JP2505215B2 - Fiber optic gyro - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical fiber gyro, and more specifically, it applies clockwise light of a certain wavelength to an optical propagation path that cooperates with a rotation axis. In particular, the present invention relates to an optical fiber gyro of a frequency changing method for simultaneously propagating in a counterclockwise direction and a light phase difference due to the Sagnac effect to obtain a signal proportional to a rotation angular velocity around a rotation axis.

[Prior Art] FIG. 5 shows a conventional frequency change type optical fiber gyro, in which the first light beam emitted from the light source (1) is
It is incident on the first optical distribution coupler (2a) and is divided into two,
It becomes the third light beam. The second light beam travels in the direction of the solid arrow and is incident on the polarizer (3). The second light beam incident on the polarizer (3) transmits only a certain polarized light,
Incident on the optical distribution coupler (2b). The second light beam incident on the second light distribution coupler (2b) is divided into two, and
It becomes the fifth light beam. The fourth light beam travels in the direction of the dashed arrow and is incident on the first acousto-optic modulator (4a) driven by the first RF amplifier circuit (202a). The fourth light beam incident on the first acousto-optic modulator (4a) undergoes + 1st order black diffraction and undergoes a frequency shift of + f _A1 . However, f _A1
Is the frequency of the drive signal (204) of the first acousto-optic modulator (4a). The frequency-shifted fourth light beam enters the phase modulator (5) and undergoes phase modulation of Φ _M · sin (ωmt). However, Φ _M is the maximum phase shift and ω m is the phase modulator driving angular frequency. The fourth light beam subjected to the phase modulation propagates counterclockwise in the light propagation path (6) formed of the polarization-maintaining single-mode optical fiber wound perpendicularly to the rotation axis, It is incident on the second acousto-optic modulator (4b) driven by the second RF amplifier (202b), undergoes + 1st order black diffraction, and undergoes a frequency shift of + f _A2 . However, f
_A2 is the frequency of the drive signal (205) of the second acousto-optic modulator (4b). The second light beam after the frequency shift re-enters the second light distribution coupler (2b).

The fifth light beam propagates from the second light distributing / combining device (2b) in the direction of the alternate long and short dash line, and the second acousto-optic modulator (4b).
When incident on, the light undergoes + 1st order black diffraction and undergoes a frequency shift of + f _A2 . After this, the fifth light beam propagates in the clockwise direction through the light propagation path (6), and then the phase modulator (5).
And is subjected to phase modulation of Φ _M · sin (ωmt). After the phase modulation, the fifth light beam enters the first acousto-optic modulator (4a), undergoes frequency modulation of + f _A1 and re-enters the second light distribution coupler (2b). The fourth and fifth light beams re-incident on the second light distribution coupler (2b) are recombined into a sixth light beam. The sixth light beam is incident on the polarizer (3), only constant polarized light is transmitted, and is incident on the first light distribution coupler (2a). The sixth light beam incident on the first optical distribution coupler (2a) is split into two, and becomes the seventh and eighth light beams. This eighth light beam is incident on the photoelectric conversion circuit (7), and the photoelectric conversion output signal (8) is output. At this time, the photoelectric conversion output signal (8) is expressed by the following equation.

V ₁ ∝ P ₀ {1 + J ₀ (h) cos [Kω-2πnL (f _A1 −f _A2 ) /
C] −2J ₁ (h) sin [Kω−2πnL (f _A1 −f _A2 ) / C] · c
os (ωmt) ・ ・ ・} Unit [V] ・ ・ ・ (1) where V _{1 is the} photoelectric conversion output signal P _{0 is} the non-interfering light quantity of the eighth light beam J ₁ : The 1st-order Bessel function h: 2Φ _M・ sin (πnLωm / C): Phase modulation index k: 4πRL / λC [rad / (rad / sec)] R: Optical propagation path radius L: Optical fiber length λ: Light wavelength in vacuum C: In vacuum Light velocity ω: Input rotation angular velocity n: Equivalent refractive index of optical fiber.

The photoelectric conversion output signal (8) is supplied to the phase modulator drive circuit (20
It is input to the synchronous detection circuit (9) together with the phase modulator drive signal (208) output from 9), and the same angular frequency component as the phase modulation drive angular frequency ωm is synchronously detected. Therefore, the output signal (210) of the synchronous detection circuit (9) is P ₀ 2J ₁ (h) si
It is proportional to n [Kω-2πnL (f _A1 −f _A2 ) / C]. The synchronous detection output signal (210) is input to the voltage controlled oscillator circuit (203). The voltage controlled oscillator circuit (203) is a drive signal (205) for the second acousto-optic modulator (4b), which is an output signal, according to the voltage level of the difference between the voltage of the synchronous detection output signal (210) and the reference voltage. Change the frequency f _A2 of.

