JPH0293319A - Optical fiber gyroscope - Google Patents

Abstract

PURPOSE:To obtain a stable scale factor by providing a light source for emitting light, a distribution means for distributing the emitting destination of the light source into two and an optical loop for guiding respective distributing destinations in mutually opposite directions. CONSTITUTION:The interference light from an optical fiber 102 is coupled with an optical fiber 105 by an optical directional coupler 131 and detected by a light detector 16 to be sent to a synchronous detector 30 as an electric signal. In this case, signal components S1, S2, S4 are supplied to an operation circuit 40 and Sagnac phase difference DELTAphi is calculated accordig to formula I by the operation circuit 40. At the same time, modulation quantity phim is calculated from the values of S2, S4 and the modulation quantity phim of a phase modulator 15 is subjected to feedback control so as to form J1(phim)=J2(phim). By this method, an operation speed is enhanced and the secondary and quadratic components of phase modulation frequency are calculated with high sensitivity and, therefore, the feedback control of phase modulation quantity phim can be stably performed.

Description

Detailed Description of the Invention [Object of the Invention] (Industrial Application Field) This invention detects the phase difference of lights propagating in opposite directions in an optical fiber loop to detect, for example, the rotational angular velocity of a rotating body. This invention relates to an optical fiber gyro for detection. (Prior Art) An optical fiber gyro is one of the methods for detecting the rotational angular velocity of a rotating body.
Sagnae) phase difference is detected. In an optical fiber gyro using this optical fiber loop, the light propagation path from the output end of the light source to the detection side of the interference light can be constructed entirely of optical fibers, and has high accuracy and a long life. This optical fiber gyro includes, for example, a phase modulation system configured as shown in FIG. First, the output light of a light source (for example, a laser diode) 12 is introduced into an optical fiber 01, and then an optical directional coupler (
coupler) 131. The optical directional coupler 131 is, for example, one in which the cores of two optical cores are joined together and connected from the optical fiber 01 to the optical directional coupler 1.
The light incident on the optical fiber 31 is separated by the action of the evanescent wave into the light that passes through the optical core ino (102) and the light that is coupled to the optical fiber 03. The loop 14 is divided into two lights propagating in opposite directions.On the other hand, the oscillator 19 outputs a phase modulation signal with a frequency f, and the phase modulation signal is amplified rA2.
After being amplified by 1, the phase modulator 15 is driven. An optical phase modulator 1 is used for both lights propagating through the optical fiber loop 14.
Phase modulation is applied by 5. The two phase-modulated lights propagating through this optical fiber loop are connected to the optical fiber 102 by an optical directional coupler 132.
The light is divided into the light that travels to the optical fiber 104 and the light that travels to the optical fiber 104.
The light from the optical directional coupling rA132 is connected to the optical fiber loop 1.
4 becomes interference light of two lights propagating in opposite directions. Note that the ends of the optical fibers 103 and 104 are non-reflective terminations. The interference light from the optical fiber 102 is transmitted to the optical directional coupler 131.
is coupled to an optical fiber 105 and converted into an electrical signal by a photodetector 16. At this time, since the incident light on the photodetector 16 is phase-modulated by the phase modulator 15, an output electrical signal as shown in FIG. 4 is obtained from the photodetector 16. This signal is amplified by an amplifier 17 and then guided to a synchronous detector 18. The synchronous detector 18 introduces the electrical signal from the amplifier 18 as well as the output of the oscillator 19 that generates the modulation frequency f 1 of the phase modulator 15, and extracts the component of the oscillation frequency f 2 of the oscillator 19. The output of this synchronous detector 18 is passed through a low-pass filter 20.
supplied to The output of this low-pass filter 20 is a DC component, which is a first-order Bessel function Jl and sinΔφ(Δφ
: Sagnac phase difference) is proportional to the product J-8InΔφ. The Bessel function is a function of the amount of phase shift 21, and if the amount of phase modulation is set at a stable point where the first-order Bessel function value does not change significantly, the output of this filter 20 will be J -5i
Since nΔφ is a sine function of Δφ, by using the linear relationship g between the output and Δφ as shown in FIG. 3, Δφ can be uniquely determined from the output. However, in the above method, since the linearly related part of sin Δφ is used, the measurable Δφ is only a small value and in a narrow range, and there is a problem that the dynamic range is narrow. To improve this problem, e.g. r ElectronicsCallers 1O
