JPH06174478A - Phase modulation type optical fiber gyroscope - Google Patents

Abstract

PURPOSE:To improve performance by providing a differential amplifier and an analog switch type AC conversion section, and preventing the generation of the wave-form distortion of a phase modulator. CONSTITUTION:An integrator constituted of resistors R1, R2, a capacitor C1, and an operation amplifier OA1 has the integral amplification characteristic, the difference value between the voltage E5 and E4 is integrated, and the voltage E7 is outputted. When the switches SW1 and SW2 of an analog switch 11 are turned on and off in turn, the voltage E7 is converted into the square- wave voltage E8 with the duty of 50%, it is shaped into the sine wave having the preset phase by a wave-form shape section 12, and the drive voltage E3 is outputted. Synchronization signals E2a, E2aa have the square wave with the duty of 50%, the square wave is constituted of only odd harmonic constituents including the fundamental wave, the wave-form of the voltage E8 is a square wave time-wise analogous to the synchronization signals E2a, E2aa, and harmful even harmonic constituents are not included in the voltage E8.

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 which uses an optical fiber to detect an angular velocity,
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 a direction and the like.

[0002]

2. Description of the Related Art A gyro (gyroscope) has been conventionally known as a sensor for detecting angular velocity, but in recent years, an optical fiber gyro has come into practical use as a solid-state gyro. Examples thereof include those described in JP-A-63-314410.

The one shown here is a basic configuration of a phase modulation type optical fiber gyro. In this case, the drive voltage of the phase modulator is adjusted by using 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 section.

Although not specifically described in Japanese Patent Laid-Open Publication No. JP-A-2004-26498, conventionally, the light output of a coherent light source is adjusted by directly detecting the light output of the coherent light source or by the amount of light incident on an optical fiber. Was detected via an optical branching device, and the detected value was controlled to be constant.

[0005]

The above-mentioned prior art does not consider the waveform distortion of the drive voltage of the phase modulator, and there is a problem that the output of the sensor causes an offset or a scale variation due to this. It was

Further, since the output of the coherent light source or the incident light amount of 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 influence of the fluctuation of the branching ratio of the optical branching portion. As a result, there is a problem that the offset value of the sensor output 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-mentioned object, the drive voltage of the phase modulator is adjusted by providing a subtraction amplifier and an analog switch type AC converter to prevent waveform distortion of the phase modulator. It was done.

In the output adjustment 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]

In the adjustment of the driving voltage of the phase modulator, the harmful even harmonic components contained in the driving voltage are reduced to 0 by driving the analog switch with an accurate square wave with a duty of 50%.
Further, by driving the phase modulator with an AC voltage having no even harmonic component, the occurrence of offset in the sensor output and the scale fluctuation are prevented.

Further, in adjusting the output of the coherent light source, the signal light is made 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 The phase modulation type optical fiber gyro according to the present invention will be described in detail below with reference to the illustrated embodiments.

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

In the figure, the coherent light source 1 of the optical system is, for example, a general laser diode or a super-emission type diode, and the optical splitters 2a and 2b are beam splitters by evanescent coupling using optical fibers. Also,
The polarizer 3 is formed by winding a special optical fiber in a coil shape so as to have polarization characteristics. The optical fiber loop 4 is formed by winding an optical fiber having a total length of several hundred meters into a coil. The phase modulator 5 is a cylinder-shaped electrostrictive element around which an optical fiber having a total length of several meters is wound, and the optical path length is changed by a change in the length of the optical fiber due to a size change of the electrostrictive element due to an electric signal, thereby giving a phase change. And functions as an AC phase biasing means for light. As the optical fiber, for example, a single mode polarization-maintaining optical fiber is used.
Further, these parts are connected by fusing optical fibers together.

The photoelectric conversion section 6 of the signal processing section mainly comprises a photodiode and a current-voltage conversion section, and converts the 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 and the synchronous signal E2a output from the signal generator 10 to obtain a phase modulator included in the signal voltage E1. The AC component (primary component) having the same frequency as the driving voltage E3 of No. 5 is detected and smoothed and output as the voltage Eout. The synchronous detectors 7b and 7c are the same as 7a. The synchronous detector 7b outputs the secondary AC component included in the signal voltage E1, and the synchronous detector 7c outputs the quaternary AC component included in the signal voltage E1. The signals are detected and smoothed, and the voltages E4 and E5 are output. 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 uses the synchronizing signals E2a and E2.
In the case of this embodiment, the oscillator outputs b and E2c.
The waveforms of the synchronizing 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, and the synchronization signal E2a
b is twice the fundamental frequency of the drive voltage E3, the synchronization signal E2c
Is four times the fundamental frequency of the drive voltage E3. Deduction part 8a
The amplification unit 9a amplifies the subtraction value E6 obtained by subtracting E4 from the voltage E5 and outputs the 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 into a square wave voltage E8. The waveform shaping unit 12 removes the harmonic component of the square wave voltage E8 to obtain a sine wave of a predetermined phase having 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 and the like, and outputs the drive voltage E3 of the phase modulator 5.

