JPH09133534A - Optical fiber gyro - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a drop in operation speed during signal processing even when a modulated high frequency ωm is set high. SOLUTION: An oprical system including a light source 101, photocouplers 102 and 104, a polarizer 103, a sensing group 105, a phase modulator 106, and a light receiver 108 is the same as conventional one. Two modulation signals of ωm and ω1 (=ωm +Δω) in frequency are sent from a programmable timer 114 to a phase modulator driving circuit 107, and they are added to each other therein so as to drive a phase modulator 106. An interference signal emitted from the light receiver is synchronized and detected by means of a signal of beat frequency including Δω and Δω that are further lower than modulated signals ωm and ω1 , in lock amplifiers 111-a to 111-c, and as a result an angular velocity is measured through operation processing, Thus, the detection time can be reduced to a half the time of conventional one.

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, and more particularly to a phase modulation type optical fiber gyro.

[0002]

2. Description of the Related Art FIG. 6 shows the structure of a conventional phase modulation type optical fiber gyro.
Optical coupler 102, polarizer 103, second optical coupler 10
4. A light receiving device 108 including a sensing loop 105 for detecting a gyro output, a preamplifier 109, and a signal processing unit 1
Equipped with 10. A phase modulator 106 is installed at one end of the sensing loop 105. The conventional phase modulation method with the above configuration is characterized in that the modulation frequency of the phase modulator 106 and the fundamental frequency of the signal detected by the lock-in amplifier 111 of the signal processing unit 110 are both the same ω _m . As another feature, the phase modulator 1
The point that the piezoelectric element is used for 06 can be raised. The output signal (gyro signal) P (t) of the phase modulation type optical fiber gyro is expressed by the following equation (1). P (t) = K {1 + vcos (φ _s + φ _e sin ω _m t)} (1) where K is the light source intensity parameter, and v is the interferometer efficiency (0 ≦
v ≦ 1), φ _s is a Sagnac phase difference proportional to the input rotation angular velocity, φ _e is a phase modulation index, and ω _m is a phase modulation angular frequency. In an actual device, phase modulation is performed by utilizing the difference in propagation time of light that rotates in the sensing loop 105 left and right. Therefore, in the phase modulation optical fiber gyro, in order to reduce the fiber length for the purpose of cost reduction and size reduction, it is necessary to set the modulation frequency ω _m itself higher than the practical modulation voltage. There is.

[0003]

However, since the modulation frequency and the frequency of the detection signal are the same in the above-mentioned prior art,
When the modulation frequency ω _m is set high, there is a problem that the detection and calculation speeds in the signal processing become strict, which makes it difficult to realize. Moreover, since a piezoelectric element is used for the phase modulator, there is a problem in structure and characteristics that the modulation frequency cannot be increased so much. Therefore, it is necessary to increase the modulation frequency ω _m and decrease the detection calculation speed.

[0004]

