JP2514532B2 - Optical interference gyro - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention detects the phase difference between light propagating as clockwise light and counterclockwise light in an optical path that makes at least one round, so as to detect the phase around the axis applied to the optical path. The present invention relates to an optical interference gyroscope for detecting an angular velocity, and particularly to improve the stability and linearity of an input / output scale factor.

[0002]

2. Description of the Related Art A conventional optical interference angular velocity meter (hereinafter referred to as FOG) will be described with reference to FIG. Light I from the light source 11
Is sequentially incident on the optical coupler 12, the polarizer 13, and the optical coupler 14, and then is incident on both ends of an optical path 15 formed by, for example, an optical fiber coil wound a plurality of times in a loop shape. Optical path 15
The right-handed light and the left-handed light propagating in are phase-modulated by the phase modulator 16 arranged between the optical path 15 and the optical coupler 14. Both lights subjected to the phase modulation are combined by the optical coupler 14 and interfere with each other, and are branched to the light receiver 17 by the optical coupler 12 and photoelectrically converted. In this figure, the optical coupler 14 and the phase modulator 16 are configured as an optical integrated circuit 18. The optical integrated circuit 18 is, for example, lead niobate (LiNbO ₃ ).
Was produced by vapor-depositing titanium (Ti) or the like on the optical crystal and heat-diffusing. In the state where the angular velocity in the circumferential direction is not applied to the optical path 15, the phase difference between the two lights in the optical path 16 is ideally zero, but the optical path 15 has an angular velocity Ω around its circumference. When applied, this angular velocity Ω causes a so-called Sagnac effect, resulting in a phase difference ΔΦs between the two lights. This phase difference ΔΦs is expressed by the following equation.

ΔΦs = 4πRLΩ / (Cλ) (1) C: speed of light λ: wavelength of light in vacuum R: radius of optical fiber coil L: length of optical fiber On the other hand, the output Vp of the light receiver 17 at this time is Phase modulator 16
When the phase modulation signal of P is set to P (t) = A sin ω _m t, it can be expressed by the following equation.

[0004] Vp = (I / 2) · Kop · Kpd {1+ cosΔΦs (Σε n · (-1) n · J 2n (X) · cos2nω m t ') - sinΔΦs (2Σ (-1) n · J 2n ₊₁ (X) · cos (2n + 1) ω _m t ′)} (2) where Σ is from n = 0 to infinity t ′ = t− (τ / 2) ε _n = 1; n = 0,2 N > 1 Kop: the light I emitted from the light source 11 is the optical fiber coil 15;
Optical loss after reaching to the light receiver 17 Kpd: Constant determined by photoelectric conversion coefficient, amplifier gain, etc. I: Light emitted from the light source 11 Io: Maximum light amount reaching the light receiver 17 (Io = Kop ·
I) Jn: First-order Bessel function X: 2Asin πfmτ ΔΦ: Phase difference between left and right light in the optical fiber coil 15 ω _m : Angular frequency of phase modulation (ω _m = 2πfm) τ: In the optical fiber coil 15 Light Propagation Time As is apparent from the equation (2), the photoelectric conversion signal from the light receiver 17 includes a term proportional to sin ΔΦs and a term proportional to cos ΔΦs. Therefore, the angular velocity Ω can be detected by measuring the intensity of the interference light. As the output of the conventional FOG, the primary sin ΔΦs component of the output of the light receiver 17 is synchronously detected and used. Below, the primary sin ΔΦs output from the synchronous detection circuit 19
The ingredients are shown. That is, the output of the light receiver 17 is the output of the synchronous detection circuit 1
9 and the same component as the phase modulation frequency, that is, the first-order component (n = 1) in the equation (1), is input to the clock circuit 2.
The reference signal Vf 1 from ₁ is received and taken out. The ripple component of the output of the synchronous detection circuit 19 is filtered, and the output is taken out to the output terminal 22 as the FOG output V ₁ .

The output V _{1 of} this FOG is expressed by the following equation. V ₁ = I · Kop · Kpd · J ₁ (X) · K _A1 · sin ΔΦs = Io · K · sin ΔΦs = K ₁ · sin ΔΦs (3) where K _A1 : gain of the synchronous detection circuit 19 and further input / output The following is done to stabilize the characteristics. That is, in the photoelectric conversion signal Vp from the photodetector 17, the double wave component of the phase modulation frequency is synchronously detected by the reference signal _Vf2 from the clock circuit 21 by the synchronous detection circuit 24, and the ripple component is filtered. The output V ₂ at that time is expressed by the following equation.

