JPH06103188B2 - Optical interference gyro - Google Patents

Description

TECHNICAL FIELD The present invention relates to a zero-position serrodyne modulation optical interference angular velocity meter by a linear phase ramp method.

"Prior Art" As a wide dynamic range and low drift optical interference gyro, on one end side and the other end side of the optical fiber coil,
A biasing phase modulator and a ramp phase modulator each having a pair of electrodes formed for the optical waveguide are provided, and the biasing phase modulator and the ramp phase modulator are biasing voltage and sawtooth wave voltage for phase modulation. Is applied to give a phase difference between the two lights propagating through the optical fiber coil, and the phase difference between the two lights propagating through the optical fiber coil and interfering is detected from the output of the photodetector. It is considered that the polarity and frequency of the sawtooth wave voltage are controlled so that the phase difference becomes a predetermined value by the detection output.

FIG. 2 is an example of a conventional optical interference angular velocity meter of the null method serrodyne modulation method by such a linear phase ramp method.

The light 1 from the light source 11 is supplied to the optical splitter / combiner 15 through the optical coupler 13 and the polarizer 14 and is split into two lights 5a and 5b. The two lights 5a and 5b are one light 5a. From one end 17a of the fiber coil 17 to the other light 5b, the optical fiber coil 1
The light 5a is supplied from the other end 17b of the optical fiber coil 17 to the optical fiber coil 17, and the light 5a is propagated in the optical fiber coil 17 as the clockwise light and the light 5b is propagated in the optical fiber coil 17 as the counterclockwise light. Two lights 7a, 7b propagated through 17, one light 7a is supplied from the other end 17b of the optical fiber coil 17, and the other light 7b is supplied from the one end 17a of the optical fiber coil 17 to the optical branching coupler 15. And interfere with each other, and the resulting interference light 9 passes through a polarizer 14 and an optical coupler 13 to form a photodetector.
The point of being supplied to 19 and converted into an electric signal is the same as that of a general optical interference gyro.

Then, the optical splitter / coupler 15 and one end 17 of the optical fiber coil 17 are
A biasing phase modulator 21 is arranged between a and, a ramp phase modulator 22 is arranged between the optical branching coupler 15 and the other end 17b of the optical fiber coil 17, and a biasing phase modulator from the oscillator 31. The biasing voltage Bi is applied to the optical fiber coil 21 in the biasing phase modulator 21.
Light 5a supplied from one end 17a of 17 to the optical fiber coil 17
And the phase of the light 7b that propagates through the optical fiber coil 17 from the other end 17b of the optical fiber coil 17 and is supplied from the one end 17a of the optical fiber coil 17 to the optical branching / coupling device 15 is shifted and the sawtooth voltage The sawtooth wave voltage Ra is applied to the ramp phase modulator 22 from the generator 40, and the other end 17b of the optical fiber coil 17 in the ramp phase modulator 22 is applied to the optical fiber coil 1
Light 5b supplied to 7 and one end 17a of the optical fiber coil 17
From the optical fiber coil 17
The phase of the light 7a supplied from the other end 17b to the optical branching / coupling device 15 is deviated, and the output Va of the photodetector 19 is supplied to the phase difference detection control unit 50 having a configuration described later to be described later. In the phase difference detection control unit 50, the phase difference between the two lights 7a, 7b interfering in the optical branching / coupling unit 15 is detected, and the output Ve of the phase difference detection control unit 50 is supplied to the sawtooth wave voltage generation unit 40. The phase difference is set to a predetermined value, that is, the phase difference generated by applying the biasing voltage Bi to the biasing phase modulator 21 is removed from the phase difference, and input to the optical fiber coil 17. The phase difference Δφ of the sum of the Sagnac phase difference Δφs caused by the addition of the angular velocity Ω and the phase difference Δφr caused by the application of the sawtooth wave voltage Ra to the ramp phase modulator 22 becomes zero or an integral multiple of 2π radians. So in general Such that the polarity and frequency of the sawtooth wave voltage Ra is controlled.

As for the biasing voltage Bi, the light 5a, 5b is the optical fiber coil 17
Is a sinusoidal voltage having a half period of the time τ required to propagate the wave, and the phase modulation in the biasing phase modulator 21 by the sinusoidal voltage is as follows. A phase difference of π / 2 radians is given between 7a and 7b to set the operating point of the optical interference gyro.

