the gyro's zero point output. Conventionally, by winding the optical fiber that forms the optical fiber coil symmetrically around its midpoint, light in both left and right directions passes through the spatially closest point at the same time, which eliminates the effects of temperature fluctuations. It is decreasing. (D.M.Shu
pe:Thermally Induced Nonr
ecoprocity in the fiber o
ptic Interferometer, APP
LIED OPTICS, Vol. 19, No. 5, p.
654, March 1980)

[0006]

[Problem to be Solved by the Invention] However, in an optical fiber gyro using a so-called symmetrically wound optical fiber coil as described above, it is certainly possible to suppress the drift of the gyro's zero point output due to temperature fluctuations of the optical fiber coil. , 56 depolarizers and 59 phase modulators in the sensing loop also cause a phase difference between the left and right beams, causing a drift in the zero point output. In order to reduce this effect, it has conventionally been necessary to increase the sensitivity to rotational angular velocity by increasing the fiber length of the optical fiber coil so that the effects of the depolarizer and phase modulator can be ignored.

The present invention solves the above-mentioned conventional problems, and provides an optical fiber gyro with stable characteristics that does not cause zero-point output drift even with temperature fluctuations of other components in the sensing loop. With the goal.

[0008]

[Means for Solving the Problems] To achieve this object, the optical fiber gyro of the present invention firstly arranges optical components in the sensing loop in the same order for counterclockwise light and clockwise light. This is what I did.

Second, two phase modulators are placed in each path from both ends of the fiber coil to both ends of the optical coupler.

Thirdly, means for controlling the polarization states of the two lights are respectively arranged in the path from both ends of the fiber coil to both ends of the optical coupler.

Fourthly, means for controlling the polarization state of light is provided at the midpoint of the optical fibers forming the optical fiber coil or between two optical fiber coils of equal length.

0012

[Operation] Firstly, the present invention has the following advantages: By arranging the optical components in the sensing loop in the same order for counterclockwise and clockwise lights, the optical path length of the components in the sensing loop can be changed due to changes in environmental temperature. Even if there is a fluctuation, the influence is canceled by the counterclockwise light and the clockwise light, so that the zero point output of the gyro does not drift.

Second, by arranging two phase modulators in each path from both ends of the fiber coil to both ends of the optical coupler, even if the optical path length of the phase modulator changes due to fluctuations in environmental temperature, This effect is canceled by the counterclockwise and clockwise lights to prevent the zero point output of the gyro from drifting.

Thirdly, by arranging means for controlling the polarization states of the two lights in each path from both ends of the fiber coil to both ends of the optical coupler, the polarization states of the lights can be controlled by fluctuations in environmental temperature. Even if the optical path length of the means for controlling changes, the effect is canceled by the counterclockwise light and the clockwise light, so that drift of the zero point output of the gyro does not occur. Furthermore, by using means for controlling the polarization states of the two lights, both the left and right lights passing through the optical fiber coil and the phase modulator are in the same polarization state, and the polarization states of the left and right lights are different. This prevents the occurrence of drift in the zero point output of the gyro caused by reciprocity.

Fourthly, by inserting the means for controlling the polarization state of light into the midpoint of the optical fiber forming the optical fiber coil, the optical path length of the means for controlling the polarization state of light can be changed by fluctuations in environmental temperature. Even if there is a fluctuation, the clockwise light and the counterclockwise light pass through the depolarizer at approximately the same time, so that the zero point output of the gyro does not drift. Furthermore, by inserting a means for controlling the polarization state of light into the midpoint of the optical fibers that form the optical fiber coil, we have achieved non-reciprocity in which the polarization states of the left-handed and right-handed light passing through the optical fiber coil are different. The counterclockwise light and the clockwise light cancel each other out to prevent the zero point output of the gyro from drifting.