In the above signal processing section, the synchronous detector 7
The other part except a is a part that plays a role of driving the phase modulator 5 with a predetermined modulation degree, and is one 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, and outputs the voltage E9. For example, a peak value detector, a half wave and a full wave rectifier are used. is there. The subtraction unit 8b subtracts the voltage E9 from the target value E10 to obtain the subtraction value E11. The amplifier 9b amplifies the subtraction value E11 and outputs a voltage E12. Here, the amplification units 9a and 9b are, for example, integral characteristics, differential characteristics, or proportional amplification characteristics, or have these characteristics appropriately. The power amplifier 14 is a simple impedance converter, and converts the voltage E12 into the 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. And is an embodiment of the light output control means of the second invention.

More specifically, the subtracting portion 8a,
Amplifier 9a, analog switch 11 and waveform shaping unit 1
FIG. 2 shows an example of the case where the part 2 is composed of analog parts. In the figure, resistors R1 and R2
The part of the integrator consisting of the capacitor C1 and the operational amplifier OA1 corresponds to the subtracting section 8a and the amplifying section 9a in FIG. 1 and has a configuration in which the amplification characteristic is the integral characteristic. In this case, it is better that the polarities of the voltages E5 and E4 are opposite to each other, and this integrator integrates the subtracted values of the voltages E5 and E4 and outputs the voltage E7. The analog switch 11 is composed of switches SW1 and SW2 which are turned on / off by synchronizing signals E2a and E2aa whose phases are mutually inverted. By alternately turning on the switches SW1 and SW2, the DC voltage E7 becomes a square wave with a duty of 50%. To be converted.
The inverter IN1 simply inverts the synchronization signal E2a to generate the synchronization signal E2aa. The signal generator 10 is shown in FIG.
Is the same as As described above, the waveform shaping unit 12 is well known, for example, a notch filter having a fundamental frequency of the voltage E8 of 2, 3, or 4 times, and a low-pass filter having a cutoff frequency of approximately twice the fundamental frequency. It is composed of a constant gain phase shifter, an amplifier of low output impedance, etc., and removes the harmonic component of the square wave voltage E8 and outputs a sinusoidal drive voltage E3. It also serves as a phase adjuster that shifts the phase of the drive voltage E3 with respect to the phase of the synchronization signal E2a so that the phases of the synchronization signals E2a, E2b, E2c and the signal voltage E1 are in phase.

If the subtracting section 8b and the amplifying section 9b in FIG. 1 are made up of analog parts, the subtracting section 8a and the amplifying section 9 will be described.
It becomes the same as the case of a, and the resistors R1 and R shown in FIG.
2, a circuit of a capacitor C1 and an operational amplifier OA1.

An example of the case where the AC amplitude detector 13 is composed of analog parts is shown in FIG. The one shown in the figure is 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 one-sided amplitude of the signal voltage E1 to make an alternating current into a pulsating current.
The resistors R5 and R6 and the capacitor C2 are circuits for smoothing the pulsating current to make it direct current. Here, the voltage E9 becomes 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 degree. For example, the resistor R4 has a resistance of 0Ω,
When the resistor R3 is opened, the gain is 1.

The operation of the embodiment will be described in detail below. Here, the basic operation of the phase modulation type optical fiber gyro will be described. First, the characteristics of the phase modulator 5,
If the input angular velocity Ωin is applied to the entire optical system or the portion of the optical fiber loop 4 when the frequency and amplitude of the drive voltage E3 are set to predetermined values in consideration of the total length of the optical fiber of the optical fiber loop 4, etc., the Sagnac effect causes The amplitude of each of the 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 is expressed by the following equation. 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) where A1 A6 is the amplitude of each angular frequency component, Kp is a variable relating to the size of the signal light and the photoelectric conversion rate, Ks is the Sagnac effect, that is, a constant relating 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, when the expressions 1 to 6 are explained,
Equation 1 is an expression representing the magnitude of the primary harmonic component equal to the fundamental frequency of the drive voltage E3 contained in the signal voltage E1, that is, the equation 2 represents the magnitude of the primary harmonic component equal to the primary component. 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 is the third harmonic component included in the signal voltage E1, and Equation 4 is the signal voltage E1. Fourth harmonic component included, Expression 5 is fifth harmonic component included in signal voltage E1, Expression 6 is included in signal voltage E1
It is an equation representing the magnitude of the next harmonic component. Note that it is actually expressed by an infinite number of mathematical expressions.

