JPH03118415A - Interference measuring method, interference sensor, interference sensor circuit, interference sensor lsi, and optical fiber gyro apparatus - Google Patents

Abstract

PURPOSE:To measure with high accuracy in a wide dynamic range by measuring time information of a characteristic point of time waveforms of an interference wave signal resulting from the interference of waves to be interfered and calculating the phase difference between the waves to be interfered. CONSTITUTION:A light beam from a light source 10 is, through a fiber coupler 21 and a polarizer 30, incident upon a fiber coupler 22, where it is divided into two beams spreading right and left around a fiber loop 40. The phase of the light beams is modulated at one end of the loop by a phase modulator 50 in correspondence to a modulating signal generated from a phase modulator driving circuit 60 and then returned to the coupler 22. Accordingly, the light beams are coupled again to be an interference light. The interference light advances in a reverse direction from the coupler 22 to return to the coupler 21 through the polarizer 30. Then, the light is divided by the coupler 21 and a part of the light reaches a photoelectric converter circuit 70 to be detected as an interference signal. The angular velocity of rotation is extracted from this interference signal in a signal processing circuit 100.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a measurement method using wave interference, and particularly relates to an interference sensor or an interference sensor LSI equipped with a phase modulation means, and an optical fiber using the same. Regarding a gyro device.

[Prior Art] Measuring devices or sensors that utilize optical interference are widely used as means for measuring physical quantities with high precision. For example, an optical fiber gyro, which is a sensor that detects rotational angular velocity, uses the measurement principle of interference between two light waves propagating in opposite directions through an optical fiber loop.

That is, the rotational angular velocity is obtained by measuring the phase difference of interference light.

Conventionally, in such interferometric measurements, various methods have been devised to improve measurement performance by introducing an optical modulator into an optical system and processing alternating current signals generated by modulation. For example, the optical fiber gyro described in Japanese Patent Application Laid-open No. 56-94680 uses a single phase modulator to improve sensitivity at zero angular velocity.

In interferometric measurements using such modulation, a method that focuses on frequency components of an interference signal obtained by photoelectrically converting interference light has conventionally been used as a means of measuring phase difference or a physical quantity to be detected. The above-mentioned Japanese Patent Application Publication No. 1983
The optical fiber gyro described in Japanese Patent No. -94680 also employs a method of synchronously detecting the modulation frequency.

In addition, Japanese Patent Application Laid-open No. 63-38111 or Electronics Letter 19 (1983) pages 997 to 999 (Electronics Latter
In the optical fiber gyro discussed in J. S., 19 (1983) pp. 997-999), a signal processing method that similarly focuses on the frequency components of interference signals is used.

[Problem to be Solved by the Invention 1] In the above conventional technology, the phase difference of the interferometer is determined by frequency analysis of the interference signal, so it is essential to measure the amplitude of the interference signal or various frequency components contained in the interference signal. It is.

For this reason, high-precision measurements require highly accurate operational amplifiers, analog/digital converters, etc., which poses a problem in that the electronic circuit becomes complicated.

This problem can also be seen as a problem in that if the above-mentioned conventional technology is implemented using a digital circuit, it becomes complicated and large-scale, and it is difficult to implement it into an LSI. This is because it is difficult to implement an analog circuit into an LSI.

In addition, it is practically difficult to measure signal amplitude with high precision using a linear circuit, and there is a problem that the dynamic range of interference measurement is limited. It is an object of the present invention to provide an interference measurement method, an interference sensor, an interference sensor circuit, an interference sensor LSI, and an optical fiber gyro device using these, which can realize measurement with high precision and a wide dynamic range without using.

[Means for Solving the Problem] In order to achieve the above object, the present invention measures the time information of the time waveform feature points of the interference wave signal caused by the interfered waves, and determines the position between the interfered waves from the measurement result. Provided is an interference measurement method characterized by calculating a phase difference.

Moreover, the present invention aims to achieve the above object.

A means for extracting waveform feature points of a time waveform of an interference wave signal, and measuring a time interval between the extracted waveform feature points or a time interval between the waveform feature point and a predetermined time reference point related to the interfered wave. Provided is an interference sensor characterized by having means for.

In addition, a phase modulation means phase-modulates the interfered signal with a phase modulation amount corresponding to the drive signal, and a waveform feature point of the time waveform of the interference wave signal by the interfered wave, which is the phase-modulated interfered signal, is extracted. With means.

An interference sensor comprising means for measuring a time interval between extracted waveform feature points or a time interval between a waveform feature point and a predetermined time reference point of a drive signal of the phase modulation means. provide.

In this interference sensor, it is preferable that the phase modulation uses a periodic signal as a drive signal, and furthermore, based on the amount of phase modulation by the phase modulation detected using the measured value of the time interval, It is desirable to provide means for compensating the amount of phase modulation.

Further, each of the interference sensors desirably sets a maximum point or a minimum point or a waveform center of the time waveform of the interference signal as the waveform feature point, and also sets the waveform characteristic point based on the time interval from the predetermined time reference point. , it is desirable to identify the type of the waveform feature point.

Further, it may include means for modulating the intensity of the interfered wave source using a local oscillation signal having a frequency spectrum different from that of the phase modulation drive signal and whose amplitude characteristics are flat up to a predetermined high-order frequency component. .