[0016]

【Example】

(Embodiment 1) FIG. 1 shows a first embodiment of the present invention. In FIG. 1, 1 is a light emitting module, 2 is a light receiving module, and is connected to an optical coupler 3 by an optical fiber. 4 is a polarizer for blocking unnecessary component light, and is inserted between the optical coupler 3 and the optical coupler 5. 6 and 7 control the polarization state of the passed light,
It is a depolarizer that depolarizes light, and is made by fusing 1:2 polarization-maintaining optical fibers with their principal axes tilted at 45 degrees. The light that exits the light emitting module 1 passes through the optical coupler 3 and the polarizer 4, and the light that exits the optical coupler 5 passes through the depolarizer 6 on one side and the phase modulator 8 that controls the phase of the light. After that, it passes clockwise through the optical fiber coil 10, passes through the phase modulator 9, the depolarizer 7, and returns to the optical coupler 5. The other light first passes through a depolarizer at 7 and a phase modulator at 9.
It passes through the optical fiber coil counterclockwise, passes through the phase modulator 8, the depolarizer 6, and returns to the optical coupler 5. At this time, when the 10 optical fiber coils are rotating with respect to the inertial space, a phase difference occurs between the left and right beams due to the Sagnac effect. The light returned to the optical coupler 5 passes through 4 polarizers, passes through an optical coupler 3, and is converted into an electrical signal by a light receiving module 2. Reference numeral 11 denotes a control circuit for the light emitting module, which controls the amount of light emitted from the light emitting module to always be constant. An oscillation circuit 13 generates a reference signal for phase modulation, and phase modulator drive circuits 15 and 16 receive the reference signal 13 to drive phase modulators 8 and 9. At this time, if the light is modulated with the same phase in the phase modulations 8 and 9, both the left and right rotation lights are phase modulated with the same phase, so there is no phase difference between the left and right rotation lights, and the effect of phase modulation is lost. Therefore, by inserting 14 inverting circuits, the modulation phase of the phase modulator 8 is made to be in opposite phase to the modulation phase of the phase modulator 9. Moreover, the phase modulators 8 and 9 do not need to have the same frequency and the same phase; for example, it is not necessary to drive the phase modulator 8 at all. At that time, the phase modulator 8 does not need to be driven, so a dummy component may be used as a dummy component whose temperature change with respect to the environmental temperature change and the optical path length change with respect to the temperature change are close to those of the phase modulator 9. The output of the 2 light receiving modules is amplified by 12 amplifiers and then synchronously detected by 17 synchronous detection circuits. The output of the synchronous detection circuit No. 17 corresponds to the phase difference between the light that rotated clockwise and the light that rotated counterclockwise through the optical fiber coil No. 10, and this output value determines the rotational angular velocity of the optical fiber coil relative to the inertial space. can be detected.

[0017] At this point, the environmental temperature changes and the depolarizer 6
When the temperature of the depolarizer 6 changes, the length changes due to the refractive index and thermal expansion of the depolarizer 6 depending on the temperature, and the optical path length of the depolarizer 6 changes with time. There is a time difference between the clockwise light passing through the depolarizer 6 and the counterclockwise light passing by the time it takes the counterclockwise light to pass through the 10 optical fiber coils. During this time difference, the depolarizer 6 is affected by temperature changes. The optical path length changes, resulting in a phase difference between the left and right beams. However, the optical path length of the depolarizer 7 similarly changes due to changes in the environmental temperature. That is, since the amount of change in the optical path length of the depolarizer 6 is almost equal to the amount of change in the optical path length of the depolarizer 7, the optical path length of the depolarizer 6 when the clockwise light passes through the depolarizer 6 and when the counterclockwise light passes through the depolarizer 6 is The difference is depolarizer 7
is almost equal to the difference in the optical path length of the depolarizer 7 when the clockwise light passes and when the counterclockwise light passes, and the phase difference between the left and right lights generated in the depolarizer 6 is equal to the difference in optical path length between the left and right lights generated in the depolarizer 7. canceled by the phase difference between the rotating lights,
Does not generate gyro output.

Similarly, the phase difference between the left and right beams caused by a change in the optical path length of the phase modulator 8 due to a change in environmental temperature is the same as the phase difference between the left and right beams caused by a change in the optical path length of the phase modulator 9. This is canceled out by the phase difference and does not cause fluctuations in the gyro output.

Therefore, according to the present invention, the depolarizers 6 and 7, the phase modulators 8 and 9, and the optical fiber coils 10 are arranged in the same order for the left-handed light and the right-handed light. Therefore, even if the environmental temperature changes, the phase difference between the left and right beams due to temperature changes in the depolarizer and phase modulator is canceled out, and there is an effect that fluctuations in the output of the gyro do not occur.

