JPH04122319U - Optical fiber gyro device - Google Patents

Abstract

(57) [Summary] [Purpose] To realize an optical fiber gyro device with a good scale factor by driving a phase modulator at a frequency with little temperature dependence. [Structure] An optical fiber gyro device including an optical fiber coil that propagates lights emitted from a light source and branched in opposite directions, and a phase modulator that modulates the phase of the light propagating within the optical fiber coil. A piezoelectric element having a drive electrode and a polarization output electrode wound around an optical fiber is used as the phase modulator, and the temperature of the vibration amplitude of the piezoelectric element is determined using the output from the polarization output electrode. The optimal frequency with the least dependence is found, and phase modulation is performed using the signal of this optimal frequency.

Description

[Detailed explanation of the idea]

0001

[Industrial application field]

The present invention relates to an optical fiber gyro device, and in particular to a phase modulation type optical fiber gyro device. In gyro equipment, the degree of modulation of the phase modulator is not affected by changes in ambient temperature. This invention relates to technology for stabilizing gyro output.

0002

[Conventional technology]

FIG. 1 shows the basic configuration of a typical optical fiber gyro device. The device shown in the figure , the laser beam emitted from a light source 1 such as a laser diode is directed in the light direction. The light enters the polarizer 2, is split into two, and one is guided to the polarizer 3. light directional The combiner 2 is made by fusion-bonding the core parts of two opposing optical fibers, and has a polarizer. 3 is composed of a single polarization fiber that passes only light with a specific polarization plane. . Only components of a specific polarization plane are transmitted through the polarizer 3 and transmitted to the second optical directional coupler 4. incident. The light incident on the second optical directional coupler 4 is divided into two parts, and a polarization maintaining fiber is used. It is guided to both ends of an optical fiber coil, that is, a sensing coil 5 consisting of a They propagate in the sensing coil 5 clockwise and counterclockwise, respectively.

0003 Such bidirectional light is transmitted by a phase modulator 6 provided at one end of the sensing coil 5. However, the clockwise light is phase modulated after propagating through the sensing coil 5. The light is then phase modulated and then re-injected into the second optical directional coupler 4. On the other hand, the counterclockwise light is Immediately after entering the sensing coil 5, it is phase modulated, and after propagating within the coil, the second light The light enters the directional coupler 4 again and enters the polarizer 3 together with the clockwise light. and , only components of a specific polarization plane are transmitted through the polarizer 3, and the first optical directional coupler 2 incident on . The light incident on the first optical directional coupler 2 is further split into two, and photoelectrically converted. The light enters the vessel 7. In the photoelectric converter 7, the light waves of the two directions are combined and interfered. A gyro signal is obtained by using the resulting optical signal as a photoelectric conversion output voltage signal I.

[0004] When the sensing coil 5 rotates at an angular velocity Ω, a phase difference occurs between the clockwise light and the counterclockwise light. The photoelectric conversion output I is: I=C/2{1+ _∞ [J ₀ (φ) + Σ2 (-1) ⁿ J _2n (φ) cos2nω _m t] coskΩ ⁿ⁼¹ _∞ − [Σ2 (-1) ⁿ J _2n+1 (φ) sin (2n+1) ω _m t] sink Ω} ⁿ⁼⁰ (1). In this equation, C is a constant, J _n (φ) is a Bessel function of the first kind, φ is the degree of modulation, k is a proportionality constant, and ω _m is the driving angular frequency of the phase modulator. Further, the modulation degree φ is φ=2a sinπf _m τ(rad) (2), where a is the amount of phase modulation (rad), and τ is the time for the light wave to propagate through the sensing coil 5 (τ=nl/ c and n are the refractive index, l is the coil length, and c is the speed of light).

[0005] From such a photoelectric conversion output I, a component of the modulation frequency f _m of the oscillator 9, ie, a fundamental wave component, is extracted by the synchronous detector 8 of FIG. If the signal of the fundamental wave component in the above formula (1) is I1, then I1=(C/2)J ₁ (φ) sinkΩ (3). As is clear from this equation, the fundamental wave component I1 becomes a signal proportional to sinkΩ with respect to the rotational angular velocity Ω. Therefore, in equation (3), if components other than sink Ω can be made constant, it becomes possible to obtain the rotational angular velocity Ω from equation (3).

