JPH0510768A - Optical rotation detecting device - Google Patents

Abstract

PURPOSE:To reduce the zero point drift of an optical fiber gyro by installing depolarizing means adjacent each other on an optical path coupled to a phase modulating means. CONSTITUTION:Light output from a light source 1 is bifurcated by a coupler 2 and is input to a coupler 5 after passing through a polarizer 4 and is uniformly bifurcated. The light of an optical path 105 travels clockwise through an optical fiber coil 6 and is depolarized and input to a depolarizing means 9 through a phase modulator 7 and re-deporalized and input to the coupler 5 from the opposite direction. The light of an optical path 109 travels in the opposite direction and is input to the coupler 5 after propagating clockwise within the means 9, the modulator 7, the means 8 and the coil 6 and is coupled to the light wave bifurcated beforehand and then propagates in the opposite direction and is input to a photodiode 3 and converted into an electric signal. Because the light is depolarized by insertion of the depolarizing means 8,9 into a sensing loop in order to reduce errors in rotation output, fluctuations in the polarized state are very small and the zero point drift of the rotation output of a gyro is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical rotation detecting device used for a moving body or the like.

[0002]

2. Description of the Related Art From a gyro used as an angular velocity sensor, not only angular velocity but also azimuth data can be obtained by integrating it. Among such gyros, the optical fiber gyro has no moving parts and can be miniaturized, and further, in terms of minimum detectable angular velocity (sensitivity), drift, measurable range (dynamic range), and scale factor stability. Since it is superior to the conventional gyro, it has been noticed and developed in recent years.

Next, taking the phase modulation type optical fiber gyro as an example, the principle thereof will be described with reference to FIG.

Light from a light source 1 which is a light emitting element such as a semiconductor laser is input to a polarizer 4 through an optical path 101, a coupler 2 and an optical path 102, and light passing through the polarizer 4 passes through an optical path 104. Is input to the coupler 5, where the optical path 10
5 and the optical path 107 are equally divided. Light path 10
The light input to the optical fiber 5 is input to the optical fiber coil 6 and the optical path 10.
6, the phase modulator 7, and the optical path 107 are passed in this order and input to the coupler 5. The light split into two in the coupler 5 and input to the optical path 107 travels in the direction completely opposite to the above-described light wave. That is, the light that has passed through the phase modulator 7 and the optical path 106 in this order propagates counterclockwise through the optical fiber coil 6, then passes through the optical path 105, and is input to the coupler 5. That is, the light waves split into two in opposite directions by the coupler 5 propagate through the optical fiber coil 6 and are then coupled by the coupler 5 again. After the combined light passes through the optical path 104, it propagates in the opposite direction through the polarizer 4, the optical path 21, and the coupler 2, and the optical path 10
By 3, it is input to the photodiode 3 and converted into an electric signal.

The optical fiber coil obtains a Sagnac phase difference corresponding to the rotational angular velocity of the optical fiber gyro, and is formed by winding a polarization-maintaining optical fiber around the coil. The phase modulator enhances the detection sensitivity of the Sagnac phase difference generated in the optical fiber coil by adding a preset optical phase. For example, a polarization plane preserving optical fiber is used for a piezoelectric vibrator or the like. Is formed by winding. The addition of this phase by the phase modulator is
The expansion and contraction of the piezoelectric vibrator applies stress to the optical fiber wound around the piezoelectric vibrator to change the effective refractive index, the propagation constant, and the like.

When the optical fiber coil is rotated when the light propagates through the optical fiber coil, a phase difference is generated between the clockwise light and the counterclockwise light due to the so-called Sagnac effect. The phase difference is detected by detecting the signal component of the interference light between the clockwise light and the counterclockwise light.

In the gyro having the above structure, all optical paths are composed of polarization-maintaining fibers. Another optical fiber that can be considered as an optical path is a single mode optical fiber, which is less expensive than a polarization-maintaining optical fiber. However, the single-mode optical fiber has a problem in maintaining the polarization plane, and a large zero-point drift (rotational output fluctuation in a stationary state) occurs in the rotation output due to disturbance such as temperature change. Uses a polarization-maintaining optical fiber.