The sawtooth wave voltage Ra becomes positive or negative as shown on the left side or the right side of FIG. 4, and the phase modulation in the ramp phase modulator 22 by the two waves propagates through the optical fiber coil 17 and interferes with each other. A phase difference Δφr of 2kπ radians (k = ± 1, ± 2 ...), which is a maximum of ± 2π radians, is given between the lights 7a and 7b to cancel the Sagnac phase difference Δφs as described above. .

That is, the two lights 7
The phase difference between a and 7b excluding the phase difference caused by applying the biasing voltage Bi to the biasing phase modulator 21 is represented by Δφ = Δφs + Δφr (1) as described above, As is well known, the Sagnac phase difference Δφs It is represented by. However, R is the radius of the optical fiber coil 17,
L is the optical fiber length in the optical fiber coil 17, λ is the wavelength of the light 5a, 5b propagating through the optical fiber coil 17, and C is the speed of light in vacuum.

Then, in the lamp phase modulator 22, the light 5b supplied from the other end 17b of the optical fiber coil 17 to the optical fiber coil 17 receives a phase shift φb according to the value of the sawtooth wave voltage Ra at that time, After a further time τ, the optical fiber coil 17
The light 7a propagating from the one end 17a of the optical fiber coil 17 to the optical branch coupler 15 from the other end 17b of the optical fiber coil 17 has a phase shift φa corresponding to the value of the sawtooth wave voltage Ra at that time. However, when the input angular velocity Ω is applied in the clockwise direction and the Sagnac phase difference Δφs becomes negative, the output Ve of the phase difference detection control unit 50 causes the sawtooth wave voltage Ra to change as shown on the left side of FIG. The phase shifts .phi.a and .phi.b are made positive, and the phase difference .DELTA..phi.r generated by applying the sawtooth wave voltage Ra to the ramp phase modulator 22 becomes positive. When the input angular velocity Ω is applied counterclockwise and the Sagnac phase difference Δφs becomes positive, the output Ve of the phase difference detection control unit 50 causes the sawtooth voltage Ra to become negative as shown on the right side of FIG. And the above phase shifts φa and φb are on the right side of FIG. As a result, the phase difference Δφr becomes negative.

Therefore, the period of the sawtooth wave voltage Ra is T, and the frequency is f _R
Then, as is clear from FIG. And the refractive index of the light in the optical fiber coil 17 is n, Because of the relationship Becomes Therefore, the polarity and frequency f _R of the sawtooth wave voltage Ra are controlled so that the phase difference Δφ represented by the equation (1) becomes zero, that is, Δφr = −Δφs (6). By Next to It is represented by. However, when the input angular velocity Ω is applied in the clockwise direction which is the negative direction and the sawtooth wave voltage Ra becomes positive, k becomes +1 and when the input angular velocity Ω is applied in the counterclockwise direction which is the positive direction, the sawtooth waveform When the wave voltage Ra becomes negative, k becomes -1.

Therefore, the direction and magnitude of the input angular velocity Ω can be measured from the polarity of the sawtooth wave voltage Ra and the frequency f _R.

The output Va of the photodetector 19 is the frequency of the biasing voltage Bi.
If fm and angular frequency are ωm, as is known It is represented by. However, Vdc is DC component, ka and kb are constant, J _2n
(X), J _{2n + 1} (x) is the Bessel coefficient of the first kind, and (9)
The first term of the equation is a direct current component, the second term is a frequency component of an even multiple of the frequency fm of the biasing voltage Bi, and the third term is a frequency component of an odd multiple of fm.

Then, in the phase difference detection control unit 50, this photodetector
From the output Va of 19: n = 0 of the third component of the equation (9)
Only the component of frequency fm at is extracted, the component of frequency fm is synchronously detected by the reference signal of the same frequency, and two lights 7a, 7
As the detection output of the phase difference between b, the detection output represented by Vd = Kc · J ₁ (x) sin Δφ (10) is obtained. However,
Kc is a constant.