Lh November lH3Vol, 19
There is a method described in Na23P, 997J. This method will be explained below. First, the output signal P of the phase modulation method has a modulation frequency f
and its high frequency components (2f, 3f. o 0
04 [ , . . . ) each include the phase difference Δφ (Δφ is proportional to the detection rate) between Sanya and Tsuk as coefficients, and appear as follows. P-Po [Jl (φ,)・sinΔφ・5ln2π
fot1st order 10J2 (φ,)・eO8Δφ・5ln4πfot2nd order+”3 (φ,)−sinΔφll51n6π[813
Next+J4 (φ,) ecosΔφ・5In8πf0t4th+・・・・・・・・・bow ・・・(
1) However, J is a zero-order Besocel function, and φ is a modulation function. Of this output P, when one component S1 of the modulation frequency and the second-order component S2 are synchronously detected and the ratio is taken, the following relationship is established: J2 (φ,) eO8Δ ψ. Therefore, the Sagnac phase difference Δφ
becomes . Therefore, the Sagnac phase difference (rate) can be detected from the first-order component S and the second-order component S2 of the modulation frequency included in the output signal P. At this time, J (φ)/
In order to make J, (φ,), that is, φ, constant, the fourth-order component S4 is also detected, and the modulation amount φ is controlled (maintained at a constant value) so that it is a constant value, improving accuracy. let That is, in this method,
By using the ratio s 1 / S 2 of the two modulation frequency components, the influence of light intensity fluctuation is removed, and the dynamic range is expanded by calculating tan ``-''. However, the method described in the document 5 As shown in the figure, the modulation amount φ with good sensitivity of the J11th order of the Bessel function
When , the sensitivity of the J2 and J44 orders of the Bessel function becomes low. That is, in order to increase the sensitivity to rotational angular velocity, it is necessary to obtain as large an output amplitude as possible, and for this purpose, as shown in FIG. 5, if the modulation amount φ1 is selected to maximize 11, then 1
This has the drawback that the sensitivity to 2 and 4 becomes low, making it difficult to control the modulation amount φ to a constant value, and as a result, J2 (φ, )/J, (φ,) becomes unstable and the detection accuracy decreases. [Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, an optical fiber gyro according to the present invention includes a light source that transmits light, and a light source that transmits light from the light source into two.
a distributing means for distributing; an optical fiber loop through which each distributed light of the distributing means is guided in opposite directions; a modulating means for applying phase modulation to two lights propagating within the optical fiber loop; a light detection means that receives interference light sent out from the fiber loop and converts it into an electrical signal;
The output signal of this photodetection means is supplied, and an extraction means extracts frequency components S++52.54 that are 1, 2, and 4 times the phase modulation frequency of the modulation means from the signal; Frequency component S2. S4 is supplied, and adjusting means adjusts the amount of modulation of the modulation means so that the first-order and second-order Bessel functions are equal based on the component ratio S 2 / b 4, and the amount of modulation extracted by the extraction means A phase difference deriving means is supplied with the frequency components S t and S 2 and derives the phase difference between the two lights propagating in the optical fiber loop in opposite directions. Ru. (Function) The fiber optic gyro with the above configuration has one of the optical detection means.
- from the output of the phase modulation frequency to 1, 2, 4 (:'
, the frequency components S > , S 2 , S 4 are extracted. Then, the ratio S 2 / s 4 of the second-order and fourth-order frequency components is determined, and based on this, the modulation amount φ is set to 2! so that the first-order and second-order Bessel functions are equal. J
Then, the Sagnac phase difference Δφ is determined from the first-order and second-order frequency components s and s . (Embodiment) An embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a block diagram showing its configuration. However, the first
In the drawings, in order to avoid duplication of explanation, the same parts as in FIG. 2 are given the same reference numerals, and the explanation thereof is omitted, and the explanation will mainly be given to the parts that are different from FIG. 2. As is clear from comparing FIG. 1 with FIG. 2, in this embodiment, a light source 12, end fibers 101 to 105, an optical fiber loop 14, a phase modulator 15, an oscillator 19 (which may include an amplifier), The photodetector 16 (which may include an amplifier) and the optical directional couplers 131 and 132 are the same as those shown in FIG. 2, and the points described below are different from those shown in FIG. 2 and are the features of this invention. . First, the output of the photodetector 416 is sent to the synchronous detector 30. The phase modulated frequency output of the oscillator 19 is also supplied to the synchronous detector 30 . The output of the synchronous detector 30 is sent to the arithmetic circuit 40