[0008]

The rotation output of the optical fiber gyro is obtained from the interference light intensity of the light rotating clockwise and the light rotating counterclockwise in the sensing loop portion,
The intensity of the interference light changes when the polarization states of the left and right lights rotate simultaneously or independently. Therefore, in order to reduce the zero point drift in the optical fiber gyro, it is necessary to maintain the polarization state of the left and right bidirectional light.

In the optical fiber gyro having the above structure,
The polarization state of the left and right lights is maintained by configuring the optical path with a polarization-maintaining optical fiber. However, polarization-maintaining fiber is more expensive than single-mode optical fiber, so using it in the optical path of an optical fiber that requires a very long optical path to obtain the Sagnac phase difference makes the cost of the optical fiber gyro To be very high.
In order to reduce the cost of the optical fiber, it is necessary to develop a method to reduce the zero-point drift in the gyro whose optical path is composed of a single mode fiber.

It is an object of the present invention to propose a structure of an optical fiber gyro which is low in cost and high in accuracy by reducing the zero point drift of the optical fiber gyro which uses a single mode optical fiber as an optical path.

[0011]

In order to achieve the above object, the present invention provides a light source, a first coupler for splitting light output from the light source into two, and a first coupler for splitting the light. A polarizer into which one of the lights is input, a second coupler that splits the light output from the polarizer into two, and an optical fiber that is coupled to the second coupler and that winds a phase modulator and an optical fiber. A sensing loop unit having at least a coil and producing a Sagnac effect; and a light receiving unit that passes one of the light beams passing through the polarizer through the sensing loop unit and branched into two by the first coupler, The second
Depolarizing means between the coupler and the phase modulator and between the phase modulator and the optical fiber coil, or depolarizing means between the second coupler and the phase modulator.

[0012]

According to the present invention, the depolarizing means is inserted in the sensing loop portion to depolarize the light passing through the sensing loop portion, thereby reducing the zero point drift of the rotation output due to the change of the polarization state. To do. Further, according to the configuration of claim 3 or 4, the light that rotates counterclockwise and the light that rotates clockwise in the sensing loop portion are depolarized before being input to the phase modulator, thereby changing the polarization state. The fluctuation of the modulation degree caused by the is eliminated, and the zero point drift of the rotation output of the optical fiber gyro is further reduced.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings. (Embodiment 1) FIG. 1 is a schematic diagram showing the configuration of an optical rotation detection device according to Embodiment 1 of the present invention.

In FIG. 1, 1 is a light source composed of a super luminescent diode, 2 is a coupler for splitting the light from the light source 1, and 4 is a polarizer for defining the polarization direction of the light (for example, a polarizer). A laminated polarizer) 5 is a coupler for bifurcating the light polarized by the polarizer 4. As the couplers 2 and 5, fiber type couplers using single mode optical fibers which are inexpensive and have high reliability are used.

Reference numeral 6 denotes an optical fiber coil formed by winding a single mode optical fiber around a bobbin for obtaining a phase difference due to the Sagnac effect. Reference numeral 7 denotes a phase modulator formed by winding a single mode optical fiber around a piezoelectric vibrator, for example, which gives a predetermined amount of phase difference to passing light.

Depolarization means 8 and 9 are inserted for the purpose of forcibly depolarizing the propagating light and removing unnecessary interference noise components due to fluctuations in the polarization state. As the depolarizing means, a LYOT-type fiber depolarizer in which the principal axis angle of the polarization-maintaining optical fiber is inclined by about 45 degrees and fused is used as the depolarizing means. The depolarizing means may be a combination of crystal plates having optical anisotropy so that the principal axes are displaced by about 45 degrees. Reference numeral 3 is a photodiode that converts the propagated light into an electric signal.

Further, in this embodiment, 101 to 109
Is an optical path, and optical paths 101, 102, 103, 104,
105, 106, 107, 108, 109, the optical path of the optical fiber coil portion, and the optical path of the phase modulator portion are
All are composed of single-mode optical fibers, but some of these may be replaced with polarization-maintaining optical fibers.

