JPS61290318A - Optical fiber gyroscope - Google Patents

Abstract

PURPOSE:To enable accurate and stable measurement of the phase difference of light travelling through an optical fiber loop in opposite directions to each other, by a method wherein a signal is made by squaring the cosine of the angle corresponding to the modulation frequency from a modulation frequency signal from a phase modulation means to perform an amplitude modulation of the photo detector output by the signal. CONSTITUTION:The phase difference of light propagating through an optical fiber loop 17 in opposite directions to each other is checked to detect the angular velocity in the rotation of a rotor. A phase modulation frequency signal from an oscillator 26 is supplied to a multiplication circuit 29 to made a signal by squaring the cosine of the angle corresponding to the modulation frequency. The output of a photo detector 23 is modulated in the amplitude with an amplitude modulator 27 by the signal while a timing control is done with a gate circuit 30 so that the output of the amplitude modulator 27 will be divided at a time interval of the half cycle of an oscillation frequency signal of the oscillator 26. Thus, the angular velocity of the rotor can be obtained easily by measuring the phase difference between outputs of band filters 31 and 32 corresponding to signals belonging to the zone of even order and at the zone of odd order.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an optical 7-eye gyro which detects the rotational angular velocity of a rotating body by detecting the phase difference of lights propagating in opposite directions in an optical 7-eye gyro. [Technical background of the invention and its problems] One of the methods for detecting the rotational angular velocity of a rotating body is to detect the phase difference (phase difference of 8 agnac) of lights that propagate in opposite directions through a light 7-iper loop fixed to a rotating body. There is a method to detect it. In an optical fiber gyro using this optical fiber loop, the light propagation path from the output end of the 11 light sources to the interference light detection side can be constructed entirely of optical fibers.

It has a high tree density and a long lifespan. This optical fiber jack has
There is a conventional device configured as shown in FIG. 3, for example. That is, a light source (e.g. a laser diode)' (11)
The output light is introduced into the optical fiber@, and then the optical coupler 0
supplied to The optical coupler α9 is made by, for example, cutting out a part of the opposing surfaces of two optical fibers and joining the two sides, and the light that enters the optical coupler 0 from the optical fiber α is evanescent wave. As a result of this action, the light is separated into the light that passes through the optical fiber I and the light that is coupled to the original fiber 9. The light transmitted through the optical fiber I is further divided by an optical coupler αe into two lights that propagate in opposite directions through the optical fiber loop αη. Phase modulation is applied to this optical fiber loop (both lights propagating through η by an optical phase Kl device 111). The two lights that propagated through the optical coupler dl19 are separated by the optical coupler dl19 into the light that travels to the optical fiber 1.14) and the light that travels to the optical fiber 119, but the light from the optical coupler dl19 loop α
This becomes interference light of two lights that propagate η in opposite directions. At the end (to), C2υ is the non-reflection termination. The interference light from the optical fiber d is transferred to the original fiber (
(c) and detected by a photodetector (c). The output electrical signal of the photodetector (c) is amplified by an amplifier and then guided to a lock-in amplifier (to).
The output of the oscillator (to) that generates the modulation frequency signal (-) of the phase modulator u8 is also guided, and the phase difference component of the two lights propagating in opposite directions through the optical fiber loop u7 is extracted by synchronous detection. .

In the system shown in FIG. 3, the output El of the lock-in amplifier (C) becomes 1 sin ψ (Kt is a constant) where E1==1 sin ψ, where ψ is the phase difference of 8υgnac. In other words, in the method shown in Fig. 3, since the output E1 changes in a periodic manner, there is no linear relationship between the output E1 and the Sagnac phase difference ψ, and the Sagnac phase difference ψ can be directly read from the output E. I can't.

As a method to improve this, there is an optical fiber gyro using a single sideband detection method. Fig. 4 shows a schematic diagram of the configuration of the second optical fiber gyro, from the light source αυ to the optical fiber loop 117), and the optical detector c! The configuration up to 3 is the same as that shown in FIG. In this single sideband detection method, phase modulation of the function φ (ωt) is applied to the light propagating in opposite directions through the optical 7-ibar loop region, and an amplitude modulator @ is applied to the output signal of the optical detector (c). G(ω
t). Then, a predetermined frequency (nω) component en(ωt) is extracted from the output of the amplitude modulator using a bandpass filter. In this case, the function φ(ωt) and the function G(ωt) are =-φ(-ω1):
#Function G (ω, t) = G (-cat): If it is an even function and the amplitude of φ(ωt) is appropriately selected, the output en(ω
t) is.

en(ωt)=1 cos(na+t+ψ+θ) or e, n(ωt)=′s Cog(n al
ψ + θ′) (where n = 1 + 2 + ”'
e Kl e K '2 +θ, θI are each constant), and the phase difference ψ of 8 agnac can be directly determined from the phase of the output en(ωt) of the bandpass filter (to). Note that n is usually selected to be l or 2.