However, as described above, since the polarity of the sawtooth wave voltage Ra and the frequency f _R are controlled so that the phase difference Δφ becomes zero,
As shown in FIG. 6, the frequency component Vm of the above fm included in the third term of the equation (9) has a very small level, whereas it is particularly included in the second term of the equation (9). The component Vs having a frequency of 2fm becomes a considerably large level, and in addition, as described above, the biasing voltage Bi generally has a half period of the time τ required for the light 5a and 5b to propagate through the optical fiber coil 17, and fm = 1 / Since 2τ is set to (11), substituting equation (4) into this, fm = C / 2nL (12), and specifically, the refractive index n of the light in the optical fiber coil 17 is set to 1.47, If the optical fiber length L in the optical fiber coil 17 is 300 meters, fm will be made considerably high so that fm will be about 340 kHz. Therefore, when the output Va of the photodetector 19 is directly supplied to the bandpass filter having the center frequency of fm, the passband width of the bandpass filter becomes wide, and therefore the frequency component Vs of 2fm from the output Va. Cannot be reliably removed to extract only the frequency component Vm of fm at a sufficient level.

Therefore, in the phase difference detection control unit 50, the output Va of the photodetector 19 is mixed with a signal having a frequency slightly deviated from fm to convert the frequency component Vm of fm into a frequency sufficiently lower than fm. Then, the mixed output is supplied to a bandpass filter whose center frequency is a frequency sufficiently lower than fm, so that only the component converted to a frequency sufficiently lower than fm is extracted, and this is a reference signal of the same frequency. The detection output Vd represented by the equation (10) is obtained by the synchronous detection by.

That is, specifically, as shown in FIG.
The output Va of 19 is supplied to the preamplifier circuit 51, and its direct current component
After Vdc is removed and the AC component is amplified, the AC component is supplied to the frequency mixing circuit 52, and the frequency is sufficiently lower than fm with respect to fm as shown in FIG. 6 obtained from the oscillator 32. As shown in FIG. 7, the signal Vca is mixed with the signal SCa having a frequency fca higher than fr, and the output Vc of the frequency mixing circuit 52 is obtained by converting the component Vm of the frequency fm described above into the frequency of fr. The frequency component Vm of the frequency of 2h is converted to the frequency of fh = 2fm + fr, and the frequency component Vs of the frequency of 2fm is fm.
The output Vc of the frequency mixing circuit 52 is obtained by including the component Vl converted to the frequency fcb which is lower by fr than
It is supplied to a bandpass filter 53 having fr as a center frequency. fr is set to 10 kHz, for example. In this way, fr, which is the center frequency of the bandpass filter 53, is made significantly lower than fm, and the passband width of the bandpass filter 53 can be sufficiently narrowed, and among the components of the output Vc of the frequency mixing circuit 52, fcb (= fm−f except for the frequency component Vr of fr
r) or more, so that only the frequency component Vr of fr, that is, the frequency component Vm of fm in the output Va of the photodetector 19 is converted to the frequency of fr from the bandpass filter 53. Only is taken out.

The frequency component Vr of fr taken out from the bandpass filter 53 is supplied to the AC amplification circuit 54 and amplified to a sufficient level, and then supplied to the synchronous detection circuit 55 by the reference signal Sr of the frequency of fr. Synchronous detection, synchronous detection circuit 55
From the two light 7a, 7b
As the detection output of the phase difference between the two, the detection output Vd represented by the equation (10) is obtained. The output Vd of the synchronous detection circuit 55 is supplied to the PID filter (proportional-integral-derivative filter) 56, and the output Ve of the PID filter 56 is supplied to the sawtooth wave voltage generator 40 as the output of the phase difference detection controller 50. As described above, the sawtooth wave voltage Ra is set so that the phase difference Δφ becomes zero.
The polarity and frequency f _R of the

In the frequency mixing circuit 52, a signal S having a frequency of fca = fm + fr
The same applies when the signal Scb having a frequency of fcb = fm-fr is mixed with the output Va of the photodetector 19 from which the DC component Vdc has been removed in the preamplifier circuit 51, instead of ca.

The reference signal Sr of the frequency of fr for the synchronous detection is the signal Sca or Scb of which the frequency of the output of the oscillator 31 is fm and the frequency of the output of the oscillator 32 is fca = fm + fr or fcb = fm−fr. Are mixed in the frequency mixing circuit 33, and a signal of frequency fr and 2fm from the frequency mixing circuit 33 are mixed.
+ Fr frequency signal or fr frequency signal and 2fm
A signal with a frequency of −fr is obtained, the output of the frequency mixing circuit 33 is supplied to a bandpass filter 34 having a center frequency of fr, and only the signal with a frequency of fr is extracted from the bandpass filter 34. It is supplied to the circuit 35 and is obtained from the waveform shaping circuit 35 as a rectangular wave signal having a frequency of fr.

