JPS61240116A - Method for detecting angular velocity - Google Patents

Abstract

PURPOSE:To perform the detection of angular velocity with high accuracy, by introducing respective beams having received different phase values into the same photosensor and applying predetermined operation to the phase difference of two beams generated in said photosensor. CONSTITUTION:The beam generated from a beam generator 3 is divided into two parts by a beam coupler 2B and only the beam to be utilized is introduced into a beam coupler 2A through a polarizer 4 and the divided beams are projected to both terminals of an optical fiber 1 from said coupler 2A to form right rotary beam CW and left rotary beam CCW. When a loop shaped optical fiber is revolved in this state, phase difference DELTAtheta is generated between the right rotary beam CW and the left rotary beam CCW. This phase difference DELTAthetais introduced into a photosensor 7 to take out a K1 sin DELTAtheta component and a K1 cos DELTAtheta component (wherein K1 is a constant) and the change-over of sin and cos is performed by using the high sensitivity region of the beam phase difference DELTAtheta.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an angular velocity detection method, and more particularly to an angular velocity detection method that utilizes phase fluctuations of light propagating through a loop-shaped optical fiber.

[Background of the invention]

An example of a method for detecting angular velocity by detecting the phase difference between oppositely directed lights input from both ends of a loop-shaped optical fiber is performed by a device as shown in FIG. That is, both ends of the optical fiber 1 wound in a loop are opposed to the beam generator 3 via the optical couplers 2A, 2B, and the optical couplers 2A, 2
A polarizer 4 is interposed between the optical coupler 2A and the optical fiber 1, and a depolarizer 5 is interposed between the optical coupler 2A and the optical fiber 1 on one side, and a phase modulator 6 is interposed on the other side. Further, a photosensor 7 is connected to a branch from the optical coupler 2B to obtain an output E0 via a lock-in amplifier 8, and an oscillator 9 is connected to the phase modulator 6 and lock-in amplifier 8. (1981 "Popular Fiber Sensor Technical Data, Published by Daiichi International Co., Ltd.")

In the device with the above configuration, the interference light component of the photosensor 7 is the output of the photosensor 7. When, E,=KJ, (η)sir+Jθ, where K is a constant and J is a linear term of the Bessel function of the first kind.

Further, it is calculated by q = 2 m fsin2 πfaT.

Therefore, when η is maximized, the coefficient of sin lθ is maximized, so it is determined from the Bessel function table that it is better to set η to 1.8. where fo is the modulation frequency, T is the propagation time of light in the optical fiber, m/
is the modulation index.

Then, the modulation index ml is usually manipulated to obtain 1.8 in η. However, the modulation index ml is the phase modulator 6
There are fluctuations in the voltage value applied to the optical fiber 1, fluctuations in the coupling coefficient between the phase modulator 6 and the optical circuit, and drift of the phase modulator 6 itself, as well as the stability of the modulation frequency f and the propagation of light due to temperature changes within the optical fiber 1. The output E is stabilized only when Δθ=0, that is, there is no phase difference between the lights incident in opposite directions, due to changes in time T, etc. When Δθ≠O, the stability of the output E read out as an analog value is poor due to the instability of η.Therefore, this is a highly sensitive phase difference detection method when Δθ is near zero. However, because the stability of the scale factor is not good, it is a zero rotation sensor. Also,
As shown in FIG. 6, when Δθ is around 90 degrees, the output E changes slowly, making it difficult to detect 10 over a wide range.

As described above, the conventional angular velocity detection methods have unstable factors, and highly accurate angular velocity detection cannot be expected.

[Purpose of the invention]

The present invention addresses the above-mentioned problems, and its purpose is to provide an angular velocity detection method that can maintain high accuracy.

[Summary of the invention]

The present invention focuses on the fact that higher-order mode output is generated by externally modulating the phase of light.

It is possible to extract the gin Δθ acid component and the cos Δθ component from that component, and use that information within a range that always has high sensitivity, and also allows the sin Δθ component and co! ! Δ
By mutually dividing the θ acid components, the instability of η was prevented from affecting the detection power.