Further, in order to achieve the above object, the present invention provides a phase modulation means for phase modulating an interfered signal with an amount of phase modulation according to a drive signal, and an interference wave generated by the interfered wave, which is a phase modulated interfered signal. means for extracting a waveform feature point of a time waveform of a signal; a measurement target signal generating means for generating a measurement target signal which is a periodic signal having a phase corresponding to the time timing of the extracted waveform feature point; measurement reference signal generation means for generating a measurement reference signal which is a periodic signal having a phase corresponding to a predetermined time timing extracted from a waveform; a first frequency conversion means for converting the frequency of the measurement target signal; and a first frequency conversion means for converting the frequency of the measurement target signal; A second frequency conversion means for converting the frequency of the reference signal; and a means for measuring the phase difference between the signal output from the first frequency conversion means and the signal output from the second frequency conversion means. An interference sensor is provided.

Further, in order to achieve the above object, a phase modulation means for phase modulating the interfered signal with an amount of phase modulation according to the drive signal, a first frequency conversion means for converting the frequency of the drive signal, and a first frequency conversion means for performing phase modulation. a second frequency conversion means for converting the frequency of the interference signal due to the interference signal, which is the interference signal; a means for extracting the waveform feature points of the time waveform of the frequency-converted interference signal; time interval, or
An interference sensor is provided, comprising means for measuring a time interval between a time reference point extracted from a time waveform of a frequency-converted drive signal and a waveform feature point extracted.

In addition, in the interference sensor equipped with these frequency conversion means, each of the frequency conversion means generates a local oscillation signal having a frequency spectrum whose amplitude characteristic is flat up to a predetermined high-order frequency component at a frequency different from the phase modulation drive signal. It is desirable to frequency-convert the frequency-converted signal using the signal. Further, each of the frequency conversion means may be realized by a frequency conversion circuit consisting of a multiplier and a filter circuit, or the local oscillation signal, the measurement target signal, and the measurement reference signal are each a rectangular wave, Each of the frequency conversion means may be realized by a frequency conversion circuit consisting of an exclusive OR circuit and a filter circuit.

Furthermore, one aspect of the present invention provides an optical fiber gyro device characterized by having the above-mentioned interference sensor and means for calculating an angular velocity from the measurement result of the interference sensor for the purpose reliability.

Further, in order to achieve the above-mentioned object, the present invention includes a measurement unit that measures time information of a time waveform feature point of an interference wave including physical quantity information, and a calculation unit that calculates the physical quantity from the measurement result of the measurement unit. An interference sensor circuit or an interference sensor LSI is provided.

In addition, the time interval between the waveform feature points of the time waveform of the interference wave signal due to the interference of interfered waves having a phase difference corresponding to a physical quantity, or the time interval between the waveform feature points and a predetermined time reference point related to the interfered wave. , or the time interval between waveform feature points of a time waveform of a frequency-converted interference wave signal, or.

a counter unit that measures the time interval between a waveform feature point of the time waveform of the frequency-converted interference wave signal and a predetermined time reference point related to the frequency-converted interfered wave; and a counter unit that measures the physical quantity based on the count result of the counter unit. The present invention also provides an interference sensor circuit or an interference sensor LSI characterized by having an arithmetic unit that calculates .

Note that each of the interference sensors is determined based on the level of the interference signal amplitude relative to a predetermined threshold level.

The waveform feature points may be identified.

Further, it is preferable that the means for measuring each time is a digital counting circuit. In this case, the counting clock of the digital counting circuit is preferably extracted from the system clock of the electronic system that utilizes the measurement results of the interference sensor.

[Operation] According to the interference measurement method according to the present invention, the phase difference of the interfered waves can be determined by measuring the time information of the time waveform feature points of the interference wave signal and by calculating the phase difference between the interfered waves based on the measurement result. It is obtained by calculating the phase difference.

Further, according to the interference sensor of the present invention, the waveform feature points of the time waveform of the interference wave signal are extracted, and the time interval between the extracted waveform feature points or a predetermined time interval related to the waveform feature point and the interfered wave is determined. Measure the time interval from the time reference point. From this measured time interval, the phase difference between the interfered waves or the physical quantity appearing in the phase difference can be determined.

Further, according to the interference sensor according to the present invention, the phase modulation means adjusts the interference phase difference between the interfered waves by phase modulating the interfered signal, and the interference between the interfered waves subjected to phase modulation is Extracting waveform feature points of the time waveform of the interference wave signal, and measuring the time interval between the extracted waveform feature points, or the time interval between the waveform feature points and a predetermined time reference point of the drive signal of the phase modulation means. do. Note that in order to simplify interference, sensor configuration, and processing, it is preferable that the phase modulation is performed by using a periodic signal as a drive signal to phase-modulate the interfered wave. It is desirable to compensate the amount of phase modulation based on the amount of phase modulation caused by the phase modulation detected using the measured value of the interval.

Further, it is preferable that the maximum point or the minimum point or the waveform center of the time waveform of the interference signal be set as the waveform feature point, and based on the time interval with the predetermined time reference point, the waveform feature point is It is desirable to identify the type. This is to simplify processing.

Further, means is provided for modulating the intensity of the interfered wave source using a local oscillation signal having a frequency spectrum whose amplitude characteristic is flat up to a predetermined high-order frequency component at a frequency different from the phase modulation drive signal, Wave motion may also be measured.

