JP2842237B2 - 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.

[0002]

2. Description of the Related Art The configuration and operation of an optical fiber gyro using a phase modulation method as an example of the prior art will be described with reference to FIG. The optical system of the optical fiber gyro includes a laser light source 1, a polarizer 3, and a sensin group 5.
(Optical fiber coil), light receiver 6, two optical couplers 2
a, 2b and a phase modulator 4 for phase modulating the propagation light of the optical fiber coil. The laser light emitted from the light source 1 is branched by the optical coupler 2a, and one of the branched lights is sent to the sensing loop 5 via the polarizer 3 and the optical coupler 2b as left-handed light and right-handed light. The light that has propagated through the sensing loop 5 is transmitted to the optical coupler 2b.
Again, and guided to the light receiver 6 via the polarizer 3 and the optical coupler 2a. When the sensing loop 5 rotates at a certain angular velocity Ω together with the moving object, the phase difference Φ due to the Sagnac effect between the left and right surrounding lights.
_s (hereinafter simply referred to as “Sagnac phase difference”). Since the proportional relationship expressed by the following equation is established between the Sagnac phase difference Φ _s and the rotational angular velocity Ω of the sensing loop, the phase difference between the left and right surrounding lights (ie, the Sagnac phase difference Φ _s ) must be measured. It is possible to obtain the rotational angular velocity Ω by the following. Ω = Φ _s / a (1) where a = 4πR1 / λc, R: radius of sensing loop, l: sensing loop length, λ: wavelength of light source,
c: speed of light. The output signal photoelectrically converted by the light receiver 6 is sent to a signal processing circuit 8 via a preamplifier 7. that time,
The modulation signal frequency and its harmonic frequency component by the phase modulator are synchronously detected. The signal processing circuit 8 has a rotational angular velocity Ω
Is performed, and the phase modulator 4 is further driven. FIG. 4 is another conventional example in which some components of the optical system of FIG. 3 are removed. In this conventional technique, a photodetector is coupled to the rear surface of a laser diode serving as a light source,
The light source is used as a light generator and an optical amplifier. That is, the light emitted from the light source 1 propagates to the sensing loop 5 and then returns to the light source via the optical coupler 2 and the polarizer 3, but the light is amplified by the laser diode and detected by the photodetector. Is done.

[0003]

In the prior art shown in FIG. 3, one light receiver, two optical couplers, and one polarizer are required in addition to the light source and the sensing loop. It takes time to assemble. On the other hand, in the prior art shown in FIG. 4, the light path and the optical coupler for the light receiving device can be omitted by integrating the light source and the light receiving device, but the polarizer is used to remove the interference noise due to the polarization state of the light. This is similar to the prior art shown in FIG. An object of the present invention is to provide a novel optical fiber gyro in which the number of components is greatly reduced by removing a polarizer without deteriorating the performance of the optical fiber gyro.

[0004]

The present invention provides a laser light source ,
In particular, in an optical fiber gyro that detects signal light with a light receiver disposed on the opposite side of the light emitting end of the GaAlAs laser diode, a polarization maintaining optical fiber is used as the optical fiber, and the current value supplied to the light source is controlled by the light source. Extinction
Value at which the light ratio ε falls within the range of −10 dB ≦ ε ≦ −2 dB
The polarizer is removed without deteriorating the performance of the optical fiber gyro having the conventional configuration by supplying the optical fiber to the light source . A current supplied to the light source;
The value is such that the polarizer p of the light source is in the range of 0.1 ≦ p ≦ 0.63.
By setting the light source to a certain value and supplying the light source to the light source, the light source can be provided with the function of a polarizer and the polarizer can be removed.

[0005]

In general, the zero point drift ΔΩp based on the polarization mode coupling is given by the following equation. ΔΩp ≦ 180 · ε · (2ζ + 4η) · p / π · a [° / s] (2) where: a: scale factor of optical fiber gyro ε: extinction ratio of polarizer ζ: cross of polarization-maintaining optical fiber talk eta: crosstalk p of the optical coupler: the polarization ratio of the light source, however, epsilon, when the present invention using no polarizer is the extinction ratio due to polarization attenuation or amplification effect of the light source, the polarization ratio p of the light source from each other If p = py / px (3) is defined by the light intensity components px and py of the orthogonal polarization axis, it is defined as ε = 10 · logp (4). Therefore, the smaller the ε, that is, the larger the difference in attenuation or amplification characteristics depending on the polarization direction of the light source, the smaller the zero point drift of the optical fiber gyro.