Next, the operation of the present optical rotation detector will be described in detail with reference to FIG.

The light output from the light source 1 is transmitted through the optical path 10
1 and is input to the coupler 2. The light split into two by the coupler 2 passes through the optical path 102, the polarizer 4 which defines the polarization state in only one direction, and the optical path 104, and then the coupler 5
Entered in. The light input to the coupler 5 is transmitted through the optical path 10
5 and 109 are equally divided into two. Optical path 105
The input light into the optical fiber coil 6 travels clockwise,
A phase modulator that passes through the optical path 106, is depolarized by the depolarizer 8, and adds a preset optical phase for increasing the detection sensitivity of the Sagnac phase generated in the optical fiber coil through the optical path 108. Optical path 1 through 7
After passing through 07, it is input to the depolarizing means 9, where it is depolarized again, and is input to the coupler 5 in the reverse direction via the optical path 109. Here, the phase modulator 7 plays a role of adding a preset optical phase in order to enhance the detection sensitivity of the Sagnac phase generated in the optical fiber coil. In addition, the coupler 5 is branched into two,
The light input to the optical path 109 travels in the opposite direction to the above-described light wave. That is, the light that has passed through the optical path 109, the depolarizing means 9, the optical path 107, the phase modulator 7, the optical path 108, the depolarizing means 8 and the optical path 106 in this order propagates counterclockwise in the optical fiber coil 6 and then the optical path 105. And is input to the coupler 5. That is, the light waves split into two in opposite directions by the coupler 5 propagate through the optical fiber coil 6 and
It is coupled again by the coupler 5. The combined light is in the optical path 104.
After passing through, the light propagates in the opposite direction through the polarizer 4, the optical path 102, and the coupler 2, and is input to the photodiode 3 by the optical path 103 and converted into an electric signal.

The optical path of the above optical fiber gyro is constituted by a single mode fiber. However, in this single mode optical fiber, the polarization state of light passing therethrough is relatively changed due to external factors such as environmental temperature and stress application. Easy to do. In the optical fiber gyro, what is observed as the rotational output is the interference intensity of the left and right bidirectional light, and therefore, when the polarization state of the left and right bidirectional light fluctuates with time, an error occurs in the rotational output.

In the present embodiment, in order to reduce the error of the rotation output, the depolarizing means is inserted in the sensing loop to depolarize the light propagating through the sensing loop. As a result, even if the polarization states of the individual polarization components of the depolarized left and right lights are changed, the change in the polarization state as a whole becomes extremely small. Therefore, the fluctuation of the signal of the interference light output is almost eliminated, and the zero point drift of the rotation output of the optical fiber gyro is reduced.

The degree of light modulation by the phase modulator varies slightly depending on the polarization direction of the input light. When the depolarizer is not inserted, the light input to the phase modulator is not input in a constant polarization state due to the change in the polarization state, and therefore the polarization state is different between the left and right lights. If the polarization states of the left and right lights that are input to the phase modulator are not temporally constant and there is a difference in the polarization state between the left and right lights, they are the same for both left and right lights, and A stable modulation factor cannot be obtained. This is one of the causes of zero drift. In order to eliminate such a change in the modulation degree caused by the change in the polarization state, the left and right lights can be depolarized by using the depolarizer just before being input to the phase modulator. The optimum insertion position of the depolarizing means having such an effect is at both ends of the phase modulator 7, that is, the optical path 1.
The light incident on the optical path 09 is between the coupler 5 and the phase modulator 7, and the light incident on the optical path 105 is between the optical fiber coil 6 and the phase modulator 7.

As described above, by inserting the depolarizing means as in the configuration of this embodiment, not only the left and right bidirectional light can be converted into the light whose polarization state is difficult to change but also the modulation generated by the phase modulator. Less susceptible to fluctuations in frequency.