will be sent to. The arithmetic circuit 40 derives the Sagnac phase difference Δφ from the output of the synchronous detector 30, and also controls the oscillator 19 so that the phase modulation m is constant. Next, the operation of the gyro with the above configuration will be explained. As in the case of FIG. 2, the output of the oscillator 19 is sent to the phase modulator 15 to apply phase modulation to the lights propagating in the opposite directions through the optical fiber loop 14. At this time, the amplitude (modulation amount φ) of the phase modulation frequency signal is set close to satisfying the Bessel function J(φ)−J2(φ,)l. The light that has undergone this phase modulation is separated by the optical directional coupler 132 into light that travels to the optical fiber 02 and light that travels to the optical fiber 04, but the light from the optical directional coupler 132 travels through the optical fiber loop 14 in opposite directions. This becomes interference light between the two propagated lights. The interference light from the optical fiber 102 is transmitted to the forward coupler 13
1 to the optical fiber 105, the photodetector 1
6 and sent as an electrical signal to the synchronous detector 30. This synchronous detector 30 synchronously detects the output of the photodetector 16 at a frequency that is an integral multiple of the phase modulation wave output of the oscillator 19, and generates a signal component s whose frequency is an integral multiple of the phase modulation frequency.
s. Extract S. These signal components s , s , s4
l 2 4 is the arithmetic circuit 4
0, and the Sagnac phase difference Δφ is determined by this arithmetic circuit 40 as follows. At the same time, the values of s and s change, 2! The J amount φ is determined, and the modulation aperture φ of the phase modulator 15 is subjected to feed pack control so that J (φ)−J2 (φ,) l is satisfied. That is, since S2/S4-J2 (φ, )/J4 (φ1.l), the modulation aperture φ can be determined from the value of J/J4 according to the characteristics shown in FIG. This is obtained by reading φ from a memory that stores the value of the modulation amount φ corresponding to the value of J2/J4. This modulation aperture φ is J − J
The modulation amount is controlled to be the modulation amount φ ' at 2. still,
φ in FIG. ', J/J4 is determined based on m, so the value of J/J (value of S2/S4) is φ. A method may also be used in which φ is controlled so that it has a value of (J − J2). In this way, the first (one point) for determining the Sagnac phase difference Δφ is j (φ ) − J2 (φl) and l
By setting the amplitude (modulation amount φ) of the phase modulator 15 so that ri The second advantage is that the second-order and fourth-order components of the phase modulation frequency can be determined with high sensitivity, so feedback control of the phase modulation amount φ can be stably performed. As a result, it has a low ability to compensate for the drawbacks of the conventional technology. [Effects of the Invention] As described above, according to the present invention, it is possible to provide an optical fiber gyro that can obtain a stable scale factor and realize high performance.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the fiber-optic gyro according to the present invention, FIG. 2 is a block diagram showing the configuration of a conventional fiber-optic gyro, and FIG. 3 is the output characteristics of the conventional fiber-optic gyro. 4 is a characteristic diagram showing the relationship between the phase modulated wave and the photodetector output in a phase modulation type optical fiber gyro, and FIG. 5 is a Bessel function curve for explaining the conventional optical fiber gyro and the present invention. FIG. 12... Light source, 14... Optical fiber loop, 15.
...Phase modulator, 16... Photodetector, 19... Oscillator, 30... Synchronous detector, 40... Arithmetic circuit, 10
1 to 5...Fiber end, 31°2... Optical directional coupler.

Claims (1)

[Claims] A light source that sends out light, a distributing means that divides the light emitted from this light source into two, an optical fiber loop through which each distributed light of this distributing means is guided in opposite directions, and two optical fiber loops that propagate within this optical fiber loop. A modulation means that applies phase modulation to the light, a light detection means that receives the interference light sent out from the optical fiber loop and converts it into an electrical signal, and an output signal of the light detection means is supplied, and from the signal. Frequency components s_1 that are 1 times, 2 times, and 4 times the phase modulation frequency of the modulation means
, s_2, s_4 and the frequency components s_2, s_4 extracted by this extraction means are supplied, and based on the component ratio s_2/s_4, the first and second order Bessel functions are an adjusting means for adjusting the amount of modulation of the modulating means; and a frequency component s extracted by the extracting means.
_1, s_2 are supplied, tan^-1(Ks_2/s
_1) (K is a constant) and a phase difference deriving means for deriving a phase difference between two lights of opposite directions propagating in the optical fiber loop.