In order to solve the above problems, the present invention comprises means for generating interference light having an optical phase difference corresponding to a physical quantity, and electrically adjusting the optical phase difference of the interference light. An optical fiber gyro for measuring the physical quantity by detecting an optical phase difference of the interference light, which is an electric signal obtained by photoelectrically converting the interference light. In an optical fiber gyro for sampling and calculating the physical quantity by calculation, first and second modulation signals are supplied to the optical phase modulator, and the modulation angular frequencies ω _m and ω _{1 of} these two signals are ω ₁ = n
An optical fiber gyro characterized by satisfying ω _m + Δω (n is a positive / negative integer; Δω <ω ₁ , ω _m ), and in particular, the absolute value of the coefficient n is set to an even number, in particular n =
It is an optical fiber gyro designed to be 2,
The optical phase modulator is an optical fiber gyro that uses a waveguide material having an electro-optical effect, and the phase modulation signal is an optical fiber gyro that is generated based on a clock signal of a signal processing unit that performs the calculation. A fiber gyro, further an optical fiber gyro configured to calculate the physical quantity based on a beat frequency component given by a mathematical expression including Δω or Δω and their harmonic components,
An optical fiber gyro is used for detecting the beat frequency component, which is synchronized with the beat frequency and uses a synchronous down-sampling method in which a sampling period is extended to one period or more of an input basic signal.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION In the optical fiber gyroscope of the present invention, ω ₁ = nω _m + Δω (n is a positive or negative integer; Δω <ω
_1, the two modulation angular frequencies omega ₁ satisfying the relation of omega _m), omega
By using _m at the same time, it becomes possible to measure the required physical quantity, especially the angular velocity, simply by detecting the beat frequencies and their harmonic components, which are given by the formulas that include Δω or Δω that is much lower than ω ₁ and ω _m. ing. Further, in particular, the absolute value of n is selected to be an even number, especially 2 so that the physical quantity due to the Δω component can be detected with optimum sensitivity. In addition, the modulation signal is generated based on the clock signal of the signal processing unit, and the beat frequency component and its harmonic component are detected by the synchronous downsampling method. Making it easy. Furthermore, by using a waveguide material that has an electro-optical effect for the optical phase modulator, especially lithium niobate, the modulation frequency required for shortening the loop length while maintaining the stability of modulation over conventional piezoelectric elements can be increased. Makes it easy.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the drawings. FIG. 1 is a configuration diagram of a phase modulation type optical fiber gyro which is a first embodiment of the present invention. The light beam from the light source 101 includes a first optical coupler 102 and a polarizer 103.
To reach the second optical coupler 104, where they are branched into two light beams that propagate left and right in the sensing loop 105. The optical phases of these light beams are modulated by the piezo cylinder phase modulator 106 according to the modulation signal generated by the phase modulator driving circuit 107. This modulation method is the core of the present invention. In the phase modulation type optical fiber gyro of the present invention, the phase modulator is driven by adding a modulation signal characterized by two angular frequencies of ω ₁ and ω _m . At this time,
The gyro signal P '(t) can be expressed by the following equation (2). P ′ (t) = K {1 + vcos (φ _s + φ _e sin ω _mt + φ ₁ sin ω ₁ t)} (2) where φ ₁ is the second phase modulation index. In the present invention,
Further conditions are added so that ω ₁ and ω _m satisfy the following equation (3).
To determine. ω ₁ = n · ω _m + Δω (3) (n is a positive or negative integer; 0 <Δω <ω _m , ω ₁ ) At this time, the gyro signal component is detected from the beat frequency component given by the formula including Δω or Δω By doing so, the Sagnac phase difference φ _s is obtained. This makes ω
_The rotational angular velocity can be calculated from a low beat frequency while maintaining ₁ and ω _m at high frequencies. This will be described specifically. Output by the programmable timer 114,
Two phase modulation signals of which frequency is ω _m and ω ₁ given by Expression (3) are added together in the phase modulator driving circuit 107 to drive the phase modulator 106. Although the modulation signal is assumed to be a sine wave, for example, when the original phase modulation signal is a rectangular wave, it is possible to add them after approximating them by a suitable filtering process. Here, as an example, considering the case where n = 1 in the equation (3), Δω, ω _m −Δω, 2ω _m − is obtained from the equation (2).
Each frequency component of Δω (beat frequency component), S _a , S
_b and S _c are Δω; S _a = 2KvJ ₁ (φ ₁ ) J ₁ (φ _e ) cos φ _s (4) ω _m −Δω; S _b = 2KvJ ₁ (φ ₁ ) J ₂ (φ _e ) sinφ _s (5) Here, J is a Bessel function. 2ω _m −Δω; S _c = 2KvJ ₁ (φ ₁ ) J ₃ (φ _e ) cos φ _s (6). The light whose phase has been modulated by the modulator 106 reaches the optical coupler 104 and is recombined into interference light. The interference light travels in the opposite direction from the optical coupler 104, passes through the polarizer 103, and returns to the first optical coupler 102. The interference light is branched at the first optical coupler 102,
A photoelectric conversion circuit 10 using a photodiode
8 is detected as an interference signal. The detected signal is amplified to an appropriate level by the preamplifier 109, and the signal processing unit 110 extracts a necessary frequency component from this interference signal and calculates the rotational angular velocity. In this first example, lock-in amplifiers 111-a, 111-b, 111-c
Is used for synchronous detection. The lock-in amplifiers 111-a, 111-b, and 111-c are supplied from the programmable timer 114 with the same synchronizing signals as the frequencies of the expressions (4), (5), and (6), and the above-mentioned frequency components are supplied. To detect.
In the A / D converter 112, the detected signals S _a , S _b , and S _c are converted into a digital amount in a constant cycle by a trigger signal of the frequency f _s supplied from the programmable timer 114. The sampled data is the calculation unit 113.
The angular velocity is calculated. The point to be noted here is that even-order and odd-order harmonic components of the modulation frequency are S _2p and S, respectively, in order to calculate the angular velocity by the conventional phase modulation method.
_{As 2p + 1} , S _2p = 2KvJ _2p (φ _e ) cos φ _s (p = 1, 2, ...) (7) S _{2p + 1} = 2KvJ _{2p + 1} (φ _e ) sinφ _s (p = 0, 1, 2, ...) (8). Thereby, for example, X = S ₁ / S ₂ = {J ₁ (φ _e ) / J ₂ (φ _e )} tan φ _s (9) Y = S ₄ / S ₂ = {J ₄ (φ _e ) / J ₂ Using the relationship of (φ _e )} (10), the angular velocity was calculated in consideration of the fluctuation compensation of the modulation index φ _e . In this example, it is necessary to detect up to the fourth harmonic component. Of course, when attention is paid to higher frequency components, it is necessary to detect higher frequency components.
On the other hand, in the first embodiment, as is clear from the equations (4) to (6), it is sufficient to detect the second harmonic component even with the highest frequency component. Then, x = S _b / S _a = {J ₂ (φ _e ) / J ₁ (φ _e )} tanφ _s (11) y = S _c / S _a = {J ₃ (φ _e ) / J ₁ (φ _e )} (12), the angular velocity can be calculated in consideration of the variation compensation of the modulation index φ _e as in the equations (9) and (10). As a result, the detection speed can be halved as compared with the conventional one, and the processing speed requirement of the calculation unit 113 can be relaxed.

