JPH07218271A - Optical fiber gyro - Google Patents

Abstract

PURPOSE:To compensate lowering of S/N due to loss and contrive decrease of a zero point drift of a detection angular velocity in simple constitution by connecting a light source for excitation between an optical fiber sensing group and a light source and casting excitation light for a profit fiber. CONSTITUTION:Light of a light source 1 leads a coupler 4 through another coupler 2 and a polarizer 3, the light branched at the coupler 4 is returned to the coupler 4 in a clockwise or counterclockwise direction of an optical fiber sensing group, and, when rotation angular velocity is produced in a loop 5, both the lights receive the influence of the rotation angular velocity. There, excitation light of a light source for excitation 7 is cast into the loop 5 through the coupler 4, and when the loop 5 is excited from both its ends, the light of the clockwise or counterclockwise direction is amplified and is received with a light receiving device 9 as interference light via the coupler 4, the polarizer 3, the coupler 2 and a narrow band-pass filter 8. Thereby, since the full intensity light is received with the light receiving device 9, lowering of S/N is compensated and a zero point drift of detection angular velocity is decreased.

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 which detects an angular velocity from the interference intensity of both lights by propagating left and right light in a sensing loop formed by looping an optical fiber, and particularly S / due to loss
The present invention relates to an optical fiber gyro that compensates for a decrease in N ratio and reduces zero-point drift of a detected angular velocity.

[0002]

2. Description of the Related Art FIG. 4 shows the structure of a conventional optical fiber gyro. This optical fiber gyro is of a phase modulation type and is composed of a light source 1, a first coupler 2, a polarizer 3, a second coupler 4, a sensing loop 5, a phase modulator 6, and an optical component of a light receiver 9. It is an open-loop type optical fiber gyro. In this configuration, the light from the light source 1 is passed through the first coupler 2 and the polarizer 3 to form good linearly polarized light. The light is incident on the sensing loop 5 as counterclockwise light and clockwise light using the second coupler 4. After propagating through the sensing loop 5, both lights are combined by the second coupler 2 and interfere with each other. The combined light (interference light)
Passes through the polarizer 3 and the first coupler 2 and is detected by the light receiver 9. At this time, when the sensing loop 5 is rotating, the intensity of interference corresponding to the rotational angular velocity is obtained, and therefore the rotational angular velocity can be detected by calculating from the intensity of light detected by the light receiver 9.

[0003]

In order to construct the optical fiber gyro shown in FIG. 4, it is necessary to connect each optical component. As shown, at least four connections are formed. At the connection, the light suffers a connection loss. Figure 4
In the above configuration, a light loss of 9 dB is theoretically generated, but the connection loss is also added to this, and the normal total loss is 1
It becomes about 3 dB. When the total loss is large as described above, the light reaching the light receiver 9 becomes weak. Therefore S /
There is a problem that the zero ratio drift of the detected angular velocity increases as the N ratio decreases.

In order to improve the S / N ratio, it is sufficient that the light reaching the photodetector 9 is strong, so that it is conceivable to increase the light output of the light source 1, for example. However, when the light output of the light source 1 is increased, the life of the light source 1 is shortened and heat generation is increased. Further, in order to solve these problems, a ring resonance type and a closed loop type, which are improved methods, have been proposed.
The configuration is very complicated compared to. A very complicated configuration causes a cost increase and a decrease in reliability, which is a problem.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above problems and provide an optical fiber gyro which has a simple structure, compensates for a decrease in S / N ratio due to loss, and reduces zero-point drift of a detected angular velocity. It is in.

[0006]

To achieve the above object, the present invention provides a light source, a light receiver, a first coupler having the light source and the light receiver as a branch, and the branch of the first coupler. A polarizer connected to the opposite side, and a second coupler connected to the polarizer and having a branch on the opposite side of the polarizer,
An optical fiber sensing loop made of a gain optical fiber and closing a branch of the second coupler, and a pumping light source connected between the optical fiber sensing loop and the light source for injecting pumping light for the gain optical fiber are provided. It is a thing.

