JP2724081B2 - Phase modulation optical fiber gyro - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber gyro for detecting an angular velocity using an optical fiber.
In particular, the present invention relates to a small-sized optical fiber gyro which is mounted on a moving body such as an automobile and is suitable for detecting an azimuth or the like.

[0002]

2. Description of the Related Art As a sensor for detecting an angular velocity, a gyro (gyroscope) has been conventionally known. In recent years, an optical fiber gyro has been put into practical use as a solid-state gyro. JP-A-63-314410 can be mentioned.

What is shown here is a basic configuration of a phase modulation type optical fiber gyro. In this case, adjustment of a drive voltage of a phase modulator uses a voltage regulator using a variable gain characteristic such as a multiplier. Therefore, when an inexpensive multiplier is used, AC waveform distortion occurs in the multiplier unit.

[0004] Further, although not particularly described in Japanese Patent Application Laid-Open No. H07-157, conventionally, the light output of the coherent light source is adjusted by directly detecting the light output of the coherent light source or by adjusting the amount of light incident on the optical fiber. Has been detected via an optical splitter, and the detection value has been controlled to be constant.

[0005]

The above-mentioned prior art does not consider the waveform distortion of the driving voltage of the phase modulator, and this causes a problem that an offset occurs in the output of the sensor or a scale fluctuation occurs. Was.

In addition, since the output of the coherent light source or the amount of incident light on the optical fiber is controlled to be constant, the signal light, which is the true output of the optical system, is constant due to the fluctuation of the branching ratio of the optical branching section. However, as a result, there is a problem that the offset value of the output of the sensor fluctuates or the scale fluctuates as in the case where the drive voltage has waveform distortion.

An object of the present invention is to provide an inexpensive and high-performance phase modulation type optical fiber gyro.

[0008]

In order to achieve the above object, the driving voltage of the phase modulator is adjusted by providing a subtracting amplifier and an analog switch type AC converter to prevent the occurrence of waveform distortion of the phase modulator. It was done.

In adjusting the output of the coherent light source, the output of the coherent light source is adjusted so that the AC amplitude of the photoelectric conversion signal of the signal light is detected and its value becomes constant.

[0010]

The driving voltage of the phase modulator is adjusted by driving the analog switch with a precise square wave having a duty of 50% to reduce harmful even harmonic components contained in the driving voltage to zero.
By driving the phase modulator with an AC voltage having no even harmonic component, occurrence of an offset in the sensor output and scale fluctuation are prevented.

In adjusting the output of the coherent light source, the signal light is kept constant by controlling the AC amplitude value of the photoelectric conversion signal to be constant, thereby preventing offset fluctuation and scale fluctuation of the sensor output.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a phase modulation type optical fiber gyro according to the present invention will be described in detail with reference to the drawings.

First, the structure will be described. FIG. 1 shows an embodiment of the present invention, which is roughly divided into a coherent light source 1, optical splitters 2a and 2b, a polarizer 3, an optical fiber loop 4,
The optical system comprises a phase modulator 5 and a signal processing unit other than the optical system. The optical system is almost the same as that of the related art, and a different part from the related art is a signal processing unit.

In FIG. 1, the coherent light source 1 of the optical system is, for example, a general laser diode or a super-light emitting diode, and the optical splitters 2a and 2b are beam splitters by evanescent coupling using optical fibers. Also,
The polarizer 3 is obtained by winding a special optical fiber in a coil shape to have polarization characteristics. The optical fiber loop 4 is formed by winding an optical fiber having a total length of several hundred meters in a coil shape. The phase modulator 5 provides a phase change by winding an optical fiber having a length of several meters around a cylindrical electrostrictive element, and changing the optical path length by changing the length of the optical fiber in accordance with a dimensional change of the electrostrictive element due to an electric signal. And functions as AC light phase bias means. The optical fiber is, for example, a single-mode polarization maintaining optical fiber.
These components are connected by fusing optical fibers to each other.

The photoelectric conversion section 6 of the signal processing section mainly comprises a photodiode and a current-voltage conversion section, and converts signal light output from the optical system into a signal voltage E1. The synchronous detector 7a is composed of, for example, an analog switch and a low-pass filter having a predetermined amplification degree. The synchronous detector 7a multiplies the signal voltage E1 by a synchronous signal E2a output from the signal generator 10, and generates a phase modulator included in the signal voltage E1. The AC component (primary component) having the same frequency as the frequency of the drive voltage E3 of No. 5 is detected and smoothed and output as a voltage Eout. The synchronous detectors 7b and 7c are the same as the synchronous detector 7a. The synchronous detector 7b detects a secondary AC component included in the signal voltage E1, and the synchronous detector 7c detects a fourth AC component included in the signal voltage E1. The signals are detected and smoothed to output voltages E4 and E5. Here, the voltage Eout is the only output of this embodiment, and the object of the present invention can be achieved if the voltage Eout can always be made proportional to the input angular velocity Ωin.

The signal generator 10 generates synchronization signals E2a and E2.
b, E2c are output. In the case of this embodiment,
The waveforms of the synchronization signals E2a, E2b, E2c are preferably square waves with a duty of 50%. The fundamental frequency of the synchronization signal E2a is equal to the fundamental frequency of the drive voltage E3,
b is twice the fundamental frequency of the drive voltage E3, and the synchronization signal E2c
Is four times the fundamental frequency of the drive voltage E3. Subtracting part 8a
The amplifier 9a amplifies a subtraction value E6 obtained by subtracting E4 from the voltage E5, and outputs a voltage E7. The analog switch 11 opens and closes in synchronization with the synchronization signal E2a, and is, for example, a CMOS switch. The analog switch 11 has a DC voltage E7.
Is intermittently converted to a square wave voltage E8. The waveform shaping unit 12 removes the harmonic components of the square wave voltage E8 and obtains a sine wave having a predetermined phase of only the first-order component as much as possible. For example, a low-pass filter or a notch filter (band elimination filter) And a phase adjuster for outputting a drive voltage E3 for the phase modulator 5.