At this time, the frequency f _A2 of the drive signal (205) of the second acousto-optic modulator (4b) is changed so that the synchronous detection output signal (210) becomes zero.

Therefore, Becomes

Here, the drive signal (204) output from the oscillator (201) and the drive signal (205) output from the voltage controlled oscillation circuit (203) are mixed to extract the beat frequency, and the beat frequency is synchronized. The gyro output (207) is changed by the counter circuit (206) that counts up or down according to the polarity of the detection output signal (210). It is obtained as a digital output corresponding to.

However, even if the input angular velocity ω is zero, the drive signals (204), (2) of the first and second acousto-optic modulators (4a), (4b)
If the frequencies f _A1 and f _{A2 in} 05) are not the same, the equivalent input angular velocity error · ω _E Is generated. For example, when λ = 0.83 μm, n = 1.45, R = 30 mm, ω _E = 1 ° / hr, (f _A1 −f _A2 ) = 0.24 H
It becomes z.

Generally, the drive frequency of an acousto-optic modulator is 80MHz to 200MH
Therefore, when the gyro output fluctuation is desired to be 1 ° / hr or less, the output signal frequency stability of the oscillator (201) and the voltage controlled oscillator (203) is required to be about 10 ^-3 ppm. However, since the frequency stability of a normal voltage controlled oscillator circuit (203) is several ppm, it is difficult to obtain a gyro characteristic with good drift stability. In addition, the drive signals (204) and (205) of the first and second acousto-optic modulators (4a) and (4b) are output from the oscillator (201) and the voltage controlled oscillation circuit (203) which are two separate circuits. Since (f _A1 −f _A2 ) is generated, drift stability may be reduced.

Furthermore, the linearity and stability of the voltage controlled oscillator circuit (203) with respect to the synchronous detection output signal (210) determine the gyro output linearity and scale factor stability, but the voltage controlled oscillator circuit (203) generally responds to environmental changes. Linearity and stability are easy to change.

Further, in the conventional optical fiber gyro, the output signal (210) of the synchronous detection circuit (9) is P ₀ 2J ₁ (h) sin
In addition to being proportional to [Kω-2πnL (f _A1 −f _A2 ) / C], the phase modulator drive signal (20) of the photoelectric conversion output signal (8)
8) Same frequency component signal and phase modulator drive signal (208)
When the phase difference between the two is θ, it is also proportional to cos θ.

Therefore, the variation of the non-interfering light amount P ₀ of the eighth light beam,
The fluctuation of the maximum phase shift Φ _{M and} the fluctuation of the phase difference θ of the phase modulator (5) may lead to deterioration of linearity and scale factor stability.

Further, the output signal (210) of the synchronous detection circuit (9) is f _A1 = f _A2 at the moment when the optical fiber gyro is activated.
Therefore, it is proportional to sin (kω).

Therefore, the maximum rotational angular velocity ω _M [rad / sec] that can be detected when the navigation body equipped with the optical fiber gyro is in motion during movement of the navigation body is limited to ± π / 2K.

[Problems to be Solved by the Invention] As described above, in the conventional frequency change type optical fiber gyro, the first and second acousto-optic modulators (4a), (4)
Since the drive signals (204) and (205) in (b) are output from different circuits from each other and the voltage control oscillation circuit (203) is used, the drive signal frequency stability is poor and the drive signal (20
There was a problem that the drift stability of the gyro was poor due to fluctuations in the frequency difference between 4) and (205). Also,
Since the voltage controlled oscillator circuit (203) is used, the linearity and stability of the input voltage and output signal frequency easily change with environmental changes, and the gyro linearity and scale factor stability are poor. .

Further, the output of the synchronous detection circuit (9) is the incoherent light amount of the eighth light beam, and the maximum phase shift Φ of the phase modulator (5).
There is a problem in that linearity and scale factor stability are likely to deteriorate due to fluctuations in the phase difference θ between the phase modulator driving frequency component of _M and the photoelectric conversion signal (8) and the phase modulator driving signal (208). It was

In addition, there is a problem that the maximum rotational angular velocity that can be detected by the gyro is limited to ± π / 2K [rad / sec] while the navigation body is in motion.