(Embodiment 2) FIG. 2 shows a second embodiment of the present invention, in which depolarizer 6 and depolarizer 7 are removed from the first embodiment of the present invention shown in FIG. are equivalent. The light that exits the light emitting module No. 1 passes through the optical coupler No. 3 and the polarizer No. 4, and the light exiting the optical combiner No. 5 passes through the phase modulator No. 8, and then passes through the optical fiber coil No. 10. The light passes through the phase modulator 9 and returns to the optical coupler 5 again. The other light first passes through the phase modulator 9, then counterclockwise through the optical fiber coil 10, passes through the phase modulator 8, and returns to the optical coupler 5. At this time, when the 10 optical fiber coils are rotating with respect to the inertial space, the phase difference between the left and right beams caused by the Sagnac effect is detected by the 17 synchronous detection circuits as described in the first embodiment. Ru.

Even if the temperature of the phase modulator 8 and the phase modulator 9 changes due to a change in the environmental temperature, the amount of change in the optical path length of the phase modulator 8 is approximately equal to the amount of change in the optical path length of the phase modulator 8. Therefore, the difference in the optical path length of the phase modulator 8 when the clockwise light passes through the phase modulator 8 and when the counterclockwise light passes through the phase modulator 8 is:
This is approximately equal to the difference in optical path length of the phase modulator 9 when the clockwise light passes through the phase modulator 9 and when the counterclockwise light passes through the phase modulator 9, and the position between the left and right lights generated in the phase modulator 8 The phase difference is canceled by the phase difference between the left and right beams generated by the phase modulator 9, and no fluctuation in the output of the gyro occurs.

Therefore, according to the present invention, since the phase modulators 8 and 9 and the optical fiber coils 10 are arranged in the same order for the counterclockwise light and the clockwise light, the environmental temperature can be reduced. Even if the temperature changes, the phase difference between the left and right beams due to the temperature change of the phase modulator is canceled out, which has the effect of not causing fluctuations in the output of the gyro.

(Embodiment 3) FIG. 3 shows a third embodiment of the present invention, in which 8 phase modulators, 14 inversion circuits, 15 This is equivalent to removing the phase modulator drive circuit. After exiting the light emitting module 1 and passing through the optical coupler 3 and the polarizer 4, and the light exiting the optical coupler 5, one passes through the depolarizer 6.
It passes clockwise through the optical fiber coil No. 10, passes through the phase modulator No. 9, the depolarizer No. 7, and returns to the optical coupler No. 5 again. The other light first passes through the depolarizer 7 and the phase modulator 9, then counterclockwise through the optical fiber coil 10, passes through the depolarizer 6, and returns to the optical coupler 5. At this time, when the 10 optical fiber coils are rotating with respect to the inertial space, the phase difference between the left and right beams caused by the Sagnac effect is detected by the 17 synchronous detection circuits as described in the first embodiment. Ru.

Even if the temperatures of the depolarizer 6 and the depolarizer 7 change due to a change in the environmental temperature, the depolarizer 6
Since the amount of change in the optical path tone is almost equal to the amount of change in the optical path length of the depolarizer 7, the difference in the optical path length of the depolarizer 6 when the clockwise light passes through the depolarizer 6 and when the counterclockwise light passes through the depolarizer 6 is The phase difference of 7 is almost equal to the difference in the optical path length of the depolarizer 7 when the clockwise light passes through the depolarizer 7 and when the counterclockwise light passes through the depolarizer 7, and the phase difference between the left and right lights generated in the depolarizer 6 is This is canceled out by the phase difference between the left and right lights generated in step 7, and no fluctuation in the gyro output occurs.

Therefore, according to the present invention, since the depolarizers 6 and 7 and the optical fiber coils 10 are arranged in the same order for the counterclockwise light and the clockwise light,
Even if the environmental temperature changes, the phase difference between the left and right beams due to the temperature change of the depolarizer is canceled out, and there is an effect that the output of the gyro does not fluctuate.