(Example of the invention) An embodiment according to the present invention will be described below with reference to FIG.

In Fig. 1, optical fiber 1 wound into a loop, optical coupler 2
A, 2B, beam generator 3. polarizer 4, depolarizer 5,
Phase modulator 6. The relationship of the photosensor 7 is the same as that shown in FIG.
In addition, the output of the photosensor 7 is introduced into the computer 13 via amplifying and synchronous detection circuits 12A and 12B, and the signals from the oscillator 9 and the branching device are amplified and amplified, respectively.
It is introduced into the synchronous detection circuits 12A and 12B.

In the above configuration, the beam generated by the beam generator 3 is split into two by the optical coupler 2B, and only the light to be used is introduced into the optical coupler 2A via the polarizer 4, and this light is transmitted from there to the optical fiber. Inject it into the edge of surface 1 to create a right-handed light CW and a left-handed light CCW. When the loop-shaped optical fiber 1 rotates in this state, a phase difference Δθ occurs between the right-handed light CW and the left-handed light CCW. Both lights CW have a zero phase difference Δθ.

The CCW is subjected to phase modulation at a modulation frequency f0 by a phase modulator 6, and is connected to an optical coupler 2A, a polarizer 4. It goes backwards through the optical coupler 2B and enters the photosensor 7.

At this time, the phase difference Δθ, the modulation frequency f0, and the output P7 of the photosensor 7. ．． The relationship between them is, assuming that the electromagnetic field of the right-handed light CW is saw and the electromagnetic field of the left-handed light CCW is a saw.

e a, = K, 5in (ωt+Δθ/2)
-(6-1)a aaw=K, 5in((11t-
±Δθ/2 from the above equation, which is Δθ/2) −(6-2), means that the light propagating through the loop-shaped optical fiber 1 has generated a relative phase difference of Δθ due to the Zabnak effect.

Next, the situation in which the phase Δθ is changed by the 1-phase modulator 6 is e(,
, = 1 sin(ωt+Δθ/2+mfsin(pt+
π/2)]...(]6-3 e,,,=Kisin(ωt-Δθ/2+mfgin(
pt-π/2))...(6-4) where pt=2πfot
.

π/2 is a fixed phase, with a phase difference of π from the right-handed light CW to the left-handed light CCW with respect to the modulation frequency. Both electromagnetic fields 8°□e0° are introduced into the photosensor 7, At this time, the input optical power p to the photosensor 7 is =2πf.

Now, (s, /hf)"xK"= and the above (6
-5) By solving the equation, P FD = Ko (1+ J @ (2m f s
inπfoT )cosΔθ−2J, (2m f
sin x f , T ) sinΔθ5in2zfa
+ 2J, (2m f sin x f, T)
cosΔθ5in4 x f a-2J, (2m f
sin πf, T) ginΔθgin6πf.

+ 2J, (2m f sin n f oT) co
s A θain8π f.

-2JS(...+...]...(6-6)
In addition, Jll=(c/2nQ)=(1/2n)(1/T)−(
6-7), where C is the speed of light, n is the average refractive index of the optical fiber, and n is the total length of the optical fiber. The output P of the photosensor, as shown in FIG. If it is synchronously detected at modulation frequency f0, its DC output p(/e) will be.

P(/a)” KtJz(2mfsins f,T)s
inJθ...(6-8) If synchronous detection is performed at a modulation frequency of 2f, the DC output P(2/@) will be.

P(2/e)”KxJs(2sfsing f,T)c
osJθ...(6-9)

By the way, FIG. 2 is a graph showing up to the 51st term of the Bessel function, and if we assume 2 mfsins and fsT = 2.6, the value of both the 51st term and the 53rd term is 0.5, and the usable output of the photosensor 7 is P. (/ @) Nio, 5
K, 5 sin ΔθP (2 f e) 20, 5 K
1 cos Δθ. That is, the output p as shown in FIG.
(fa).