[Problems to be Solved by the Invention] The sawtooth wave voltage Ra applied to the ramp phase modulator 22 is shown as an ideal sawtooth wave voltage with a flyback time of zero in FIG. In this way, it is impossible to make the flyback time of the sawtooth wave voltage Ra zero, and the sawtooth wave voltage Ra has a flyback time of several tens of nanoseconds or more. In addition, due to problems in the characteristics of the sawtooth wave voltage generator 40 and the ramp phase modulator 22, the phase difference Δ
It is practically impossible to make the maximum value of φr exactly ± 2π radians.

Since the sawtooth wave voltage Ra has a flyback time and the maximum value of the phase difference Δφr does not exactly become ± 2π radian, the two lights 7a that propagate through the optical fiber coil 17 and interfere with each other. , 7b has an error component consisting of a fundamental wave component of the frequency f _R of the sawtooth wave voltage Ra and a harmonic component of a frequency that is an integral multiple thereof, and this error component is output from the photodetector 19. During Va, as shown in FIG.
fm frequency component Vm appears as upper sideband components U1, U2 ... And lower sideband components L1, L2 ..
Since the frequency f _R is changed according to the input angular velocity Omega, the upper sideband components U1, U2 ... and lower side bands components L1, L2 ... also the frequency of the changes according to the input angular velocity Omega.

Therefore, when f _R becomes equal to twice the frequency fr of the reference signal Sr for the above-mentioned synchronous detection in the phase difference detection control unit 50, as shown in FIG. 9, the upper sideband component U1 or the lower sideband component L1 is fia = fm + 2fr or fib = fm−2, respectively
When the frequency is equal to fr, and 3 times f _R is equal to 2 times fr, the upper sideband component U3 or the lower sideband component L3 coincides with the frequency of fia or fib, respectively, as shown in FIG. Thus, under a specific input angular velocity that is generally f _R −2fr / n (n = 1,2,3 ...), the upper sideband components U1, U2 ...
, Or any of the lower sideband components L1, L2 ... Is mixed with the output Va of the photodetector 19 in the frequency mixing circuit 52 of the phase difference detection control unit 50 as described above.
Or, in accordance with the frequency fia or fib which is the image frequency of fm with respect to the frequency fca or fcb of Scb, and is mixed with the signal Sca or Scb in the frequency mixing circuit 52, together with the above-described frequency component Vm of fm. The frequency of fr is converted, and the sideband wave component converted to the frequency of fr is amplified by the AC amplification circuit 54 through the bandpass filter 53 and supplied to the synchronous detection circuit 55, whereby the output of the optical interference angular velocity meter Causes a scale factor error.

However, as shown in FIG. 9, the scale factor error is such that the upper sideband component U1 or the lower sideband component L1 corresponding to the fundamental wave component of the frequency f _R of the sawtooth wave voltage Ra is fi respectively.
It appears most when it matches the frequency of a or fib,
As shown in FIG. 10 as an example, it generally becomes small when the upper sideband component or the lower sideband component corresponding to the harmonic component matches the frequency of fia or fib, respectively.

Further, the lamp phase modulator 22 is generally configured by forming a single mode optical waveguide by diffusion of titanium or the like in an electro-optic crystal made of lithium niobate, etc., and forming a pair of electrodes with respect to the optical waveguide. , When the sawtooth wave voltage Ra is applied between the pair of electrodes, the refractive index of the optical waveguide is changed and the phase of the light passing through the optical waveguide is deviated. Part of the light leaks from the optical waveguide according to the applied voltage value, and consequently the intensity of light passing through the optical waveguide is modulated by the sawtooth wave voltage Ra, and the change in the intensity is in the output Va of the photodetector 19, As shown in FIG. 11, it occurs as the fundamental wave component R ₁ of the frequency f _R of the sawtooth wave voltage Ra and the harmonic components R ₂ ... Rn ... Of the integral multiple frequency.

Therefore, under a specific input angular velocity, the fundamental wave component
When R ₁ or the harmonic component R ₂ ... Rn ... matches the above-mentioned frequency of fia or fib, the fundamental wave component R ₁ or the harmonic component R ₂ ... Rn ... of the frequency mixing circuit of the phase difference detection control unit 50. At 52, the signal Sca and Scb are mixed with each other to be converted to a frequency of fr together with the above-described frequency component Vm of fm, and the fundamental wave component or the harmonic component converted to the frequency of fr is band-pass filter 53. Through, is amplified by the AC amplification circuit 54 and supplied to the synchronous detection circuit 55, so that a scale factor error occurs in the output of the optical interference gyro.