The voltage Eout of the output of the synchronous detector 7a
When is expressed by a mathematical expression, K is added to the right side of Expression 1 as shown in Expression 7.
Multiplying by a · cos ω (t−τ / 2), the AC term is removed (action of low-pass filter). Similarly,
When the voltages E4 and E5 of the outputs of the synchronous detectors 7b and 7c are expressed by mathematical expressions, the expressions 8 and 9 are obtained.

Eout = Ka · Kp · sin KsΩin · J1 (Km) (Equation 7) E4 = Kb · Kp · cosKsΩin · J2 (Km) (Equation 8) E5 = −Kc · Kp · cosKsΩin · J4 (Km) (Equation 9) where Ka, Kb, Kc are synchronous detectors 7a, 7b, 7
It is the amplification degree of c.

Therefore, according to Equation 1, the input angular velocity Ω
It is understood that Ka, Kp, Ks, and J1 (Km) need to be constant in order to obtain an accurate voltage Eout proportional to sin of in. Since Ka and Ks are constants that do not change easily from the beginning, there is no need to control them, but Kp is a variable related to the optical output, and J1 (Km) is a function related to the degree of phase modulation, and both are very easy to change. Therefore, some kind of control is required. J1
The portion that keeps (Km) constant is the phase modulation control means of the first invention, and the portion that keeps Kp constant is the light output control means of the second invention.

First, one 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 phase modulation degree, and J is changed by changing the phase modulation degree.
A 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 degrees of change of J2 (Km) and J4 (Km) in Eqs. 8 and 9 do not match when Km changes, and J2 (Km) and J4 ( Km) is compared and the drive voltage E3 of the phase modulator 5 is adjusted so that the ratio becomes constant.

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

Next, the method of using the subtractor is shown in FIG.
Explained by. First, in Eqs. 8 and 9, assuming that Kp can be controlled to be constant by some method, and assuming that the input angular velocity Ωin is 0 and Km is 2.5 to 2.7, the voltage E4 in Eq. Approximately 5 of absolute value of voltage E5 of 9
Double. Therefore, by making the value of Kc 5 times Kb, the absolute values of the voltages E4 and E5 become substantially equal.
Since this relationship holds even when the input angular velocity Ωin is not 0, the positive voltage E4 and the negative voltage E5 are subtracted from each other by the subtracting unit 8.
That is, a subtraction of signals of different signs can be easily realized by adding a to the resistors R1 and R2 of FIG. The subtraction result is integrated by the operational amplifier OA2 section, and the voltage E7 is output. The polarity of the voltage E7 must always be negative in this case, and it is essential that the value of the voltage E4 be slightly larger than the absolute value of the voltage E5, assuming that the resistors R1 and R2 have the same value. Is. When the polarity of the voltage E7 becomes positive when the device of the present invention is started, a defect such as a shift to the positive side stable point and a phase inversion of the drive voltage E3 occurs, so that a starting circuit or the like is provided in the operational amplifier OA1 section. Therefore, it is necessary to devise to make the polarity of the voltage E7 always negative or positive.

As described above, the DC voltage E7 is converted into a square wave voltage E8 having a duty of 50% by alternately turning on and off the switches SW1 and SW2 of the analog switch 11. The voltage E8 is shaped into a sine wave having a predetermined phase by the waveform shaping unit 12, and the drive voltage E3 is output. Here, since the waveforms of the synchronization signals E2a and E2aa are square waves with a duty of 50% and are composed of only odd harmonic components including the fundamental wave, there is no harmful even harmonic component that originally causes an offset. Therefore, unless the analog switch 11 has an on-off asymmetrical delay that disturbs the duty, the waveform of the voltage E8 becomes a square wave temporally similar to the synchronization signals E2a and E2aa, and the even harmonic components harmful to the voltage E8 are generated. Is never included.
Further, by using an amplifier having good linearity even in a high frequency region as a filter, a phase shifter, etc. of the waveform processing unit 12, the waveform shaping unit 12 does not generate even harmonics, and the phase modulator 5 The drive voltage E3 can be made to have a waveform close to a sine wave without harmful even harmonic components. When the drive voltage E3 contains a small number of odd-order harmonic components, the modulation is an odd harmonic multiplex modulation including the fundamental wave, and the amplitude of each frequency included in the signal voltage E1 is from several to several. Although not as shown in 6, when the input angular velocity Ωin is 0, the amplitudes A1, A3, A5 of the equations 1, 3 and 5 disappear at 0,
That is, no offset occurs. In addition, the waveforms of the synchronization signals 7a, 7b, 7c are set to the duty 5
It is easy to make a square wave of 0%, and as an example, it suffices to provide a flip-flop type frequency divider of a high-speed digital IC in the output section.