Next, a second embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. FIG. 2 has exactly the same hardware configuration as that of the first embodiment shown in FIG.
= 2. The two phase modulation signals output by the programmable timer 114 and having a frequency of ω _m and ω ₁ given by equation (3) (where n = 2) are added together in the phase modulator drive circuit 107,
The phase modulator 106 is driven. The phase modulator 106 modulates the optical phase according to the modulation signal generated by the phase modulator driving circuit 107. Here, in the equation (3), n =
In the case of 2, the beat frequencies Δω, 2Δω, 4 are calculated from the equation (2).
Focusing on the component of Δω, each frequency component is Δω; S _a ′ = 2KvJ ₂ (φ _e ) J ₁ (φ ₁ ) sinφ _s (13) 2Δω; S _b ′ = 2KvJ ₄ (φ _e ). J ₂ (φ ₁ ) cosφ _s (14) 4Δω; S _c ′ = 2KvJ ₈ (φ _e ) J ₄ (φ ₁ ) cosφ _s (15) Regarding the φ _s dependence, comparing these with the conventional phase modulation method (modulation frequency ω _m ), from equations (7) and (8), Δω, 2Δω, and 4Δω components are ω _m , 2ω as they are.
It can be seen that it corresponds to the _m , 4ω _m components. This signal is taken into the signal processing unit 110 in the same manner as in the first embodiment. In this embodiment, the lock-in amplifiers 111-a, 11
The 1-b and 111-c are supplied from the programmable timer 114 with the same synchronizing signals as the frequencies of the expressions (13), (14) and (15), and the above-mentioned frequency components are detected. The detected signals S _a ′, S _b ′, and S _c ′ are converted into digital quantities in a constant cycle by the A / D converter 112 by the trigger signal of frequency f _s supplied from the programmable timer 114. The sampled data is taken into the calculation unit 113 and the angular velocity is calculated. Here, x ′ = _Sa ′ / _Sb ′ = [{J ₂ (φ _e ) J ₁ (φ ₁ )} / {J ₄ (φ _e ) / J ₂ (φ ₁ )}] tanφ _s (16 ) Y ′ = S _c ′ / S _b ′ = {J ₈ (φ _e ) J ₄ (φ ₁ )} / {J ₄ (φ _e ) / J ₂ (φ ₁ )} (17) The angular velocity can be calculated in consideration of the fluctuation compensation of the index φ _e . In this example, it is possible to detect only the frequency component four times Δω. In the second embodiment, that is, in the case where n = 2 in the formula (3), the request for the arithmetic processing speed is relaxed as compared with the case in which n = 1 in the first embodiment, that is, the formula (3). In that respect, a larger effect can be obtained. Component of the fundamental frequency Δω beat is proportional to phi _s, that is, that now behave in an optimal sensitivity is also important point different from the first embodiment for small phi _s.