Further, according to the interference sensor according to the present invention, the phase modulation means adjusts the interference phase difference between the interfered waves by phase modulating the interfered signal, and the interference between the interfered waves subjected to phase modulation is The waveform feature points of the time waveform of the interference wave signal are extracted, and the measurement target signal, which is a periodic signal with a phase corresponding to the time timing of the extracted waveform feature points, and a predetermined signal extracted from the time waveform of the phase modulation drive signal are A measurement reference signal, which is a periodic signal having a phase corresponding to the time timing, is generated, and after converting the frequencies of these measurement target signals and the total reference signal, the phase difference between the two signals is measured.

Further, according to the interference sensor according to the present invention, the phase modulation means adjusts the interference phase difference between the interfered waves by yA by phase modulating the interfered signal, and the interference between the phase modulated interfered waves Frequency and phase change of interference wave signal due to! g
After converting the frequency of the llIi motion signal, extract the waveform feature points of the time waveform of the frequency-converted interference signal, and calculate the time interval between the extracted waveform feature points or the time waveform of the frequency-converted phase modulation drive signal. The time interval between the time reference point extracted from and the extracted waveform feature point is measured.

In addition, in the interference sensor equipped with these frequency conversion means, each of the frequency conversion means generates a local oscillation signal having a frequency spectrum whose amplitude characteristic is flat up to a predetermined high-order frequency component at a frequency different from the phase modulation drive signal. It is desirable to frequency-convert the frequency-converted signal using the signal. This is because the original time waveform can be saved even after frequency conversion.

Further, the one frequency conversion means may be realized by a frequency conversion circuit consisting of a multiplier and a filter circuit. In this case, the filter circuit only converts a predetermined low frequency component of the signal to be converted and the signal multiplied by the local oscillation signal. Take out.

Alternatively, the local oscillation signal, measurement target signal, and measurement reference signal may each be rectangular waves, and these signals may be applied to an exclusive OR circuit and a filter circuit in this order.

Furthermore, according to the optical fiber gyro device according to the present invention,
The Sagnac effect, which appears as a phase difference in the interference wave signal of light traveling in the opposite direction through the optical fiber loop, is measured by the interference sensor, and the rotational angular velocity of the optical fiber loop is determined.

Moreover, the interference sensor circuit or interference sensor L according to the present invention
According to SI, a measurement unit measures time information of a time waveform feature point of an interference wave that includes physical quantity information, and a calculation unit calculates the physical quantity from the measurement result of the measurement unit.

Moreover, the interference sensor circuit or interference sensor L according to the present invention
According to SI, the counter section measures the time interval between waveform feature points of the time waveform of an interference wave signal due to interference of interfered waves having a phase difference corresponding to a physical quantity, or the time interval between waveform feature points and the interfered wave. the time interval with respect to a predetermined time reference point,
Or, the time interval between the waveform feature points of the time waveform of the frequency-converted interference wave signal, or the predetermined time interval between the waveform feature points of the time waveform of the frequency-converted interference wave signal and the frequency-converted interfered wave. The calculation unit calculates the physical quantity from the count result of the counter unit.

As described above, according to the present invention, the phase difference between interfered waves is determined by time measurement, and time measurement can be performed with high precision using a digital counting circuit or the like, and high precision analog/digital conversion can be performed. This can be achieved without using any equipment. In particular, digital counting circuits are not only easy to apply integrated circuit technology to, but also can achieve high resolution by increasing the operating frequency of the circuit, that is, the counting clock. Therefore, it is possible to expand the dynamic range by increasing the speed of the circuit.

(The following is a blank space) [Example] Hereinafter, an example of the present invention will be described using an example of application to an optical fiber gyro device.

FIG. 1 shows the optical system configuration of a phase modulation type optical fiber gyro. This optical system has essentially the same optical system configuration as the optical fiber gyro disclosed in JP-A-56-94680, but it is different from that disclosed in JP-A-56-94680. However, the phase modulation frequency is not particularly limited.

Hereinafter, the range necessary for explaining the present invention regarding the generation of interference signals in this optical system will be described.

The detailed principle of rotation detection is described in Japanese Patent Laid-Open No. 56-94680, etc., so the description thereof will be omitted.

A light beam from a light source 10 is transmitted to a first fiber coupler 2
1. The light beam propagates through the polarizer 30 and reaches the second fiber coupler 22, where it is split into two light beams that propagate counterclockwise and clockwise through the fiber loop 40. These light beams are modulated in optical phase by a phase modulator 5o according to a modulation signal generated by a 1-phase modulator drive circuit 60 at one end of the loop, and then reach the fiber coupler 22.
They combine again to become interference light.

This interference light travels in the opposite direction from the fiber coupler 22, passes through the polarizer 30, and returns to the first fiber coupler 21.

The interference light is split at the first fiber coupler 21,
Photoelectric conversion circuit 7, part of which uses photodiodes etc.
0 and is detected as an interference signal.

The signal processing circuit 100 extracts the rotational angular velocity from this interference signal.

Here, before explaining the signal processing circuit 100, the properties of the interference signal will be described, the focus of the present invention will be reconfirmed, and the application in this embodiment will be clarified.

If the interference signal is P, from the principle of interference, this can be expressed as (1),
It can be expressed by equation (2).