Next, the drive voltage E3 is the phase modulator 5 of FIG.
To the light that makes one round in the opposite direction through the optical fiber loop 4, that is,
Phase modulation is applied, and as a result, the synchronous detectors 7a and 7a
The voltages Eout, E4, E5 of the outputs of b, 7c increase / decrease with the change of the variable Km relating to the modulation degree as shown in Eqs. 7, 8, and 9.

More specifically, when the variable Km is in the range of 2.5 to 2.7, the absolute value of the voltage E4 and the absolute value of the voltage E5 both increase as the variable Km increases as the driving voltage E3 increases. However, compared to the rate of increase of voltage E4, voltage E5
Since the increase rate of the absolute value of is large, the subtraction value becomes negative and the absolute value of the voltage E7 decreases. This is a positive and negative feedback action, which causes the drive voltage E of the phase modulator 5 so that the value of the voltage 4 becomes much larger than the absolute value of the voltage 5.
3 is automatically adjusted to maintain the degree of phase modulation at a predetermined value. Finally, the variable Km is always kept constant regardless of the magnitude of the input angular velocity Ωin.

Therefore, if the variable Km becomes constant, the voltage Eout of equation 7, that is, the output voltage of the phase modulation type optical fiber gyro is always proportional to sinKsΩin, so that the value of voltage Eout can be accurately calculated using the inverse function of sin. The input angular velocity Ωin can be obtained. Where KsΩin
It is needless to say that it is not necessary to use the inverse function of sin because sinKsΩin and Ωin have a substantially proportional relationship in the range where the absolute value of is small.

As described above, according to the present embodiment, the degree of phase modulation can always be kept constant and the input and output can be kept constant despite the fact that the numerical operation section is not used at all. It has the effect of keeping 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 output offset from being generated due to the harmful harmonic components contained in the drive voltage E3 of the phase modulator 5. Further, since the signal processing unit does not use an expensive numerical operation unit or a multiplier, there is an effect that the device can be made compact 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-order harmonic component and the voltage E5 of the fourth-order harmonic component is compared by the subtraction unit 8a, but the present invention is not limited to this, and the variable Km is about 5.1.
Value of the Bessel function J2 (Km), that is, 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 drive voltage E3 of the phase modulator 5 may be controlled so that In this case, there are the effects described above and the effect that the synchronous detector 7c for detecting the fourth harmonic component can be omitted.

E4 / E5 = −KC / Kb · J4 (Km) / J2 (Km) (Equation 10) Further, when the ratio of the voltage E4 to the voltage E5 is calculated as shown in Equation 10, the Bessel function J2 (Km ) And J4 (Km) are obtained, for example, the ratio of the voltage E4 and the voltage E5 is obtained by an analog divider or numerical operation, and the voltage and the target value proportional to the ratio are subtracted by the subtracting unit 8a, You may control so that the ratio of the voltage E4 and the voltage E5 may become constant. According to this embodiment, although the number of parts is slightly increased, theoretically, the ratio of the voltage E4 to the voltage E5 is not affected by the magnitude of the signal light, that is, the fluctuation of the variable Kp, as shown in the equation 10, so that the variable Km is set to It can be controlled with high precision, and as a result, it has the 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 relating to the modulation degree is a predetermined value, for example, Assume that Km is always kept at 2.6.

First, when the size 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. Voltage E11 has a positive value. Amplifier 9
When the positive voltage E11 is input to b, the voltage E12 of the output of the amplifier 9b is converted into the drive current E13 by the power amplifier 14. The drive current E13 is added to the coherent light source 1 to cause the coherent light source 1 to emit light, and as the drive current E13 increases, the light output also increases. When 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 until the voltage E9 and the target value E10 become substantially equal (E9 = E10 when the amplification degree of the amplifier 9b is infinite).
Then, 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.

If the current of the coherent light source 1 is kept constant by some method, the AC amplitude of the signal voltage E1 is increased by a large input angular velocity Ωin, or
When the variable Km relating to the degree of phase modulation changes significantly with respect to 2.6, it changes toward a smaller value, but the value of the variable Km is about 2.6 and the absolute value of Ks · Ωin is π / 2.
Below radians, the AC amplitude changes little.

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 of the equations 1 to 9 becomes constant. Therefore, as can be seen from equation 7, Ka, Kp, J1
Since the (Km) can always be kept constant, the input angular velocity Ωi is always
An accurate voltage Eout corresponding to n can be obtained. On the contrary, the input angular velocity Ωin can be accurately obtained from this voltage Eout. According to the present embodiment, since the true target point of control and the detection point coincide with each other, there is an effect that the signal voltage E1 which is the target point of control is most accurately made constant.
Further, 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 of the case where the subtracting portion 8b and the amplifying portion 9b are formed by analog circuits is shown. The resistors R1 and R2 and the operational amplifier OA shown in FIG. 2 are shown.
The integrator is composed of a capacitor C1 and a subtraction circuit with a different sign. Even in this way, the effect of the embodiment does not change.

