JP2729290B2 - Fiber optic gyro - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber gyro for detecting the phase of clockwise light and counterclockwise light propagating through an optical fiber coil and detecting the angular velocity about an axis applied to the optical fiber coil. .

[0002]

2. Description of the Related Art A conventional optical interference angular velocity meter (hereinafter referred to as FOG) will be described with reference to FIG. Light I from light source 11
Are input from both ends of an optical fiber coil 15 as an optical path via an optical coupler 12, a polarizer 13, and an optical coupler 14. The clockwise light and the counterclockwise light propagating through the optical fiber coil 15 are phase-modulated by a phase modulator 16 disposed between one end of the optical fiber coil 15 and the optical coupler 14. Both lights subjected to the phase modulation are combined by the optical coupler 14, interfere with each other, pass through the polarizer 13 again, and are branched by the optical coupler 12 to the light receiver 17.

The output V _p of the photodetector 17 at this time can be expressed by the following equation, where P (t) = A sin ω _mt for the phase modulation signal. V _p = (I / 2) · K _op · K _pd ｛1 + cosΔΦ (Σε _n · (-1) ⁿ · J _2n (X) · cos _2n ω _mt ′) − sin ΔΦ (2Σ (-1) ⁿ · J _{2n + 1} (X) · cos (2n + 1) ω _m t ′)｝ (1) where Σ is from n = 0 to infinity t ^′ = t−τ / 2ε _n = 1; n = 0, 2; n ≧ 1 K _op : the light I emitted from the light source 11 is the optical fiber coil 15
K _pd : constant determined by photoelectric conversion coefficient, amplifier gain, etc. I: light emitted from light source 11 I _o : maximum light amount reaching light receiver 17 (I _o = K _op)・
I) J _n : Bessel function of the first kind X: 2A sin πfm τ ΔΦ: phase difference between left and right surrounding light in optical fiber coil 15 ω _m : angular frequency of phase modulation (ω _m = 2π fm) τ: in optical fiber coil 15 The output of the light receiver 17 is input to a synchronous detection circuit 18, where the same component as the phase modulation frequency, that is, the primary component (n = 1) in the equation (1) receives the reference signal from the clock circuit 19. Taken out. The output of the synchronous detection circuit 18 is
Further, the AC component is filtered by a low-pass filter (LPF) 19 and set to an appropriate gain, and is taken out to a terminal 20 as a FOG output.

[0004] The output V _O of the FOG is expressed by the following equation. V _O = I · K _op · K _pd · J ₁ (x) · K _A1 · sin ΔΦ = K · K _op · sin ΔΦ (2) K _A1 : Gain Here, the phase difference ΔΦ between the two lights is the optical fiber coil 15. (Sagnac) generated when a rotational angular velocity Ω is applied to
ac) Indicates the phase difference ΔΦ _s and is expressed by the following equation.

ΔΦ _s = 4πRL · Ω / Cλ (3) where C: speed of light λ: wavelength of light in vacuum R: radius of optical fiber coil 15 L: length of optical fiber of optical fiber coil 15 by measuring the output V _O of 19,
The input rotation angular velocity Ω can be known.

The clock circuit 21 is connected to the drive circuit 22
The modulation signal is applied to the phase modulator 16 through. The light source 11 is driven by a light source driving circuit 23.

[0007]

However, in an optical fiber gyro used in a periodic vibration environment, for example, 1) a part of a structure constituting the optical fiber gyro mechanically resonates, The stress such as torsion and tension generated at that time is transmitted to a part of the optical fiber coil 15.

Or 2) a part of the optical fiber coil 15 itself resonates and stress is applied to the optical fiber. In either case, the optical fiber coil 15
Synchronized with the vibration frequency at that time,
Assuming that a periodic phase change occurs and the Sagnac phase difference is zero, the phase difference ΔΦ between the left and right both-way light is expressed by the following equation.

ΔΦ = ΔΦ _V sinω _V t (4) ΔΦ _V : amplitude of periodic phase difference caused by vibration ω _V : angular frequency of vibration At the same time, the optical fiber coil 15 and other optical components Causes a periodic loss change in the light propagating through the optical fiber coil 15. Therefore, the optical loss K ' _OP from the light source 11 to the light receiver 17 is expressed by the following equation.