[0006]

[Problem that the idea aims to solve]

However, in the conventional optical fiber gyro device, a circular phase modulator 6 is used. A cylindrical piezoelectric element with an optical fiber cable wound around it is used. The frequency of the signal that drives the piezoelectric element, that is, the modulation frequency, is set to vibration frequency was used. In other words, conventionally, the resonant frequency of the cylindrical piezoelectric element It was doing phase modulation. However, piezoelectric elements can be used in fiber optic gyro devices. Because the resonant frequency exhibits temperature dependence in the normally required operating temperature range. , the vibration amplitude fluctuates due to temperature changes. Therefore, phase modulation due to temperature changes fiber optic gyro because the degree changes and the scale factor of the gyro output varies. However, there was a problem that the accuracy of the device decreased.

[0007] The purpose of this invention is to solve the problems with the conventional equipment and to solve the problem of temperature fluctuation. This reduces fluctuations in the vibration amplitude of the phase modulator, thereby stabilizing the gyro output and achieving high precision. The objective is to make it possible to realize a highly advanced optical fiber gyro device.

[0008]

[Means to solve the problem]

In order to achieve the above object, according to the present invention, a phase modulation type optical fiber In this device, in addition to the drive electrode, a polarization output electrode is provided as a phase modulator. An electrical element with an optical fiber wound around it is used, and the output from the polarization output electrode is The optimum frequency with the least temperature dependence of the vibration amplitude of the piezoelectric element is determined using The method is characterized in that phase modulation is performed by applying a signal with an optimal frequency to the driving electrode. do.

[0009]

[Effect]

In the above configuration, the drive frequency vs. polarization output characteristics at each temperature of the phase modulator The piezoelectric element is driven at the drive frequency with the least temperature dependence. This results in , can the vibration amplitude and therefore the modulation depth of the piezoelectric element be kept constant over a wide range of temperatures? As a result, the scale factor of the gyro output is stabilized and high precision optical fiber gyro equipment is achieved. position is obtained.

0010

【Example】

Embodiments of the present invention will be described below with reference to the drawings. Figure 2 shows one example of this invention. 1 shows an external appearance of a phase modulator used in an optical fiber gyro device according to an example. same The phase modulator shown in the figure is used as the phase modulator 6 in FIG. The same polarization preserving single module as that used for the sensing coil is placed on the outer peripheral surface of the electronic element 200. The coded optical fiber 201 is wound with appropriate tension and fixed with adhesive etc. It is. When the piezoelectric element 200 is vibrated in the radial direction, the optical fiber 201 is vibrated. It expands and contracts with movement. Therefore, depending on the drive frequency of the piezoelectric element 200, the optical fiber The optical path length of the fiber 201 changes, and the phase of the light inside the wound optical fiber 201 changes. will be adjusted.

[0011] Electrodes are provided on the inner and outer circumferential surfaces of the piezoelectric element 200, and the electrodes on the outer circumferential surface are It is divided into a dynamic electrode and a polarization output electrode. Then, the voltage of the oscillator 202 becomes The voltage is applied between the electrode on the inner circumferential surface and the driving electrode on the outer circumferential surface by the drive side lead wire 203. be done. When voltage is applied to the drive electrode, distortion occurs in the piezoelectric element, and as described above, oscillates in the radial direction at the driving frequency. This distortion creates a piezoelectric effect between the polarization output electrodes. A voltage is induced by This induced voltage is caused by the polarization output lead wire 204. taken out.

0012 FIG. 3 shows details of each electrode provided on the piezoelectric element 200. That is, cylindrical On the outer peripheral surface of the piezoelectric element 200, in addition to the drive electrode 301, there is a A polarization output electrode 302 is provided. The polarization output electrode 302 is the piezoelectric element 20 A part of the outer circumferential surface of the drive electrode 301 is formed as a small area insulated from the drive electrode 301. ing. Each electrode 301 and 302 has a folded electrode 304 and a lead wire connection. and 305 are respectively provided, and leads are provided near the upper edge of the outer peripheral surface of the piezoelectric element 200. connected to the line. With this structure, it is easy to connect an optical fiber to the piezoelectric element 200. It becomes possible to wind it. In addition, each folded electrode 304, 305 is the inner peripheral surface electrode 3. It is electrically insulated from 03.