Another configuration is a light source, a light receiver arranged behind it, and a polarizer connected in front of the light source.
A coupler that is connected to this polarizer and has a branch on the opposite side of the polarizer, an optical fiber sensing loop that is composed of a gain optical fiber and closes the branches of the coupler, and is connected between this optical fiber sensing loop and the light source. And a pumping light source for injecting pumping light for the gain optical fiber.

The light from the light source is in the 1.55 μm band, and the gain optical fiber is an erbium-doped optical fiber,
In addition, the light of the excitation light source may be in the 1.48 μm band.

[0009]

With the above structure, the light from the light source is emitted from the first coupler,
After reaching the optical fiber sensing loop via the polarizer and the second coupler, and rotating counterclockwise and clockwise, the second coupler,
The light is received by the light receiver as interference light via the polarizer and the first coupler. At this time, the pumping light is injected into the optical fiber sensing loop including the gain optical fiber, so that the left-handed and right-handed lights are amplified with the same gain. Since the amplified light is received by the light receiver, the decrease in the S / N ratio is compensated and the zero point drift of the detected angular velocity is reduced. Further, in this configuration, the optical fiber sensing loop is replaced with a gain optical fiber and a pumping light source is added to the conventional configuration, so that the configuration is simple.

In the configuration in which the light receiver is arranged behind the light source, the light from the light source reaches the optical fiber sensing loop via the polarizer and the coupler, and is amplified in the counterclockwise direction while being amplified as described above. After turning clockwise, the light is received by the light receiver as interference light via the coupler and the polarizer. Since the amplified light is received by the light receiver, the decrease in S / N ratio is compensated,
Zero-point drift of the detected angular velocity is reduced. In this case, light is directly incident on the light receiver from the light source, which can be electrically cut as a direct current component. Furthermore, in this configuration,
The first coupler is not required and the structure is simple.

An erbium-doped optical fiber obtained by adding erbium to an optical fiber material is used as the gain optical fiber. In this case, when pumping light in the 1.48 μm band is injected into the gain optical fiber, erbium produces light in the 1.55 μm band, so that amplification in the 1.55 μm band is possible. Therefore, it is possible to use light in the 1.55 μm band as the light source light and utilize the amplification in the optical fiber sensing loop to allow the light receiver to receive light of sufficient intensity.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

As shown in FIG. 1, the optical fiber gyroscope includes a light source 1, a first coupler 2, a polarizer 3, a second coupler 4, an optical fiber sensing loop (hereinafter referred to as a sensing loop) 5, and a phase modulation. It is composed of optical components such as a device 6, an excitation light source 7, a narrow band filter 8 and a light receiver 9.

As the light source 1, a light emitting diode or a laser diode can be used. In this embodiment, the light source 1
Is a laser diode which supplies a light source light having a wavelength of 1.55 μm, and its optical output is about 1 mW. This light source 1
One of the optical fibers (2a) forming the branch of the first coupler 2 is coupled to. Both the first coupler 2 and a second coupler 4 described later are fusion-spreading type couplers using optical fibers, and branches formed of two optical fibers are formed on both sides. The first coupler 2 has a wavelength of 1.
It operates at 3 dB at 55 μm and has a wavelength of 1.48 μ.
There are no restrictions on the characteristics at m. The first coupler 2 includes one of the optical fibers (4
The polarizer 3 is connected to c). The polarizer 3 is an optical fiber type polarizer using an elliptical jacket type polarization-maintaining optical fiber and operates at a wavelength of 1.55 μm. One of the optical fibers (4a) constituting the branch of the second coupler 4 is provided on the polarizer 3 on the side opposite to the first coupler 2.
Are connected. The second coupler 4 is a wavelength-independent type that can operate at 3 dB for both wavelengths of at least 1.55 μm and 1.48 μm. As described above, as the second coupler 4, a coupler having good propagation characteristics for the light source light having the wavelength of 1.55 μm and the pumping light having the wavelength of 1.48 μm is used. Both ends of the sensing loop 5 are connected to the two optical fibers (4c, 4d) forming the branch on the opposite side of the second coupler 4 so as to close the branches. A core expansion technique is used to connect the second coupler 4 and the sensing loop 5. The splice loss is about 0.1 dB.