In the above description of the embodiment, the AC amplitude detector 13 is an analog type, but 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. Alternatively, the AC amplitude of the signal voltage E1 may be obtained by performing the processing in a section, and the value may be D / A converted to form a voltage E9, and this voltage E9 may be added to the subtracting section 8b. This method seems complicated and meaningless, but a method that already has a numerical operation unit, for example, a waveform analysis of the signal voltage E1 is executed using a high-speed A / D converter and a digital signal processor. In the case of the method of calculating the input angular velocity Ωin, it is not necessary to add a new numerical operation unit,
The comparatively simple structure 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 again, if you look at equations 7 and 8 in detail,
SinKs · Ωin on the right side of Equation 7, and cosK on the right side of Equation 8.
Since there is a term of s · Ωin, the formula of mathematical trigonometric function si
Considering nθ · sinθ + cosθ · cosθ = 1, the variable Kp,
If Km and constants Ka and Kb are constant, a value obtained by adding the squared value to the right side of Equation 7 and the squared value 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, and 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 is the variable K relating to the magnitude of the signal light.
It will change as p changes.

Therefore, it is also possible to multiply each of the voltage Eout and the voltage E4 by an appropriate coefficient in the numerical calculation section, square them, sum the values, and convert the total value to obtain the voltage E9. According to this embodiment, there is no restriction on the input angular velocity Ωin and the size 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 there is an effect that the input angular velocity Ωin can be detected more accurately.

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

In the figure, the A / D converter 15 comprises an analog signal switch and an A / D converter. For example, the voltages E4 and E5 are switched by the switch at predetermined time intervals.
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 the two signals and outputs an up signal (UP signal) or a down signal (DWN signal) as a determination signal. The analog switch 17 is a switch for turning on one of the switches SW3 and SW4 in response to an up signal or a down signal of the numerical calculation section 16 and flowing a positive or negative current through an integrator composed of 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 changing the number of pulses by fixing the pulse width, and a kind of integral type D / A converter is formed.

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 of the equations 8 and 9 is about 5 times Kb and the degree of phase modulation is small and the variable Km of the equations 8 and 9 is smaller than the target value, the absolute value of the voltage E5 is greater than the voltage E4. It is small. At this time, the numerical calculation unit 16 outputs an up signal as a determination signal, and the switch SW3 is closed to close the operational amplifier OA1.
A positive current flows through the integrator section composed of the capacitor C1 and the capacitor C1 to be integrated, and the voltage E7 increases in the negative direction. Voltage E7
Becomes larger, the drive voltage E3 of the phase modulator 5 in FIG. 1 becomes larger and the degree of phase modulation becomes larger. The variable Km increases as the degree of phase modulation increases, and the Bessel function J2 (K
m) and J4 (Km) both increase. As described above, the degree of increase is greater 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 and the value of the voltage E4 become substantially equal. , The up signal output from the numerical calculation section 16 becomes 0, the switch SW3 is turned off, that is, the hold state is set, and the voltage E
7 is held at some negative value. On the other hand, when 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 discrimination signal, and the switch SW4 is turned on. When the switch SW4 is closed, a negative signal flows in the integrator section, and the absolute value of the voltage E7 becomes small until the variable Km becomes 2.6.

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

In the above embodiment, the numerical value calculator 16 compares the magnitudes of the voltages E4 and E5. However, the present invention is not limited to this, and the ratio of the voltages E4 and E5 and the target value of the ratio (not necessarily from the outside). (There is no need to input) and the discrimination signal may be output. Further, by utilizing that the voltage E4 or the voltage E5 becomes 0 when the variable Km reaches a specific value, it is determined whether or not the voltage E4 or the voltage E5 is 0, and a determination signal is output according to the result. May be. 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 implemented in the light output control means of the second invention will be described. This circuit includes a subtracting section 8b and an amplifying section 9b of the embodiment shown in FIG.
Corresponding to the part (1), 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, and as shown in the parentheses in FIG. 4, the target value is the voltage E10 (not necessarily input from the outside),
The negative feedback signal is the voltage E9 at the output of the AC amplitude detector 13. First, the magnitude of the signal voltage E1 is insufficient and the target value E
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, the current is integrated, and the voltage E12
Rises in the positive direction. When the voltage E12 rises, the drive current E13 in FIG. 1 increases, the optical output of the coherent light source 1 increases, and the signal voltage E1 increases. When the absolute values of the target value E10 and the voltage E9 become equal, 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 issued from the numerical calculation section 16 to reduce the signal voltage E1. 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 structure.