In the above signal processing section, the synchronous detector 7
The other part except a serves to drive the phase modulator 5 at a predetermined modulation factor, and is an embodiment of the phase modulation control means of the first invention.

The AC amplitude detector 13 detects the AC amplitude of the signal voltage E1 and converts it to DC to output a voltage E9. For example, a peak value detector, a half-wave and full-wave rectifier are used. is there. The subtraction unit 8b subtracts the voltage E9 from the target value E10 to obtain a subtraction value E11. The amplifier 9b amplifies the subtraction value E11 and outputs a voltage E12. Here, the amplifiers 9a and 9b have, for example, an integral characteristic, a differential characteristic, a proportional amplification characteristic, or a combination of these characteristics. The power amplification unit 14 is a simple impedance converter, and converts the voltage E12 into a drive current E13 of the coherent light source 1.

The AC amplitude detector 13, the subtracting unit 8b, the amplifying unit 9b, and the power amplifying unit 14 control the drive current E13 of the coherent light source 1 so that the signal light output from the optical system becomes constant. This is an embodiment of the light output control means of the second invention.

More specifically, the subtraction sections 8a,
Amplifying section 9a, analog switch 11, and waveform shaping section 1
FIG. 2 shows an example of a case where the part 2 is constituted by analog parts. In the figure, resistors R1, R2
The integrator portion including the capacitor C1 and the operational amplifier OA1 corresponds to the subtracting unit 8a and the amplifying unit 9a in FIG. 1, and has a configuration in which the amplification characteristic is an integration characteristic. In this case, it is better if the polarities of the voltages E5 and E4 are opposite to each other, and this integrator integrates the difference between the voltages E5 and E4 to output the voltage E7. The analog switch 11 includes switches SW1 and SW2 that are turned on and off by synchronous signals E2a and E2aa whose phases are inverted with each other. When the switches SW1 and SW2 are turned on alternately, the DC voltage E7 becomes a square wave with a duty of 50%. Is converted.
The inverter IN1 simply inverts the synchronization signal E2a to generate a synchronization signal E2aa. The signal generator 10 is shown in FIG.
Is the same as As described above, the waveform shaping unit 12 is, for example, a notch filter whose frequency is twice, three times, or four times the fundamental frequency of the voltage E8, and a low-pass filter whose cutoff frequency is about twice the fundamental frequency. It comprises a constant gain phase shifter, an amplifier with low output impedance, etc., and outputs a sine-wave drive voltage E3 by removing harmonic components of the square wave voltage E8. Further, the phase of the drive voltage E3 is shifted with respect to the phase of the synchronization signal E2a, so that the phase of the synchronization signals E2a, E2b, and E2c and the phase of the signal voltage E1 become the same.

When the subtraction section 8b and the amplification section 9b in FIG. 1 are constituted by analog parts, the subtraction section 8a and the amplification section 9
a, and the resistors R1 and R2 shown in FIG.
2, a circuit of the capacitor C1 and the operational amplifier OA1.

FIG. 3 shows an example in which the AC amplitude detector 13 is constituted by analog parts. The figure shows an example in which the AC amplitude detector 13 is a half-wave rectifier circuit. In the figure, resistors R3 and R4
The operational amplifier OA2 and the diode D1 detect the one-sided amplitude of the signal voltage E1 and make the alternating current a pulsating current.
The portions of the resistors R5 and R6 and the capacitor C2 are circuits for smoothing the pulsating current to make it DC. Here, the voltage E9 is a negative DC voltage proportional to the amplitude of the signal voltage E1. The resistors R3 and R4 adjust the resistance value of each resistor to change the amplification. For example, the resistor R4 is set to 0Ω,
When the resistor R3 is opened, the amplification becomes 1.

Hereinafter, the operation of the embodiment will be described in detail. Here, the basic operation of the phase modulation type optical fiber gyro will be described.
When the frequency and amplitude of the drive voltage E3 are set to predetermined values in consideration of the entire length of the optical fiber of the optical fiber loop 4, if the input angular velocity Ωin is applied to the entire optical system or the portion of the optical fiber loop 4, the Sagnac effect is generated. The amplitude of each of various frequencies included in the signal light changes. A signal obtained by photoelectrically converting the signal light, that is, various frequency components included in the signal voltage E1 output from the photoelectric conversion unit 6 are represented by the following equations. A1 = Kp · sinKsΩin · J1 (Km) · cosω (t−τ / 2) (Equation 1) A2 = Kp · cosKsΩin · J2 (Km) · cos2ω (t−τ / 2) (Equation 2) A3 = −Kp · sinKsΩin · J3 (Km) · cos3ω (t−τ / 2) ··· (Equation 3) A4 = −Kp · cosKsΩin · J4 (Km) · cos4ω (t−τ / 2) ··· (Equation 4) A5 = Kp · sinKsΩin · J5 (Km) · cos5ω (t−τ / 2) (Equation 5) A6 = Kp · cosKsΩin · J6 (Km) · cos6ω (t−τ / 2) (Equation 6) Here, A1 A6 is the amplitude for each angular frequency component, Kp is a variable related to the magnitude and photoelectric conversion rate of the signal light, Ks is a Sagnac effect, that is, a constant related to the sensitivity of the optical system,
Ωin is the input angular velocity, J1 (Km) to J6 (Km) are Bessel functions, ω is the angular velocity of the fundamental frequency of the drive voltage E3,
t is time, and τ is the time required for light to pass through the optical fiber loop.

