JPS6022619A - Optical fiber gyroscope - Google Patents

Abstract

PURPOSE:To detect a signal with high sensitivity even if rotation is slow and to detect stably the signal by using a phase modulating means. CONSTITUTION:A phase modulator 7 for light is constituted of, for example, a Pockels element. Photodetecting elements 8a, 8b arrange the planes of polarization for incident light and exit light to and from an optical fiber 3. Band-pass filters 9a, 9b discriminate the output from a photodetector 5. A divider 11 detects the ratio between the output from a peak detector 10 and the output from the filter 9b. A synchronous detector 12 detects the output from the divider 11 in synchronization with an oscillator 15a. A gain controller 13 controls a gain variable amplifier 14 so as to maintain constant the output from the detector 12. The rotating angular speed of a moving body is detected by monitoring the control voltage of the controller 13.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for detecting the angular velocity of a moving object using an optical fiber.

Conventionally, as this type of device, the one shown in FIG. 1 is known. In the figure, (1) is a laser driven by an oscillator (not shown), (2) is a beam splinter that splits the light from laser (1) into two, and (3) is a beam splinter that splits the light from laser (1) into two, and (3) is a beam splinter that is driven by a laser beam that is driven by an oscillator (not shown). Molded single mode optical fiber, (4
a).

(4b) is a lens, (5) is a photodetector that detects the light emitted from the end face of the optical fiber (3), and (6) is a photodetector (
This is an amplifier that amplifies the output of 5).

Next, the operation will be explained. The light from the laser (1) is split into two by the beam splinter (2), and
b) into the single mode optical fiber (3) and propagated clockwise and counterclockwise.

If this system is stationary, there will be no phase difference between the left and right beams, but if this system rotates, for example clockwise, within the plane that includes the optical fiber loop (3), the optical fiber loop (3) will rotate clockwise. Light traveling clockwise takes a longer time to reach the output end, while light traveling counterclockwise takes a shorter time. As a result, a phase difference Δθ occurs between the left and right beams. This phenomenon is called the Sagnaci J effect, and it is known that the phase difference Δθ is given by the following equation.

Here, L is the optical fiber length, a is the loop radius of the optical fiber, C2λ is the speed and wavelength of light, and Ω is the angular velocity of rotation. When the two lights having this phase difference Δθ are caused to interfere on the light receiving surface of the photodetector (5), Δθ can be converted into a light intensity, that is, an electrical signal. If the output voltage of this photodetector is amplified by an amplifier (6) and detected, the angular velocity Ω can be determined from equation (1).

! As can be seen from Equation 11, the detection sensitivity can be increased by increasing the length of the optical fiber.

Since the conventional fiber optic gyroscope is constructed as described above, the optical path difference in both left and right directions is completely equal in the stationary state, so the output of the photodetector is cos
(Δθ). Therefore, there are disadvantages in that sensitivity is poor during low speed rotation, detection is difficult because the output is direct current, and fluctuations in optical power lead to measurement errors.

This invention was made to eliminate the drawbacks of the conventional ones as described above, and provides an optical fiber gyroscope that has a simple configuration, can perform detection with high sensitivity even when rotating at low speed, and is not affected by optical power fluctuations. is intended to provide.

An embodiment of the present invention will be described below with reference to the drawings. Second
In the figure, the same parts as in Fig. F are denoted by the same reference numerals.

(7) is an optical phase modulator composed of, for example, a Bockel element; (8a) and (8b) are analyzers that align the polarization planes of the incident light and the output light into the optical fiber (3); (9a), (
9b) is a bandpass filter that discriminates the output of the photodetector (5), (10) is a peak detector, and (11) is a peak detection! (10) is a divider that detects the ratio of the output of bandpass filter (9b), (12) is a synchronous detector, (
13) is a gain controller, (14) is a variable gain amplifier, (1
5a), (15b) are oscillators, and (16) is a DC power supply. The synchronous detector (12) detects the output of the divider (11) in synchronization with the oscillator (15a), and the gain controller (13) maintains the output of the synchronous detector (12) constant. It controls the variable gain amplifier (14), and by monitoring the control voltage of this gain controller (13), the rotational angular velocity of the moving object can be detected.

The operation of the fiber optic gyroscope according to the present invention will be described below. In Figure 2, light from a laser (1) is split into two by a beam splitter (2), each of which is input into a single mode optical fiber (3),
) propagates clockwise and counterclockwise. Of these, the light propagating counterclockwise is subjected to phase modulation at an angular frequency ωm by a phase modulator (7).

Now, if the electric fields of the light after propagating in the left and right directions in the optical fiber are Eccw and Ecw, respectively, then ω, t+φ
bsinωm (t+τ)+φcwlεpupil・E2e−(
2) It can be expressed as In the above equations (1) and (2), E is the electric field strength of the light in both left and right directions, ω is the angular frequency of the light, τ is the propagation time of the light in the optical fiber loop, and φ. is a constant indicating the depth of phase modulation, and φCCW + φ are phase changes caused by the Sagnac effect that the left-handed and right-handed lights receive, respectively. When these two lights are caused to interfere on the photodetector (5), the following signal is obtained.

1 =lEccw+Ecwl"=E?+E',+
28. E, zcos (ψ, sinωmt-et al sin
0m (t+τ)+φsag) ---(3)(3
), where φsag ”'φcctn-φctv.

