JP3153891B2 - Optical resonance angular velocity meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is called a passive ring resonator type optical gyro, in which coherent light is shifted in frequency and introduced into a ring-shaped optical path so as to orbit in opposite directions to each other. Multiplexed around the optical path, took out a part of the circulated light circulating in the opposite direction to the multiplexed interference, detecting these light intensities respectively, and using these detection outputs, the corresponding clockwise light and counterclockwise light. The present invention relates to an optical resonance gyro that detects the angular velocity input to a ring-shaped optical path by performing negative feedback control on a frequency shift.

[0002]

2. Description of the Related Art Before describing such a conventional optical resonance gyro, an optical ring resonator will be described. In an optical ring resonator, when the effective optical path length for one round of the ring is an integral multiple of the optical wavelength, the multiple interference light in the resonator satisfies the resonance condition, becomes bright, and has large energy. As shown in FIG. 5, coherent light is introduced from the light source 12 to the ring resonator 11 through the light directional coupler 13 and circulates (clockwise in the drawing), and a part of the circulating light is optically directionally coupled. When the light intensity of the derived light is detected by the light receiver 15, the intensity I has a characteristic shown by a curve 16 with respect to the optical frequency of the light source 12. At a frequency that satisfies the resonance condition, the detected light intensity increases in a sharp pulse shape. At this time, a bright state is set.

On the other hand, even in the light directional coupler 13 which introduces light into the ring resonator 11, a part of the circulating light beam in the ring resonator 11 is led out to the outside, and this led light beam interferes with the incident light beam, When the intensity of the interference light is detected by the light receiver 17, the frequency characteristic is as shown by a curve 18. This is a frequency that satisfies the resonance condition, and the intensity of the detected light decreases in a sharp pulse shape, and becomes a dark state. The characteristic 16 obtained by the light receiver 15 may be referred to as the transmission characteristic of the optical ring resonator 11, and the characteristic 18 obtained by the light receiver 17 may be referred to as a reflection characteristic. Either of them can be used to constitute an optical gyro. Usually, when an optical coupler is added to an optical ring resonator, the characteristics of the optical ring resonator are deteriorated. Therefore, reflection characteristics are often used. Therefore, an outline of a conventional optical gyro will be described below with reference to an example utilizing the reflection characteristic. The reflection characteristic 18 is expressed by the following equation.

I = I _O ν [1−α / (1 + βsin ² (fτ / 2))] I: output light intensity, I _O : incident light intensity, ν: optical coupler loss α, β: determined by optical system Constant, f: optical frequency τ: one-round propagation time of the ring of the optical ring resonator 11 The principle of the optical gyro generally depends on the Sagnac effect regardless of the method. The Sagnac effect is based on the fact that when a ring-shaped optical path surrounding a finite closed area makes an angular velocity motion about the normal direction of the closed area, the effective round-trip propagation time for light traveling in opposite directions in the ring-shaped optical path (bidirectional light) To make a difference.

The effective orbit propagation time difference Δτ is expressed by the following equation.
Be forgotten. Δτ = (4S / C^Two) Ω S: Closed area, C: Speed of light, Ω: Angular velocity If the ring-shaped optical path now forms a resonator, the resonance condition of light
Case f_r= M / τf_r: Optical resonance frequency, τ: At the time of one round propagation of the ring optical path
In between, m: integer also produces a difference in both-sided light due to this Sagnac effect,
Resonance frequency difference Δf _rIs Δf_r= (4S / λL) Ω λ: Optical wavelength, L: Perimeter of ring-shaped optical path. Therefore, an optical ring resonator is prepared,
While introducing coherent light from the
If the resonance frequency difference is detected, it is input to the optical ring resonator.
The angular velocity can be determined. An gyro based on this principle is a passive type
It is called a ring resonator type optical gyro.

FIG. 6 shows a conventional structure. The light from the light source 12 is split into two by the optical directional coupler 19, and both of these lights are optically frequency-modulated by the optical frequency shifters 21 and 22, respectively. , Are introduced into the ring-shaped optical path 11 composed of an optical waveguide made of glass or optical crystal as counter-rotating light.
The oscillation output of the oscillator 23 is normally a sine wave, and the sine wave signal is applied as a control signal to variable frequency oscillators (VCOs) 26 and 27 through addition circuits 24 and 25, respectively. Is changed at the time of the sine wave. These variable frequency oscillators 26 and 27
Of the optical frequency shifters 21 and 22,
Is modulated.

