JPH07113647A - Optical fiber gyro - Google Patents

Abstract

PURPOSE:To provide an optical fiber gyro having a means eliminating interference noises based on polarized light without using a plarizer. CONSTITUTION:A photodetector is arranged on the reverse side to the optical outgoing end of a laser beam source 1, beams emitted from the laser beam source 1 are transmitted over an optical-fiber sensing loop 5 as left and right gyrating beams through an optical coupler 2, and return beams are projected to the photodetector through the optical coupler 2 again. A polarization-plane conserving optical fiber is used as an optical fiber, and an optical fiber gyro is constituted so that distance difference acquired from phase difference at a time when two orthogonal polarized light obtained from optical fiber length from the beam source 1 to the optical coupler 2 and the wavelength of the beam source and the coupling length of the optical fiber is propagated from the beam source 1 to the optical coupler 2 reaches the coherent distance or more of the beam source. Accordingly, the beam source incorporated into the photodetector is employed, and the polarizer is removed, thus facilitating assembly, then also improving reliability after assembly.

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 As an example of a conventional technique, an optical fiber gyro using a phase modulation method 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 sensor 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 as left-handed light and right-handed light via the polarizer 3 and the optical coupler 2b. The light propagated through the sensing loop 5 is the optical coupler 2b.
Are combined again by and are guided to the light receiver 6 through the polarizer 3 and the optical coupler 2a. When the sensing loop 5 rotates with a moving body at a certain angular velocity Ω, the phase difference Φ due to the Sagnac effect occurs between the left and right rotating lights.
_s (hereinafter simply referred to as "Sagnac phase difference") occurs. Since the proportional relationship shown by the following equation is established between the Sagnac phase difference Φ _s and the rotational angular velocity Ω of the sensing loop, measure the phase difference between the left and right rotating lights (that is, the Sagnac phase difference Φ _s ). The rotational angular velocity Ω can be obtained by Ω = Φ _s / a (1) where a = 4πRl / 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 the signal processing circuit 8 via the preamplifier 7. At this time, the frequency of the modulated signal by the phase modulator and its harmonic frequency component are synchronously detected. The signal processing circuit 8 executes processing and calculation for obtaining the rotational angular velocity Ω, and further drives the phase modulator 4. FIG. 4 shows another conventional example in which some parts are removed from the configuration of FIG. In this conventional technique, a light detecting element is coupled to the rear surface of a laser diode serving as a light source, and the light source is used as a light generator and an optical amplifier. That is, the light emitted from the light source 1 is propagated to the sensing loop 5 and then returns to the light source again via the optical coupler 2 and the polarizer 3, but the light is amplified by the laser diode and then detected by the photodetector. To be done.

[0003]

In the prior art shown in FIG. 3, in addition to the light source and the sensing loop, one light receiver, two optical couplers and one polarizer are required, and the number of parts is large and the cost is high. It also takes time to assemble. On the other hand, in the prior art of FIG. 4, the light path and the optical coupler for the light receiver can be omitted by integrating the light source and the light receiver, but a polarizer is used to remove interference noise due to the polarization state of light. This is the same as the conventional technique shown in FIG. It is an object of the present invention to provide a novel optical fiber gyro that eliminates the polarizer without deteriorating the performance of the optical fiber gyro, thereby significantly reducing the number of parts and eliminating the drawbacks of the prior art. .

[0004]

SUMMARY OF THE INVENTION The present invention is an optical fiber gyro that detects signal light with a light receiver arranged on the opposite side of a light emitting end of a laser light source, using a polarization-maintaining optical fiber as an optical fiber, The coherence length of the light source is the distance difference obtained from the phase difference when two orthogonal polarizations propagate from the light source to the optical coupler, which is obtained from the optical fiber length from the light source to the optical coupler, the wavelength of the light source, and the coupling length of the optical fiber. It is configured as described above. Further, in particular, when a laser light source having a characteristic close to linearly polarized light is used, in the above configuration, the light is emitted with the polarization axis of the light emitted from the light source being inclined by about 45 degrees with respect to the intrinsic polarization axis of the polarization-maintaining optical fiber. To configure. This significantly reduces the number of parts without degrading the performance of the optical fiber gyro.