P = I (], + υ cos ψ) (1) ψ = φS
+φ (1) −φ (7-) (2) where ψ is the optical phase difference, P is the intensity of the interference light, υ is the visibility (contrast) of the interferometer, and φS is proportional to the rotational angular velocity of the optical fiber loop. This is the Sagnac phase difference. Further, τ is the propagation delay time of the light wave propagating through the fiber loop, and is given by equation (3).

τ = nα/c (3
) where n is the refractive index of the fiber, Q is the fiber length, and C is the speed of light.

In this embodiment, an example will be explained in which a sine wave with a period T is used as the phase modulation signal.

In this case, assuming that the characteristics of the phase modulator 50 are ideal, the optical phase difference ψ can be expressed by equations (4) to (6).

ψ=φS+ηCO8θ
(4) 020m (t-τ/2)
(5) η=2φm 5in (ωmτ/2)
(6) Here, η is the effective phase modulation index, ωm=2π/T is the modulation angular frequency, and φm is the modulation amplitude.

The first example will be described below.

In the first embodiment, attention is focused on the maximum and minimum points of the interference signal time waveform as waveform feature points.

At the maximum and minimum points, equation (7) holds true for the differential signal of the interference signal as a necessary condition.

d P/d t = −I v ωmy7sinθsi
nψ=O(7) However, dφs/dt40. d 77/
dt'40 was assumed.

Therefore, the time when sin O= Ol or sinψ=O
At t, the interference signal takes an extreme value.

Here, in the first embodiment, the following equations (8) to (10) are set as design conditions for the optical fiber gyro.

■Effective phase modulation index: π/2≦η〈π (8) ■Measured phase difference: 1φsl<π/2 (9) ■Optical phase difference = 1ψ1〈π (10) Under this condition, the interference signal time The waveform becomes a time waveform as shown in FIG. 2, and four maximum and minimum points appear during one cycle of one phase modulator signal.

Let the solution of sinθ=0 be 01, θ3, and the solution of sinψ=O be 02, θ4, then with θ1=O as the reference, θ
3=π, and from equations (4) and (9), φS=-
ηcosθ2=−ηcosθ4 (11) holds true.

Therefore, the time positions of the maximum points θ2 and θ4 change according to equation (11) according to the measured light phase difference φS (proportional to the rotational angular velocity in this embodiment).

Moreover, the minimum points θ1 and θ3 are fixed points that do not depend on φS. η is a constant determined by the phase modulator characteristics and the phase modulator drive signal.

Therefore, θ2 (or
By measuring the phase difference θ4), the measured phase difference φS can be found using equation (11).

Also, from equation (4), in Fig. 2, from equation (4), 0
Since the phase distances between 2 and 03=π and θ4 and 03=π are equal, even if the phase difference between 02 and 04 is measured, the measured phase difference φS can be obtained using equation (11).

The phase difference measurement of the above maximum and minimum points is as follows: (5)
From the equation, it is equivalent to measuring the time interval at each point. Therefore, in this embodiment, this time difference is measured.

As a time reference for time interval measurement, a highly accurate and highly stable clock can be obtained relatively easily using a crystal oscillator or the like. Additionally, by using a faster clock, you can increase the resolution and number of significant digits in your measurements.

In other words, the dynamic range can be expanded.

Furthermore, as is clear from equation (11), when φS=O, which is the zero point of the rotational angular velocity, cosθ2 = cosθ4
=0, that is, θ2=04 = 90'±180°.

Therefore, when φS≠0, φS=±TlCO3
It can be expressed as (90'+80)=±η5in(80). The change in phase with respect to the change in value of ±η5in (Δθ), which is a sine function, is at its zero point, that is, φS=±
It is largest near ηsin (Δθ)=0.

On the other hand, according to equation (5), the change in time position is proportional to the change in phase.

Therefore, in the measurement of φS by time position measurement at the θ2.04 point according to this embodiment, the measurement sensitivity can be maximized near φS=0.

As described above, an aim of the present invention is to use highly accurate time measurement to facilitate interference measurement and improve performance.

The signal processing circuit 100 according to the embodiment of Mizui 1 will be described below.

FIG. 3 shows the configuration of a signal processing circuit 100 according to one embodiment.

In the figure, 70 is a photoelectric conversion circuit that converts interference light into an electrical signal and outputs the interference signal. The interference signal output from the photoelectric conversion circuit 70 is input to a differentiation circuit 101 and differentiated. The zero crossing detection circuit 102 detects the zero crossing point of this differential signal,
Generates an extremum timing pulse train that indicates the moments of maximum and minimum of the interference signal.

The level comparison circuit 104 compares the level of the interference signal with the predetermined threshold level and outputs a level signal which is a rectangular wave corresponding to the level of the interference signal. A predetermined phase timing is created using the modulation signal as a reference input.

The count control circuit 105 controls the count of the counting circuit 106 based on the extreme value timing pulse output from the zero crossing detection circuit 102, the fixed timing pulse output from the fixed phase pulse generation circuit 103, and the level signal output from the level comparison circuit 104. Generates count start and count end pulses that control operations.

The counting circuit 106 counts the count clock from the count clock generation circuit 107 in accordance with the instruction to start and end counting. The arithmetic processing circuit 108 is a counting circuit 106
The measured phase difference φS is calculated using equation (11), and then this is converted into a rotational angular velocity.

Note that the means for instantaneous detection of the maximum and minimum of the interference signal described above may be realized by a peak detection circuit or the like.