[0007] Each of the ring-shaped optical paths 11 circulates multiple times.
A part of each of the two-way light that has undergone multiple interference is led out to the outside by the optical directional coupler 13, and the derived lights are output from the optical frequency shifters 21 and 22 incident on the directional coupler 13. The light interferes with the light, and the respective interference light passes through the optical directional couplers 28 and 29, respectively.
At 1 and 32, they are converted into electric signals. The outputs of the light receivers 31 and 32 are output from lock-in amplifiers 33
At 34, synchronous detection is performed at the output of the oscillator 23, and these detected outputs are added to the oscillators 23 and 25 by the adders 24 and 25, respectively.
Is supplied to the VCOs 26 and 27 as control signals.

The frequency of the output light of one optical frequency shifter 21 is frequency-modulated by the output sine wave of the oscillator 23 as shown by a curve 35 in FIG. 7A, and the center frequency is changed to one of the reflection characteristics 18 in FIG. When the frequency is matched with the frequency at the minimum value of the drop, the intensity of the signal obtained from the optical directional coupler 28 and obtained by the light receiver 31 with respect to the one drop characteristic 36 is represented by a curve 37, as shown in a curve 37.
Fluctuates at twice the output frequency. Therefore, the output of the lock-in amplifier 33, that is, the synchronous detection output becomes zero.

However, when the angular velocity around the axis is input to the ring-shaped optical path 11, the resonance frequency of the ring-shaped optical path 11 shifts due to the Sagnac effect, and for example, as shown in FIG. The frequency at which the minimum value of the reflection characteristic 36 of the reflection characteristic is deviated from the center of the frequency of the signal, and as a result, the signal intensity obtained at the output of the photodetector 31 mainly depends on the output frequency of the oscillator Ingredients. Therefore, the output of the lock-in amplifier 33, that is, the synchronous detection output, corresponds to the input angular velocity. The output of the lock-in amplifier 33 is negatively fed back to the VCO 26 through the adder circuit 24, and the center frequency of the optical frequency modulation by the optical frequency shifter 21 is shifted so that the deviation from the frequency at which the reflection characteristic 36 has the minimum value is returned. It is.

The output light of the other optical frequency shifter 22 is also introduced into the ring-shaped optical path 11 with respect to the light,
The same operation is performed by the lock-in amplifier 34, the addition circuit 25, and the VCO 27. Accordingly, the two-way light in the ring-shaped optical path 11 is controlled such that the center of each frequency always resonates in the ring-shaped optical path 11. The frequency difference between the outputs of the VCOs 26 and 27 is detected by the double balanced mixer 38 as the frequency difference between these two round lights, and the difference frequency is a detection amount indicating the input angular velocity to the ring-shaped optical path 11.

As the optical frequency shifters 21 and 22, an acousto-optic device utilizing black diffraction is typical.

[0012]

The passive ring resonator type optical gyro as described above requires two optical frequency shifters 21 and 22, and furthermore, an optical frequency shifter as an actual device. The acousto-optic element is large in size and weight, has high light loss, high power consumption, unstable operation, and radiates a high-frequency electromagnetic field, causing a large noise factor. Further, since the modulated light beam must be transmitted as an airborne light beam, it is extremely difficult to implement optical axis alignment or the like in mounting. In addition, the drive electric circuit generates a great deal of heat.

As an optical frequency shift means which does not have such a difficulty, particularly when a semiconductor laser is used as a light source, a characteristic in which a laser oscillation light frequency is linearly shifted in a practical range according to a laser driving current is used. , So-called direct modulation. However, as described above, the passive ring resonator type optical gyro requires independent optical frequency control means for the two-way light in the ring-shaped optical path, so that the light source is shared by the two-way light. On the other hand, even if direct modulation is applied, it is necessary to additionally provide at least one external optical frequency shifter according to the conventional method.

An object of the present invention is to provide an optical resonance gyro which eliminates the above-mentioned difficulty by realizing the detection of the resonance frequency difference between the two surrounding lights using a single optical frequency shift means.

[0015]

According to the present invention, the light frequency-shifted by one optical frequency shifting means is introduced into the ring-shaped optical path by the one optical coupling means as lights circling in opposite directions to each other, Each part of the circulating light that circulates in the opposite direction to each other and multiplexly circulates the ring-shaped optical path, and the light flux whose frequency is shifted by the optical frequency shifting means are interfered by the optical coupling means, respectively. The intensity of each interference light beam is detected by the first and second photodetectors, respectively. The rectangular signal from the rectangular signal generating means is supplied to the optical frequency shifting means as a drive signal, and the output of the first photodetector is supplied to the first and third periods in which one cycle of the rectangular signal is divided into four.
The difference between the outputs is taken out by the deviation signal detection means, and the difference between the outputs is used as the first deviation signal. The output of the second photodetector is detected as the second deviation signal during the second period and the fourth period obtained by dividing one cycle of the rectangular signal into four. The difference between the outputs is taken as a second deviation signal. The first deviation signal is supplied to the optical frequency shifting means in a negative feedback manner during the first and third periods so that the first deviation signal becomes zero, and the second deviation signal is transmitted during the second and fourth periods so as to become zero. Negative feedback is supplied to the frequency shifting means.