As described in detail in the modification of the AC amplitude detector 13 described above, each of the voltage Eout and the voltage E4 is multiplied by a predetermined coefficient in the numerical calculation unit 16 of FIG. Then, the drive current E13 in FIG. 1 is controlled so that the total value becomes constant, and the signal voltage E1
The AC amplitude of may be kept constant. According to this embodiment, in addition to the same effect as the above embodiment, the AC amplitude detector 13
There is an effect that can be omitted.

Further, as described above, the relatively high speed A /
The waveform of the signal voltage E1 is digitized by using the D converter, and FIG.
The numerical value calculation unit 16 of the
Alternatively, the AC amplitude of the signal voltage E1 may be calculated to control the drive current E13 in FIG. 1 so that the AC amplitude is constant. According to this embodiment, since the AC amplitude of the signal voltage E1 is directly detected and kept constant, the AC amplitude of the signal voltage E1 is most accurately kept constant.

As described above, the two inventions have some effects even if they are separately implemented.
When two inventions are carried out at the same time, the device can be simplified by sharing the A / D conversion unit, the numerical operation unit, and the like provided in the phase modulation control unit and the optical output control unit, respectively, and by the synergistic effect, respectively. There is an effect that the target value can be controlled more accurately, and an effect that an all-analog type that has no numerical operation unit as in the basic configuration shown in FIG.

Further, in the case of the embodiment provided with the numerical operation section,
Needless to say, the numerical calculation unit executes the processes of phase modulation control and optical output control, but there is no problem even if the 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 through an inverse function of sin and digitized and output as a detected value of the input angular velocity Ωin. Also, as can be seen from Equations 7 and 8, the ratio of the voltage Eout to the voltage E4 is sinKsΩ.
Since the value is proportional to in / cosKsΩin = tanKsΩin, it is possible to remove the influence of fluctuations in the magnitude of the signal light by processing this value with the inverse function of tan. According to this embodiment, the linearity is improved, and the input angular velocity Ωin can be accurately detected, digitized, and output.

In the above description of the embodiments, the optical system to be implemented has the most basic configuration of the all-optical fiber type phase modulation type optical fiber gyro. 1, an optical system in which the optical branching device 2a is omitted, or an optical system in which the optical branching device 2b and the phase modulator 5 are replaced by a waveguide type optical branching device with a phase modulator, or the optical branching device 2a, There is no problem even if the optical system in which the portions 2b and the polarizer 3 are composed of individual components that are not of the optical fiber type is used.

In the above optical system of the phase modulation type optical fiber gyro, the polarizer 3 is not an essential component,
The polarizer 3 can be omitted when high performance is not required. Even if the present invention is applied to an optical system in which such a polarizer 3 is omitted, the effect does not change. Further, as shown in FIG. 5, the optical system is integrated with a Y-shaped optical branching device and a phase modulator section. It is configured by the waveguide type optical branching device 18, the optical fiber loop 4 and the coherent light source 1, and photoelectrically transmits the signal light passing through the coherent light source 1 and emitted from the back surface (the surface opposite to the light emitting surface). The signal processing unit other than this may be the same as the signal processing unit of FIG. Note that, in FIG. 5, components having the same reference numerals as those in FIG. 1 are components that operate in the same manner as in FIG.
The waveguide type optical branching device 18 is composed of, for example, a Y branching waveguide on a substrate of lithium niobate and a phase modulator in which electrodes are arranged on both sides of the waveguide. Further, although there is a theoretical 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 through with a gain of about 1 time. According to this embodiment, the photodiode of the photoelectric conversion unit 6 can be replaced by the photodiode for monitoring the optical output attached to the laser diode.

Further, in the above description, each component of the optical system has a polarization plane preserving characteristic. However, the present invention is not limited to this. For example, as shown in FIG. You may. In the figure, the depolarizer 20
Reference characters a and 20b are for converting a polarized light wave into a non-polarized light wave, for example, two polarization plane-maintaining optical fibers of a certain length fused together with their propagation axes orthogonal to each other. . The optical splitters 21a and 21b are fused single-mode optical fibers having no polarization-preserving characteristics, and the optical fiber loop 22 is an ordinary single-mode optical fiber having a polarization-preserving characteristic of several hundred meters. It is wound in a coil. With such a configuration of the optical system, the performance of the optical system becomes almost the same as that of a component having polarization-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, it is possible to prevent fluctuations in the size of the signal light and to reduce the cost of the components of the optical system. There is.

[0059]

As described above, according to the inventions described in the first and fourteenth aspects, since the phase modulator can be stably driven by an AC voltage having no harmful harmonic component, an offset occurs in the output. It is possible to provide a phase-modulation type optical fiber gyro that does not have variations and does not have scale fluctuations.