The sensing loop 5 is formed by looping an optical fiber 10 having a loop radius of 50 mm and a total length of 150 m. This optical fiber 10 is an elliptic core type polarization-maintaining optical fiber, the relative refractive index difference between the core and the cladding is about 1.3%, the loss is 0.35 dB / Km at a wavelength of 1.55 μm, and the extinction ratio is 1 Km. -30dB per hit
Is. Further, erbium is added to the optical fiber 10. The amount of erbium added is about 60 ppm, which is a lower concentration than usual. This erbium-doped optical fiber can act as a gain optical fiber.

The phase modulator 6 phase-modulates the light propagating through the optical fiber and is inserted in the optical fiber 10 forming the sensing loop 5.

The pumping light source 7 is coupled to the optical fiber (4b) at the other end of the second coupler 4. The pumping light source 7 is a laser diode that supplies pumping light having a wavelength of 1.48 μm, and its fiber output is about 33 mW. By injecting pumping light having a wavelength of 1.48 μm from the pumping light source 7 to excite the sensing loop 5 to act as a gain optical fiber, a sensing loop amplifier can be formed. This sensing loop amplifier is of a bidirectional amplification system having the same amplification characteristic in both directions, and the amplification characteristic has a small signal gain of about 28 dB,
The saturated light output is 13 dBm and the noise figure (NF) is 7 dB. The scale factor of the sensing loop 5 as a gyro is about 0.2.

The narrow band filter 8 is coupled to the optical fiber (2b) at the other end of the first coupler 2. A light receiver 9 is provided on the opposite side of the narrow band filter 8, and the narrow band filter 8 is inserted immediately before the light receiver 9. The narrow band filter 8 is for removing amplified spontaneous emission noise from the light returning via the sensing loop 5.

The connection portion (marked with X) for connecting each optical component is
It is formed at four places as shown.

Next, the operation of the embodiment will be described.

Light having a wavelength of 1.55 μm emitted from the light source 1 reaches the sensing loop 5 via the first coupler 2, the polarizer 3 and the second coupler 4. The light branched by the second coupler 4 rotates counterclockwise and clockwise in the sensing loop 5 and returns to the second coupler 4. When the rotational angular velocity is generated in the sensing loop 5, both lights are affected by the rotational angular velocity. On the other hand, the wavelength of 1.48 emitted from the excitation light source 7
The μm light is injected into the sensing loop 5 via the second coupler 4 and excites the sensing loop 5 from both ends. Since the sensing loop 5 is excited to generate light having a wavelength of 1.55 μm, the left-handed light and the right-handed light are amplified and the light intensity is increased. Since the bidirectional light has the same amplification characteristic, the counterclockwise light and the clockwise light are similarly amplified. In this way, the two lights that are affected by the rotational angular velocity and amplified are passed through the second coupler 4, the polarizer 3, the first coupler 2, and the narrow band filter 8 as a light receiver 9 as interference light. Is received by.

In the above-mentioned operation, when the light source light propagates through the respective optical components, the above-mentioned optical components cause a loss, and at the respective connection portions (marked by X), a connection loss occurs. At the same time, it is amplified in the sensing loop 5 by the gain optical fiber. As a result, the light receiver 9 receives light of sufficient intensity. By this, S
The decrease in the / N ratio is compensated, and the zero drift of the detected angular velocity is reduced.