Further, Equations 1 to 6 will be described.
Equation 1 is a mathematical expression representing one time the fundamental frequency of the drive voltage E3 included in the signal voltage E1, ie, the magnitude of the primary harmonic component equal to the primary component, and Equation 2 is the equation of the drive voltage E3 included in the signal voltage E1. A mathematical expression representing twice the fundamental frequency, that is, the magnitude of the secondary harmonic component equal to the secondary component. Similarly, Equation 3 represents the third harmonic component contained in the signal voltage E1, and Equation 4 represents the signal voltage E1. The fourth harmonic component included, Equation 5 is the fifth harmonic component included in the signal voltage E1, and Equation 6 is 6 included in the signal voltage E1.
This is a mathematical expression representing the magnitude of the next harmonic component. Note that the number is actually represented by an infinite number of mathematical expressions.

The output voltage Eout of the synchronous detector 7a
Is expressed by an equation, as shown in Equation 7, K
By multiplying by a · cosω (t−τ / 2), the AC term is removed (the effect of the low-pass filter). Similarly,
When the voltages E4 and E5 of the outputs of the synchronous detectors 7b and 7c are expressed by equations, they are as shown in Expressions 8 and 9.

Eout = Ka · Kp · sinKsΩin · J1 (Km) (Equation 7) E4 = Kb · Kp · cosKsΩin · J2 (Km)… (Equation 8) E5 = −Kc · Kp · cosKsΩin · J4 (Km) (Equation 9) Here, Ka, Kb, and Kc are synchronous detectors 7a, 7b, and 7 respectively.
c is the degree of amplification.

Therefore, according to equation (1), the input angular velocity Ω
It can be seen that it is necessary to keep Ka, Kp, Ks, and J1 (Km) constant in order to obtain an accurate voltage Eout proportional to sin of in. Since Ka and Ks are inherently hard-to-change constants, there is no need to control them at all, but Kp is a variable related to optical output, J1 (Km) is a function related to the degree of phase modulation, and both are very variable. Therefore, some control is required. J1
The part for keeping (Km) constant is the phase modulation control means of the first invention, and the part for keeping Kp constant is the light output control means of the second invention.

First, an embodiment of the phase modulation control means of the first invention will be described in detail. As described above, the variable Km of the Bessel function J1 (Km) is a variable related to the degree of phase modulation, and is changed by changing the degree of phase modulation.
The value of 1 (Km) can be adjusted. Therefore,
By keeping the phase modulation constant, Km becomes constant, and the value of J1 (Km) becomes constant. As one method of keeping Km constant, paying attention to the fact that the degree of change of J2 (Km) and J4 (Km) in Equations 8 and 9 does not match when Km changes, J2 (Km) and J4 ( Km), there is a method of adjusting the drive voltage E3 of the phase modulator 5 so that the ratio becomes constant.

As a method of comparing J2 (Km) and J4 (Km) to obtain a ratio, a divider is generally used. However, since a high-precision analog type divider is expensive, the present embodiment Uses a subtractor instead of a divider.

Next, a method using a subtractor will be described with reference to FIG.
It will be explained by. First, in Equations 8 and 9, it is assumed that Kp can be controlled to be constant by some method, and further, assuming that the input angular velocity Ωin is 0 and Km is 2.5 to 2.7, the voltage E4 in Equation 8 becomes 9 of the absolute value of the voltage E5
Double. Therefore, by making the value of Kc five times Kb, the absolute values of the voltages E4 and E5 become almost equal.
Since this relationship is satisfied even when the input angular velocity Ωin is not 0, the voltage E4 of the positive voltage and the voltage E5 of the negative voltage are subtracted by the subtractor 8.
a In other words, subtraction of signals having different signs can be easily realized by adding the resistors to the resistors R1 and R2 in FIG. The result of the subtraction is integrated by the operational amplifier OA2, and the voltage E7 is output. The polarity of the voltage E7 must always be negative in this case, and assuming that the values of the resistors R1 and R2 are equal, it is essential that the value of the voltage E4 be slightly larger than the absolute value of the voltage E5. It is. If the polarity of the voltage E7 becomes positive, for example, when starting the device of the present invention, a problem occurs such that the phase shifts to the positive-side stable point and the drive voltage E3 is inverted. To make the polarity of the voltage E7 always negative or positive.

As described above, the DC voltage E7 is converted to a square wave voltage E8 with a duty of 50% by turning on and off the switches SW1 and SW2 of the analog switch 11 alternately. The voltage E8 is shaped into a sine wave having a predetermined phase by the waveform shaping unit 12, and the driving voltage E3 is output. Here, the waveforms of the synchronization signals E2a and E2aa are square waves having a duty of 50%, and are composed of only odd harmonic components including the fundamental wave. Therefore, there is no harmful even harmonic component that originally causes an offset. Therefore, unless the analog switch 11 has an on-off asymmetric delay that changes the duty, the waveform of the voltage E8 becomes a square wave similar in time to the synchronization signals E2a and E2aa, and an even harmonic component harmful to the voltage E8. Is not included.
Further, by using an amplifier having good linearity even in a high frequency band for the filter, the phase shifter, and the like of the waveform processing unit 12, even harmonics do not occur in the waveform shaping unit 12, and the phase modulator 5 The drive voltage E3 can have a waveform close to a sine wave with no harmful even harmonic components. When the drive voltage E3 contains a small number of odd-order harmonic components, the modulation is multiplex modulation of odd harmonics including the fundamental wave, and the amplitude of each frequency included in the signal voltage E1 is expressed by the following equation. 6, but when the input angular velocity Ωin is 0, the amplitudes A1, A3, and A5 of Equations 1, 3, and 5 become non-zero.
That is, no offset occurs. Further, the waveforms of the synchronization signals 7a, 7b, 7c are
It is easy to make a square wave of 0%. For example, it is only necessary to provide a flip-flop type frequency divider of a high-speed digital IC at the output part.