Furthermore, according to the present invention, since both the clockwise light and the counterclockwise light are made non-polarized by the depolarizers 6 and 7, respectively, when both the clockwise and counterclockwise lights pass through the phase modulator 9 and the optical fiber coil 10, both clockwise and counterclockwise lights are depolarized. Both of the rotating lights are in an unpolarized state. Therefore, there is no non-reciprocity that occurs in the conventional case where one light is in an unpolarized state and the other light is in a linear state, and no phase difference occurs between the two directions of light. This effect reduces the zero point drift of the optical fiber gyro output even when the environmental temperature is constant.

(Embodiment 4) FIG. 4 shows a fourth embodiment of the present invention. In FIG. 4, 1 is a light emitting module, 2 is a light receiving module, and is connected to an optical coupler 3 by an optical fiber. 4 is a polarizer for blocking unnecessary component light, and is inserted between the optical coupler 3 and the optical coupler 5. 41 and 42 are optical fiber coils for detecting rotational angular velocity by the Sagnac effect, and are wound with fibers of equal length. 43 is a depolarizer that depolarizes the passing light, and the length is 1:
It is made by fusing two polarization-maintaining optical fibers with their respective principal axes tilted at 45 degrees. The light that exits the light emitting module No. 1 passes through the optical coupler No. 3 and the polarizer No. 4, and the light exiting the optical combiner No. 5 passes clockwise through the optical fiber coil No. 41, and then passes through the depolarizer No. 43. It passes clockwise through the optical fiber coil 42, passes through the phase modulator 9, and returns to the optical coupler 5. The other light first passes through the phase modulator at 9, then passes through the optical fiber coil at 42 counterclockwise, passes through the depolarizer at 43, passes through the optical fiber coil at 41 counterclockwise, and returns to the optical fiber coil at 5. Return to optical coupler. At this time, when the optical fiber coils 41 and 42 are rotating with respect to the inertial space, a phase difference occurs between the left and right beams due to the Sagnac effect. The light exiting the optical coupler 5 passes through 4 polarizers, passes through the optical coupler 3, and is converted into an electrical signal by the light receiving module 2. Reference numeral 11 denotes a control circuit for the light emitting module, which controls the amount of light emitted from the light emitting module to always be constant. An oscillation circuit 13 generates a reference signal for phase modulation, and a phase modulator drive circuit 16 receives the reference signal 9 and drives the phase modulator 6. The output of the 2 light receiving modules is amplified by 12 amplifiers and then synchronously detected by 17 synchronous detection circuits. The output of the synchronous detection circuit 17 corresponds to the phase difference between the light that rotated clockwise and the light that rotated counterclockwise through the optical fiber coils 41 and 42, and this output value determines the rotation of the optical fiber coil with respect to the inertial space. Angular velocity can be detected.

When the temperature of the depolarizer 43 changes due to a change in the environmental temperature, the length of the depolarizer 43 changes depending on the temperature due to the refractive index and thermal expansion, and the optical path adjustment of the depolarizer 43 changes with time. However, according to the present invention, the time for the clockwise light to pass through the depolarizer 43 and the time for the counterclockwise light to pass are approximately the same time, so as a result, no phase difference occurs between the left and right lights.

Therefore, according to the present invention, since the counterclockwise light and the clockwise light pass through the depolarizer 43 at approximately the same time, even if the environmental temperature changes, the phase difference between the left and right lights will not change due to the temperature change of the depolarizer. This has the effect of not causing fluctuations in the output of the gyro.

Furthermore, according to the present invention, the position between the two directions of light, which is caused by the non-reciprocity that the clockwise light is linearly polarized and the counterclockwise light is unpolarized when passing through the optical fiber coil 41, is The phase difference is canceled by the phase difference between the two directions of light caused by the non-reciprocity that the right-handed light is unpolarized and the left-handed light is linearly polarized when passing through the optical fiber coil 42. No phase difference occurs between the two-way lights while the two-way lights are branched by the optical coupler 5 and return to the optical coupler 5 again. This effect reduces the zero point drift of the optical fiber gyro output even when the environmental temperature is constant.

In this embodiment, a depolarizer is inserted between two optical fiber coils of equal length, but the clockwise light and the counterclockwise light branched from the optical coupler 5 at the same time are split at almost the same time. It is sufficient to pass through a depolarizer, and therefore, the same effect can be obtained even if a single optical fiber coil is used and a depolarizer is inserted at a point of equal length from both ends.