FIG. 3 shows an example of detecting the rotational angular velocity by the optical fiber gyro of the present invention and a conventional example of detection. In each graph, the horizontal axis represents time, and the vertical axis represents gyro output = rotational angular velocity. The conventional example of FIG. 3B is detected when the rotational angular velocity in the positive direction is intermittently generated, but the zero point gradually drifts largely to the negative side, and then turns to the positive side. There is. Therefore, the detected value that can be read from the scale does not accurately represent the actual rotational angular velocity, and some detected value occurs even when the rotational angular velocity is not given. In contrast, the example of the present invention is
It is detected when the rotational angular velocity occurs once in the negative direction and once in the positive direction, but since there is no zero drift, the detected value that can be read from the scale accurately represents the actual rotational angular velocity. When is not given, the detected value correctly shows zero.

As described above, the optical fiber gyro of the present invention is an ultrahigh-precision optical fiber gyro in which the zero-point drift is greatly reduced, and its configuration is realized by a simple configuration by the open loop phase modulation method. Has been done.

Next, another embodiment will be described.

The optical fiber gyro shown in FIG. 2 comprises optical components of a light source 1, a polarizer 3, a coupler 21, a sensing loop 5, a phase modulator 6, a pumping light source 7, and a light receiver 22. In comparison with FIG. 1, if the coupler 21 corresponds to the second coupler 4, the first coupler 2 and the narrow band filter 8 do not exist, and the side of the polarizer 3 is in front of the light source 1. , The light receiver 22 is behind, that is, the polarizer 3
Is located on the opposite side of. In this example, the light receiver 22 is integrated with the light source 1, which normally includes a monitor PD (photodiode) 24 mounted in association with the laser diode 23 of the light source for detecting the rotational angular velocity. It is also used for the light receiver 22. The component of the light that directly enters the light receiver 22 from the light source 1 can be removed as a direct current component in an electric circuit (not shown) placed in the subsequent stage of the light receiver 22.

In this configuration, as in the configuration of FIG. 1, the loss of each optical component and the connecting portion (marked with X) is canceled by the amplification of the sensing loop 5. This compensates for the decrease in the S / N ratio and reduces the zero-point drift of the detected angular velocity. Further, in this configuration, since the first coupler 2 is not required, the loss is small and the configuration is simple.

[0028]

The present invention exhibits the following excellent effects.

(1) It is possible to obtain an ultrahigh-precision optical fiber gyro in which the zero point drift is greatly reduced.

(2) Since it can be realized with a simple structure, it does not cause an increase in cost and a decrease in reliability.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical fiber gyro showing an embodiment of the present invention.

FIG. 2 is a configuration diagram of an optical fiber gyro showing another embodiment of the present invention.

FIG. 3A is a time change graph of the detection output of the rotational angular velocity of the present invention and FIG.

FIG. 4 is a configuration diagram of an optical fiber gyro showing a conventional example.

[Explanation of symbols]

 1 Light Source 2 First Coupler 3 Polarizer 4 Second Coupler 5 Optical Fiber Sensing Loop (Sensing Loop) 7 Excitation Light Source 9 Light Receiver

Claims (3)

[Claims] 1. An optical fiber gyro that propagates left and right light in an optical fiber sensing loop and detects an angular velocity from the interference intensity of the two lights, a light source, a light receiver, and a branch of the light source and the light receiver. A coupler, a polarizer connected to the opposite side of the branch of the first coupler, a second coupler connected to the polarizer and having a branch on the opposite side of the polarizer, and a gain optical fiber And a pumping light source connected between the optical fiber sensing loop and the light source to inject pumping light for the gain optical fiber. And a fiber optic gyro. 2. An optical fiber gyro that propagates left and right light in an optical fiber sensing loop and detects an angular velocity from the interference intensity of both lights, a light source, a light receiver arranged behind the light source, and a light source in front of the light source. A polarizer to be connected, a coupler connected to the polarizer and having a branch on the opposite side of the polarizer, an optical fiber sensing loop formed of a gain optical fiber and closing the branches of the coupler, and the optical fiber sensing loop. And a pumping light source for injecting pumping light for a gain optical fiber, the fiber optic gyro. 3. The light from the light source is in the 1.55 μm band, the gain optical fiber is an erbium-doped optical fiber, and the pumping light is in the 1.48 μm band. 2. The optical fiber gyro described in 2.