The present invention has been made to solve the above problems, and reduces the frequency drift of the acousto-optic modulator drive signal, stabilizes the modulation degree of phase modulation, and changes the light amount and the synchronous detection circuit (9 ), The drift stability of the gyro can be minimized by removing the influence of the phase difference fluctuation between the photoelectric conversion output signal and the phase modulator drive signal, and the linearity and scale factor stability can be increased to improve the gyro's stability. The objective is to obtain a frequency-changing optical fiber gyro that can expand the maximum detected rotational angular velocity to ± π / K [rad / sec].

[Means for Solving the Problems] The optical fiber gyro according to the present invention extracts the same frequency component as the phase modulator driving frequency from the photoelectric conversion output signal output from the photoelectric conversion circuit, and first and second analog signals. And a first synchronous detection circuit that has an automatic sensitivity switching function and outputs sensitivity information as a first digital signal, and extracts a frequency component that is twice the drive frequency of the phase modulator from the photoelectric conversion output signal. A second synchronous detection circuit for outputting a third and a fourth analog signal; and a third for outputting a fifth and a sixth analog signal by extracting a frequency component four times the phase modulator driving frequency from the photoelectric conversion output signal. Synchronous detection circuit, an isolation amplifier that electrically insulates and outputs the first to sixth analog signals, and electrically isolated from the isolation amplifier An A / D converter that converts the 1st to 6th analog signals into a 2nd digital signal, and a frequency component that is twice or four times the driving frequency of the phase modulator of the photoelectric conversion output from the first and second digital signals. The phase difference due to the Sagnac effect between the third digital signal that makes the ratio of the absolute values of the amplitudes of the signals constant and the frequency component that is the same as or twice the driving frequency of the phase modulator of the photoelectric conversion output is ± π [ra
the ratio of the absolute values of the amplitudes up to d] is zero, and
The fourth and fifth digital signals whose sums are constant and A /
A sixth digital signal that controls the D converter, an arithmetic / control circuit that outputs a seventh digital signal that is proportional to the rotational angular velocity, a master clock circuit that outputs a clock signal, and a third clock that is frequency-synchronized with the clock signal. A seventh analog signal having an amplitude corresponding to the digital signal, an eighth analog signal having a frequency twice that of the seventh analog signal, and a ninth analog signal having a frequency four times that of the seventh analog signal. It has a first direct synthesizer synthesizer that outputs an analog signal, a buffer amplifier that inputs a seventh analog signal and drives a phase modulator, and has a frequency that is frequency-synchronized with the clock signal and that corresponds to the fourth digital signal. A second direct synthesis synthesizer which outputs a tenth analog signal, and an eleventh signal which is frequency-synchronized with the clock signal and has a frequency corresponding to the fifth digital signal. A third direct synthesis synthesizer that outputs an analog signal, a first high-frequency oscillator that outputs a first high-frequency analog signal, a tenth analog signal and a first high-frequency analog signal are input, and the frequencies of both signals are input. A first SSB generating circuit that outputs a second high-frequency analog signal that drives the first acousto-optic modulator and that has a sum frequency of, and that inputs the eleventh analog signal and the first high-frequency analog signal, A second SSB generating circuit that outputs a third high-frequency analog signal that has a frequency that is the sum of the frequencies of both signals and that drives the second acousto-optic modulator.

[Operation] In the present invention, the ratio of the absolute value of the amplitude of the frequency component of the phase modulator drive frequency of the photoelectric conversion output signal extracted by the second and third synchronous detection circuits is twice and four times constant. As described above, the arithmetic / control circuit controls the output amplitude of the first direct synthesis synthesizer and drives the phase modulator, whereby the modulation degree of the phase modulation is stabilized.

In addition, the phase difference due to the Sagnac effect of the frequency component of the phase modulator driving frequency of the photoelectric conversion output signal extracted by the first and second synchronous detection circuits is twice as much as ±.
The arithmetic / control circuit controls the output frequencies of the second and third direct synthesizer synthesizers so that the ratio of the absolute values of the amplitudes in the range up to π [rad] becomes zero. With the sum of the output frequencies of the high frequency oscillator of 1,
Signals for driving the first and second acousto-optic modulators are generated by the first and second SSB generation circuits. As a result, the maximum detected angular velocity range is expanded, and the influence of the fluctuation of the light amount and the fluctuation of the phase difference between the photoelectric conversion output signal and the phase modulator drive signal is removed.

At this time, the output signals of the second and third direct synthesis system synthesizers are both frequency-synchronized with the clock signal of the master clock circuit, and the output signals of the second and third direct synthesis system synthesizers are The first and second acousto-optic modulator drive signals operate in such a manner that a minute difference between both drive signal frequencies is stably given to shift the frequency of the drive signals, and fluctuations in these frequency differences can be almost ignored.