V ₂ = I · Kop · Kpd · J ₂ (X) · K _A2 · cos ΔΦs = Io · K · cos ΔΦs = K ₂ · cos ΔΦs (4) where K _A2 : gain of the synchronous detection circuit 24 The outputs V ₁ and V ₂ are squared by the multipliers 25 and 26, respectively, and then added by the adder 27. Output V of adder 27
s is expressed by the following equation.

Vs = V ₁ ² + V ₂ ² (5) where K = K _A1 · J ₁ (X) · Kpd = K _A2 · J ₂ (X) · K
When the gain is adjusted and set to be pd, the equation (5) is expressed by the following equation. Vs = Io ² · K ² · (sin ² ΔΦ + cos ² ΔΦ) = Io ² · K ² (6) The output Vs of the adder 27 is different from the reference signal V _R from the reference voltage generator 29 in the differential amplifier 28. It is calculated dynamically. The output Ve of the differential amplifier 28 is expressed by the following equation.

[0008] The output Ve of _{Ve = V R -V S = V} R -Io 2 · K 2 (7) The differential amplifier 28 is applied to the electro-filter 31. The electric filter 31 is, for example, an integrator, and its output is applied to a light source drive circuit 32 that controls the light amount of the light source 11, and the light amount I of the light source 11 is controlled. Here, in the initial stage, V _R = Io ² · K ² = K _R
If the input angular velocity is not applied to the optical fiber coil 15, that is, if the phase difference ΔΦ between the two lights of the optical fiber coil 15 is zero, Ve becomes zero. Here, it is assumed that the ambient temperature changes and the light amount Io reaching the light receiver 17 decreases. As a result, Ve produces a positive voltage according to the equation (7). This positive voltage is applied to the next electric filter 31 to generate a positive integrated voltage. The light source drive circuit 32 uses the positive integrated voltage to drive the light source 11
If the light amount is adjusted to increase, the input of the electric filter 31, that is, the output Ve of the differential amplifier 28 is controlled to be always zero. As a result, the following equation holds.

V _R = Io ² · K ² (8) By operating such a light quantity stabilizing circuit, F
The output of the OG is expressed by the following equation from the equations (3) and (8). _{V 1 = Io · K · sin} ΔΦs = sin ΔΦs · √V R (9) (9) Using the above conventional scale factor stabilizing circuit as apparent from the equation, to keep the scale factor of the FOG stable I can.

When the linearity Li is calculated based on the equation (9), it is expressed by the following equation. Li = [(sin ΔΦs−ΔΦs) / ΔΦs] × 100 [%] (10) FIG. 4A shows the linearity based on the expression (10). The phase modulator 16 is driven by the signal from the clock circuit 21 through the drive circuit 30.

[0011]

As is clear from the equation (3), K ₁ is a constant and therefore shows a constant value under a constant condition, but the elements constituting the constant K ₁ are large or small. The input / output gain K _{1 of the} FOG, that is, the scale factor, changes depending on the temperature. First, if the phase modulation degree is adjusted so that X = 1.84, the first-order Bessel function J ₁ (X) becomes stable with respect to temperature fluctuation of the phase modulation degree, and Kpd and K _A are The temperature coefficient is essentially small. However, it is considered that the constant Kop fluctuates by nearly 30% with a temperature change of −20 ° C. to + 70 ° C. However, in the prior art, Japanese Patent Laid-Open No. 64-63871 discloses a prior art.
It was possible to stabilize the FOG scale factor by using the technology described in. However, the output V of the FOG
_As is clear from Eq. (9), ₁ still holds K · Io constant by using the stabilizing technology of scale factor (10).
As shown by the equation, an inherent linearity error due to the SIN function occurs.

That is, as understood from FIG. 4A, for example, when the phase difference ΔΦs is 45 °, a linearity error of 10% occurs. An object of the present invention is to provide an optical interference gyro that improves the temperature stability of the scale factor and the linearity with respect to the input.