[0032]

As described above, as an effect of the present invention, even if the optical path length of the optical component in the sensing loop changes due to a change in environmental temperature, no drift of the zero point output occurs. It is possible to provide an optical fiber gyro with stable characteristics. Furthermore, it has the effect of canceling out the non-reciprocity effect caused by the different polarization states of the left and right lights in the sensing loop and reducing the drift of the zero point output.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an optical fiber gyro according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram of an optical fiber gyro according to a second embodiment of the present invention.

FIG. 3 is a schematic diagram of an optical fiber gyro according to a third embodiment of the present invention.

FIG. 4 is a schematic diagram of an optical fiber gyro according to a fourth embodiment of the present invention.

[Figure 5] Schematic diagram of an example of a conventional optical fiber gyro

[Explanation of symbols]

1. Light emitting module 2 Light receiving module 3. Optical coupler 4 Polarizer 5 Optical coupler 6 Depolarizer 7 Depolarizer 8 Phase modulator 9 Phase modulator 10 Optical fiber coil 11 Light emitting module control circuit 12 Amplifier 13 Oscillator 14 Inversion circuit 15 Phase modulator drive circuit 16 Phase modulator drive circuit 17 Synchronous detection circuit 51 Light emitting module 52 Light receiving module 53 Optical coupler 54 Polarizer 55 Optical coupler 56 Depolarizer 59 Phase modulator 60 Optical fiber coil 61 Light emitting module control circuit 62 Amplifier 63 Oscillator 66 Phase modulator drive circuit 67 Synchronous detection circuit

Claims (4)

[Claims] Claim 1: A light emitting element, a means for branching light from the light emitting element, an optical fiber coil formed by winding an optical fiber into a ring, and a means for controlling the phase of the light or the polarization state of the light. An optical fiber gyro comprising at least means for detecting a phase difference occurring between lights propagating in opposite directions through the optical fiber coil, wherein one of the lights branched from the light branching means returns the light. The order of the optical fiber coil, the means for controlling the phase of the light, or the means for controlling the polarization state of the light, through which the light passes before returning to the means for branching, is different from the means for branching the light. The order of the optical fiber coil through which the other light passes before returning to the light branching means and the means for controlling the phase of the light or the means for controlling the polarization state of the light is the same. Optical fiber gyro configured. 2. A light-emitting element, a means for branching light from the light-emitting element, and an optical fiber coil formed by winding an optical fiber into a ring shape, the optical fiber coil being used to split light propagating in opposite directions. The optical fiber gyro detects a phase difference occurring between the lights, and the optical fiber gyro includes means for controlling the phase of the first light on a path from the means for branching the light until one of the lights branched from the light reaches the optical fiber coil. and means for controlling the phase of the second light, which is similar to the means for controlling the phase of the first light, on a path until the other light branched from the light branching means reaches the optical fiber coil. , or an optical fiber gyro provided with a light transmission means having a characteristic similar to that of the means for controlling the phase of the first light according to a change in optical path length with respect to a change in environmental temperature. 3. The invention comprises at least a light emitting element, a means for branching light from the light emitting element, and an optical fiber coil formed by winding an optical fiber into a ring shape, the optical fiber coil being used to split light propagating in opposite directions. The optical fiber gyro detects a phase difference occurring between the light beams, and controls the polarization state of the first light beam on the path of one of the beams branched from the light beam branching means to the optical fiber coil. An optical fiber gyro comprising means for controlling the polarization state of the second light on a path from the means for branching the light until the other light branched from the light branching means reaches the optical fiber coil. 4. The optical fiber coil comprises at least a light emitting element, a means for branching light from the light emitting element, an optical fiber coil having an optical fiber wound in a ring shape, and a means for controlling the polarization state of the light. is an optical fiber gyro that detects a phase difference occurring between lights propagating in opposite directions, the optical fiber gyro detecting a phase difference occurring between lights propagating in opposite directions, the optical fiber gyro is configured to An optical fiber gyro comprising means for controlling the polarization state of the light between the optical fiber coils.