[Embodiment] FIG. 1 shows an embodiment of the present invention. The first, second and third synchronous detection circuits (9a), (9b), (9c), isolation amplifier (16), A / D converter (17), arithmetic / control circuit (19), master clock circuit (21), first and second,
Third direct synthesis synthesizer (22a), (22b),
(22c), first and second SSB generation circuits (30a), (30b),
It is composed of a first high-frequency oscillator (28). The same reference numerals as those in FIG. 5 denote the same parts, and the description thereof will be omitted.

 Next, the operation will be described.

The first light beam emitted from the light source (1) enters the first light distribution coupler (2a) and is divided into two light beams, that is, second and third light beams, and the second light beam is a solid line. The light travels in the direction of the arrow and enters the polarizer (3). Second through the polarizer (3)
The light beam of is incident on the second light distribution coupler (2b) and becomes the fourth and fifth light beams. The fourth and fifth light beams pass through the first and second acousto-optic modulators (4a) and (4b), the phase modulator (5), and the light propagation path (6), and then the second light distribution. The sixth light beam is recombined by the combiner (2b). Sixth
After passing through the polarizer (3) again, it enters the first light distribution coupler (2a), and is divided into two parts to become the seventh and eighth light beams. This eighth light beam is a photoelectric conversion circuit (7)
And becomes a photoelectric conversion output signal (8) and becomes a signal represented by the equation (1).

The operation up to this point is exactly the same as the operation described as the conventional technique.

In this embodiment, the photoelectric conversion output signal (8) is input to the first, second and third synchronous detection circuits (9a), (9b) and (9c).

In the first synchronous detection circuit (9a), the same frequency component as the phase modulator driving angular frequency ωm of the photoelectric conversion output signal (8) is taken out, and the first and second analog signals (10) and (11) are extracted.
Is output. The first and second analog signals (10),
(11) is given by the following equation.

First analog signal: Vm, ₁ ∝P ₀ · 2J ₁ (h) sin [Kω−2πnL (f _A1 −f _A2 ) / C] ・ cos θm ・ ・ ・ (2
a) Second analog signal: Vm, ₂ ∝P ₀・ 2J ₁ (h) sin [Kω-2πnL (f _A1 −f _A2 ) / C] ・ sin θm ・ ・ ・ (2
b) where θm: ωm component of the photoelectric conversion output signal (8) and ω
It is the phase difference from the seventh analog signal (23) having an angular frequency of m.

The second synchronous detection circuit (9b) extracts the 2ωm component of the photoelectric conversion output signal (8) and outputs the third and fourth analog signals (12) and (13). The third and fourth analog signals (12) and (13) are given by the following equation.

Third analog signal: V ₂ m, ₁ ∝P ₀ · 2J ₂ (h) cos [Kω−2πnL (f _A1 −f _A2 ) / C] · cos θ ₂ m ... (3
a) Fourth analog signal: V ₂ m, ₂ ∝P ₀ · 2J ₂ (h) cos [Kω−2πnL (f _A1 −f _A2 ) / C] · cos θ ₂ m ・ ・ ・ (3
b) where θ ₂ m is the phase difference between the 2ωm component of the photoelectric conversion output signal (8) and the eighth analog signal (24) having an angular frequency of 2ωm.

The third synchronous detection circuit (9c) extracts the 4ωm component of the photoelectric conversion output signal (8) and outputs the fifth and sixth analog signals (14) and (15). The fifth and sixth analog signals (14) and (15) are given by the following equation.

Fifth analog signal: V ₄ m, ₁ ∝P ₀ · 2J ₄ (h) cos [Kω−2πnL (f _A1 −f _A2 ) / C] · cos θ ₄ m ・ ・ ・ (4
a) Sixth analog signal: V ₄ m, ₂ ∝P ₀ · 2J ₄ (h) cos [Kω−2πnL (f _A1 −f _A2 ) / C] ・ cos θ ₄ m ・ ・ ・ (4
a) where θ ₄ m is the phase difference between the 4ωm component of the photoelectric conversion output signal (8) and the ninth analog signal (25) having an angular frequency of 4ωm.

The above first to sixth analog signals (10), (11),
(12), (13), (14) and (15) are electrically isolated from the synchronous detection circuits (9a) to (9c) by the isolation amplifier (16), and the expressions (2a) and (2b) are used. ), (3a), (3
The outputs shown in b), (4a), and (4b) are input to the A / D converter (17) while being held. The A / D converter (17) converts the analog signal from the isolation amplifier (16) into a second digital signal (18b). The second digital signal (18b) is a digital signal represented by, for example, a binary number.