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

Further, according to the inventions described in the tenth and sixteenth aspects, the synergistic effect of simultaneously carrying out the two inventions makes the respective controls more accurate, there is no offset in the output, and the scale fluctuations. It is possible to provide a non-phase modulation optical fiber gyro.

[Brief description of drawings]

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

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

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

FIG. 4 is a configuration diagram showing an embodiment in which a subtraction process is performed by a numerical calculation 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 showing an example of an optical system composed of components having no polarization plane preservation characteristic.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Coherent light source, 2, 21 ... Optical branching device, 4, 22 ... Optical fiber loop, 5 ... Phase modulator, 6 ... Photoelectric conversion part, 8
... subtraction section, 9 ... amplification section, 11, 17 ... analog switch, 12 ... waveform shaping section, 13 ... AC amplitude detection section, 14 ...
Power amplification section, 15 ... A / D conversion section, 16 ... Numerical value calculation section,
20 ... Depolarizer.

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[Procedure amendment]

[Submission date] February 4, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0058

[Correction method] Change

[Correction content]

Further, in the above description, each component of the optical system has a polarization plane preserving characteristic. However, the present invention is not limited to this. For example, as shown in FIG. You may. In the figure, the depolarizer 20
Reference numerals a and 20b are for converting 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 °. It is a thing. The optical splitters 21a and 21b are fused single-mode optical fibers having no polarization-preserving characteristics, and the optical fiber loop 22 is an ordinary single-mode optical fiber having a polarization-preserving characteristic of several hundred meters. It is wound in a coil. With such a configuration of the optical system, the performance of the optical system becomes almost the same as that of a component having polarization-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, it is possible to prevent fluctuations in the size of the signal light and to reduce the cost of the components of the optical system. There is.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigeru Oho 7-1-1 Omika-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi Research Laboratory (72) Inventor Hiroshi Kajioka 880, Sunazawa-machi, Hitachi-shi, Ibaraki Hitachi (72) Inventor, Tatsuya Kumagai, Tatsuya Kumagai, Electric Wire Co., Ltd.Hitachi, Takasago Branch, Hitachi City, Hitachi, Ltd. (72) Yukio Uesugi, Sunazawa, Hitachi, Ibaraki Prefecture 880, Machi Hitachi Cable Co., Ltd. Hidaka Factory Takasago Branch Factory

Claims (16)