Next, the driving voltage E3 is changed to the phase modulator 5 of FIG.
Is applied to the optical fiber loop 4 in a direction opposite to each other in an AC bias, that is,
Phase modulation is applied, and as a result, the synchronous detectors 7a, 7
The voltages Eout, E4, and E5 of the outputs b and 7c increase and decrease as the variable Km related to the modulation factor changes as shown in Expressions 7, 8, and 9.

More specifically, when the variable Km is in the range of 2.5 to 2.7, when the variable Km increases with an increase in the drive voltage E3, the absolute values of the voltage E4 and the voltage E5 both increase. Is higher than the increase rate of the voltage E4.
Is large, the subtraction value becomes negative, and the absolute value of the voltage E7 decreases. This is a positive negative feedback effect, whereby the driving voltage E of the phase modulator 5 is adjusted so that the value of the voltage 4 becomes extremely slightly larger than the absolute value of the voltage 5.
3 is automatically adjusted, and the phase modulation degree is kept at a predetermined value. Finally, the variable Km is always kept constant irrespective of the magnitude of the input angular velocity Ωin.

Therefore, if the variable Km becomes constant, the voltage Eout of the equation (7), that is, the output voltage of the phase modulation type optical fiber gyro is always proportional to sinKsΩin. The input angular velocity Ωin can be obtained. Where KsΩin
In a range where the absolute value of is small, sinKsΩin and Ωin are almost in a proportional relationship, so that it is not necessary to use the inverse function of sin.

As described above, according to the present embodiment, the degree of phase modulation can always be kept constant and the input and output levels can be kept constant, despite the relatively simple configuration not using any numerical operation unit. This has the effect of making the relationship, that is, the scale constant. Further, since a multiplier or the like is not used for controlling the phase modulation, there is an effect of preventing the occurrence of an output offset due to the influence of harmful harmonic components included in the drive voltage E3 of the phase modulator 5. In addition, since an expensive numerical operation unit, multiplier, or the like is not used in the signal processing unit, there is an effect that the device can be reduced in size and inexpensive.

Next, another embodiment of the first invention will be described. First, in the above description, the magnitude of the voltage E4 of the second harmonic component and the magnitude of the voltage E5 of the fourth harmonic component are compared in the subtracting unit 8a. However, the present invention is not limited to this, and the variable Km is about 5.1.
, The value of the Bessel function J2 (Km), ie, 2
Using the fact that the voltage E4 of the next harmonic component becomes 0, the target value 0 and the voltage E4 are subtracted by the subtraction unit 8a, and the value of the voltage E4 becomes 0.
The driving voltage E3 of the phase modulator 5 may be controlled so that In this case, there is an effect that the above-described effect and the synchronous detector 7c for detecting the fourth harmonic component can be omitted.

E4 / E5 = −KC / Kb · J4 (Km) / J2 (Km) (Equation 10) Further, as shown in Equation 10, when the ratio between the voltage E4 and the voltage E5 is obtained, the Bessel function J2 (Km ) And J4 (Km), the ratio between the voltage E4 and the voltage E5 is determined by, for example, an analog divider or a numerical operation, and the voltage proportional to the ratio and the target value are subtracted by the subtractor 8a. Control may be performed so that the ratio between the voltage E4 and the voltage E5 is constant. According to this embodiment, although the number of components increases slightly, the ratio between the voltage E4 and the voltage E5 is theoretically not affected by the magnitude of the signal light, that is, the variation of the variable Kp, as shown in Expression 10, so that the variable Km is Control can be performed with high accuracy, and as a result, there is an effect of further stabilizing the scale.

Next, the operation of one embodiment of the light output control means of the second invention will be described with reference to FIG. The configuration of the invention is as described above. Here, in order to facilitate the description, the drive voltage E3 of the phase modulator 5 is controlled by some method, and the value of the variable Km related to the modulation is set to a predetermined value, for example, It is assumed that Km = 2.6 is always maintained.

First, when the magnitude of the signal light entering the photoelectric conversion unit 6 is insufficient, the signal voltage E1 is small, the voltage E9 of the output of the AC amplitude detector 13 is smaller than the target value E10, and the output of the subtraction unit 8b is small. Has a positive value. Amplifier 9
When a positive voltage E11 is input to b, the voltage E12 output from the amplifier 9b is converted into a drive current E13 by the power amplifier 14. The driving current E13 is applied to the coherent light source 1, and the coherent light source 1 emits light. As the driving current E13 increases, the optical output also increases. As the light output of the coherent light source 1 increases, the signal voltage E1 and the voltage E9 increase in proportion thereto. The voltage E9 is input to the subtraction unit 8b as a negative signal, that is, a negative feedback. Therefore, the signal voltage E
The value of 1 is maintained until the voltage E9 becomes substantially equal to the target value E10 (E9 = E10 when the amplification of the amplifier 9b is infinite).
), And thereafter, the voltage E9 is automatically controlled to be slightly smaller than the target value E10, and finally, the AC amplitude of the signal voltage E1 is controlled to be constant.

Here, assuming that the current of the coherent light source 1 is kept constant by some method, the AC amplitude of the signal voltage E1 becomes large when the large input angular velocity Ωin is applied,
When the variable Km related to the degree of phase modulation greatly changes with respect to 2.6, the value changes in the direction of decreasing, but the value of the variable Km is about 2.6 and the absolute value of Ks · Ωin is π / 2.
At radians or less, the AC amplitude hardly changes.

Therefore, by controlling the signal voltage E1 to be constant, the optical output of the optical system, that is, the magnitude of the signal light becomes constant, and the variable Kp in the formulas 1 to 9 becomes constant. Therefore, as can be seen from Equation 7, Ka, Kp, J1
(Km) can always be kept constant, so that the input angular velocity Ωi
An accurate voltage Eout corresponding to n can be obtained. Conversely, the input angular velocity Ωin can be accurately obtained from the voltage Eout. According to this embodiment, since the true target point of the control coincides with the detection point, there is an effect that the signal voltage E1, which is the target point of the control, is most accurately made constant.
In addition, there is no need to separately provide an optical output detection unit for negative feedback, which has the effect of reducing the cost of the device.