This second digital signal (18b) is taken into the arithmetic / control circuit (19) according to the sixth digital signal (20d) which controls the A / D converter (17) of the arithmetic / control circuit (19). Be done. Further, at this time, the first synchronous detection circuit (9a) has an automatic sensitivity switching function, and this sensitivity information is output as the first digital signal (18a) and taken into the arithmetic / control circuit (19). . The arithmetic / control circuit (19) makes the following logical determination from the first and second digital signals (18a) and (18b). Here, the first and third analog signals (10), (12)
Is the normalized synchronous detection circuit output (101), (10
It corresponds to 2). As can be seen from FIG. 2, the phase of light;
Table 1 shows the signs of the normalized synchronous detection circuit outputs (101) and (102) for the range of [Kω-2πnL (f _A1 −f _A2 ) / C]. Therefore, the range of the phase of light; [Kω-2πnL (f _A1 −f _A2 ) / C] is determined by these logical determinations.

Next, the arithmetic / control circuit (19) performs the next arithmetic operation from the first and second digital signals (18a) and (18b).

The calculated values expressed by equations (5a) and (5b) are (10
3) and (104), respectively. From the range of the optical phase [Kω-2πnL (f _A1 −f _A2 ) / C] according to the logical judgment shown in Table 1 and the calculated values of the equations (5a) and (5b) shown in FIG. The circuit (19) detects the phase of light [Kω-2πnL (f _A1
-F _A2 ) / C], judge as shown in Table 2.

The arithmetic / control circuit (19) reverses the sign of the judgment value shown in Table 2, multiplies it by the proportional coefficient: α, and converts it into M (integer).

At this time, the arithmetic / control circuit (19) sets (N + M) to the fourth
Of the digital signal (20b) and (NM) as the fifth digital signal (20c). However, N
Is a bias value and is a positive integer. In addition, (N ±
M) is also a positive integer. The second and third direct synthesizer synthesizers (22b) and (22c) respectively use the clock signal output from the master clock circuit (21) and the fourth and fifth digital signals (20b) and (20c). (N +
_{M) f L, (N-} M) 10, 11 analog signal having a frequency of f _L (27a), and outputs the (27b). Where f _L is the second and third direct synthesizer synthesizers (22b), (22c)
It is a fundamental frequency that is frequency-synchronized with the clock signal generated in.

The first high frequency oscillator (28) outputs a first high frequency analog signal (29). The first high frequency analog signal (2
9) is the first and second SSB generating circuits (30a) and (30), respectively, together with the tenth and eleventh analog signals (27a) and (27b).
Entered in b). The first SSB generation circuit (30a) is
High frequency analog signal (29) and tenth analog signal (27
The second high frequency analog signal (31a) having a frequency of [f _H + (N + M) f _L ] of the frequency sum of a) is output. However, f _H is the frequency of the first high-frequency analog signal (29). At this time, the second SSB generation circuit (30b) is configured so that the first high frequency analog signal (29) and the eleventh analog signal (27b)
The sum of the frequencies of [f _H + (N−M) f _L ]
The high frequency analog signal (31b) of is output.

Second and third high frequency analog signals (31a), (31b)
Are the first and second acousto-optic modulators (4a) and (4
It becomes the drive signal of b).

Here, the arithmetic / control circuit (19) sets the value shown in equation (5a) to zero, in other words, the first and second analog signals output from the first synchronous detection circuit (9a). (Ten),
By operating so that (11) becomes zero, f _A1 −f _A2 = 2Rω / λn unit [Hz] (6)

Also, from f _A1 = f _H + (N + M) f _L・ ・ ・ (7a) f _A2 = f _H + (NM) f _L・ ・ ・ (7b), f _A1- f _A2 = 2Mf _L・ ・・ It becomes (8).

From equations (6) and (8), M = Rω / λnf _L (9)

The above M is obtained by the seventh digital signal (32) as a gyro output from the arithmetic / control circuit (19).

At this time, the first and second acousto-optic modulators (4a), (4
b) The second and third high frequency analog signals (31a) and (31b), which are the respective drive signals, are output from the master clock circuit (21) at the frequency f _{H of} the first high frequency analog signal (29). It commonly includes a fundamental frequency f _L generated by the second and third direct synthesizer synthesizers (22b) and (22c) in frequency synchronization with the clock signal. As a result, when the input angular velocity ω is zero, that is, when M = 0, f _A1 = f _A2 , and the first, second, and third high-frequency analog signals (29),
The frequency stability of (31a) and (31b) does not affect the drift stability of the gyro.