In the present embodiment, for the above reason, two depolarizing means are inserted, one is inserted between the coupler 5 and the phase modulator, and the other is inserted between the optical fiber coil 6 and the phase modulator. is doing. As a result, fluctuations in the modulation factor due to fluctuations in the polarization state are removed, and the zero-point drift of the rotation output of the optical fiber gyro is further reduced.

In the above configuration, the fluctuation of the rotational output in the stationary state, that is, the zero point drift is 0.08 (degrees / second).
It became within. The zero-point drift in the configuration of the conventional example is within 2.25 (degrees / second), and the zero-point drift in Example 1 is extremely small as compared with the zero-point drift in the conventional example. (Embodiment 2) FIG. 2 is an overall schematic view of an optical rotation detecting device according to Embodiment 2 of the present invention.

The structure and operation described in the first embodiment will be described in detail though there are some portions that overlap.

In FIG. 2, reference numeral 1 is a light source composed of a super luminescent diode, 2 is a coupler for splitting the light from the light source 1, and 4 is a polarizer for defining the polarization direction of the light (eg, a polarizer). A laminated polarizer) 5 is a coupler for bifurcating the light polarized by the polarizer 4. As the couplers 2 and 5, fiber type couplers using single mode optical fibers which are inexpensive and have high reliability are used.

An optical fiber coil 6 is formed by winding a single mode optical fiber around the coil, and is provided for providing a phase difference by the Sagnac effect. Reference numeral 7 denotes a phase modulator formed by winding a single mode optical fiber around a piezoelectric vibrator, for example, which gives a predetermined amount of phase difference to passing light.

Depolarization means 10 is inserted for the purpose of forcibly depolarizing the propagating light and removing the unnecessary interference noise component due to the change of the polarization state. As the depolarizing means, a LYOT-type fiber-type depolarizer in which the principal axis angle of the polarization-maintaining optical fiber is inclined by about 45 degrees and fused is used. The depolarizing means may be a combination of crystal plates having optical anisotropy so that the principal axes are displaced by about 45 degrees. Reference numeral 3 is a photodiode that converts the propagated light into an electric signal.

In the present embodiment, 101 to 107, 1
Reference numeral 10 denotes an optical path, and the optical paths 101, 102, 103, 10
4, 105, 106, 107, 110, the optical path of the optical fiber coil portion, and the optical path of the phase modulator portion are all composed of a single mode optical fiber. It does not matter if the fiber is used.

Next, the operation of the present optical rotation detecting device will be briefly described with reference to FIG. The optical output output from the light source 1 passes through the optical path 101 and is input to the coupler 2. The light split into two by the coupler 2 passes through the optical path 102, passes through the polarizer 4 which defines the polarization state in only one direction, and the optical path 104, and then is input to the coupler 5. The light input to the coupler 5 is equally divided into two light paths 105 and 110. The input light to the optical path 105 travels in the clockwise direction through the optical fiber coil 6, and then the optical path 106, the phase modulator 7, and the optical path 107.
After passing through in this order, the light is input to the depolarizer 10 to be depolarized, and then input to the coupler 5 in the reverse direction via the optical path 110. Further, similarly to the first embodiment, the phase modulator 7 plays a role of adding a preset optical phase in order to enhance the detection sensitivity of the Sagnac phase generated in the optical fiber coil.

Further, the coupler 5 is branched into two,
The light input to the optical path 110 travels in the opposite direction to the above-described light wave. That is, the optical path 110, the depolarizer 10,
The light that has passed through the optical path 107, the phase modulator 7, and the optical path 106 in this order propagates counterclockwise in the optical fiber coil 6, passes through the optical path 105, and is input to the coupler 5. That is, the light waves split into two in opposite directions by the coupler 5 propagate through the optical fiber coil 6 and are then coupled by the coupler 5 again. After the combined light passes through the optical path 104, the polarizer 4 and the optical path 2
1, the coupler 2 propagates in the opposite direction, and the optical path 103 causes
It is input to the photodiode 3 and converted into an electric signal.