As described above, an example in which the subtraction unit 8b and the amplification unit 9b are configured by analog circuits is shown in FIG. 2. The resistors R1 and R2 and the operational amplifier OA shown in FIG.
1, an integrator with a subtraction circuit of a different sign composed of the capacitor C1. This does not change the effect of the embodiment.

In the above description of the embodiment, the AC amplitude detector 13 is of the analog type. However, the present invention is not limited to this. For example, the waveform of the signal voltage E1 is digitized by an A / D converter and the numerical value is calculated. The AC voltage amplitude of the signal voltage E1 may be obtained by processing in the section, the value may be D / A converted to generate a voltage E9, and this voltage E9 may be applied to the subtraction section 8b. Although this method seems complicated and meaningless, a waveform analysis of the signal voltage E1 is performed using a method already having a numerical operation unit, for example, using a high-speed A / D converter and a digital signal processor, and from the analysis result, In the case of a method of calculating the input angular velocity Ωin, there is no need to add a new numerical operation unit,
The relatively simple configuration has the effect of always keeping the AC amplitude of the signal voltage E1 accurately and constant.

Another modification of the AC amplitude detector 13 will be described. Here, looking again at Equations 7 and 8 in detail,
The right side of Equation 7 is sinKs · Ωin, and the right side of Equation 8 is cosK
Since there is a term of s · Ωin, the mathematical trigonometric formula si
Considering nθ · sinθ + cosθ · cosθ = 1, the variables Kp,
Assuming that Km and the constants Ka and Kb are constant, a value obtained by adding the value squared to the right side of Equation 7 and the value squared to the right side of Equation 8 (E
z) should be constant. That is, it can be seen that Ez becomes constant without being affected by the magnitude of the input angular velocity Ωin at all, and that the value of Ez changes only when the variables Kp and Km change. Therefore, when the variable Km is made constant by some means, the value of Ez becomes the variable K regarding the magnitude of the signal light.
It will change as p changes.

Therefore, the voltage calculation unit may multiply each of the voltage Eout and the voltage E4 by an appropriate coefficient, square the sum, sum the values, and convert the sum to obtain the voltage E9. According to this embodiment, there is no restriction on the input angular velocity Ωin and the magnitude of the variable Km, and the voltage E9 changes only by the change of the variable Kp related to the signal light.
By keeping 9 constant, the signal voltage E1 can be kept constant, and finally, the input angular velocity Ωin can be detected more accurately.

In the above description of the embodiment, the subtraction unit 8
Although the description has been given of the case where analog circuits are used for the amplifiers a and 8b and the amplifiers 9a and 9b, the present invention is not limited to this, and a numerical calculation unit and an analog circuit may be combined as shown in FIG. Hereinafter, FIG. 4 will be described in detail.

In the figure, an A / D converter 15 comprises an analog signal switch and an A / D converter. For example, the switches E4 and E5 are switched at predetermined time intervals by switches.
Each voltage is converted into a digital signal Dn. The numerical operation unit 16 takes in the voltages E4 and E5 as a digital signal Dn, compares these two signals, and outputs an up signal (UP signal) or a down signal (DWN signal) as a discrimination signal. The analog switch 17 turns on one of the switches SW3 and SW4 in response to an up signal or a down signal from the numerical operation unit 16, and causes a positive or negative current to flow through an integrator including the resistors R7 and R8, the operational amplifier OA1, and the capacitor C1. is there. The resistors R7 and R8 are current limiting resistors. The up signal and the down signal are output, for example, by changing the pulse width or by changing the number of pulses while fixing the pulse width to form a kind of integral D / A converter.

Next, the operation when this circuit is applied to the phase modulation control means of the first invention will be described. First, assuming that the constant Kc in Equations 8 and 9 is about five times Kb, if the phase modulation factor is small and the variable Km in Equations 8 and 9 is smaller than the target value, the absolute value of the voltage E5 is smaller than the voltage E4. At this time, the numerical operation unit 16 outputs an up signal as a discrimination signal, the switch SW3 is closed, and the operational amplifier OA1
A positive current flows through the integrator unit including the capacitor C1 and the capacitor C1, and the voltage is integrated and the voltage E7 increases in the negative direction. Voltage E7
Increases, the driving voltage E3 of the phase modulator 5 in FIG. 1 increases, and the degree of phase modulation increases. As the degree of phase modulation increases, the variable Km increases, and the Bessel function J2 (K
m) and J4 (Km) both increase. As described above, the degree of the increase is larger in J4 (Km) than in J2 (Km). For example, when the variable Km reaches the target value of about 2.6, the absolute value of the voltage E5 becomes substantially equal to the value of the voltage E4. , The up signal output from the numerical operation unit 16 becomes 0, the switch SW3 is turned off, that is, the switch SW3 enters the hold state, and the voltage E
7 is kept at a negative value. On the other hand, if the degree of phase modulation becomes too large and the variable Km exceeds 2.6, the absolute value of the voltage E5 becomes larger than the voltage E4.
Outputs a down signal as a determination signal, and the switch SW4 is turned on. When the switch SW4 is closed, a negative signal flows to the integrator section, and the absolute value of the voltage E7 decreases until the variable Km becomes 2.6.

According to this embodiment, the D / A converter provided at the connection between the numerical operation unit 16 and the analog circuit, and the subsequent subtractor 8a and amplifier 9a are composed of the analog switch 17 and the resistors R7, R8, the capacitor C1, Since it is composed of only general parts such as the operational amplifier OA1, the device is inexpensive, and the degree of phase modulation can be precisely controlled, so that the input angular velocity Ωin can be obtained most accurately.