[0006]

FIG. 1 shows an embodiment of an optical fiber gyro according to the present invention. The laser light source 1 has a photodetector disposed on the side opposite to the emission end thereof, and the laser light source 1 has an orthogonal 2
A polarized light having an attenuation rate or an amplification rate that differs depending on the polarization direction is used. The optical coupler 2, the phase modulator 4, and the sensing loop 5 have the same configuration as that used in the conventional optical fiber gyro, but the polarizer is removed. Although an electronic circuit such as a signal processing circuit is omitted in FIG. 1, it is connected to the detector as in the conventional example. Optical fiber is
All use polarization-maintaining optical fibers. P as receiver
An experimental result using a GaAlAs laser diode having a built-in IN photodiode as a light source will be described.
FIG. 2 shows the relationship between the current supplied to the light source and the extinction ratio. According to this figure, if the supply current is increased, the extinction ratio decreases, and therefore, the polarization ratio of the light source also decreases. However, on the other hand, when the supply current is increased, the spectral width of the light source becomes narrower, and a problem arises that interference noise in the optical fiber gyro increases. From various experimental results, when a multi-mode semiconductor laser is used, the interference noise is very small if the current value is equal to or less than the laser oscillation threshold value. In FIG. 2, the supply current of the light source is 35-4.
5 mA is appropriate, and the extinction ratio ε or the polarization ratio p
-10 dB ≦ ε ≦ −2 dB (5) or 0.1 ≦ p ≦ 0.63 (6) is the optimal numerical range. In particular, ε = −5 dB (p =
0.32) is the optimal value. As shown in FIG. 5, the static drift characteristic of the optical fiber gyro according to the present invention is −30.
The temperature was measured in the temperature range of ℃ to 85 ℃, and when compared with the characteristics of the optical fiber gyro using the conventional polarizer shown in FIG. 6, the same characteristics were shown. In the above embodiment, the open loop type of the phase modulation method has been described as an example, but the present invention can also be applied to a closed type optical fiber gyro.

[0007]

According to the present invention, an optical fiber gyro can be constituted by a single light source, optical coupler, and sensing loop each having a built-in photodetector without deteriorating the performance of the optical fiber gyro having the conventional configuration. And assembling becomes easier. In addition, since the number of parts is reduced, failures and deviations after assembly are reduced, and reliability can be improved.

[Brief description of the drawings]

FIG. 1 shows an arrangement of an optical system of an optical fiber gyro according to the present invention.
FIG .

FIG. 2 is a characteristic diagram showing a relationship between a supply current of a light source used in an embodiment of the present invention and an extinction ratio.

FIG. 3 is a configuration diagram showing an example of a conventional technique.

FIG. 4 is a configuration diagram showing another example of the related art.

FIG. 5 is a characteristic diagram showing a static drift characteristic of the optical fiber gyro of the present invention.

FIG. 6 is a characteristic diagram showing a static drift characteristic of a conventional optical fiber gyro using a polarizer.

[Explanation of symbols]

 Reference Signs List 1 laser light source 2 optical coupler 3 polarizer 4 phase modulator 5 sensing loop 6 light receiver 7 preamplifier 8 signal processing circuit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-129859 (JP, A) JP-A-6-174478 (JP, A) JP-A-6-186043 (JP, A) JP-A-61- 277014 (JP, A) JP-A-62-44620 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01S 3/083 G01C 19/72 H01S 3/08 H01S 3/18

Claims (2)

(57) [Claims] And 1. A <br/> light source using a GaAlAs laser diode, an optical fiber sensing loop, fed to the optical fiber sensing loop as the left and right around light by branching the light emitted from the light source, the same loop an optical coupler for recombined light back propagated, for receiving the combined light, a photodetector disposed opposite the light emitting end of the light source,
An electronic circuit that obtains a rotational angular velocity by processing a signal detected by a light receiver, using a polarization-maintaining optical fiber as an optical fiber, and a current value supplied to the light source.
Is set to a value such that the extinction ratio ε of the light source is in the range of −10 dB ≦ ε ≦ −2 dB and supplied to the light source . 2. A <br/> light source using a GaAlAs laser diode, an optical fiber sensing loop, fed to the optical fiber sensing loop as the left and right around light by branching the light emitted from the light source, the same loop an optical coupler for recombined light back propagated, for receiving the combined light, a photodetector disposed opposite the light emitting end of the light source,
An electronic circuit that obtains a rotational angular velocity by processing a signal detected by a light receiver, using a polarization-maintaining optical fiber as an optical fiber, and a current value supplied to the light source.
Is set to a value such that the polarization ratio p of the light source is within a range of 0.1 ≦ p ≦ 0.63 , and the light is supplied to the light source .