The second and third direct synthesizer synthesizers (22
In b) and (22c), f _L = 0.1mHz is (N ± M) f _L = 0.1mHz
The frequency stability of the clock signal of the master clock circuit (21) is preserved as it is while being maintained over a wide frequency range of up to 1.2 MHz.

Therefore, the gyro drift caused by the frequency instability of the acousto-optic modulator driving signal, which is found in the conventional frequency change type optical fiber gyro, is also minimized.

Also, the frequency deviation Mf of the acousto-optic modulator drive signal
_L is an output of the second and third direct synthesizer synthesizers (22b) and (22c), which are frequency shifters, where the analog outputs of the synchronous detection circuits (9a) to (9c) are digitally processed. Since it is linearly related to the tenth and eleventh analog outputs (27a) and (27b), the gyro linearity and scale factor stability are improved by the isolation amplifier (16) and the A / D converter (17). 2) and the frequency stability of the clock signal which is the output of the master clock circuit (21), the accuracy can be remarkably improved as compared with the conventional frequency change type optical fiber gyro.

Further, in the present invention, in the arithmetic / control circuit (19),
The output of the first synchronous detection circuit (9a) shown in formulas (2a) and (2b) and the second synchronous detection circuit (9b) shown in formulas (3a) and (3b)
The outputs shown in Equations (5a) and (5b) are calculated to shift the output frequencies of the second and third direct synthesizer synthesizers. Therefore, the non-interfering light intensity P ₀ of the eighth light beam Gyro linearity and scale due to fluctuations and fluctuations in phase difference θm and θ ₂ m with the seventh and eighth analog signals (23) and (24) having angular frequencies of ωm and 2ωm of the photoelectric conversion output signal (8) There is no deterioration of factor stability.

Further, by the logical discrimination and calculation shown in Tables 1 and 2, the maximum rotational angular velocity ω _M [red / sec that can be detected when the gyro is activated while the navigation body equipped with the optical fiber gyro is in operation. ] Is expanded to ± π / K.

Now, the arithmetic / control circuit (19) performs the following arithmetic operation from the first and second digital signals (18a) and (18b).

The arithmetic / control circuit (19) outputs a third digital signal (20a) that keeps the value shown in equation (10) constant. The first direct synthesis synthesizer (22a) is frequency-synchronized with the clock signal which is the output signal of the master clock circuit (21) and has a seventh analog signal having an output amplitude corresponding to the third digital signal (20a). Output (23). Seventh
The analog signal (23) is input to the buffer amplifier (26) and becomes a drive signal for the phase modulator (5). At this time, the modulation index h of the phase modulator (5) is made constant by forcibly changing the maximum phase shift Φ _M of the phase modulator (5) with the amplitude of the seventh analog signal (23). . This allows
Degradation of gyro linearity and scale factor stability caused by a change in the modulation index h due to a change in the maximum phase shift Φ _M is prevented.

Table 3 shows the optical phase [Kω- of the arithmetic / control circuit (19).
Another embodiment of the judgment value for 2πnL (f _A1 −f _A2 ) / C] will be described.

FIG. 4 shows a specific example of the SSB generation circuits (30a) and (30b). The 0 ° divider (39) inputs the first high-frequency analog signal (29), divides the power into 2 and outputs the same. To do.
The first 90 ° hybrid circuit (38a) inputs the fourth high-frequency analog signal (37), divides the power into two, and
One is in phase with the input signal (0 °), the other is 90 degrees with the input signal.
° Phase shift and output. The output signal of the 0 ° divider (39) and the 0 ° phase output signal of the first 90 ° hybrid circuit (38a) are mixed in the frequency by the second DBM (33b) and output. Similarly, the output signal of the 0 ° divider (39) and the 90 ° phase output signal of the first 90 ° hybrid circuit (38a) are mixed in the frequency by the third DBM (33c) and output. The output signals of the second and third DBMs (33b) and (33c) are input to the 0 ° port and 90 ° port of the second 90 ° hybrid circuit (38b), respectively, and the fourth high frequency analog signal (37) is input. And a twelfth analog signal (40) having a frequency difference between the first high-frequency analog signal (29) and the first high-frequency analog signal (29). The twelfth analog signal (40) is the tenth (11th) analog signal (27
a) It is input to the first DBM (33a) along with [(27b)],
The frequencies are mixed and output. The output signal (34) of the first DBM (33a) is input to the voltage comparison circuit (35) and compared with the reference voltage. The output signal of the voltage comparison circuit (35) is input to the voltage controlled oscillator circuit (36) and has a frequency proportional to the output signal of the voltage comparison circuit (35) and the frequency of the first high frequency analog signal (29). And a fourth high frequency analog signal (37) having a frequency of the sum of the frequencies of the tenth (11th) analog signal (27a) [(27b)]. The fourth analog signal (37) is power-amplified by the RF amplifier circuit (41) and is the second (third) drive signal for the first (second) acousto-optic modulator (4a) [(4b)]. High frequency analog signal (31a)
It becomes [(31b)].

