JPH01265111A - Optical interference angular velocity meter - Google Patents

Abstract

PURPOSE:To stabilize a scale factor which is the input/output characteristic of the optical interference angular velocity meter by holding a desired input signal of a synchronous detecting circuit and a reference signal in phase with each other even if the input/output phase characteristic of a phase modulator 15 varies owing to environmental variation. CONSTITUTION:The output of a photodetector 17 is detected by the synchronous detecting circuit 25 synchronously with the reference signal VR1. At this time, the synchronously detected component has its AC component removed by a low-pass filter 26 and is outputted to the output terminal 29 of the optical interference angular velocity meter. The phase difference between a driving signal applied to the phase modulator and the phase modulation of light is affected by the environmental variation, so high-frequency components of high order in a signal that interference light contains are used for phase correction. The output of the photodetector 17 is set by a logic circuit 30 previously so as to obtain an output V2 by the synchronous detecting circuit 27, and inputted to an integrator 28 to control an automatic phase adjusting device 31 capable of varying a phase difference with the output of the integrator 28, thereby performing control so that the phase difference is equal.

Description

Detailed Description of the Invention "Industrial Application Field" This invention passes clockwise light and counterclockwise light through an optical path that goes around at least once, and calculates the angular velocity applied around the axis of the optical path between the clockwise light and counterclockwise light. This invention relates to an optical interference gyrometer that detects the phase difference between the two.

``Prior Art'' Figure 2 shows a conventional optical interference angular velocity meter. The emitted light 21 from the light source 11 passes through the light distribution coupler 12, the polarizer 13, and the light distribution coupler 14, and is split into a clockwise light 22 and a counterclockwise light 23 into a circular optical path 16. light 22
, the phase of the counterclockwise light 23 is modulated by a modulation signal from an oscillator 19 in a phase modulator 15 disposed at one end of the optical path 16.

An interference light 24 obtained by interfering the clockwise light 22 and the counterclockwise light 23 is obtained from the optical splitting/coupling device 12. The intensity ■ of the interference light 24 in this case. is the following formula.

To=c (i+cosΔφ(J6(X) +2Σ(-
1) "Jz-(x)・cos2n(ωt+θ))-si
nΔφ・(2Σ(-1)'・Jzll−+(x)・co
s(2n+1)(ωt+θ)]...1ll C two constant J,: n-th order Benssel function of the first kind x: 2 As1nπfllτ A: amplitude of optical phase modulation τ: propagation time ω of light passing through optical path 16 : Drive angular frequency (ω-2πf,)Δ of the phase modulator 15
φ: 4πR between the two lights propagating in opposite directions through the optical path 16
L Phase difference Δφ=□・Ω=K・Ω Cλ R: Radius of optical path 16 L: Length of optical path 16 configured in a loop C: Speed of light λ: Wavelength of light Ω: Constructed in a loop Angular velocity applied in the circumferential direction of the optical path 16 2 Drive voltage applied to the phase modulator 15 v rzt=
The phase difference between -5inωt and the advanced modulation by the phase modulator 15 (as is clear from equation 11, the intensity I0 of the interference light 24 includes a term proportional to cosΔφ and a term proportional to sinΔφ .

Usually, s is used to optimize sensitivity in the small input angular velocity range.
A term proportional to inΔφ is used.

For this purpose, a signal obtained by photoelectrically converting the interference light 24 by the photoreceiver 17 is synchronously detected with a phase modulation frequency f or a harmonic signal of an odd multiple thereof. - For boat fishing, synchronous detection is performed at a lower order (in this case - order) modulation frequency due to the ease and accuracy of processing.

In FIG. 2, the signal applied to the phase modulator 15 in order to extract the -th order sin Δφ component is used as the reference signal for the synchronous detection circuit 18.

"L1 problem to be solved by the invention" In order to appropriately extract the first-order sinΔφ from the signal photoelectrically converted by the photoreceiver 17, the phase of the photoelectrically converted first-order sinΔφ component and the reference signal must be in phase. There is a need.

” However, the phase difference θ between the driving voltage applied to the phase modulator 15 and the fundamental frequency component of the interference light is
varies depending on the environmental conditions to which it is exposed, especially temperature. Since the phase modulator 15 is manufactured by winding an optical fiber around a cylindrical electrostrictive vibrator, for example, the input/output phase characteristics are inherently likely to change depending on environmental conditions, and the resonance point of the phase modulator 15 If the operating point (modulation frequency) is set at , it will fluctuate significantly depending on the environmental conditions.

Therefore, the reference signal in the periodic detection circuit 18 and the photoelectrically converted first-order sine component are not in phase, leading to instability of the scale factor as the output of the optical interference gyrometer.