Also, in the above embodiment, the magnitudes of the voltages E4 and E5 are compared by the numerical calculation unit 16, but the present invention is not limited to this, and the ratio between the voltages E4 and E5 and the target value of the ratio (necessarily from outside) (It is not necessary to input.) To output a discrimination signal. Utilizing that the voltage E4 or the voltage E5 becomes 0 when the variable Km reaches a specific value, it is determined whether the voltage E4 or the voltage E5 is 0, and a determination signal is output based on the result. You may. Even if the determination method is changed in this way, the effect of the embodiment is the same as the effect of the above embodiment.

Next, the case where the circuit shown in FIG. 4 is applied to the light output control means of the second invention will be described. This circuit includes the subtraction unit 8b and the amplification unit 9b of the embodiment shown in FIG.
And the basic operation of the circuit is as described above. The different parts are the control target and the signal of the negative feedback. As shown in the parentheses in FIG. 4, the target value is the voltage E10 (not necessarily input from the outside),
The signal of the negative feedback is the voltage E9 of the output of the AC amplitude detector 13. First, the target voltage E1 is not sufficient because the magnitude of the signal voltage E1 is insufficient.
When the absolute value of the voltage E9 is smaller than 10, the numerical operation unit 1
6 outputs a down signal, the switch SW4 is turned on, a negative current flows through the integrator, and the current is integrated to generate a voltage E12.
Rises in the positive direction. When the voltage E12 increases, the driving current E13 in FIG. 1 increases, the light output of the coherent light source 1 increases, and the signal voltage E1 increases. When the absolute value of the target value E10 becomes equal to the absolute value of the voltage E9, the value of the signal voltage E1 reaches the target value, the down signal becomes 0, and the switch S
W4 turns off and enters the hold state. When the signal voltage E1 becomes larger than the target value, the absolute value of the voltage E9 becomes larger than the target value E10, and an up signal is output from the numerical operation unit 16 to make the signal voltage E1 smaller. According to this embodiment, there is an effect that the AC amplitude of the signal voltage E1 is accurately kept constant despite the relatively simple configuration.

As described in detail in the above-described modification of the AC amplitude detector 13, the numerical operation unit 16 of FIG. 4 multiplies each of the voltage Eout and the voltage E4 by a predetermined coefficient, squares each of them, and sums them. Then, the driving current E13 in FIG. 1 is controlled so that the total value is constant, and the signal voltage E1 is controlled.
May be kept constant. According to this embodiment, in addition to the same effect as the above embodiment, the AC amplitude detector 13
Has the effect of being able to omit.

As described above, the relatively high speed A /
The waveform of the signal voltage E1 is digitized using a D converter, and FIG.
And the numerical value is taken into the numerical operation unit 16.
To calculate the AC amplitude of the signal voltage E1, and control the drive current E13 in FIG. 1 so that the AC amplitude becomes constant. According to this embodiment, since the AC amplitude of the signal voltage E1 is directly detected and kept constant, there is an effect that the AC amplitude of the signal voltage E1 is most accurately kept constant.

As described above, the two inventions can exert their effects even if they are implemented separately.
When the two inventions are implemented at the same time, the A / D converter, the numerical operation unit, and the like provided in each of the phase modulation control unit and the optical output control unit are shared, and the apparatus can be simplified. There is an effect that the control can be performed more accurately with respect to the target value, and an effect that an all-analog type having no numerical operation unit as in the basic configuration shown in FIG.

Further, in the case of the embodiment provided with the numerical operation unit,
It goes without saying that the numerical operation unit executes the processes of the phase modulation control and the light output control, but there is no problem even if other processes are performed. For example, as can be seen from Expression 7, the voltage Eout in FIG. 1 may not be output as it is, but may be linearized via an inverse function of sin, and may be output as a numerical value as a detected value of the input angular velocity Ωin. As can be seen from Equations 7 and 8, the ratio between the voltage Eout and the voltage E4 is sinKsΩ.
in / cosKsΩin = tanKsΩin Since the value is proportional to tan, the value can be processed by the inverse function of tan to remove the influence of the fluctuation of the magnitude of the signal light. According to this embodiment, the linearity is improved, and there is an effect that the input angular velocity Ωin can be accurately detected, digitized, and output.

In the above description of the embodiment, the optical system to be implemented has the most basic configuration of the all-optical fiber type phase modulation type optical fiber gyro, but is not limited thereto. An optical system in which the first optical splitter 2a is omitted, or an optical system in which the optical splitter 2b and the phase modulator 5 are replaced by a waveguide type optical splitter with a phase modulator, or the optical splitter 2a, There is no problem even in the case of an optical system in which the parts 2b and the polarizer 3 are constituted by individual parts which are not optical fiber type.

In the optical system of the phase modulation type optical fiber gyro, the polarizer 3 is not an indispensable part.
When high performance is not required, the polarizer 3 can be omitted. Even if the present invention is applied to an optical system in which the polarizer 3 is omitted, the effect is not changed. Further, as shown in FIG. 5, the optical system is formed by integrating a Y-type optical splitter and a phase modulator. A signal light emitted from the back surface (the surface opposite to the light emission surface) passing through the coherent light source 1 is formed by photoelectric conversion. The other signal processing unit may be the same as the signal processing unit of FIG. In FIG. 5, components having the same reference numerals as those in FIG. 1 are components having the same functions as those in FIG. 1, and other components are not illustrated because they are not necessary for description.
The waveguide type optical branching device 18 is composed of, for example, a Y-branch waveguide on a lithium niobate substrate and a phase modulator in which electrodes are arranged on both sides of the waveguide. Although there is a theoretically unclear point in the phenomenon that the signal light passes through the coherent light source 1, for example, a laser diode, it is true that the signal light passes with a gain of about one time. According to this embodiment, there is an effect that the photodiode of the photoelectric conversion unit 6 can be replaced with the photodiode for monitoring the optical output attached to the laser diode.