Further, as the waveform feature point of the time waveform of the interference signal, other feature points such as the waveform center determined from the zero-order moment of the time waveform may be used.

The operation of the first embodiment will be explained below.

In this embodiment, the zero crossing detection circuit 102 generates four extreme value timing pulses during one period of phase modulation.

In order to calculate φS using the above equation (11), it is necessary to associate each of these four pulses with 01 to θ4. Therefore, in the embodiment, the fixed phase pulse generation circuit 103, which generates a predetermined phase timing using the modulation signal generated by the phase modulator drive circuit 60 as a reference input, compares the level of the interference signal level and the predetermined threshold level. A level comparison circuit 10 that outputs a level signal that is a rectangular wave corresponding to
4 was established.

The count control circuit 105 controls the count of the counting circuit 106 based on the extreme value timing pulse output from the zero crossing detection circuit 102, the fixed timing pulse output from the fixed phase pulse generation circuit 103, and the level signal output from the level comparison circuit 104. Generates count start and count end pulses that control operations. In this embodiment, as shown in FIG. 2, the time interval between θ2 and 04 is measured by generating a count start pulse at the timing of the maximum point θ2 and a count end pulse at the timing of the maximum point θ4. . The counting circuit 106 follows this count start/end instruction and starts the count clock generation circuit 107.
Count the count clock from. Arithmetic processing circuit 10
8 reads the count value of the counting circuit 106, and formula (11)
) is used to calculate the measured phase difference φS, and then convert this into a rotational angular velocity. The fixed timing pulse provides the start timing for the above series of operations.

Note that the phase modulator drive circuit 60 generates a phase modulation signal based on the count clock from the count clock generation circuit 107. Therefore, the phase modulator drive circuit 60 and the signal processing circuit 100 operate synchronously.

A second embodiment of the present invention will be described below.

When a piezoceramic element is used as a phase modulator, significant temperature dependence may be seen in the modulation characteristics. For this reason, the effective phase modulation index η will drift with temperature, and temperature characteristics will appear in the optical fiber gyro output, which is undesirable.

Therefore, in the second embodiment, an example will be described in which the signal processing circuit 100 is provided with means for compensating for fluctuations in the modulation index η.

The design conditions for the optical fiber gyro in the second embodiment are as follows:
The following equations (12) to (14) are used.

■Effective phase modulation index: π≦η〈2π (12) ■Measured phase difference: 1φsl<π (13) ■Optical phase difference; 1ψ1×2π (14) In this case, the interference signal time waveform is shown in Figure 4. Thus, from the zero point of the differential signal, eight maximum and minimum points occur during one period of phase modulation.

As shown in Figure 4, these extreme values are respectively 01~
Let it be θ8.

01 to θ4 are the same as the first example, sin O=O
This is a solution that satisfies l and sinψ=0. Therefore, θ1=O and θ3=π are fixed points that do not depend on the measured phase difference (proportional to the rotational angular velocity in this embodiment) φS. θ5=π to θ8 are solutions that satisfy sin ψ=O added by changing the design conditions of the optical fiber gyro to equations (12) to (14). The phases of θ2 and 04, and 05 to θ8 are all determined depending on φS.

Therefore, these maxima.

Similarly to the first embodiment, φS can be measured by measuring the phase difference between the minimum points or the time interval.

FIG. 5 shows the configuration of a signal processing circuit 100 according to a second embodiment.

The configuration of the signal processing circuit 100 according to the second embodiment is as follows.
Although the signal processing circuit according to the second embodiment is almost the same as the signal processing circuit according to the second embodiment, a counting circuit 109 is newly provided in the second embodiment. Also,
The count control circuit 105 is replaced by the second count control circuit 11
5, the arithmetic processing circuit 108 is replaced with the second arithmetic processing circuit 118.
Replaced with . The other parts are the same as the parts with the same reference numerals of the signal processing device according to the first embodiment (see FIG. 3), so the explanation will be omitted.

The operation will be explained below.

The second count control circuit 115 generates a count start pulse at phase timing θ1, and first and second count end pulses at phase timings 02 and θ3.

The counting circuit 107 and the counting circuit 109 respectively follow the cues of the count start pulse, the first and second count end pulses, and set the time interval Δ1 between θ5 and 01, and the time interval Δ1 between θ2 and O1.
The time interval Δ2 is measured. At this time, the following (15),
Equation (16) holds true.

φS+ηcosωIΔ1=π (15
)φs+ηcosωmΔ2=O(16) The second arithmetic processing circuit 118 solves equations (15) and (16) as simultaneous equations for φS and η, and calculates φS and η. As a result, if the effective phase modulation index η differs from the predetermined value (Equation (6)), the second control processing circuit 118 adjusts the control signal to the phase modulator drive circuit 60 to set η to the predetermined value. keep.

Obtaining the rotational angular velocity from the measured phase difference φS is the same as in the first embodiment.

It is also the same as in the first embodiment that a fixed timing pulse provides the start timing of the above sequence.

Note that the control signal to the phase modulator drive circuit 60 is adjusted so that η
Instead of keeping η at a predetermined value, the calculation processing circuit 118 may perform calculations by compensating for the deviation of η.

A third embodiment of the present invention will be described below.

FIG. 6 shows the configuration of a signal processing device 100 according to a third embodiment.