[0013]

According to the present invention, a light receiver
Of the output from the optical path due to the angular velocity applied to the optical path.
Demodulate the sin ΔΦs component of the Sagnac phase difference ΔΦs
Of the outputs from the first demodulation means and the light receiver, cos ΔΦs
From the second demodulation means for demodulating the component and the first demodulation means
Output Vsin (V in the embodiment₁Said) and the above
2 The output Vcos from the demodulation means is squared and added
First computing means for₀+ A₁× Vsin + A₂× Vsi
n² + A₃× Vsin³ + A_Four× Vsin^Four + ... + An
× Vsin ⁿSecond computing means for computing (An: coefficient),
Each output from the first calculation means and the second calculation means
The addition means for adding and the output from the addition means are constant.
Adjust the gain of the electric circuit so that
Control the amount of light.

By doing so, it is possible to suppress the influence of the loss of the optical system which fluctuates depending on the ambient temperature, keep the input / output scale factor of the FOG stable, and reduce the scale factor linearity with respect to the input.
When the initial setting value of the adding means is A and the output from the adding means is Vs, the initial setting gain of the output means is A
It may be multiplied by / Vs.

[0015]

FIG. 1 shows an embodiment of the present invention, in which parts corresponding to those in FIG. 3 are designated by the same reference numerals. Conventional FOG is (1
A linearity error occurs as shown in equation (0). Therefore, in the present invention, the linearity error amount ε = Io · K · (sin ΔΦs
The output V ₁ is input so that −ΔΦs) becomes zero, the correction signal generation circuit 34 generates the correction signal Vc, and the adder 35 adds Vs to generate the signal Vss. The correction signal Vc is expressed by the following equation when the input signal V ₁ of the correction signal generating circuit 34 is expressed as X.

Vc = Ao + A ₁ .X + A ₂ .X ² + A ₃ .X ³ + A ₄ .X ⁴ + ... + An.X ⁿ (11) The output Vss of the adder 35 is expressed by the following equation. Vss = Io ² · K ² + Vc (12) The output Vss of the adder 35 is differentially calculated by the differential amplifier 28 with the reference signal V _R from the reference signal generator 29. The output Vee of the differential amplifier 28 is expressed by the following equation.

The output Vee of _{Vee = V R -Vss = V R} -Io 2 · K 2 -Vc (13) The differential amplifier 28 is applied to the electric filter 31. The electric filter 31 is, for example, an integrator, and its output is applied to a light source drive circuit 32 that controls the light amount of the light source 11, and the light amount I of the light source 11 is controlled.
If V _R = Io ² · K ² is set in the initial stage, the input angular velocity is not applied to the optical fiber coil 15, that is, the phase difference ΔΦs between the two lights of the optical fiber coil 15 is zero. In this case, Vee becomes zero. Here, it is assumed that the ambient temperature changes and the light amount Io reaching the light receiver 17 decreases.

As a result, a positive voltage is generated in Vee according to the equation (13). It is assumed that this positive voltage is applied to the electric filter 31 to generate a positive integrated voltage. Light source drive circuit 32
Is controlled such that the light amount of the light source 11 is increased by the positive integrated voltage, the input of the electric filter 31, that is, the output Vee of the differential amplifier 28 is always zero. As a result, the following equation holds.

V _R = Io ² · K ² −Vc (14) FO obtained by operating such a light quantity stabilizing circuit
The output V ₁ of G is expressed by the following equation from the equations (3) and (14). _{V 1 = Io · K · sin} ΔΦs = sin ΔΦs · √ (V R -Vc) (15) This (15) when obtaining the linearity Li based on equation expressed by the following equation.

[0020] Li = [(sin ΔΦs · √ (V R -Vc) -ΔΦs · √V R) / (ΔΦs · √V R)] · 100 [%] (16) (16) the correction signal Vc in formula When it is zero, the same linearity as the conventional example is shown as shown in the graph of FIG. 4A.
Therefore, in order to improve this linearity, the correction signal Vc is generated by obtaining each coefficient in the equation (11) by the least square method so that the numerator of the equation (16) becomes zero with respect to the Sagnac phase difference ΔΦs. FIG. 4B shows a graph in which the linearity is improved by using the data of the output V _{1 in} the range where the Sagnac phase difference ΔΦs is up to 40 ° to find the coefficients up to the 4th order to generate the correction signal Vc.