In the above description, each component of the optical system has the polarization maintaining property. However, the present invention is not limited to this. For example, as shown in FIG. May be. In the figure, the depolarizer 20
a and 20b convert a polarized light wave into a non-polarized light wave. For example, two polarization-maintaining optical fibers of a certain length are fused by rotating the propagation axis by about 45 °. Things. The optical splitters 21a and 21b are obtained by fusion-spreading an ordinary single mode optical fiber having no polarization preserving property, and the optical fiber loop 22 is an ordinary single mode optical fiber having a polarization maintaining property of several hundred meters. It is coiled. By configuring the optical system in such a manner, the performance of the optical system becomes almost the same as that of the optical system composed of components having polarization plane preserving characteristics. According to the embodiment in which such an optical system is combined with the signal processing unit of the present invention shown in FIG. 1, the effect of preventing the fluctuation of the magnitude of the signal light and reducing the price of the components of the optical system is reduced. There is.

[0059]

As described above, according to the first and fourteenth aspects of the present invention, the phase modulator can be stably driven with an AC voltage having no harmful harmonic components, so that an offset is generated in the output. And a phase modulation type optical fiber gyro without scale fluctuation can be provided.

According to the invention described in the sixth and fifteenth aspects, a signal voltage proportional to the magnitude of the signal light is detected.
Since it is kept constant, it is possible to provide a phase modulation type optical fiber gyro having no output offset and no scale fluctuation.

Further, according to the tenth and sixteenth aspects of the present invention, the synergistic effect of simultaneously implementing the two aspects of the present invention makes each control more accurate, has no output offset, and has a scale fluctuation. A phase modulation type optical fiber gyro can be provided.

[Brief description of the drawings]

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

FIG. 2 is a configuration diagram illustrating an example of a subtraction unit and an amplification unit.

FIG. 3 is a configuration diagram illustrating an example of an AC amplitude detector.

FIG. 4 is a configuration diagram illustrating an embodiment in which a subtraction process is performed by a numerical operation unit.

FIG. 5 is a block diagram showing an example of another optical system to which the present invention can be applied.

FIG. 6 is a block diagram illustrating an example of an optical system including components having no polarization plane preserving property.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Coherent light source, 2,21 ... Optical splitter, 4,22 ... Optical fiber loop, 5 ... Phase modulator, 6 ... Photoelectric conversion part, 8
... Subtraction unit, 9 Amplification unit, 11, 17 Analog switch, 12 Waveform shaping unit, 13 AC amplitude detection unit, 14
Power amplifying unit, 15 A / D converter, 16 numerical calculation unit,
20 ... Depolarizer.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tatsuya Kumagai 880 Sunasawa-cho, Hitachi City, Ibaraki Prefecture Hitachi Cable Hidaka Plant Inside Takasago Plant (72) Inventor Yukio Uesugi 880, Sunasawa-machi, Hitachi City, Ibaraki Prefecture Hitachi Cable Examiner, Masayuki Akita, Takasago Plant, Hidaka Plant Co., Ltd. (56) References JP-A-3-156314 (JP, A) JP-A-62-108110 (JP, A) JP-A-62-12811 (JP, A A) JP-A-63-38111 (JP, A) JP-A-2-236113 (JP, A) JP-A-62-239014 (JP, A) JP-A-63-16219 (JP, A) JP-A-61-21 -147106 (JP, A) JP-A-64-63870 (JP, A) JP-A-4-106416 (JP, A)

Claims (16)