Next, a third embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. FIG. 3 shows a case where a phase modulator 301 using lithium niobate as a waveguide is used at the location of the piezoelectric cylinder phase modulator 106 used in the first and second embodiments. Lithium niobate phase modulator 3
When 01 is used, it is easier to apply stable optical phase modulation up to a high frequency of several hundred kHz based on the electro-optic effect, as compared with the piezo cylinder phase modulator 106 that utilizes structural resonance of the piezoelectric element. Therefore, in combination with the phase modulation method of the present invention, the shortening of the sensing loop length by increasing the modulation frequency can be easily realized by hardware. Of course, the phase modulator is not limited to lithium niobate, and other members having an electro-optical effect may be used. When using a member having an electro-optical effect represented by lithium niobate, it is possible to expect a more stable operation in terms of temperature than a conventional piezo cylinder. Although the example of FIG. 3 shows the signal processing using Δω, 2Δω, and 4Δω, in this case, for example, the signal processing using only Δω and 2Δω can be performed. That is, it is not necessary to compensate the fluctuation of the modulation index φ _e in the equations (12) and (17) in the first and second embodiments. Therefore, in the present embodiment, the required detection speed can be further halved as compared with the case of the first and second embodiments. On the contrary, the case where the modulation index needs to be compensated but the 4Δω component is too small from the equation (15) and cannot be used for signal processing can be actually assumed. In this case 4
By using the DC component S _D ′ of the interference signal S instead of the Δω component, S _a ′ / S instead of the equations (16) and (17)
It is also possible to use _D ', _Sb ' / _SD 'for signal processing.

Next, a fourth embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. In FIG. 4, an element (optical IC) 402 in which a phase modulator, a polarizer, and a Y-branch (optical coupler) are integrated in a phase modulation type optical fiber gyro is used, and the return light passing through the position of the light source is used as a light source. It is a block diagram when it is set as the SCOOP system which detects on the back surface. SCOOP
Since the system is used, the optical coupler is not necessary other than the Y branch of the optical IC. The light beam from the light source 401 with a light receiver reaches the optical IC 402 and is polarized. Further, it becomes two light beams that branch in two directions inside and propagate in the sensing loop 105 in the left and right directions. These light beams reach the optical IC 402 again, and inside thereof, the optical phase is modulated according to the modulation signal generated by the phase modulator driving circuit 107. The light whose phase is modulated is recombined by the optical IC 402 and detected as an interference signal by the light source 401 with a light receiver. For the phase modulation, in addition to the method of modulating in one waveguide of the Y branch, for example, a Push-Pull configuration in which modulation is performed in two waveguides in opposite phases can be used. The detected signal is amplified to an appropriate level by the preamplifier 109 and processed in the same manner as in the first to third embodiments to calculate the angular velocity.

Next, a fifth embodiment of the present invention will be described with reference to FIG. FIG. 5 is a configuration diagram in the case where a synchronous downsampling method is incorporated in the signal processing unit 110 in the optical system similar to that of the fourth embodiment. As in the fourth embodiment, the interference signal detected by the light source 401 with a light receiver is amplified by the preamplifier 109 to an appropriate level. If a light emitting element such as a laser diode incorporating a monitor photodiode is used as the light source, the photodiode itself can be used as a light detecting element. Here, it is assumed that n = 2 in the equation (3) and each frequency component Δω, 2Δω, 4Δω given by the equations (13) to (15) is detected, but of course, extension to other cases is possible. Is easy.
On the other hand, the above-mentioned Δω, 2
The downsampling frequency f _d for detecting Δω and 4Δω may be set as follows: f _d = {8 / (8k + 1)} · (Δω / 2π) (18) with Δω as the fundamental frequency. The programmable timer 114 supplies the sampling frequency f _d to the A / D converter 112. The amplified interference signal is taken in by the signal processing unit 501, and A /
In the D converter 112, it is converted into a digital amount at a constant cycle. The sampled data is taken into the calculation unit 502, and the angular velocity is calculated based on it. The phase modulation method using the two modulation signals and the synchronous downsampling method are effective in mitigating the detection speed and the calculation processing speed, respectively, and by combining them, a further effect can be realized. Also, since the synchronous downsampling method reduces the number of parts in the analog electronic circuit part,
A significant cost reduction can be expected by combining these methods.

[0011]

In the optical fiber gyro of the present invention, ω ₁ = nω _m + Δω (n is a positive or negative integer; Δω <
two modulation angular frequencies ω ₁ , satisfying the relationship of ω ₁ , ω _m ),
By using ω _m at the same time, it is possible to measure the required physical quantity, particularly the angular velocity, simply by detecting the beat frequencies and their harmonic components, which are given by the mathematical formulas containing Δω or Δω, which are much lower than ω ₁ and ω _m . Also, by selecting the absolute value of n to be an even number, and especially to be 2, it is possible to detect the above physical quantity due to the Δω component with optimum sensitivity. In addition, the modulated signal is generated based on the clock signal of the signal processing unit, and the beat frequency component and its harmonic component are detected by the synchronous down-sampling method, whereby the phase modulation method and digital signal processing of the present invention are performed. Can be easily combined. Furthermore, by using a waveguide material having an electro-optical effect for the optical phase modulator, especially lithium niobate, the modulation frequency required for shortening the loop length while maintaining the stability of modulation with respect to the conventional piezoelectric element can be obtained. It can be pulled up easily. As described above, it is possible to reduce the load on the signal processing unit and provide an optical fiber gyro with excellent responsiveness. Also, by shortening the length of the optical fiber used for the sensing loop, a low-cost optical fiber gyro can be obtained. Can be provided.