The design conditions of the optical fiber gyro according to this example are as follows:
However, in this embodiment, the local oscillator 16
0 was newly established and a frequency conversion means was introduced to improve the accuracy of extreme timing phase difference measurement.

FIG. 6 shows the configuration of the signal processing device according to this embodiment.

In the figure, the local oscillator 160 has an angular frequency ω expressed by equation (17).
A local oscillation signal, which is a sine wave of e, is generated.

ωe=ωm−Δω (17)
In other words, the local oscillation frequency 0 section is the phase modulation angular frequency ωm
differs by the angular frequency Δω. Further, both vending machines operate based on a clock signal generated by the count clock generation circuit 107.

70 is a photoelectric conversion circuit that converts interference light into an electric signal and outputs the interference signal. The interference signal output from the photoelectric conversion circuit 70 is input to a differentiation circuit 101 and differentiated. The zero crossing detection circuit 102 detects the zero crossing point of this differential signal. The phase measurement oscillator 110 inputs the extreme value timing pulse from the zero crossing detection circuit 102 and the level signal from the level comparison circuit 104, and generates a measurement target signal that is a sine wave whose zero crossing point is the phase of the maximum point. Further, a fixed timing pulse from the fixed phase pulse generation circuit 103 is also input, and a measurement reference signal which is a sine wave with this phase as a zero crossing point is also generated. The timing relationship of each of the above signals is as follows.
As shown in the figure, the angular frequencies of the measurement target signal and the measurement reference signal are equal to the phase modulation angular frequency ωm.

The measurement target signals output from the phase measurement oscillators 1 and 10 are input to the mixer circuit 111 and multiplied by the local oscillation signal. Thereafter, from the output of the mixer circuit, a low-pass filter 113 extracts only the beat signal to be measured whose angular frequency is the difference frequency Δω between the phase modulation angular frequency ωm and the local oscillation frequency ω.

That is, the frequency is converted by extracting only the difference frequency component of a signal having a fractional frequency component of the difference and the sum of the angular frequencies of the respective multiplicable signals obtained by multiplication.

Furthermore, in the same way, the measurement reference signal has an angular frequency Δω
is converted into a measurement reference beat signal.

The second count control circuit 115 detects a zero crossing point between the measurement reference beat signal and the measurement target beat signal.

Count start and end pulses are generated at each timing. 106 counts the count clock from the count clock generation circuit 107 in accordance with the instruction to start and end the count. The arithmetic processing circuit 108 reads the count value of the counting circuit 106, calculates the measured phase difference φS, and then converts this into a rotational angular velocity.

The phase modulator drive circuit 60 is the count clock generation circuit 1
A phase modulation signal is generated based on the count clock from 07.

Hereinafter, the operation of the embodiment of Sui-Tei 3 will be explained.

Since the phase of the measurement reference signal is fixed and known in advance, the angular velocity output of the optical fiber gyro can be expressed as (11)
To calculate using the formula, as shown in the first embodiment, the phase difference Δθ of the measurement target signal with respect to the measurement reference signal is calculated.
All you have to do is measure it.

Alternatively, since there are two maximum points in one cycle of phase modulation as in the first embodiment, the first and second measurement target signals may be generated from the timing of these maximum points. In this case, the first and second maximum points can be easily distinguished using the fixed timing pulse as a reference. In this case, the phase difference of the light to be measured can be obtained from the phase difference between the first and second signals to be measured, as in the first embodiment.

In the third embodiment, the measurement target signal and the measurement reference signal are
It is characterized in that it is mixed with the local oscillation signal and converted into a low frequency beat signal.

That is, the measurement target signal output from the phase measurement oscillator 110 is input to the mixer circuit 111 and multiplied by the local oscillation signal. The output of the mixer circuit passes through a low-pass filter 113 and is converted into a beat signal to be measured whose angular frequency is the difference frequency Δω between the phase modulation angular frequency ωm and the local oscillation frequency ω.

Furthermore, in the same way, the measurement reference signal has an angular frequency Δω
is converted into a measurement standard beat signal.

The period T' of these beat signals is expressed by equation (18).

T' = 2π/Δω (1
8) In the above frequency conversion process, if the phase characteristics of the low-pass filters 113 and 114 are the same, the phase difference between the measurement target signal and the measurement reference signal is completely preserved as the phase difference between the measurement target beat signal and the measurement reference beat signal. Ru.

That is, as shown in FIG. 8, the phase relationship between the measurement target beat signal and the measurement reference beat signal is equal to the phase relationship between the measurement target signal and the measurement reference signal before frequency conversion. Therefore, since the frequency has shifted to the beat signal frequency Δω in the low frequency region, phase difference measurement becomes relatively easy.

Furthermore, even if the phase characteristics of the low-pass filters are not exactly equal, it is sufficient to check in advance the offset phase difference that depends on the phase characteristics of the filter circuit and correct it.

The measurement of the phase difference between the measurement target beat signal and the measurement reference beat signal can be realized in the same manner as in the first embodiment.

That is, in FIG. 6, the second count control circuit 11
5 detects the zero crossing points of the measurement reference beat signal and the measurement target beat signal, and generates count start and end pulses at respective timings.

Then, according to the instructions from the count control circuit 115, the count clock is counted by the counting circuit 106, and from the counting result,
The calculation of the angular velocity by the calculation processing circuit 108 using equation (11) is the same as in the first embodiment. FIG. 8 shows the timing relationship of the above signals.