Here, if we choose the frequency of the oscillator (16a) so that ωm-=2πfm and τ-; then sin 0m (
t+ τ )=sin(ωmt π)=−sin ω
IIIt·-(4), and the signal current I becomes as follows.

! =E, +E, +2. E, E2cos (2 tons
in ωmt+φsag ) −(51 By doing this, phase modulation can be efficiently applied without being affected by the reciprocity of the phase modulator (7). This signal is passed through a bandpass filter (9d) with a center frequency fm. And, assuming the proportional score is 8, V1=AE, E2cos (-
2A sin ωmt+φsag )=AE, E2((J
, (2φ,)+2ΣJ! ? ': 2φ, )=1 cos2v ωmt) cos φsag-(2ΣJ,
, -, (2φ#) 1'H+ sin (2 sea 1) 0φII sin φsag
) Pez AE, E2 (J.

(2φII)CO5φsag −2J, (2φ,)sj
n φsagωmt+2JL (2φ,)cos φs
ag cos2ωmtl---(A signal of 61 is obtained.

However, as it is, the intensity of the light emitted from the optical fiber is E.

The signal voltage ν also fluctuates due to the fluctuation in the signal voltage ν. To prevent this, the laser (1) is driven not only by the DC power supply (16) but also by superimposing an AC signal (frequency fs) from the oscillator (15b). As a result, the signal detected by the photodetector (5) is a superposition of the signal at the frequency fm from the phase modulator (7) and the signal at the frequency fs. This signal is passed through a bandpass filter (9a) with a center frequency fs.
, a signal as shown in the following equation is obtained with B as a constant.

Vz=BIE, , E, sin 2πfst --(7]
When the peak of this signal is detected by a peak detector (10), a signal of VB=BE, E2-481 is obtained. Next, by calculating the ratio between this signal and the output signal of the bandpass filter (9b) using a divider (11), a signal as shown in the following equation is obtained.

v+=發=total(J,,(2φ,)cosφsag-2J
, (2 sin φsag sinωmt+2Jz (2
ψ, ), costpsagcos2(13111t
) -(91 This signal has the output light intensity E from the optical fiber (3),
It does not depend on E2. Therefore, stable signal detection can be performed even if optical output fluctuations occur. This divider (11)
The output signal v4 of the phase modulator (7) is set to the driving frequency fm
(by oscillator (15a)) and synchronization detector (1
2), a signal ν5 as expressed by the following equation is obtained.

VB 42J, (2φ,,) sinφsag″87
-2J, (2φ,)φs a g −α When the optical fiber loop (3) rotates around its central axis, φsag will change accordingly, but how will φsag change? Both, always v5
The gain controller (13) controls the gain of the variable gain amplifier (14) for driving the phase modulator (7) so that the value of is constant. The rotational angular velocity (which is proportional to φsag) can be detected by monitoring the control voltage of the gain controller (13). With this method, zero-order modulation is achieved, and the dynamic range is widened to an infinitesimal extent.

In the above embodiment, the zero position method was used as the rotation detection method, but there is no need to use the zero position method, and the rotation can be detected by directly monitoring the output of the synchronous detector (12) which is proportional to the rotational angular velocity. You may.

As described above, according to the present invention, since the phase modulation means is used, signals can be detected with high sensitivity even during low speed rotation. Further, even if the output intensity of the light source fluctuates or the coupling efficiency with the optical fiber fluctuates, stable signal detection can be performed without being affected by the fluctuations. Furthermore, when rotation detection is performed using the zero-position method, there is also the effect that the dynamic range of detection becomes larger than the egg weight.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a conventional fiber optic gyroscope.
FIG. 2 is a block diagram of an optical fiber gyroscope according to an embodiment of the present invention. (1)...Laser, (2)...Beam splitter,
(3)...Single mode optical fiber, (4a), (4b
)...Lens, (5)...Photodetector, (6)...
・Amplifier, (7)...Phase modulator, (8a), (8b
)...Analyzer, (9a), (9b)...Band pass filter, (10)...Peak detector, (11)
...Divider, '(12) ...Synchronization detector, (13
)...Gain controller, (14)...Variable gain amplifier,
(15a), (15b) - oscillator, (16)...DC power supply. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] (11) Both ends of an optical fiber which divides the light from the light generating means that is driven by the first oscillator into two and forms a loop along the rotational direction of the rotating system. In an optical fiber gyroscope equipped with a photodetector that detects two lights entering from a surface and exiting from both end faces of the optical fiber, phase modulation of light provided in one optical path of the split light a second oscillator for driving the phase modulator; a first bandpass filter for discriminating the output of the photodetector whose center frequency is equal to the oscillation frequency of the first oscillator; and a second bandpass filter whose center frequency is equal to that of the first oscillator. a second bandpass filter equal to the oscillation frequency of the oscillator; a peak detector for detecting the output of the first bandpass filter; and a ratio of the output of the peak detector to the output of the second bandpass filter. (2) A synchronous detector that detects the output of the divider in synchronization with a second oscillator; The optical fiber gyroscope according to claim 1, further comprising a gain controller that controls a variable gain amplifier provided on the output side of the second oscillator so as to keep the output constant. (3) 2. The fiber optic gyroscope according to claim 1, wherein the light generating means comprises a laser.