With the above configuration, a high frequency signal of about 100 MHz and a frequency sum output in the range of DC to several MHz are possible.

[Advantages of the Invention] As is apparent from the above description, the present invention is
The drive signal of the second acousto-optic modulator is generated from the same high-frequency oscillator, frequency-shifted, and further affected by fluctuations in the amount of light, fluctuations in the phase modulation index, and fluctuations in the phase difference between the photoelectric conversion output and the phase modulation signal. Is removed, and in order to increase the maximum detected rotational angular velocity, processing is performed by a circuit mainly composed of an arithmetic / control circuit and a direct synthesis synthesizer.
The drift stability of the gyro characteristic is minimized, and the linearity and scale factor stability can be improved.

[Brief description of drawings]

1 to 4 show an embodiment of the present invention, FIG. 1 is an optical and electric circuit diagram, FIG. 2 is an output diagram of a standardized synchronous detection circuit, and FIG. FIG. 4 is a partial circuit diagram of FIG. 1 and FIG. FIG. 5 is an optical and electric circuit diagram of a conventional optical fiber gyro. (1) ... light source, (2a), (2b) ... first and second light distribution coupler, (3) ... polarizer, (4a), (4b) ... first and second Acousto-optic modulator, (5) ... Phase modulator,
(6) ... Optical propagation path, (7) ... Photoelectric conversion circuit, (8)
...... Photoelectric conversion output signal, (9a) to (9c) ...... First to third
Synchronous detection circuit, (10) to (15) ... first to sixth analog signals, (16) ... isolation amplifier, (17)
...... A / D converter, (18a), (18b) ...... First and second digital signals, (19) ...... Operation / control circuit, (20a) to (2)
0b) ... third to sixth digital signals, (21) ... master clock circuit, (22a) to (22c) ... first to third direct synthesizer synthesizers, (23) to (25) ... … Seventh to ninth analog signals, (26) …… Buffer amplifier, (27
a) (27b) …… 10th and 11th analog signals, (28) ……
First high-frequency oscillator, (29), (31a), (31b) ... First to third high-frequency analog signals, (30a), (30b) ....
1st and 2nd SSB generation circuit, (32) ... 7th digital signal (gyro output), (33a)-(33c) ... 1st-3rd DBM, (35) ... voltage comparison circuit , (36) ... voltage controlled oscillator, (37) ... fourth high frequency analog signal,
(38a), (38b) ... first and second 90 ° hybrid circuits, (39) ... 0 ° divider, (40) ... twelfth analog signal, (41) ... RF amplifier circuit. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (3)