As the insertion position of the depolarizing means in the present embodiment, a construction is adopted in which the depolarizing means is inserted only between the coupler 5 and the phase modulator. With this configuration, the light that rotates counterclockwise around the optical fiber coil is depolarized by the depolarizer immediately before being input to the phase modulator. As for the clockwise light, it passes through the optical fiber coil formed by the single mode optical fiber before it is input to the phase modulator, so the polarization state when the counterclockwise light is input to the phase modulator. Compared to, it is in a state where it is considerably depolarized. Therefore, the zero-point drift of the rotation output is slightly larger than that of the first embodiment in which the left and right bidirectional light before being input to the phase modulator is depolarized by the depolarizer, but is extremely smaller than that of the conventional example. This configuration has less light loss than the configuration in the first embodiment,
It has an advantage that the process can be simplified.

The rotational output in the stationary state, that is, the zero-point drift in the above-mentioned configuration is within 0.11 (degrees / second), which is slightly larger than the zero-point drift in the first embodiment, but in the conventional optical fiber gyro. It is much smaller than the zero-point drift, and there is no practical problem. (Embodiment 3) FIG. 3 is an overall schematic view of an optical rotation detecting device in Embodiment 3 of the present invention.

The structure and operation described in the first embodiment will be described in detail though there are some portions that overlap.

In FIG. 3, 1 is a light source composed of a super luminescent diode, 2 is a coupler for splitting the light from the light source 1, and 4 is a polarizer for defining the polarization direction of the light (eg, a polarizer). A laminated polarizer) 5 is a coupler for bifurcating the light polarized by the polarizer 4. As the couplers 2 and 5, fiber type couplers using single mode optical fibers which are inexpensive and have high reliability are used.

Reference numeral 6 is an optical fiber coil constructed by winding a single mode optical fiber around the coil, and is for providing a phase difference by the Sagnac effect. Reference numeral 7 denotes a phase modulator formed by winding a single mode optical fiber around a piezoelectric vibrator, for example, which gives a predetermined amount of phase difference to passing light.

Depolarization means 11 is inserted for the purpose of forcibly depolarizing the propagating light and removing unnecessary interference noise components due to fluctuations in the polarization state. As the depolarizing means, a LYOT-type fiber-type depolarizer in which the principal axis angle of the polarization-maintaining optical fiber is inclined by about 45 degrees and fused is used. The depolarizing means may be a combination of crystal plates having optical anisotropy so that the principal axes are displaced by about 45 degrees. Reference numeral 3 is a photodiode that converts the propagated light into an electric signal.

In this embodiment, 101 to 107, 1
Reference numeral 11 denotes an optical path, and the optical paths 101, 102, 103, 10
4, 105, 106, 107, 111, the optical path of the optical fiber coil portion, and the optical path of the phase modulator portion are all composed of a single mode optical fiber. It does not matter if the fiber is used.

Next, the operation of the present optical rotation detecting device will be briefly described with reference to FIG. The optical output output from the light source 1 passes through the optical path 101 and is input to the coupler 2. The light split into two by the coupler 2 passes through the optical path 102, passes through the polarizer 4 which defines the polarization state in only one direction, and the optical path 104, and then is input to the coupler 5. The light input to the coupler 5 is equally divided into two light paths 105 and 107. The input light to the optical path 105 travels clockwise in the optical fiber coil 6 and then passes through the optical path 111 to depolarize the light.
Is input to the coupler 5, is depolarized, passes through the phase modulator 7 and the optical path 107 in this order via the optical path 108, and is input to the coupler 5 in the reverse direction. Further, similarly to the first embodiment, the phase modulator 7 plays a role of adding a preset optical phase in order to enhance the detection sensitivity of the Sagnac phase generated in the optical fiber coil.

Further, the coupler 5 is branched into two,
The light input to the optical path 107 travels in the opposite direction to the above-described light wave. That is, the light that has passed through the optical path 107, the phase modulator 7, and the optical path 108 in this order propagates counterclockwise in the optical fiber coil 6, passes through the optical path 105, and is input to the coupler 5. That is, the light waves split into two in opposite directions by the coupler 5 propagate through the optical fiber coil 6 and are then coupled by the coupler 5 again. After the combined light passes through the optical path 104, it propagates in the reverse direction through the polarizer 4, the optical path 21, and the coupler 2, and is input into the photodiode 3 by the optical path 103 and converted into an electric signal.