The present invention provides an optical interference gyrometer that keeps a desired input signal and a reference signal in a synchronous detection circuit in phase and keeps the gyro scale factor stable even if the input/output phase characteristics of the phase modulator 15 change due to environmental changes. The purpose is to

"Means for Solving the Problems" According to the present invention, second synchronous detection means is provided for synchronously detecting even-numbered wave components related to the modulation frequency of the phase modulator out of the output from the optical receiver. The signal from the second synchronous detection means is used as an input signal and a reference signal in the first synchronous detection means, that is, means for synchronously detecting odd wave components related to the modulation frequency of the phase modulator in the output from the optical receiver. control is performed so that the phase difference between the signals becomes substantially the same phase, and the phase difference between the human input signal and the reference signal in the second synchronous detection means becomes substantially 90°.

Embodiment FIG. 1 shows the main part of an embodiment of the present invention. The output of the photoreceiver 17 is synchronously detected in a synchronous detection circuit 25 using a reference signal V□ having a frequency f□. At this time, the component to be synchronously detected is the component of the fundamental frequency f of the signal shown by equation (1), and the result is filtered by the low-pass filter 26 to remove the alternating current component. It is output to the output terminal 29 of. The signal Vl from which this alternating current component has been removed becomes a signal proportional to sin Δφ. At this time, the output V1 is V+=+・sinΔφ・cos(θ−θt)−(2)
K1: Constant θf: Phase difference between the drive voltage applied to the phase modulator 15 and the reference signal V□. Here, the phase difference θ is the phase difference between the drive voltage applied to the phase modulator 15 and the phase modulation of light, as described above, and this varies greatly depending on the environment, especially the temperature, and is substantially the same as the output of the optical interference gyrometer. ■ to be done.

destabilizes the scale factor of

Therefore, in the present invention, even-order high frequency components of the signals included in the interference light are used for phase correction. Here, a secondary high frequency component is used.

The output of the optical receiver 17 is transmitted to the synchronous detection circuit 27 at a frequency f.
Synchronous detection is performed using the reference signal Vllll of 8□. Reference signal V
112 is set in advance by the logic circuit 30 so that the next output v2 can be obtained from the synchronous detection circuit 27.

Vz=Kz-cosΔφ-sin f2(θ-θr)
l-+3+This signal ■2 is input to the integrator 28, and the output of the integrator 28 is used as an automatic phase adjuster 3 that can vary the phase difference θ.
1, and the phase difference θ is automatically controlled to be the same as the phase difference θ. The output of the converter 19 is supplied to a logic circuit 30 through an automatic phase adjuster 31, and the logic circuit 30 generates a reference signal □.

V112 is created. The automatic phase adjuster 31 is controlled so that (θ-θ,) is always kept at zero, that is, the output of the integrator 28 is always zero.

As a result, Equation (2) becomes V + = + · sin Δφ ・ (41) Even if the environmental conditions, especially the ambient temperature change, and the phase difference θ between the input and output in the phase modulator 15 changes, the traffic characteristics of the optical interference gyro meter It is possible to suppress fluctuations in the scale factor.

The reason why even harmonics are used for phase correction is (3)
As is clear from the equation, even when the input angular velocity Ω applied to the optical path 16 is zero or small, that is, even when the phase difference Δφ between the two lights propagating through the optical path 16 is small, the control signal is proportional to cosΔφ. This is because a sufficient amount of values can be obtained as .

Note that, as is clear from equation (2), the odd-order components are extremely small when the input angular velocity is minute, and therefore are inappropriate as control signals for phase correction.

However, as can be seen from equation (3) for even-order components, as the input angular velocity increases, the phase difference Δφ increases and the V2 signal as the control signal decreases.

However, in an optical interference gyrometer in which the phase difference Δφ between the two lights propagating through the optical path 16 at the required maximum input angular velocity is about 45° or less, the decrease in the secondary output v2 is about 30% or less. It can be fully used as a control signal.

"Effects of the Invention" As described above, according to the present invention, even if the environmental conditions change and the input/output phase of the phase modulator 15 fluctuates, the phase modulator 1'5 remains stable over the zero to maximum input angular velocity range. By correcting phase fluctuations, the scale factor, which is the input/output characteristic of the optical interference gyrometer, can be kept stable.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the main parts of an embodiment of the present invention, and FIG. 2 is a block diagram showing a conventional optical interference gyrometer.

Claims (1)

[Claims] (1) an optical path that goes around at least once; a means for passing clockwise light and counterclockwise light into the optical path; and an interference means for interfering with the clockwise light and counterclockwise light that have propagated through the optical path; a phase modulation means that is disposed continuously between the interference means and one end of the optical path to change the phase of the clockwise light and the counterclockwise light; and a phase modulation means that detects the optical intensity of the interference light as an electrical signal. a photoreceiver; a first synchronous detection means for synchronously detecting an odd-numbered wave component related to the modulation frequency of the phase modulation means from the output from the photoreceiver; and a phase modulation means from the output from the photoreceiver. a second synchronous detection means for synchronously detecting an even-numbered wave component related to a modulation frequency; and a signal from the second synchronous detection means such that the phase difference between the input signal and the reference signal in the first synchronous detection means is substantially an optical interference gyrometer comprising means for controlling the input signal and the reference signal so that they are in phase and that the phase difference between the input signal and the reference signal in the interlocked second synchronous detection means becomes substantially 90 degrees.