(57) [Claims] 1. A light source that emits a first light beam, a first light distribution coupler that distributes the first light beam into second and third light beams, and a second light beam of the second light beam. A polarizer that transmits only a fixed polarized wave; and a second optical distribution coupler that divides the second light beam into fourth and fifth light beams and then recombines them to form a sixth light beam. A first and a second acousto-optic modulator for giving frequency shifts to the fourth and fifth light beams, a phase modulator for phase-modulating the fourth and fifth light beams, and a rotational angular velocity The fourth with the rotation axis to be measured as the center,
A light propagation path for propagating the fifth light beam in the clockwise direction and the counterclockwise direction in opposite directions to generate a phase difference of light due to the Sagnac effect, and the polarizer in which only a constant polarization is transmitted. A photoelectric conversion circuit for photoelectrically converting the seventh light beam obtained by distributing the sixth light beam to the seventh and eighth light beams by the first light distribution coupler, and outputting a photoelectric conversion output signal; It has a sensitivity switching function, outputs sensitivity information as a first digital signal, extracts the same frequency component as the drive frequency of the phase modulator from the photoelectric conversion output signal,
A first synchronous detection circuit for outputting a second analog signal; and a second for outputting a third and a fourth analog signal by taking out a frequency component having twice the driving frequency of the phase modulator from the photoelectric conversion output signal. And a third synchronous detection circuit for extracting a frequency component four times as high as the phase modulator driving frequency from the photoelectric conversion output signal and outputting fifth and sixth analog signals. An isolation amplifier which electrically insulates and outputs a sixth analog signal, and an A / D converter which converts the electrically isolated first to sixth analog signals into a second digital signal. A third digital signal that keeps a ratio of absolute values of amplitudes of frequency components that are twice or four times the phase modulator driving frequency of the photoelectric conversion output from the first and second digital signals,
The ratio of the absolute value of the frequency component that is the same as or twice the driving frequency of the phase modulator of the photoelectric conversion output is calculated to zero until the phase difference due to the Sagnac effect is within a range of ± π [rad], and the sum of them is calculated. 4th and 5th digital signals that are constant, a 6th digital signal that controls data acquisition from the A / D converter, and a 7th digital signal that is proportional to the rotational angular velocity.
An operation / control circuit for outputting a digital signal, a master clock circuit for outputting a clock signal, a frequency synchronization with the clock signal, an amplitude corresponding to the third digital signal, and a first synchronous detection circuit A seventh analog signal connected to the second analog detection circuit, an eighth analog signal having a frequency twice that of the seventh analog signal and connected to the second synchronous detection circuit, and the seventh analog signal. A first direct-synthesizing synthesizer having a frequency four times as high as that of the signal and connected to the third synchronous detection circuit to output a ninth analog signal; and the phase modulation by inputting the seventh analog signal. Amplifier for driving a circuit, and a second direct synthesis method for outputting a tenth analog signal having a frequency corresponding to the fourth digital signal in frequency synchronization with the clock signal. A synthesizer; a third direct synthesis method synthesizer which outputs an eleventh analog signal having a frequency corresponding to the fifth digital signal in frequency synchronization with the clock signal; and a third high frequency analog signal which outputs a first high frequency analog signal. A first high frequency oscillator; and a second high frequency analog for inputting the tenth analog signal and the first high frequency analog signal and having a frequency that is the sum of the frequencies of both signals and driving the first acousto-optic modulator. A first SSB generating circuit that outputs a signal, and inputs the eleventh analog signal and the first high-frequency analog signal, and drives the second acousto-optic modulator having a frequency that is the sum of the frequencies of both signals. An optical fiber gyro including a second SSB generating circuit that outputs a third high frequency analog signal. 2. An arithmetic / control circuit uses a first analog signal which is an output signal of a first synchronous detection circuit and a third analog signal which is an output signal of a second synchronous detection circuit to code both signals. The phase of the light by -π <~ <-π / 2 -π / 2 -π / 2 <~ <0 0 0 <~ <π / 2 π / 2 π / 2 <~ <π [rad] A function of logically determining a range, the first and second analog signals that are output signals of the first synchronous detection circuit, and the third and fourth analog signals that are output signals of the second synchronous detection circuit A signal is used to set the phase of the light together with the result of the logical determination as −π <˜ <−3 / 4π, π / 2 <˜ ≦ 3 / 4π −3 / 4π ≦ ˜ <−π / 2,3 / 4π <~ <π [rad] -π / 2 ≤ ~ <-π / 4 -π / 4 ≤ ~ <0 0 ≤ ~ ≤ π / 4 π / 4 <~ ≤ π / 2 An optical fiber gyro according to claim 1, comprising: 3. A first and a second SSB generation circuit inputs a first high frequency analog signal, inputs a 0 ° divider that divides power in two and outputs the same, and inputs a fourth high frequency analog signal. The power is split into two, and one is in phase with the input signal (0 °) and the other is with the input signal.
A first 90 ° hybrid circuit that outputs by phase shifting by 90 °, and a second 90 ° hybrid circuit that inputs the 0 ° phase output signal of the first 90 ° hybrid circuit and the output of the 0 ° divider and outputs a mixed frequency signal. DBM, a third DBM for inputting the 90 ° phase output signal of the first 90 ° hybrid circuit and the output of the 0 ° divider, and performing frequency mixing output, and a second DBM output signal for the 0 ° port , The third DBM
A second 90 ° hybrid circuit for inputting an output signal to a 90 ° port and outputting a twelfth analog signal having a frequency which is a difference between the frequency of the fourth high frequency analog signal and the frequency of the first high frequency analog signal. A first DBM for inputting a tenth (11th) analog signal and the twelfth analog signal and mixing and outputting the frequency; and a voltage comparison circuit for comparing and outputting the first DBM output signal with a reference voltage. A frequency proportional to the output signal of the voltage comparison circuit, and
A voltage controlled oscillator circuit for outputting the fourth high frequency analog signal having a frequency of a sum of the frequency of the tenth (11th) analog signal and the frequency of the first high frequency analog signal; and the fourth high frequency analog Power amplification of signal, first
The optical fiber gyro according to claim 1, further comprising: an RF amplifier circuit that outputs a second (third) high frequency analog signal that is a drive signal for the (second) acousto-optic modulator.