As described above, in the third embodiment, phase difference measurement is moved to a low frequency region by frequency conversion, and even if the same count clock frequency is used, it is possible to measure time intervals with higher resolution than in the first embodiment, that is, phase difference measurement. made possible.

Note that in the third embodiment, the local oscillation signal, the measurement target signal,
Although the measurement reference signal and the measurement reference signal are sinusoidal waves, they may be other periodic signals such as a rectangular wave. In the case of rectangular waves, the mixer circuits 111 and 112 may be logic circuits based on exclusive OR.

The frequency conversion used in the third embodiment can also be realized by other means.

An example will be shown below as a fourth embodiment.

In the fourth embodiment, the interference signal itself and the phase modulation signal are mixed with a locally generated signal and modulated to a low frequency.

FIG. 9 shows the configuration of a signal processing circuit 100 according to a fourth embodiment.

Mixer circuit 111 and low-pass filter 113 frequency-convert the interference signal, and mixer circuit 112 and low-pass filter 114 frequency-convert the phase modulator drive signal. The waveform shaping circuit 120 shapes the local oscillation signal generated by the local oscillator 160. The other parts are the same as those in the first embodiment.
Since this is the same functional section as the code section, the explanation will be omitted.

The operation of the fourth embodiment will be explained below.

The optical fiber gyro design conditions of the fourth embodiment are the same as those of the first embodiment, and the signal timing relationship is also similar, but the first embodiment differs only in that the signal is processed in the low frequency region after frequency conversion. Different from the example.

Therefore, in phase measurement or time interval measurement, the weight per pulse of the count clock generated by the count clock generation circuit 107 is reduced, and resolution is improved by counting a large number of pulses.

Note that in order to preserve the time waveform of the interference signal in the low frequency region, the locally generated signal must contain the phase modulation angular frequency and its harmonic components with equal amplitude strength. Therefore, the fourth embodiment includes a waveform shaping circuit 120 that shapes the local oscillation signal generated by the local oscillator 160.

In addition, in the fourth embodiment, an example was explained in which the time waveform of the frequency-converted signal is saved even after one frequency conversion, but it is not necessarily necessary to perform the conversion to save the time waveform, and it is not necessary to perform the conversion to save the time waveform. It may also be realized by frequency conversion that can establish a correspondence relationship. In this case, the phase difference between the interfered signals can be obtained by measuring the time information of the points of the converted signal corresponding to the waveform feature points of the converted signal, depending on the conversion performed.

Next, a fifth example will be described.

In the fifth embodiment, the mixer circuit in the fourth embodiment is modified by modulating the intensity of the light source 70 with a locally generated signal.
frequency conversion.

Similar to the fourth embodiment, each frequency spectrum of one locally generated signal is made to have the same amplitude in order to preserve the interference signal waveform in a low frequency region.

FIG. 10 shows the configuration of a signal processing device 100 according to a fifth embodiment.

The configuration of the signal processing device according to the fifth embodiment is the same as the configuration of the signal processing device according to the fourth embodiment, except that the mixer circuit for the interference signal and the local oscillation signal is omitted. Therefore, the explanation will be omitted.

The embodiments of the present invention have been described above using an optical fiber gyro as an example. However, the present invention utilizes the general properties of waves, and is not limited to optical fiber gyros. The present invention can be applied as is to devices and techniques that measure physical quantities by interference of interfered waves such as (including 1), sound waves, and electron beams.

According to each of the above embodiments, the optical phase difference of the interferometer can be obtained by focusing on the time waveform of the interference signal and measuring the phase of the waveform feature point of the time waveform, that is, the time position or time interval. Therefore, there is no need for a highly accurate operational amplifier or an analog/digital converter, and there is an effect that the electronic circuit can be simplified. It is also possible to correct the drift of modulation means such as a phase modulator. Furthermore, unlike the method of measuring signal voltage fluctuations with high precision using a linear circuit, the dynamic range of interference measurement can be expanded by using a high-speed clock or by using a frequency conversion means.

[Effects of the Invention] As described above, the present invention provides an interference measurement method, an interference sensor, an interference sensor circuit, and an interference sensor that can realize measurement with high precision and a wide dynamic range without using a complicated linear circuit. LSIs and optical fiber gyros using these can be provided.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a phase modulation type optical fiber gyro, FIG. 2 is an explanatory diagram showing signal timing in the first embodiment of the present invention, and FIG. 3 is a diagram showing the first embodiment of the present invention. A block diagram showing the configuration of a signal processing circuit in
FIG. 4 is an explanatory diagram showing signal timing in the second embodiment of the present invention, FIG. 5 is a block diagram showing the configuration of a signal processing circuit in the second embodiment of the present invention, and FIG. 6 is a diagram showing the structure of the signal processing circuit in the second embodiment of the invention. 7 and 8 are explanatory diagrams showing signal timing in the third embodiment of the present invention, and FIG. 9 is a block diagram showing the configuration of the signal processing circuit in the third embodiment of the present invention. FIG. 10 is a block diagram showing the configuration of a signal processing circuit in a fifth embodiment of the present invention. 10... Light source, 30... Polarizer, 21.22...
Fiber coupler, 40...Fiber loop, 50...
... Optical phase modulator, 60... Optical phase modulator Iv! 70... Photoelectric conversion circuit, 100... Signal processing circuit, 101... Differential circuit, 102... Zero crossing detection circuit, 103... Fixed phase pulse generation circuit, 104...
- Level comparison circuit, 105.115... Count control circuit, 106... Counting circuit, 107... Count clock generation circuit, 108.118... Arithmetic processing circuit,
110... Phase measurement oscillator, 111.112... Mixer circuit, 113.114... Low pass filter, 1
20... Waveform shaping circuit, 160... Local oscillator