Figure 12 shows the scale factor error described above, where fr is
This is the case when set to 10 kHz. Frequency f of sawtooth wave voltage Ra
The output pulse number of the optical interference angular velocity meter corresponding to _R changes according to the input angular velocity Ω, but the scale factor of the output of the optical interference angular velocity meter, that is, the number of output pulses per rotation of the optical interference angular velocity meter is the input angular velocity Ω. It should be constant regardless of. However, the maximum value of the phase difference Δφr is accurate because the flyback time exists in the sawtooth wave voltage Ra as described above, or because of the characteristic problem of the sawtooth wave voltage generator 40 or the ramp phase modulator 22. Is not ± 2π radians, or the intensity of light passing through the optical waveguide in the ramp phase modulator 22 is modulated by the sawtooth wave voltage Ra, as shown in FIG. Therefore, the number of output pulses per rotation of the optical interference angular velocity meter deviates from a predetermined number, and a scale factor error occurs in the output of the optical interference angular velocity meter. In the figure, the reason why a particularly large scale factor error occurs under an input angular velocity of 34 ° / sec. Corresponds to the fundamental wave component of the frequency f _R of the sawtooth wave voltage Ra as described in FIG. This is because the upper sideband component U1 or the lower sideband component L1 matches the frequency of fia or fib, respectively.

Therefore, in the present invention, the flyback time is present in the sawtooth wave voltage for phase modulation applied to the ramp phase modulator in the optical interferometric gyro of the null method serrodyne modulation method by the linear phase ramp method as described above. It is possible to significantly reduce the scale factor error that occurs in the output of the optical coherence gyro under a specific input angular velocity due to various causes such as, and remarkably improve the linearity of the input / output characteristics of the optical coherence gyro. It was made possible.

[Means for Solving the Problem] In the present invention, the frequency of the sawtooth wave voltage is oscillated by adding the external signal to the output of the phase difference detection control unit and supplying it to the sawtooth wave voltage generation unit.

The external signal may be a composite of sine wave signals of a plurality of frequencies or a sine wave signal of a single frequency as long as it vibrates the frequency of the sawtooth wave voltage, but random noise is most preferable.

[Operation] In the optical interference angular velocity meter of the present invention configured as described above, the frequency of the sawtooth wave voltage oscillates due to an external signal even under a specific input angular velocity, that is, the frequency of the sawtooth wave voltage. Can be changed in both the increasing and decreasing directions, so the sawtooth voltage is due to the phase difference between the two lights that propagate and interfere in the fiber optic coil due to the flyback time of the sawtooth voltage. Error component that consists of the fundamental wave component of the frequency and the harmonic component of the frequency that is an integral multiple of this, and this error component is generated in the output of the photodetector.The upper sideband component and the lower sideband component of the biasing voltage frequency component. , Or the intensity of light passing through the optical waveguide in the lamp phase modulator is modulated by the sawtooth voltage, and the change in the intensity is the frequency of the sawtooth voltage in the output of the photodetector. Even if it appears as a fundamental wave component of and a harmonic component of a frequency that is an integral multiple thereof, under a specific input angular velocity,
The upper sideband component, the lower sideband component, the fundamental wave component, or the higher harmonic component appearing in the output of the photodetector is biased to the frequency of the signal mixed with the output of the photodetector in the phase difference detection control unit. By matching the image frequency with the specific frequency, the probability of being converted into a predetermined frequency together with the frequency component of the biasing voltage and being supplied to the synchronous detection circuit through the band pass filter is significantly reduced. Moreover, by changing the frequency of the sawtooth wave voltage in both the increasing direction and the decreasing direction, the positive scale factor error and the negative scale factor error cancel each other out. Therefore, the scale factor error that occurs in the output of the optical interference angular velocity meter under a specific input angular velocity is significantly reduced, and the linearity of the input / output characteristics of the optical interference angular velocity meter is significantly improved.

"Embodiment" FIG. 1 is an example of the optical interference angular velocity meter of the present invention.