[Claims] 1. A light output control means of a minimum coherent light source,
An optical branching unit for branching and combining lights from coherent light sources in two directions, an optical fiber loop for propagating the branched lights in mutually reverse rotations, and a phase modulation for applying an AC phase bias to the branched lights. In the phase modulation type optical fiber gyro, which comprises a control means, a photoelectric conversion part for converting the signal light of these optical systems into an electric signal, and a signal processing part for outputting a detection value of the input angular velocity from the electric signal, the phase modulation The control means is provided with a subtraction amplification unit for a plurality of signals relating to the degree of phase modulation, and an AC conversion unit that converts the output of this subtraction amplification unit into an AC of a predetermined frequency, and the output of this AC conversion unit forms a phase modulator. A phase-modulation optical fiber gyro characterized by being driven so that the degree of phase modulation follows a target value. 2. The phase modulation type optical fiber gyro according to claim 1, wherein the AC conversion section is composed of an analog switch and a waveform shaping section. 3. The phase modulation system according to claim 1, wherein the subtraction amplification unit subtracts and amplifies the second harmonic component and the fourth harmonic component of the predetermined frequency included in the electric signal. Fiber optic gyro. 4. The subtraction amplifying unit according to claim 1, wherein the target value of the modulation factor and the predetermined frequency included in the electric signal are set to two.
A phase modulation type optical fiber gyro, which is characterized by performing subtraction and amplification between the ratio of the next harmonic component and the fourth harmonic component. 5. The subtraction amplifying unit according to claim 1, wherein the target value of the modulation factor and the predetermined frequency included in the electric signal are set to two.
A phase-modulation optical fiber gyro, which is characterized by performing subtraction and amplification between a second harmonic component and any one of a fourth harmonic component. 6. A light output control means of a minimum coherent light source,
An optical branching unit for branching and combining lights from coherent light sources in two directions, an optical fiber loop for propagating the branched lights in mutually reverse rotations, and a phase modulation for applying an AC phase bias to the branched lights. In the phase modulation type optical fiber gyro, which comprises a control unit, a photoelectric conversion unit that converts the signal light of these optical systems into an electric signal, and a signal processing unit that outputs a detection value of the input angular velocity from the electric signal, the optical output The control means is provided with an AC amplitude detection unit for the electric signal, a subtraction amplification unit for the target value of the output and the optical output of the AC amplitude detection unit, and a power amplification unit for the output of the subtraction amplification unit. A phase modulation type optical fiber gyro, wherein a 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. The phase modulation type optical fiber gyro according to claim 6, wherein the AC amplitude detector is a peak value detector. 8. The phase modulation optical fiber gyro according to claim 6, wherein the AC amplitude detector is a half-wave or full-wave rectifier. 9. The AC amplitude detection unit according to claim 6,
A phase modulation optical fiber gyro, which is a numerical operation unit including a / D converter. 10. A phase modulation optical fiber gyro according to claim 1 or 6, wherein the subtraction amplifying section outputs an integrated value of the subtraction value. 11. A phase modulation optical fiber gyro according to claim 1, wherein the subtraction amplification section is an analog circuit and outputs an integrated value of the subtraction value. 12. A phase modulation optical fiber gyro according to claim 1 or 6, wherein the subtraction amplification section performs the subtraction by a numerical calculation section and the amplification by an analog circuit. 13. A light output control means of a minimum coherent light source, an optical branching unit for branching and combining lights from the coherent light source in two directions, and light for propagating the branched lights in mutually reverse rotations. A fiber loop, a phase modulation control unit that gives an AC phase bias to the branched light, a photoelectric conversion unit that converts the signal light of these optical systems into an electric signal, and a detected value of the input angular velocity from the electric signal. In a phase modulation type optical fiber gyro consisting of a signal processing unit for outputting, an AC amplitude detection unit of the electric signal in the optical output control unit, a subtraction amplification unit of the output of the AC amplitude detection unit and a target value of the optical output, An output power amplification section of the subtraction amplification section is provided, and further, the phase modulation control means converts the subtraction amplification section of a plurality of signals relating to the degree of phase modulation and the output of the subtraction amplification section into an alternating current of 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 the light of the coherent light source into non-polarized light, and a polarization device for branching the non-polarized light into two directions. A first optical branching portion having no wavefront preserving characteristic, a polarizer that polarizes the unpolarized light, and a second optical brancher having no polarization preserving characteristic that splits and combines the polarized light in two directions, A second depolarizer, which is connected to one of the outlets of the second optical branching device to convert polarized light into non-polarized light again, and polarization plane preservation characteristics of propagating the branched light in opposite rotations. There is no optical fiber loop, a phase modulation control means for applying an AC phase bias to the branched light, a photoelectric conversion part for converting signal light of these optical systems into an electric signal, and detection of an input angular velocity from the electric signal. Phase modulation optical fiber jar consisting of a signal processing unit 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 of a predetermined frequency is provided, and the phase modulator is driven by the output of the AC converter to cause the phase modulation degree to follow a target value. Modulation type optical fiber gyro. 15. A light output control means of the minimum coherent light source, a first depolarizer for converting the light of the coherent light source into non-polarized light, and a polarization device for branching the non-polarized light into two directions. A first optical branching portion having no wavefront preserving characteristic, a polarizer that polarizes the unpolarized light, and a second optical brancher having no polarization preserving characteristic that splits and combines the polarized light in two directions, A second depolarizer, which is connected to one of the outlets of the second optical branching device to convert polarized light into non-polarized light again, and polarization plane preservation characteristics of propagating the branched light in opposite rotations. There is no optical fiber loop, a phase modulation control means for applying an AC phase bias to the branched light, a photoelectric conversion part for converting signal light of these optical systems into an electric signal, and detection of an input angular velocity from the electric signal. Phase modulation optical fiber jar consisting of a signal processing unit that outputs a value In (b), the optical output control means includes an AC amplitude detection unit for the electrical 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. And a coherent light source is driven by the output of the power amplification unit 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 the light of the coherent light source into non-polarized light, and a polarization device for branching the non-polarized light into two directions. A first optical branching portion having no wavefront preserving characteristic, a polarizer that polarizes the unpolarized light, and a second optical brancher having no polarization preserving characteristic that splits and combines the polarized light in two directions, A second depolarizer, which is connected to one of the outlets of the second optical branching device to convert polarized light into non-polarized light again, and polarization plane preservation characteristics of propagating the branched light in opposite rotations. There is no optical fiber loop, a phase modulation control means for applying an AC phase bias to the branched light, a photoelectric conversion part for converting signal light of these optical systems into an electric signal, and detection of an input angular velocity from the electric signal. Phase modulation optical fiber jar consisting of a signal processing unit that outputs a value In (b), the optical output control means includes an AC amplitude detection unit of the electric signal, a subtraction amplification unit of the output of the AC amplitude detection unit and a target value of the optical output, and a power amplification unit of the output of the subtraction amplification unit. Further, the phase modulation control means is provided with a subtraction amplification section for a plurality of signals relating to the degree of phase modulation, and an AC conversion section for converting the output of the subtraction amplification section into an AC of a predetermined frequency. A phase-modulation optical fiber gyro characterized in that the degree of modulation follows the target value.