FIG. 2A shows a concrete example of the correction signal generating circuit 34 for generating the correction signal Vc. First, the absolute value circuit 36
Signal V ₁ or X becomes | X |
The value of has been converted into an absolute value and has no relation to the polarity of the input angular velocity, but it can be implemented without expressing it as an absolute value. However, in this case, in order to make the correction accuracy the same,
A higher-order coefficient, that is, a multiplication means is further required in this example). The first-order correction signal Vc ₁ is multiplied by A ₁ by the amplifier 37, so that Vc ₁ = A ₁ · | X |, and the second-order correction signal Vc ₂ is squared by | X | in the _{double A, Vc 2 = A 2 ·} | X | 2 , and the 3
The next correction signal Vc ₃ is multiplied by the output of the multiplier 38 and | X | in the multiplier 41, multiplied by A _{3 in} the amplifier 42, and then Vc
₃ = A ₃ · | X | ³ and the fourth-order correction signal Vc ₄ becomes
The output of the multiplier 38 is squared by the multiplier 43, and the amplifier 44
Is multiplied by A ₄ , and Vc ₄ = A ₄ · | X | ⁴ . These correction signals are added by the adder 43 and output as a linear correction signal Vc. Here, the amplifiers 37, 39, 4
The gains A ₁ , A ₂ , A ₃ , and A ₄ of ₂ and 44 are set to the same values as the coefficients in the equation (11).

Incidentally, each coefficient of the correction signal in the graph shown in FIG. 4B is as follows. A ₀ = 0 A ₁ = 0.000997 A ₂ = -0.3324 A ₃ = 0.01106 A ₄ = -0.02808 The reference signal V _R is set to 3.162V. As described above, by adding the correction signal Vc to the signal Vs which has been conventionally used for stabilizing the scale factor, the linearity can be improved to within 0.001% (ΔΦs = 0 to 40 °). . In the above description, the output of the electric filter 31 is fed back to the light source drive circuit 32, but instead of the light source drive circuit 32, the light receiver 1
The same effect can be obtained by feeding back to the automatic gain adjustment circuit 46 inserted on the output side of 7 to control the gain (a part of Kpd) of the electric circuit in the expression (3).

FIG. 2B shows the essential parts of another embodiment of the present invention. Output Vss of adder 35 and reference voltage generator 4 in FIG.
The output V _R of No. 7 is subjected to the operation of the following equation in the divider 48. _{Vd = V R / Vss = V} R / (Io 2 -K 2 + Vc) (17) automatic gain controller in the output Vd of the divider 48 (AGC) 49
The gain is adjusted so that V ₁ becomes V ₁ ′. This V ₁ 'is given by the following equation.

V ₁ ′ = V ₁ · Vd = Io · K · sin ΔΦs / [1 + Vc / (Io ² · K ² )] (18) On the other hand, the linearity L of the output V ₁ ′ of the automatic gain controller 49
i is represented by _{Li = [(V 1 '-Io} · K · ΔΦs) / Io · K · ΔΦs] × 100 [%] (19).

Here, in order to improve the linearity,
The correction signal Vc may be generated so that the numerator of the equation (19) becomes zero with respect to the Sagnac phase difference ΔΦs. To do _{this, (V 1 '-Io · K} · ΔΦs) = 0 and becomes Vc correction signal generating circuit shown in calculated view 2A each coefficient by the least square method from the data of the amplifier 37,39,42,44
It suffices to set each amplification degree of.

In the above description, the optical coupler 14 and the phase modulator 16
However, it is also possible to use optical fiber couplers as the optical couplers 12 and 14 and to use the phase modulator 16 in which the optical fiber is wound around a cylindrical electrostrictive oscillator, for example. Further, although the phase detection frequency component is extracted from the output of the photodetector 17 by the synchronous detection circuit 19, it is generally sufficient to extract the odd harmonic component of the phase modulation frequency. Similarly, the synchronous detection circuit 24 extracts the second harmonic component of the phase modulation frequency from the output of the photodetector 17, but generally, the even harmonic component of the phase modulation frequency may be extracted.