Light source 11, optical coupler 13, polarizer 14, optical branching coupler 15, optical fiber coil 17, photodetector 19, biasing phase modulator
21, a ramp phase modulator 22, an oscillator 31 constituting a biasing voltage generator, a sawtooth wave voltage generator 40 and a phase difference detection controller 50 are provided, and the phase difference detection controller 50 is Specifically, the preamplification circuit 51, the frequency mixing circuit 52, the bandpass filter 53, the AC amplification circuit 54, the synchronous detection circuit 55, and the PID filter 56 are included in the conventional optical circuit shown in FIG. This is the same as the interference angular velocity meter, and its operation is the same as that of the conventional optical interference angular velocity shown in FIG. 2 except that the frequency f _R of the sawtooth wave voltage Ra is vibrated by the external signal Vn as described later. It is the same as the total.

However, the sawtooth wave voltage generation unit 40, in this example,
A voltage-current conversion circuit 42 that converts an output voltage Vf of a capacitor 41 and an external signal generation / addition unit 60, which will be described later, which is an input voltage of the sawtooth wave voltage generation unit 40, into a current and supplies the current to the capacitor 41.
And a switch 43 for discharging the capacitor 41, and a capacitor
The voltage comparison circuit 45 that compares the charging voltage of 41 with the positive reference voltage + Vpr, and the charging voltage of the capacitor 41 with the negative reference voltage −Vm
voltage comparison circuit 46 to compare with r and voltage comparison circuits 45 and 4
OR gate 47 that obtains the logical sum of the outputs of 6 and OR gate 47
The output voltage Ve of the phase difference detection control unit 50 becomes positive, and the output voltage Vf of the external signal generation addition unit 60 becomes positive. When the charging voltage reaches the reference voltage + Vpr, the output of the voltage comparison circuit 45, and thus the output of the OR gate 47 rises from the low level to the high level, and the monostable multivibrator 48 becomes By repeating the operation of being triggered, turning on the switch 43 and discharging the capacitor 41, a positive sawtooth voltage whose maximum value is equal to the reference voltage + Vpr as the sawtooth voltage Ra across the capacitor 41. When the output voltage Ve of the phase difference detection control unit 50 becomes negative and the output voltage Vf of the external signal generation addition unit 60 becomes negative, the capacitor 41 is charged negatively. It is, when the charging voltage reaches the reference voltage -Vmr, the output of the voltage comparator circuit 46,
Therefore, the output of the OR gate 47 rises from the low level to the high level, the monostable multivibrator 48 is triggered, the switch 43 is turned on, and the operation of discharging the capacitor 41 is repeated. The minimum value of the wave voltage Ra is the reference voltage −Vmr
A negative sawtooth voltage equal to is obtained.

In this case, as the switch 43, a switching element such as a field effect transistor having a sufficiently small leak current in the off state and a resistance in the on state is used, and the time during which the switch 43 is turned on, that is, the sawtooth shape. The time constant of the monostable multivibrator 48 is set so that the flyback time of the wave voltage Ra is sufficiently short.

Further, in the present invention, the external signal generation / addition unit 60 is provided between the phase difference detection control unit 50 and the sawtooth wave voltage generation unit 40. The external signal generation adder 60 is an external signal generation circuit.
61 and the external signal Vn obtained from the phase difference detection controller
The output voltage Ve of 50 is added, and the added voltage Vf is used as the output voltage of the external signal generation / addition unit 60 to generate a sawtooth wave voltage.
It is composed of an adder circuit 62 for supplying to 40. As the external signal Vn, specifically, random noise is used,
As a result, the frequency f _R of the sawtooth wave voltage Ra obtained from the sawtooth wave voltage generator 40 is oscillated.