[0013] The inner peripheral surface electrode 303 serves as an electrode facing the drive electrode 301 and also for polarization output. It is commonly used as an electrode opposite to electrode 302. Therefore, the driving electrode 301 A drive signal for phase modulation is applied between the inner peripheral surface electrode 303 and the polarization output electrode 303. 302 and the inner peripheral surface electrode 303 for monitoring the vibration of the piezoelectric element. power voltage is taken out.

[0014] Next, determine the driving frequency to be applied to the phase modulator having the above structure. The method will be explained. First, we will discuss the driving frequency and polarization output of the phase modulator with the above structure. Find the relationship between the power and voltage for each ambient temperature.

FIG. 4 shows the relationship between the polarization output voltage of the phase modulator and the drive frequency determined in this manner over a temperature range of -10 degrees Celsius to +50 degrees Celsius. Furthermore, FIG. 5 shows the rate of variation of the polarization output voltage at each frequency based on temperature changes. Note that these data relate to a cylindrical piezoelectric element made of lead zirconate titanate (PbZrTiO ₃ ) with an outer diameter of 38 mm, an inner diameter of 34 mm, and a height of 7 mm.

[0016] Referring to Figure 4, the resonant frequency of the piezoelectric element, that is, the frequency of the peak output voltage has a temperature coefficient of 115 ppm/℃ with respect to temperature change, and the temperature decreases. It can be seen that the resonance frequency increases and the vibration amplitude decreases.

Next, the amplitude fluctuation range with respect to the drive frequency shown in FIG. 5 varies by a maximum of ±19% in the temperature range near 25.0kHz, but at a drive frequency of 25.564kHz it varies by ±0.87%. The fluctuation range has been reduced. Therefore, in the optical fiber gyro device according to the present invention, the frequency with substantially the smallest variation width is applied to the phase modulator as the optimum frequency f _p . In other words, by performing phase modulation at such an optimal frequency _fp , even if the resonant frequency changes due to temperature changes, the vibration amplitude of the piezoelectric element, that is, the modulation degree, changes very little, resulting in an optical fiber gyro with a stable scale factor. A device is obtained. In addition, in all the samples tested, the optimum frequency f _p was a frequency slightly higher than the resonance frequency. Therefore, for example, it is possible to find the resonance frequency at a predetermined frequency and determine the optimum frequency f _p to be a frequency higher than the resonance frequency by a predetermined frequency.

[0018]

[Effect of the idea]

As described above, according to the present invention, a phase modulator used in an optical fiber gyro device Select a frequency where the vibration amplitude of the piezoelectric element constituting the piezoelectric element changes little with temperature, and Since the phase modulator is driven by A gyro output with a scale factor of This makes it possible to realize an advanced device.

[Brief explanation of drawings]

FIG. 1 is a schematic block diagram showing the configuration of a general optical fiber gyro device.

FIG. 2 is an explanatory perspective view showing the appearance of a phase modulator used in an optical fiber gyro device according to an embodiment of the present invention.

FIG. 3 is a schematic perspective view showing the shape of each electrode formed on the piezoelectric element used in the phase modulator of FIG. 2;

FIG. 4 is a graph showing the relationship between the drive frequency and polarization output voltage of a piezoelectric element used in a phase modulator at each temperature.

FIG. 5 is a graph showing the temperature fluctuation rate of polarization output with respect to the driving frequency of the phase modulator having the characteristics shown in FIG. 4;

[Explanation of symbols]

1 light source 2,4 Optical directional coupler 3 Polarizer 5 Sensing coil 6 Phase modulator 7 Photoelectric converter 8 Synchronous detector 9 Oscillator 200 piezoelectric element 201 Optical fiber 202 Oscillator 203 Drive side lead wire 204 Polarization side lead wire 301 Drive electrode 302 Polarization output electrode 303 Inner peripheral surface electrode 304,305 Folded electrode

Claims (1)

[Scope of utility model registration request] 1. An optical fiber gyro comprising: an optical fiber coil that propagates lights emitted and branched from a light source in opposite directions; and a phase modulator that modulates the phase of the light propagating within the optical fiber coil. In the device, the phase modulator is configured by winding an optical fiber around a piezoelectric element provided with a drive electrode and a polarization output electrode, and uses the output from the polarization output electrode to control the vibration amplitude of the piezoelectric element. An optical fiber gyro device characterized in that an optimum frequency with the least temperature dependence is determined, and a signal of this optimum frequency is applied to the driving electrode to perform phase modulation.