[0027]

As described above, according to the first aspect of the invention, of the outputs from the light receiver 17, the sin of the Sagnac phase difference ΔΦs caused by the angular velocity applied to the optical path 15 is calculated.
A first demodulation means for demodulating the ΔΦs component and a second demodulation means for demodulating the cos ΔΦs component of the output from the light receiver 17;
A first arithmetic means for squaring and adding the output Vsin from the first demodulation means and the output Vcos from the second demodulation means, and A ₀ + A ₁ × Vsin + A ₂ × Vsin ² + A ₃ × Vsin ³
+ A ₄ × Vsin ⁴ + ... + An × Vsin ⁿ (An: coefficient), second calculating means, adding means for adding respective outputs from the first calculating means and the second calculating means, and the adding means. The output of the FOG is controlled by adjusting the gain of the electric circuit so that the output from the device becomes constant, and by controlling the amount of light reaching the light receiver, thereby suppressing the effects of the loss of the optical system that fluctuates depending on the ambient temperature. The scale factor was kept stable and the scale factor linearity for the input was greatly improved.

According to the invention of claim 2, when the initial setting value of the adding means in the invention of claim 1 is V _R and the output from the adding means is Vss, the output of the first demodulating means is adjusted in gain. The initial setting gain of the output means for outputting the output is multiplied by V _R / Vss, and the same effect as the invention of claim 1 can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the invention of claim 1;

2 is a block diagram showing a concrete example of a correction signal generating circuit in FIG. 1, and B is a block diagram showing an essential part of an embodiment of the invention of claim 2;

FIG. 3 is a block diagram showing a conventional optical interference angular velocity meter.

4A is a graph showing an example of scale factor linearity of a conventional apparatus, and FIG. 4B is a graph showing an example of scale factor linearity of the embodiment of the present invention.

Claims (4)

(57) [Claims] 1. An optical path that makes at least one round, branching means for passing clockwise light and counterclockwise light with respect to the optical path, and interference means for interfering the clockwise light and counterclockwise light propagating through the optical path. A phase modulation means for providing a phase change to the clockwise light and the counterclockwise light, which is arranged in cascade between the branching means and one end of the optical path, and the light intensity of the interference light as an electric signal. Of the optical receiver to be detected and the output from the optical receiver, sin ΔΦ of the Sagnac phase difference ΔΦs generated by the angular velocity input to the optical path
First demodulation means for demodulating the s component, second demodulation means for demodulating the cos ΔΦs component of the output from the photodetector, output Vsin from the first demodulation means and output Vcos from the second demodulation means And a first calculation means for squaring and adding, and A ₀ + A ₁ × Vsin + A ₂ × Vsin ² + A ₃ × Vsin ³ + A
₄ × Vsin ⁴ + ... + An × Vsin ⁿ (An: coefficient), second calculating means, adding means for adding respective outputs from the first calculating means and the second calculating means, An optical interference angular velocity meter comprising: a control unit that controls the output from the adding unit to be constant. 2. The optical interference angular velocity meter according to claim 1, wherein the control means is means for adjusting a gain of an electric circuit. 3. The optical interference angular velocity meter according to claim 1, wherein the control means is means for controlling the amount of light reaching the light receiver. 4. An optical path that makes at least one round, branching means for passing clockwise light and counterclockwise light to the optical path, and interference means for interfering the clockwise light and counterclockwise light propagating through the optical path. A phase modulating means for providing a phase change to the clockwise light and the counterclockwise light, which are arranged in cascade between the branching means and one end of the optical path, and an electric signal for the optical intensity of the interference light. Of the Sagnac phase difference ΔΦs caused by the angular velocity input to the optical path among the outputs from the photodetector detected as
first demodulation means for demodulating the s component, second demodulation means for demodulating the cos ΔΦs component of the output from the photodetector, output means for adjusting the output from the first demodulation means to a predetermined gain, A first calculating means for squaring and adding the output Vsin from the first demodulating means and the output Vcos from the second demodulating means, and A ₀ + A ₁ × Vsin + A ₂ × Vsin ² + A ₃ × Vsin ³ + A
₄ × Vsin ⁴ + ... + An × Vsin ⁿ (An: coefficient), second calculating means, adding means for adding respective outputs from the first calculating means and the second calculating means, When the initial setting value of the adding means is V _R and the output from the adding means is Vss, the initial setting gain of the output means is V
An optical interference gyro having a gain adjusting means for multiplying _R / Vss.