As the insertion position of the depolarizer in this embodiment, the depolarizer is inserted only between the optical fiber coil 6 and the phase modulator 7. With this configuration, the zero-point drift of the rotation output is slightly larger than that in the first embodiment in which the left and right bidirectional light before being input to the phase modulator is depolarized by the depolarizer, but it is extremely larger than that in the conventional example. Get smaller. This configuration has advantages that the loss of light is small and the process can be simplified as compared with the configuration of the first embodiment.

The rotational output in the stationary state, that is, the zero-point drift in the above configuration is within 0.28 (degrees / second), which is slightly larger than the zero-point drift in the first embodiment, but in the conventional optical fiber gyro. It is much smaller than the zero-point drift, and there is no practical problem.

[0044]

In summary, in the optical fiber gyro using the single mode fiber in the optical path, the depolarizing means is inserted in the sensing loop to depolarize the light propagating through the sensing loop, thereby changing the polarization state. Fluctuation of the interference output due to is suppressed, and the zero point drift of the rotation output of the optical fiber gyro is reduced.

The depolarizing means may be inserted at two positions between the optical fiber coil 6 and the phase modulator 7 and between the phase modulator 7 and the coupler 5, or either one of them. By doing so, the fluctuation of the modulation degree due to the fluctuation of the polarization state is removed, and the zero point drift is further reduced.

As described above, the zero-point drift of the optical fiber gyro using the single-mode optical fiber, which is less expensive than the polarization-maintaining optical fiber, in the sensing loop is reduced, and the cost of the optical fiber gyro is reduced.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an optical rotation detection device according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram of an optical rotation detection device according to a second embodiment of the present invention.

FIG. 3 is a schematic diagram of an optical rotation detection device according to a third embodiment of the present invention.

FIG. 4 is a schematic diagram of an optical rotation detection device in a conventional example.

[Explanation of symbols]

1 light source 2 coupler 3 photodiodes 4 Polarizer 5 coupler 6 Optical fiber coil 7 Phase modulator 8 Depolarization means 9 Depolarization means 10 Depolarization means

Continued front page    (72) Inventor Yoshihiko Honjoya             4-3-1 Tsunashima-higashi, Kohoku-ku, Yokohama-shi, Kanagawa             Matsushita Communication Industry Co., Ltd.

Claims (6)

[Claims] 1. A sensing loop section having a light source, a depolarizing means, a phase modulating means, and an optical path section for producing a Sagnac effect when light emitted from the light source enters through a predetermined optical path, and the sensing loop section. An optical rotation detecting device comprising a light receiving means for receiving the emitted light via a predetermined optical path, and the depolarizing means being installed adjacent to the optical path coupled to the phase modulating means. 2. A first coupler that splits light emitted from a light source into two, a polarizer into which one of the light split by the first coupler is incident, and a light emitted from the polarizer that splits into two. A second coupler, wherein the sensing group section is composed of an optical fiber coil formed by winding a single mode optical fiber coupled to the second coupler, producing a Sagnac effect, and the light receiving means passes through the sensing loop section. The second coupler receives one of the two light beams branched by the first coupler through the polarizer, the depolarizing means between the phase modulating means and the optical fiber coil, and the phase modulating means. The optical rotation detection device according to claim 1, wherein the optical rotation detection device is arranged at least on one side between the means and the second coupler. 3. The optical rotation detector according to claim 2, wherein the depolarizing means is inserted between the second coupler and the phase modulating means and between the phase modulating means and the optical fiber coil. 4. The optical rotation detector according to claim 2, wherein the depolarizing means is inserted between the second coupler and the phase modulating means. 5. The optical rotation detecting device according to claim 2, wherein the depolarizing means is inserted between the phase modulating means and the optical fiber coil. 6. The optical rotation detector according to claim 3, wherein the depolarizing means is a fiber type depolarizer formed by fusing two polarization maintaining optical fibers.