(57) [Claims] 1. A light output control means of a minimum coherent light source,
An optical splitter for splitting and combining light from a coherent light source in two directions, an optical fiber loop for transmitting the split light by rotating in opposite directions, and a phase modulation for applying an alternating phase bias to the split light A phase modulation type optical fiber gyro comprising: a control unit; a photoelectric conversion unit that converts signal light of these optical systems into an electric signal; and a signal processing unit that outputs a detected value of an input angular velocity from the electric signal. The control means includes a subtraction amplification unit for a plurality of signals related to the degree of phase modulation, and an AC conversion unit for converting an output of the subtraction amplification unit into an alternating current having a predetermined frequency. A phase modulation type optical fiber gyro, which is driven to cause a phase modulation degree to follow a target value. 2. A phase modulation type optical fiber gyro according to claim 1, wherein said AC conversion section comprises an analog switch and a waveform shaping section. 3. The phase modulation system according to claim 1, wherein the subtraction amplification section subtracts and amplifies a second harmonic component and a fourth harmonic component of the predetermined frequency included in the electric signal. Optical fiber gyro. 4. The subtraction amplification section according to claim 1, wherein the subtraction amplification section includes a target value of a modulation factor and a value of the predetermined frequency included in the electric signal.
A phase modulation type optical fiber gyro, which performs subtraction and amplification of a ratio between a second harmonic component and a fourth harmonic component. 5. The subtraction amplification section according to claim 1, wherein the subtraction amplification section includes a target value of the modulation factor and a value of the predetermined frequency included in the electric signal.
A phase modulation type optical fiber gyro, which performs subtraction and amplification of one of a fourth harmonic component and a fourth harmonic component. 6. A light output control means of a minimum coherent light source,
An optical splitter for splitting and combining light from a coherent light source in two directions, an optical fiber loop for transmitting the split light by rotating in opposite directions, and a phase modulation for applying an alternating phase bias to the split light A phase modulation type optical fiber gyro comprising: a control unit; a photoelectric conversion unit that converts signal light of these optical systems into an electric signal; and a signal processing unit that outputs a detected value of an input angular velocity from the electric signal. The control means includes an AC amplitude detection section for the electric signal, a subtraction amplification section for the target value of the output of the AC amplitude detection section and a target value of the optical output, and a power amplification section for the output of the subtraction amplification section. A phase modulation type optical fiber gyro, characterized in that the coherent light source is driven by the output of the section to cause the AC amplitude of the electric signal to follow a target value. 7. A phase modulation type optical fiber gyro according to claim 6, wherein said AC amplitude detector is a peak value detector. 8. A phase modulation type optical fiber gyro according to claim 6, wherein said AC amplitude detector is a half-wave or full-wave rectifier. 9. An apparatus according to claim 6, wherein said AC amplitude detecting section comprises:
A phase modulation type optical fiber gyro, which is a numerical operation unit including a / D converter. 10. A phase modulation type optical fiber gyro according to claim 1, wherein the subtraction amplification section outputs an integrated value of the subtraction value. 11. A phase modulation type optical fiber gyro according to claim 1, wherein said subtracting amplifier is an analog circuit and outputs an integrated value of said subtracting value. 12. A phase modulation type optical fiber gyro according to claim 1, wherein said subtraction amplification section performs subtraction by a numerical operation section and performs amplification by an analog circuit. 13. A light output control means for a minimum coherent light source, an optical splitter for splitting and combining light from the coherent light source in two directions, and light for transmitting the split light in opposite rotations. A fiber loop, phase modulation control means for applying an AC phase bias to the branched light, a photoelectric conversion unit for converting signal light of these optical systems into an electric signal, and detecting a detected value of an input angular velocity from the electric signal. In a phase modulation type optical fiber gyro comprising a signal processing unit to output, an AC amplitude detection unit of the electric signal to the optical output control unit, a subtraction amplification unit of a target value of an output of the AC amplitude detection unit and an optical output, A power amplifying unit for the output of the subtraction amplifying unit; and a phase amplifying unit for subtracting and amplifying a plurality of signals related to the degree of phase modulation, and converting an output of the subtraction amplifying unit to an alternating current having a predetermined frequency. Exchange A section provided, the AC amplitude and phase modulation type optical fiber gyro, characterized in that to follow the phase modulation index to each target value. 14. A light output control means of a minimum coherent light source, a first depolarizer for converting light of the coherent light source to non-polarized light, and a polarization splitter for splitting the non-polarized light into two directions. A first optical splitter having no wavefront preserving property, a polarizer for polarizing the unpolarized light, and a second optical splitter having no polarization preserving property for splitting and combining the polarized light in two directions; A second depolarizer connected to one of the outlets of the second optical splitter to convert the polarized light into non-polarized light again; and a polarization preserving characteristic for transmitting the split light by reverse rotation with respect to each other. Optical fiber loop, phase modulation control means for applying an AC phase bias to the branched light, a photoelectric conversion unit for converting signal light of these optical systems into an electric signal, and detection of an input angular velocity from the electric signal Phase-modulated optical fiber jar consisting of a signal processor that outputs a value In Russia, the phase modulation control unit, a subtraction amplifier portion of the plurality of signals related to the phase modulation index,
An AC converter for converting the output of the subtraction amplifier to an AC having a predetermined frequency, and driving the phase modulator with the output of the AC converter to cause the phase modulation degree to follow a target value. Modulated optical fiber gyro. 15. A light output control means of a minimum coherent light source, a first depolarizer for converting light of the coherent light source to non-polarized light, and a polarization splitter for splitting the non-polarized light into two directions. A first optical splitter having no wavefront preserving property, a polarizer for polarizing the unpolarized light, and a second optical splitter having no polarization preserving property for splitting and combining the polarized light in two directions; A second depolarizer connected to one of the outlets of the second optical splitter to convert the polarized light into non-polarized light again; and a polarization preserving characteristic for transmitting the split light by reverse rotation with respect to each other. Optical fiber loop, phase modulation control means for applying an AC phase bias to the branched light, a photoelectric conversion unit for converting signal light of these optical systems into an electric signal, and detection of an input angular velocity from the electric signal Phase-modulated optical fiber jar consisting of a signal processor that outputs a value In (B), the optical output control means includes an AC amplitude detector for the electric signal, a subtraction amplifier for the output of the AC amplitude detector and a target value of the optical output, and a power amplifier for the output of the subtraction amplifier. A phase modulation type optical fiber gyro, wherein an output of the power amplifier drives a coherent light source to cause the AC amplitude of the electric signal to follow a target value. 16. A light output control means of a minimum coherent light source, a first depolarizer for converting light of the coherent light source to non-polarized light, and a polarization splitter for splitting the non-polarized light into two directions. A first optical splitter having no wavefront preserving property, a polarizer for polarizing the unpolarized light, and a second optical splitter having no polarization preserving property for splitting and combining the polarized light in two directions; A second depolarizer connected to one of the outlets of the second optical splitter to convert the polarized light into non-polarized light again; and a polarization preserving characteristic for transmitting the split light by reverse rotation with respect to each other. Optical fiber loop, phase modulation control means for applying an AC phase bias to the branched light, a photoelectric conversion unit for converting signal light of these optical systems into an electric signal, and detection of an input angular velocity from the electric signal Phase-modulated optical fiber jar consisting of a signal processor that outputs a value In (b), the optical output control means includes an AC amplitude detection unit for the electric signal, a subtraction amplification unit for the output of the AC amplitude detection unit and a target value of the optical output, and a power amplification unit for the output of the subtraction amplification unit. Further, the phase modulation control means includes a subtraction amplification unit for a plurality of signals related to the degree of phase modulation, and an AC conversion unit for converting an output of the subtraction amplification unit into an alternating current having a predetermined frequency. A phase modulation type optical fiber gyro characterized in that a modulation degree follows a target value.