Light from both sides of the ring-shaped optical path, which is different from the light introducing section, is detected and supplied to the first and second photodetectors, respectively, and the outputs of the first and second photodetectors are respectively detected. , The first and third periods, and the second and fourth periods, respectively, and one optical frequency shift means may be subjected to negative feedback control in the same manner as described above. As described above, in the present invention, one optical frequency shift means is used, which is time-divided into two, and is used for both round lights of the ring-shaped optical path. Now, corresponding to FIG. 7, consider frequency-modulating light with a rectangular signal instead of frequency-modulating light with a sine wave as shown in FIG. When the center of the optical frequency coincides with the minimum position (resonant frequency) of one of the reflection characteristics 36 as shown by the curve 39 in FIG. 8A, the derived light intensity I is constant as shown by the line 41. Value. However, curve 43 in FIG.
When the center of the optical frequency shifts from the minimum position of the drop (resonance frequency) as shown in (2), the light intensity of the derived light changes in a rectangular wave shape at the same frequency as the curve 39 as shown by the curve 42 according to the shift, Its amplitude corresponds to the frequency shift. Therefore, by performing negative feedback control on the frequency center of the light according to the amplitude, the center value of the frequency of the light can be locked to the resonance frequency of the ring-shaped optical path.

As shown by a curve 39 in FIG. 9, the frequency of light is changed by a rectangular wave, and one cycle of the rectangular wave
The fourth period _{A +, B +, A -} , B - is divided into, that is, the first period half of the high level of the rectangular wave A _+, late second period B _+, the first half of the low-level third period A _- the second half of the fourth period B _- to. It is assumed that the resonance characteristic for one surrounding light in the ring-shaped optical path is a curve 36A, and the resonance characteristic for the other surrounding light is a curve 36B. At this time, the light intensity detection output for the resonance characteristic 36A (for example, the output of the first photodetector) becomes a curve 42A, and the light intensity detection output for the resonance characteristic 36B (for example, the output of the second photodetector) becomes a curve 42B. The first in this invention, the third period A _+, A _- detecting the light intensity with respect to resonant characteristics 36A of, as the difference becomes zero, a first rectangular modulation of the optical frequency, the third period A _+, A _- a controlled as dotted curve 39, second, fourth period B _+,
B _- detecting the light intensity against a resonance characteristic 36B of,
Second rectangular modulation of the optical frequency as the difference becomes zero, the fourth period B _+, B _- a controlled as dotted curve 39.
In this way, one optical frequency shifting means is time-divisionally utilized.

[0018]

FIG. 1 shows an embodiment of the present invention, in which parts corresponding to those in FIG. 6 are denoted by the same reference numerals. The light emitted from the light source 12 is incident on the optical waveguide 40 and is transmitted to the optical directional coupler 19.
Is split into two luminous fluxes by a ring-shaped optical path 1
1 is introduced through the optical directional coupler 13 as bidirectional light. Both circulating light beams in the ring-shaped light path 11 are again guided to the outside via the light directional coupler 13 and reach the two photodetectors 31 and 32. In this case, the light directional coupler 13 Interference light is formed, and what is detected by the photodetectors 31 and 32 is the intensity of the interference light. That is, the output light intensity with respect to the frequency of the incident light has characteristics similar to the reflection characteristics 18 in FIG.

On the other hand, a semiconductor laser is used as the light source 12, and the characteristic that the frequency of the emitted light from the semiconductor laser is linearly shifted practically according to the injection current to the semiconductor laser is used for the optical frequency shifting means. I do. That is, the light source 12 also functions as an optical frequency shifter. Light having the same frequency is always incident on the ring-shaped optical path 11 as the two-way light. The frequency of this incident light is subjected to rectangular modulation as shown by a curve 39 in FIG. 9, and the outputs of the light receivers 31 and 32 are output by the signal processing unit 43 to the light receivers 31 in the first and third periods A ₊ and A _−. The detection levels become equal, and during the second and fourth periods, B ₊ , B ₋
The rectangular modulation of light is controlled so that the levels of the photodetectors 32 are equal. As a result, for example, as shown in FIG. 3, the optical resonant frequencies for the two-handed light period in the extension 39 A _- and A ₊ median f _rA of the period B _- and B _+, respectively median f _rB of It will be located, both the resonance point f _rA, detecting input angular velocity as the difference f _rB.