Since the by external signals Vn even under particular input angular frequency f _R of the sawtooth wave voltage Ra oscillates, i.e. changed to both the decreasing direction and the frequency f _R is the increasing direction of the sawtooth wave voltage Ra Therefore, because the flyback time exists in the sawtooth voltage Ra, or the sawtooth voltage generator 40
Due to the problem of characteristics of the lamp phase modulator 22 and the like, two lights 7a and 7b which propagate through the optical fiber coil 17 and interfere by applying the sawtooth wave voltage Ra to the lamp phase modulator 22.
Since the maximum value of the phase difference Δφr that occurs between the two is not exactly ± 2π radians, the sawtooth wave voltage Ra depends on the phase difference between the two lights 7a and 7b propagating through the optical fiber coil 17 and interfering with each other.
Error component consisting of the fundamental wave component of the frequency f _R and the harmonic component of the frequency that is an integral multiple thereof is generated in the output Va of the photodetector 19 as shown in FIG. Although appearing as upper sideband components U1, U2 ... And lower sideband components L1, L2 ... Of the component Vm of frequency fm, or the intensity of light passing through the optical waveguide in the ramp phase modulator 22 is modulated by the sawtooth voltage Ra. Then, the change in the intensity is reflected in the output voltage Va of the photodetector 19 as shown in FIG.
Of the fundamental wave component R ₁ of the frequency f _R and the harmonic component R ₂ ... Rn ... of the frequency that is an integral multiple thereof, appear in the output Va of the photodetector 19 under a specific input angular velocity. upper sideband components U1, U2 ... or lower sideband components L1, L2 ... or the fundamental wave component R ₁ or harmonic component R ₂ ... Rn ... the phase difference detection control unit
The frequency component of fm by matching the frequency fia or fib which becomes the image frequency of fm with respect to the frequency fca or fcb of the signal Sca or Scb mixed with the output Va of the photodetector 19 in the frequency mixing circuit 52 of 50. Converted to the frequency of fr together with Vm, band pass filter 53 and AC amplification circuit
The probability of being supplied to the synchronous detection circuit 55 through 54 is significantly reduced. Moreover, by changing the frequency of the sawtooth wave voltage Ra in both the increasing direction and the decreasing direction, the positive scale factor error and the negative scale factor error cancel each other out. Therefore, the scale factor error that occurs in the output of the optical interference angular velocity meter under a specific input angular velocity is significantly reduced, and the linearity of the input / output characteristics of the optical interference angular velocity meter is significantly improved.

Specifically, when random noise is used as the external signal Vn, the scale factor error is reduced to about 1/5 of the conventional one.

A filter having the same function may be used instead of the PID filter 56 of the phase difference detection control unit 50.

As described above, according to the present invention, the frequency of the sawtooth wave voltage is oscillated by adding the external signal to the output of the phase difference detection control unit and supplying it to the sawtooth wave voltage generation unit. Therefore, due to various factors such as the presence of flyback time in the sawtooth voltage for phase modulation applied to the ramp phase modulator, the scale factor error that occurs in the output of the optical interferometer gyro under a specific input angular velocity. Can be significantly reduced, and the linearity of the input / output characteristics of the optical interference gyro can be significantly improved.

[Brief description of drawings]

FIG. 1 is a system diagram showing an example of the optical interference angular velocity meter of the present invention, FIG. 2 is a system diagram showing an example of a conventional optical interference angular velocity meter, and FIGS. 3, 4, and 5 are FIG. 6, FIG. 7 and FIG. 7 which show aspects of the biasing voltage, the sawtooth wave voltage, and the phase shift of light in the ramp phase modulator, respectively.
FIG. 8, FIG. 9, FIG. 10, FIG. 10 and FIG. 11 are diagrams showing the frequency relationship of the components contained in the output of each photodetector and the signals mixed with them, and FIG. It is a figure which shows the example of the scale factor error which occurs in an output in the conventional optical interference angular velocity meter shown in FIG.

Claims (2)

[Claims] 1. A light source, an optical fiber coil, and light from the light source is branched into two and supplied to the optical fiber coil from one end and the other end of the optical fiber coil, and propagates through the optical fiber coil. The optical branching / coupling device for interfering the two light beams, the photodetector for detecting the interference light obtained from the optical branching / coupling device, and the optical branching / coupling device and one end of the optical fiber coil. A biasing phase modulator, a biasing voltage generator that generates a biasing voltage for phase modulation applied to the biasing phase modulator, and the biasing phase modulator are arranged between the optical branch coupler and the other end of the optical fiber coil. A ramp phase modulator, a sawtooth wave voltage generator that generates a sawtooth wave voltage for phase modulation applied to the ramp phase modulator, and the optical component from the output of the photodetector. Phase difference detection control that detects the phase difference between two light beams that interfere in the coupler, and controls the oscillation frequency of the sawtooth wave voltage generator so that the phase difference converges to a predetermined value based on the detection output. And a sawtooth wave voltage generator that generates an external signal, adds the external signal to the output of the phase difference detection control unit, and supplies the added signal to the sawtooth wave voltage generation unit. An optical interference gyro that is provided with an external signal generation adder that vibrates the frequency of. 2. The optical interference angular velocity meter according to claim 1, wherein the external signal is random noise.