[Brief description of the drawings]

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

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

FIG. 3 is a configuration diagram showing a third embodiment of the optical fiber gyro of the present invention.

FIG. 4 is a configuration diagram showing a fourth embodiment of an optical fiber gyro of the present invention.

FIG. 5 is a configuration diagram showing a fifth embodiment of the optical fiber gyro of the present invention.

FIG. 6 is a configuration diagram showing an example of a conventional optical fiber gyro.

[Explanation of symbols]

Reference Signs List 101 light source 301 lithium niobate phase modulator 102 optical coupler 401 light source with light receiver 103 polarizer 402 optical IC 104 optical coupler 501 signal processing unit 105 sensing loop 502 operation unit 106 piezo cylinder phase modulator 107 phase modulator driving circuit 108 light reception Device 109 Preamplifier 110 Signal processing unit 111 Lock-in amplifier 112 A / D converter 113 Operation unit 114 Programmable timer

Front page continuation (72) Inventor Hisao Sonobe 7-1-1 Omika-cho, Hitachi-shi, Ibaraki Hitachi Research Laboratory, Hitachi Ltd. (72) Inventor Shigeru Oho 7-1-1 Omika-cho, Hitachi-shi, Ibaraki Hitachi, Ltd., Hitachi Research Laboratory

Claims (12)

[Claims] 1. An optical phase difference is provided which comprises means for generating interference light having an optical phase difference corresponding to a physical quantity, and an optical phase modulator which electrically adjusts the optical phase difference of the interference light. By detecting, is an optical fiber gyro that measures the physical quantity, sampling an interference signal that is an electrical signal obtained by photoelectrically converting the interference light, in an optical fiber gyro that calculates the physical quantity by calculation, The first and second modulation signals are supplied to the optical phase modulator, and the modulation angular frequencies ω _m and ω _{1 of} these two signals are ω
₁ = nω _m + Δω (n is a positive or negative integer; Δω <ω ₁ , ω
_m )) fiber optic gyro characterized by being adapted to meet. 2. The optical fiber gyro according to claim 1, wherein | n | is an even number. 3. The optical fiber gyro according to claim 2, wherein | n | = 2. 4. The optical fiber gyro according to claim 1, wherein a waveguide material having an electro-optic effect is used for the optical phase modulator. 5. The optical fiber gyro according to claim 4, wherein lithium niobate is used as a waveguide material having an electro-optical effect. 6. The optical fiber gyro according to claim 4 or 5, wherein the optical phase modulator is integrated with optical elements such as an optical coupler and a polarizer, and is formed by using a waveguide material having an electro-optical effect. A fiber optic gyro that is characterized by 7. The optical fiber gyro according to any one of claims 1 to 6, wherein the first and second modulated signals are supplied in synchronization with a clock signal of a signal processing unit that performs an operation by sampling an interference signal. An optical fiber gyro characterized by the above. 8. The optical fiber gyro according to claim 7, wherein the first and second modulated signals are generated from a clock signal. 9. The optical fiber gyro according to any one of claims 1 to 8, wherein a fundamental wave component of a beat frequency given by a mathematical expression including Δω or Δω and one or more harmonic components thereof are detected from the interference signal, and they are detected. An optical fiber gyro, which is characterized in that a physical quantity is calculated by calculation based on the calculation. 10. The optical fiber gyro according to claim 9, wherein a beat frequency is Δω, a harmonic thereof is 2Δω, each frequency component is detected, and a physical quantity is calculated based on the detected frequency components. Characteristic optical fiber gyro. 11. The optical fiber gyro according to claim 10, in addition to detecting each frequency component of Δω, 2Δω,
An optical fiber gyro characterized by detecting fluctuations in the DC component of an interference signal and correcting the signal. 12. The optical fiber gyro according to claim 9, wherein detection of a beat frequency component is synchronized with a beat frequency, and a synchronous down-sampling method in which a sampling cycle is extended to one cycle or more of an input basic signal is used. An optical fiber gyro characterized by performing.