Regarding this single sideband detection method, for example,
TATI side AND MEASUREMENlr, V
OL, IM-30, No. 2.

JUNE 1981 P, 152-P, 154 and I
EEEJOURNAL OF QUANTLIM EL
ECTRONIC8, VOL, QE-18, NO, l
, JANUAaYl 982 P, 124~P
.

It is also described in 129 etc. , in this single sideband detection method, the function G(ωt) is G(ωt)
=1. A method in which the function φ(ωt) is a sawtooth wave is often used. In this case, in order to make the function φ(ωt) a sawtooth wave function, the phase modulator needs to have a wide band, but a sine wave oscillator is used as the first oscillator (to), and the output of the optical detector (c) is may be switched and output every half cycle from peak to peak of the sine waveform of the oscillator.

□That is, if the output of the oscillator (to) is a sine wave, the phase change given by the phase modulator u8 is also Δφsinωt (sinusoidal) (Δ
φ is the maximum phase change (°). Synchronizing with the phase change given by this phase modulator (lI), if G(att) in the amplitude modulator (equipment) is a function as shown in Figs. 6 and 9, then from the amplitude modulator As shown in the figure, the signal output corresponds to the period from the minimum to the maximum phase change given by the phase modulator A barrel, or the signal output corresponds to the period from the maximum to the minimum trap phase change as shown in Figure 10. When these signal outputs are introduced into a bandpass filter (to) and a component with a frequency of 1 m is extracted, for the signal output corresponding to Fig. 7, en(ωt) = en(ωt) at a certain Δφ. to 1c
For the signal output corresponding to os(nQIt+ψ+0) in FIG. 10, an output of e' n(ωt)=2cos(nwt-ψ+θ) is obtained at the same Δφ. Therefore, if the phase of e'n(ωt) of the output of the bandpass filter (to) is measured using en(ωt) as a reference, a phase difference (2ψ) of 8 agnac can be easily obtained. In this method.

There is an advantage that a narrow-band phase modulator α barrel providing a phase change of Δφ5inaIt is sufficient to provide a single sinusoidal waveform. However, with this method, if there is a variation in the maximum phase change Δφ or a phase shift between the rectangular waves of Δφsinωt and G(ωt), it may not be possible to measure the Sagnac phase difference ψ, which will have a large effect on the measurement and cause errors. It becomes a factor.

[Purpose of the invention]

The present invention provides a variation of the maximum phase change Δφ and a phase change Δφs
An optical fiber that can more accurately and stably measure the phase difference of lights traveling in opposite directions through an optical fiber route by eliminating the influence of the phase shift between inωt and the function G(ωt) in an amplitude modulator. [Summary of the Invention] The optical fiber gyro according to the present invention creates a signal of the square of the cosine of an angle corresponding to a modulation frequency aK from a phase modulation frequency signal from a phase modulation means, and At the same time, the amplitude modulated output is divided into half periods of the phase modulated frequency signal based on the phase modulated frequency signal, and the even numbered division and the second half period of the phase modulated frequency signal are divided. This method measures the phase difference between the outputs of the bandpass filters corresponding to the signals of each section.

[Embodiments of the invention]

Hereinafter, one embodiment of the optical fiber gyro according to the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a schematic diagram illustrating an embodiment of the optical fiber gyro according to the present invention. In the optical fiber gyro shown in FIG. 1, parts having the same configuration as those in FIG. 3 or 4 are given the same numbers and explanations are omitted.
The oscillation signal (→) is supplied to the multiplier circuit (to), and a 2ω signal with twice the frequency is created. A predetermined DC component is added to this 2 = frequency signal, and this signal is used to generate a photodetector (to). C)
0, the output signal of the multiplier circuit (to) modulates the amplitude with the modulator @ (multiplier), is l+cos2ω
With t = 2 cos2ut, the signal of CO32ωt as shown in Fig. 2 is obtained.0 Thus, in Fig. 1, the function G(ωt) at the amplitude adjuster (5) is set in the form of C082ωt, but this is This can be easily created using the oscillation station tBL signal of the excavator (c). The output of the amplitude modulator (2) is supplied with the gate circuit voltage and is switched and outputted every half period of the oscillation frequency (ie, phase modulation frequency) signal of the oscillator. The switching timing of the gate circuit (TO) is controlled by the oscillation signal of the oscillator (TO), and is switched when the amplitude of one oscillator signal reaches the maximum or minimum. Therefore, the gate circuit changes the output of the amplitude modulator from the maximum to the minimum (or minimum to maximum) of the oscillator output amplitude.
The signals of the even-numbered divisions are outputted from the Itto terminal, and the signals of the triangular divisions are outputted from the Tatsuki terminal. In other words, the gate circuit (
(to) outputs a signal by switching the terminal every time the output width of the oscillator (c) takes an extreme value. The outputs from the gate circuits (to) are supplied to bandpass filters 0υ and 04 with a center frequency nω, respectively, and the components en(ωt) and e'n(ωt
) are extracted respectively. Bandpass filter 3υ.