K ′ _OP = K _OP + ΔK _OP sin (ω _V t + θ) (5) θ: Phase shift between a portion where a periodic phase difference occurs and a portion where a periodic loss change of light occurs (3) The optical fiber gyro output of the equation is as follows. V ₀ = K · a _{(K OP + ΔK OP sin (} ω V t + θ)) × sin (ΔΦ V sinω V t) The sin (ΔΦ _V sinω _V t) developed with Bessel function, the following is small its third order terms If omitted, V ₀ is approximated by the following equation.

[0011] _{V 0 ≒ K · (2K OP} J 1 (ΔΦ V) sinω V t + ΔK OP sinθJ 1 (ΔΦ V) sin2ω V t + 2ΔK OP cosθJ 1 (ΔΦ V) sin 2 ω V t) ··· (6 ) the first term of this equation, the second term becomes alternating-current error component and the third term is because it contains the term of the square of sin .omega _V t, of the optical fiber gyro become a DC error component Appears in the output.

As described above, in the conventional optical fiber gyro, an AC and DC error element appears in the output under a vibration environment, and therefore, there is a disadvantage that the stability of the bias of the optical fiber gyro is remarkably deteriorated. An object of the present invention is to provide an optical fiber gyro that can obtain a stabilized output even under a vibration environment.

[0013]

According to the present invention, a counterclockwise light,
Receiving a signal from the light receiver for electrically converting an interference light of the right-handed light, the oscillation frequency component that is expected under vibration environment,
Eliminates the lowest frequency below the expected external vibration
High-pass filter,
Even with a low-pass filter that filters out higher frequencies
The vibration frequency component is extracted from the vibration noise detection circuit configured , and the extracted vibration frequency component is negatively fed back to the drive circuit of the light source so as to cancel the vibration noise component in the output of the light receiver.

[0014]

FIG. 1A shows an embodiment according to the present invention, and portions corresponding to those in FIG. 4 are denoted by the same reference numerals. When external vibration omega _V is applied to the optical fiber gyro, the output V _P of the light receiver 17 is as follows.

V _P = (I / 2) (K _OP + ΔK · sin (ω _V t + θ)) · K _Pd × ｛1 + cos (ΔΦ _V sin ω _V t) × (Σε _n (−1) ⁿ · J _2n (X _{) · cos2nω m t) -sin (} ΔΦ V sinω V t) × (Σ (-1) n · J 2n + 1 (X) · cos (2n + 1) ω m t)} ···· (6) Σ is From n = 0 to infinity In the present invention, the output of the light receiver 17 is branched and input to the vibration noise detection circuit 25. An external vibration frequency component predicted by the vibration noise detection circuit 25, that is, a variation in optical path loss is detected, and the detected variation is supplied to the light source driving circuit 23 so as to cancel the variation.

The vibration noise detecting circuit 25 uses a low-pass filter 26 as shown in FIG. 1B, for example, to detect the highest frequency under the predicted external vibration conditions, for example, 2000 Hz.
Are cut off at higher frequencies, for example, at 3000 Hz or higher, and higher-order frequency components in equation (6), ie, ω
_{The term m} (phase modulation angular frequency) is removed. The phase modulation frequency f _m which is usually several tens kHz~ several hundred kHz. Also,
The high-pass filter 27 simultaneously removes the lowest frequency under the predicted external vibration condition, for example, the frequency component lower than 100 Hz and the DC component. Therefore, only the AC component applied by the external vibration, that is, only the vibration noise component can be extracted. That is, the output V _e of the vibration noise detection circuit 25 is as follows: V _e = ΔK sin (ω _V t + θ) (7)

A light source driving circuit 23 receives light from a semiconductor laser 28 as a light source 11 by a light receiving element 29, and converts the converted photocurrent into a voltage by a circuit 31. the difference between the reference voltage V _R of the output of the differential amplifier 33 is taken by the differential amplifier 33 is integrated by the integrator 34, the driving current generating circuit 35 for the semiconductor laser 28 in accordance with the integrated output is controlled, By controlling the output of the differential amplifier 33 to be zero, the light source 11
The intensity of light from the light source is kept constant. For such a light source driving circuit, for example, the output of the integrator 34 is added to the output of the integrator 34 by the differential amplifier 36 so as to cancel out the fluctuation due to the vibration in the output of the light receiver 17. In this way, the fluctuation of the optical path loss is canceled. The gain of the system including the vibration noise detection circuit 25 is selected in consideration of the conversion gain of the light receiver 17, the conversion gain of the light source drive circuit 23, and the like, so that the optical loss fluctuation due to vibration is exactly canceled.