[0005]

In general, the light source used for the interference type optical fiber gyro has a low coherence, and the emitted light is not perfectly linearly polarized light. Therefore, in general, a polarizer is used to make linearly polarized light, and interference of only one polarized light is detected to remove interference noise. According to the present invention, a distance difference of not less than the interference distance λ ² / Δλ determined by the wavelength λ of the light source and the spectral half width Δλ is 2
The interference noise is eliminated by giving the polarized light a mutual incoherent relationship.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the optical fiber gyro of the present invention will be described with reference to FIG. As the laser light source 1, a laser light source in which a light receiver is arranged on the side opposite to the emission end 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 electronic circuits such as a signal processing circuit are omitted in the figure, they are connected to the detector as in the conventional example. In the present invention, the optical fiber including the sensing loop is used as the optical fiber, and the optical fiber length from the light source to the optical coupler is L, the wavelength of the light source is λ, and the optical fiber coupling length is L _b. , Propagation distance difference λ · L / L _b that occurs while two orthogonal polarizations propagate through the optical fiber length L
For the interference distance λ ² / Δλ determined by the wavelength λ of the light source and the spectral half width Δλ, design the distance from the light source to the optical coupler under the condition of λ · L / L _b > λ ² / Δλ (2) To do. GaAl with a built-in PIN photodiode as the light source
As a result of measurement using an As laser diode and an elliptic core type polarization-maintaining optical fiber as the optical fiber, the coupling length of the polarization-maintaining optical fiber is about 2 mm at a light source wavelength of 0.78 μm, Interference distance is about 1m
m, therefore, by substituting each numerical value in the above equation to obtain the optical fiber length L, it is possible to reduce the interference noise at L> 2.564m (3). On the other hand, if the light source has characteristics close to linearly polarized light, the light incident on the sensing loop will not be in a non-polarized state even if the above-described design is implemented. Therefore, as shown in FIG. 2, it is necessary to adopt a configuration in which the polarization axis of the light emitted from the light source is inclined by 45 degrees with respect to the intrinsic polarization axis of the polarization-maintaining optical fiber and the light is incident. When the angular velocity drift characteristic of the optical fiber gyro of the present invention was actually measured with the optical fiber length L set to 3 m, the same evaluation result as that of the conventional optical fiber gyro was obtained even though the optical coupler and one polarizer were removed. Was given. In the above embodiment, the open loop type of the phase modulation system is described as an example, but it can be applied to a closed type optical fiber gyro.

[0007]

According to the present invention, an optical fiber gyro can be constructed with a light source with a built-in optical receiver, an optical coupler, and a sensing loop without degrading the performance of the conventional optical fiber gyro. And easy to assemble. Moreover, since the number of parts is reduced, failures and errors after assembly are reduced, and reliability can be improved.
Further, since a commercially available inexpensive laser having a certain degree of coherency can be applied as the light source, the economical efficiency is increased.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of an optical fiber gyro according to the present invention.

FIG. 2 is an explanatory diagram showing a relationship between light emitted from a light source and polarization axis directions of a polarization-maintaining optical fiber.

FIG. 3 is a configuration diagram showing a first example of a conventional optical fiber gyro.

FIG. 4 is a configuration diagram showing a second example of a conventional optical fiber gyro.

[Explanation of symbols]

 1 Laser Light Source 2 Optical Coupler 3 Polarizer 4 Phase Modulator 5 Sensing Loop 6 Light Receiver 7 Preamplifier 8 Signal Processing Circuit 9 Lens 10 Elliptical Core Type Polarization-Maintaining Optical Fiber

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Wataru Onuki Wataru Onuki 5-1-1, Hidaka-cho, Hitachi-shi, Ibaraki Hidaka Plant, Hitachi Cable, Ltd. (72) Inventor Toshiyuki Tetsu 5 Hidaka-cho, Hitachi-shi, Ibaraki 1-1-1 Hitachi Cable Co., Ltd. Hidaka Factory

Claims (2)

[Claims] 1. A laser light source, an optical fiber sensing loop, and light emitted from the laser light source is branched and sent to the optical fiber sensing loop as left and right circular light,
An optical coupler for recombining the light propagating through the loop, an optical fiber for connecting the optical elements, and a light receiver for receiving the combined light, which is arranged on the opposite side of the light emitting end of the laser light source. In the optical fiber gyro equipped with an electronic circuit that obtains a rotational angular velocity by processing a signal detected by a light receiver, a polarization-maintaining optical fiber is used as the optical fiber, and an optical fiber length from the light source to the optical coupler is used. And the wavelength difference of the light source and the coupling length of the optical fiber, the distance difference obtained from the phase difference when the two orthogonal polarizations propagate from the light source to the optical coupler is greater than the coherence length of the light source. Characteristic optical fiber gyro. 2. The optical fiber according to claim 1, wherein the polarization axis of the light emitted from the laser light source is inclined by about 45 degrees with respect to the intrinsic polarization axis of the polarization-maintaining optical fiber, and the light is incident. gyro.