Since P(2f,) is obtained, conventionally Δθ is 90
However, in this example, when Δθ is around 45 degrees, the change from p(f*) to P(2f
By switching the signal handled to o), it is possible to always use the portion where the output of the photosensor 7 changes largely with respect to Δθ. Therefore, Δθ can be detected over a wide range while always maintaining high accuracy.

In the above description, for convenience, the value of 2mfginπf,r was set to 2.6, but this value may be any value such that the J1 term gJz term does not become zero.

FIG. 4 shows another embodiment according to the present invention.

The difference from FIG. 1 is that a component satisfying J a (x) = O is extracted from the output component of the photosensor 7 via a DC amplifier 14 and fed back to the amplifier 11. As shown in Figure 2, the zero term of the Bessel function is.

J, (2,4)=0, so in the above equation (6-6), Ja(2mf
If control is performed to feed back the modulation index mf to the amplifier 11 so that sinsfoT)=Q.

, L(2m fsins foT)cosΔθ=0, and control with a highly sensitive value is possible. As a result, J
, (2mfsin 10T) and L(2mfsinπf
, T) is fixed, so when using such control, P (f,)/P (2fa) = Kotan
A e can be found, nπ−π/2 (n
= 1 t 2 t3...), i.e. π/2, 3π/
2. It becomes possible to obtain Δθ by processing the singular points. Of course, sin and co explained in FIG.
There is no problem even if the switching method of o is used.In addition, in the output signals from the width increaser/synchronization detection circuits 12A and 12B in FIG. 2,4) K,
佽J, (2,4) will be hailed.

Furthermore, the computer 13 shown in FIG.
Correction of linearity of cotsΔθ, (ginΔθ)/(co
It is used to perform control such as calculation of sΔθ) and switching between sin lθ and cosΔθ, and to calculate conversion to angular velocity and direction of generation of angular velocity. This is Δθ=(4π
This is because it is obtained from R1)/(λ.)×Ω. Here, R is the radius of the optical fiber loop, λ is the wavelength of light, and Ω is the rotational angular velocity of the optical fiber loop.

〔Effect of the invention〕

As explained above, devices suitable for detecting low angular velocities have a narrow detection angular velocity range, and conversely, devices with a wide detection angular velocity range have difficulty detecting low angular velocities.

In addition, the measurement scale fluctuates greatly due to the drift of the optical power of the light source, making it impossible to detect angular velocity with high precision.1 The present invention achieves both angular velocity resolution ability and angular velocity detection range while maintaining high accuracy. Since it is possible to correct fluctuations in the optical power of the light source, highly accurate angular velocity detection can be performed.

[Brief explanation of the drawing]

FIG. 1 shows the method for detecting angular velocity according to the present invention.
FIG. 2 is a graph showing a type 1 Bessel function, FIG. 3 is an output diagram of the cow photosensor shown in FIG. 1, and FIG. 5 is a block diagram showing an example of a device implementing the present invention. 5 is a block diagram showing an example of a conventional angular velocity detection method, and FIG.
FIG. 3 is an output diagram of the photosensor shown in the figure. DESCRIPTION OF SYMBOLS 1... Loop-shaped optical fiber, 2A, 2B... Optical coupler, 3... Beam generation lid, 6... Phase modulator, 7
... Photo sensor, 9... Oscillator, 11... Amplifier, 12A. 12B... Amplified/synchronous detection circuit, 13... Conview Figure 2 Jo(x>, It(z), J#), JaCx) 3rd
Figure 50 Horror 6 (2) E.

Claims (1)

[Claims] 1. An interference system that detects the effective component of optical power by interfering the lights input from both ends of an optical fiber wound in a loop, and a modulation circuit that gives the two lights a phase value different from the phase of the light. In an optical circuit having an optical system equipped with,
When the respective lights that have received the different phase values are introduced into the same photosensor, and the phase difference between the two lights generated there is Δθ, the K_1sinΔθ component and the K_1cosΔθ component (K_1 is a constant) are calculated from the photosensor. Take it out,
Using the high sensitivity region of the optical phase difference Δθ, the sin and c
An angular velocity detection method characterized by switching an OS.