There is no phase difference between the outputs en(ωt) and e'n(ωt) when no angular velocity acts on the base, but a phase difference occurs when the angular velocity acts on the base, and this phase difference is Sa
Corresponds to the phase difference of gnac. Therefore, the angular velocity of the substrate can be obtained more easily than by measuring the phase difference between the outputs of the bandpass filters 6υ and G4. In the optical fiber gyro shown in Fig. 1, the oscillator (1) may be a narrow band type that outputs a single sine wave, and a function G (ωt) is created based on the oscillation signal of this oscillator (1). Gate circuit (
) controls the switching timing. Therefore, since the switching of the gate circuit OI is carried out with good timing when the oscillation output of the oscillator (to) is in the 1st direction, measurement errors due to shifts in switching timing are reduced. Furthermore, in the case of function G(ωt)=1 as shown in FIG. 6 or FIG. 9, if the maximum phase change Δφ at phase modulator α fluctuates, the output of bandpass filter Cυ, Since the sideband components of are dusty, error components are included in addition to the Sagnac phase difference component, making it impossible to accurately measure the Sagnac phase difference. However, as shown in Figure 2, the function G (
ωt)=cos2ωt, the maximum phase change Δφ
The change in the sideband component of the output of the bandpass filter Gυ, 07J (change in width) with respect to the change in the value (change around a preset value) becomes smaller, so the maximum phase change Δ with respect to the measurement
The influence of fluctuations in φ is reduced. Therefore, even if the modulation characteristics of the phase modulator circle change due to changes in environmental conditions such as a degree, and the maximum phase change Δφ that light undergoes changes, there is little effect on the output of the bandpass filter (II), 83. Therefore, even under conditions where the modulation characteristics change, the angular velocity can be measured with a single sideband detection power formula with much less error.

〔Effect of the invention〕

As explained above, according to the optical fiber gyro according to the present invention, the variation of the maximum phase change Δφ and the phase change Δφsi
The influence of the phase shift between nωt and the function G(ωt) can be reduced, and the phase difference of light can be measured more accurately and stably, which has a great practical effect.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram illustrating an embodiment of the optical fiber gyro according to the present invention, FIG. 2 is a waveform diagram of the function G(ωt) in the amplitude modulator shown in FIG. 1, and FIGS. 3 and 4 5 is a schematic diagram illustrating a conventional fiber optic gyro.
10 to 10 are waveform diagrams of a function G(ωt) related to loss width modulation or a function φ(ωt) related to phase modulation, respectively, for explaining the operation of the optical fiber gyro shown in FIG. WC4. αυ...Light S, (Ia, α4.@...Light 7 Aipa,
13. (11... Optical coupler, αη... Optical fiber Rouge, u8... Phase modulator, (To)... Detector, @... Amplitude modulator, (To)... Multiplier circuit , (7)
...Gate circuit, 6υ, Oa...Band filter 0 Representative 1m person Nori Chika Ken Yudo Takehana Kikuyu

Claims (1)

[Claims] A light source that outputs light, a distribution means for guiding and distributing light from this light source, a fiber loop through which light from this distribution means is propagated in opposite directions, and a fiber loop for transmitting light through this fiber loop. A phase modulation means for applying phase modulation, a detector for detecting interference light of light propagated in opposite directions through the fiber loop, and a cosine of an angle corresponding to the modulation frequency from which the modulation frequency signal of the phase modulation means is guided. means for obtaining a signal with the square of a selection means for dividing into a first signal of an even-numbered division and a second signal of an odd-numbered division, and the first and second signals from the selection means are supplied and a predetermined frequency component The phase difference of the light propagating in opposite directions through the fiber loop based on the phase difference between the filter to be extracted, the output signal of the filter corresponding to the first signal, and the output signal of the filter corresponding to the second signal. An optical fiber gyro comprising means for detecting.