FIG. 2 shows a specific example of the processing section 43. Clock
Clock from the clock generator 44 is halved by the frequency divider 45
The frequency is divided and the divided output is used as a switch in the rectangular signal generating means 46.
The switch 47 is controlled to be switched, and the reference level register 4
Reference high level V from 8,49 _HAnd reference low level V_LAnd
The signals are output alternately to create a digital rectangular signal.
Signal is supplied to the DA converter 52 through the adder circuit 51.
Is supplied and converted to an analog rectangular signal.
Is supplied to the drive circuit 53, and the light source of FIG.
The injection current of the semiconductor laser diode as 12 is rectangular
Controlled by signals. Switch 47 is a high-level reference register
Is connected to the first and second periods A₊, B₊
And is connected to the low level reference register 49.
Is the third and fourth period A_-, B_-It is.

From the clock generator 44, the first and third periods A
₊, A_-The sampling pulse located at each intermediate part of
In the sample and hold circuit 54A, the
The output is sampled and held. Sample hold circuit
The output of 54A is converted to a digital signal by AD converter 55A
The converted digital signal is stored in a register 56A.
The difference from the digital signal one sample cycle before is the difference circuit 5.
7A, and register immediately before the next sampling
56A. That is, from the difference circuit 57A,
3 period A₊, A_-The difference between the respective light intensities is detected.
The output of the difference circuit 57A is digitally filtered as needed.
After the noise is removed by the data adder 58A,
Is integrated. The output of the accumulating circuit 59A is
3 period A ₊, A_-Of the optical frequency of the
11. The resonance frequency f of one of the orbital resonance characteristics 36A_rAWith
It corresponds to the deviation signal indicating the difference.

The sun for the sample and hold circuit 54A
Sampling 180 degrees out of phase with the pulling
By the clock, the second and fourth periods B₊, B_-In the center of
The output of the optical device 32 is sampled by the sample and hold circuit 54B.
Is held. This sample and hold circuit 54B
For the output, the output of the sample and hold circuit 54A
The AD converter 55B and the register 56
B, difference circuit 57B, digital filter 58B, cumulative addition
Processed by the circuit 59B, and
The center value and the other round resonance characteristic 36B of the ring-shaped optical path 11
Resonance frequency f _rBIs obtained.

According to a control signal from clock generator 44,
The switch 61 is controlled to be switched, and the first and third periods A₊, A
_-In this case, the output of the accumulator 59A is in the second and fourth periods.
B₊, B _-In addition, the output of the accumulative addition circuit 59B is added.
The signal is supplied to the arithmetic circuit 51,
And the resonance frequency of the ring-shaped optical path 11
Number and first and third period A₊, A_-The median optical frequency of
Second and fourth period B₊, B_-And the median of the optical frequency
Negative feedback control of the optical frequency is performed so as to match each other. Accumulation
The difference between the two outputs of the adders 59A and 59B is taken by a difference circuit 62.
The analog signal is output by the DA converter 63 if necessary.
And the input angular velocity is detected and output. Figure 2
Between the AD converters 55A and 55B and the DA converter 52.
May be performed by a microcomputer. Sun
The pull-hold circuits 54A and 54B are omitted and the period
A₊, A_-(B₊, B_-), The output of the light receiver 31 (32)
May be directly input to the AD converter 55A (55B).

As shown in FIG. 4A, a ring-shaped optical path 11
In addition to the light introducing light directional coupler 13, a light deriving light directional coupler 14 is coupled so as to derive both circulating lights in the ring-shaped optical path 11 and supply them to the light receivers 31 and 32. Is also good. In this case, the transmission characteristic 16 in FIG. 5 is used. Furthermore the optical frequency control corresponding to the clockwise resonance in the above, was performed alternately and an optical frequency control corresponding to the counterclockwise resonant, as shown in FIG. 4B, the optical frequency for clockwise resonance, in the period A ₊ performed on a high frequency, the next period a _- performed for a lower frequency, then the optical frequency for the left-handed resonance is performed with respect to the high frequency period B _+, period B _- performed on a low frequency Repeat that,
That period _{A +, A -, B +} , B - and forward in one cycle of,
The optical frequency shift means may be used in a time-division manner with respect to both circulating lights.