Claims (16)

[Claims] 1. An interference measurement method characterized by measuring time information of time waveform feature points of an interference wave signal caused by interference of interfered waves, and calculating a phase difference between interfered waves from the measurement results. 2. A means for extracting waveform feature points of a time waveform of an interference wave signal, and a time interval between the extracted waveform feature points, or
An interference sensor comprising means for measuring a time interval between a waveform feature point and a predetermined time reference point related to an interfered wave. 3. a phase modulation means for phase modulating an interfered signal with an amount of phase modulation according to a drive signal; and a means for extracting a waveform characteristic point of a time waveform of an interference wave signal caused by an interfered wave, which is a phase modulated interfered signal. An interference sensor comprising means for measuring a time interval between extracted waveform feature points, or a time interval between a waveform feature point and a predetermined time reference point of a drive signal of the phase modulation means. 4. 4. The interference sensor according to claim 3, wherein the phase modulation means phase modulates the interfered signal with an amount of phase modulation depending on the drive signal which is a periodic signal. 5. It is characterized by comprising means for modulating the intensity of the interfered wave source using a local oscillation signal having a frequency spectrum whose amplitude characteristics are flat up to a predetermined high-order frequency component at a frequency different from that of the phase modulated disturbance signal. The interference sensor according to claim 3 or 4. 6. 6. The interference sensor according to claim 3, further comprising means for compensating the amount of phase modulation based on the amount of phase modulation caused by the phase modulation detected using the measured value of the time interval. 7. 7. The interference sensor according to claim 2, wherein the waveform feature point is a maximum point, a minimum point, or a waveform center of a time waveform of the interference signal. 8. 8. The interference sensor according to claim 2, wherein the type of the waveform feature point is identified based on a time interval with the predetermined time reference point. 9. a phase modulation means for phase modulating an interfered signal with an amount of phase modulation according to a drive signal; and a means for extracting a waveform characteristic point of a time waveform of an interference wave signal caused by an interfered wave, which is a phase modulated interfered signal. , a measurement target signal generating means for generating a measurement target signal which is a periodic signal having a phase corresponding to the time timing of the extracted waveform feature point; a measurement reference signal generation means for generating a measurement reference signal which is a periodic signal having a periodic signal; a first frequency conversion means for converting the frequency of the measurement target signal; and a second frequency conversion means for converting the frequency of the measurement reference signal. An interference sensor comprising: and means for measuring a phase difference between a signal output from the first frequency conversion means and a signal output from the second frequency conversion means. 10. A phase modulation means that phase-modulates the interfered signal with a phase modulation amount corresponding to the drive signal, a first frequency conversion means that converts the frequency of the drive signal, and an interfered wave that is the phase-modulated interfered signal. a second frequency conversion means for converting the frequency of the interference signal; a means for extracting waveform feature points of the time waveform of the frequency-converted interference signal; and a time interval between the extracted waveform feature points or a frequency-converted drive. An interference sensor comprising means for measuring a time interval between a time reference point extracted from a time waveform of a signal and a waveform feature point extracted. 11. 11. The interference sensor according to claim 9, wherein each of the frequency conversion means generates a local oscillation signal having a frequency spectrum whose amplitude characteristic is flat up to a predetermined high-order frequency component at a frequency different from the phase modulation drive signal. make use of,
An interference sensor characterized by frequency-converting a frequency-converted signal. 12. The interference sensor according to claim 9, 10, or 11, wherein each of the frequency conversion means is a frequency conversion circuit including a multiplier and a filter circuit. 13. The interference sensor according to claim 9, 10, or 11, wherein each of the local oscillation signal, the measurement target signal, and the measurement reference signal is a rectangular wave, and each of the frequency conversion means
An interference sensor characterized by being a frequency conversion circuit consisting of an exclusive OR circuit and a filter circuit. 14. Claims 2, 3, 4, 5, 6, 7, in which interference light is measured.
, 8, 9, 10, 11, 12, or 13. An optical fiber gyro device comprising: the interference sensor according to any of the above, and means for calculating an angular velocity from the measurement results of the interference sensor. 15. An interference sensor circuit or an interference sensor LSI comprising: a measurement unit that measures time information of a time waveform feature point of an interference wave that includes physical quantity information; and a calculation unit that calculates the physical quantity from the measurement result of the measurement unit. . 16. The time interval between the waveform feature points of the time waveform of an interference wave signal due to the interference of interfered waves having a phase difference corresponding to a physical quantity, or the time between the waveform feature point and a predetermined time reference point related to the interfered wave. The interval, or the time interval between the waveform feature points of the time waveform of the frequency-converted interference wave signal, or the time interval between the waveform feature points of the time waveform of the frequency-converted interference wave signal and the frequency-converted interfered wave. An interference sensor circuit or an interference sensor LSI comprising: a counter section that measures a time interval with a predetermined time reference point; and an arithmetic section that calculates the physical quantity from the count result of the counter section.