The output V ' ₀ of the synchronous detection circuit 18 is V' ₀ = K · K _OP · sin (ΔΦ _V sin ω _V t), and the periodic phase change based on the vibration is an AC noise component. Remains as. However, it is possible to obtain a stabilized optical fiber gyro output by removing the low-pass filter 19, for example.

The output of the vibration noise detecting circuit 25 may be input to the input side of an integrator 34 in the light source driving circuit 23 as shown in FIG. 2A. Further, in the above description, the vibration noise was canceled by controlling the light source drive circuit 23 with the detected vibration noise component. However, as shown in FIG. 2B, a differential circuit 37 was inserted in front of the synchronous detection circuit 18 and a photodetector was added thereto. 17 and the output of the vibration noise detection circuit 25 may be supplied to electrically cancel each other.

In the above description, the optical coupler 14, the phase modulator 1
6 may be constituted by an optical integrated circuit. In the above description, the present invention is applied to an open-loop optical fiber gyro, but can also be applied to a closed-loop optical fiber gyro.

[0021]

As described above, according to the present invention, a circuit for detecting an angular vibration noise component, a circuit for controlling the light source light amount so as to cancel out the light amount of the noise component by the detection output, or electrically. By providing a circuit for canceling out, a stable detected angular velocity output can be obtained even under vibration.

[Brief description of the drawings]

FIG. 1A is a block diagram showing an embodiment of the present invention, and FIG. 1B is a block diagram showing a specific example of a light source drive circuit 23 and a vibration noise detection circuit 25.

FIG. 2A is a block diagram showing another example of the light source driving circuit 23, and FIG. 2B is a block diagram showing another embodiment of the present invention.

FIG. 3 is a block diagram showing a conventional optical interference gyro.

Claims (2)

(57) [Claims] 1. A light from a light source is incident on both ends of an optical fiber coil as right-handed light and left-handed light by branching means.
The right-handed light and the left-handed light are phase-modulated with an alternating signal by a phase modulator inserted between one end of the optical fiber coil and the branching means, propagated through the optical fiber coil, and interfered by the branching means. The interference light of the clockwise light and the counterclockwise light is converted into an electric signal by a light receiver, and the phase difference between the clockwise light and the counterclockwise light is detected from the electric signal. In an optical fiber gyro for detecting an applied angular velocity, the output of the above-mentioned photodetector is used to estimate the maximum external vibration.
High-pass filter that removes even lower frequencies
Above the highest frequency of external vibration
A low-pass filter that detects a vibration noise component, and supplies the vibration noise component detected by the vibration noise detection circuit to the light source driving circuit of the light source as a control signal to generate the vibration noise component. An optical fiber gyro, comprising: means for canceling; 2. A light from a light source is incident on both ends of an optical fiber coil as right-handed light and left-handed light by branching means.
The right-handed light and the left-handed light are phase-modulated with an alternating signal by a phase modulator inserted between one end of the optical fiber coil and the branching means, propagated through the optical fiber coil, and interfered by the branching means. The interference light of the clockwise light and the counterclockwise light is converted into an electric signal by a photodetector, and the phase difference between the clockwise light and the counterclockwise light is detected from the electric signal. In an optical fiber gyro for detecting an applied angular velocity, the output of the above-mentioned photodetector is used to estimate the maximum external vibration.
High-pass filter that removes even lower frequencies
Above the highest frequency of external vibration
A vibration noise detection circuit for detecting a vibration noise component by a low-pass filter, and the vibration noise component detected by the vibration noise detection circuit is differentially added to the output of the photodetector to cancel the vibration noise component. An optical fiber gyro, comprising: a differential circuit;