[0025]

As described above, according to the present invention, it is possible to perform time-division control on one optical frequency shift means to control the respective medians of the frequencies of both circulating lights in the ring optical path to resonate. Then, the output at the corresponding time is extracted from the output of each photodetector and processed, so that only one optical frequency shift means needs to be used. Therefore, the configuration becomes simpler. Particularly, when a semiconductor laser is used as the light source and the optical frequency shift is performed by controlling the injection current, the optical system can be configured by using only the ring-shaped optical path as a main component. The gyro can be significantly reduced in size.

[Brief description of the drawings]

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

FIG. 2 is a block diagram showing a specific example of a signal processing unit 34 in FIG. 1;

FIG. 3 is a diagram showing an optical frequency change and an example of the intensity of both-sided light in the present invention.

FIG. 4A is a diagram showing another embodiment of the present invention, and FIG. 4B is a diagram showing another method of time division use of the optical frequency shift means.

FIG. 5 is a diagram illustrating an optical ring resonator.

FIG. 6 is a block diagram showing a conventional optical resonance angular velocity meter.

FIG. 7 is a diagram showing a relationship between a change in optical frequency and the derived light intensity in FIG. 6;

FIG. 8 is a diagram showing the derived light intensity when the optical frequency change is rectangular.

FIG. 9 is a diagram showing a relationship between a change in optical frequency and the intensity of both circulating lights for explaining the principle of the present invention.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-207621 (JP, A) JP-A-2-96611 (JP, A) JP-A-62-281515 (JP, A) JP-A-62-162 47516 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01C 19/64-19/72

Claims (4)

(57) [Claims] 1. A light source that supplies light having sufficient coherence, an optical frequency shifter that shifts the frequency of the coherent light according to an input signal, and multiplexing of light surrounding a finite closed area. A ring-shaped optical path that can be circulated, optical coupling means for introducing a light flux frequency-shifted by the optical frequency shifting means into the ring-shaped optical path so as to circulate in opposite directions, and the ring-shaped optical path. Multiplexed, each part of the light circulating in the opposite direction of the multiple interference, and the intensity of each interference light flux formed in the optical coupling means of the light flux frequency-shifted by the optical frequency shifting means. first and second optical detector, 4 divided into a rectangular signal generating means for supplying, one cycle of the rectangular signal and generates a rectangular waveform signal as a frequency shift drive signal to the optical frequency shift means for detecting, respectively 1st period and 3rd period First deviation signal detection means for extracting an output of the first photodetector and detecting a difference between the outputs as a first deviation signal; and a second period and a fourth period obtained by dividing one cycle of the rectangular signal into four. A second deviation signal detecting means for extracting an output of the second photodetector and detecting a difference between the outputs as a second deviation signal; and the first deviation signal being zero during the first and third periods. Switching means for negatively feeding the second deviation signal to the optical frequency shifting means so that the second deviation signal becomes zero during the second and fourth periods; and the first deviation signal and the second deviation Output means for taking a difference from a signal and outputting the difference as an input angular velocity to the ring-shaped optical path. 2. A light source for supplying light having sufficient coherence, an optical frequency shifter for shifting the frequency of the coherent light according to an input signal, and multiplexing of light surrounding a finite closed area. A ring-shaped optical path that can be circulated, first optical coupling means for introducing a light beam frequency-shifted by the optical frequency shifting means into the ring-shaped optical path so as to circulate in opposite directions, and the ring A second optical coupling unit that derives each part of the light that circulates in the optical path in multiple directions and multiplexly interferes and circulates in opposite directions, and detects the intensities of both circulating lights derived from the second optical coupling unit, respectively. first and second optical detector, a first which is divided into four rectangular signal generating means for supplying, one cycle of the rectangular signal and generates a rectangular waveform signal on the optical frequency shift means as the frequency shift drive signal In the first photodetector during the period and the third period. A first deviation signal detecting means for extracting an output and detecting a difference between the outputs as a first deviation signal; an output of the second photodetector in a second period and a fourth period obtained by dividing one cycle of the rectangular signal into four. And a second deviation signal detecting means for detecting the difference between the outputs as a second deviation signal; and detecting the first and second deviation signals in the first and third periods so that the first deviation signal becomes zero. Switching means for supplying the second deviation signal to the optical frequency shifting means in a negative feedback manner so that the second deviation signal becomes zero during four periods; and taking the difference between the first deviation signal and the second deviation signal, Output means for outputting as an input angular velocity to the ring-shaped optical path. 3. The method according to claim 2, wherein the light source is a semiconductor laser, and the optical frequency shifting means is means for controlling an injection current to the semiconductor laser to shift the frequency of light emitted from the semiconductor laser. The optical resonance angular velocity meter according to claim 1 or 2, wherein: 4. The optical resonance angular velocity meter according to claim 1, wherein the ring-shaped optical path is an optical waveguide made of glass or optical crystal.